diff --git a/demo_test/vendor/google.golang.org/grpc/.travis.yml b/demo_test/vendor/google.golang.org/grpc/.travis.yml
new file mode 100644
index 0000000..a11e8cb
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/.travis.yml
@@ -0,0 +1,42 @@
+language: go
+
+matrix:
+  include:
+  - go: 1.13.x
+    env: VET=1 GO111MODULE=on
+  - go: 1.13.x
+    env: RACE=1 GO111MODULE=on
+  - go: 1.13.x
+    env: RUN386=1
+  - go: 1.13.x
+    env: GRPC_GO_RETRY=on
+  - go: 1.13.x
+    env: TESTEXTRAS=1
+  - go: 1.12.x
+    env: GO111MODULE=on
+  - go: 1.11.x
+    env: GO111MODULE=on
+  - go: 1.9.x
+    env: GAE=1
+
+go_import_path: google.golang.org/grpc
+
+before_install:
+  - if [[ "${GO111MODULE}" = "on" ]]; then mkdir "${HOME}/go"; export GOPATH="${HOME}/go"; fi
+  - if [[ -n "${RUN386}" ]]; then export GOARCH=386; fi
+  - if [[ "${TRAVIS_EVENT_TYPE}" = "cron" && -z "${RUN386}" ]]; then RACE=1; fi
+  - if [[ "${TRAVIS_EVENT_TYPE}" != "cron" ]]; then export VET_SKIP_PROTO=1; fi
+
+install:
+  - try3() { eval "$*" || eval "$*" || eval "$*"; }
+  - try3 'if [[ "${GO111MODULE}" = "on" ]]; then go mod download; else make testdeps; fi'
+  - if [[ -n "${GAE}" ]]; then source ./install_gae.sh; make testappenginedeps; fi
+  - if [[ -n "${VET}" ]]; then ./vet.sh -install; fi
+
+script:
+  - set -e
+  - if [[ -n "${TESTEXTRAS}" ]]; then examples/examples_test.sh; interop/interop_test.sh; make testsubmodule; exit 0; fi
+  - if [[ -n "${VET}" ]]; then ./vet.sh; fi
+  - if [[ -n "${GAE}" ]]; then make testappengine; exit 0; fi
+  - if [[ -n "${RACE}" ]]; then make testrace; exit 0; fi
+  - make test
diff --git a/demo_test/vendor/google.golang.org/grpc/AUTHORS b/demo_test/vendor/google.golang.org/grpc/AUTHORS
new file mode 100644
index 0000000..e491a9e
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/AUTHORS
@@ -0,0 +1 @@
+Google Inc.
diff --git a/demo_test/vendor/google.golang.org/grpc/CODE-OF-CONDUCT.md b/demo_test/vendor/google.golang.org/grpc/CODE-OF-CONDUCT.md
new file mode 100644
index 0000000..9d4213e
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/CODE-OF-CONDUCT.md
@@ -0,0 +1,3 @@
+## Community Code of Conduct
+
+gRPC follows the [CNCF Code of Conduct](https://github.com/cncf/foundation/blob/master/code-of-conduct.md).
diff --git a/demo_test/vendor/google.golang.org/grpc/CONTRIBUTING.md b/demo_test/vendor/google.golang.org/grpc/CONTRIBUTING.md
new file mode 100644
index 0000000..4f1567e
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/CONTRIBUTING.md
@@ -0,0 +1,62 @@
+# How to contribute
+
+We definitely welcome your patches and contributions to gRPC! Please read the gRPC
+organization's [governance rules](https://github.com/grpc/grpc-community/blob/master/governance.md)
+and [contribution guidelines](https://github.com/grpc/grpc-community/blob/master/CONTRIBUTING.md) before proceeding.
+
+If you are new to github, please start by reading [Pull Request howto](https://help.github.com/articles/about-pull-requests/)
+
+## Legal requirements
+
+In order to protect both you and ourselves, you will need to sign the
+[Contributor License Agreement](https://identity.linuxfoundation.org/projects/cncf).
+
+## Guidelines for Pull Requests
+How to get your contributions merged smoothly and quickly.
+
+- Create **small PRs** that are narrowly focused on **addressing a single
+  concern**. We often times receive PRs that are trying to fix several things at
+  a time, but only one fix is considered acceptable, nothing gets merged and
+  both author's & review's time is wasted. Create more PRs to address different
+  concerns and everyone will be happy.
+
+- The grpc package should only depend on standard Go packages and a small number
+  of exceptions. If your contribution introduces new dependencies which are NOT
+  in the [list](https://godoc.org/google.golang.org/grpc?imports), you need a
+  discussion with gRPC-Go authors and consultants.
+
+- For speculative changes, consider opening an issue and discussing it first. If
+  you are suggesting a behavioral or API change, consider starting with a [gRFC
+  proposal](https://github.com/grpc/proposal).
+
+- Provide a good **PR description** as a record of **what** change is being made
+  and **why** it was made. Link to a github issue if it exists.
+
+- Don't fix code style and formatting unless you are already changing that line
+  to address an issue. PRs with irrelevant changes won't be merged. If you do
+  want to fix formatting or style, do that in a separate PR.
+
+- Unless your PR is trivial, you should expect there will be reviewer comments
+  that you'll need to address before merging. We expect you to be reasonably
+  responsive to those comments, otherwise the PR will be closed after 2-3 weeks
+  of inactivity.
+
+- Maintain **clean commit history** and use **meaningful commit messages**. PRs
+  with messy commit history are difficult to review and won't be merged. Use
+  `rebase -i upstream/master` to curate your commit history and/or to bring in
+  latest changes from master (but avoid rebasing in the middle of a code
+  review).
+
+- Keep your PR up to date with upstream/master (if there are merge conflicts, we
+  can't really merge your change).
+
+- **All tests need to be passing** before your change can be merged. We
+  recommend you **run tests locally** before creating your PR to catch breakages
+  early on.
+  - `make all` to test everything, OR
+  - `make vet` to catch vet errors
+  - `make test` to run the tests
+  - `make testrace` to run tests in race mode
+  - optional `make testappengine` to run tests with appengine
+
+- Exceptions to the rules can be made if there's a compelling reason for doing so.
diff --git a/demo_test/vendor/google.golang.org/grpc/GOVERNANCE.md b/demo_test/vendor/google.golang.org/grpc/GOVERNANCE.md
new file mode 100644
index 0000000..d6ff267
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/GOVERNANCE.md
@@ -0,0 +1 @@
+This repository is governed by the gRPC organization's [governance rules](https://github.com/grpc/grpc-community/blob/master/governance.md).
diff --git a/demo_test/vendor/google.golang.org/grpc/LICENSE b/demo_test/vendor/google.golang.org/grpc/LICENSE
new file mode 100644
index 0000000..d645695
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/LICENSE
@@ -0,0 +1,202 @@
+
+                                 Apache License
+                           Version 2.0, January 2004
+                        http://www.apache.org/licenses/
+
+   TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION
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+      the conditions stated in this License.
+
+   5. Submission of Contributions. Unless You explicitly state otherwise,
+      any Contribution intentionally submitted for inclusion in the Work
+      by You to the Licensor shall be under the terms and conditions of
+      this License, without any additional terms or conditions.
+      Notwithstanding the above, nothing herein shall supersede or modify
+      the terms of any separate license agreement you may have executed
+      with Licensor regarding such Contributions.
+
+   6. Trademarks. This License does not grant permission to use the trade
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+      whether in tort (including negligence), contract, or otherwise,
+      unless required by applicable law (such as deliberate and grossly
+      negligent acts) or agreed to in writing, shall any Contributor be
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+
+   APPENDIX: How to apply the Apache License to your work.
+
+      To apply the Apache License to your work, attach the following
+      boilerplate notice, with the fields enclosed by brackets "[]"
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+   Copyright [yyyy] [name of copyright owner]
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
diff --git a/demo_test/vendor/google.golang.org/grpc/MAINTAINERS.md b/demo_test/vendor/google.golang.org/grpc/MAINTAINERS.md
new file mode 100644
index 0000000..093c82b
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/MAINTAINERS.md
@@ -0,0 +1,27 @@
+This page lists all active maintainers of this repository. If you were a
+maintainer and would like to add your name to the Emeritus list, please send us a
+PR.
+
+See [GOVERNANCE.md](https://github.com/grpc/grpc-community/blob/master/governance.md)
+for governance guidelines and how to become a maintainer.
+See [CONTRIBUTING.md](https://github.com/grpc/grpc-community/blob/master/CONTRIBUTING.md)
+for general contribution guidelines.
+
+## Maintainers (in alphabetical order)
+- [canguler](https://github.com/canguler), Google LLC
+- [cesarghali](https://github.com/cesarghali), Google LLC
+- [dfawley](https://github.com/dfawley), Google LLC
+- [easwars](https://github.com/easwars), Google LLC
+- [jadekler](https://github.com/jadekler), Google LLC
+- [menghanl](https://github.com/menghanl), Google LLC
+- [srini100](https://github.com/srini100), Google LLC
+
+## Emeritus Maintainers (in alphabetical order)
+- [adelez](https://github.com/adelez), Google LLC
+- [iamqizhao](https://github.com/iamqizhao), Google LLC
+- [jtattermusch](https://github.com/jtattermusch), Google LLC
+- [lyuxuan](https://github.com/lyuxuan), Google LLC
+- [makmukhi](https://github.com/makmukhi), Google LLC
+- [matt-kwong](https://github.com/matt-kwong), Google LLC
+- [nicolasnoble](https://github.com/nicolasnoble), Google LLC
+- [yongni](https://github.com/yongni), Google LLC
diff --git a/demo_test/vendor/google.golang.org/grpc/Makefile b/demo_test/vendor/google.golang.org/grpc/Makefile
new file mode 100644
index 0000000..410f7d5
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/Makefile
@@ -0,0 +1,63 @@
+all: vet test testrace
+
+build: deps
+	go build google.golang.org/grpc/...
+
+clean:
+	go clean -i google.golang.org/grpc/...
+
+deps:
+	go get -d -v google.golang.org/grpc/...
+
+proto:
+	@ if ! which protoc > /dev/null; then \
+		echo "error: protoc not installed" >&2; \
+		exit 1; \
+	fi
+	go generate google.golang.org/grpc/...
+
+test: testdeps
+	go test -cpu 1,4 -timeout 7m google.golang.org/grpc/...
+
+testsubmodule: testdeps
+	cd security/advancedtls && go test -cpu 1,4 -timeout 7m google.golang.org/grpc/security/advancedtls/...
+
+testappengine: testappenginedeps
+	goapp test -cpu 1,4 -timeout 7m google.golang.org/grpc/...
+
+testappenginedeps:
+	goapp get -d -v -t -tags 'appengine appenginevm' google.golang.org/grpc/...
+
+testdeps:
+	go get -d -v -t google.golang.org/grpc/...
+
+testrace: testdeps
+	go test -race -cpu 1,4 -timeout 7m google.golang.org/grpc/...
+
+updatedeps:
+	go get -d -v -u -f google.golang.org/grpc/...
+
+updatetestdeps:
+	go get -d -v -t -u -f google.golang.org/grpc/...
+
+vet: vetdeps
+	./vet.sh
+
+vetdeps:
+	./vet.sh -install
+
+.PHONY: \
+	all \
+	build \
+	clean \
+	deps \
+	proto \
+	test \
+	testappengine \
+	testappenginedeps \
+	testdeps \
+	testrace \
+	updatedeps \
+	updatetestdeps \
+	vet \
+	vetdeps
diff --git a/demo_test/vendor/google.golang.org/grpc/README.md b/demo_test/vendor/google.golang.org/grpc/README.md
new file mode 100644
index 0000000..800e7bd
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/README.md
@@ -0,0 +1,141 @@
+# gRPC-Go
+
+[![Build Status](https://travis-ci.org/grpc/grpc-go.svg)](https://travis-ci.org/grpc/grpc-go)
+[![GoDoc](https://godoc.org/google.golang.org/grpc?status.svg)](https://godoc.org/google.golang.org/grpc)
+[![GoReportCard](https://goreportcard.com/badge/grpc/grpc-go)](https://goreportcard.com/report/github.com/grpc/grpc-go)
+
+The Go implementation of [gRPC](https://grpc.io/): A high performance, open
+source, general RPC framework that puts mobile and HTTP/2 first. For more
+information see the [gRPC Quick Start:
+Go](https://grpc.io/docs/quickstart/go.html) guide.
+
+Installation
+------------
+
+To install this package, you need to install Go and setup your Go workspace on
+your computer. The simplest way to install the library is to run:
+
+```
+$ go get -u google.golang.org/grpc
+```
+
+With Go module support (Go 1.11+), simply `import "google.golang.org/grpc"` in
+your source code and `go [build|run|test]` will automatically download the
+necessary dependencies ([Go modules
+ref](https://github.com/golang/go/wiki/Modules)).
+
+If you are trying to access grpc-go from within China, please see the
+[FAQ](#FAQ) below.
+
+Prerequisites
+-------------
+gRPC-Go requires Go 1.9 or later.
+
+Documentation
+-------------
+- See [godoc](https://godoc.org/google.golang.org/grpc) for package and API
+  descriptions.
+- Documentation on specific topics can be found in the [Documentation
+  directory](Documentation/).
+- Examples can be found in the [examples directory](examples/).
+
+Performance
+-----------
+Performance benchmark data for grpc-go and other languages is maintained in
+[this
+dashboard](https://performance-dot-grpc-testing.appspot.com/explore?dashboard=5652536396611584&widget=490377658&container=1286539696).
+
+Status
+------
+General Availability [Google Cloud Platform Launch
+Stages](https://cloud.google.com/terms/launch-stages).
+
+FAQ
+---
+
+#### I/O Timeout Errors
+
+The `golang.org` domain may be blocked from some countries.  `go get` usually
+produces an error like the following when this happens:
+
+```
+$ go get -u google.golang.org/grpc
+package google.golang.org/grpc: unrecognized import path "google.golang.org/grpc" (https fetch: Get https://google.golang.org/grpc?go-get=1: dial tcp 216.239.37.1:443: i/o timeout)
+```
+
+To build Go code, there are several options:
+
+- Set up a VPN and access google.golang.org through that.
+
+- Without Go module support: `git clone` the repo manually:
+
+  ```
+  git clone https://github.com/grpc/grpc-go.git $GOPATH/src/google.golang.org/grpc
+  ```
+
+  You will need to do the same for all of grpc's dependencies in `golang.org`,
+  e.g. `golang.org/x/net`.
+
+- With Go module support: it is possible to use the `replace` feature of `go
+  mod` to create aliases for golang.org packages.  In your project's directory:
+
+  ```
+  go mod edit -replace=google.golang.org/grpc=github.com/grpc/grpc-go@latest
+  go mod tidy
+  go mod vendor
+  go build -mod=vendor
+  ```
+
+  Again, this will need to be done for all transitive dependencies hosted on
+  golang.org as well.  Please refer to [this
+  issue](https://github.com/golang/go/issues/28652) in the golang repo regarding
+  this concern.
+
+#### Compiling error, undefined: grpc.SupportPackageIsVersion
+
+##### If you are using Go modules:
+
+Please ensure your gRPC-Go version is `require`d at the appropriate version in
+the same module containing the generated `.pb.go` files.  For example,
+`SupportPackageIsVersion6` needs `v1.27.0`, so in your `go.mod` file:
+
+```
+module <your module name>
+
+require (
+    google.golang.org/grpc v1.27.0
+)
+```
+
+##### If you are *not* using Go modules:
+
+Please update proto package, gRPC package and rebuild the proto files:
+ - `go get -u github.com/golang/protobuf/{proto,protoc-gen-go}`
+ - `go get -u google.golang.org/grpc`
+ - `protoc --go_out=plugins=grpc:. *.proto`
+
+#### How to turn on logging
+
+The default logger is controlled by the environment variables. Turn everything
+on by setting:
+
+```
+GRPC_GO_LOG_VERBOSITY_LEVEL=99 GRPC_GO_LOG_SEVERITY_LEVEL=info
+```
+
+#### The RPC failed with error `"code = Unavailable desc = transport is closing"`
+
+This error means the connection the RPC is using was closed, and there are many
+possible reasons, including:
+ 1. mis-configured transport credentials, connection failed on handshaking
+ 1. bytes disrupted, possibly by a proxy in between
+ 1. server shutdown
+ 1. Keepalive parameters caused connection shutdown, for example if you have configured
+    your server to terminate connections regularly to [trigger DNS lookups](https://github.com/grpc/grpc-go/issues/3170#issuecomment-552517779).
+    If this is the case, you may want to increase your [MaxConnectionAgeGrace](https://pkg.go.dev/google.golang.org/grpc/keepalive?tab=doc#ServerParameters),
+    to allow longer RPC calls to finish.
+
+It can be tricky to debug this because the error happens on the client side but
+the root cause of the connection being closed is on the server side. Turn on
+logging on __both client and server__, and see if there are any transport
+errors.
diff --git a/demo_test/vendor/google.golang.org/grpc/attributes/attributes.go b/demo_test/vendor/google.golang.org/grpc/attributes/attributes.go
new file mode 100644
index 0000000..68ffc62
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/attributes/attributes.go
@@ -0,0 +1,70 @@
+/*
+ *
+ * Copyright 2019 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+// Package attributes defines a generic key/value store used in various gRPC
+// components.
+//
+// All APIs in this package are EXPERIMENTAL.
+package attributes
+
+import "fmt"
+
+// Attributes is an immutable struct for storing and retrieving generic
+// key/value pairs.  Keys must be hashable, and users should define their own
+// types for keys.
+type Attributes struct {
+	m map[interface{}]interface{}
+}
+
+// New returns a new Attributes containing all key/value pairs in kvs.  If the
+// same key appears multiple times, the last value overwrites all previous
+// values for that key.  Panics if len(kvs) is not even.
+func New(kvs ...interface{}) *Attributes {
+	if len(kvs)%2 != 0 {
+		panic(fmt.Sprintf("attributes.New called with unexpected input: len(kvs) = %v", len(kvs)))
+	}
+	a := &Attributes{m: make(map[interface{}]interface{}, len(kvs)/2)}
+	for i := 0; i < len(kvs)/2; i++ {
+		a.m[kvs[i*2]] = kvs[i*2+1]
+	}
+	return a
+}
+
+// WithValues returns a new Attributes containing all key/value pairs in a and
+// kvs.  Panics if len(kvs) is not even.  If the same key appears multiple
+// times, the last value overwrites all previous values for that key.  To
+// remove an existing key, use a nil value.
+func (a *Attributes) WithValues(kvs ...interface{}) *Attributes {
+	if len(kvs)%2 != 0 {
+		panic(fmt.Sprintf("attributes.New called with unexpected input: len(kvs) = %v", len(kvs)))
+	}
+	n := &Attributes{m: make(map[interface{}]interface{}, len(a.m)+len(kvs)/2)}
+	for k, v := range a.m {
+		n.m[k] = v
+	}
+	for i := 0; i < len(kvs)/2; i++ {
+		n.m[kvs[i*2]] = kvs[i*2+1]
+	}
+	return n
+}
+
+// Value returns the value associated with these attributes for key, or nil if
+// no value is associated with key.
+func (a *Attributes) Value(key interface{}) interface{} {
+	return a.m[key]
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/backoff.go b/demo_test/vendor/google.golang.org/grpc/backoff.go
new file mode 100644
index 0000000..ff7c3ee
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/backoff.go
@@ -0,0 +1,58 @@
+/*
+ *
+ * Copyright 2017 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+// See internal/backoff package for the backoff implementation. This file is
+// kept for the exported types and API backward compatibility.
+
+package grpc
+
+import (
+	"time"
+
+	"google.golang.org/grpc/backoff"
+)
+
+// DefaultBackoffConfig uses values specified for backoff in
+// https://github.com/grpc/grpc/blob/master/doc/connection-backoff.md.
+//
+// Deprecated: use ConnectParams instead. Will be supported throughout 1.x.
+var DefaultBackoffConfig = BackoffConfig{
+	MaxDelay: 120 * time.Second,
+}
+
+// BackoffConfig defines the parameters for the default gRPC backoff strategy.
+//
+// Deprecated: use ConnectParams instead. Will be supported throughout 1.x.
+type BackoffConfig struct {
+	// MaxDelay is the upper bound of backoff delay.
+	MaxDelay time.Duration
+}
+
+// ConnectParams defines the parameters for connecting and retrying. Users are
+// encouraged to use this instead of the BackoffConfig type defined above. See
+// here for more details:
+// https://github.com/grpc/grpc/blob/master/doc/connection-backoff.md.
+//
+// This API is EXPERIMENTAL.
+type ConnectParams struct {
+	// Backoff specifies the configuration options for connection backoff.
+	Backoff backoff.Config
+	// MinConnectTimeout is the minimum amount of time we are willing to give a
+	// connection to complete.
+	MinConnectTimeout time.Duration
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/backoff/backoff.go b/demo_test/vendor/google.golang.org/grpc/backoff/backoff.go
new file mode 100644
index 0000000..0787d0b
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/backoff/backoff.go
@@ -0,0 +1,52 @@
+/*
+ *
+ * Copyright 2019 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+// Package backoff provides configuration options for backoff.
+//
+// More details can be found at:
+// https://github.com/grpc/grpc/blob/master/doc/connection-backoff.md.
+//
+// All APIs in this package are experimental.
+package backoff
+
+import "time"
+
+// Config defines the configuration options for backoff.
+type Config struct {
+	// BaseDelay is the amount of time to backoff after the first failure.
+	BaseDelay time.Duration
+	// Multiplier is the factor with which to multiply backoffs after a
+	// failed retry. Should ideally be greater than 1.
+	Multiplier float64
+	// Jitter is the factor with which backoffs are randomized.
+	Jitter float64
+	// MaxDelay is the upper bound of backoff delay.
+	MaxDelay time.Duration
+}
+
+// DefaultConfig is a backoff configuration with the default values specfied
+// at https://github.com/grpc/grpc/blob/master/doc/connection-backoff.md.
+//
+// This should be useful for callers who want to configure backoff with
+// non-default values only for a subset of the options.
+var DefaultConfig = Config{
+	BaseDelay:  1.0 * time.Second,
+	Multiplier: 1.6,
+	Jitter:     0.2,
+	MaxDelay:   120 * time.Second,
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/balancer.go b/demo_test/vendor/google.golang.org/grpc/balancer.go
new file mode 100644
index 0000000..a8eb0f4
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/balancer.go
@@ -0,0 +1,391 @@
+/*
+ *
+ * Copyright 2016 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package grpc
+
+import (
+	"context"
+	"net"
+	"sync"
+
+	"google.golang.org/grpc/codes"
+	"google.golang.org/grpc/credentials"
+	"google.golang.org/grpc/grpclog"
+	"google.golang.org/grpc/naming"
+	"google.golang.org/grpc/status"
+)
+
+// Address represents a server the client connects to.
+//
+// Deprecated: please use package balancer.
+type Address struct {
+	// Addr is the server address on which a connection will be established.
+	Addr string
+	// Metadata is the information associated with Addr, which may be used
+	// to make load balancing decision.
+	Metadata interface{}
+}
+
+// BalancerConfig specifies the configurations for Balancer.
+//
+// Deprecated: please use package balancer.  May be removed in a future 1.x release.
+type BalancerConfig struct {
+	// DialCreds is the transport credential the Balancer implementation can
+	// use to dial to a remote load balancer server. The Balancer implementations
+	// can ignore this if it does not need to talk to another party securely.
+	DialCreds credentials.TransportCredentials
+	// Dialer is the custom dialer the Balancer implementation can use to dial
+	// to a remote load balancer server. The Balancer implementations
+	// can ignore this if it doesn't need to talk to remote balancer.
+	Dialer func(context.Context, string) (net.Conn, error)
+}
+
+// BalancerGetOptions configures a Get call.
+//
+// Deprecated: please use package balancer.  May be removed in a future 1.x release.
+type BalancerGetOptions struct {
+	// BlockingWait specifies whether Get should block when there is no
+	// connected address.
+	BlockingWait bool
+}
+
+// Balancer chooses network addresses for RPCs.
+//
+// Deprecated: please use package balancer.  May be removed in a future 1.x release.
+type Balancer interface {
+	// Start does the initialization work to bootstrap a Balancer. For example,
+	// this function may start the name resolution and watch the updates. It will
+	// be called when dialing.
+	Start(target string, config BalancerConfig) error
+	// Up informs the Balancer that gRPC has a connection to the server at
+	// addr. It returns down which is called once the connection to addr gets
+	// lost or closed.
+	// TODO: It is not clear how to construct and take advantage of the meaningful error
+	// parameter for down. Need realistic demands to guide.
+	Up(addr Address) (down func(error))
+	// Get gets the address of a server for the RPC corresponding to ctx.
+	// i) If it returns a connected address, gRPC internals issues the RPC on the
+	// connection to this address;
+	// ii) If it returns an address on which the connection is under construction
+	// (initiated by Notify(...)) but not connected, gRPC internals
+	//  * fails RPC if the RPC is fail-fast and connection is in the TransientFailure or
+	//  Shutdown state;
+	//  or
+	//  * issues RPC on the connection otherwise.
+	// iii) If it returns an address on which the connection does not exist, gRPC
+	// internals treats it as an error and will fail the corresponding RPC.
+	//
+	// Therefore, the following is the recommended rule when writing a custom Balancer.
+	// If opts.BlockingWait is true, it should return a connected address or
+	// block if there is no connected address. It should respect the timeout or
+	// cancellation of ctx when blocking. If opts.BlockingWait is false (for fail-fast
+	// RPCs), it should return an address it has notified via Notify(...) immediately
+	// instead of blocking.
+	//
+	// The function returns put which is called once the rpc has completed or failed.
+	// put can collect and report RPC stats to a remote load balancer.
+	//
+	// This function should only return the errors Balancer cannot recover by itself.
+	// gRPC internals will fail the RPC if an error is returned.
+	Get(ctx context.Context, opts BalancerGetOptions) (addr Address, put func(), err error)
+	// Notify returns a channel that is used by gRPC internals to watch the addresses
+	// gRPC needs to connect. The addresses might be from a name resolver or remote
+	// load balancer. gRPC internals will compare it with the existing connected
+	// addresses. If the address Balancer notified is not in the existing connected
+	// addresses, gRPC starts to connect the address. If an address in the existing
+	// connected addresses is not in the notification list, the corresponding connection
+	// is shutdown gracefully. Otherwise, there are no operations to take. Note that
+	// the Address slice must be the full list of the Addresses which should be connected.
+	// It is NOT delta.
+	Notify() <-chan []Address
+	// Close shuts down the balancer.
+	Close() error
+}
+
+// RoundRobin returns a Balancer that selects addresses round-robin. It uses r to watch
+// the name resolution updates and updates the addresses available correspondingly.
+//
+// Deprecated: please use package balancer/roundrobin. May be removed in a future 1.x release.
+func RoundRobin(r naming.Resolver) Balancer {
+	return &roundRobin{r: r}
+}
+
+type addrInfo struct {
+	addr      Address
+	connected bool
+}
+
+type roundRobin struct {
+	r      naming.Resolver
+	w      naming.Watcher
+	addrs  []*addrInfo // all the addresses the client should potentially connect
+	mu     sync.Mutex
+	addrCh chan []Address // the channel to notify gRPC internals the list of addresses the client should connect to.
+	next   int            // index of the next address to return for Get()
+	waitCh chan struct{}  // the channel to block when there is no connected address available
+	done   bool           // The Balancer is closed.
+}
+
+func (rr *roundRobin) watchAddrUpdates() error {
+	updates, err := rr.w.Next()
+	if err != nil {
+		grpclog.Warningf("grpc: the naming watcher stops working due to %v.", err)
+		return err
+	}
+	rr.mu.Lock()
+	defer rr.mu.Unlock()
+	for _, update := range updates {
+		addr := Address{
+			Addr:     update.Addr,
+			Metadata: update.Metadata,
+		}
+		switch update.Op {
+		case naming.Add:
+			var exist bool
+			for _, v := range rr.addrs {
+				if addr == v.addr {
+					exist = true
+					grpclog.Infoln("grpc: The name resolver wanted to add an existing address: ", addr)
+					break
+				}
+			}
+			if exist {
+				continue
+			}
+			rr.addrs = append(rr.addrs, &addrInfo{addr: addr})
+		case naming.Delete:
+			for i, v := range rr.addrs {
+				if addr == v.addr {
+					copy(rr.addrs[i:], rr.addrs[i+1:])
+					rr.addrs = rr.addrs[:len(rr.addrs)-1]
+					break
+				}
+			}
+		default:
+			grpclog.Errorln("Unknown update.Op ", update.Op)
+		}
+	}
+	// Make a copy of rr.addrs and write it onto rr.addrCh so that gRPC internals gets notified.
+	open := make([]Address, len(rr.addrs))
+	for i, v := range rr.addrs {
+		open[i] = v.addr
+	}
+	if rr.done {
+		return ErrClientConnClosing
+	}
+	select {
+	case <-rr.addrCh:
+	default:
+	}
+	rr.addrCh <- open
+	return nil
+}
+
+func (rr *roundRobin) Start(target string, config BalancerConfig) error {
+	rr.mu.Lock()
+	defer rr.mu.Unlock()
+	if rr.done {
+		return ErrClientConnClosing
+	}
+	if rr.r == nil {
+		// If there is no name resolver installed, it is not needed to
+		// do name resolution. In this case, target is added into rr.addrs
+		// as the only address available and rr.addrCh stays nil.
+		rr.addrs = append(rr.addrs, &addrInfo{addr: Address{Addr: target}})
+		return nil
+	}
+	w, err := rr.r.Resolve(target)
+	if err != nil {
+		return err
+	}
+	rr.w = w
+	rr.addrCh = make(chan []Address, 1)
+	go func() {
+		for {
+			if err := rr.watchAddrUpdates(); err != nil {
+				return
+			}
+		}
+	}()
+	return nil
+}
+
+// Up sets the connected state of addr and sends notification if there are pending
+// Get() calls.
+func (rr *roundRobin) Up(addr Address) func(error) {
+	rr.mu.Lock()
+	defer rr.mu.Unlock()
+	var cnt int
+	for _, a := range rr.addrs {
+		if a.addr == addr {
+			if a.connected {
+				return nil
+			}
+			a.connected = true
+		}
+		if a.connected {
+			cnt++
+		}
+	}
+	// addr is only one which is connected. Notify the Get() callers who are blocking.
+	if cnt == 1 && rr.waitCh != nil {
+		close(rr.waitCh)
+		rr.waitCh = nil
+	}
+	return func(err error) {
+		rr.down(addr, err)
+	}
+}
+
+// down unsets the connected state of addr.
+func (rr *roundRobin) down(addr Address, err error) {
+	rr.mu.Lock()
+	defer rr.mu.Unlock()
+	for _, a := range rr.addrs {
+		if addr == a.addr {
+			a.connected = false
+			break
+		}
+	}
+}
+
+// Get returns the next addr in the rotation.
+func (rr *roundRobin) Get(ctx context.Context, opts BalancerGetOptions) (addr Address, put func(), err error) {
+	var ch chan struct{}
+	rr.mu.Lock()
+	if rr.done {
+		rr.mu.Unlock()
+		err = ErrClientConnClosing
+		return
+	}
+
+	if len(rr.addrs) > 0 {
+		if rr.next >= len(rr.addrs) {
+			rr.next = 0
+		}
+		next := rr.next
+		for {
+			a := rr.addrs[next]
+			next = (next + 1) % len(rr.addrs)
+			if a.connected {
+				addr = a.addr
+				rr.next = next
+				rr.mu.Unlock()
+				return
+			}
+			if next == rr.next {
+				// Has iterated all the possible address but none is connected.
+				break
+			}
+		}
+	}
+	if !opts.BlockingWait {
+		if len(rr.addrs) == 0 {
+			rr.mu.Unlock()
+			err = status.Errorf(codes.Unavailable, "there is no address available")
+			return
+		}
+		// Returns the next addr on rr.addrs for failfast RPCs.
+		addr = rr.addrs[rr.next].addr
+		rr.next++
+		rr.mu.Unlock()
+		return
+	}
+	// Wait on rr.waitCh for non-failfast RPCs.
+	if rr.waitCh == nil {
+		ch = make(chan struct{})
+		rr.waitCh = ch
+	} else {
+		ch = rr.waitCh
+	}
+	rr.mu.Unlock()
+	for {
+		select {
+		case <-ctx.Done():
+			err = ctx.Err()
+			return
+		case <-ch:
+			rr.mu.Lock()
+			if rr.done {
+				rr.mu.Unlock()
+				err = ErrClientConnClosing
+				return
+			}
+
+			if len(rr.addrs) > 0 {
+				if rr.next >= len(rr.addrs) {
+					rr.next = 0
+				}
+				next := rr.next
+				for {
+					a := rr.addrs[next]
+					next = (next + 1) % len(rr.addrs)
+					if a.connected {
+						addr = a.addr
+						rr.next = next
+						rr.mu.Unlock()
+						return
+					}
+					if next == rr.next {
+						// Has iterated all the possible address but none is connected.
+						break
+					}
+				}
+			}
+			// The newly added addr got removed by Down() again.
+			if rr.waitCh == nil {
+				ch = make(chan struct{})
+				rr.waitCh = ch
+			} else {
+				ch = rr.waitCh
+			}
+			rr.mu.Unlock()
+		}
+	}
+}
+
+func (rr *roundRobin) Notify() <-chan []Address {
+	return rr.addrCh
+}
+
+func (rr *roundRobin) Close() error {
+	rr.mu.Lock()
+	defer rr.mu.Unlock()
+	if rr.done {
+		return errBalancerClosed
+	}
+	rr.done = true
+	if rr.w != nil {
+		rr.w.Close()
+	}
+	if rr.waitCh != nil {
+		close(rr.waitCh)
+		rr.waitCh = nil
+	}
+	if rr.addrCh != nil {
+		close(rr.addrCh)
+	}
+	return nil
+}
+
+// pickFirst is used to test multi-addresses in one addrConn in which all addresses share the same addrConn.
+// It is a wrapper around roundRobin balancer. The logic of all methods works fine because balancer.Get()
+// returns the only address Up by resetTransport().
+type pickFirst struct {
+	*roundRobin
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/balancer/balancer.go b/demo_test/vendor/google.golang.org/grpc/balancer/balancer.go
new file mode 100644
index 0000000..9258858
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/balancer/balancer.go
@@ -0,0 +1,454 @@
+/*
+ *
+ * Copyright 2017 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+// Package balancer defines APIs for load balancing in gRPC.
+// All APIs in this package are experimental.
+package balancer
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"net"
+	"strings"
+
+	"google.golang.org/grpc/connectivity"
+	"google.golang.org/grpc/credentials"
+	"google.golang.org/grpc/internal"
+	"google.golang.org/grpc/metadata"
+	"google.golang.org/grpc/resolver"
+	"google.golang.org/grpc/serviceconfig"
+)
+
+var (
+	// m is a map from name to balancer builder.
+	m = make(map[string]Builder)
+)
+
+// Register registers the balancer builder to the balancer map. b.Name
+// (lowercased) will be used as the name registered with this builder.  If the
+// Builder implements ConfigParser, ParseConfig will be called when new service
+// configs are received by the resolver, and the result will be provided to the
+// Balancer in UpdateClientConnState.
+//
+// NOTE: this function must only be called during initialization time (i.e. in
+// an init() function), and is not thread-safe. If multiple Balancers are
+// registered with the same name, the one registered last will take effect.
+func Register(b Builder) {
+	m[strings.ToLower(b.Name())] = b
+}
+
+// unregisterForTesting deletes the balancer with the given name from the
+// balancer map.
+//
+// This function is not thread-safe.
+func unregisterForTesting(name string) {
+	delete(m, name)
+}
+
+func init() {
+	internal.BalancerUnregister = unregisterForTesting
+}
+
+// Get returns the resolver builder registered with the given name.
+// Note that the compare is done in a case-insensitive fashion.
+// If no builder is register with the name, nil will be returned.
+func Get(name string) Builder {
+	if b, ok := m[strings.ToLower(name)]; ok {
+		return b
+	}
+	return nil
+}
+
+// SubConn represents a gRPC sub connection.
+// Each sub connection contains a list of addresses. gRPC will
+// try to connect to them (in sequence), and stop trying the
+// remainder once one connection is successful.
+//
+// The reconnect backoff will be applied on the list, not a single address.
+// For example, try_on_all_addresses -> backoff -> try_on_all_addresses.
+//
+// All SubConns start in IDLE, and will not try to connect. To trigger
+// the connecting, Balancers must call Connect.
+// When the connection encounters an error, it will reconnect immediately.
+// When the connection becomes IDLE, it will not reconnect unless Connect is
+// called.
+//
+// This interface is to be implemented by gRPC. Users should not need a
+// brand new implementation of this interface. For the situations like
+// testing, the new implementation should embed this interface. This allows
+// gRPC to add new methods to this interface.
+type SubConn interface {
+	// UpdateAddresses updates the addresses used in this SubConn.
+	// gRPC checks if currently-connected address is still in the new list.
+	// If it's in the list, the connection will be kept.
+	// If it's not in the list, the connection will gracefully closed, and
+	// a new connection will be created.
+	//
+	// This will trigger a state transition for the SubConn.
+	UpdateAddresses([]resolver.Address)
+	// Connect starts the connecting for this SubConn.
+	Connect()
+}
+
+// NewSubConnOptions contains options to create new SubConn.
+type NewSubConnOptions struct {
+	// CredsBundle is the credentials bundle that will be used in the created
+	// SubConn. If it's nil, the original creds from grpc DialOptions will be
+	// used.
+	CredsBundle credentials.Bundle
+	// HealthCheckEnabled indicates whether health check service should be
+	// enabled on this SubConn
+	HealthCheckEnabled bool
+}
+
+// State contains the balancer's state relevant to the gRPC ClientConn.
+type State struct {
+	// State contains the connectivity state of the balancer, which is used to
+	// determine the state of the ClientConn.
+	ConnectivityState connectivity.State
+	// Picker is used to choose connections (SubConns) for RPCs.
+	Picker V2Picker
+}
+
+// ClientConn represents a gRPC ClientConn.
+//
+// This interface is to be implemented by gRPC. Users should not need a
+// brand new implementation of this interface. For the situations like
+// testing, the new implementation should embed this interface. This allows
+// gRPC to add new methods to this interface.
+type ClientConn interface {
+	// NewSubConn is called by balancer to create a new SubConn.
+	// It doesn't block and wait for the connections to be established.
+	// Behaviors of the SubConn can be controlled by options.
+	NewSubConn([]resolver.Address, NewSubConnOptions) (SubConn, error)
+	// RemoveSubConn removes the SubConn from ClientConn.
+	// The SubConn will be shutdown.
+	RemoveSubConn(SubConn)
+
+	// UpdateBalancerState is called by balancer to notify gRPC that some internal
+	// state in balancer has changed.
+	//
+	// gRPC will update the connectivity state of the ClientConn, and will call pick
+	// on the new picker to pick new SubConn.
+	//
+	// Deprecated: use UpdateState instead
+	UpdateBalancerState(s connectivity.State, p Picker)
+
+	// UpdateState notifies gRPC that the balancer's internal state has
+	// changed.
+	//
+	// gRPC will update the connectivity state of the ClientConn, and will call pick
+	// on the new picker to pick new SubConns.
+	UpdateState(State)
+
+	// ResolveNow is called by balancer to notify gRPC to do a name resolving.
+	ResolveNow(resolver.ResolveNowOptions)
+
+	// Target returns the dial target for this ClientConn.
+	//
+	// Deprecated: Use the Target field in the BuildOptions instead.
+	Target() string
+}
+
+// BuildOptions contains additional information for Build.
+type BuildOptions struct {
+	// DialCreds is the transport credential the Balancer implementation can
+	// use to dial to a remote load balancer server. The Balancer implementations
+	// can ignore this if it does not need to talk to another party securely.
+	DialCreds credentials.TransportCredentials
+	// CredsBundle is the credentials bundle that the Balancer can use.
+	CredsBundle credentials.Bundle
+	// Dialer is the custom dialer the Balancer implementation can use to dial
+	// to a remote load balancer server. The Balancer implementations
+	// can ignore this if it doesn't need to talk to remote balancer.
+	Dialer func(context.Context, string) (net.Conn, error)
+	// ChannelzParentID is the entity parent's channelz unique identification number.
+	ChannelzParentID int64
+	// Target contains the parsed address info of the dial target. It is the same resolver.Target as
+	// passed to the resolver.
+	// See the documentation for the resolver.Target type for details about what it contains.
+	Target resolver.Target
+}
+
+// Builder creates a balancer.
+type Builder interface {
+	// Build creates a new balancer with the ClientConn.
+	Build(cc ClientConn, opts BuildOptions) Balancer
+	// Name returns the name of balancers built by this builder.
+	// It will be used to pick balancers (for example in service config).
+	Name() string
+}
+
+// ConfigParser parses load balancer configs.
+type ConfigParser interface {
+	// ParseConfig parses the JSON load balancer config provided into an
+	// internal form or returns an error if the config is invalid.  For future
+	// compatibility reasons, unknown fields in the config should be ignored.
+	ParseConfig(LoadBalancingConfigJSON json.RawMessage) (serviceconfig.LoadBalancingConfig, error)
+}
+
+// PickInfo contains additional information for the Pick operation.
+type PickInfo struct {
+	// FullMethodName is the method name that NewClientStream() is called
+	// with. The canonical format is /service/Method.
+	FullMethodName string
+	// Ctx is the RPC's context, and may contain relevant RPC-level information
+	// like the outgoing header metadata.
+	Ctx context.Context
+}
+
+// DoneInfo contains additional information for done.
+type DoneInfo struct {
+	// Err is the rpc error the RPC finished with. It could be nil.
+	Err error
+	// Trailer contains the metadata from the RPC's trailer, if present.
+	Trailer metadata.MD
+	// BytesSent indicates if any bytes have been sent to the server.
+	BytesSent bool
+	// BytesReceived indicates if any byte has been received from the server.
+	BytesReceived bool
+	// ServerLoad is the load received from server. It's usually sent as part of
+	// trailing metadata.
+	//
+	// The only supported type now is *orca_v1.LoadReport.
+	ServerLoad interface{}
+}
+
+var (
+	// ErrNoSubConnAvailable indicates no SubConn is available for pick().
+	// gRPC will block the RPC until a new picker is available via UpdateBalancerState().
+	ErrNoSubConnAvailable = errors.New("no SubConn is available")
+	// ErrTransientFailure indicates all SubConns are in TransientFailure.
+	// WaitForReady RPCs will block, non-WaitForReady RPCs will fail.
+	ErrTransientFailure = TransientFailureError(errors.New("all SubConns are in TransientFailure"))
+)
+
+// Picker is used by gRPC to pick a SubConn to send an RPC.
+// Balancer is expected to generate a new picker from its snapshot every time its
+// internal state has changed.
+//
+// The pickers used by gRPC can be updated by ClientConn.UpdateBalancerState().
+//
+// Deprecated: use V2Picker instead
+type Picker interface {
+	// Pick returns the SubConn to be used to send the RPC.
+	// The returned SubConn must be one returned by NewSubConn().
+	//
+	// This functions is expected to return:
+	// - a SubConn that is known to be READY;
+	// - ErrNoSubConnAvailable if no SubConn is available, but progress is being
+	//   made (for example, some SubConn is in CONNECTING mode);
+	// - other errors if no active connecting is happening (for example, all SubConn
+	//   are in TRANSIENT_FAILURE mode).
+	//
+	// If a SubConn is returned:
+	// - If it is READY, gRPC will send the RPC on it;
+	// - If it is not ready, or becomes not ready after it's returned, gRPC will
+	//   block until UpdateBalancerState() is called and will call pick on the
+	//   new picker. The done function returned from Pick(), if not nil, will be
+	//   called with nil error, no bytes sent and no bytes received.
+	//
+	// If the returned error is not nil:
+	// - If the error is ErrNoSubConnAvailable, gRPC will block until UpdateBalancerState()
+	// - If the error is ErrTransientFailure or implements IsTransientFailure()
+	//   bool, returning true:
+	//   - If the RPC is wait-for-ready, gRPC will block until UpdateBalancerState()
+	//     is called to pick again;
+	//   - Otherwise, RPC will fail with unavailable error.
+	// - Else (error is other non-nil error):
+	//   - The RPC will fail with the error's status code, or Unknown if it is
+	//     not a status error.
+	//
+	// The returned done() function will be called once the rpc has finished,
+	// with the final status of that RPC.  If the SubConn returned is not a
+	// valid SubConn type, done may not be called.  done may be nil if balancer
+	// doesn't care about the RPC status.
+	Pick(ctx context.Context, info PickInfo) (conn SubConn, done func(DoneInfo), err error)
+}
+
+// PickResult contains information related to a connection chosen for an RPC.
+type PickResult struct {
+	// SubConn is the connection to use for this pick, if its state is Ready.
+	// If the state is not Ready, gRPC will block the RPC until a new Picker is
+	// provided by the balancer (using ClientConn.UpdateState).  The SubConn
+	// must be one returned by ClientConn.NewSubConn.
+	SubConn SubConn
+
+	// Done is called when the RPC is completed.  If the SubConn is not ready,
+	// this will be called with a nil parameter.  If the SubConn is not a valid
+	// type, Done may not be called.  May be nil if the balancer does not wish
+	// to be notified when the RPC completes.
+	Done func(DoneInfo)
+}
+
+type transientFailureError struct {
+	error
+}
+
+func (e *transientFailureError) IsTransientFailure() bool { return true }
+
+// TransientFailureError wraps err in an error implementing
+// IsTransientFailure() bool, returning true.
+func TransientFailureError(err error) error {
+	return &transientFailureError{error: err}
+}
+
+// V2Picker is used by gRPC to pick a SubConn to send an RPC.
+// Balancer is expected to generate a new picker from its snapshot every time its
+// internal state has changed.
+//
+// The pickers used by gRPC can be updated by ClientConn.UpdateBalancerState().
+type V2Picker interface {
+	// Pick returns the connection to use for this RPC and related information.
+	//
+	// Pick should not block.  If the balancer needs to do I/O or any blocking
+	// or time-consuming work to service this call, it should return
+	// ErrNoSubConnAvailable, and the Pick call will be repeated by gRPC when
+	// the Picker is updated (using ClientConn.UpdateState).
+	//
+	// If an error is returned:
+	//
+	// - If the error is ErrNoSubConnAvailable, gRPC will block until a new
+	//   Picker is provided by the balancer (using ClientConn.UpdateState).
+	//
+	// - If the error implements IsTransientFailure() bool, returning true,
+	//   wait for ready RPCs will wait, but non-wait for ready RPCs will be
+	//   terminated with this error's Error() string and status code
+	//   Unavailable.
+	//
+	// - Any other errors terminate all RPCs with the code and message
+	//   provided.  If the error is not a status error, it will be converted by
+	//   gRPC to a status error with code Unknown.
+	Pick(info PickInfo) (PickResult, error)
+}
+
+// Balancer takes input from gRPC, manages SubConns, and collects and aggregates
+// the connectivity states.
+//
+// It also generates and updates the Picker used by gRPC to pick SubConns for RPCs.
+//
+// HandleSubConnectionStateChange, HandleResolvedAddrs and Close are guaranteed
+// to be called synchronously from the same goroutine.
+// There's no guarantee on picker.Pick, it may be called anytime.
+type Balancer interface {
+	// HandleSubConnStateChange is called by gRPC when the connectivity state
+	// of sc has changed.
+	// Balancer is expected to aggregate all the state of SubConn and report
+	// that back to gRPC.
+	// Balancer should also generate and update Pickers when its internal state has
+	// been changed by the new state.
+	//
+	// Deprecated: if V2Balancer is implemented by the Balancer,
+	// UpdateSubConnState will be called instead.
+	HandleSubConnStateChange(sc SubConn, state connectivity.State)
+	// HandleResolvedAddrs is called by gRPC to send updated resolved addresses to
+	// balancers.
+	// Balancer can create new SubConn or remove SubConn with the addresses.
+	// An empty address slice and a non-nil error will be passed if the resolver returns
+	// non-nil error to gRPC.
+	//
+	// Deprecated: if V2Balancer is implemented by the Balancer,
+	// UpdateClientConnState will be called instead.
+	HandleResolvedAddrs([]resolver.Address, error)
+	// Close closes the balancer. The balancer is not required to call
+	// ClientConn.RemoveSubConn for its existing SubConns.
+	Close()
+}
+
+// SubConnState describes the state of a SubConn.
+type SubConnState struct {
+	// ConnectivityState is the connectivity state of the SubConn.
+	ConnectivityState connectivity.State
+	// ConnectionError is set if the ConnectivityState is TransientFailure,
+	// describing the reason the SubConn failed.  Otherwise, it is nil.
+	ConnectionError error
+}
+
+// ClientConnState describes the state of a ClientConn relevant to the
+// balancer.
+type ClientConnState struct {
+	ResolverState resolver.State
+	// The parsed load balancing configuration returned by the builder's
+	// ParseConfig method, if implemented.
+	BalancerConfig serviceconfig.LoadBalancingConfig
+}
+
+// ErrBadResolverState may be returned by UpdateClientConnState to indicate a
+// problem with the provided name resolver data.
+var ErrBadResolverState = errors.New("bad resolver state")
+
+// V2Balancer is defined for documentation purposes.  If a Balancer also
+// implements V2Balancer, its UpdateClientConnState method will be called
+// instead of HandleResolvedAddrs and its UpdateSubConnState will be called
+// instead of HandleSubConnStateChange.
+type V2Balancer interface {
+	// UpdateClientConnState is called by gRPC when the state of the ClientConn
+	// changes.  If the error returned is ErrBadResolverState, the ClientConn
+	// will begin calling ResolveNow on the active name resolver with
+	// exponential backoff until a subsequent call to UpdateClientConnState
+	// returns a nil error.  Any other errors are currently ignored.
+	UpdateClientConnState(ClientConnState) error
+	// ResolverError is called by gRPC when the name resolver reports an error.
+	ResolverError(error)
+	// UpdateSubConnState is called by gRPC when the state of a SubConn
+	// changes.
+	UpdateSubConnState(SubConn, SubConnState)
+	// Close closes the balancer. The balancer is not required to call
+	// ClientConn.RemoveSubConn for its existing SubConns.
+	Close()
+}
+
+// ConnectivityStateEvaluator takes the connectivity states of multiple SubConns
+// and returns one aggregated connectivity state.
+//
+// It's not thread safe.
+type ConnectivityStateEvaluator struct {
+	numReady      uint64 // Number of addrConns in ready state.
+	numConnecting uint64 // Number of addrConns in connecting state.
+}
+
+// RecordTransition records state change happening in subConn and based on that
+// it evaluates what aggregated state should be.
+//
+//  - If at least one SubConn in Ready, the aggregated state is Ready;
+//  - Else if at least one SubConn in Connecting, the aggregated state is Connecting;
+//  - Else the aggregated state is TransientFailure.
+//
+// Idle and Shutdown are not considered.
+func (cse *ConnectivityStateEvaluator) RecordTransition(oldState, newState connectivity.State) connectivity.State {
+	// Update counters.
+	for idx, state := range []connectivity.State{oldState, newState} {
+		updateVal := 2*uint64(idx) - 1 // -1 for oldState and +1 for new.
+		switch state {
+		case connectivity.Ready:
+			cse.numReady += updateVal
+		case connectivity.Connecting:
+			cse.numConnecting += updateVal
+		}
+	}
+
+	// Evaluate.
+	if cse.numReady > 0 {
+		return connectivity.Ready
+	}
+	if cse.numConnecting > 0 {
+		return connectivity.Connecting
+	}
+	return connectivity.TransientFailure
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/balancer/base/balancer.go b/demo_test/vendor/google.golang.org/grpc/balancer/base/balancer.go
new file mode 100644
index 0000000..80559b8
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/balancer/base/balancer.go
@@ -0,0 +1,286 @@
+/*
+ *
+ * Copyright 2017 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package base
+
+import (
+	"context"
+	"errors"
+	"fmt"
+
+	"google.golang.org/grpc/balancer"
+	"google.golang.org/grpc/connectivity"
+	"google.golang.org/grpc/grpclog"
+	"google.golang.org/grpc/resolver"
+)
+
+type baseBuilder struct {
+	name            string
+	pickerBuilder   PickerBuilder
+	v2PickerBuilder V2PickerBuilder
+	config          Config
+}
+
+func (bb *baseBuilder) Build(cc balancer.ClientConn, opt balancer.BuildOptions) balancer.Balancer {
+	bal := &baseBalancer{
+		cc:              cc,
+		pickerBuilder:   bb.pickerBuilder,
+		v2PickerBuilder: bb.v2PickerBuilder,
+
+		subConns: make(map[resolver.Address]balancer.SubConn),
+		scStates: make(map[balancer.SubConn]connectivity.State),
+		csEvltr:  &balancer.ConnectivityStateEvaluator{},
+		config:   bb.config,
+	}
+	// Initialize picker to a picker that always returns
+	// ErrNoSubConnAvailable, because when state of a SubConn changes, we
+	// may call UpdateState with this picker.
+	if bb.pickerBuilder != nil {
+		bal.picker = NewErrPicker(balancer.ErrNoSubConnAvailable)
+	} else {
+		bal.v2Picker = NewErrPickerV2(balancer.ErrNoSubConnAvailable)
+	}
+	return bal
+}
+
+func (bb *baseBuilder) Name() string {
+	return bb.name
+}
+
+var _ balancer.V2Balancer = (*baseBalancer)(nil) // Assert that we implement V2Balancer
+
+type baseBalancer struct {
+	cc              balancer.ClientConn
+	pickerBuilder   PickerBuilder
+	v2PickerBuilder V2PickerBuilder
+
+	csEvltr *balancer.ConnectivityStateEvaluator
+	state   connectivity.State
+
+	subConns map[resolver.Address]balancer.SubConn
+	scStates map[balancer.SubConn]connectivity.State
+	picker   balancer.Picker
+	v2Picker balancer.V2Picker
+	config   Config
+
+	resolverErr error // the last error reported by the resolver; cleared on successful resolution
+	connErr     error // the last connection error; cleared upon leaving TransientFailure
+}
+
+func (b *baseBalancer) HandleResolvedAddrs(addrs []resolver.Address, err error) {
+	panic("not implemented")
+}
+
+func (b *baseBalancer) ResolverError(err error) {
+	b.resolverErr = err
+	if len(b.subConns) == 0 {
+		b.state = connectivity.TransientFailure
+	}
+	if b.state != connectivity.TransientFailure {
+		// The picker will not change since the balancer does not currently
+		// report an error.
+		return
+	}
+	b.regeneratePicker()
+	if b.picker != nil {
+		b.cc.UpdateBalancerState(b.state, b.picker)
+	} else {
+		b.cc.UpdateState(balancer.State{
+			ConnectivityState: b.state,
+			Picker:            b.v2Picker,
+		})
+	}
+}
+
+func (b *baseBalancer) UpdateClientConnState(s balancer.ClientConnState) error {
+	// TODO: handle s.ResolverState.Err (log if not nil) once implemented.
+	// TODO: handle s.ResolverState.ServiceConfig?
+	if grpclog.V(2) {
+		grpclog.Infoln("base.baseBalancer: got new ClientConn state: ", s)
+	}
+	// Successful resolution; clear resolver error and ensure we return nil.
+	b.resolverErr = nil
+	// addrsSet is the set converted from addrs, it's used for quick lookup of an address.
+	addrsSet := make(map[resolver.Address]struct{})
+	for _, a := range s.ResolverState.Addresses {
+		addrsSet[a] = struct{}{}
+		if _, ok := b.subConns[a]; !ok {
+			// a is a new address (not existing in b.subConns).
+			sc, err := b.cc.NewSubConn([]resolver.Address{a}, balancer.NewSubConnOptions{HealthCheckEnabled: b.config.HealthCheck})
+			if err != nil {
+				grpclog.Warningf("base.baseBalancer: failed to create new SubConn: %v", err)
+				continue
+			}
+			b.subConns[a] = sc
+			b.scStates[sc] = connectivity.Idle
+			sc.Connect()
+		}
+	}
+	for a, sc := range b.subConns {
+		// a was removed by resolver.
+		if _, ok := addrsSet[a]; !ok {
+			b.cc.RemoveSubConn(sc)
+			delete(b.subConns, a)
+			// Keep the state of this sc in b.scStates until sc's state becomes Shutdown.
+			// The entry will be deleted in HandleSubConnStateChange.
+		}
+	}
+	// If resolver state contains no addresses, return an error so ClientConn
+	// will trigger re-resolve. Also records this as an resolver error, so when
+	// the overall state turns transient failure, the error message will have
+	// the zero address information.
+	if len(s.ResolverState.Addresses) == 0 {
+		b.ResolverError(errors.New("produced zero addresses"))
+		return balancer.ErrBadResolverState
+	}
+	return nil
+}
+
+// mergeErrors builds an error from the last connection error and the last
+// resolver error.  Must only be called if b.state is TransientFailure.
+func (b *baseBalancer) mergeErrors() error {
+	// connErr must always be non-nil unless there are no SubConns, in which
+	// case resolverErr must be non-nil.
+	if b.connErr == nil {
+		return fmt.Errorf("last resolver error: %v", b.resolverErr)
+	}
+	if b.resolverErr == nil {
+		return fmt.Errorf("last connection error: %v", b.connErr)
+	}
+	return fmt.Errorf("last connection error: %v; last resolver error: %v", b.connErr, b.resolverErr)
+}
+
+// regeneratePicker takes a snapshot of the balancer, and generates a picker
+// from it. The picker is
+//  - errPicker if the balancer is in TransientFailure,
+//  - built by the pickerBuilder with all READY SubConns otherwise.
+func (b *baseBalancer) regeneratePicker() {
+	if b.state == connectivity.TransientFailure {
+		if b.pickerBuilder != nil {
+			b.picker = NewErrPicker(balancer.ErrTransientFailure)
+		} else {
+			b.v2Picker = NewErrPickerV2(balancer.TransientFailureError(b.mergeErrors()))
+		}
+		return
+	}
+	if b.pickerBuilder != nil {
+		readySCs := make(map[resolver.Address]balancer.SubConn)
+
+		// Filter out all ready SCs from full subConn map.
+		for addr, sc := range b.subConns {
+			if st, ok := b.scStates[sc]; ok && st == connectivity.Ready {
+				readySCs[addr] = sc
+			}
+		}
+		b.picker = b.pickerBuilder.Build(readySCs)
+	} else {
+		readySCs := make(map[balancer.SubConn]SubConnInfo)
+
+		// Filter out all ready SCs from full subConn map.
+		for addr, sc := range b.subConns {
+			if st, ok := b.scStates[sc]; ok && st == connectivity.Ready {
+				readySCs[sc] = SubConnInfo{Address: addr}
+			}
+		}
+		b.v2Picker = b.v2PickerBuilder.Build(PickerBuildInfo{ReadySCs: readySCs})
+	}
+}
+
+func (b *baseBalancer) HandleSubConnStateChange(sc balancer.SubConn, s connectivity.State) {
+	panic("not implemented")
+}
+
+func (b *baseBalancer) UpdateSubConnState(sc balancer.SubConn, state balancer.SubConnState) {
+	s := state.ConnectivityState
+	if grpclog.V(2) {
+		grpclog.Infof("base.baseBalancer: handle SubConn state change: %p, %v", sc, s)
+	}
+	oldS, ok := b.scStates[sc]
+	if !ok {
+		if grpclog.V(2) {
+			grpclog.Infof("base.baseBalancer: got state changes for an unknown SubConn: %p, %v", sc, s)
+		}
+		return
+	}
+	if oldS == connectivity.TransientFailure && s == connectivity.Connecting {
+		// Once a subconn enters TRANSIENT_FAILURE, ignore subsequent
+		// CONNECTING transitions to prevent the aggregated state from being
+		// always CONNECTING when many backends exist but are all down.
+		return
+	}
+	b.scStates[sc] = s
+	switch s {
+	case connectivity.Idle:
+		sc.Connect()
+	case connectivity.Shutdown:
+		// When an address was removed by resolver, b called RemoveSubConn but
+		// kept the sc's state in scStates. Remove state for this sc here.
+		delete(b.scStates, sc)
+	case connectivity.TransientFailure:
+		// Save error to be reported via picker.
+		b.connErr = state.ConnectionError
+	}
+
+	b.state = b.csEvltr.RecordTransition(oldS, s)
+
+	// Regenerate picker when one of the following happens:
+	//  - this sc entered or left ready
+	//  - the aggregated state of balancer is TransientFailure
+	//    (may need to update error message)
+	if (s == connectivity.Ready) != (oldS == connectivity.Ready) ||
+		b.state == connectivity.TransientFailure {
+		b.regeneratePicker()
+	}
+
+	if b.picker != nil {
+		b.cc.UpdateBalancerState(b.state, b.picker)
+	} else {
+		b.cc.UpdateState(balancer.State{ConnectivityState: b.state, Picker: b.v2Picker})
+	}
+}
+
+// Close is a nop because base balancer doesn't have internal state to clean up,
+// and it doesn't need to call RemoveSubConn for the SubConns.
+func (b *baseBalancer) Close() {
+}
+
+// NewErrPicker returns a picker that always returns err on Pick().
+func NewErrPicker(err error) balancer.Picker {
+	return &errPicker{err: err}
+}
+
+type errPicker struct {
+	err error // Pick() always returns this err.
+}
+
+func (p *errPicker) Pick(context.Context, balancer.PickInfo) (balancer.SubConn, func(balancer.DoneInfo), error) {
+	return nil, nil, p.err
+}
+
+// NewErrPickerV2 returns a V2Picker that always returns err on Pick().
+func NewErrPickerV2(err error) balancer.V2Picker {
+	return &errPickerV2{err: err}
+}
+
+type errPickerV2 struct {
+	err error // Pick() always returns this err.
+}
+
+func (p *errPickerV2) Pick(info balancer.PickInfo) (balancer.PickResult, error) {
+	return balancer.PickResult{}, p.err
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/balancer/base/base.go b/demo_test/vendor/google.golang.org/grpc/balancer/base/base.go
new file mode 100644
index 0000000..4192918
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/balancer/base/base.go
@@ -0,0 +1,93 @@
+/*
+ *
+ * Copyright 2017 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+// Package base defines a balancer base that can be used to build balancers with
+// different picking algorithms.
+//
+// The base balancer creates a new SubConn for each resolved address. The
+// provided picker will only be notified about READY SubConns.
+//
+// This package is the base of round_robin balancer, its purpose is to be used
+// to build round_robin like balancers with complex picking algorithms.
+// Balancers with more complicated logic should try to implement a balancer
+// builder from scratch.
+//
+// All APIs in this package are experimental.
+package base
+
+import (
+	"google.golang.org/grpc/balancer"
+	"google.golang.org/grpc/resolver"
+)
+
+// PickerBuilder creates balancer.Picker.
+type PickerBuilder interface {
+	// Build takes a slice of ready SubConns, and returns a picker that will be
+	// used by gRPC to pick a SubConn.
+	Build(readySCs map[resolver.Address]balancer.SubConn) balancer.Picker
+}
+
+// V2PickerBuilder creates balancer.V2Picker.
+type V2PickerBuilder interface {
+	// Build returns a picker that will be used by gRPC to pick a SubConn.
+	Build(info PickerBuildInfo) balancer.V2Picker
+}
+
+// PickerBuildInfo contains information needed by the picker builder to
+// construct a picker.
+type PickerBuildInfo struct {
+	// ReadySCs is a map from all ready SubConns to the Addresses used to
+	// create them.
+	ReadySCs map[balancer.SubConn]SubConnInfo
+}
+
+// SubConnInfo contains information about a SubConn created by the base
+// balancer.
+type SubConnInfo struct {
+	Address resolver.Address // the address used to create this SubConn
+}
+
+// NewBalancerBuilder returns a balancer builder. The balancers
+// built by this builder will use the picker builder to build pickers.
+func NewBalancerBuilder(name string, pb PickerBuilder) balancer.Builder {
+	return NewBalancerBuilderWithConfig(name, pb, Config{})
+}
+
+// Config contains the config info about the base balancer builder.
+type Config struct {
+	// HealthCheck indicates whether health checking should be enabled for this specific balancer.
+	HealthCheck bool
+}
+
+// NewBalancerBuilderWithConfig returns a base balancer builder configured by the provided config.
+func NewBalancerBuilderWithConfig(name string, pb PickerBuilder, config Config) balancer.Builder {
+	return &baseBuilder{
+		name:          name,
+		pickerBuilder: pb,
+		config:        config,
+	}
+}
+
+// NewBalancerBuilderV2 returns a base balancer builder configured by the provided config.
+func NewBalancerBuilderV2(name string, pb V2PickerBuilder, config Config) balancer.Builder {
+	return &baseBuilder{
+		name:            name,
+		v2PickerBuilder: pb,
+		config:          config,
+	}
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/balancer/roundrobin/roundrobin.go b/demo_test/vendor/google.golang.org/grpc/balancer/roundrobin/roundrobin.go
new file mode 100644
index 0000000..d4d6455
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/balancer/roundrobin/roundrobin.go
@@ -0,0 +1,81 @@
+/*
+ *
+ * Copyright 2017 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+// Package roundrobin defines a roundrobin balancer. Roundrobin balancer is
+// installed as one of the default balancers in gRPC, users don't need to
+// explicitly install this balancer.
+package roundrobin
+
+import (
+	"sync"
+
+	"google.golang.org/grpc/balancer"
+	"google.golang.org/grpc/balancer/base"
+	"google.golang.org/grpc/grpclog"
+	"google.golang.org/grpc/internal/grpcrand"
+)
+
+// Name is the name of round_robin balancer.
+const Name = "round_robin"
+
+// newBuilder creates a new roundrobin balancer builder.
+func newBuilder() balancer.Builder {
+	return base.NewBalancerBuilderV2(Name, &rrPickerBuilder{}, base.Config{HealthCheck: true})
+}
+
+func init() {
+	balancer.Register(newBuilder())
+}
+
+type rrPickerBuilder struct{}
+
+func (*rrPickerBuilder) Build(info base.PickerBuildInfo) balancer.V2Picker {
+	grpclog.Infof("roundrobinPicker: newPicker called with info: %v", info)
+	if len(info.ReadySCs) == 0 {
+		return base.NewErrPickerV2(balancer.ErrNoSubConnAvailable)
+	}
+	var scs []balancer.SubConn
+	for sc := range info.ReadySCs {
+		scs = append(scs, sc)
+	}
+	return &rrPicker{
+		subConns: scs,
+		// Start at a random index, as the same RR balancer rebuilds a new
+		// picker when SubConn states change, and we don't want to apply excess
+		// load to the first server in the list.
+		next: grpcrand.Intn(len(scs)),
+	}
+}
+
+type rrPicker struct {
+	// subConns is the snapshot of the roundrobin balancer when this picker was
+	// created. The slice is immutable. Each Get() will do a round robin
+	// selection from it and return the selected SubConn.
+	subConns []balancer.SubConn
+
+	mu   sync.Mutex
+	next int
+}
+
+func (p *rrPicker) Pick(balancer.PickInfo) (balancer.PickResult, error) {
+	p.mu.Lock()
+	sc := p.subConns[p.next]
+	p.next = (p.next + 1) % len(p.subConns)
+	p.mu.Unlock()
+	return balancer.PickResult{SubConn: sc}, nil
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/balancer_conn_wrappers.go b/demo_test/vendor/google.golang.org/grpc/balancer_conn_wrappers.go
new file mode 100644
index 0000000..f8667a2
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/balancer_conn_wrappers.go
@@ -0,0 +1,271 @@
+/*
+ *
+ * Copyright 2017 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package grpc
+
+import (
+	"fmt"
+	"sync"
+
+	"google.golang.org/grpc/balancer"
+	"google.golang.org/grpc/connectivity"
+	"google.golang.org/grpc/internal/buffer"
+	"google.golang.org/grpc/internal/channelz"
+	"google.golang.org/grpc/internal/grpcsync"
+	"google.golang.org/grpc/resolver"
+)
+
+// scStateUpdate contains the subConn and the new state it changed to.
+type scStateUpdate struct {
+	sc    balancer.SubConn
+	state connectivity.State
+	err   error
+}
+
+// ccBalancerWrapper is a wrapper on top of cc for balancers.
+// It implements balancer.ClientConn interface.
+type ccBalancerWrapper struct {
+	cc         *ClientConn
+	balancerMu sync.Mutex // synchronizes calls to the balancer
+	balancer   balancer.Balancer
+	scBuffer   *buffer.Unbounded
+	done       *grpcsync.Event
+
+	mu       sync.Mutex
+	subConns map[*acBalancerWrapper]struct{}
+}
+
+func newCCBalancerWrapper(cc *ClientConn, b balancer.Builder, bopts balancer.BuildOptions) *ccBalancerWrapper {
+	ccb := &ccBalancerWrapper{
+		cc:       cc,
+		scBuffer: buffer.NewUnbounded(),
+		done:     grpcsync.NewEvent(),
+		subConns: make(map[*acBalancerWrapper]struct{}),
+	}
+	go ccb.watcher()
+	ccb.balancer = b.Build(ccb, bopts)
+	return ccb
+}
+
+// watcher balancer functions sequentially, so the balancer can be implemented
+// lock-free.
+func (ccb *ccBalancerWrapper) watcher() {
+	for {
+		select {
+		case t := <-ccb.scBuffer.Get():
+			ccb.scBuffer.Load()
+			if ccb.done.HasFired() {
+				break
+			}
+			ccb.balancerMu.Lock()
+			su := t.(*scStateUpdate)
+			if ub, ok := ccb.balancer.(balancer.V2Balancer); ok {
+				ub.UpdateSubConnState(su.sc, balancer.SubConnState{ConnectivityState: su.state, ConnectionError: su.err})
+			} else {
+				ccb.balancer.HandleSubConnStateChange(su.sc, su.state)
+			}
+			ccb.balancerMu.Unlock()
+		case <-ccb.done.Done():
+		}
+
+		if ccb.done.HasFired() {
+			ccb.balancer.Close()
+			ccb.mu.Lock()
+			scs := ccb.subConns
+			ccb.subConns = nil
+			ccb.mu.Unlock()
+			for acbw := range scs {
+				ccb.cc.removeAddrConn(acbw.getAddrConn(), errConnDrain)
+			}
+			ccb.UpdateState(balancer.State{ConnectivityState: connectivity.Connecting, Picker: nil})
+			return
+		}
+	}
+}
+
+func (ccb *ccBalancerWrapper) close() {
+	ccb.done.Fire()
+}
+
+func (ccb *ccBalancerWrapper) handleSubConnStateChange(sc balancer.SubConn, s connectivity.State, err error) {
+	// When updating addresses for a SubConn, if the address in use is not in
+	// the new addresses, the old ac will be tearDown() and a new ac will be
+	// created. tearDown() generates a state change with Shutdown state, we
+	// don't want the balancer to receive this state change. So before
+	// tearDown() on the old ac, ac.acbw (acWrapper) will be set to nil, and
+	// this function will be called with (nil, Shutdown). We don't need to call
+	// balancer method in this case.
+	if sc == nil {
+		return
+	}
+	ccb.scBuffer.Put(&scStateUpdate{
+		sc:    sc,
+		state: s,
+		err:   err,
+	})
+}
+
+func (ccb *ccBalancerWrapper) updateClientConnState(ccs *balancer.ClientConnState) error {
+	ccb.balancerMu.Lock()
+	defer ccb.balancerMu.Unlock()
+	if ub, ok := ccb.balancer.(balancer.V2Balancer); ok {
+		return ub.UpdateClientConnState(*ccs)
+	}
+	ccb.balancer.HandleResolvedAddrs(ccs.ResolverState.Addresses, nil)
+	return nil
+}
+
+func (ccb *ccBalancerWrapper) resolverError(err error) {
+	if ub, ok := ccb.balancer.(balancer.V2Balancer); ok {
+		ccb.balancerMu.Lock()
+		ub.ResolverError(err)
+		ccb.balancerMu.Unlock()
+	}
+}
+
+func (ccb *ccBalancerWrapper) NewSubConn(addrs []resolver.Address, opts balancer.NewSubConnOptions) (balancer.SubConn, error) {
+	if len(addrs) <= 0 {
+		return nil, fmt.Errorf("grpc: cannot create SubConn with empty address list")
+	}
+	ccb.mu.Lock()
+	defer ccb.mu.Unlock()
+	if ccb.subConns == nil {
+		return nil, fmt.Errorf("grpc: ClientConn balancer wrapper was closed")
+	}
+	ac, err := ccb.cc.newAddrConn(addrs, opts)
+	if err != nil {
+		return nil, err
+	}
+	acbw := &acBalancerWrapper{ac: ac}
+	acbw.ac.mu.Lock()
+	ac.acbw = acbw
+	acbw.ac.mu.Unlock()
+	ccb.subConns[acbw] = struct{}{}
+	return acbw, nil
+}
+
+func (ccb *ccBalancerWrapper) RemoveSubConn(sc balancer.SubConn) {
+	acbw, ok := sc.(*acBalancerWrapper)
+	if !ok {
+		return
+	}
+	ccb.mu.Lock()
+	defer ccb.mu.Unlock()
+	if ccb.subConns == nil {
+		return
+	}
+	delete(ccb.subConns, acbw)
+	ccb.cc.removeAddrConn(acbw.getAddrConn(), errConnDrain)
+}
+
+func (ccb *ccBalancerWrapper) UpdateBalancerState(s connectivity.State, p balancer.Picker) {
+	ccb.mu.Lock()
+	defer ccb.mu.Unlock()
+	if ccb.subConns == nil {
+		return
+	}
+	// Update picker before updating state.  Even though the ordering here does
+	// not matter, it can lead to multiple calls of Pick in the common start-up
+	// case where we wait for ready and then perform an RPC.  If the picker is
+	// updated later, we could call the "connecting" picker when the state is
+	// updated, and then call the "ready" picker after the picker gets updated.
+	ccb.cc.blockingpicker.updatePicker(p)
+	ccb.cc.csMgr.updateState(s)
+}
+
+func (ccb *ccBalancerWrapper) UpdateState(s balancer.State) {
+	ccb.mu.Lock()
+	defer ccb.mu.Unlock()
+	if ccb.subConns == nil {
+		return
+	}
+	// Update picker before updating state.  Even though the ordering here does
+	// not matter, it can lead to multiple calls of Pick in the common start-up
+	// case where we wait for ready and then perform an RPC.  If the picker is
+	// updated later, we could call the "connecting" picker when the state is
+	// updated, and then call the "ready" picker after the picker gets updated.
+	ccb.cc.blockingpicker.updatePickerV2(s.Picker)
+	ccb.cc.csMgr.updateState(s.ConnectivityState)
+}
+
+func (ccb *ccBalancerWrapper) ResolveNow(o resolver.ResolveNowOptions) {
+	ccb.cc.resolveNow(o)
+}
+
+func (ccb *ccBalancerWrapper) Target() string {
+	return ccb.cc.target
+}
+
+// acBalancerWrapper is a wrapper on top of ac for balancers.
+// It implements balancer.SubConn interface.
+type acBalancerWrapper struct {
+	mu sync.Mutex
+	ac *addrConn
+}
+
+func (acbw *acBalancerWrapper) UpdateAddresses(addrs []resolver.Address) {
+	acbw.mu.Lock()
+	defer acbw.mu.Unlock()
+	if len(addrs) <= 0 {
+		acbw.ac.tearDown(errConnDrain)
+		return
+	}
+	if !acbw.ac.tryUpdateAddrs(addrs) {
+		cc := acbw.ac.cc
+		opts := acbw.ac.scopts
+		acbw.ac.mu.Lock()
+		// Set old ac.acbw to nil so the Shutdown state update will be ignored
+		// by balancer.
+		//
+		// TODO(bar) the state transition could be wrong when tearDown() old ac
+		// and creating new ac, fix the transition.
+		acbw.ac.acbw = nil
+		acbw.ac.mu.Unlock()
+		acState := acbw.ac.getState()
+		acbw.ac.tearDown(errConnDrain)
+
+		if acState == connectivity.Shutdown {
+			return
+		}
+
+		ac, err := cc.newAddrConn(addrs, opts)
+		if err != nil {
+			channelz.Warningf(acbw.ac.channelzID, "acBalancerWrapper: UpdateAddresses: failed to newAddrConn: %v", err)
+			return
+		}
+		acbw.ac = ac
+		ac.mu.Lock()
+		ac.acbw = acbw
+		ac.mu.Unlock()
+		if acState != connectivity.Idle {
+			ac.connect()
+		}
+	}
+}
+
+func (acbw *acBalancerWrapper) Connect() {
+	acbw.mu.Lock()
+	defer acbw.mu.Unlock()
+	acbw.ac.connect()
+}
+
+func (acbw *acBalancerWrapper) getAddrConn() *addrConn {
+	acbw.mu.Lock()
+	defer acbw.mu.Unlock()
+	return acbw.ac
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/balancer_v1_wrapper.go b/demo_test/vendor/google.golang.org/grpc/balancer_v1_wrapper.go
new file mode 100644
index 0000000..db04b08
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/balancer_v1_wrapper.go
@@ -0,0 +1,334 @@
+/*
+ *
+ * Copyright 2017 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package grpc
+
+import (
+	"sync"
+
+	"google.golang.org/grpc/balancer"
+	"google.golang.org/grpc/connectivity"
+	"google.golang.org/grpc/grpclog"
+	"google.golang.org/grpc/resolver"
+)
+
+type balancerWrapperBuilder struct {
+	b Balancer // The v1 balancer.
+}
+
+func (bwb *balancerWrapperBuilder) Build(cc balancer.ClientConn, opts balancer.BuildOptions) balancer.Balancer {
+	bwb.b.Start(opts.Target.Endpoint, BalancerConfig{
+		DialCreds: opts.DialCreds,
+		Dialer:    opts.Dialer,
+	})
+	_, pickfirst := bwb.b.(*pickFirst)
+	bw := &balancerWrapper{
+		balancer:   bwb.b,
+		pickfirst:  pickfirst,
+		cc:         cc,
+		targetAddr: opts.Target.Endpoint,
+		startCh:    make(chan struct{}),
+		conns:      make(map[resolver.Address]balancer.SubConn),
+		connSt:     make(map[balancer.SubConn]*scState),
+		csEvltr:    &balancer.ConnectivityStateEvaluator{},
+		state:      connectivity.Idle,
+	}
+	cc.UpdateState(balancer.State{ConnectivityState: connectivity.Idle, Picker: bw})
+	go bw.lbWatcher()
+	return bw
+}
+
+func (bwb *balancerWrapperBuilder) Name() string {
+	return "wrapper"
+}
+
+type scState struct {
+	addr Address // The v1 address type.
+	s    connectivity.State
+	down func(error)
+}
+
+type balancerWrapper struct {
+	balancer  Balancer // The v1 balancer.
+	pickfirst bool
+
+	cc         balancer.ClientConn
+	targetAddr string // Target without the scheme.
+
+	mu     sync.Mutex
+	conns  map[resolver.Address]balancer.SubConn
+	connSt map[balancer.SubConn]*scState
+	// This channel is closed when handling the first resolver result.
+	// lbWatcher blocks until this is closed, to avoid race between
+	// - NewSubConn is created, cc wants to notify balancer of state changes;
+	// - Build hasn't return, cc doesn't have access to balancer.
+	startCh chan struct{}
+
+	// To aggregate the connectivity state.
+	csEvltr *balancer.ConnectivityStateEvaluator
+	state   connectivity.State
+}
+
+// lbWatcher watches the Notify channel of the balancer and manages
+// connections accordingly.
+func (bw *balancerWrapper) lbWatcher() {
+	<-bw.startCh
+	notifyCh := bw.balancer.Notify()
+	if notifyCh == nil {
+		// There's no resolver in the balancer. Connect directly.
+		a := resolver.Address{
+			Addr: bw.targetAddr,
+			Type: resolver.Backend,
+		}
+		sc, err := bw.cc.NewSubConn([]resolver.Address{a}, balancer.NewSubConnOptions{})
+		if err != nil {
+			grpclog.Warningf("Error creating connection to %v. Err: %v", a, err)
+		} else {
+			bw.mu.Lock()
+			bw.conns[a] = sc
+			bw.connSt[sc] = &scState{
+				addr: Address{Addr: bw.targetAddr},
+				s:    connectivity.Idle,
+			}
+			bw.mu.Unlock()
+			sc.Connect()
+		}
+		return
+	}
+
+	for addrs := range notifyCh {
+		grpclog.Infof("balancerWrapper: got update addr from Notify: %v", addrs)
+		if bw.pickfirst {
+			var (
+				oldA  resolver.Address
+				oldSC balancer.SubConn
+			)
+			bw.mu.Lock()
+			for oldA, oldSC = range bw.conns {
+				break
+			}
+			bw.mu.Unlock()
+			if len(addrs) <= 0 {
+				if oldSC != nil {
+					// Teardown old sc.
+					bw.mu.Lock()
+					delete(bw.conns, oldA)
+					delete(bw.connSt, oldSC)
+					bw.mu.Unlock()
+					bw.cc.RemoveSubConn(oldSC)
+				}
+				continue
+			}
+
+			var newAddrs []resolver.Address
+			for _, a := range addrs {
+				newAddr := resolver.Address{
+					Addr:       a.Addr,
+					Type:       resolver.Backend, // All addresses from balancer are all backends.
+					ServerName: "",
+					Metadata:   a.Metadata,
+				}
+				newAddrs = append(newAddrs, newAddr)
+			}
+			if oldSC == nil {
+				// Create new sc.
+				sc, err := bw.cc.NewSubConn(newAddrs, balancer.NewSubConnOptions{})
+				if err != nil {
+					grpclog.Warningf("Error creating connection to %v. Err: %v", newAddrs, err)
+				} else {
+					bw.mu.Lock()
+					// For pickfirst, there should be only one SubConn, so the
+					// address doesn't matter. All states updating (up and down)
+					// and picking should all happen on that only SubConn.
+					bw.conns[resolver.Address{}] = sc
+					bw.connSt[sc] = &scState{
+						addr: addrs[0], // Use the first address.
+						s:    connectivity.Idle,
+					}
+					bw.mu.Unlock()
+					sc.Connect()
+				}
+			} else {
+				bw.mu.Lock()
+				bw.connSt[oldSC].addr = addrs[0]
+				bw.mu.Unlock()
+				oldSC.UpdateAddresses(newAddrs)
+			}
+		} else {
+			var (
+				add []resolver.Address // Addresses need to setup connections.
+				del []balancer.SubConn // Connections need to tear down.
+			)
+			resAddrs := make(map[resolver.Address]Address)
+			for _, a := range addrs {
+				resAddrs[resolver.Address{
+					Addr:       a.Addr,
+					Type:       resolver.Backend, // All addresses from balancer are all backends.
+					ServerName: "",
+					Metadata:   a.Metadata,
+				}] = a
+			}
+			bw.mu.Lock()
+			for a := range resAddrs {
+				if _, ok := bw.conns[a]; !ok {
+					add = append(add, a)
+				}
+			}
+			for a, c := range bw.conns {
+				if _, ok := resAddrs[a]; !ok {
+					del = append(del, c)
+					delete(bw.conns, a)
+					// Keep the state of this sc in bw.connSt until its state becomes Shutdown.
+				}
+			}
+			bw.mu.Unlock()
+			for _, a := range add {
+				sc, err := bw.cc.NewSubConn([]resolver.Address{a}, balancer.NewSubConnOptions{})
+				if err != nil {
+					grpclog.Warningf("Error creating connection to %v. Err: %v", a, err)
+				} else {
+					bw.mu.Lock()
+					bw.conns[a] = sc
+					bw.connSt[sc] = &scState{
+						addr: resAddrs[a],
+						s:    connectivity.Idle,
+					}
+					bw.mu.Unlock()
+					sc.Connect()
+				}
+			}
+			for _, c := range del {
+				bw.cc.RemoveSubConn(c)
+			}
+		}
+	}
+}
+
+func (bw *balancerWrapper) HandleSubConnStateChange(sc balancer.SubConn, s connectivity.State) {
+	bw.mu.Lock()
+	defer bw.mu.Unlock()
+	scSt, ok := bw.connSt[sc]
+	if !ok {
+		return
+	}
+	if s == connectivity.Idle {
+		sc.Connect()
+	}
+	oldS := scSt.s
+	scSt.s = s
+	if oldS != connectivity.Ready && s == connectivity.Ready {
+		scSt.down = bw.balancer.Up(scSt.addr)
+	} else if oldS == connectivity.Ready && s != connectivity.Ready {
+		if scSt.down != nil {
+			scSt.down(errConnClosing)
+		}
+	}
+	sa := bw.csEvltr.RecordTransition(oldS, s)
+	if bw.state != sa {
+		bw.state = sa
+	}
+	bw.cc.UpdateState(balancer.State{ConnectivityState: bw.state, Picker: bw})
+	if s == connectivity.Shutdown {
+		// Remove state for this sc.
+		delete(bw.connSt, sc)
+	}
+}
+
+func (bw *balancerWrapper) HandleResolvedAddrs([]resolver.Address, error) {
+	bw.mu.Lock()
+	defer bw.mu.Unlock()
+	select {
+	case <-bw.startCh:
+	default:
+		close(bw.startCh)
+	}
+	// There should be a resolver inside the balancer.
+	// All updates here, if any, are ignored.
+}
+
+func (bw *balancerWrapper) Close() {
+	bw.mu.Lock()
+	defer bw.mu.Unlock()
+	select {
+	case <-bw.startCh:
+	default:
+		close(bw.startCh)
+	}
+	bw.balancer.Close()
+}
+
+// The picker is the balancerWrapper itself.
+// It either blocks or returns error, consistent with v1 balancer Get().
+func (bw *balancerWrapper) Pick(info balancer.PickInfo) (result balancer.PickResult, err error) {
+	failfast := true // Default failfast is true.
+	if ss, ok := rpcInfoFromContext(info.Ctx); ok {
+		failfast = ss.failfast
+	}
+	a, p, err := bw.balancer.Get(info.Ctx, BalancerGetOptions{BlockingWait: !failfast})
+	if err != nil {
+		return balancer.PickResult{}, toRPCErr(err)
+	}
+	if p != nil {
+		result.Done = func(balancer.DoneInfo) { p() }
+		defer func() {
+			if err != nil {
+				p()
+			}
+		}()
+	}
+
+	bw.mu.Lock()
+	defer bw.mu.Unlock()
+	if bw.pickfirst {
+		// Get the first sc in conns.
+		for _, result.SubConn = range bw.conns {
+			return result, nil
+		}
+		return balancer.PickResult{}, balancer.ErrNoSubConnAvailable
+	}
+	var ok1 bool
+	result.SubConn, ok1 = bw.conns[resolver.Address{
+		Addr:       a.Addr,
+		Type:       resolver.Backend,
+		ServerName: "",
+		Metadata:   a.Metadata,
+	}]
+	s, ok2 := bw.connSt[result.SubConn]
+	if !ok1 || !ok2 {
+		// This can only happen due to a race where Get() returned an address
+		// that was subsequently removed by Notify.  In this case we should
+		// retry always.
+		return balancer.PickResult{}, balancer.ErrNoSubConnAvailable
+	}
+	switch s.s {
+	case connectivity.Ready, connectivity.Idle:
+		return result, nil
+	case connectivity.Shutdown, connectivity.TransientFailure:
+		// If the returned sc has been shut down or is in transient failure,
+		// return error, and this RPC will fail or wait for another picker (if
+		// non-failfast).
+		return balancer.PickResult{}, balancer.ErrTransientFailure
+	default:
+		// For other states (connecting or unknown), the v1 balancer would
+		// traditionally wait until ready and then issue the RPC.  Returning
+		// ErrNoSubConnAvailable will be a slight improvement in that it will
+		// allow the balancer to choose another address in case others are
+		// connected.
+		return balancer.PickResult{}, balancer.ErrNoSubConnAvailable
+	}
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/binarylog/grpc_binarylog_v1/binarylog.pb.go b/demo_test/vendor/google.golang.org/grpc/binarylog/grpc_binarylog_v1/binarylog.pb.go
new file mode 100644
index 0000000..f393bb6
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/binarylog/grpc_binarylog_v1/binarylog.pb.go
@@ -0,0 +1,900 @@
+// Code generated by protoc-gen-go. DO NOT EDIT.
+// source: grpc/binarylog/grpc_binarylog_v1/binarylog.proto
+
+package grpc_binarylog_v1 // import "google.golang.org/grpc/binarylog/grpc_binarylog_v1"
+
+import proto "github.com/golang/protobuf/proto"
+import fmt "fmt"
+import math "math"
+import duration "github.com/golang/protobuf/ptypes/duration"
+import timestamp "github.com/golang/protobuf/ptypes/timestamp"
+
+// Reference imports to suppress errors if they are not otherwise used.
+var _ = proto.Marshal
+var _ = fmt.Errorf
+var _ = math.Inf
+
+// This is a compile-time assertion to ensure that this generated file
+// is compatible with the proto package it is being compiled against.
+// A compilation error at this line likely means your copy of the
+// proto package needs to be updated.
+const _ = proto.ProtoPackageIsVersion2 // please upgrade the proto package
+
+// Enumerates the type of event
+// Note the terminology is different from the RPC semantics
+// definition, but the same meaning is expressed here.
+type GrpcLogEntry_EventType int32
+
+const (
+	GrpcLogEntry_EVENT_TYPE_UNKNOWN GrpcLogEntry_EventType = 0
+	// Header sent from client to server
+	GrpcLogEntry_EVENT_TYPE_CLIENT_HEADER GrpcLogEntry_EventType = 1
+	// Header sent from server to client
+	GrpcLogEntry_EVENT_TYPE_SERVER_HEADER GrpcLogEntry_EventType = 2
+	// Message sent from client to server
+	GrpcLogEntry_EVENT_TYPE_CLIENT_MESSAGE GrpcLogEntry_EventType = 3
+	// Message sent from server to client
+	GrpcLogEntry_EVENT_TYPE_SERVER_MESSAGE GrpcLogEntry_EventType = 4
+	// A signal that client is done sending
+	GrpcLogEntry_EVENT_TYPE_CLIENT_HALF_CLOSE GrpcLogEntry_EventType = 5
+	// Trailer indicates the end of the RPC.
+	// On client side, this event means a trailer was either received
+	// from the network or the gRPC library locally generated a status
+	// to inform the application about a failure.
+	// On server side, this event means the server application requested
+	// to send a trailer. Note: EVENT_TYPE_CANCEL may still arrive after
+	// this due to races on server side.
+	GrpcLogEntry_EVENT_TYPE_SERVER_TRAILER GrpcLogEntry_EventType = 6
+	// A signal that the RPC is cancelled. On client side, this
+	// indicates the client application requests a cancellation.
+	// On server side, this indicates that cancellation was detected.
+	// Note: This marks the end of the RPC. Events may arrive after
+	// this due to races. For example, on client side a trailer
+	// may arrive even though the application requested to cancel the RPC.
+	GrpcLogEntry_EVENT_TYPE_CANCEL GrpcLogEntry_EventType = 7
+)
+
+var GrpcLogEntry_EventType_name = map[int32]string{
+	0: "EVENT_TYPE_UNKNOWN",
+	1: "EVENT_TYPE_CLIENT_HEADER",
+	2: "EVENT_TYPE_SERVER_HEADER",
+	3: "EVENT_TYPE_CLIENT_MESSAGE",
+	4: "EVENT_TYPE_SERVER_MESSAGE",
+	5: "EVENT_TYPE_CLIENT_HALF_CLOSE",
+	6: "EVENT_TYPE_SERVER_TRAILER",
+	7: "EVENT_TYPE_CANCEL",
+}
+var GrpcLogEntry_EventType_value = map[string]int32{
+	"EVENT_TYPE_UNKNOWN":           0,
+	"EVENT_TYPE_CLIENT_HEADER":     1,
+	"EVENT_TYPE_SERVER_HEADER":     2,
+	"EVENT_TYPE_CLIENT_MESSAGE":    3,
+	"EVENT_TYPE_SERVER_MESSAGE":    4,
+	"EVENT_TYPE_CLIENT_HALF_CLOSE": 5,
+	"EVENT_TYPE_SERVER_TRAILER":    6,
+	"EVENT_TYPE_CANCEL":            7,
+}
+
+func (x GrpcLogEntry_EventType) String() string {
+	return proto.EnumName(GrpcLogEntry_EventType_name, int32(x))
+}
+func (GrpcLogEntry_EventType) EnumDescriptor() ([]byte, []int) {
+	return fileDescriptor_binarylog_264c8c9c551ce911, []int{0, 0}
+}
+
+// Enumerates the entity that generates the log entry
+type GrpcLogEntry_Logger int32
+
+const (
+	GrpcLogEntry_LOGGER_UNKNOWN GrpcLogEntry_Logger = 0
+	GrpcLogEntry_LOGGER_CLIENT  GrpcLogEntry_Logger = 1
+	GrpcLogEntry_LOGGER_SERVER  GrpcLogEntry_Logger = 2
+)
+
+var GrpcLogEntry_Logger_name = map[int32]string{
+	0: "LOGGER_UNKNOWN",
+	1: "LOGGER_CLIENT",
+	2: "LOGGER_SERVER",
+}
+var GrpcLogEntry_Logger_value = map[string]int32{
+	"LOGGER_UNKNOWN": 0,
+	"LOGGER_CLIENT":  1,
+	"LOGGER_SERVER":  2,
+}
+
+func (x GrpcLogEntry_Logger) String() string {
+	return proto.EnumName(GrpcLogEntry_Logger_name, int32(x))
+}
+func (GrpcLogEntry_Logger) EnumDescriptor() ([]byte, []int) {
+	return fileDescriptor_binarylog_264c8c9c551ce911, []int{0, 1}
+}
+
+type Address_Type int32
+
+const (
+	Address_TYPE_UNKNOWN Address_Type = 0
+	// address is in 1.2.3.4 form
+	Address_TYPE_IPV4 Address_Type = 1
+	// address is in IPv6 canonical form (RFC5952 section 4)
+	// The scope is NOT included in the address string.
+	Address_TYPE_IPV6 Address_Type = 2
+	// address is UDS string
+	Address_TYPE_UNIX Address_Type = 3
+)
+
+var Address_Type_name = map[int32]string{
+	0: "TYPE_UNKNOWN",
+	1: "TYPE_IPV4",
+	2: "TYPE_IPV6",
+	3: "TYPE_UNIX",
+}
+var Address_Type_value = map[string]int32{
+	"TYPE_UNKNOWN": 0,
+	"TYPE_IPV4":    1,
+	"TYPE_IPV6":    2,
+	"TYPE_UNIX":    3,
+}
+
+func (x Address_Type) String() string {
+	return proto.EnumName(Address_Type_name, int32(x))
+}
+func (Address_Type) EnumDescriptor() ([]byte, []int) {
+	return fileDescriptor_binarylog_264c8c9c551ce911, []int{7, 0}
+}
+
+// Log entry we store in binary logs
+type GrpcLogEntry struct {
+	// The timestamp of the binary log message
+	Timestamp *timestamp.Timestamp `protobuf:"bytes,1,opt,name=timestamp,proto3" json:"timestamp,omitempty"`
+	// Uniquely identifies a call. The value must not be 0 in order to disambiguate
+	// from an unset value.
+	// Each call may have several log entries, they will all have the same call_id.
+	// Nothing is guaranteed about their value other than they are unique across
+	// different RPCs in the same gRPC process.
+	CallId uint64 `protobuf:"varint,2,opt,name=call_id,json=callId,proto3" json:"call_id,omitempty"`
+	// The entry sequence id for this call. The first GrpcLogEntry has a
+	// value of 1, to disambiguate from an unset value. The purpose of
+	// this field is to detect missing entries in environments where
+	// durability or ordering is not guaranteed.
+	SequenceIdWithinCall uint64                 `protobuf:"varint,3,opt,name=sequence_id_within_call,json=sequenceIdWithinCall,proto3" json:"sequence_id_within_call,omitempty"`
+	Type                 GrpcLogEntry_EventType `protobuf:"varint,4,opt,name=type,proto3,enum=grpc.binarylog.v1.GrpcLogEntry_EventType" json:"type,omitempty"`
+	Logger               GrpcLogEntry_Logger    `protobuf:"varint,5,opt,name=logger,proto3,enum=grpc.binarylog.v1.GrpcLogEntry_Logger" json:"logger,omitempty"`
+	// The logger uses one of the following fields to record the payload,
+	// according to the type of the log entry.
+	//
+	// Types that are valid to be assigned to Payload:
+	//	*GrpcLogEntry_ClientHeader
+	//	*GrpcLogEntry_ServerHeader
+	//	*GrpcLogEntry_Message
+	//	*GrpcLogEntry_Trailer
+	Payload isGrpcLogEntry_Payload `protobuf_oneof:"payload"`
+	// true if payload does not represent the full message or metadata.
+	PayloadTruncated bool `protobuf:"varint,10,opt,name=payload_truncated,json=payloadTruncated,proto3" json:"payload_truncated,omitempty"`
+	// Peer address information, will only be recorded on the first
+	// incoming event. On client side, peer is logged on
+	// EVENT_TYPE_SERVER_HEADER normally or EVENT_TYPE_SERVER_TRAILER in
+	// the case of trailers-only. On server side, peer is always
+	// logged on EVENT_TYPE_CLIENT_HEADER.
+	Peer                 *Address `protobuf:"bytes,11,opt,name=peer,proto3" json:"peer,omitempty"`
+	XXX_NoUnkeyedLiteral struct{} `json:"-"`
+	XXX_unrecognized     []byte   `json:"-"`
+	XXX_sizecache        int32    `json:"-"`
+}
+
+func (m *GrpcLogEntry) Reset()         { *m = GrpcLogEntry{} }
+func (m *GrpcLogEntry) String() string { return proto.CompactTextString(m) }
+func (*GrpcLogEntry) ProtoMessage()    {}
+func (*GrpcLogEntry) Descriptor() ([]byte, []int) {
+	return fileDescriptor_binarylog_264c8c9c551ce911, []int{0}
+}
+func (m *GrpcLogEntry) XXX_Unmarshal(b []byte) error {
+	return xxx_messageInfo_GrpcLogEntry.Unmarshal(m, b)
+}
+func (m *GrpcLogEntry) XXX_Marshal(b []byte, deterministic bool) ([]byte, error) {
+	return xxx_messageInfo_GrpcLogEntry.Marshal(b, m, deterministic)
+}
+func (dst *GrpcLogEntry) XXX_Merge(src proto.Message) {
+	xxx_messageInfo_GrpcLogEntry.Merge(dst, src)
+}
+func (m *GrpcLogEntry) XXX_Size() int {
+	return xxx_messageInfo_GrpcLogEntry.Size(m)
+}
+func (m *GrpcLogEntry) XXX_DiscardUnknown() {
+	xxx_messageInfo_GrpcLogEntry.DiscardUnknown(m)
+}
+
+var xxx_messageInfo_GrpcLogEntry proto.InternalMessageInfo
+
+func (m *GrpcLogEntry) GetTimestamp() *timestamp.Timestamp {
+	if m != nil {
+		return m.Timestamp
+	}
+	return nil
+}
+
+func (m *GrpcLogEntry) GetCallId() uint64 {
+	if m != nil {
+		return m.CallId
+	}
+	return 0
+}
+
+func (m *GrpcLogEntry) GetSequenceIdWithinCall() uint64 {
+	if m != nil {
+		return m.SequenceIdWithinCall
+	}
+	return 0
+}
+
+func (m *GrpcLogEntry) GetType() GrpcLogEntry_EventType {
+	if m != nil {
+		return m.Type
+	}
+	return GrpcLogEntry_EVENT_TYPE_UNKNOWN
+}
+
+func (m *GrpcLogEntry) GetLogger() GrpcLogEntry_Logger {
+	if m != nil {
+		return m.Logger
+	}
+	return GrpcLogEntry_LOGGER_UNKNOWN
+}
+
+type isGrpcLogEntry_Payload interface {
+	isGrpcLogEntry_Payload()
+}
+
+type GrpcLogEntry_ClientHeader struct {
+	ClientHeader *ClientHeader `protobuf:"bytes,6,opt,name=client_header,json=clientHeader,proto3,oneof"`
+}
+
+type GrpcLogEntry_ServerHeader struct {
+	ServerHeader *ServerHeader `protobuf:"bytes,7,opt,name=server_header,json=serverHeader,proto3,oneof"`
+}
+
+type GrpcLogEntry_Message struct {
+	Message *Message `protobuf:"bytes,8,opt,name=message,proto3,oneof"`
+}
+
+type GrpcLogEntry_Trailer struct {
+	Trailer *Trailer `protobuf:"bytes,9,opt,name=trailer,proto3,oneof"`
+}
+
+func (*GrpcLogEntry_ClientHeader) isGrpcLogEntry_Payload() {}
+
+func (*GrpcLogEntry_ServerHeader) isGrpcLogEntry_Payload() {}
+
+func (*GrpcLogEntry_Message) isGrpcLogEntry_Payload() {}
+
+func (*GrpcLogEntry_Trailer) isGrpcLogEntry_Payload() {}
+
+func (m *GrpcLogEntry) GetPayload() isGrpcLogEntry_Payload {
+	if m != nil {
+		return m.Payload
+	}
+	return nil
+}
+
+func (m *GrpcLogEntry) GetClientHeader() *ClientHeader {
+	if x, ok := m.GetPayload().(*GrpcLogEntry_ClientHeader); ok {
+		return x.ClientHeader
+	}
+	return nil
+}
+
+func (m *GrpcLogEntry) GetServerHeader() *ServerHeader {
+	if x, ok := m.GetPayload().(*GrpcLogEntry_ServerHeader); ok {
+		return x.ServerHeader
+	}
+	return nil
+}
+
+func (m *GrpcLogEntry) GetMessage() *Message {
+	if x, ok := m.GetPayload().(*GrpcLogEntry_Message); ok {
+		return x.Message
+	}
+	return nil
+}
+
+func (m *GrpcLogEntry) GetTrailer() *Trailer {
+	if x, ok := m.GetPayload().(*GrpcLogEntry_Trailer); ok {
+		return x.Trailer
+	}
+	return nil
+}
+
+func (m *GrpcLogEntry) GetPayloadTruncated() bool {
+	if m != nil {
+		return m.PayloadTruncated
+	}
+	return false
+}
+
+func (m *GrpcLogEntry) GetPeer() *Address {
+	if m != nil {
+		return m.Peer
+	}
+	return nil
+}
+
+// XXX_OneofFuncs is for the internal use of the proto package.
+func (*GrpcLogEntry) XXX_OneofFuncs() (func(msg proto.Message, b *proto.Buffer) error, func(msg proto.Message, tag, wire int, b *proto.Buffer) (bool, error), func(msg proto.Message) (n int), []interface{}) {
+	return _GrpcLogEntry_OneofMarshaler, _GrpcLogEntry_OneofUnmarshaler, _GrpcLogEntry_OneofSizer, []interface{}{
+		(*GrpcLogEntry_ClientHeader)(nil),
+		(*GrpcLogEntry_ServerHeader)(nil),
+		(*GrpcLogEntry_Message)(nil),
+		(*GrpcLogEntry_Trailer)(nil),
+	}
+}
+
+func _GrpcLogEntry_OneofMarshaler(msg proto.Message, b *proto.Buffer) error {
+	m := msg.(*GrpcLogEntry)
+	// payload
+	switch x := m.Payload.(type) {
+	case *GrpcLogEntry_ClientHeader:
+		b.EncodeVarint(6<<3 | proto.WireBytes)
+		if err := b.EncodeMessage(x.ClientHeader); err != nil {
+			return err
+		}
+	case *GrpcLogEntry_ServerHeader:
+		b.EncodeVarint(7<<3 | proto.WireBytes)
+		if err := b.EncodeMessage(x.ServerHeader); err != nil {
+			return err
+		}
+	case *GrpcLogEntry_Message:
+		b.EncodeVarint(8<<3 | proto.WireBytes)
+		if err := b.EncodeMessage(x.Message); err != nil {
+			return err
+		}
+	case *GrpcLogEntry_Trailer:
+		b.EncodeVarint(9<<3 | proto.WireBytes)
+		if err := b.EncodeMessage(x.Trailer); err != nil {
+			return err
+		}
+	case nil:
+	default:
+		return fmt.Errorf("GrpcLogEntry.Payload has unexpected type %T", x)
+	}
+	return nil
+}
+
+func _GrpcLogEntry_OneofUnmarshaler(msg proto.Message, tag, wire int, b *proto.Buffer) (bool, error) {
+	m := msg.(*GrpcLogEntry)
+	switch tag {
+	case 6: // payload.client_header
+		if wire != proto.WireBytes {
+			return true, proto.ErrInternalBadWireType
+		}
+		msg := new(ClientHeader)
+		err := b.DecodeMessage(msg)
+		m.Payload = &GrpcLogEntry_ClientHeader{msg}
+		return true, err
+	case 7: // payload.server_header
+		if wire != proto.WireBytes {
+			return true, proto.ErrInternalBadWireType
+		}
+		msg := new(ServerHeader)
+		err := b.DecodeMessage(msg)
+		m.Payload = &GrpcLogEntry_ServerHeader{msg}
+		return true, err
+	case 8: // payload.message
+		if wire != proto.WireBytes {
+			return true, proto.ErrInternalBadWireType
+		}
+		msg := new(Message)
+		err := b.DecodeMessage(msg)
+		m.Payload = &GrpcLogEntry_Message{msg}
+		return true, err
+	case 9: // payload.trailer
+		if wire != proto.WireBytes {
+			return true, proto.ErrInternalBadWireType
+		}
+		msg := new(Trailer)
+		err := b.DecodeMessage(msg)
+		m.Payload = &GrpcLogEntry_Trailer{msg}
+		return true, err
+	default:
+		return false, nil
+	}
+}
+
+func _GrpcLogEntry_OneofSizer(msg proto.Message) (n int) {
+	m := msg.(*GrpcLogEntry)
+	// payload
+	switch x := m.Payload.(type) {
+	case *GrpcLogEntry_ClientHeader:
+		s := proto.Size(x.ClientHeader)
+		n += 1 // tag and wire
+		n += proto.SizeVarint(uint64(s))
+		n += s
+	case *GrpcLogEntry_ServerHeader:
+		s := proto.Size(x.ServerHeader)
+		n += 1 // tag and wire
+		n += proto.SizeVarint(uint64(s))
+		n += s
+	case *GrpcLogEntry_Message:
+		s := proto.Size(x.Message)
+		n += 1 // tag and wire
+		n += proto.SizeVarint(uint64(s))
+		n += s
+	case *GrpcLogEntry_Trailer:
+		s := proto.Size(x.Trailer)
+		n += 1 // tag and wire
+		n += proto.SizeVarint(uint64(s))
+		n += s
+	case nil:
+	default:
+		panic(fmt.Sprintf("proto: unexpected type %T in oneof", x))
+	}
+	return n
+}
+
+type ClientHeader struct {
+	// This contains only the metadata from the application.
+	Metadata *Metadata `protobuf:"bytes,1,opt,name=metadata,proto3" json:"metadata,omitempty"`
+	// The name of the RPC method, which looks something like:
+	// /<service>/<method>
+	// Note the leading "/" character.
+	MethodName string `protobuf:"bytes,2,opt,name=method_name,json=methodName,proto3" json:"method_name,omitempty"`
+	// A single process may be used to run multiple virtual
+	// servers with different identities.
+	// The authority is the name of such a server identitiy.
+	// It is typically a portion of the URI in the form of
+	// <host> or <host>:<port> .
+	Authority string `protobuf:"bytes,3,opt,name=authority,proto3" json:"authority,omitempty"`
+	// the RPC timeout
+	Timeout              *duration.Duration `protobuf:"bytes,4,opt,name=timeout,proto3" json:"timeout,omitempty"`
+	XXX_NoUnkeyedLiteral struct{}           `json:"-"`
+	XXX_unrecognized     []byte             `json:"-"`
+	XXX_sizecache        int32              `json:"-"`
+}
+
+func (m *ClientHeader) Reset()         { *m = ClientHeader{} }
+func (m *ClientHeader) String() string { return proto.CompactTextString(m) }
+func (*ClientHeader) ProtoMessage()    {}
+func (*ClientHeader) Descriptor() ([]byte, []int) {
+	return fileDescriptor_binarylog_264c8c9c551ce911, []int{1}
+}
+func (m *ClientHeader) XXX_Unmarshal(b []byte) error {
+	return xxx_messageInfo_ClientHeader.Unmarshal(m, b)
+}
+func (m *ClientHeader) XXX_Marshal(b []byte, deterministic bool) ([]byte, error) {
+	return xxx_messageInfo_ClientHeader.Marshal(b, m, deterministic)
+}
+func (dst *ClientHeader) XXX_Merge(src proto.Message) {
+	xxx_messageInfo_ClientHeader.Merge(dst, src)
+}
+func (m *ClientHeader) XXX_Size() int {
+	return xxx_messageInfo_ClientHeader.Size(m)
+}
+func (m *ClientHeader) XXX_DiscardUnknown() {
+	xxx_messageInfo_ClientHeader.DiscardUnknown(m)
+}
+
+var xxx_messageInfo_ClientHeader proto.InternalMessageInfo
+
+func (m *ClientHeader) GetMetadata() *Metadata {
+	if m != nil {
+		return m.Metadata
+	}
+	return nil
+}
+
+func (m *ClientHeader) GetMethodName() string {
+	if m != nil {
+		return m.MethodName
+	}
+	return ""
+}
+
+func (m *ClientHeader) GetAuthority() string {
+	if m != nil {
+		return m.Authority
+	}
+	return ""
+}
+
+func (m *ClientHeader) GetTimeout() *duration.Duration {
+	if m != nil {
+		return m.Timeout
+	}
+	return nil
+}
+
+type ServerHeader struct {
+	// This contains only the metadata from the application.
+	Metadata             *Metadata `protobuf:"bytes,1,opt,name=metadata,proto3" json:"metadata,omitempty"`
+	XXX_NoUnkeyedLiteral struct{}  `json:"-"`
+	XXX_unrecognized     []byte    `json:"-"`
+	XXX_sizecache        int32     `json:"-"`
+}
+
+func (m *ServerHeader) Reset()         { *m = ServerHeader{} }
+func (m *ServerHeader) String() string { return proto.CompactTextString(m) }
+func (*ServerHeader) ProtoMessage()    {}
+func (*ServerHeader) Descriptor() ([]byte, []int) {
+	return fileDescriptor_binarylog_264c8c9c551ce911, []int{2}
+}
+func (m *ServerHeader) XXX_Unmarshal(b []byte) error {
+	return xxx_messageInfo_ServerHeader.Unmarshal(m, b)
+}
+func (m *ServerHeader) XXX_Marshal(b []byte, deterministic bool) ([]byte, error) {
+	return xxx_messageInfo_ServerHeader.Marshal(b, m, deterministic)
+}
+func (dst *ServerHeader) XXX_Merge(src proto.Message) {
+	xxx_messageInfo_ServerHeader.Merge(dst, src)
+}
+func (m *ServerHeader) XXX_Size() int {
+	return xxx_messageInfo_ServerHeader.Size(m)
+}
+func (m *ServerHeader) XXX_DiscardUnknown() {
+	xxx_messageInfo_ServerHeader.DiscardUnknown(m)
+}
+
+var xxx_messageInfo_ServerHeader proto.InternalMessageInfo
+
+func (m *ServerHeader) GetMetadata() *Metadata {
+	if m != nil {
+		return m.Metadata
+	}
+	return nil
+}
+
+type Trailer struct {
+	// This contains only the metadata from the application.
+	Metadata *Metadata `protobuf:"bytes,1,opt,name=metadata,proto3" json:"metadata,omitempty"`
+	// The gRPC status code.
+	StatusCode uint32 `protobuf:"varint,2,opt,name=status_code,json=statusCode,proto3" json:"status_code,omitempty"`
+	// An original status message before any transport specific
+	// encoding.
+	StatusMessage string `protobuf:"bytes,3,opt,name=status_message,json=statusMessage,proto3" json:"status_message,omitempty"`
+	// The value of the 'grpc-status-details-bin' metadata key. If
+	// present, this is always an encoded 'google.rpc.Status' message.
+	StatusDetails        []byte   `protobuf:"bytes,4,opt,name=status_details,json=statusDetails,proto3" json:"status_details,omitempty"`
+	XXX_NoUnkeyedLiteral struct{} `json:"-"`
+	XXX_unrecognized     []byte   `json:"-"`
+	XXX_sizecache        int32    `json:"-"`
+}
+
+func (m *Trailer) Reset()         { *m = Trailer{} }
+func (m *Trailer) String() string { return proto.CompactTextString(m) }
+func (*Trailer) ProtoMessage()    {}
+func (*Trailer) Descriptor() ([]byte, []int) {
+	return fileDescriptor_binarylog_264c8c9c551ce911, []int{3}
+}
+func (m *Trailer) XXX_Unmarshal(b []byte) error {
+	return xxx_messageInfo_Trailer.Unmarshal(m, b)
+}
+func (m *Trailer) XXX_Marshal(b []byte, deterministic bool) ([]byte, error) {
+	return xxx_messageInfo_Trailer.Marshal(b, m, deterministic)
+}
+func (dst *Trailer) XXX_Merge(src proto.Message) {
+	xxx_messageInfo_Trailer.Merge(dst, src)
+}
+func (m *Trailer) XXX_Size() int {
+	return xxx_messageInfo_Trailer.Size(m)
+}
+func (m *Trailer) XXX_DiscardUnknown() {
+	xxx_messageInfo_Trailer.DiscardUnknown(m)
+}
+
+var xxx_messageInfo_Trailer proto.InternalMessageInfo
+
+func (m *Trailer) GetMetadata() *Metadata {
+	if m != nil {
+		return m.Metadata
+	}
+	return nil
+}
+
+func (m *Trailer) GetStatusCode() uint32 {
+	if m != nil {
+		return m.StatusCode
+	}
+	return 0
+}
+
+func (m *Trailer) GetStatusMessage() string {
+	if m != nil {
+		return m.StatusMessage
+	}
+	return ""
+}
+
+func (m *Trailer) GetStatusDetails() []byte {
+	if m != nil {
+		return m.StatusDetails
+	}
+	return nil
+}
+
+// Message payload, used by CLIENT_MESSAGE and SERVER_MESSAGE
+type Message struct {
+	// Length of the message. It may not be the same as the length of the
+	// data field, as the logging payload can be truncated or omitted.
+	Length uint32 `protobuf:"varint,1,opt,name=length,proto3" json:"length,omitempty"`
+	// May be truncated or omitted.
+	Data                 []byte   `protobuf:"bytes,2,opt,name=data,proto3" json:"data,omitempty"`
+	XXX_NoUnkeyedLiteral struct{} `json:"-"`
+	XXX_unrecognized     []byte   `json:"-"`
+	XXX_sizecache        int32    `json:"-"`
+}
+
+func (m *Message) Reset()         { *m = Message{} }
+func (m *Message) String() string { return proto.CompactTextString(m) }
+func (*Message) ProtoMessage()    {}
+func (*Message) Descriptor() ([]byte, []int) {
+	return fileDescriptor_binarylog_264c8c9c551ce911, []int{4}
+}
+func (m *Message) XXX_Unmarshal(b []byte) error {
+	return xxx_messageInfo_Message.Unmarshal(m, b)
+}
+func (m *Message) XXX_Marshal(b []byte, deterministic bool) ([]byte, error) {
+	return xxx_messageInfo_Message.Marshal(b, m, deterministic)
+}
+func (dst *Message) XXX_Merge(src proto.Message) {
+	xxx_messageInfo_Message.Merge(dst, src)
+}
+func (m *Message) XXX_Size() int {
+	return xxx_messageInfo_Message.Size(m)
+}
+func (m *Message) XXX_DiscardUnknown() {
+	xxx_messageInfo_Message.DiscardUnknown(m)
+}
+
+var xxx_messageInfo_Message proto.InternalMessageInfo
+
+func (m *Message) GetLength() uint32 {
+	if m != nil {
+		return m.Length
+	}
+	return 0
+}
+
+func (m *Message) GetData() []byte {
+	if m != nil {
+		return m.Data
+	}
+	return nil
+}
+
+// A list of metadata pairs, used in the payload of client header,
+// server header, and server trailer.
+// Implementations may omit some entries to honor the header limits
+// of GRPC_BINARY_LOG_CONFIG.
+//
+// Header keys added by gRPC are omitted. To be more specific,
+// implementations will not log the following entries, and this is
+// not to be treated as a truncation:
+// - entries handled by grpc that are not user visible, such as those
+//   that begin with 'grpc-' (with exception of grpc-trace-bin)
+//   or keys like 'lb-token'
+// - transport specific entries, including but not limited to:
+//   ':path', ':authority', 'content-encoding', 'user-agent', 'te', etc
+// - entries added for call credentials
+//
+// Implementations must always log grpc-trace-bin if it is present.
+// Practically speaking it will only be visible on server side because
+// grpc-trace-bin is managed by low level client side mechanisms
+// inaccessible from the application level. On server side, the
+// header is just a normal metadata key.
+// The pair will not count towards the size limit.
+type Metadata struct {
+	Entry                []*MetadataEntry `protobuf:"bytes,1,rep,name=entry,proto3" json:"entry,omitempty"`
+	XXX_NoUnkeyedLiteral struct{}         `json:"-"`
+	XXX_unrecognized     []byte           `json:"-"`
+	XXX_sizecache        int32            `json:"-"`
+}
+
+func (m *Metadata) Reset()         { *m = Metadata{} }
+func (m *Metadata) String() string { return proto.CompactTextString(m) }
+func (*Metadata) ProtoMessage()    {}
+func (*Metadata) Descriptor() ([]byte, []int) {
+	return fileDescriptor_binarylog_264c8c9c551ce911, []int{5}
+}
+func (m *Metadata) XXX_Unmarshal(b []byte) error {
+	return xxx_messageInfo_Metadata.Unmarshal(m, b)
+}
+func (m *Metadata) XXX_Marshal(b []byte, deterministic bool) ([]byte, error) {
+	return xxx_messageInfo_Metadata.Marshal(b, m, deterministic)
+}
+func (dst *Metadata) XXX_Merge(src proto.Message) {
+	xxx_messageInfo_Metadata.Merge(dst, src)
+}
+func (m *Metadata) XXX_Size() int {
+	return xxx_messageInfo_Metadata.Size(m)
+}
+func (m *Metadata) XXX_DiscardUnknown() {
+	xxx_messageInfo_Metadata.DiscardUnknown(m)
+}
+
+var xxx_messageInfo_Metadata proto.InternalMessageInfo
+
+func (m *Metadata) GetEntry() []*MetadataEntry {
+	if m != nil {
+		return m.Entry
+	}
+	return nil
+}
+
+// A metadata key value pair
+type MetadataEntry struct {
+	Key                  string   `protobuf:"bytes,1,opt,name=key,proto3" json:"key,omitempty"`
+	Value                []byte   `protobuf:"bytes,2,opt,name=value,proto3" json:"value,omitempty"`
+	XXX_NoUnkeyedLiteral struct{} `json:"-"`
+	XXX_unrecognized     []byte   `json:"-"`
+	XXX_sizecache        int32    `json:"-"`
+}
+
+func (m *MetadataEntry) Reset()         { *m = MetadataEntry{} }
+func (m *MetadataEntry) String() string { return proto.CompactTextString(m) }
+func (*MetadataEntry) ProtoMessage()    {}
+func (*MetadataEntry) Descriptor() ([]byte, []int) {
+	return fileDescriptor_binarylog_264c8c9c551ce911, []int{6}
+}
+func (m *MetadataEntry) XXX_Unmarshal(b []byte) error {
+	return xxx_messageInfo_MetadataEntry.Unmarshal(m, b)
+}
+func (m *MetadataEntry) XXX_Marshal(b []byte, deterministic bool) ([]byte, error) {
+	return xxx_messageInfo_MetadataEntry.Marshal(b, m, deterministic)
+}
+func (dst *MetadataEntry) XXX_Merge(src proto.Message) {
+	xxx_messageInfo_MetadataEntry.Merge(dst, src)
+}
+func (m *MetadataEntry) XXX_Size() int {
+	return xxx_messageInfo_MetadataEntry.Size(m)
+}
+func (m *MetadataEntry) XXX_DiscardUnknown() {
+	xxx_messageInfo_MetadataEntry.DiscardUnknown(m)
+}
+
+var xxx_messageInfo_MetadataEntry proto.InternalMessageInfo
+
+func (m *MetadataEntry) GetKey() string {
+	if m != nil {
+		return m.Key
+	}
+	return ""
+}
+
+func (m *MetadataEntry) GetValue() []byte {
+	if m != nil {
+		return m.Value
+	}
+	return nil
+}
+
+// Address information
+type Address struct {
+	Type    Address_Type `protobuf:"varint,1,opt,name=type,proto3,enum=grpc.binarylog.v1.Address_Type" json:"type,omitempty"`
+	Address string       `protobuf:"bytes,2,opt,name=address,proto3" json:"address,omitempty"`
+	// only for TYPE_IPV4 and TYPE_IPV6
+	IpPort               uint32   `protobuf:"varint,3,opt,name=ip_port,json=ipPort,proto3" json:"ip_port,omitempty"`
+	XXX_NoUnkeyedLiteral struct{} `json:"-"`
+	XXX_unrecognized     []byte   `json:"-"`
+	XXX_sizecache        int32    `json:"-"`
+}
+
+func (m *Address) Reset()         { *m = Address{} }
+func (m *Address) String() string { return proto.CompactTextString(m) }
+func (*Address) ProtoMessage()    {}
+func (*Address) Descriptor() ([]byte, []int) {
+	return fileDescriptor_binarylog_264c8c9c551ce911, []int{7}
+}
+func (m *Address) XXX_Unmarshal(b []byte) error {
+	return xxx_messageInfo_Address.Unmarshal(m, b)
+}
+func (m *Address) XXX_Marshal(b []byte, deterministic bool) ([]byte, error) {
+	return xxx_messageInfo_Address.Marshal(b, m, deterministic)
+}
+func (dst *Address) XXX_Merge(src proto.Message) {
+	xxx_messageInfo_Address.Merge(dst, src)
+}
+func (m *Address) XXX_Size() int {
+	return xxx_messageInfo_Address.Size(m)
+}
+func (m *Address) XXX_DiscardUnknown() {
+	xxx_messageInfo_Address.DiscardUnknown(m)
+}
+
+var xxx_messageInfo_Address proto.InternalMessageInfo
+
+func (m *Address) GetType() Address_Type {
+	if m != nil {
+		return m.Type
+	}
+	return Address_TYPE_UNKNOWN
+}
+
+func (m *Address) GetAddress() string {
+	if m != nil {
+		return m.Address
+	}
+	return ""
+}
+
+func (m *Address) GetIpPort() uint32 {
+	if m != nil {
+		return m.IpPort
+	}
+	return 0
+}
+
+func init() {
+	proto.RegisterType((*GrpcLogEntry)(nil), "grpc.binarylog.v1.GrpcLogEntry")
+	proto.RegisterType((*ClientHeader)(nil), "grpc.binarylog.v1.ClientHeader")
+	proto.RegisterType((*ServerHeader)(nil), "grpc.binarylog.v1.ServerHeader")
+	proto.RegisterType((*Trailer)(nil), "grpc.binarylog.v1.Trailer")
+	proto.RegisterType((*Message)(nil), "grpc.binarylog.v1.Message")
+	proto.RegisterType((*Metadata)(nil), "grpc.binarylog.v1.Metadata")
+	proto.RegisterType((*MetadataEntry)(nil), "grpc.binarylog.v1.MetadataEntry")
+	proto.RegisterType((*Address)(nil), "grpc.binarylog.v1.Address")
+	proto.RegisterEnum("grpc.binarylog.v1.GrpcLogEntry_EventType", GrpcLogEntry_EventType_name, GrpcLogEntry_EventType_value)
+	proto.RegisterEnum("grpc.binarylog.v1.GrpcLogEntry_Logger", GrpcLogEntry_Logger_name, GrpcLogEntry_Logger_value)
+	proto.RegisterEnum("grpc.binarylog.v1.Address_Type", Address_Type_name, Address_Type_value)
+}
+
+func init() {
+	proto.RegisterFile("grpc/binarylog/grpc_binarylog_v1/binarylog.proto", fileDescriptor_binarylog_264c8c9c551ce911)
+}
+
+var fileDescriptor_binarylog_264c8c9c551ce911 = []byte{
+	// 900 bytes of a gzipped FileDescriptorProto
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+	0xae, 0x62, 0x50, 0xd0, 0x88, 0x2c, 0x28, 0x3a, 0x85, 0x2a, 0x59, 0x8a, 0x39, 0xe3, 0x81, 0x58,
+	0xcb, 0xb1, 0xad, 0xe2, 0x2d, 0x80, 0x2e, 0x40, 0x4f, 0x17, 0x01, 0x5b, 0x0a, 0x39, 0xae, 0xb5,
+	0xf6, 0xf3, 0x9d, 0x9d, 0x71, 0x95, 0x6d, 0x26, 0x9c, 0x33, 0xad, 0x3e, 0xd4, 0x8b, 0x1d, 0xff,
+	0x9f, 0x0f, 0x6f, 0xfd, 0xa1, 0x81, 0x9e, 0x75, 0xf0, 0xff, 0xaa, 0x40, 0x22, 0x88, 0x58, 0x26,
+	0xee, 0x8c, 0x79, 0xaa, 0x02, 0x0d, 0x0c, 0x0a, 0xea, 0x31, 0x8f, 0xa2, 0xcf, 0xe0, 0x30, 0x23,
+	0xe4, 0x73, 0xa8, 0xca, 0xd0, 0x50, 0x68, 0x36, 0x7a, 0x05, 0x9a, 0x47, 0x05, 0x09, 0xc2, 0x44,
+	0x56, 0xa4, 0x9e, 0xd3, 0xae, 0x14, 0x68, 0xbd, 0x04, 0x3d, 0x8f, 0x78, 0x0a, 0x95, 0x90, 0x46,
+	0xbe, 0x98, 0xcb, 0x03, 0x37, 0x70, 0x66, 0x21, 0x04, 0x65, 0x79, 0x8d, 0x3d, 0x19, 0x2f, 0xbf,
+	0xad, 0x2e, 0x1c, 0xe4, 0x67, 0x47, 0x97, 0xb0, 0x4f, 0xd3, 0xcd, 0x65, 0x6a, 0xcd, 0x52, 0xab,
+	0xd6, 0x6e, 0x7e, 0xe0, 0x9e, 0x72, 0xc3, 0x61, 0x45, 0xb7, 0x5e, 0x41, 0xe3, 0x1f, 0x38, 0x32,
+	0xa0, 0xf4, 0x2b, 0x5d, 0xcb, 0xec, 0x55, 0x9c, 0x7e, 0xa2, 0x63, 0xd8, 0x5f, 0x91, 0x70, 0x49,
+	0xb3, 0xdc, 0xca, 0xb0, 0xfe, 0xd4, 0x40, 0xcf, 0xe6, 0x18, 0x5d, 0x64, 0xdb, 0x59, 0x93, 0xcb,
+	0xf5, 0xec, 0xf1, 0x89, 0xb7, 0x0b, 0x3b, 0xd9, 0x04, 0x9d, 0x28, 0x34, 0xeb, 0xb0, 0xdc, 0x4c,
+	0x1f, 0x8f, 0x20, 0x76, 0x63, 0xc6, 0x85, 0xac, 0x6a, 0x03, 0x57, 0x82, 0x78, 0xcc, 0xb8, 0xb0,
+	0x1c, 0x28, 0xcb, 0x1d, 0x61, 0x40, 0xfd, 0xde, 0x76, 0x68, 0x40, 0x55, 0x22, 0x83, 0xf1, 0xed,
+	0xd7, 0x86, 0x56, 0x34, 0x2f, 0x8d, 0xbd, 0x8d, 0xf9, 0x76, 0x34, 0xf8, 0xc1, 0x28, 0x75, 0x7f,
+	0x86, 0xe3, 0x80, 0xed, 0x1e, 0xb2, 0x7b, 0xd8, 0x95, 0xd6, 0x90, 0xf9, 0xe3, 0xb4, 0x51, 0xc7,
+	0xda, 0x4f, 0xed, 0xac, 0x71, 0x7d, 0x16, 0x92, 0xc8, 0xb7, 0x19, 0x57, 0x4f, 0xf3, 0x87, 0x5e,
+	0xea, 0xbb, 0x8a, 0xec, 0xf2, 0x8b, 0xbf, 0x03, 0x00, 0x00, 0xff, 0xff, 0xe7, 0xf6, 0x4b, 0x50,
+	0xd4, 0x07, 0x00, 0x00,
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/call.go b/demo_test/vendor/google.golang.org/grpc/call.go
new file mode 100644
index 0000000..9e20e4d
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/call.go
@@ -0,0 +1,74 @@
+/*
+ *
+ * Copyright 2014 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package grpc
+
+import (
+	"context"
+)
+
+// Invoke sends the RPC request on the wire and returns after response is
+// received.  This is typically called by generated code.
+//
+// All errors returned by Invoke are compatible with the status package.
+func (cc *ClientConn) Invoke(ctx context.Context, method string, args, reply interface{}, opts ...CallOption) error {
+	// allow interceptor to see all applicable call options, which means those
+	// configured as defaults from dial option as well as per-call options
+	opts = combine(cc.dopts.callOptions, opts)
+
+	if cc.dopts.unaryInt != nil {
+		return cc.dopts.unaryInt(ctx, method, args, reply, cc, invoke, opts...)
+	}
+	return invoke(ctx, method, args, reply, cc, opts...)
+}
+
+func combine(o1 []CallOption, o2 []CallOption) []CallOption {
+	// we don't use append because o1 could have extra capacity whose
+	// elements would be overwritten, which could cause inadvertent
+	// sharing (and race conditions) between concurrent calls
+	if len(o1) == 0 {
+		return o2
+	} else if len(o2) == 0 {
+		return o1
+	}
+	ret := make([]CallOption, len(o1)+len(o2))
+	copy(ret, o1)
+	copy(ret[len(o1):], o2)
+	return ret
+}
+
+// Invoke sends the RPC request on the wire and returns after response is
+// received.  This is typically called by generated code.
+//
+// DEPRECATED: Use ClientConn.Invoke instead.
+func Invoke(ctx context.Context, method string, args, reply interface{}, cc *ClientConn, opts ...CallOption) error {
+	return cc.Invoke(ctx, method, args, reply, opts...)
+}
+
+var unaryStreamDesc = &StreamDesc{ServerStreams: false, ClientStreams: false}
+
+func invoke(ctx context.Context, method string, req, reply interface{}, cc *ClientConn, opts ...CallOption) error {
+	cs, err := newClientStream(ctx, unaryStreamDesc, cc, method, opts...)
+	if err != nil {
+		return err
+	}
+	if err := cs.SendMsg(req); err != nil {
+		return err
+	}
+	return cs.RecvMsg(reply)
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/clientconn.go b/demo_test/vendor/google.golang.org/grpc/clientconn.go
new file mode 100644
index 0000000..0740693
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/clientconn.go
@@ -0,0 +1,1534 @@
+/*
+ *
+ * Copyright 2014 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package grpc
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"math"
+	"net"
+	"reflect"
+	"strings"
+	"sync"
+	"sync/atomic"
+	"time"
+
+	"google.golang.org/grpc/balancer"
+	"google.golang.org/grpc/balancer/base"
+	"google.golang.org/grpc/codes"
+	"google.golang.org/grpc/connectivity"
+	"google.golang.org/grpc/credentials"
+	"google.golang.org/grpc/internal/backoff"
+	"google.golang.org/grpc/internal/channelz"
+	"google.golang.org/grpc/internal/grpcsync"
+	"google.golang.org/grpc/internal/grpcutil"
+	"google.golang.org/grpc/internal/transport"
+	"google.golang.org/grpc/keepalive"
+	"google.golang.org/grpc/resolver"
+	"google.golang.org/grpc/serviceconfig"
+	"google.golang.org/grpc/status"
+
+	_ "google.golang.org/grpc/balancer/roundrobin"           // To register roundrobin.
+	_ "google.golang.org/grpc/internal/resolver/dns"         // To register dns resolver.
+	_ "google.golang.org/grpc/internal/resolver/passthrough" // To register passthrough resolver.
+)
+
+const (
+	// minimum time to give a connection to complete
+	minConnectTimeout = 20 * time.Second
+	// must match grpclbName in grpclb/grpclb.go
+	grpclbName = "grpclb"
+)
+
+var (
+	// ErrClientConnClosing indicates that the operation is illegal because
+	// the ClientConn is closing.
+	//
+	// Deprecated: this error should not be relied upon by users; use the status
+	// code of Canceled instead.
+	ErrClientConnClosing = status.Error(codes.Canceled, "grpc: the client connection is closing")
+	// errConnDrain indicates that the connection starts to be drained and does not accept any new RPCs.
+	errConnDrain = errors.New("grpc: the connection is drained")
+	// errConnClosing indicates that the connection is closing.
+	errConnClosing = errors.New("grpc: the connection is closing")
+	// errBalancerClosed indicates that the balancer is closed.
+	errBalancerClosed = errors.New("grpc: balancer is closed")
+	// invalidDefaultServiceConfigErrPrefix is used to prefix the json parsing error for the default
+	// service config.
+	invalidDefaultServiceConfigErrPrefix = "grpc: the provided default service config is invalid"
+)
+
+// The following errors are returned from Dial and DialContext
+var (
+	// errNoTransportSecurity indicates that there is no transport security
+	// being set for ClientConn. Users should either set one or explicitly
+	// call WithInsecure DialOption to disable security.
+	errNoTransportSecurity = errors.New("grpc: no transport security set (use grpc.WithInsecure() explicitly or set credentials)")
+	// errTransportCredsAndBundle indicates that creds bundle is used together
+	// with other individual Transport Credentials.
+	errTransportCredsAndBundle = errors.New("grpc: credentials.Bundle may not be used with individual TransportCredentials")
+	// errTransportCredentialsMissing indicates that users want to transmit security
+	// information (e.g., OAuth2 token) which requires secure connection on an insecure
+	// connection.
+	errTransportCredentialsMissing = errors.New("grpc: the credentials require transport level security (use grpc.WithTransportCredentials() to set)")
+	// errCredentialsConflict indicates that grpc.WithTransportCredentials()
+	// and grpc.WithInsecure() are both called for a connection.
+	errCredentialsConflict = errors.New("grpc: transport credentials are set for an insecure connection (grpc.WithTransportCredentials() and grpc.WithInsecure() are both called)")
+)
+
+const (
+	defaultClientMaxReceiveMessageSize = 1024 * 1024 * 4
+	defaultClientMaxSendMessageSize    = math.MaxInt32
+	// http2IOBufSize specifies the buffer size for sending frames.
+	defaultWriteBufSize = 32 * 1024
+	defaultReadBufSize  = 32 * 1024
+)
+
+// Dial creates a client connection to the given target.
+func Dial(target string, opts ...DialOption) (*ClientConn, error) {
+	return DialContext(context.Background(), target, opts...)
+}
+
+// DialContext creates a client connection to the given target. By default, it's
+// a non-blocking dial (the function won't wait for connections to be
+// established, and connecting happens in the background). To make it a blocking
+// dial, use WithBlock() dial option.
+//
+// In the non-blocking case, the ctx does not act against the connection. It
+// only controls the setup steps.
+//
+// In the blocking case, ctx can be used to cancel or expire the pending
+// connection. Once this function returns, the cancellation and expiration of
+// ctx will be noop. Users should call ClientConn.Close to terminate all the
+// pending operations after this function returns.
+//
+// The target name syntax is defined in
+// https://github.com/grpc/grpc/blob/master/doc/naming.md.
+// e.g. to use dns resolver, a "dns:///" prefix should be applied to the target.
+func DialContext(ctx context.Context, target string, opts ...DialOption) (conn *ClientConn, err error) {
+	cc := &ClientConn{
+		target:            target,
+		csMgr:             &connectivityStateManager{},
+		conns:             make(map[*addrConn]struct{}),
+		dopts:             defaultDialOptions(),
+		blockingpicker:    newPickerWrapper(),
+		czData:            new(channelzData),
+		firstResolveEvent: grpcsync.NewEvent(),
+	}
+	cc.retryThrottler.Store((*retryThrottler)(nil))
+	cc.ctx, cc.cancel = context.WithCancel(context.Background())
+
+	for _, opt := range opts {
+		opt.apply(&cc.dopts)
+	}
+
+	chainUnaryClientInterceptors(cc)
+	chainStreamClientInterceptors(cc)
+
+	defer func() {
+		if err != nil {
+			cc.Close()
+		}
+	}()
+
+	if channelz.IsOn() {
+		if cc.dopts.channelzParentID != 0 {
+			cc.channelzID = channelz.RegisterChannel(&channelzChannel{cc}, cc.dopts.channelzParentID, target)
+			channelz.AddTraceEvent(cc.channelzID, 0, &channelz.TraceEventDesc{
+				Desc:     "Channel Created",
+				Severity: channelz.CtINFO,
+				Parent: &channelz.TraceEventDesc{
+					Desc:     fmt.Sprintf("Nested Channel(id:%d) created", cc.channelzID),
+					Severity: channelz.CtINFO,
+				},
+			})
+		} else {
+			cc.channelzID = channelz.RegisterChannel(&channelzChannel{cc}, 0, target)
+			channelz.Info(cc.channelzID, "Channel Created")
+		}
+		cc.csMgr.channelzID = cc.channelzID
+	}
+
+	if !cc.dopts.insecure {
+		if cc.dopts.copts.TransportCredentials == nil && cc.dopts.copts.CredsBundle == nil {
+			return nil, errNoTransportSecurity
+		}
+		if cc.dopts.copts.TransportCredentials != nil && cc.dopts.copts.CredsBundle != nil {
+			return nil, errTransportCredsAndBundle
+		}
+	} else {
+		if cc.dopts.copts.TransportCredentials != nil || cc.dopts.copts.CredsBundle != nil {
+			return nil, errCredentialsConflict
+		}
+		for _, cd := range cc.dopts.copts.PerRPCCredentials {
+			if cd.RequireTransportSecurity() {
+				return nil, errTransportCredentialsMissing
+			}
+		}
+	}
+
+	if cc.dopts.defaultServiceConfigRawJSON != nil {
+		scpr := parseServiceConfig(*cc.dopts.defaultServiceConfigRawJSON)
+		if scpr.Err != nil {
+			return nil, fmt.Errorf("%s: %v", invalidDefaultServiceConfigErrPrefix, scpr.Err)
+		}
+		cc.dopts.defaultServiceConfig, _ = scpr.Config.(*ServiceConfig)
+	}
+	cc.mkp = cc.dopts.copts.KeepaliveParams
+
+	if cc.dopts.copts.Dialer == nil {
+		cc.dopts.copts.Dialer = func(ctx context.Context, addr string) (net.Conn, error) {
+			network, addr := parseDialTarget(addr)
+			return (&net.Dialer{}).DialContext(ctx, network, addr)
+		}
+		if cc.dopts.withProxy {
+			cc.dopts.copts.Dialer = newProxyDialer(cc.dopts.copts.Dialer)
+		}
+	}
+
+	if cc.dopts.copts.UserAgent != "" {
+		cc.dopts.copts.UserAgent += " " + grpcUA
+	} else {
+		cc.dopts.copts.UserAgent = grpcUA
+	}
+
+	if cc.dopts.timeout > 0 {
+		var cancel context.CancelFunc
+		ctx, cancel = context.WithTimeout(ctx, cc.dopts.timeout)
+		defer cancel()
+	}
+	defer func() {
+		select {
+		case <-ctx.Done():
+			conn, err = nil, ctx.Err()
+		default:
+		}
+	}()
+
+	scSet := false
+	if cc.dopts.scChan != nil {
+		// Try to get an initial service config.
+		select {
+		case sc, ok := <-cc.dopts.scChan:
+			if ok {
+				cc.sc = &sc
+				scSet = true
+			}
+		default:
+		}
+	}
+	if cc.dopts.bs == nil {
+		cc.dopts.bs = backoff.DefaultExponential
+	}
+
+	// Determine the resolver to use.
+	cc.parsedTarget = grpcutil.ParseTarget(cc.target)
+	channelz.Infof(cc.channelzID, "parsed scheme: %q", cc.parsedTarget.Scheme)
+	resolverBuilder := cc.getResolver(cc.parsedTarget.Scheme)
+	if resolverBuilder == nil {
+		// If resolver builder is still nil, the parsed target's scheme is
+		// not registered. Fallback to default resolver and set Endpoint to
+		// the original target.
+		channelz.Infof(cc.channelzID, "scheme %q not registered, fallback to default scheme", cc.parsedTarget.Scheme)
+		cc.parsedTarget = resolver.Target{
+			Scheme:   resolver.GetDefaultScheme(),
+			Endpoint: target,
+		}
+		resolverBuilder = cc.getResolver(cc.parsedTarget.Scheme)
+		if resolverBuilder == nil {
+			return nil, fmt.Errorf("could not get resolver for default scheme: %q", cc.parsedTarget.Scheme)
+		}
+	}
+
+	creds := cc.dopts.copts.TransportCredentials
+	if creds != nil && creds.Info().ServerName != "" {
+		cc.authority = creds.Info().ServerName
+	} else if cc.dopts.insecure && cc.dopts.authority != "" {
+		cc.authority = cc.dopts.authority
+	} else {
+		// Use endpoint from "scheme://authority/endpoint" as the default
+		// authority for ClientConn.
+		cc.authority = cc.parsedTarget.Endpoint
+	}
+
+	if cc.dopts.scChan != nil && !scSet {
+		// Blocking wait for the initial service config.
+		select {
+		case sc, ok := <-cc.dopts.scChan:
+			if ok {
+				cc.sc = &sc
+			}
+		case <-ctx.Done():
+			return nil, ctx.Err()
+		}
+	}
+	if cc.dopts.scChan != nil {
+		go cc.scWatcher()
+	}
+
+	var credsClone credentials.TransportCredentials
+	if creds := cc.dopts.copts.TransportCredentials; creds != nil {
+		credsClone = creds.Clone()
+	}
+	cc.balancerBuildOpts = balancer.BuildOptions{
+		DialCreds:        credsClone,
+		CredsBundle:      cc.dopts.copts.CredsBundle,
+		Dialer:           cc.dopts.copts.Dialer,
+		ChannelzParentID: cc.channelzID,
+		Target:           cc.parsedTarget,
+	}
+
+	// Build the resolver.
+	rWrapper, err := newCCResolverWrapper(cc, resolverBuilder)
+	if err != nil {
+		return nil, fmt.Errorf("failed to build resolver: %v", err)
+	}
+	cc.mu.Lock()
+	cc.resolverWrapper = rWrapper
+	cc.mu.Unlock()
+
+	// A blocking dial blocks until the clientConn is ready.
+	if cc.dopts.block {
+		for {
+			s := cc.GetState()
+			if s == connectivity.Ready {
+				break
+			} else if cc.dopts.copts.FailOnNonTempDialError && s == connectivity.TransientFailure {
+				if err = cc.blockingpicker.connectionError(); err != nil {
+					terr, ok := err.(interface {
+						Temporary() bool
+					})
+					if ok && !terr.Temporary() {
+						return nil, err
+					}
+				}
+			}
+			if !cc.WaitForStateChange(ctx, s) {
+				// ctx got timeout or canceled.
+				return nil, ctx.Err()
+			}
+		}
+	}
+
+	return cc, nil
+}
+
+// chainUnaryClientInterceptors chains all unary client interceptors into one.
+func chainUnaryClientInterceptors(cc *ClientConn) {
+	interceptors := cc.dopts.chainUnaryInts
+	// Prepend dopts.unaryInt to the chaining interceptors if it exists, since unaryInt will
+	// be executed before any other chained interceptors.
+	if cc.dopts.unaryInt != nil {
+		interceptors = append([]UnaryClientInterceptor{cc.dopts.unaryInt}, interceptors...)
+	}
+	var chainedInt UnaryClientInterceptor
+	if len(interceptors) == 0 {
+		chainedInt = nil
+	} else if len(interceptors) == 1 {
+		chainedInt = interceptors[0]
+	} else {
+		chainedInt = func(ctx context.Context, method string, req, reply interface{}, cc *ClientConn, invoker UnaryInvoker, opts ...CallOption) error {
+			return interceptors[0](ctx, method, req, reply, cc, getChainUnaryInvoker(interceptors, 0, invoker), opts...)
+		}
+	}
+	cc.dopts.unaryInt = chainedInt
+}
+
+// getChainUnaryInvoker recursively generate the chained unary invoker.
+func getChainUnaryInvoker(interceptors []UnaryClientInterceptor, curr int, finalInvoker UnaryInvoker) UnaryInvoker {
+	if curr == len(interceptors)-1 {
+		return finalInvoker
+	}
+	return func(ctx context.Context, method string, req, reply interface{}, cc *ClientConn, opts ...CallOption) error {
+		return interceptors[curr+1](ctx, method, req, reply, cc, getChainUnaryInvoker(interceptors, curr+1, finalInvoker), opts...)
+	}
+}
+
+// chainStreamClientInterceptors chains all stream client interceptors into one.
+func chainStreamClientInterceptors(cc *ClientConn) {
+	interceptors := cc.dopts.chainStreamInts
+	// Prepend dopts.streamInt to the chaining interceptors if it exists, since streamInt will
+	// be executed before any other chained interceptors.
+	if cc.dopts.streamInt != nil {
+		interceptors = append([]StreamClientInterceptor{cc.dopts.streamInt}, interceptors...)
+	}
+	var chainedInt StreamClientInterceptor
+	if len(interceptors) == 0 {
+		chainedInt = nil
+	} else if len(interceptors) == 1 {
+		chainedInt = interceptors[0]
+	} else {
+		chainedInt = func(ctx context.Context, desc *StreamDesc, cc *ClientConn, method string, streamer Streamer, opts ...CallOption) (ClientStream, error) {
+			return interceptors[0](ctx, desc, cc, method, getChainStreamer(interceptors, 0, streamer), opts...)
+		}
+	}
+	cc.dopts.streamInt = chainedInt
+}
+
+// getChainStreamer recursively generate the chained client stream constructor.
+func getChainStreamer(interceptors []StreamClientInterceptor, curr int, finalStreamer Streamer) Streamer {
+	if curr == len(interceptors)-1 {
+		return finalStreamer
+	}
+	return func(ctx context.Context, desc *StreamDesc, cc *ClientConn, method string, opts ...CallOption) (ClientStream, error) {
+		return interceptors[curr+1](ctx, desc, cc, method, getChainStreamer(interceptors, curr+1, finalStreamer), opts...)
+	}
+}
+
+// connectivityStateManager keeps the connectivity.State of ClientConn.
+// This struct will eventually be exported so the balancers can access it.
+type connectivityStateManager struct {
+	mu         sync.Mutex
+	state      connectivity.State
+	notifyChan chan struct{}
+	channelzID int64
+}
+
+// updateState updates the connectivity.State of ClientConn.
+// If there's a change it notifies goroutines waiting on state change to
+// happen.
+func (csm *connectivityStateManager) updateState(state connectivity.State) {
+	csm.mu.Lock()
+	defer csm.mu.Unlock()
+	if csm.state == connectivity.Shutdown {
+		return
+	}
+	if csm.state == state {
+		return
+	}
+	csm.state = state
+	channelz.Infof(csm.channelzID, "Channel Connectivity change to %v", state)
+	if csm.notifyChan != nil {
+		// There are other goroutines waiting on this channel.
+		close(csm.notifyChan)
+		csm.notifyChan = nil
+	}
+}
+
+func (csm *connectivityStateManager) getState() connectivity.State {
+	csm.mu.Lock()
+	defer csm.mu.Unlock()
+	return csm.state
+}
+
+func (csm *connectivityStateManager) getNotifyChan() <-chan struct{} {
+	csm.mu.Lock()
+	defer csm.mu.Unlock()
+	if csm.notifyChan == nil {
+		csm.notifyChan = make(chan struct{})
+	}
+	return csm.notifyChan
+}
+
+// ClientConnInterface defines the functions clients need to perform unary and
+// streaming RPCs.  It is implemented by *ClientConn, and is only intended to
+// be referenced by generated code.
+type ClientConnInterface interface {
+	// Invoke performs a unary RPC and returns after the response is received
+	// into reply.
+	Invoke(ctx context.Context, method string, args interface{}, reply interface{}, opts ...CallOption) error
+	// NewStream begins a streaming RPC.
+	NewStream(ctx context.Context, desc *StreamDesc, method string, opts ...CallOption) (ClientStream, error)
+}
+
+// Assert *ClientConn implements ClientConnInterface.
+var _ ClientConnInterface = (*ClientConn)(nil)
+
+// ClientConn represents a virtual connection to a conceptual endpoint, to
+// perform RPCs.
+//
+// A ClientConn is free to have zero or more actual connections to the endpoint
+// based on configuration, load, etc. It is also free to determine which actual
+// endpoints to use and may change it every RPC, permitting client-side load
+// balancing.
+//
+// A ClientConn encapsulates a range of functionality including name
+// resolution, TCP connection establishment (with retries and backoff) and TLS
+// handshakes. It also handles errors on established connections by
+// re-resolving the name and reconnecting.
+type ClientConn struct {
+	ctx    context.Context
+	cancel context.CancelFunc
+
+	target       string
+	parsedTarget resolver.Target
+	authority    string
+	dopts        dialOptions
+	csMgr        *connectivityStateManager
+
+	balancerBuildOpts balancer.BuildOptions
+	blockingpicker    *pickerWrapper
+
+	mu              sync.RWMutex
+	resolverWrapper *ccResolverWrapper
+	sc              *ServiceConfig
+	conns           map[*addrConn]struct{}
+	// Keepalive parameter can be updated if a GoAway is received.
+	mkp             keepalive.ClientParameters
+	curBalancerName string
+	balancerWrapper *ccBalancerWrapper
+	retryThrottler  atomic.Value
+
+	firstResolveEvent *grpcsync.Event
+
+	channelzID int64 // channelz unique identification number
+	czData     *channelzData
+}
+
+// WaitForStateChange waits until the connectivity.State of ClientConn changes from sourceState or
+// ctx expires. A true value is returned in former case and false in latter.
+// This is an EXPERIMENTAL API.
+func (cc *ClientConn) WaitForStateChange(ctx context.Context, sourceState connectivity.State) bool {
+	ch := cc.csMgr.getNotifyChan()
+	if cc.csMgr.getState() != sourceState {
+		return true
+	}
+	select {
+	case <-ctx.Done():
+		return false
+	case <-ch:
+		return true
+	}
+}
+
+// GetState returns the connectivity.State of ClientConn.
+// This is an EXPERIMENTAL API.
+func (cc *ClientConn) GetState() connectivity.State {
+	return cc.csMgr.getState()
+}
+
+func (cc *ClientConn) scWatcher() {
+	for {
+		select {
+		case sc, ok := <-cc.dopts.scChan:
+			if !ok {
+				return
+			}
+			cc.mu.Lock()
+			// TODO: load balance policy runtime change is ignored.
+			// We may revisit this decision in the future.
+			cc.sc = &sc
+			cc.mu.Unlock()
+		case <-cc.ctx.Done():
+			return
+		}
+	}
+}
+
+// waitForResolvedAddrs blocks until the resolver has provided addresses or the
+// context expires.  Returns nil unless the context expires first; otherwise
+// returns a status error based on the context.
+func (cc *ClientConn) waitForResolvedAddrs(ctx context.Context) error {
+	// This is on the RPC path, so we use a fast path to avoid the
+	// more-expensive "select" below after the resolver has returned once.
+	if cc.firstResolveEvent.HasFired() {
+		return nil
+	}
+	select {
+	case <-cc.firstResolveEvent.Done():
+		return nil
+	case <-ctx.Done():
+		return status.FromContextError(ctx.Err()).Err()
+	case <-cc.ctx.Done():
+		return ErrClientConnClosing
+	}
+}
+
+var emptyServiceConfig *ServiceConfig
+
+func init() {
+	cfg := parseServiceConfig("{}")
+	if cfg.Err != nil {
+		panic(fmt.Sprintf("impossible error parsing empty service config: %v", cfg.Err))
+	}
+	emptyServiceConfig = cfg.Config.(*ServiceConfig)
+}
+
+func (cc *ClientConn) maybeApplyDefaultServiceConfig(addrs []resolver.Address) {
+	if cc.sc != nil {
+		cc.applyServiceConfigAndBalancer(cc.sc, addrs)
+		return
+	}
+	if cc.dopts.defaultServiceConfig != nil {
+		cc.applyServiceConfigAndBalancer(cc.dopts.defaultServiceConfig, addrs)
+	} else {
+		cc.applyServiceConfigAndBalancer(emptyServiceConfig, addrs)
+	}
+}
+
+func (cc *ClientConn) updateResolverState(s resolver.State, err error) error {
+	defer cc.firstResolveEvent.Fire()
+	cc.mu.Lock()
+	// Check if the ClientConn is already closed. Some fields (e.g.
+	// balancerWrapper) are set to nil when closing the ClientConn, and could
+	// cause nil pointer panic if we don't have this check.
+	if cc.conns == nil {
+		cc.mu.Unlock()
+		return nil
+	}
+
+	if err != nil {
+		// May need to apply the initial service config in case the resolver
+		// doesn't support service configs, or doesn't provide a service config
+		// with the new addresses.
+		cc.maybeApplyDefaultServiceConfig(nil)
+
+		if cc.balancerWrapper != nil {
+			cc.balancerWrapper.resolverError(err)
+		}
+
+		// No addresses are valid with err set; return early.
+		cc.mu.Unlock()
+		return balancer.ErrBadResolverState
+	}
+
+	var ret error
+	if cc.dopts.disableServiceConfig || s.ServiceConfig == nil {
+		cc.maybeApplyDefaultServiceConfig(s.Addresses)
+		// TODO: do we need to apply a failing LB policy if there is no
+		// default, per the error handling design?
+	} else {
+		if sc, ok := s.ServiceConfig.Config.(*ServiceConfig); s.ServiceConfig.Err == nil && ok {
+			cc.applyServiceConfigAndBalancer(sc, s.Addresses)
+		} else {
+			ret = balancer.ErrBadResolverState
+			if cc.balancerWrapper == nil {
+				var err error
+				if s.ServiceConfig.Err != nil {
+					err = status.Errorf(codes.Unavailable, "error parsing service config: %v", s.ServiceConfig.Err)
+				} else {
+					err = status.Errorf(codes.Unavailable, "illegal service config type: %T", s.ServiceConfig.Config)
+				}
+				cc.blockingpicker.updatePicker(base.NewErrPicker(err))
+				cc.csMgr.updateState(connectivity.TransientFailure)
+				cc.mu.Unlock()
+				return ret
+			}
+		}
+	}
+
+	var balCfg serviceconfig.LoadBalancingConfig
+	if cc.dopts.balancerBuilder == nil && cc.sc != nil && cc.sc.lbConfig != nil {
+		balCfg = cc.sc.lbConfig.cfg
+	}
+
+	cbn := cc.curBalancerName
+	bw := cc.balancerWrapper
+	cc.mu.Unlock()
+	if cbn != grpclbName {
+		// Filter any grpclb addresses since we don't have the grpclb balancer.
+		for i := 0; i < len(s.Addresses); {
+			if s.Addresses[i].Type == resolver.GRPCLB {
+				copy(s.Addresses[i:], s.Addresses[i+1:])
+				s.Addresses = s.Addresses[:len(s.Addresses)-1]
+				continue
+			}
+			i++
+		}
+	}
+	uccsErr := bw.updateClientConnState(&balancer.ClientConnState{ResolverState: s, BalancerConfig: balCfg})
+	if ret == nil {
+		ret = uccsErr // prefer ErrBadResolver state since any other error is
+		// currently meaningless to the caller.
+	}
+	return ret
+}
+
+// switchBalancer starts the switching from current balancer to the balancer
+// with the given name.
+//
+// It will NOT send the current address list to the new balancer. If needed,
+// caller of this function should send address list to the new balancer after
+// this function returns.
+//
+// Caller must hold cc.mu.
+func (cc *ClientConn) switchBalancer(name string) {
+	if strings.EqualFold(cc.curBalancerName, name) {
+		return
+	}
+
+	channelz.Infof(cc.channelzID, "ClientConn switching balancer to %q", name)
+	if cc.dopts.balancerBuilder != nil {
+		channelz.Info(cc.channelzID, "ignoring balancer switching: Balancer DialOption used instead")
+		return
+	}
+	if cc.balancerWrapper != nil {
+		cc.balancerWrapper.close()
+	}
+
+	builder := balancer.Get(name)
+	if builder == nil {
+		channelz.Warningf(cc.channelzID, "Channel switches to new LB policy %q due to fallback from invalid balancer name", PickFirstBalancerName)
+		channelz.Infof(cc.channelzID, "failed to get balancer builder for: %v, using pick_first instead", name)
+		builder = newPickfirstBuilder()
+	} else {
+		channelz.Infof(cc.channelzID, "Channel switches to new LB policy %q", name)
+	}
+
+	cc.curBalancerName = builder.Name()
+	cc.balancerWrapper = newCCBalancerWrapper(cc, builder, cc.balancerBuildOpts)
+}
+
+func (cc *ClientConn) handleSubConnStateChange(sc balancer.SubConn, s connectivity.State, err error) {
+	cc.mu.Lock()
+	if cc.conns == nil {
+		cc.mu.Unlock()
+		return
+	}
+	// TODO(bar switching) send updates to all balancer wrappers when balancer
+	// gracefully switching is supported.
+	cc.balancerWrapper.handleSubConnStateChange(sc, s, err)
+	cc.mu.Unlock()
+}
+
+// newAddrConn creates an addrConn for addrs and adds it to cc.conns.
+//
+// Caller needs to make sure len(addrs) > 0.
+func (cc *ClientConn) newAddrConn(addrs []resolver.Address, opts balancer.NewSubConnOptions) (*addrConn, error) {
+	ac := &addrConn{
+		state:        connectivity.Idle,
+		cc:           cc,
+		addrs:        addrs,
+		scopts:       opts,
+		dopts:        cc.dopts,
+		czData:       new(channelzData),
+		resetBackoff: make(chan struct{}),
+	}
+	ac.ctx, ac.cancel = context.WithCancel(cc.ctx)
+	// Track ac in cc. This needs to be done before any getTransport(...) is called.
+	cc.mu.Lock()
+	if cc.conns == nil {
+		cc.mu.Unlock()
+		return nil, ErrClientConnClosing
+	}
+	if channelz.IsOn() {
+		ac.channelzID = channelz.RegisterSubChannel(ac, cc.channelzID, "")
+		channelz.AddTraceEvent(ac.channelzID, 0, &channelz.TraceEventDesc{
+			Desc:     "Subchannel Created",
+			Severity: channelz.CtINFO,
+			Parent: &channelz.TraceEventDesc{
+				Desc:     fmt.Sprintf("Subchannel(id:%d) created", ac.channelzID),
+				Severity: channelz.CtINFO,
+			},
+		})
+	}
+	cc.conns[ac] = struct{}{}
+	cc.mu.Unlock()
+	return ac, nil
+}
+
+// removeAddrConn removes the addrConn in the subConn from clientConn.
+// It also tears down the ac with the given error.
+func (cc *ClientConn) removeAddrConn(ac *addrConn, err error) {
+	cc.mu.Lock()
+	if cc.conns == nil {
+		cc.mu.Unlock()
+		return
+	}
+	delete(cc.conns, ac)
+	cc.mu.Unlock()
+	ac.tearDown(err)
+}
+
+func (cc *ClientConn) channelzMetric() *channelz.ChannelInternalMetric {
+	return &channelz.ChannelInternalMetric{
+		State:                    cc.GetState(),
+		Target:                   cc.target,
+		CallsStarted:             atomic.LoadInt64(&cc.czData.callsStarted),
+		CallsSucceeded:           atomic.LoadInt64(&cc.czData.callsSucceeded),
+		CallsFailed:              atomic.LoadInt64(&cc.czData.callsFailed),
+		LastCallStartedTimestamp: time.Unix(0, atomic.LoadInt64(&cc.czData.lastCallStartedTime)),
+	}
+}
+
+// Target returns the target string of the ClientConn.
+// This is an EXPERIMENTAL API.
+func (cc *ClientConn) Target() string {
+	return cc.target
+}
+
+func (cc *ClientConn) incrCallsStarted() {
+	atomic.AddInt64(&cc.czData.callsStarted, 1)
+	atomic.StoreInt64(&cc.czData.lastCallStartedTime, time.Now().UnixNano())
+}
+
+func (cc *ClientConn) incrCallsSucceeded() {
+	atomic.AddInt64(&cc.czData.callsSucceeded, 1)
+}
+
+func (cc *ClientConn) incrCallsFailed() {
+	atomic.AddInt64(&cc.czData.callsFailed, 1)
+}
+
+// connect starts creating a transport.
+// It does nothing if the ac is not IDLE.
+// TODO(bar) Move this to the addrConn section.
+func (ac *addrConn) connect() error {
+	ac.mu.Lock()
+	if ac.state == connectivity.Shutdown {
+		ac.mu.Unlock()
+		return errConnClosing
+	}
+	if ac.state != connectivity.Idle {
+		ac.mu.Unlock()
+		return nil
+	}
+	// Update connectivity state within the lock to prevent subsequent or
+	// concurrent calls from resetting the transport more than once.
+	ac.updateConnectivityState(connectivity.Connecting, nil)
+	ac.mu.Unlock()
+
+	// Start a goroutine connecting to the server asynchronously.
+	go ac.resetTransport()
+	return nil
+}
+
+// tryUpdateAddrs tries to update ac.addrs with the new addresses list.
+//
+// If ac is Connecting, it returns false. The caller should tear down the ac and
+// create a new one. Note that the backoff will be reset when this happens.
+//
+// If ac is TransientFailure, it updates ac.addrs and returns true. The updated
+// addresses will be picked up by retry in the next iteration after backoff.
+//
+// If ac is Shutdown or Idle, it updates ac.addrs and returns true.
+//
+// If ac is Ready, it checks whether current connected address of ac is in the
+// new addrs list.
+//  - If true, it updates ac.addrs and returns true. The ac will keep using
+//    the existing connection.
+//  - If false, it does nothing and returns false.
+func (ac *addrConn) tryUpdateAddrs(addrs []resolver.Address) bool {
+	ac.mu.Lock()
+	defer ac.mu.Unlock()
+	channelz.Infof(ac.channelzID, "addrConn: tryUpdateAddrs curAddr: %v, addrs: %v", ac.curAddr, addrs)
+	if ac.state == connectivity.Shutdown ||
+		ac.state == connectivity.TransientFailure ||
+		ac.state == connectivity.Idle {
+		ac.addrs = addrs
+		return true
+	}
+
+	if ac.state == connectivity.Connecting {
+		return false
+	}
+
+	// ac.state is Ready, try to find the connected address.
+	var curAddrFound bool
+	for _, a := range addrs {
+		if reflect.DeepEqual(ac.curAddr, a) {
+			curAddrFound = true
+			break
+		}
+	}
+	channelz.Infof(ac.channelzID, "addrConn: tryUpdateAddrs curAddrFound: %v", curAddrFound)
+	if curAddrFound {
+		ac.addrs = addrs
+	}
+
+	return curAddrFound
+}
+
+// GetMethodConfig gets the method config of the input method.
+// If there's an exact match for input method (i.e. /service/method), we return
+// the corresponding MethodConfig.
+// If there isn't an exact match for the input method, we look for the default config
+// under the service (i.e /service/). If there is a default MethodConfig for
+// the service, we return it.
+// Otherwise, we return an empty MethodConfig.
+func (cc *ClientConn) GetMethodConfig(method string) MethodConfig {
+	// TODO: Avoid the locking here.
+	cc.mu.RLock()
+	defer cc.mu.RUnlock()
+	if cc.sc == nil {
+		return MethodConfig{}
+	}
+	m, ok := cc.sc.Methods[method]
+	if !ok {
+		i := strings.LastIndex(method, "/")
+		m = cc.sc.Methods[method[:i+1]]
+	}
+	return m
+}
+
+func (cc *ClientConn) healthCheckConfig() *healthCheckConfig {
+	cc.mu.RLock()
+	defer cc.mu.RUnlock()
+	if cc.sc == nil {
+		return nil
+	}
+	return cc.sc.healthCheckConfig
+}
+
+func (cc *ClientConn) getTransport(ctx context.Context, failfast bool, method string) (transport.ClientTransport, func(balancer.DoneInfo), error) {
+	t, done, err := cc.blockingpicker.pick(ctx, failfast, balancer.PickInfo{
+		Ctx:            ctx,
+		FullMethodName: method,
+	})
+	if err != nil {
+		return nil, nil, toRPCErr(err)
+	}
+	return t, done, nil
+}
+
+func (cc *ClientConn) applyServiceConfigAndBalancer(sc *ServiceConfig, addrs []resolver.Address) {
+	if sc == nil {
+		// should never reach here.
+		return
+	}
+	cc.sc = sc
+
+	if cc.sc.retryThrottling != nil {
+		newThrottler := &retryThrottler{
+			tokens: cc.sc.retryThrottling.MaxTokens,
+			max:    cc.sc.retryThrottling.MaxTokens,
+			thresh: cc.sc.retryThrottling.MaxTokens / 2,
+			ratio:  cc.sc.retryThrottling.TokenRatio,
+		}
+		cc.retryThrottler.Store(newThrottler)
+	} else {
+		cc.retryThrottler.Store((*retryThrottler)(nil))
+	}
+
+	if cc.dopts.balancerBuilder == nil {
+		// Only look at balancer types and switch balancer if balancer dial
+		// option is not set.
+		var newBalancerName string
+		if cc.sc != nil && cc.sc.lbConfig != nil {
+			newBalancerName = cc.sc.lbConfig.name
+		} else {
+			var isGRPCLB bool
+			for _, a := range addrs {
+				if a.Type == resolver.GRPCLB {
+					isGRPCLB = true
+					break
+				}
+			}
+			if isGRPCLB {
+				newBalancerName = grpclbName
+			} else if cc.sc != nil && cc.sc.LB != nil {
+				newBalancerName = *cc.sc.LB
+			} else {
+				newBalancerName = PickFirstBalancerName
+			}
+		}
+		cc.switchBalancer(newBalancerName)
+	} else if cc.balancerWrapper == nil {
+		// Balancer dial option was set, and this is the first time handling
+		// resolved addresses. Build a balancer with dopts.balancerBuilder.
+		cc.curBalancerName = cc.dopts.balancerBuilder.Name()
+		cc.balancerWrapper = newCCBalancerWrapper(cc, cc.dopts.balancerBuilder, cc.balancerBuildOpts)
+	}
+}
+
+func (cc *ClientConn) resolveNow(o resolver.ResolveNowOptions) {
+	cc.mu.RLock()
+	r := cc.resolverWrapper
+	cc.mu.RUnlock()
+	if r == nil {
+		return
+	}
+	go r.resolveNow(o)
+}
+
+// ResetConnectBackoff wakes up all subchannels in transient failure and causes
+// them to attempt another connection immediately.  It also resets the backoff
+// times used for subsequent attempts regardless of the current state.
+//
+// In general, this function should not be used.  Typical service or network
+// outages result in a reasonable client reconnection strategy by default.
+// However, if a previously unavailable network becomes available, this may be
+// used to trigger an immediate reconnect.
+//
+// This API is EXPERIMENTAL.
+func (cc *ClientConn) ResetConnectBackoff() {
+	cc.mu.Lock()
+	conns := cc.conns
+	cc.mu.Unlock()
+	for ac := range conns {
+		ac.resetConnectBackoff()
+	}
+}
+
+// Close tears down the ClientConn and all underlying connections.
+func (cc *ClientConn) Close() error {
+	defer cc.cancel()
+
+	cc.mu.Lock()
+	if cc.conns == nil {
+		cc.mu.Unlock()
+		return ErrClientConnClosing
+	}
+	conns := cc.conns
+	cc.conns = nil
+	cc.csMgr.updateState(connectivity.Shutdown)
+
+	rWrapper := cc.resolverWrapper
+	cc.resolverWrapper = nil
+	bWrapper := cc.balancerWrapper
+	cc.balancerWrapper = nil
+	cc.mu.Unlock()
+
+	cc.blockingpicker.close()
+
+	if rWrapper != nil {
+		rWrapper.close()
+	}
+	if bWrapper != nil {
+		bWrapper.close()
+	}
+
+	for ac := range conns {
+		ac.tearDown(ErrClientConnClosing)
+	}
+	if channelz.IsOn() {
+		ted := &channelz.TraceEventDesc{
+			Desc:     "Channel Deleted",
+			Severity: channelz.CtINFO,
+		}
+		if cc.dopts.channelzParentID != 0 {
+			ted.Parent = &channelz.TraceEventDesc{
+				Desc:     fmt.Sprintf("Nested channel(id:%d) deleted", cc.channelzID),
+				Severity: channelz.CtINFO,
+			}
+		}
+		channelz.AddTraceEvent(cc.channelzID, 0, ted)
+		// TraceEvent needs to be called before RemoveEntry, as TraceEvent may add trace reference to
+		// the entity being deleted, and thus prevent it from being deleted right away.
+		channelz.RemoveEntry(cc.channelzID)
+	}
+	return nil
+}
+
+// addrConn is a network connection to a given address.
+type addrConn struct {
+	ctx    context.Context
+	cancel context.CancelFunc
+
+	cc     *ClientConn
+	dopts  dialOptions
+	acbw   balancer.SubConn
+	scopts balancer.NewSubConnOptions
+
+	// transport is set when there's a viable transport (note: ac state may not be READY as LB channel
+	// health checking may require server to report healthy to set ac to READY), and is reset
+	// to nil when the current transport should no longer be used to create a stream (e.g. after GoAway
+	// is received, transport is closed, ac has been torn down).
+	transport transport.ClientTransport // The current transport.
+
+	mu      sync.Mutex
+	curAddr resolver.Address   // The current address.
+	addrs   []resolver.Address // All addresses that the resolver resolved to.
+
+	// Use updateConnectivityState for updating addrConn's connectivity state.
+	state connectivity.State
+
+	backoffIdx   int // Needs to be stateful for resetConnectBackoff.
+	resetBackoff chan struct{}
+
+	channelzID int64 // channelz unique identification number.
+	czData     *channelzData
+}
+
+// Note: this requires a lock on ac.mu.
+func (ac *addrConn) updateConnectivityState(s connectivity.State, lastErr error) {
+	if ac.state == s {
+		return
+	}
+	ac.state = s
+	channelz.Infof(ac.channelzID, "Subchannel Connectivity change to %v", s)
+	ac.cc.handleSubConnStateChange(ac.acbw, s, lastErr)
+}
+
+// adjustParams updates parameters used to create transports upon
+// receiving a GoAway.
+func (ac *addrConn) adjustParams(r transport.GoAwayReason) {
+	switch r {
+	case transport.GoAwayTooManyPings:
+		v := 2 * ac.dopts.copts.KeepaliveParams.Time
+		ac.cc.mu.Lock()
+		if v > ac.cc.mkp.Time {
+			ac.cc.mkp.Time = v
+		}
+		ac.cc.mu.Unlock()
+	}
+}
+
+func (ac *addrConn) resetTransport() {
+	for i := 0; ; i++ {
+		if i > 0 {
+			ac.cc.resolveNow(resolver.ResolveNowOptions{})
+		}
+
+		ac.mu.Lock()
+		if ac.state == connectivity.Shutdown {
+			ac.mu.Unlock()
+			return
+		}
+
+		addrs := ac.addrs
+		backoffFor := ac.dopts.bs.Backoff(ac.backoffIdx)
+		// This will be the duration that dial gets to finish.
+		dialDuration := minConnectTimeout
+		if ac.dopts.minConnectTimeout != nil {
+			dialDuration = ac.dopts.minConnectTimeout()
+		}
+
+		if dialDuration < backoffFor {
+			// Give dial more time as we keep failing to connect.
+			dialDuration = backoffFor
+		}
+		// We can potentially spend all the time trying the first address, and
+		// if the server accepts the connection and then hangs, the following
+		// addresses will never be tried.
+		//
+		// The spec doesn't mention what should be done for multiple addresses.
+		// https://github.com/grpc/grpc/blob/master/doc/connection-backoff.md#proposed-backoff-algorithm
+		connectDeadline := time.Now().Add(dialDuration)
+
+		ac.updateConnectivityState(connectivity.Connecting, nil)
+		ac.transport = nil
+		ac.mu.Unlock()
+
+		newTr, addr, reconnect, err := ac.tryAllAddrs(addrs, connectDeadline)
+		if err != nil {
+			// After exhausting all addresses, the addrConn enters
+			// TRANSIENT_FAILURE.
+			ac.mu.Lock()
+			if ac.state == connectivity.Shutdown {
+				ac.mu.Unlock()
+				return
+			}
+			ac.updateConnectivityState(connectivity.TransientFailure, err)
+
+			// Backoff.
+			b := ac.resetBackoff
+			ac.mu.Unlock()
+
+			timer := time.NewTimer(backoffFor)
+			select {
+			case <-timer.C:
+				ac.mu.Lock()
+				ac.backoffIdx++
+				ac.mu.Unlock()
+			case <-b:
+				timer.Stop()
+			case <-ac.ctx.Done():
+				timer.Stop()
+				return
+			}
+			continue
+		}
+
+		ac.mu.Lock()
+		if ac.state == connectivity.Shutdown {
+			ac.mu.Unlock()
+			newTr.Close()
+			return
+		}
+		ac.curAddr = addr
+		ac.transport = newTr
+		ac.backoffIdx = 0
+
+		hctx, hcancel := context.WithCancel(ac.ctx)
+		ac.startHealthCheck(hctx)
+		ac.mu.Unlock()
+
+		// Block until the created transport is down. And when this happens,
+		// we restart from the top of the addr list.
+		<-reconnect.Done()
+		hcancel()
+		// restart connecting - the top of the loop will set state to
+		// CONNECTING.  This is against the current connectivity semantics doc,
+		// however it allows for graceful behavior for RPCs not yet dispatched
+		// - unfortunate timing would otherwise lead to the RPC failing even
+		// though the TRANSIENT_FAILURE state (called for by the doc) would be
+		// instantaneous.
+		//
+		// Ideally we should transition to Idle here and block until there is
+		// RPC activity that leads to the balancer requesting a reconnect of
+		// the associated SubConn.
+	}
+}
+
+// tryAllAddrs tries to creates a connection to the addresses, and stop when at the
+// first successful one. It returns the transport, the address and a Event in
+// the successful case. The Event fires when the returned transport disconnects.
+func (ac *addrConn) tryAllAddrs(addrs []resolver.Address, connectDeadline time.Time) (transport.ClientTransport, resolver.Address, *grpcsync.Event, error) {
+	var firstConnErr error
+	for _, addr := range addrs {
+		ac.mu.Lock()
+		if ac.state == connectivity.Shutdown {
+			ac.mu.Unlock()
+			return nil, resolver.Address{}, nil, errConnClosing
+		}
+
+		ac.cc.mu.RLock()
+		ac.dopts.copts.KeepaliveParams = ac.cc.mkp
+		ac.cc.mu.RUnlock()
+
+		copts := ac.dopts.copts
+		if ac.scopts.CredsBundle != nil {
+			copts.CredsBundle = ac.scopts.CredsBundle
+		}
+		ac.mu.Unlock()
+
+		channelz.Infof(ac.channelzID, "Subchannel picks a new address %q to connect", addr.Addr)
+
+		newTr, reconnect, err := ac.createTransport(addr, copts, connectDeadline)
+		if err == nil {
+			return newTr, addr, reconnect, nil
+		}
+		if firstConnErr == nil {
+			firstConnErr = err
+		}
+		ac.cc.blockingpicker.updateConnectionError(err)
+	}
+
+	// Couldn't connect to any address.
+	return nil, resolver.Address{}, nil, firstConnErr
+}
+
+// createTransport creates a connection to addr. It returns the transport and a
+// Event in the successful case. The Event fires when the returned transport
+// disconnects.
+func (ac *addrConn) createTransport(addr resolver.Address, copts transport.ConnectOptions, connectDeadline time.Time) (transport.ClientTransport, *grpcsync.Event, error) {
+	prefaceReceived := make(chan struct{})
+	onCloseCalled := make(chan struct{})
+	reconnect := grpcsync.NewEvent()
+
+	authority := ac.cc.authority
+	// addr.ServerName takes precedent over ClientConn authority, if present.
+	if addr.ServerName != "" {
+		authority = addr.ServerName
+	}
+
+	target := transport.TargetInfo{
+		Addr:      addr.Addr,
+		Metadata:  addr.Metadata,
+		Authority: authority,
+	}
+
+	once := sync.Once{}
+	onGoAway := func(r transport.GoAwayReason) {
+		ac.mu.Lock()
+		ac.adjustParams(r)
+		once.Do(func() {
+			if ac.state == connectivity.Ready {
+				// Prevent this SubConn from being used for new RPCs by setting its
+				// state to Connecting.
+				//
+				// TODO: this should be Idle when grpc-go properly supports it.
+				ac.updateConnectivityState(connectivity.Connecting, nil)
+			}
+		})
+		ac.mu.Unlock()
+		reconnect.Fire()
+	}
+
+	onClose := func() {
+		ac.mu.Lock()
+		once.Do(func() {
+			if ac.state == connectivity.Ready {
+				// Prevent this SubConn from being used for new RPCs by setting its
+				// state to Connecting.
+				//
+				// TODO: this should be Idle when grpc-go properly supports it.
+				ac.updateConnectivityState(connectivity.Connecting, nil)
+			}
+		})
+		ac.mu.Unlock()
+		close(onCloseCalled)
+		reconnect.Fire()
+	}
+
+	onPrefaceReceipt := func() {
+		close(prefaceReceived)
+	}
+
+	connectCtx, cancel := context.WithDeadline(ac.ctx, connectDeadline)
+	defer cancel()
+	if channelz.IsOn() {
+		copts.ChannelzParentID = ac.channelzID
+	}
+
+	newTr, err := transport.NewClientTransport(connectCtx, ac.cc.ctx, target, copts, onPrefaceReceipt, onGoAway, onClose)
+	if err != nil {
+		// newTr is either nil, or closed.
+		channelz.Warningf(ac.channelzID, "grpc: addrConn.createTransport failed to connect to %v. Err: %v. Reconnecting...", addr, err)
+		return nil, nil, err
+	}
+
+	select {
+	case <-time.After(time.Until(connectDeadline)):
+		// We didn't get the preface in time.
+		newTr.Close()
+		channelz.Warningf(ac.channelzID, "grpc: addrConn.createTransport failed to connect to %v: didn't receive server preface in time. Reconnecting...", addr)
+		return nil, nil, errors.New("timed out waiting for server handshake")
+	case <-prefaceReceived:
+		// We got the preface - huzzah! things are good.
+	case <-onCloseCalled:
+		// The transport has already closed - noop.
+		return nil, nil, errors.New("connection closed")
+		// TODO(deklerk) this should bail on ac.ctx.Done(). Add a test and fix.
+	}
+	return newTr, reconnect, nil
+}
+
+// startHealthCheck starts the health checking stream (RPC) to watch the health
+// stats of this connection if health checking is requested and configured.
+//
+// LB channel health checking is enabled when all requirements below are met:
+// 1. it is not disabled by the user with the WithDisableHealthCheck DialOption
+// 2. internal.HealthCheckFunc is set by importing the grpc/healthcheck package
+// 3. a service config with non-empty healthCheckConfig field is provided
+// 4. the load balancer requests it
+//
+// It sets addrConn to READY if the health checking stream is not started.
+//
+// Caller must hold ac.mu.
+func (ac *addrConn) startHealthCheck(ctx context.Context) {
+	var healthcheckManagingState bool
+	defer func() {
+		if !healthcheckManagingState {
+			ac.updateConnectivityState(connectivity.Ready, nil)
+		}
+	}()
+
+	if ac.cc.dopts.disableHealthCheck {
+		return
+	}
+	healthCheckConfig := ac.cc.healthCheckConfig()
+	if healthCheckConfig == nil {
+		return
+	}
+	if !ac.scopts.HealthCheckEnabled {
+		return
+	}
+	healthCheckFunc := ac.cc.dopts.healthCheckFunc
+	if healthCheckFunc == nil {
+		// The health package is not imported to set health check function.
+		//
+		// TODO: add a link to the health check doc in the error message.
+		channelz.Error(ac.channelzID, "Health check is requested but health check function is not set.")
+		return
+	}
+
+	healthcheckManagingState = true
+
+	// Set up the health check helper functions.
+	currentTr := ac.transport
+	newStream := func(method string) (interface{}, error) {
+		ac.mu.Lock()
+		if ac.transport != currentTr {
+			ac.mu.Unlock()
+			return nil, status.Error(codes.Canceled, "the provided transport is no longer valid to use")
+		}
+		ac.mu.Unlock()
+		return newNonRetryClientStream(ctx, &StreamDesc{ServerStreams: true}, method, currentTr, ac)
+	}
+	setConnectivityState := func(s connectivity.State, lastErr error) {
+		ac.mu.Lock()
+		defer ac.mu.Unlock()
+		if ac.transport != currentTr {
+			return
+		}
+		ac.updateConnectivityState(s, lastErr)
+	}
+	// Start the health checking stream.
+	go func() {
+		err := ac.cc.dopts.healthCheckFunc(ctx, newStream, setConnectivityState, healthCheckConfig.ServiceName)
+		if err != nil {
+			if status.Code(err) == codes.Unimplemented {
+				channelz.Error(ac.channelzID, "Subchannel health check is unimplemented at server side, thus health check is disabled")
+			} else {
+				channelz.Errorf(ac.channelzID, "HealthCheckFunc exits with unexpected error %v", err)
+			}
+		}
+	}()
+}
+
+func (ac *addrConn) resetConnectBackoff() {
+	ac.mu.Lock()
+	close(ac.resetBackoff)
+	ac.backoffIdx = 0
+	ac.resetBackoff = make(chan struct{})
+	ac.mu.Unlock()
+}
+
+// getReadyTransport returns the transport if ac's state is READY.
+// Otherwise it returns nil, false.
+// If ac's state is IDLE, it will trigger ac to connect.
+func (ac *addrConn) getReadyTransport() (transport.ClientTransport, bool) {
+	ac.mu.Lock()
+	if ac.state == connectivity.Ready && ac.transport != nil {
+		t := ac.transport
+		ac.mu.Unlock()
+		return t, true
+	}
+	var idle bool
+	if ac.state == connectivity.Idle {
+		idle = true
+	}
+	ac.mu.Unlock()
+	// Trigger idle ac to connect.
+	if idle {
+		ac.connect()
+	}
+	return nil, false
+}
+
+// tearDown starts to tear down the addrConn.
+// TODO(zhaoq): Make this synchronous to avoid unbounded memory consumption in
+// some edge cases (e.g., the caller opens and closes many addrConn's in a
+// tight loop.
+// tearDown doesn't remove ac from ac.cc.conns.
+func (ac *addrConn) tearDown(err error) {
+	ac.mu.Lock()
+	if ac.state == connectivity.Shutdown {
+		ac.mu.Unlock()
+		return
+	}
+	curTr := ac.transport
+	ac.transport = nil
+	// We have to set the state to Shutdown before anything else to prevent races
+	// between setting the state and logic that waits on context cancellation / etc.
+	ac.updateConnectivityState(connectivity.Shutdown, nil)
+	ac.cancel()
+	ac.curAddr = resolver.Address{}
+	if err == errConnDrain && curTr != nil {
+		// GracefulClose(...) may be executed multiple times when
+		// i) receiving multiple GoAway frames from the server; or
+		// ii) there are concurrent name resolver/Balancer triggered
+		// address removal and GoAway.
+		// We have to unlock and re-lock here because GracefulClose => Close => onClose, which requires locking ac.mu.
+		ac.mu.Unlock()
+		curTr.GracefulClose()
+		ac.mu.Lock()
+	}
+	if channelz.IsOn() {
+		channelz.AddTraceEvent(ac.channelzID, 0, &channelz.TraceEventDesc{
+			Desc:     "Subchannel Deleted",
+			Severity: channelz.CtINFO,
+			Parent: &channelz.TraceEventDesc{
+				Desc:     fmt.Sprintf("Subchanel(id:%d) deleted", ac.channelzID),
+				Severity: channelz.CtINFO,
+			},
+		})
+		// TraceEvent needs to be called before RemoveEntry, as TraceEvent may add trace reference to
+		// the entity being deleted, and thus prevent it from being deleted right away.
+		channelz.RemoveEntry(ac.channelzID)
+	}
+	ac.mu.Unlock()
+}
+
+func (ac *addrConn) getState() connectivity.State {
+	ac.mu.Lock()
+	defer ac.mu.Unlock()
+	return ac.state
+}
+
+func (ac *addrConn) ChannelzMetric() *channelz.ChannelInternalMetric {
+	ac.mu.Lock()
+	addr := ac.curAddr.Addr
+	ac.mu.Unlock()
+	return &channelz.ChannelInternalMetric{
+		State:                    ac.getState(),
+		Target:                   addr,
+		CallsStarted:             atomic.LoadInt64(&ac.czData.callsStarted),
+		CallsSucceeded:           atomic.LoadInt64(&ac.czData.callsSucceeded),
+		CallsFailed:              atomic.LoadInt64(&ac.czData.callsFailed),
+		LastCallStartedTimestamp: time.Unix(0, atomic.LoadInt64(&ac.czData.lastCallStartedTime)),
+	}
+}
+
+func (ac *addrConn) incrCallsStarted() {
+	atomic.AddInt64(&ac.czData.callsStarted, 1)
+	atomic.StoreInt64(&ac.czData.lastCallStartedTime, time.Now().UnixNano())
+}
+
+func (ac *addrConn) incrCallsSucceeded() {
+	atomic.AddInt64(&ac.czData.callsSucceeded, 1)
+}
+
+func (ac *addrConn) incrCallsFailed() {
+	atomic.AddInt64(&ac.czData.callsFailed, 1)
+}
+
+type retryThrottler struct {
+	max    float64
+	thresh float64
+	ratio  float64
+
+	mu     sync.Mutex
+	tokens float64 // TODO(dfawley): replace with atomic and remove lock.
+}
+
+// throttle subtracts a retry token from the pool and returns whether a retry
+// should be throttled (disallowed) based upon the retry throttling policy in
+// the service config.
+func (rt *retryThrottler) throttle() bool {
+	if rt == nil {
+		return false
+	}
+	rt.mu.Lock()
+	defer rt.mu.Unlock()
+	rt.tokens--
+	if rt.tokens < 0 {
+		rt.tokens = 0
+	}
+	return rt.tokens <= rt.thresh
+}
+
+func (rt *retryThrottler) successfulRPC() {
+	if rt == nil {
+		return
+	}
+	rt.mu.Lock()
+	defer rt.mu.Unlock()
+	rt.tokens += rt.ratio
+	if rt.tokens > rt.max {
+		rt.tokens = rt.max
+	}
+}
+
+type channelzChannel struct {
+	cc *ClientConn
+}
+
+func (c *channelzChannel) ChannelzMetric() *channelz.ChannelInternalMetric {
+	return c.cc.channelzMetric()
+}
+
+// ErrClientConnTimeout indicates that the ClientConn cannot establish the
+// underlying connections within the specified timeout.
+//
+// Deprecated: This error is never returned by grpc and should not be
+// referenced by users.
+var ErrClientConnTimeout = errors.New("grpc: timed out when dialing")
+
+func (cc *ClientConn) getResolver(scheme string) resolver.Builder {
+	for _, rb := range cc.dopts.resolvers {
+		if scheme == rb.Scheme() {
+			return rb
+		}
+	}
+	return resolver.Get(scheme)
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/codec.go b/demo_test/vendor/google.golang.org/grpc/codec.go
new file mode 100644
index 0000000..1297765
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/codec.go
@@ -0,0 +1,50 @@
+/*
+ *
+ * Copyright 2014 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package grpc
+
+import (
+	"google.golang.org/grpc/encoding"
+	_ "google.golang.org/grpc/encoding/proto" // to register the Codec for "proto"
+)
+
+// baseCodec contains the functionality of both Codec and encoding.Codec, but
+// omits the name/string, which vary between the two and are not needed for
+// anything besides the registry in the encoding package.
+type baseCodec interface {
+	Marshal(v interface{}) ([]byte, error)
+	Unmarshal(data []byte, v interface{}) error
+}
+
+var _ baseCodec = Codec(nil)
+var _ baseCodec = encoding.Codec(nil)
+
+// Codec defines the interface gRPC uses to encode and decode messages.
+// Note that implementations of this interface must be thread safe;
+// a Codec's methods can be called from concurrent goroutines.
+//
+// Deprecated: use encoding.Codec instead.
+type Codec interface {
+	// Marshal returns the wire format of v.
+	Marshal(v interface{}) ([]byte, error)
+	// Unmarshal parses the wire format into v.
+	Unmarshal(data []byte, v interface{}) error
+	// String returns the name of the Codec implementation.  This is unused by
+	// gRPC.
+	String() string
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/codegen.sh b/demo_test/vendor/google.golang.org/grpc/codegen.sh
new file mode 100644
index 0000000..4cdc6ba
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/codegen.sh
@@ -0,0 +1,17 @@
+#!/usr/bin/env bash
+
+# This script serves as an example to demonstrate how to generate the gRPC-Go
+# interface and the related messages from .proto file.
+#
+# It assumes the installation of i) Google proto buffer compiler at
+# https://github.com/google/protobuf (after v2.6.1) and ii) the Go codegen
+# plugin at https://github.com/golang/protobuf (after 2015-02-20). If you have
+# not, please install them first.
+#
+# We recommend running this script at $GOPATH/src.
+#
+# If this is not what you need, feel free to make your own scripts. Again, this
+# script is for demonstration purpose.
+#
+proto=$1
+protoc --go_out=plugins=grpc:. $proto
diff --git a/demo_test/vendor/google.golang.org/grpc/codes/code_string.go b/demo_test/vendor/google.golang.org/grpc/codes/code_string.go
new file mode 100644
index 0000000..0b206a5
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/codes/code_string.go
@@ -0,0 +1,62 @@
+/*
+ *
+ * Copyright 2017 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package codes
+
+import "strconv"
+
+func (c Code) String() string {
+	switch c {
+	case OK:
+		return "OK"
+	case Canceled:
+		return "Canceled"
+	case Unknown:
+		return "Unknown"
+	case InvalidArgument:
+		return "InvalidArgument"
+	case DeadlineExceeded:
+		return "DeadlineExceeded"
+	case NotFound:
+		return "NotFound"
+	case AlreadyExists:
+		return "AlreadyExists"
+	case PermissionDenied:
+		return "PermissionDenied"
+	case ResourceExhausted:
+		return "ResourceExhausted"
+	case FailedPrecondition:
+		return "FailedPrecondition"
+	case Aborted:
+		return "Aborted"
+	case OutOfRange:
+		return "OutOfRange"
+	case Unimplemented:
+		return "Unimplemented"
+	case Internal:
+		return "Internal"
+	case Unavailable:
+		return "Unavailable"
+	case DataLoss:
+		return "DataLoss"
+	case Unauthenticated:
+		return "Unauthenticated"
+	default:
+		return "Code(" + strconv.FormatInt(int64(c), 10) + ")"
+	}
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/codes/codes.go b/demo_test/vendor/google.golang.org/grpc/codes/codes.go
new file mode 100644
index 0000000..0273883
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/codes/codes.go
@@ -0,0 +1,198 @@
+/*
+ *
+ * Copyright 2014 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+// Package codes defines the canonical error codes used by gRPC. It is
+// consistent across various languages.
+package codes // import "google.golang.org/grpc/codes"
+
+import (
+	"fmt"
+	"strconv"
+)
+
+// A Code is an unsigned 32-bit error code as defined in the gRPC spec.
+type Code uint32
+
+const (
+	// OK is returned on success.
+	OK Code = 0
+
+	// Canceled indicates the operation was canceled (typically by the caller).
+	Canceled Code = 1
+
+	// Unknown error. An example of where this error may be returned is
+	// if a Status value received from another address space belongs to
+	// an error-space that is not known in this address space. Also
+	// errors raised by APIs that do not return enough error information
+	// may be converted to this error.
+	Unknown Code = 2
+
+	// InvalidArgument indicates client specified an invalid argument.
+	// Note that this differs from FailedPrecondition. It indicates arguments
+	// that are problematic regardless of the state of the system
+	// (e.g., a malformed file name).
+	InvalidArgument Code = 3
+
+	// DeadlineExceeded means operation expired before completion.
+	// For operations that change the state of the system, this error may be
+	// returned even if the operation has completed successfully. For
+	// example, a successful response from a server could have been delayed
+	// long enough for the deadline to expire.
+	DeadlineExceeded Code = 4
+
+	// NotFound means some requested entity (e.g., file or directory) was
+	// not found.
+	NotFound Code = 5
+
+	// AlreadyExists means an attempt to create an entity failed because one
+	// already exists.
+	AlreadyExists Code = 6
+
+	// PermissionDenied indicates the caller does not have permission to
+	// execute the specified operation. It must not be used for rejections
+	// caused by exhausting some resource (use ResourceExhausted
+	// instead for those errors). It must not be
+	// used if the caller cannot be identified (use Unauthenticated
+	// instead for those errors).
+	PermissionDenied Code = 7
+
+	// ResourceExhausted indicates some resource has been exhausted, perhaps
+	// a per-user quota, or perhaps the entire file system is out of space.
+	ResourceExhausted Code = 8
+
+	// FailedPrecondition indicates operation was rejected because the
+	// system is not in a state required for the operation's execution.
+	// For example, directory to be deleted may be non-empty, an rmdir
+	// operation is applied to a non-directory, etc.
+	//
+	// A litmus test that may help a service implementor in deciding
+	// between FailedPrecondition, Aborted, and Unavailable:
+	//  (a) Use Unavailable if the client can retry just the failing call.
+	//  (b) Use Aborted if the client should retry at a higher-level
+	//      (e.g., restarting a read-modify-write sequence).
+	//  (c) Use FailedPrecondition if the client should not retry until
+	//      the system state has been explicitly fixed. E.g., if an "rmdir"
+	//      fails because the directory is non-empty, FailedPrecondition
+	//      should be returned since the client should not retry unless
+	//      they have first fixed up the directory by deleting files from it.
+	//  (d) Use FailedPrecondition if the client performs conditional
+	//      REST Get/Update/Delete on a resource and the resource on the
+	//      server does not match the condition. E.g., conflicting
+	//      read-modify-write on the same resource.
+	FailedPrecondition Code = 9
+
+	// Aborted indicates the operation was aborted, typically due to a
+	// concurrency issue like sequencer check failures, transaction aborts,
+	// etc.
+	//
+	// See litmus test above for deciding between FailedPrecondition,
+	// Aborted, and Unavailable.
+	Aborted Code = 10
+
+	// OutOfRange means operation was attempted past the valid range.
+	// E.g., seeking or reading past end of file.
+	//
+	// Unlike InvalidArgument, this error indicates a problem that may
+	// be fixed if the system state changes. For example, a 32-bit file
+	// system will generate InvalidArgument if asked to read at an
+	// offset that is not in the range [0,2^32-1], but it will generate
+	// OutOfRange if asked to read from an offset past the current
+	// file size.
+	//
+	// There is a fair bit of overlap between FailedPrecondition and
+	// OutOfRange. We recommend using OutOfRange (the more specific
+	// error) when it applies so that callers who are iterating through
+	// a space can easily look for an OutOfRange error to detect when
+	// they are done.
+	OutOfRange Code = 11
+
+	// Unimplemented indicates operation is not implemented or not
+	// supported/enabled in this service.
+	Unimplemented Code = 12
+
+	// Internal errors. Means some invariants expected by underlying
+	// system has been broken. If you see one of these errors,
+	// something is very broken.
+	Internal Code = 13
+
+	// Unavailable indicates the service is currently unavailable.
+	// This is a most likely a transient condition and may be corrected
+	// by retrying with a backoff. Note that it is not always safe to retry
+	// non-idempotent operations.
+	//
+	// See litmus test above for deciding between FailedPrecondition,
+	// Aborted, and Unavailable.
+	Unavailable Code = 14
+
+	// DataLoss indicates unrecoverable data loss or corruption.
+	DataLoss Code = 15
+
+	// Unauthenticated indicates the request does not have valid
+	// authentication credentials for the operation.
+	Unauthenticated Code = 16
+
+	_maxCode = 17
+)
+
+var strToCode = map[string]Code{
+	`"OK"`: OK,
+	`"CANCELLED"`:/* [sic] */ Canceled,
+	`"UNKNOWN"`:             Unknown,
+	`"INVALID_ARGUMENT"`:    InvalidArgument,
+	`"DEADLINE_EXCEEDED"`:   DeadlineExceeded,
+	`"NOT_FOUND"`:           NotFound,
+	`"ALREADY_EXISTS"`:      AlreadyExists,
+	`"PERMISSION_DENIED"`:   PermissionDenied,
+	`"RESOURCE_EXHAUSTED"`:  ResourceExhausted,
+	`"FAILED_PRECONDITION"`: FailedPrecondition,
+	`"ABORTED"`:             Aborted,
+	`"OUT_OF_RANGE"`:        OutOfRange,
+	`"UNIMPLEMENTED"`:       Unimplemented,
+	`"INTERNAL"`:            Internal,
+	`"UNAVAILABLE"`:         Unavailable,
+	`"DATA_LOSS"`:           DataLoss,
+	`"UNAUTHENTICATED"`:     Unauthenticated,
+}
+
+// UnmarshalJSON unmarshals b into the Code.
+func (c *Code) UnmarshalJSON(b []byte) error {
+	// From json.Unmarshaler: By convention, to approximate the behavior of
+	// Unmarshal itself, Unmarshalers implement UnmarshalJSON([]byte("null")) as
+	// a no-op.
+	if string(b) == "null" {
+		return nil
+	}
+	if c == nil {
+		return fmt.Errorf("nil receiver passed to UnmarshalJSON")
+	}
+
+	if ci, err := strconv.ParseUint(string(b), 10, 32); err == nil {
+		if ci >= _maxCode {
+			return fmt.Errorf("invalid code: %q", ci)
+		}
+
+		*c = Code(ci)
+		return nil
+	}
+
+	if jc, ok := strToCode[string(b)]; ok {
+		*c = jc
+		return nil
+	}
+	return fmt.Errorf("invalid code: %q", string(b))
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/connectivity/connectivity.go b/demo_test/vendor/google.golang.org/grpc/connectivity/connectivity.go
new file mode 100644
index 0000000..34ec36f
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/connectivity/connectivity.go
@@ -0,0 +1,73 @@
+/*
+ *
+ * Copyright 2017 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+// Package connectivity defines connectivity semantics.
+// For details, see https://github.com/grpc/grpc/blob/master/doc/connectivity-semantics-and-api.md.
+// All APIs in this package are experimental.
+package connectivity
+
+import (
+	"context"
+
+	"google.golang.org/grpc/grpclog"
+)
+
+// State indicates the state of connectivity.
+// It can be the state of a ClientConn or SubConn.
+type State int
+
+func (s State) String() string {
+	switch s {
+	case Idle:
+		return "IDLE"
+	case Connecting:
+		return "CONNECTING"
+	case Ready:
+		return "READY"
+	case TransientFailure:
+		return "TRANSIENT_FAILURE"
+	case Shutdown:
+		return "SHUTDOWN"
+	default:
+		grpclog.Errorf("unknown connectivity state: %d", s)
+		return "Invalid-State"
+	}
+}
+
+const (
+	// Idle indicates the ClientConn is idle.
+	Idle State = iota
+	// Connecting indicates the ClientConn is connecting.
+	Connecting
+	// Ready indicates the ClientConn is ready for work.
+	Ready
+	// TransientFailure indicates the ClientConn has seen a failure but expects to recover.
+	TransientFailure
+	// Shutdown indicates the ClientConn has started shutting down.
+	Shutdown
+)
+
+// Reporter reports the connectivity states.
+type Reporter interface {
+	// CurrentState returns the current state of the reporter.
+	CurrentState() State
+	// WaitForStateChange blocks until the reporter's state is different from the given state,
+	// and returns true.
+	// It returns false if <-ctx.Done() can proceed (ctx got timeout or got canceled).
+	WaitForStateChange(context.Context, State) bool
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/credentials/credentials.go b/demo_test/vendor/google.golang.org/grpc/credentials/credentials.go
new file mode 100644
index 0000000..e438fda
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/credentials/credentials.go
@@ -0,0 +1,255 @@
+/*
+ *
+ * Copyright 2014 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+// Package credentials implements various credentials supported by gRPC library,
+// which encapsulate all the state needed by a client to authenticate with a
+// server and make various assertions, e.g., about the client's identity, role,
+// or whether it is authorized to make a particular call.
+package credentials // import "google.golang.org/grpc/credentials"
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"net"
+
+	"github.com/golang/protobuf/proto"
+	"google.golang.org/grpc/internal"
+)
+
+// PerRPCCredentials defines the common interface for the credentials which need to
+// attach security information to every RPC (e.g., oauth2).
+type PerRPCCredentials interface {
+	// GetRequestMetadata gets the current request metadata, refreshing
+	// tokens if required. This should be called by the transport layer on
+	// each request, and the data should be populated in headers or other
+	// context. If a status code is returned, it will be used as the status
+	// for the RPC. uri is the URI of the entry point for the request.
+	// When supported by the underlying implementation, ctx can be used for
+	// timeout and cancellation. Additionally, RequestInfo data will be
+	// available via ctx to this call.
+	// TODO(zhaoq): Define the set of the qualified keys instead of leaving
+	// it as an arbitrary string.
+	GetRequestMetadata(ctx context.Context, uri ...string) (map[string]string, error)
+	// RequireTransportSecurity indicates whether the credentials requires
+	// transport security.
+	RequireTransportSecurity() bool
+}
+
+// SecurityLevel defines the protection level on an established connection.
+//
+// This API is experimental.
+type SecurityLevel int
+
+const (
+	// NoSecurity indicates a connection is insecure.
+	// The zero SecurityLevel value is invalid for backward compatibility.
+	NoSecurity SecurityLevel = iota + 1
+	// IntegrityOnly indicates a connection only provides integrity protection.
+	IntegrityOnly
+	// PrivacyAndIntegrity indicates a connection provides both privacy and integrity protection.
+	PrivacyAndIntegrity
+)
+
+// String returns SecurityLevel in a string format.
+func (s SecurityLevel) String() string {
+	switch s {
+	case NoSecurity:
+		return "NoSecurity"
+	case IntegrityOnly:
+		return "IntegrityOnly"
+	case PrivacyAndIntegrity:
+		return "PrivacyAndIntegrity"
+	}
+	return fmt.Sprintf("invalid SecurityLevel: %v", int(s))
+}
+
+// CommonAuthInfo contains authenticated information common to AuthInfo implementations.
+// It should be embedded in a struct implementing AuthInfo to provide additional information
+// about the credentials.
+//
+// This API is experimental.
+type CommonAuthInfo struct {
+	SecurityLevel SecurityLevel
+}
+
+// GetCommonAuthInfo returns the pointer to CommonAuthInfo struct.
+func (c *CommonAuthInfo) GetCommonAuthInfo() *CommonAuthInfo {
+	return c
+}
+
+// ProtocolInfo provides information regarding the gRPC wire protocol version,
+// security protocol, security protocol version in use, server name, etc.
+type ProtocolInfo struct {
+	// ProtocolVersion is the gRPC wire protocol version.
+	ProtocolVersion string
+	// SecurityProtocol is the security protocol in use.
+	SecurityProtocol string
+	// SecurityVersion is the security protocol version.  It is a static version string from the
+	// credentials, not a value that reflects per-connection protocol negotiation.  To retrieve
+	// details about the credentials used for a connection, use the Peer's AuthInfo field instead.
+	//
+	// Deprecated: please use Peer.AuthInfo.
+	SecurityVersion string
+	// ServerName is the user-configured server name.
+	ServerName string
+}
+
+// AuthInfo defines the common interface for the auth information the users are interested in.
+// A struct that implements AuthInfo should embed CommonAuthInfo by including additional
+// information about the credentials in it.
+type AuthInfo interface {
+	AuthType() string
+}
+
+// ErrConnDispatched indicates that rawConn has been dispatched out of gRPC
+// and the caller should not close rawConn.
+var ErrConnDispatched = errors.New("credentials: rawConn is dispatched out of gRPC")
+
+// TransportCredentials defines the common interface for all the live gRPC wire
+// protocols and supported transport security protocols (e.g., TLS, SSL).
+type TransportCredentials interface {
+	// ClientHandshake does the authentication handshake specified by the corresponding
+	// authentication protocol on rawConn for clients. It returns the authenticated
+	// connection and the corresponding auth information about the connection.
+	// The auth information should embed CommonAuthInfo to return additional information about
+	// the credentials. Implementations must use the provided context to implement timely cancellation.
+	// gRPC will try to reconnect if the error returned is a temporary error
+	// (io.EOF, context.DeadlineExceeded or err.Temporary() == true).
+	// If the returned error is a wrapper error, implementations should make sure that
+	// the error implements Temporary() to have the correct retry behaviors.
+	//
+	// If the returned net.Conn is closed, it MUST close the net.Conn provided.
+	ClientHandshake(context.Context, string, net.Conn) (net.Conn, AuthInfo, error)
+	// ServerHandshake does the authentication handshake for servers. It returns
+	// the authenticated connection and the corresponding auth information about
+	// the connection. The auth information should embed CommonAuthInfo to return additional information
+	// about the credentials.
+	//
+	// If the returned net.Conn is closed, it MUST close the net.Conn provided.
+	ServerHandshake(net.Conn) (net.Conn, AuthInfo, error)
+	// Info provides the ProtocolInfo of this TransportCredentials.
+	Info() ProtocolInfo
+	// Clone makes a copy of this TransportCredentials.
+	Clone() TransportCredentials
+	// OverrideServerName overrides the server name used to verify the hostname on the returned certificates from the server.
+	// gRPC internals also use it to override the virtual hosting name if it is set.
+	// It must be called before dialing. Currently, this is only used by grpclb.
+	OverrideServerName(string) error
+}
+
+// Bundle is a combination of TransportCredentials and PerRPCCredentials.
+//
+// It also contains a mode switching method, so it can be used as a combination
+// of different credential policies.
+//
+// Bundle cannot be used together with individual TransportCredentials.
+// PerRPCCredentials from Bundle will be appended to other PerRPCCredentials.
+//
+// This API is experimental.
+type Bundle interface {
+	TransportCredentials() TransportCredentials
+	PerRPCCredentials() PerRPCCredentials
+	// NewWithMode should make a copy of Bundle, and switch mode. Modifying the
+	// existing Bundle may cause races.
+	//
+	// NewWithMode returns nil if the requested mode is not supported.
+	NewWithMode(mode string) (Bundle, error)
+}
+
+// RequestInfo contains request data attached to the context passed to GetRequestMetadata calls.
+//
+// This API is experimental.
+type RequestInfo struct {
+	// The method passed to Invoke or NewStream for this RPC. (For proto methods, this has the format "/some.Service/Method")
+	Method string
+	// AuthInfo contains the information from a security handshake (TransportCredentials.ClientHandshake, TransportCredentials.ServerHandshake)
+	AuthInfo AuthInfo
+}
+
+// requestInfoKey is a struct to be used as the key when attaching a RequestInfo to a context object.
+type requestInfoKey struct{}
+
+// RequestInfoFromContext extracts the RequestInfo from the context if it exists.
+//
+// This API is experimental.
+func RequestInfoFromContext(ctx context.Context) (ri RequestInfo, ok bool) {
+	ri, ok = ctx.Value(requestInfoKey{}).(RequestInfo)
+	return
+}
+
+// CheckSecurityLevel checks if a connection's security level is greater than or equal to the specified one.
+// It returns success if 1) the condition is satisified or 2) AuthInfo struct does not implement GetCommonAuthInfo() method
+// or 3) CommonAuthInfo.SecurityLevel has an invalid zero value. For 2) and 3), it is for the purpose of backward-compatibility.
+//
+// This API is experimental.
+func CheckSecurityLevel(ctx context.Context, level SecurityLevel) error {
+	type internalInfo interface {
+		GetCommonAuthInfo() *CommonAuthInfo
+	}
+	ri, _ := RequestInfoFromContext(ctx)
+	if ri.AuthInfo == nil {
+		return errors.New("unable to obtain SecurityLevel from context")
+	}
+	if ci, ok := ri.AuthInfo.(internalInfo); ok {
+		// CommonAuthInfo.SecurityLevel has an invalid value.
+		if ci.GetCommonAuthInfo().SecurityLevel == 0 {
+			return nil
+		}
+		if ci.GetCommonAuthInfo().SecurityLevel < level {
+			return fmt.Errorf("requires SecurityLevel %v; connection has %v", level, ci.GetCommonAuthInfo().SecurityLevel)
+		}
+	}
+	// The condition is satisfied or AuthInfo struct does not implement GetCommonAuthInfo() method.
+	return nil
+}
+
+func init() {
+	internal.NewRequestInfoContext = func(ctx context.Context, ri RequestInfo) context.Context {
+		return context.WithValue(ctx, requestInfoKey{}, ri)
+	}
+}
+
+// ChannelzSecurityInfo defines the interface that security protocols should implement
+// in order to provide security info to channelz.
+//
+// This API is experimental.
+type ChannelzSecurityInfo interface {
+	GetSecurityValue() ChannelzSecurityValue
+}
+
+// ChannelzSecurityValue defines the interface that GetSecurityValue() return value
+// should satisfy. This interface should only be satisfied by *TLSChannelzSecurityValue
+// and *OtherChannelzSecurityValue.
+//
+// This API is experimental.
+type ChannelzSecurityValue interface {
+	isChannelzSecurityValue()
+}
+
+// OtherChannelzSecurityValue defines the struct that non-TLS protocol should return
+// from GetSecurityValue(), which contains protocol specific security info. Note
+// the Value field will be sent to users of channelz requesting channel info, and
+// thus sensitive info should better be avoided.
+//
+// This API is experimental.
+type OtherChannelzSecurityValue struct {
+	ChannelzSecurityValue
+	Name  string
+	Value proto.Message
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/credentials/go12.go b/demo_test/vendor/google.golang.org/grpc/credentials/go12.go
new file mode 100644
index 0000000..ccbf35b
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/credentials/go12.go
@@ -0,0 +1,30 @@
+// +build go1.12
+
+/*
+ *
+ * Copyright 2019 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package credentials
+
+import "crypto/tls"
+
+// This init function adds cipher suite constants only defined in Go 1.12.
+func init() {
+	cipherSuiteLookup[tls.TLS_AES_128_GCM_SHA256] = "TLS_AES_128_GCM_SHA256"
+	cipherSuiteLookup[tls.TLS_AES_256_GCM_SHA384] = "TLS_AES_256_GCM_SHA384"
+	cipherSuiteLookup[tls.TLS_CHACHA20_POLY1305_SHA256] = "TLS_CHACHA20_POLY1305_SHA256"
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/credentials/internal/syscallconn.go b/demo_test/vendor/google.golang.org/grpc/credentials/internal/syscallconn.go
new file mode 100644
index 0000000..2f4472b
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/credentials/internal/syscallconn.go
@@ -0,0 +1,61 @@
+// +build !appengine
+
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+// Package internal contains credentials-internal code.
+package internal
+
+import (
+	"net"
+	"syscall"
+)
+
+type sysConn = syscall.Conn
+
+// syscallConn keeps reference of rawConn to support syscall.Conn for channelz.
+// SyscallConn() (the method in interface syscall.Conn) is explicitly
+// implemented on this type,
+//
+// Interface syscall.Conn is implemented by most net.Conn implementations (e.g.
+// TCPConn, UnixConn), but is not part of net.Conn interface. So wrapper conns
+// that embed net.Conn don't implement syscall.Conn. (Side note: tls.Conn
+// doesn't embed net.Conn, so even if syscall.Conn is part of net.Conn, it won't
+// help here).
+type syscallConn struct {
+	net.Conn
+	// sysConn is a type alias of syscall.Conn. It's necessary because the name
+	// `Conn` collides with `net.Conn`.
+	sysConn
+}
+
+// WrapSyscallConn tries to wrap rawConn and newConn into a net.Conn that
+// implements syscall.Conn. rawConn will be used to support syscall, and newConn
+// will be used for read/write.
+//
+// This function returns newConn if rawConn doesn't implement syscall.Conn.
+func WrapSyscallConn(rawConn, newConn net.Conn) net.Conn {
+	sysConn, ok := rawConn.(syscall.Conn)
+	if !ok {
+		return newConn
+	}
+	return &syscallConn{
+		Conn:    newConn,
+		sysConn: sysConn,
+	}
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/credentials/internal/syscallconn_appengine.go b/demo_test/vendor/google.golang.org/grpc/credentials/internal/syscallconn_appengine.go
new file mode 100644
index 0000000..d4346e9
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/credentials/internal/syscallconn_appengine.go
@@ -0,0 +1,30 @@
+// +build appengine
+
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package internal
+
+import (
+	"net"
+)
+
+// WrapSyscallConn returns newConn on appengine.
+func WrapSyscallConn(rawConn, newConn net.Conn) net.Conn {
+	return newConn
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/credentials/tls.go b/demo_test/vendor/google.golang.org/grpc/credentials/tls.go
new file mode 100644
index 0000000..86e956b
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/credentials/tls.go
@@ -0,0 +1,235 @@
+/*
+ *
+ * Copyright 2014 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package credentials
+
+import (
+	"context"
+	"crypto/tls"
+	"crypto/x509"
+	"fmt"
+	"io/ioutil"
+	"net"
+
+	"google.golang.org/grpc/credentials/internal"
+)
+
+// TLSInfo contains the auth information for a TLS authenticated connection.
+// It implements the AuthInfo interface.
+type TLSInfo struct {
+	State tls.ConnectionState
+	CommonAuthInfo
+}
+
+// AuthType returns the type of TLSInfo as a string.
+func (t TLSInfo) AuthType() string {
+	return "tls"
+}
+
+// GetSecurityValue returns security info requested by channelz.
+func (t TLSInfo) GetSecurityValue() ChannelzSecurityValue {
+	v := &TLSChannelzSecurityValue{
+		StandardName: cipherSuiteLookup[t.State.CipherSuite],
+	}
+	// Currently there's no way to get LocalCertificate info from tls package.
+	if len(t.State.PeerCertificates) > 0 {
+		v.RemoteCertificate = t.State.PeerCertificates[0].Raw
+	}
+	return v
+}
+
+// tlsCreds is the credentials required for authenticating a connection using TLS.
+type tlsCreds struct {
+	// TLS configuration
+	config *tls.Config
+}
+
+func (c tlsCreds) Info() ProtocolInfo {
+	return ProtocolInfo{
+		SecurityProtocol: "tls",
+		SecurityVersion:  "1.2",
+		ServerName:       c.config.ServerName,
+	}
+}
+
+func (c *tlsCreds) ClientHandshake(ctx context.Context, authority string, rawConn net.Conn) (_ net.Conn, _ AuthInfo, err error) {
+	// use local cfg to avoid clobbering ServerName if using multiple endpoints
+	cfg := cloneTLSConfig(c.config)
+	if cfg.ServerName == "" {
+		serverName, _, err := net.SplitHostPort(authority)
+		if err != nil {
+			// If the authority had no host port or if the authority cannot be parsed, use it as-is.
+			serverName = authority
+		}
+		cfg.ServerName = serverName
+	}
+	conn := tls.Client(rawConn, cfg)
+	errChannel := make(chan error, 1)
+	go func() {
+		errChannel <- conn.Handshake()
+		close(errChannel)
+	}()
+	select {
+	case err := <-errChannel:
+		if err != nil {
+			conn.Close()
+			return nil, nil, err
+		}
+	case <-ctx.Done():
+		conn.Close()
+		return nil, nil, ctx.Err()
+	}
+	return internal.WrapSyscallConn(rawConn, conn), TLSInfo{conn.ConnectionState(), CommonAuthInfo{PrivacyAndIntegrity}}, nil
+}
+
+func (c *tlsCreds) ServerHandshake(rawConn net.Conn) (net.Conn, AuthInfo, error) {
+	conn := tls.Server(rawConn, c.config)
+	if err := conn.Handshake(); err != nil {
+		conn.Close()
+		return nil, nil, err
+	}
+	return internal.WrapSyscallConn(rawConn, conn), TLSInfo{conn.ConnectionState(), CommonAuthInfo{PrivacyAndIntegrity}}, nil
+}
+
+func (c *tlsCreds) Clone() TransportCredentials {
+	return NewTLS(c.config)
+}
+
+func (c *tlsCreds) OverrideServerName(serverNameOverride string) error {
+	c.config.ServerName = serverNameOverride
+	return nil
+}
+
+const alpnProtoStrH2 = "h2"
+
+func appendH2ToNextProtos(ps []string) []string {
+	for _, p := range ps {
+		if p == alpnProtoStrH2 {
+			return ps
+		}
+	}
+	ret := make([]string, 0, len(ps)+1)
+	ret = append(ret, ps...)
+	return append(ret, alpnProtoStrH2)
+}
+
+// NewTLS uses c to construct a TransportCredentials based on TLS.
+func NewTLS(c *tls.Config) TransportCredentials {
+	tc := &tlsCreds{cloneTLSConfig(c)}
+	tc.config.NextProtos = appendH2ToNextProtos(tc.config.NextProtos)
+	return tc
+}
+
+// NewClientTLSFromCert constructs TLS credentials from the provided root
+// certificate authority certificate(s) to validate server connections. If
+// certificates to establish the identity of the client need to be included in
+// the credentials (eg: for mTLS), use NewTLS instead, where a complete
+// tls.Config can be specified.
+// serverNameOverride is for testing only. If set to a non empty string,
+// it will override the virtual host name of authority (e.g. :authority header
+// field) in requests.
+func NewClientTLSFromCert(cp *x509.CertPool, serverNameOverride string) TransportCredentials {
+	return NewTLS(&tls.Config{ServerName: serverNameOverride, RootCAs: cp})
+}
+
+// NewClientTLSFromFile constructs TLS credentials from the provided root
+// certificate authority certificate file(s) to validate server connections. If
+// certificates to establish the identity of the client need to be included in
+// the credentials (eg: for mTLS), use NewTLS instead, where a complete
+// tls.Config can be specified.
+// serverNameOverride is for testing only. If set to a non empty string,
+// it will override the virtual host name of authority (e.g. :authority header
+// field) in requests.
+func NewClientTLSFromFile(certFile, serverNameOverride string) (TransportCredentials, error) {
+	b, err := ioutil.ReadFile(certFile)
+	if err != nil {
+		return nil, err
+	}
+	cp := x509.NewCertPool()
+	if !cp.AppendCertsFromPEM(b) {
+		return nil, fmt.Errorf("credentials: failed to append certificates")
+	}
+	return NewTLS(&tls.Config{ServerName: serverNameOverride, RootCAs: cp}), nil
+}
+
+// NewServerTLSFromCert constructs TLS credentials from the input certificate for server.
+func NewServerTLSFromCert(cert *tls.Certificate) TransportCredentials {
+	return NewTLS(&tls.Config{Certificates: []tls.Certificate{*cert}})
+}
+
+// NewServerTLSFromFile constructs TLS credentials from the input certificate file and key
+// file for server.
+func NewServerTLSFromFile(certFile, keyFile string) (TransportCredentials, error) {
+	cert, err := tls.LoadX509KeyPair(certFile, keyFile)
+	if err != nil {
+		return nil, err
+	}
+	return NewTLS(&tls.Config{Certificates: []tls.Certificate{cert}}), nil
+}
+
+// TLSChannelzSecurityValue defines the struct that TLS protocol should return
+// from GetSecurityValue(), containing security info like cipher and certificate used.
+//
+// This API is EXPERIMENTAL.
+type TLSChannelzSecurityValue struct {
+	ChannelzSecurityValue
+	StandardName      string
+	LocalCertificate  []byte
+	RemoteCertificate []byte
+}
+
+var cipherSuiteLookup = map[uint16]string{
+	tls.TLS_RSA_WITH_RC4_128_SHA:                "TLS_RSA_WITH_RC4_128_SHA",
+	tls.TLS_RSA_WITH_3DES_EDE_CBC_SHA:           "TLS_RSA_WITH_3DES_EDE_CBC_SHA",
+	tls.TLS_RSA_WITH_AES_128_CBC_SHA:            "TLS_RSA_WITH_AES_128_CBC_SHA",
+	tls.TLS_RSA_WITH_AES_256_CBC_SHA:            "TLS_RSA_WITH_AES_256_CBC_SHA",
+	tls.TLS_RSA_WITH_AES_128_GCM_SHA256:         "TLS_RSA_WITH_AES_128_GCM_SHA256",
+	tls.TLS_RSA_WITH_AES_256_GCM_SHA384:         "TLS_RSA_WITH_AES_256_GCM_SHA384",
+	tls.TLS_ECDHE_ECDSA_WITH_RC4_128_SHA:        "TLS_ECDHE_ECDSA_WITH_RC4_128_SHA",
+	tls.TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA:    "TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA",
+	tls.TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA:    "TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA",
+	tls.TLS_ECDHE_RSA_WITH_RC4_128_SHA:          "TLS_ECDHE_RSA_WITH_RC4_128_SHA",
+	tls.TLS_ECDHE_RSA_WITH_3DES_EDE_CBC_SHA:     "TLS_ECDHE_RSA_WITH_3DES_EDE_CBC_SHA",
+	tls.TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA:      "TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA",
+	tls.TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA:      "TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA",
+	tls.TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256:   "TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256",
+	tls.TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256: "TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256",
+	tls.TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384:   "TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384",
+	tls.TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384: "TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384",
+	tls.TLS_FALLBACK_SCSV:                       "TLS_FALLBACK_SCSV",
+	tls.TLS_RSA_WITH_AES_128_CBC_SHA256:         "TLS_RSA_WITH_AES_128_CBC_SHA256",
+	tls.TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA256: "TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA256",
+	tls.TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256:   "TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256",
+	tls.TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305:    "TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305",
+	tls.TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305:  "TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305",
+}
+
+// cloneTLSConfig returns a shallow clone of the exported
+// fields of cfg, ignoring the unexported sync.Once, which
+// contains a mutex and must not be copied.
+//
+// If cfg is nil, a new zero tls.Config is returned.
+//
+// TODO: inline this function if possible.
+func cloneTLSConfig(cfg *tls.Config) *tls.Config {
+	if cfg == nil {
+		return &tls.Config{}
+	}
+
+	return cfg.Clone()
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/dialoptions.go b/demo_test/vendor/google.golang.org/grpc/dialoptions.go
new file mode 100644
index 0000000..35bde10
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/dialoptions.go
@@ -0,0 +1,606 @@
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package grpc
+
+import (
+	"context"
+	"fmt"
+	"net"
+	"time"
+
+	"google.golang.org/grpc/backoff"
+	"google.golang.org/grpc/balancer"
+	"google.golang.org/grpc/credentials"
+	"google.golang.org/grpc/grpclog"
+	"google.golang.org/grpc/internal"
+	internalbackoff "google.golang.org/grpc/internal/backoff"
+	"google.golang.org/grpc/internal/envconfig"
+	"google.golang.org/grpc/internal/transport"
+	"google.golang.org/grpc/keepalive"
+	"google.golang.org/grpc/resolver"
+	"google.golang.org/grpc/stats"
+)
+
+// dialOptions configure a Dial call. dialOptions are set by the DialOption
+// values passed to Dial.
+type dialOptions struct {
+	unaryInt  UnaryClientInterceptor
+	streamInt StreamClientInterceptor
+
+	chainUnaryInts  []UnaryClientInterceptor
+	chainStreamInts []StreamClientInterceptor
+
+	cp          Compressor
+	dc          Decompressor
+	bs          internalbackoff.Strategy
+	block       bool
+	insecure    bool
+	timeout     time.Duration
+	scChan      <-chan ServiceConfig
+	authority   string
+	copts       transport.ConnectOptions
+	callOptions []CallOption
+	// This is used by v1 balancer dial option WithBalancer to support v1
+	// balancer, and also by WithBalancerName dial option.
+	balancerBuilder             balancer.Builder
+	channelzParentID            int64
+	disableServiceConfig        bool
+	disableRetry                bool
+	disableHealthCheck          bool
+	healthCheckFunc             internal.HealthChecker
+	minConnectTimeout           func() time.Duration
+	defaultServiceConfig        *ServiceConfig // defaultServiceConfig is parsed from defaultServiceConfigRawJSON.
+	defaultServiceConfigRawJSON *string
+	// This is used by ccResolverWrapper to backoff between successive calls to
+	// resolver.ResolveNow(). The user will have no need to configure this, but
+	// we need to be able to configure this in tests.
+	resolveNowBackoff func(int) time.Duration
+	resolvers         []resolver.Builder
+	withProxy         bool
+}
+
+// DialOption configures how we set up the connection.
+type DialOption interface {
+	apply(*dialOptions)
+}
+
+// EmptyDialOption does not alter the dial configuration. It can be embedded in
+// another structure to build custom dial options.
+//
+// This API is EXPERIMENTAL.
+type EmptyDialOption struct{}
+
+func (EmptyDialOption) apply(*dialOptions) {}
+
+// funcDialOption wraps a function that modifies dialOptions into an
+// implementation of the DialOption interface.
+type funcDialOption struct {
+	f func(*dialOptions)
+}
+
+func (fdo *funcDialOption) apply(do *dialOptions) {
+	fdo.f(do)
+}
+
+func newFuncDialOption(f func(*dialOptions)) *funcDialOption {
+	return &funcDialOption{
+		f: f,
+	}
+}
+
+// WithWriteBufferSize determines how much data can be batched before doing a
+// write on the wire. The corresponding memory allocation for this buffer will
+// be twice the size to keep syscalls low. The default value for this buffer is
+// 32KB.
+//
+// Zero will disable the write buffer such that each write will be on underlying
+// connection. Note: A Send call may not directly translate to a write.
+func WithWriteBufferSize(s int) DialOption {
+	return newFuncDialOption(func(o *dialOptions) {
+		o.copts.WriteBufferSize = s
+	})
+}
+
+// WithReadBufferSize lets you set the size of read buffer, this determines how
+// much data can be read at most for each read syscall.
+//
+// The default value for this buffer is 32KB. Zero will disable read buffer for
+// a connection so data framer can access the underlying conn directly.
+func WithReadBufferSize(s int) DialOption {
+	return newFuncDialOption(func(o *dialOptions) {
+		o.copts.ReadBufferSize = s
+	})
+}
+
+// WithInitialWindowSize returns a DialOption which sets the value for initial
+// window size on a stream. The lower bound for window size is 64K and any value
+// smaller than that will be ignored.
+func WithInitialWindowSize(s int32) DialOption {
+	return newFuncDialOption(func(o *dialOptions) {
+		o.copts.InitialWindowSize = s
+	})
+}
+
+// WithInitialConnWindowSize returns a DialOption which sets the value for
+// initial window size on a connection. The lower bound for window size is 64K
+// and any value smaller than that will be ignored.
+func WithInitialConnWindowSize(s int32) DialOption {
+	return newFuncDialOption(func(o *dialOptions) {
+		o.copts.InitialConnWindowSize = s
+	})
+}
+
+// WithMaxMsgSize returns a DialOption which sets the maximum message size the
+// client can receive.
+//
+// Deprecated: use WithDefaultCallOptions(MaxCallRecvMsgSize(s)) instead.  Will
+// be supported throughout 1.x.
+func WithMaxMsgSize(s int) DialOption {
+	return WithDefaultCallOptions(MaxCallRecvMsgSize(s))
+}
+
+// WithDefaultCallOptions returns a DialOption which sets the default
+// CallOptions for calls over the connection.
+func WithDefaultCallOptions(cos ...CallOption) DialOption {
+	return newFuncDialOption(func(o *dialOptions) {
+		o.callOptions = append(o.callOptions, cos...)
+	})
+}
+
+// WithCodec returns a DialOption which sets a codec for message marshaling and
+// unmarshaling.
+//
+// Deprecated: use WithDefaultCallOptions(ForceCodec(_)) instead.  Will be
+// supported throughout 1.x.
+func WithCodec(c Codec) DialOption {
+	return WithDefaultCallOptions(CallCustomCodec(c))
+}
+
+// WithCompressor returns a DialOption which sets a Compressor to use for
+// message compression. It has lower priority than the compressor set by the
+// UseCompressor CallOption.
+//
+// Deprecated: use UseCompressor instead.  Will be supported throughout 1.x.
+func WithCompressor(cp Compressor) DialOption {
+	return newFuncDialOption(func(o *dialOptions) {
+		o.cp = cp
+	})
+}
+
+// WithDecompressor returns a DialOption which sets a Decompressor to use for
+// incoming message decompression.  If incoming response messages are encoded
+// using the decompressor's Type(), it will be used.  Otherwise, the message
+// encoding will be used to look up the compressor registered via
+// encoding.RegisterCompressor, which will then be used to decompress the
+// message.  If no compressor is registered for the encoding, an Unimplemented
+// status error will be returned.
+//
+// Deprecated: use encoding.RegisterCompressor instead.  Will be supported
+// throughout 1.x.
+func WithDecompressor(dc Decompressor) DialOption {
+	return newFuncDialOption(func(o *dialOptions) {
+		o.dc = dc
+	})
+}
+
+// WithBalancer returns a DialOption which sets a load balancer with the v1 API.
+// Name resolver will be ignored if this DialOption is specified.
+//
+// Deprecated: use the new balancer APIs in balancer package and
+// WithBalancerName.  Will be removed in a future 1.x release.
+func WithBalancer(b Balancer) DialOption {
+	return newFuncDialOption(func(o *dialOptions) {
+		o.balancerBuilder = &balancerWrapperBuilder{
+			b: b,
+		}
+	})
+}
+
+// WithBalancerName sets the balancer that the ClientConn will be initialized
+// with. Balancer registered with balancerName will be used. This function
+// panics if no balancer was registered by balancerName.
+//
+// The balancer cannot be overridden by balancer option specified by service
+// config.
+//
+// Deprecated: use WithDefaultServiceConfig and WithDisableServiceConfig
+// instead.  Will be removed in a future 1.x release.
+func WithBalancerName(balancerName string) DialOption {
+	builder := balancer.Get(balancerName)
+	if builder == nil {
+		panic(fmt.Sprintf("grpc.WithBalancerName: no balancer is registered for name %v", balancerName))
+	}
+	return newFuncDialOption(func(o *dialOptions) {
+		o.balancerBuilder = builder
+	})
+}
+
+// WithServiceConfig returns a DialOption which has a channel to read the
+// service configuration.
+//
+// Deprecated: service config should be received through name resolver or via
+// WithDefaultServiceConfig, as specified at
+// https://github.com/grpc/grpc/blob/master/doc/service_config.md.  Will be
+// removed in a future 1.x release.
+func WithServiceConfig(c <-chan ServiceConfig) DialOption {
+	return newFuncDialOption(func(o *dialOptions) {
+		o.scChan = c
+	})
+}
+
+// WithConnectParams configures the dialer to use the provided ConnectParams.
+//
+// The backoff configuration specified as part of the ConnectParams overrides
+// all defaults specified in
+// https://github.com/grpc/grpc/blob/master/doc/connection-backoff.md. Consider
+// using the backoff.DefaultConfig as a base, in cases where you want to
+// override only a subset of the backoff configuration.
+//
+// This API is EXPERIMENTAL.
+func WithConnectParams(p ConnectParams) DialOption {
+	return newFuncDialOption(func(o *dialOptions) {
+		o.bs = internalbackoff.Exponential{Config: p.Backoff}
+		o.minConnectTimeout = func() time.Duration {
+			return p.MinConnectTimeout
+		}
+	})
+}
+
+// WithBackoffMaxDelay configures the dialer to use the provided maximum delay
+// when backing off after failed connection attempts.
+//
+// Deprecated: use WithConnectParams instead. Will be supported throughout 1.x.
+func WithBackoffMaxDelay(md time.Duration) DialOption {
+	return WithBackoffConfig(BackoffConfig{MaxDelay: md})
+}
+
+// WithBackoffConfig configures the dialer to use the provided backoff
+// parameters after connection failures.
+//
+// Deprecated: use WithConnectParams instead. Will be supported throughout 1.x.
+func WithBackoffConfig(b BackoffConfig) DialOption {
+	bc := backoff.DefaultConfig
+	bc.MaxDelay = b.MaxDelay
+	return withBackoff(internalbackoff.Exponential{Config: bc})
+}
+
+// withBackoff sets the backoff strategy used for connectRetryNum after a failed
+// connection attempt.
+//
+// This can be exported if arbitrary backoff strategies are allowed by gRPC.
+func withBackoff(bs internalbackoff.Strategy) DialOption {
+	return newFuncDialOption(func(o *dialOptions) {
+		o.bs = bs
+	})
+}
+
+// WithBlock returns a DialOption which makes caller of Dial blocks until the
+// underlying connection is up. Without this, Dial returns immediately and
+// connecting the server happens in background.
+func WithBlock() DialOption {
+	return newFuncDialOption(func(o *dialOptions) {
+		o.block = true
+	})
+}
+
+// WithInsecure returns a DialOption which disables transport security for this
+// ClientConn. Note that transport security is required unless WithInsecure is
+// set.
+func WithInsecure() DialOption {
+	return newFuncDialOption(func(o *dialOptions) {
+		o.insecure = true
+	})
+}
+
+// WithNoProxy returns a DialOption which disables the use of proxies for this
+// ClientConn. This is ignored if WithDialer or WithContextDialer are used.
+//
+// This API is EXPERIMENTAL.
+func WithNoProxy() DialOption {
+	return newFuncDialOption(func(o *dialOptions) {
+		o.withProxy = false
+	})
+}
+
+// WithTransportCredentials returns a DialOption which configures a connection
+// level security credentials (e.g., TLS/SSL). This should not be used together
+// with WithCredentialsBundle.
+func WithTransportCredentials(creds credentials.TransportCredentials) DialOption {
+	return newFuncDialOption(func(o *dialOptions) {
+		o.copts.TransportCredentials = creds
+	})
+}
+
+// WithPerRPCCredentials returns a DialOption which sets credentials and places
+// auth state on each outbound RPC.
+func WithPerRPCCredentials(creds credentials.PerRPCCredentials) DialOption {
+	return newFuncDialOption(func(o *dialOptions) {
+		o.copts.PerRPCCredentials = append(o.copts.PerRPCCredentials, creds)
+	})
+}
+
+// WithCredentialsBundle returns a DialOption to set a credentials bundle for
+// the ClientConn.WithCreds. This should not be used together with
+// WithTransportCredentials.
+//
+// This API is experimental.
+func WithCredentialsBundle(b credentials.Bundle) DialOption {
+	return newFuncDialOption(func(o *dialOptions) {
+		o.copts.CredsBundle = b
+	})
+}
+
+// WithTimeout returns a DialOption that configures a timeout for dialing a
+// ClientConn initially. This is valid if and only if WithBlock() is present.
+//
+// Deprecated: use DialContext instead of Dial and context.WithTimeout
+// instead.  Will be supported throughout 1.x.
+func WithTimeout(d time.Duration) DialOption {
+	return newFuncDialOption(func(o *dialOptions) {
+		o.timeout = d
+	})
+}
+
+// WithContextDialer returns a DialOption that sets a dialer to create
+// connections. If FailOnNonTempDialError() is set to true, and an error is
+// returned by f, gRPC checks the error's Temporary() method to decide if it
+// should try to reconnect to the network address.
+func WithContextDialer(f func(context.Context, string) (net.Conn, error)) DialOption {
+	return newFuncDialOption(func(o *dialOptions) {
+		o.copts.Dialer = f
+	})
+}
+
+func init() {
+	internal.WithHealthCheckFunc = withHealthCheckFunc
+}
+
+// WithDialer returns a DialOption that specifies a function to use for dialing
+// network addresses. If FailOnNonTempDialError() is set to true, and an error
+// is returned by f, gRPC checks the error's Temporary() method to decide if it
+// should try to reconnect to the network address.
+//
+// Deprecated: use WithContextDialer instead.  Will be supported throughout
+// 1.x.
+func WithDialer(f func(string, time.Duration) (net.Conn, error)) DialOption {
+	return WithContextDialer(
+		func(ctx context.Context, addr string) (net.Conn, error) {
+			if deadline, ok := ctx.Deadline(); ok {
+				return f(addr, time.Until(deadline))
+			}
+			return f(addr, 0)
+		})
+}
+
+// WithStatsHandler returns a DialOption that specifies the stats handler for
+// all the RPCs and underlying network connections in this ClientConn.
+func WithStatsHandler(h stats.Handler) DialOption {
+	return newFuncDialOption(func(o *dialOptions) {
+		o.copts.StatsHandler = h
+	})
+}
+
+// FailOnNonTempDialError returns a DialOption that specifies if gRPC fails on
+// non-temporary dial errors. If f is true, and dialer returns a non-temporary
+// error, gRPC will fail the connection to the network address and won't try to
+// reconnect. The default value of FailOnNonTempDialError is false.
+//
+// FailOnNonTempDialError only affects the initial dial, and does not do
+// anything useful unless you are also using WithBlock().
+//
+// This is an EXPERIMENTAL API.
+func FailOnNonTempDialError(f bool) DialOption {
+	return newFuncDialOption(func(o *dialOptions) {
+		o.copts.FailOnNonTempDialError = f
+	})
+}
+
+// WithUserAgent returns a DialOption that specifies a user agent string for all
+// the RPCs.
+func WithUserAgent(s string) DialOption {
+	return newFuncDialOption(func(o *dialOptions) {
+		o.copts.UserAgent = s
+	})
+}
+
+// WithKeepaliveParams returns a DialOption that specifies keepalive parameters
+// for the client transport.
+func WithKeepaliveParams(kp keepalive.ClientParameters) DialOption {
+	if kp.Time < internal.KeepaliveMinPingTime {
+		grpclog.Warningf("Adjusting keepalive ping interval to minimum period of %v", internal.KeepaliveMinPingTime)
+		kp.Time = internal.KeepaliveMinPingTime
+	}
+	return newFuncDialOption(func(o *dialOptions) {
+		o.copts.KeepaliveParams = kp
+	})
+}
+
+// WithUnaryInterceptor returns a DialOption that specifies the interceptor for
+// unary RPCs.
+func WithUnaryInterceptor(f UnaryClientInterceptor) DialOption {
+	return newFuncDialOption(func(o *dialOptions) {
+		o.unaryInt = f
+	})
+}
+
+// WithChainUnaryInterceptor returns a DialOption that specifies the chained
+// interceptor for unary RPCs. The first interceptor will be the outer most,
+// while the last interceptor will be the inner most wrapper around the real call.
+// All interceptors added by this method will be chained, and the interceptor
+// defined by WithUnaryInterceptor will always be prepended to the chain.
+func WithChainUnaryInterceptor(interceptors ...UnaryClientInterceptor) DialOption {
+	return newFuncDialOption(func(o *dialOptions) {
+		o.chainUnaryInts = append(o.chainUnaryInts, interceptors...)
+	})
+}
+
+// WithStreamInterceptor returns a DialOption that specifies the interceptor for
+// streaming RPCs.
+func WithStreamInterceptor(f StreamClientInterceptor) DialOption {
+	return newFuncDialOption(func(o *dialOptions) {
+		o.streamInt = f
+	})
+}
+
+// WithChainStreamInterceptor returns a DialOption that specifies the chained
+// interceptor for unary RPCs. The first interceptor will be the outer most,
+// while the last interceptor will be the inner most wrapper around the real call.
+// All interceptors added by this method will be chained, and the interceptor
+// defined by WithStreamInterceptor will always be prepended to the chain.
+func WithChainStreamInterceptor(interceptors ...StreamClientInterceptor) DialOption {
+	return newFuncDialOption(func(o *dialOptions) {
+		o.chainStreamInts = append(o.chainStreamInts, interceptors...)
+	})
+}
+
+// WithAuthority returns a DialOption that specifies the value to be used as the
+// :authority pseudo-header. This value only works with WithInsecure and has no
+// effect if TransportCredentials are present.
+func WithAuthority(a string) DialOption {
+	return newFuncDialOption(func(o *dialOptions) {
+		o.authority = a
+	})
+}
+
+// WithChannelzParentID returns a DialOption that specifies the channelz ID of
+// current ClientConn's parent. This function is used in nested channel creation
+// (e.g. grpclb dial).
+//
+// This API is EXPERIMENTAL.
+func WithChannelzParentID(id int64) DialOption {
+	return newFuncDialOption(func(o *dialOptions) {
+		o.channelzParentID = id
+	})
+}
+
+// WithDisableServiceConfig returns a DialOption that causes gRPC to ignore any
+// service config provided by the resolver and provides a hint to the resolver
+// to not fetch service configs.
+//
+// Note that this dial option only disables service config from resolver. If
+// default service config is provided, gRPC will use the default service config.
+func WithDisableServiceConfig() DialOption {
+	return newFuncDialOption(func(o *dialOptions) {
+		o.disableServiceConfig = true
+	})
+}
+
+// WithDefaultServiceConfig returns a DialOption that configures the default
+// service config, which will be used in cases where:
+//
+// 1. WithDisableServiceConfig is also used.
+// 2. Resolver does not return a service config or if the resolver returns an
+//    invalid service config.
+//
+// This API is EXPERIMENTAL.
+func WithDefaultServiceConfig(s string) DialOption {
+	return newFuncDialOption(func(o *dialOptions) {
+		o.defaultServiceConfigRawJSON = &s
+	})
+}
+
+// WithDisableRetry returns a DialOption that disables retries, even if the
+// service config enables them.  This does not impact transparent retries, which
+// will happen automatically if no data is written to the wire or if the RPC is
+// unprocessed by the remote server.
+//
+// Retry support is currently disabled by default, but will be enabled by
+// default in the future.  Until then, it may be enabled by setting the
+// environment variable "GRPC_GO_RETRY" to "on".
+//
+// This API is EXPERIMENTAL.
+func WithDisableRetry() DialOption {
+	return newFuncDialOption(func(o *dialOptions) {
+		o.disableRetry = true
+	})
+}
+
+// WithMaxHeaderListSize returns a DialOption that specifies the maximum
+// (uncompressed) size of header list that the client is prepared to accept.
+func WithMaxHeaderListSize(s uint32) DialOption {
+	return newFuncDialOption(func(o *dialOptions) {
+		o.copts.MaxHeaderListSize = &s
+	})
+}
+
+// WithDisableHealthCheck disables the LB channel health checking for all
+// SubConns of this ClientConn.
+//
+// This API is EXPERIMENTAL.
+func WithDisableHealthCheck() DialOption {
+	return newFuncDialOption(func(o *dialOptions) {
+		o.disableHealthCheck = true
+	})
+}
+
+// withHealthCheckFunc replaces the default health check function with the
+// provided one. It makes tests easier to change the health check function.
+//
+// For testing purpose only.
+func withHealthCheckFunc(f internal.HealthChecker) DialOption {
+	return newFuncDialOption(func(o *dialOptions) {
+		o.healthCheckFunc = f
+	})
+}
+
+func defaultDialOptions() dialOptions {
+	return dialOptions{
+		disableRetry:    !envconfig.Retry,
+		healthCheckFunc: internal.HealthCheckFunc,
+		copts: transport.ConnectOptions{
+			WriteBufferSize: defaultWriteBufSize,
+			ReadBufferSize:  defaultReadBufSize,
+		},
+		resolveNowBackoff: internalbackoff.DefaultExponential.Backoff,
+		withProxy:         true,
+	}
+}
+
+// withGetMinConnectDeadline specifies the function that clientconn uses to
+// get minConnectDeadline. This can be used to make connection attempts happen
+// faster/slower.
+//
+// For testing purpose only.
+func withMinConnectDeadline(f func() time.Duration) DialOption {
+	return newFuncDialOption(func(o *dialOptions) {
+		o.minConnectTimeout = f
+	})
+}
+
+// withResolveNowBackoff specifies the function that clientconn uses to backoff
+// between successive calls to resolver.ResolveNow().
+//
+// For testing purpose only.
+func withResolveNowBackoff(f func(int) time.Duration) DialOption {
+	return newFuncDialOption(func(o *dialOptions) {
+		o.resolveNowBackoff = f
+	})
+}
+
+// WithResolvers allows a list of resolver implementations to be registered
+// locally with the ClientConn without needing to be globally registered via
+// resolver.Register.  They will be matched against the scheme used for the
+// current Dial only, and will take precedence over the global registry.
+//
+// This API is EXPERIMENTAL.
+func WithResolvers(rs ...resolver.Builder) DialOption {
+	return newFuncDialOption(func(o *dialOptions) {
+		o.resolvers = append(o.resolvers, rs...)
+	})
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/doc.go b/demo_test/vendor/google.golang.org/grpc/doc.go
new file mode 100644
index 0000000..187adbb
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/doc.go
@@ -0,0 +1,24 @@
+/*
+ *
+ * Copyright 2015 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+/*
+Package grpc implements an RPC system called gRPC.
+
+See grpc.io for more information about gRPC.
+*/
+package grpc // import "google.golang.org/grpc"
diff --git a/demo_test/vendor/google.golang.org/grpc/encoding/encoding.go b/demo_test/vendor/google.golang.org/grpc/encoding/encoding.go
new file mode 100644
index 0000000..195e844
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/encoding/encoding.go
@@ -0,0 +1,122 @@
+/*
+ *
+ * Copyright 2017 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+// Package encoding defines the interface for the compressor and codec, and
+// functions to register and retrieve compressors and codecs.
+//
+// This package is EXPERIMENTAL.
+package encoding
+
+import (
+	"io"
+	"strings"
+)
+
+// Identity specifies the optional encoding for uncompressed streams.
+// It is intended for grpc internal use only.
+const Identity = "identity"
+
+// Compressor is used for compressing and decompressing when sending or
+// receiving messages.
+type Compressor interface {
+	// Compress writes the data written to wc to w after compressing it.  If an
+	// error occurs while initializing the compressor, that error is returned
+	// instead.
+	Compress(w io.Writer) (io.WriteCloser, error)
+	// Decompress reads data from r, decompresses it, and provides the
+	// uncompressed data via the returned io.Reader.  If an error occurs while
+	// initializing the decompressor, that error is returned instead.
+	Decompress(r io.Reader) (io.Reader, error)
+	// Name is the name of the compression codec and is used to set the content
+	// coding header.  The result must be static; the result cannot change
+	// between calls.
+	Name() string
+	// EXPERIMENTAL: if a Compressor implements
+	// DecompressedSize(compressedBytes []byte) int, gRPC will call it
+	// to determine the size of the buffer allocated for the result of decompression.
+	// Return -1 to indicate unknown size.
+}
+
+var registeredCompressor = make(map[string]Compressor)
+
+// RegisterCompressor registers the compressor with gRPC by its name.  It can
+// be activated when sending an RPC via grpc.UseCompressor().  It will be
+// automatically accessed when receiving a message based on the content coding
+// header.  Servers also use it to send a response with the same encoding as
+// the request.
+//
+// NOTE: this function must only be called during initialization time (i.e. in
+// an init() function), and is not thread-safe.  If multiple Compressors are
+// registered with the same name, the one registered last will take effect.
+func RegisterCompressor(c Compressor) {
+	registeredCompressor[c.Name()] = c
+}
+
+// GetCompressor returns Compressor for the given compressor name.
+func GetCompressor(name string) Compressor {
+	return registeredCompressor[name]
+}
+
+// Codec defines the interface gRPC uses to encode and decode messages.  Note
+// that implementations of this interface must be thread safe; a Codec's
+// methods can be called from concurrent goroutines.
+type Codec interface {
+	// Marshal returns the wire format of v.
+	Marshal(v interface{}) ([]byte, error)
+	// Unmarshal parses the wire format into v.
+	Unmarshal(data []byte, v interface{}) error
+	// Name returns the name of the Codec implementation. The returned string
+	// will be used as part of content type in transmission.  The result must be
+	// static; the result cannot change between calls.
+	Name() string
+}
+
+var registeredCodecs = make(map[string]Codec)
+
+// RegisterCodec registers the provided Codec for use with all gRPC clients and
+// servers.
+//
+// The Codec will be stored and looked up by result of its Name() method, which
+// should match the content-subtype of the encoding handled by the Codec.  This
+// is case-insensitive, and is stored and looked up as lowercase.  If the
+// result of calling Name() is an empty string, RegisterCodec will panic. See
+// Content-Type on
+// https://github.com/grpc/grpc/blob/master/doc/PROTOCOL-HTTP2.md#requests for
+// more details.
+//
+// NOTE: this function must only be called during initialization time (i.e. in
+// an init() function), and is not thread-safe.  If multiple Compressors are
+// registered with the same name, the one registered last will take effect.
+func RegisterCodec(codec Codec) {
+	if codec == nil {
+		panic("cannot register a nil Codec")
+	}
+	if codec.Name() == "" {
+		panic("cannot register Codec with empty string result for Name()")
+	}
+	contentSubtype := strings.ToLower(codec.Name())
+	registeredCodecs[contentSubtype] = codec
+}
+
+// GetCodec gets a registered Codec by content-subtype, or nil if no Codec is
+// registered for the content-subtype.
+//
+// The content-subtype is expected to be lowercase.
+func GetCodec(contentSubtype string) Codec {
+	return registeredCodecs[contentSubtype]
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/encoding/proto/proto.go b/demo_test/vendor/google.golang.org/grpc/encoding/proto/proto.go
new file mode 100644
index 0000000..66b97a6
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/encoding/proto/proto.go
@@ -0,0 +1,110 @@
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+// Package proto defines the protobuf codec. Importing this package will
+// register the codec.
+package proto
+
+import (
+	"math"
+	"sync"
+
+	"github.com/golang/protobuf/proto"
+	"google.golang.org/grpc/encoding"
+)
+
+// Name is the name registered for the proto compressor.
+const Name = "proto"
+
+func init() {
+	encoding.RegisterCodec(codec{})
+}
+
+// codec is a Codec implementation with protobuf. It is the default codec for gRPC.
+type codec struct{}
+
+type cachedProtoBuffer struct {
+	lastMarshaledSize uint32
+	proto.Buffer
+}
+
+func capToMaxInt32(val int) uint32 {
+	if val > math.MaxInt32 {
+		return uint32(math.MaxInt32)
+	}
+	return uint32(val)
+}
+
+func marshal(v interface{}, cb *cachedProtoBuffer) ([]byte, error) {
+	protoMsg := v.(proto.Message)
+	newSlice := make([]byte, 0, cb.lastMarshaledSize)
+
+	cb.SetBuf(newSlice)
+	cb.Reset()
+	if err := cb.Marshal(protoMsg); err != nil {
+		return nil, err
+	}
+	out := cb.Bytes()
+	cb.lastMarshaledSize = capToMaxInt32(len(out))
+	return out, nil
+}
+
+func (codec) Marshal(v interface{}) ([]byte, error) {
+	if pm, ok := v.(proto.Marshaler); ok {
+		// object can marshal itself, no need for buffer
+		return pm.Marshal()
+	}
+
+	cb := protoBufferPool.Get().(*cachedProtoBuffer)
+	out, err := marshal(v, cb)
+
+	// put back buffer and lose the ref to the slice
+	cb.SetBuf(nil)
+	protoBufferPool.Put(cb)
+	return out, err
+}
+
+func (codec) Unmarshal(data []byte, v interface{}) error {
+	protoMsg := v.(proto.Message)
+	protoMsg.Reset()
+
+	if pu, ok := protoMsg.(proto.Unmarshaler); ok {
+		// object can unmarshal itself, no need for buffer
+		return pu.Unmarshal(data)
+	}
+
+	cb := protoBufferPool.Get().(*cachedProtoBuffer)
+	cb.SetBuf(data)
+	err := cb.Unmarshal(protoMsg)
+	cb.SetBuf(nil)
+	protoBufferPool.Put(cb)
+	return err
+}
+
+func (codec) Name() string {
+	return Name
+}
+
+var protoBufferPool = &sync.Pool{
+	New: func() interface{} {
+		return &cachedProtoBuffer{
+			Buffer:            proto.Buffer{},
+			lastMarshaledSize: 16,
+		}
+	},
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/go.mod b/demo_test/vendor/google.golang.org/grpc/go.mod
new file mode 100644
index 0000000..ecef1ab
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/go.mod
@@ -0,0 +1,16 @@
+module google.golang.org/grpc
+
+go 1.11
+
+require (
+	github.com/cncf/udpa/go v0.0.0-20191209042840-269d4d468f6f
+	github.com/envoyproxy/go-control-plane v0.9.4
+	github.com/golang/glog v0.0.0-20160126235308-23def4e6c14b
+	github.com/golang/mock v1.1.1
+	github.com/golang/protobuf v1.3.3
+	github.com/google/go-cmp v0.2.0
+	golang.org/x/net v0.0.0-20190311183353-d8887717615a
+	golang.org/x/oauth2 v0.0.0-20180821212333-d2e6202438be
+	golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a
+	google.golang.org/genproto v0.0.0-20190819201941-24fa4b261c55
+)
diff --git a/demo_test/vendor/google.golang.org/grpc/go.sum b/demo_test/vendor/google.golang.org/grpc/go.sum
new file mode 100644
index 0000000..0bf9f07
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/go.sum
@@ -0,0 +1,64 @@
+cloud.google.com/go v0.26.0 h1:e0WKqKTd5BnrG8aKH3J3h+QvEIQtSUcf2n5UZ5ZgLtQ=
+cloud.google.com/go v0.26.0/go.mod h1:aQUYkXzVsufM+DwF1aE+0xfcU+56JwCaLick0ClmMTw=
+github.com/BurntSushi/toml v0.3.1 h1:WXkYYl6Yr3qBf1K79EBnL4mak0OimBfB0XUf9Vl28OQ=
+github.com/BurntSushi/toml v0.3.1/go.mod h1:xHWCNGjB5oqiDr8zfno3MHue2Ht5sIBksp03qcyfWMU=
+github.com/census-instrumentation/opencensus-proto v0.2.1/go.mod h1:f6KPmirojxKA12rnyqOA5BBL4O983OfeGPqjHWSTneU=
+github.com/client9/misspell v0.3.4 h1:ta993UF76GwbvJcIo3Y68y/M3WxlpEHPWIGDkJYwzJI=
+github.com/client9/misspell v0.3.4/go.mod h1:qj6jICC3Q7zFZvVWo7KLAzC3yx5G7kyvSDkc90ppPyw=
+github.com/cncf/udpa/go v0.0.0-20191209042840-269d4d468f6f h1:WBZRG4aNOuI15bLRrCgN8fCq8E5Xuty6jGbmSNEvSsU=
+github.com/cncf/udpa/go v0.0.0-20191209042840-269d4d468f6f/go.mod h1:M8M6+tZqaGXZJjfX53e64911xZQV5JYwmTeXPW+k8Sc=
+github.com/envoyproxy/go-control-plane v0.9.0/go.mod h1:YTl/9mNaCwkRvm6d1a2C3ymFceY/DCBVvsKhRF0iEA4=
+github.com/envoyproxy/go-control-plane v0.9.4 h1:rEvIZUSZ3fx39WIi3JkQqQBitGwpELBIYWeBVh6wn+E=
+github.com/envoyproxy/go-control-plane v0.9.4/go.mod h1:6rpuAdCZL397s3pYoYcLgu1mIlRU8Am5FuJP05cCM98=
+github.com/envoyproxy/protoc-gen-validate v0.1.0 h1:EQciDnbrYxy13PgWoY8AqoxGiPrpgBZ1R8UNe3ddc+A=
+github.com/envoyproxy/protoc-gen-validate v0.1.0/go.mod h1:iSmxcyjqTsJpI2R4NaDN7+kN2VEUnK/pcBlmesArF7c=
+github.com/golang/glog v0.0.0-20160126235308-23def4e6c14b h1:VKtxabqXZkF25pY9ekfRL6a582T4P37/31XEstQ5p58=
+github.com/golang/glog v0.0.0-20160126235308-23def4e6c14b/go.mod h1:SBH7ygxi8pfUlaOkMMuAQtPIUF8ecWP5IEl/CR7VP2Q=
+github.com/golang/mock v1.1.1 h1:G5FRp8JnTd7RQH5kemVNlMeyXQAztQ3mOWV95KxsXH8=
+github.com/golang/mock v1.1.1/go.mod h1:oTYuIxOrZwtPieC+H1uAHpcLFnEyAGVDL/k47Jfbm0A=
+github.com/golang/protobuf v1.2.0/go.mod h1:6lQm79b+lXiMfvg/cZm0SGofjICqVBUtrP5yJMmIC1U=
+github.com/golang/protobuf v1.3.2 h1:6nsPYzhq5kReh6QImI3k5qWzO4PEbvbIW2cwSfR/6xs=
+github.com/golang/protobuf v1.3.2/go.mod h1:6lQm79b+lXiMfvg/cZm0SGofjICqVBUtrP5yJMmIC1U=
+github.com/golang/protobuf v1.3.3 h1:gyjaxf+svBWX08ZjK86iN9geUJF0H6gp2IRKX6Nf6/I=
+github.com/golang/protobuf v1.3.3/go.mod h1:vzj43D7+SQXF/4pzW/hwtAqwc6iTitCiVSaWz5lYuqw=
+github.com/google/go-cmp v0.2.0 h1:+dTQ8DZQJz0Mb/HjFlkptS1FeQ4cWSnN941F8aEG4SQ=
+github.com/google/go-cmp v0.2.0/go.mod h1:oXzfMopK8JAjlY9xF4vHSVASa0yLyX7SntLO5aqRK0M=
+github.com/prometheus/client_model v0.0.0-20190812154241-14fe0d1b01d4/go.mod h1:xMI15A0UPsDsEKsMN9yxemIoYk6Tm2C1GtYGdfGttqA=
+golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
+golang.org/x/exp v0.0.0-20190121172915-509febef88a4/go.mod h1:CJ0aWSM057203Lf6IL+f9T1iT9GByDxfZKAQTCR3kQA=
+golang.org/x/lint v0.0.0-20181026193005-c67002cb31c3/go.mod h1:UVdnD1Gm6xHRNCYTkRU2/jEulfH38KcIWyp/GAMgvoE=
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+golang.org/x/lint v0.0.0-20190313153728-d0100b6bd8b3 h1:XQyxROzUlZH+WIQwySDgnISgOivlhjIEwaQaJEJrrN0=
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+golang.org/x/net v0.0.0-20180724234803-3673e40ba225/go.mod h1:mL1N/T3taQHkDXs73rZJwtUhF3w3ftmwwsq0BUmARs4=
+golang.org/x/net v0.0.0-20180826012351-8a410e7b638d/go.mod h1:mL1N/T3taQHkDXs73rZJwtUhF3w3ftmwwsq0BUmARs4=
+golang.org/x/net v0.0.0-20190213061140-3a22650c66bd/go.mod h1:mL1N/T3taQHkDXs73rZJwtUhF3w3ftmwwsq0BUmARs4=
+golang.org/x/net v0.0.0-20190311183353-d8887717615a h1:oWX7TPOiFAMXLq8o0ikBYfCJVlRHBcsciT5bXOrH628=
+golang.org/x/net v0.0.0-20190311183353-d8887717615a/go.mod h1:t9HGtf8HONx5eT2rtn7q6eTqICYqUVnKs3thJo3Qplg=
+golang.org/x/oauth2 v0.0.0-20180821212333-d2e6202438be h1:vEDujvNQGv4jgYKudGeI/+DAX4Jffq6hpD55MmoEvKs=
+golang.org/x/oauth2 v0.0.0-20180821212333-d2e6202438be/go.mod h1:N/0e6XlmueqKjAGxoOufVs8QHGRruUQn6yWY3a++T0U=
+golang.org/x/sync v0.0.0-20180314180146-1d60e4601c6f/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
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diff --git a/demo_test/vendor/google.golang.org/grpc/grpclog/grpclog.go b/demo_test/vendor/google.golang.org/grpc/grpclog/grpclog.go
new file mode 100644
index 0000000..c8bb2be
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/grpclog/grpclog.go
@@ -0,0 +1,132 @@
+/*
+ *
+ * Copyright 2017 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+// Package grpclog defines logging for grpc.
+//
+// All logs in transport and grpclb packages only go to verbose level 2.
+// All logs in other packages in grpc are logged in spite of the verbosity level.
+//
+// In the default logger,
+// severity level can be set by environment variable GRPC_GO_LOG_SEVERITY_LEVEL,
+// verbosity level can be set by GRPC_GO_LOG_VERBOSITY_LEVEL.
+package grpclog // import "google.golang.org/grpc/grpclog"
+
+import (
+	"os"
+
+	"google.golang.org/grpc/internal/grpclog"
+)
+
+func init() {
+	SetLoggerV2(newLoggerV2())
+}
+
+// V reports whether verbosity level l is at least the requested verbose level.
+func V(l int) bool {
+	return grpclog.Logger.V(l)
+}
+
+// Info logs to the INFO log.
+func Info(args ...interface{}) {
+	grpclog.Logger.Info(args...)
+}
+
+// Infof logs to the INFO log. Arguments are handled in the manner of fmt.Printf.
+func Infof(format string, args ...interface{}) {
+	grpclog.Logger.Infof(format, args...)
+}
+
+// Infoln logs to the INFO log. Arguments are handled in the manner of fmt.Println.
+func Infoln(args ...interface{}) {
+	grpclog.Logger.Infoln(args...)
+}
+
+// Warning logs to the WARNING log.
+func Warning(args ...interface{}) {
+	grpclog.Logger.Warning(args...)
+}
+
+// Warningf logs to the WARNING log. Arguments are handled in the manner of fmt.Printf.
+func Warningf(format string, args ...interface{}) {
+	grpclog.Logger.Warningf(format, args...)
+}
+
+// Warningln logs to the WARNING log. Arguments are handled in the manner of fmt.Println.
+func Warningln(args ...interface{}) {
+	grpclog.Logger.Warningln(args...)
+}
+
+// Error logs to the ERROR log.
+func Error(args ...interface{}) {
+	grpclog.Logger.Error(args...)
+}
+
+// Errorf logs to the ERROR log. Arguments are handled in the manner of fmt.Printf.
+func Errorf(format string, args ...interface{}) {
+	grpclog.Logger.Errorf(format, args...)
+}
+
+// Errorln logs to the ERROR log. Arguments are handled in the manner of fmt.Println.
+func Errorln(args ...interface{}) {
+	grpclog.Logger.Errorln(args...)
+}
+
+// Fatal logs to the FATAL log. Arguments are handled in the manner of fmt.Print.
+// It calls os.Exit() with exit code 1.
+func Fatal(args ...interface{}) {
+	grpclog.Logger.Fatal(args...)
+	// Make sure fatal logs will exit.
+	os.Exit(1)
+}
+
+// Fatalf logs to the FATAL log. Arguments are handled in the manner of fmt.Printf.
+// It calls os.Exit() with exit code 1.
+func Fatalf(format string, args ...interface{}) {
+	grpclog.Logger.Fatalf(format, args...)
+	// Make sure fatal logs will exit.
+	os.Exit(1)
+}
+
+// Fatalln logs to the FATAL log. Arguments are handled in the manner of fmt.Println.
+// It calle os.Exit()) with exit code 1.
+func Fatalln(args ...interface{}) {
+	grpclog.Logger.Fatalln(args...)
+	// Make sure fatal logs will exit.
+	os.Exit(1)
+}
+
+// Print prints to the logger. Arguments are handled in the manner of fmt.Print.
+//
+// Deprecated: use Info.
+func Print(args ...interface{}) {
+	grpclog.Logger.Info(args...)
+}
+
+// Printf prints to the logger. Arguments are handled in the manner of fmt.Printf.
+//
+// Deprecated: use Infof.
+func Printf(format string, args ...interface{}) {
+	grpclog.Logger.Infof(format, args...)
+}
+
+// Println prints to the logger. Arguments are handled in the manner of fmt.Println.
+//
+// Deprecated: use Infoln.
+func Println(args ...interface{}) {
+	grpclog.Logger.Infoln(args...)
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/grpclog/logger.go b/demo_test/vendor/google.golang.org/grpc/grpclog/logger.go
new file mode 100644
index 0000000..ef06a48
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/grpclog/logger.go
@@ -0,0 +1,87 @@
+/*
+ *
+ * Copyright 2015 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package grpclog
+
+import "google.golang.org/grpc/internal/grpclog"
+
+// Logger mimics golang's standard Logger as an interface.
+//
+// Deprecated: use LoggerV2.
+type Logger interface {
+	Fatal(args ...interface{})
+	Fatalf(format string, args ...interface{})
+	Fatalln(args ...interface{})
+	Print(args ...interface{})
+	Printf(format string, args ...interface{})
+	Println(args ...interface{})
+}
+
+// SetLogger sets the logger that is used in grpc. Call only from
+// init() functions.
+//
+// Deprecated: use SetLoggerV2.
+func SetLogger(l Logger) {
+	grpclog.Logger = &loggerWrapper{Logger: l}
+}
+
+// loggerWrapper wraps Logger into a LoggerV2.
+type loggerWrapper struct {
+	Logger
+}
+
+func (g *loggerWrapper) Info(args ...interface{}) {
+	g.Logger.Print(args...)
+}
+
+func (g *loggerWrapper) Infoln(args ...interface{}) {
+	g.Logger.Println(args...)
+}
+
+func (g *loggerWrapper) Infof(format string, args ...interface{}) {
+	g.Logger.Printf(format, args...)
+}
+
+func (g *loggerWrapper) Warning(args ...interface{}) {
+	g.Logger.Print(args...)
+}
+
+func (g *loggerWrapper) Warningln(args ...interface{}) {
+	g.Logger.Println(args...)
+}
+
+func (g *loggerWrapper) Warningf(format string, args ...interface{}) {
+	g.Logger.Printf(format, args...)
+}
+
+func (g *loggerWrapper) Error(args ...interface{}) {
+	g.Logger.Print(args...)
+}
+
+func (g *loggerWrapper) Errorln(args ...interface{}) {
+	g.Logger.Println(args...)
+}
+
+func (g *loggerWrapper) Errorf(format string, args ...interface{}) {
+	g.Logger.Printf(format, args...)
+}
+
+func (g *loggerWrapper) V(l int) bool {
+	// Returns true for all verbose level.
+	return true
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/grpclog/loggerv2.go b/demo_test/vendor/google.golang.org/grpc/grpclog/loggerv2.go
new file mode 100644
index 0000000..23612b7
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/grpclog/loggerv2.go
@@ -0,0 +1,214 @@
+/*
+ *
+ * Copyright 2017 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package grpclog
+
+import (
+	"io"
+	"io/ioutil"
+	"log"
+	"os"
+	"strconv"
+
+	"google.golang.org/grpc/internal/grpclog"
+)
+
+// LoggerV2 does underlying logging work for grpclog.
+type LoggerV2 interface {
+	// Info logs to INFO log. Arguments are handled in the manner of fmt.Print.
+	Info(args ...interface{})
+	// Infoln logs to INFO log. Arguments are handled in the manner of fmt.Println.
+	Infoln(args ...interface{})
+	// Infof logs to INFO log. Arguments are handled in the manner of fmt.Printf.
+	Infof(format string, args ...interface{})
+	// Warning logs to WARNING log. Arguments are handled in the manner of fmt.Print.
+	Warning(args ...interface{})
+	// Warningln logs to WARNING log. Arguments are handled in the manner of fmt.Println.
+	Warningln(args ...interface{})
+	// Warningf logs to WARNING log. Arguments are handled in the manner of fmt.Printf.
+	Warningf(format string, args ...interface{})
+	// Error logs to ERROR log. Arguments are handled in the manner of fmt.Print.
+	Error(args ...interface{})
+	// Errorln logs to ERROR log. Arguments are handled in the manner of fmt.Println.
+	Errorln(args ...interface{})
+	// Errorf logs to ERROR log. Arguments are handled in the manner of fmt.Printf.
+	Errorf(format string, args ...interface{})
+	// Fatal logs to ERROR log. Arguments are handled in the manner of fmt.Print.
+	// gRPC ensures that all Fatal logs will exit with os.Exit(1).
+	// Implementations may also call os.Exit() with a non-zero exit code.
+	Fatal(args ...interface{})
+	// Fatalln logs to ERROR log. Arguments are handled in the manner of fmt.Println.
+	// gRPC ensures that all Fatal logs will exit with os.Exit(1).
+	// Implementations may also call os.Exit() with a non-zero exit code.
+	Fatalln(args ...interface{})
+	// Fatalf logs to ERROR log. Arguments are handled in the manner of fmt.Printf.
+	// gRPC ensures that all Fatal logs will exit with os.Exit(1).
+	// Implementations may also call os.Exit() with a non-zero exit code.
+	Fatalf(format string, args ...interface{})
+	// V reports whether verbosity level l is at least the requested verbose level.
+	V(l int) bool
+}
+
+// SetLoggerV2 sets logger that is used in grpc to a V2 logger.
+// Not mutex-protected, should be called before any gRPC functions.
+func SetLoggerV2(l LoggerV2) {
+	grpclog.Logger = l
+	grpclog.DepthLogger, _ = l.(grpclog.DepthLoggerV2)
+}
+
+const (
+	// infoLog indicates Info severity.
+	infoLog int = iota
+	// warningLog indicates Warning severity.
+	warningLog
+	// errorLog indicates Error severity.
+	errorLog
+	// fatalLog indicates Fatal severity.
+	fatalLog
+)
+
+// severityName contains the string representation of each severity.
+var severityName = []string{
+	infoLog:    "INFO",
+	warningLog: "WARNING",
+	errorLog:   "ERROR",
+	fatalLog:   "FATAL",
+}
+
+// loggerT is the default logger used by grpclog.
+type loggerT struct {
+	m []*log.Logger
+	v int
+}
+
+// NewLoggerV2 creates a loggerV2 with the provided writers.
+// Fatal logs will be written to errorW, warningW, infoW, followed by exit(1).
+// Error logs will be written to errorW, warningW and infoW.
+// Warning logs will be written to warningW and infoW.
+// Info logs will be written to infoW.
+func NewLoggerV2(infoW, warningW, errorW io.Writer) LoggerV2 {
+	return NewLoggerV2WithVerbosity(infoW, warningW, errorW, 0)
+}
+
+// NewLoggerV2WithVerbosity creates a loggerV2 with the provided writers and
+// verbosity level.
+func NewLoggerV2WithVerbosity(infoW, warningW, errorW io.Writer, v int) LoggerV2 {
+	var m []*log.Logger
+	m = append(m, log.New(infoW, severityName[infoLog]+": ", log.LstdFlags))
+	m = append(m, log.New(io.MultiWriter(infoW, warningW), severityName[warningLog]+": ", log.LstdFlags))
+	ew := io.MultiWriter(infoW, warningW, errorW) // ew will be used for error and fatal.
+	m = append(m, log.New(ew, severityName[errorLog]+": ", log.LstdFlags))
+	m = append(m, log.New(ew, severityName[fatalLog]+": ", log.LstdFlags))
+	return &loggerT{m: m, v: v}
+}
+
+// newLoggerV2 creates a loggerV2 to be used as default logger.
+// All logs are written to stderr.
+func newLoggerV2() LoggerV2 {
+	errorW := ioutil.Discard
+	warningW := ioutil.Discard
+	infoW := ioutil.Discard
+
+	logLevel := os.Getenv("GRPC_GO_LOG_SEVERITY_LEVEL")
+	switch logLevel {
+	case "", "ERROR", "error": // If env is unset, set level to ERROR.
+		errorW = os.Stderr
+	case "WARNING", "warning":
+		warningW = os.Stderr
+	case "INFO", "info":
+		infoW = os.Stderr
+	}
+
+	var v int
+	vLevel := os.Getenv("GRPC_GO_LOG_VERBOSITY_LEVEL")
+	if vl, err := strconv.Atoi(vLevel); err == nil {
+		v = vl
+	}
+	return NewLoggerV2WithVerbosity(infoW, warningW, errorW, v)
+}
+
+func (g *loggerT) Info(args ...interface{}) {
+	g.m[infoLog].Print(args...)
+}
+
+func (g *loggerT) Infoln(args ...interface{}) {
+	g.m[infoLog].Println(args...)
+}
+
+func (g *loggerT) Infof(format string, args ...interface{}) {
+	g.m[infoLog].Printf(format, args...)
+}
+
+func (g *loggerT) Warning(args ...interface{}) {
+	g.m[warningLog].Print(args...)
+}
+
+func (g *loggerT) Warningln(args ...interface{}) {
+	g.m[warningLog].Println(args...)
+}
+
+func (g *loggerT) Warningf(format string, args ...interface{}) {
+	g.m[warningLog].Printf(format, args...)
+}
+
+func (g *loggerT) Error(args ...interface{}) {
+	g.m[errorLog].Print(args...)
+}
+
+func (g *loggerT) Errorln(args ...interface{}) {
+	g.m[errorLog].Println(args...)
+}
+
+func (g *loggerT) Errorf(format string, args ...interface{}) {
+	g.m[errorLog].Printf(format, args...)
+}
+
+func (g *loggerT) Fatal(args ...interface{}) {
+	g.m[fatalLog].Fatal(args...)
+	// No need to call os.Exit() again because log.Logger.Fatal() calls os.Exit().
+}
+
+func (g *loggerT) Fatalln(args ...interface{}) {
+	g.m[fatalLog].Fatalln(args...)
+	// No need to call os.Exit() again because log.Logger.Fatal() calls os.Exit().
+}
+
+func (g *loggerT) Fatalf(format string, args ...interface{}) {
+	g.m[fatalLog].Fatalf(format, args...)
+	// No need to call os.Exit() again because log.Logger.Fatal() calls os.Exit().
+}
+
+func (g *loggerT) V(l int) bool {
+	return l <= g.v
+}
+
+// DepthLoggerV2 logs at a specified call frame. If a LoggerV2 also implements
+// DepthLoggerV2, the below functions will be called with the appropriate stack
+// depth set for trivial functions the logger may ignore.
+//
+// This API is EXPERIMENTAL.
+type DepthLoggerV2 interface {
+	// InfoDepth logs to INFO log at the specified depth. Arguments are handled in the manner of fmt.Print.
+	InfoDepth(depth int, args ...interface{})
+	// WarningDepth logs to WARNING log at the specified depth. Arguments are handled in the manner of fmt.Print.
+	WarningDepth(depth int, args ...interface{})
+	// ErrorDetph logs to ERROR log at the specified depth. Arguments are handled in the manner of fmt.Print.
+	ErrorDepth(depth int, args ...interface{})
+	// FatalDepth logs to FATAL log at the specified depth. Arguments are handled in the manner of fmt.Print.
+	FatalDepth(depth int, args ...interface{})
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/install_gae.sh b/demo_test/vendor/google.golang.org/grpc/install_gae.sh
new file mode 100644
index 0000000..7c7bcad
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/install_gae.sh
@@ -0,0 +1,6 @@
+#!/bin/bash
+
+TMP=$(mktemp -d /tmp/sdk.XXX) \
+&& curl -o $TMP.zip "https://storage.googleapis.com/appengine-sdks/featured/go_appengine_sdk_linux_amd64-1.9.68.zip" \
+&& unzip -q $TMP.zip -d $TMP \
+&& export PATH="$PATH:$TMP/go_appengine"
diff --git a/demo_test/vendor/google.golang.org/grpc/interceptor.go b/demo_test/vendor/google.golang.org/grpc/interceptor.go
new file mode 100644
index 0000000..8b73500
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/interceptor.go
@@ -0,0 +1,77 @@
+/*
+ *
+ * Copyright 2016 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package grpc
+
+import (
+	"context"
+)
+
+// UnaryInvoker is called by UnaryClientInterceptor to complete RPCs.
+type UnaryInvoker func(ctx context.Context, method string, req, reply interface{}, cc *ClientConn, opts ...CallOption) error
+
+// UnaryClientInterceptor intercepts the execution of a unary RPC on the client. invoker is the handler to complete the RPC
+// and it is the responsibility of the interceptor to call it.
+// This is an EXPERIMENTAL API.
+type UnaryClientInterceptor func(ctx context.Context, method string, req, reply interface{}, cc *ClientConn, invoker UnaryInvoker, opts ...CallOption) error
+
+// Streamer is called by StreamClientInterceptor to create a ClientStream.
+type Streamer func(ctx context.Context, desc *StreamDesc, cc *ClientConn, method string, opts ...CallOption) (ClientStream, error)
+
+// StreamClientInterceptor intercepts the creation of ClientStream. It may return a custom ClientStream to intercept all I/O
+// operations. streamer is the handler to create a ClientStream and it is the responsibility of the interceptor to call it.
+// This is an EXPERIMENTAL API.
+type StreamClientInterceptor func(ctx context.Context, desc *StreamDesc, cc *ClientConn, method string, streamer Streamer, opts ...CallOption) (ClientStream, error)
+
+// UnaryServerInfo consists of various information about a unary RPC on
+// server side. All per-rpc information may be mutated by the interceptor.
+type UnaryServerInfo struct {
+	// Server is the service implementation the user provides. This is read-only.
+	Server interface{}
+	// FullMethod is the full RPC method string, i.e., /package.service/method.
+	FullMethod string
+}
+
+// UnaryHandler defines the handler invoked by UnaryServerInterceptor to complete the normal
+// execution of a unary RPC. If a UnaryHandler returns an error, it should be produced by the
+// status package, or else gRPC will use codes.Unknown as the status code and err.Error() as
+// the status message of the RPC.
+type UnaryHandler func(ctx context.Context, req interface{}) (interface{}, error)
+
+// UnaryServerInterceptor provides a hook to intercept the execution of a unary RPC on the server. info
+// contains all the information of this RPC the interceptor can operate on. And handler is the wrapper
+// of the service method implementation. It is the responsibility of the interceptor to invoke handler
+// to complete the RPC.
+type UnaryServerInterceptor func(ctx context.Context, req interface{}, info *UnaryServerInfo, handler UnaryHandler) (resp interface{}, err error)
+
+// StreamServerInfo consists of various information about a streaming RPC on
+// server side. All per-rpc information may be mutated by the interceptor.
+type StreamServerInfo struct {
+	// FullMethod is the full RPC method string, i.e., /package.service/method.
+	FullMethod string
+	// IsClientStream indicates whether the RPC is a client streaming RPC.
+	IsClientStream bool
+	// IsServerStream indicates whether the RPC is a server streaming RPC.
+	IsServerStream bool
+}
+
+// StreamServerInterceptor provides a hook to intercept the execution of a streaming RPC on the server.
+// info contains all the information of this RPC the interceptor can operate on. And handler is the
+// service method implementation. It is the responsibility of the interceptor to invoke handler to
+// complete the RPC.
+type StreamServerInterceptor func(srv interface{}, ss ServerStream, info *StreamServerInfo, handler StreamHandler) error
diff --git a/demo_test/vendor/google.golang.org/grpc/internal/backoff/backoff.go b/demo_test/vendor/google.golang.org/grpc/internal/backoff/backoff.go
new file mode 100644
index 0000000..5fc0ee3
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/internal/backoff/backoff.go
@@ -0,0 +1,73 @@
+/*
+ *
+ * Copyright 2017 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+// Package backoff implement the backoff strategy for gRPC.
+//
+// This is kept in internal until the gRPC project decides whether or not to
+// allow alternative backoff strategies.
+package backoff
+
+import (
+	"time"
+
+	grpcbackoff "google.golang.org/grpc/backoff"
+	"google.golang.org/grpc/internal/grpcrand"
+)
+
+// Strategy defines the methodology for backing off after a grpc connection
+// failure.
+type Strategy interface {
+	// Backoff returns the amount of time to wait before the next retry given
+	// the number of consecutive failures.
+	Backoff(retries int) time.Duration
+}
+
+// DefaultExponential is an exponential backoff implementation using the
+// default values for all the configurable knobs defined in
+// https://github.com/grpc/grpc/blob/master/doc/connection-backoff.md.
+var DefaultExponential = Exponential{Config: grpcbackoff.DefaultConfig}
+
+// Exponential implements exponential backoff algorithm as defined in
+// https://github.com/grpc/grpc/blob/master/doc/connection-backoff.md.
+type Exponential struct {
+	// Config contains all options to configure the backoff algorithm.
+	Config grpcbackoff.Config
+}
+
+// Backoff returns the amount of time to wait before the next retry given the
+// number of retries.
+func (bc Exponential) Backoff(retries int) time.Duration {
+	if retries == 0 {
+		return bc.Config.BaseDelay
+	}
+	backoff, max := float64(bc.Config.BaseDelay), float64(bc.Config.MaxDelay)
+	for backoff < max && retries > 0 {
+		backoff *= bc.Config.Multiplier
+		retries--
+	}
+	if backoff > max {
+		backoff = max
+	}
+	// Randomize backoff delays so that if a cluster of requests start at
+	// the same time, they won't operate in lockstep.
+	backoff *= 1 + bc.Config.Jitter*(grpcrand.Float64()*2-1)
+	if backoff < 0 {
+		return 0
+	}
+	return time.Duration(backoff)
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/internal/balancerload/load.go b/demo_test/vendor/google.golang.org/grpc/internal/balancerload/load.go
new file mode 100644
index 0000000..3a905d9
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/internal/balancerload/load.go
@@ -0,0 +1,46 @@
+/*
+ * Copyright 2019 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+// Package balancerload defines APIs to parse server loads in trailers. The
+// parsed loads are sent to balancers in DoneInfo.
+package balancerload
+
+import (
+	"google.golang.org/grpc/metadata"
+)
+
+// Parser converts loads from metadata into a concrete type.
+type Parser interface {
+	// Parse parses loads from metadata.
+	Parse(md metadata.MD) interface{}
+}
+
+var parser Parser
+
+// SetParser sets the load parser.
+//
+// Not mutex-protected, should be called before any gRPC functions.
+func SetParser(lr Parser) {
+	parser = lr
+}
+
+// Parse calls parser.Read().
+func Parse(md metadata.MD) interface{} {
+	if parser == nil {
+		return nil
+	}
+	return parser.Parse(md)
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/internal/binarylog/binarylog.go b/demo_test/vendor/google.golang.org/grpc/internal/binarylog/binarylog.go
new file mode 100644
index 0000000..8b10516
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/internal/binarylog/binarylog.go
@@ -0,0 +1,167 @@
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+// Package binarylog implementation binary logging as defined in
+// https://github.com/grpc/proposal/blob/master/A16-binary-logging.md.
+package binarylog
+
+import (
+	"fmt"
+	"os"
+
+	"google.golang.org/grpc/grpclog"
+)
+
+// Logger is the global binary logger. It can be used to get binary logger for
+// each method.
+type Logger interface {
+	getMethodLogger(methodName string) *MethodLogger
+}
+
+// binLogger is the global binary logger for the binary. One of this should be
+// built at init time from the configuration (environment variable or flags).
+//
+// It is used to get a methodLogger for each individual method.
+var binLogger Logger
+
+// SetLogger sets the binarg logger.
+//
+// Only call this at init time.
+func SetLogger(l Logger) {
+	binLogger = l
+}
+
+// GetMethodLogger returns the methodLogger for the given methodName.
+//
+// methodName should be in the format of "/service/method".
+//
+// Each methodLogger returned by this method is a new instance. This is to
+// generate sequence id within the call.
+func GetMethodLogger(methodName string) *MethodLogger {
+	if binLogger == nil {
+		return nil
+	}
+	return binLogger.getMethodLogger(methodName)
+}
+
+func init() {
+	const envStr = "GRPC_BINARY_LOG_FILTER"
+	configStr := os.Getenv(envStr)
+	binLogger = NewLoggerFromConfigString(configStr)
+}
+
+type methodLoggerConfig struct {
+	// Max length of header and message.
+	hdr, msg uint64
+}
+
+type logger struct {
+	all      *methodLoggerConfig
+	services map[string]*methodLoggerConfig
+	methods  map[string]*methodLoggerConfig
+
+	blacklist map[string]struct{}
+}
+
+// newEmptyLogger creates an empty logger. The map fields need to be filled in
+// using the set* functions.
+func newEmptyLogger() *logger {
+	return &logger{}
+}
+
+// Set method logger for "*".
+func (l *logger) setDefaultMethodLogger(ml *methodLoggerConfig) error {
+	if l.all != nil {
+		return fmt.Errorf("conflicting global rules found")
+	}
+	l.all = ml
+	return nil
+}
+
+// Set method logger for "service/*".
+//
+// New methodLogger with same service overrides the old one.
+func (l *logger) setServiceMethodLogger(service string, ml *methodLoggerConfig) error {
+	if _, ok := l.services[service]; ok {
+		return fmt.Errorf("conflicting service rules for service %v found", service)
+	}
+	if l.services == nil {
+		l.services = make(map[string]*methodLoggerConfig)
+	}
+	l.services[service] = ml
+	return nil
+}
+
+// Set method logger for "service/method".
+//
+// New methodLogger with same method overrides the old one.
+func (l *logger) setMethodMethodLogger(method string, ml *methodLoggerConfig) error {
+	if _, ok := l.blacklist[method]; ok {
+		return fmt.Errorf("conflicting blacklist rules for method %v found", method)
+	}
+	if _, ok := l.methods[method]; ok {
+		return fmt.Errorf("conflicting method rules for method %v found", method)
+	}
+	if l.methods == nil {
+		l.methods = make(map[string]*methodLoggerConfig)
+	}
+	l.methods[method] = ml
+	return nil
+}
+
+// Set blacklist method for "-service/method".
+func (l *logger) setBlacklist(method string) error {
+	if _, ok := l.blacklist[method]; ok {
+		return fmt.Errorf("conflicting blacklist rules for method %v found", method)
+	}
+	if _, ok := l.methods[method]; ok {
+		return fmt.Errorf("conflicting method rules for method %v found", method)
+	}
+	if l.blacklist == nil {
+		l.blacklist = make(map[string]struct{})
+	}
+	l.blacklist[method] = struct{}{}
+	return nil
+}
+
+// getMethodLogger returns the methodLogger for the given methodName.
+//
+// methodName should be in the format of "/service/method".
+//
+// Each methodLogger returned by this method is a new instance. This is to
+// generate sequence id within the call.
+func (l *logger) getMethodLogger(methodName string) *MethodLogger {
+	s, m, err := parseMethodName(methodName)
+	if err != nil {
+		grpclog.Infof("binarylogging: failed to parse %q: %v", methodName, err)
+		return nil
+	}
+	if ml, ok := l.methods[s+"/"+m]; ok {
+		return newMethodLogger(ml.hdr, ml.msg)
+	}
+	if _, ok := l.blacklist[s+"/"+m]; ok {
+		return nil
+	}
+	if ml, ok := l.services[s]; ok {
+		return newMethodLogger(ml.hdr, ml.msg)
+	}
+	if l.all == nil {
+		return nil
+	}
+	return newMethodLogger(l.all.hdr, l.all.msg)
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/internal/binarylog/binarylog_testutil.go b/demo_test/vendor/google.golang.org/grpc/internal/binarylog/binarylog_testutil.go
new file mode 100644
index 0000000..1ee00a3
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/internal/binarylog/binarylog_testutil.go
@@ -0,0 +1,42 @@
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+// This file contains exported variables/functions that are exported for testing
+// only.
+//
+// An ideal way for this would be to put those in a *_test.go but in binarylog
+// package. But this doesn't work with staticcheck with go module. Error was:
+// "MdToMetadataProto not declared by package binarylog". This could be caused
+// by the way staticcheck looks for files for a certain package, which doesn't
+// support *_test.go files.
+//
+// Move those to binary_test.go when staticcheck is fixed.
+
+package binarylog
+
+var (
+	// AllLogger is a logger that logs all headers/messages for all RPCs. It's
+	// for testing only.
+	AllLogger = NewLoggerFromConfigString("*")
+	// MdToMetadataProto converts metadata to a binary logging proto message.
+	// It's for testing only.
+	MdToMetadataProto = mdToMetadataProto
+	// AddrToProto converts an address to a binary logging proto message. It's
+	// for testing only.
+	AddrToProto = addrToProto
+)
diff --git a/demo_test/vendor/google.golang.org/grpc/internal/binarylog/env_config.go b/demo_test/vendor/google.golang.org/grpc/internal/binarylog/env_config.go
new file mode 100644
index 0000000..be30d0e
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/internal/binarylog/env_config.go
@@ -0,0 +1,210 @@
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package binarylog
+
+import (
+	"errors"
+	"fmt"
+	"regexp"
+	"strconv"
+	"strings"
+
+	"google.golang.org/grpc/grpclog"
+)
+
+// NewLoggerFromConfigString reads the string and build a logger. It can be used
+// to build a new logger and assign it to binarylog.Logger.
+//
+// Example filter config strings:
+//  - "" Nothing will be logged
+//  - "*" All headers and messages will be fully logged.
+//  - "*{h}" Only headers will be logged.
+//  - "*{m:256}" Only the first 256 bytes of each message will be logged.
+//  - "Foo/*" Logs every method in service Foo
+//  - "Foo/*,-Foo/Bar" Logs every method in service Foo except method /Foo/Bar
+//  - "Foo/*,Foo/Bar{m:256}" Logs the first 256 bytes of each message in method
+//    /Foo/Bar, logs all headers and messages in every other method in service
+//    Foo.
+//
+// If two configs exist for one certain method or service, the one specified
+// later overrides the previous config.
+func NewLoggerFromConfigString(s string) Logger {
+	if s == "" {
+		return nil
+	}
+	l := newEmptyLogger()
+	methods := strings.Split(s, ",")
+	for _, method := range methods {
+		if err := l.fillMethodLoggerWithConfigString(method); err != nil {
+			grpclog.Warningf("failed to parse binary log config: %v", err)
+			return nil
+		}
+	}
+	return l
+}
+
+// fillMethodLoggerWithConfigString parses config, creates methodLogger and adds
+// it to the right map in the logger.
+func (l *logger) fillMethodLoggerWithConfigString(config string) error {
+	// "" is invalid.
+	if config == "" {
+		return errors.New("empty string is not a valid method binary logging config")
+	}
+
+	// "-service/method", blacklist, no * or {} allowed.
+	if config[0] == '-' {
+		s, m, suffix, err := parseMethodConfigAndSuffix(config[1:])
+		if err != nil {
+			return fmt.Errorf("invalid config: %q, %v", config, err)
+		}
+		if m == "*" {
+			return fmt.Errorf("invalid config: %q, %v", config, "* not allowed in blacklist config")
+		}
+		if suffix != "" {
+			return fmt.Errorf("invalid config: %q, %v", config, "header/message limit not allowed in blacklist config")
+		}
+		if err := l.setBlacklist(s + "/" + m); err != nil {
+			return fmt.Errorf("invalid config: %v", err)
+		}
+		return nil
+	}
+
+	// "*{h:256;m:256}"
+	if config[0] == '*' {
+		hdr, msg, err := parseHeaderMessageLengthConfig(config[1:])
+		if err != nil {
+			return fmt.Errorf("invalid config: %q, %v", config, err)
+		}
+		if err := l.setDefaultMethodLogger(&methodLoggerConfig{hdr: hdr, msg: msg}); err != nil {
+			return fmt.Errorf("invalid config: %v", err)
+		}
+		return nil
+	}
+
+	s, m, suffix, err := parseMethodConfigAndSuffix(config)
+	if err != nil {
+		return fmt.Errorf("invalid config: %q, %v", config, err)
+	}
+	hdr, msg, err := parseHeaderMessageLengthConfig(suffix)
+	if err != nil {
+		return fmt.Errorf("invalid header/message length config: %q, %v", suffix, err)
+	}
+	if m == "*" {
+		if err := l.setServiceMethodLogger(s, &methodLoggerConfig{hdr: hdr, msg: msg}); err != nil {
+			return fmt.Errorf("invalid config: %v", err)
+		}
+	} else {
+		if err := l.setMethodMethodLogger(s+"/"+m, &methodLoggerConfig{hdr: hdr, msg: msg}); err != nil {
+			return fmt.Errorf("invalid config: %v", err)
+		}
+	}
+	return nil
+}
+
+const (
+	// TODO: this const is only used by env_config now. But could be useful for
+	// other config. Move to binarylog.go if necessary.
+	maxUInt = ^uint64(0)
+
+	// For "p.s/m" plus any suffix. Suffix will be parsed again. See test for
+	// expected output.
+	longMethodConfigRegexpStr = `^([\w./]+)/((?:\w+)|[*])(.+)?$`
+
+	// For suffix from above, "{h:123,m:123}". See test for expected output.
+	optionalLengthRegexpStr      = `(?::(\d+))?` // Optional ":123".
+	headerConfigRegexpStr        = `^{h` + optionalLengthRegexpStr + `}$`
+	messageConfigRegexpStr       = `^{m` + optionalLengthRegexpStr + `}$`
+	headerMessageConfigRegexpStr = `^{h` + optionalLengthRegexpStr + `;m` + optionalLengthRegexpStr + `}$`
+)
+
+var (
+	longMethodConfigRegexp    = regexp.MustCompile(longMethodConfigRegexpStr)
+	headerConfigRegexp        = regexp.MustCompile(headerConfigRegexpStr)
+	messageConfigRegexp       = regexp.MustCompile(messageConfigRegexpStr)
+	headerMessageConfigRegexp = regexp.MustCompile(headerMessageConfigRegexpStr)
+)
+
+// Turn "service/method{h;m}" into "service", "method", "{h;m}".
+func parseMethodConfigAndSuffix(c string) (service, method, suffix string, _ error) {
+	// Regexp result:
+	//
+	// in:  "p.s/m{h:123,m:123}",
+	// out: []string{"p.s/m{h:123,m:123}", "p.s", "m", "{h:123,m:123}"},
+	match := longMethodConfigRegexp.FindStringSubmatch(c)
+	if match == nil {
+		return "", "", "", fmt.Errorf("%q contains invalid substring", c)
+	}
+	service = match[1]
+	method = match[2]
+	suffix = match[3]
+	return
+}
+
+// Turn "{h:123;m:345}" into 123, 345.
+//
+// Return maxUInt if length is unspecified.
+func parseHeaderMessageLengthConfig(c string) (hdrLenStr, msgLenStr uint64, err error) {
+	if c == "" {
+		return maxUInt, maxUInt, nil
+	}
+	// Header config only.
+	if match := headerConfigRegexp.FindStringSubmatch(c); match != nil {
+		if s := match[1]; s != "" {
+			hdrLenStr, err = strconv.ParseUint(s, 10, 64)
+			if err != nil {
+				return 0, 0, fmt.Errorf("failed to convert %q to uint", s)
+			}
+			return hdrLenStr, 0, nil
+		}
+		return maxUInt, 0, nil
+	}
+
+	// Message config only.
+	if match := messageConfigRegexp.FindStringSubmatch(c); match != nil {
+		if s := match[1]; s != "" {
+			msgLenStr, err = strconv.ParseUint(s, 10, 64)
+			if err != nil {
+				return 0, 0, fmt.Errorf("failed to convert %q to uint", s)
+			}
+			return 0, msgLenStr, nil
+		}
+		return 0, maxUInt, nil
+	}
+
+	// Header and message config both.
+	if match := headerMessageConfigRegexp.FindStringSubmatch(c); match != nil {
+		// Both hdr and msg are specified, but one or two of them might be empty.
+		hdrLenStr = maxUInt
+		msgLenStr = maxUInt
+		if s := match[1]; s != "" {
+			hdrLenStr, err = strconv.ParseUint(s, 10, 64)
+			if err != nil {
+				return 0, 0, fmt.Errorf("failed to convert %q to uint", s)
+			}
+		}
+		if s := match[2]; s != "" {
+			msgLenStr, err = strconv.ParseUint(s, 10, 64)
+			if err != nil {
+				return 0, 0, fmt.Errorf("failed to convert %q to uint", s)
+			}
+		}
+		return hdrLenStr, msgLenStr, nil
+	}
+	return 0, 0, fmt.Errorf("%q contains invalid substring", c)
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/internal/binarylog/method_logger.go b/demo_test/vendor/google.golang.org/grpc/internal/binarylog/method_logger.go
new file mode 100644
index 0000000..160f6e8
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/internal/binarylog/method_logger.go
@@ -0,0 +1,423 @@
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package binarylog
+
+import (
+	"net"
+	"strings"
+	"sync/atomic"
+	"time"
+
+	"github.com/golang/protobuf/proto"
+	"github.com/golang/protobuf/ptypes"
+	pb "google.golang.org/grpc/binarylog/grpc_binarylog_v1"
+	"google.golang.org/grpc/grpclog"
+	"google.golang.org/grpc/metadata"
+	"google.golang.org/grpc/status"
+)
+
+type callIDGenerator struct {
+	id uint64
+}
+
+func (g *callIDGenerator) next() uint64 {
+	id := atomic.AddUint64(&g.id, 1)
+	return id
+}
+
+// reset is for testing only, and doesn't need to be thread safe.
+func (g *callIDGenerator) reset() {
+	g.id = 0
+}
+
+var idGen callIDGenerator
+
+// MethodLogger is the sub-logger for each method.
+type MethodLogger struct {
+	headerMaxLen, messageMaxLen uint64
+
+	callID          uint64
+	idWithinCallGen *callIDGenerator
+
+	sink Sink // TODO(blog): make this plugable.
+}
+
+func newMethodLogger(h, m uint64) *MethodLogger {
+	return &MethodLogger{
+		headerMaxLen:  h,
+		messageMaxLen: m,
+
+		callID:          idGen.next(),
+		idWithinCallGen: &callIDGenerator{},
+
+		sink: defaultSink, // TODO(blog): make it plugable.
+	}
+}
+
+// Log creates a proto binary log entry, and logs it to the sink.
+func (ml *MethodLogger) Log(c LogEntryConfig) {
+	m := c.toProto()
+	timestamp, _ := ptypes.TimestampProto(time.Now())
+	m.Timestamp = timestamp
+	m.CallId = ml.callID
+	m.SequenceIdWithinCall = ml.idWithinCallGen.next()
+
+	switch pay := m.Payload.(type) {
+	case *pb.GrpcLogEntry_ClientHeader:
+		m.PayloadTruncated = ml.truncateMetadata(pay.ClientHeader.GetMetadata())
+	case *pb.GrpcLogEntry_ServerHeader:
+		m.PayloadTruncated = ml.truncateMetadata(pay.ServerHeader.GetMetadata())
+	case *pb.GrpcLogEntry_Message:
+		m.PayloadTruncated = ml.truncateMessage(pay.Message)
+	}
+
+	ml.sink.Write(m)
+}
+
+func (ml *MethodLogger) truncateMetadata(mdPb *pb.Metadata) (truncated bool) {
+	if ml.headerMaxLen == maxUInt {
+		return false
+	}
+	var (
+		bytesLimit = ml.headerMaxLen
+		index      int
+	)
+	// At the end of the loop, index will be the first entry where the total
+	// size is greater than the limit:
+	//
+	// len(entry[:index]) <= ml.hdr && len(entry[:index+1]) > ml.hdr.
+	for ; index < len(mdPb.Entry); index++ {
+		entry := mdPb.Entry[index]
+		if entry.Key == "grpc-trace-bin" {
+			// "grpc-trace-bin" is a special key. It's kept in the log entry,
+			// but not counted towards the size limit.
+			continue
+		}
+		currentEntryLen := uint64(len(entry.Value))
+		if currentEntryLen > bytesLimit {
+			break
+		}
+		bytesLimit -= currentEntryLen
+	}
+	truncated = index < len(mdPb.Entry)
+	mdPb.Entry = mdPb.Entry[:index]
+	return truncated
+}
+
+func (ml *MethodLogger) truncateMessage(msgPb *pb.Message) (truncated bool) {
+	if ml.messageMaxLen == maxUInt {
+		return false
+	}
+	if ml.messageMaxLen >= uint64(len(msgPb.Data)) {
+		return false
+	}
+	msgPb.Data = msgPb.Data[:ml.messageMaxLen]
+	return true
+}
+
+// LogEntryConfig represents the configuration for binary log entry.
+type LogEntryConfig interface {
+	toProto() *pb.GrpcLogEntry
+}
+
+// ClientHeader configs the binary log entry to be a ClientHeader entry.
+type ClientHeader struct {
+	OnClientSide bool
+	Header       metadata.MD
+	MethodName   string
+	Authority    string
+	Timeout      time.Duration
+	// PeerAddr is required only when it's on server side.
+	PeerAddr net.Addr
+}
+
+func (c *ClientHeader) toProto() *pb.GrpcLogEntry {
+	// This function doesn't need to set all the fields (e.g. seq ID). The Log
+	// function will set the fields when necessary.
+	clientHeader := &pb.ClientHeader{
+		Metadata:   mdToMetadataProto(c.Header),
+		MethodName: c.MethodName,
+		Authority:  c.Authority,
+	}
+	if c.Timeout > 0 {
+		clientHeader.Timeout = ptypes.DurationProto(c.Timeout)
+	}
+	ret := &pb.GrpcLogEntry{
+		Type: pb.GrpcLogEntry_EVENT_TYPE_CLIENT_HEADER,
+		Payload: &pb.GrpcLogEntry_ClientHeader{
+			ClientHeader: clientHeader,
+		},
+	}
+	if c.OnClientSide {
+		ret.Logger = pb.GrpcLogEntry_LOGGER_CLIENT
+	} else {
+		ret.Logger = pb.GrpcLogEntry_LOGGER_SERVER
+	}
+	if c.PeerAddr != nil {
+		ret.Peer = addrToProto(c.PeerAddr)
+	}
+	return ret
+}
+
+// ServerHeader configs the binary log entry to be a ServerHeader entry.
+type ServerHeader struct {
+	OnClientSide bool
+	Header       metadata.MD
+	// PeerAddr is required only when it's on client side.
+	PeerAddr net.Addr
+}
+
+func (c *ServerHeader) toProto() *pb.GrpcLogEntry {
+	ret := &pb.GrpcLogEntry{
+		Type: pb.GrpcLogEntry_EVENT_TYPE_SERVER_HEADER,
+		Payload: &pb.GrpcLogEntry_ServerHeader{
+			ServerHeader: &pb.ServerHeader{
+				Metadata: mdToMetadataProto(c.Header),
+			},
+		},
+	}
+	if c.OnClientSide {
+		ret.Logger = pb.GrpcLogEntry_LOGGER_CLIENT
+	} else {
+		ret.Logger = pb.GrpcLogEntry_LOGGER_SERVER
+	}
+	if c.PeerAddr != nil {
+		ret.Peer = addrToProto(c.PeerAddr)
+	}
+	return ret
+}
+
+// ClientMessage configs the binary log entry to be a ClientMessage entry.
+type ClientMessage struct {
+	OnClientSide bool
+	// Message can be a proto.Message or []byte. Other messages formats are not
+	// supported.
+	Message interface{}
+}
+
+func (c *ClientMessage) toProto() *pb.GrpcLogEntry {
+	var (
+		data []byte
+		err  error
+	)
+	if m, ok := c.Message.(proto.Message); ok {
+		data, err = proto.Marshal(m)
+		if err != nil {
+			grpclog.Infof("binarylogging: failed to marshal proto message: %v", err)
+		}
+	} else if b, ok := c.Message.([]byte); ok {
+		data = b
+	} else {
+		grpclog.Infof("binarylogging: message to log is neither proto.message nor []byte")
+	}
+	ret := &pb.GrpcLogEntry{
+		Type: pb.GrpcLogEntry_EVENT_TYPE_CLIENT_MESSAGE,
+		Payload: &pb.GrpcLogEntry_Message{
+			Message: &pb.Message{
+				Length: uint32(len(data)),
+				Data:   data,
+			},
+		},
+	}
+	if c.OnClientSide {
+		ret.Logger = pb.GrpcLogEntry_LOGGER_CLIENT
+	} else {
+		ret.Logger = pb.GrpcLogEntry_LOGGER_SERVER
+	}
+	return ret
+}
+
+// ServerMessage configs the binary log entry to be a ServerMessage entry.
+type ServerMessage struct {
+	OnClientSide bool
+	// Message can be a proto.Message or []byte. Other messages formats are not
+	// supported.
+	Message interface{}
+}
+
+func (c *ServerMessage) toProto() *pb.GrpcLogEntry {
+	var (
+		data []byte
+		err  error
+	)
+	if m, ok := c.Message.(proto.Message); ok {
+		data, err = proto.Marshal(m)
+		if err != nil {
+			grpclog.Infof("binarylogging: failed to marshal proto message: %v", err)
+		}
+	} else if b, ok := c.Message.([]byte); ok {
+		data = b
+	} else {
+		grpclog.Infof("binarylogging: message to log is neither proto.message nor []byte")
+	}
+	ret := &pb.GrpcLogEntry{
+		Type: pb.GrpcLogEntry_EVENT_TYPE_SERVER_MESSAGE,
+		Payload: &pb.GrpcLogEntry_Message{
+			Message: &pb.Message{
+				Length: uint32(len(data)),
+				Data:   data,
+			},
+		},
+	}
+	if c.OnClientSide {
+		ret.Logger = pb.GrpcLogEntry_LOGGER_CLIENT
+	} else {
+		ret.Logger = pb.GrpcLogEntry_LOGGER_SERVER
+	}
+	return ret
+}
+
+// ClientHalfClose configs the binary log entry to be a ClientHalfClose entry.
+type ClientHalfClose struct {
+	OnClientSide bool
+}
+
+func (c *ClientHalfClose) toProto() *pb.GrpcLogEntry {
+	ret := &pb.GrpcLogEntry{
+		Type:    pb.GrpcLogEntry_EVENT_TYPE_CLIENT_HALF_CLOSE,
+		Payload: nil, // No payload here.
+	}
+	if c.OnClientSide {
+		ret.Logger = pb.GrpcLogEntry_LOGGER_CLIENT
+	} else {
+		ret.Logger = pb.GrpcLogEntry_LOGGER_SERVER
+	}
+	return ret
+}
+
+// ServerTrailer configs the binary log entry to be a ServerTrailer entry.
+type ServerTrailer struct {
+	OnClientSide bool
+	Trailer      metadata.MD
+	// Err is the status error.
+	Err error
+	// PeerAddr is required only when it's on client side and the RPC is trailer
+	// only.
+	PeerAddr net.Addr
+}
+
+func (c *ServerTrailer) toProto() *pb.GrpcLogEntry {
+	st, ok := status.FromError(c.Err)
+	if !ok {
+		grpclog.Info("binarylogging: error in trailer is not a status error")
+	}
+	var (
+		detailsBytes []byte
+		err          error
+	)
+	stProto := st.Proto()
+	if stProto != nil && len(stProto.Details) != 0 {
+		detailsBytes, err = proto.Marshal(stProto)
+		if err != nil {
+			grpclog.Infof("binarylogging: failed to marshal status proto: %v", err)
+		}
+	}
+	ret := &pb.GrpcLogEntry{
+		Type: pb.GrpcLogEntry_EVENT_TYPE_SERVER_TRAILER,
+		Payload: &pb.GrpcLogEntry_Trailer{
+			Trailer: &pb.Trailer{
+				Metadata:      mdToMetadataProto(c.Trailer),
+				StatusCode:    uint32(st.Code()),
+				StatusMessage: st.Message(),
+				StatusDetails: detailsBytes,
+			},
+		},
+	}
+	if c.OnClientSide {
+		ret.Logger = pb.GrpcLogEntry_LOGGER_CLIENT
+	} else {
+		ret.Logger = pb.GrpcLogEntry_LOGGER_SERVER
+	}
+	if c.PeerAddr != nil {
+		ret.Peer = addrToProto(c.PeerAddr)
+	}
+	return ret
+}
+
+// Cancel configs the binary log entry to be a Cancel entry.
+type Cancel struct {
+	OnClientSide bool
+}
+
+func (c *Cancel) toProto() *pb.GrpcLogEntry {
+	ret := &pb.GrpcLogEntry{
+		Type:    pb.GrpcLogEntry_EVENT_TYPE_CANCEL,
+		Payload: nil,
+	}
+	if c.OnClientSide {
+		ret.Logger = pb.GrpcLogEntry_LOGGER_CLIENT
+	} else {
+		ret.Logger = pb.GrpcLogEntry_LOGGER_SERVER
+	}
+	return ret
+}
+
+// metadataKeyOmit returns whether the metadata entry with this key should be
+// omitted.
+func metadataKeyOmit(key string) bool {
+	switch key {
+	case "lb-token", ":path", ":authority", "content-encoding", "content-type", "user-agent", "te":
+		return true
+	case "grpc-trace-bin": // grpc-trace-bin is special because it's visiable to users.
+		return false
+	}
+	return strings.HasPrefix(key, "grpc-")
+}
+
+func mdToMetadataProto(md metadata.MD) *pb.Metadata {
+	ret := &pb.Metadata{}
+	for k, vv := range md {
+		if metadataKeyOmit(k) {
+			continue
+		}
+		for _, v := range vv {
+			ret.Entry = append(ret.Entry,
+				&pb.MetadataEntry{
+					Key:   k,
+					Value: []byte(v),
+				},
+			)
+		}
+	}
+	return ret
+}
+
+func addrToProto(addr net.Addr) *pb.Address {
+	ret := &pb.Address{}
+	switch a := addr.(type) {
+	case *net.TCPAddr:
+		if a.IP.To4() != nil {
+			ret.Type = pb.Address_TYPE_IPV4
+		} else if a.IP.To16() != nil {
+			ret.Type = pb.Address_TYPE_IPV6
+		} else {
+			ret.Type = pb.Address_TYPE_UNKNOWN
+			// Do not set address and port fields.
+			break
+		}
+		ret.Address = a.IP.String()
+		ret.IpPort = uint32(a.Port)
+	case *net.UnixAddr:
+		ret.Type = pb.Address_TYPE_UNIX
+		ret.Address = a.String()
+	default:
+		ret.Type = pb.Address_TYPE_UNKNOWN
+	}
+	return ret
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/internal/binarylog/regenerate.sh b/demo_test/vendor/google.golang.org/grpc/internal/binarylog/regenerate.sh
new file mode 100644
index 0000000..113d40c
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/internal/binarylog/regenerate.sh
@@ -0,0 +1,33 @@
+#!/bin/bash
+# Copyright 2018 gRPC authors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+set -eux -o pipefail
+
+TMP=$(mktemp -d)
+
+function finish {
+  rm -rf "$TMP"
+}
+trap finish EXIT
+
+pushd "$TMP"
+mkdir -p grpc/binarylog/grpc_binarylog_v1
+curl https://raw.githubusercontent.com/grpc/grpc-proto/master/grpc/binlog/v1/binarylog.proto > grpc/binarylog/grpc_binarylog_v1/binarylog.proto
+
+protoc --go_out=plugins=grpc,paths=source_relative:. -I. grpc/binarylog/grpc_binarylog_v1/*.proto
+popd
+rm -f ./grpc_binarylog_v1/*.pb.go
+cp "$TMP"/grpc/binarylog/grpc_binarylog_v1/*.pb.go ../../binarylog/grpc_binarylog_v1/
+
diff --git a/demo_test/vendor/google.golang.org/grpc/internal/binarylog/sink.go b/demo_test/vendor/google.golang.org/grpc/internal/binarylog/sink.go
new file mode 100644
index 0000000..a2e7c34
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/internal/binarylog/sink.go
@@ -0,0 +1,162 @@
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package binarylog
+
+import (
+	"bufio"
+	"encoding/binary"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"sync"
+	"time"
+
+	"github.com/golang/protobuf/proto"
+	pb "google.golang.org/grpc/binarylog/grpc_binarylog_v1"
+	"google.golang.org/grpc/grpclog"
+)
+
+var (
+	defaultSink Sink = &noopSink{} // TODO(blog): change this default (file in /tmp).
+)
+
+// SetDefaultSink sets the sink where binary logs will be written to.
+//
+// Not thread safe. Only set during initialization.
+func SetDefaultSink(s Sink) {
+	if defaultSink != nil {
+		defaultSink.Close()
+	}
+	defaultSink = s
+}
+
+// Sink writes log entry into the binary log sink.
+type Sink interface {
+	// Write will be called to write the log entry into the sink.
+	//
+	// It should be thread-safe so it can be called in parallel.
+	Write(*pb.GrpcLogEntry) error
+	// Close will be called when the Sink is replaced by a new Sink.
+	Close() error
+}
+
+type noopSink struct{}
+
+func (ns *noopSink) Write(*pb.GrpcLogEntry) error { return nil }
+func (ns *noopSink) Close() error                 { return nil }
+
+// newWriterSink creates a binary log sink with the given writer.
+//
+// Write() marshals the proto message and writes it to the given writer. Each
+// message is prefixed with a 4 byte big endian unsigned integer as the length.
+//
+// No buffer is done, Close() doesn't try to close the writer.
+func newWriterSink(w io.Writer) *writerSink {
+	return &writerSink{out: w}
+}
+
+type writerSink struct {
+	out io.Writer
+}
+
+func (ws *writerSink) Write(e *pb.GrpcLogEntry) error {
+	b, err := proto.Marshal(e)
+	if err != nil {
+		grpclog.Infof("binary logging: failed to marshal proto message: %v", err)
+	}
+	hdr := make([]byte, 4)
+	binary.BigEndian.PutUint32(hdr, uint32(len(b)))
+	if _, err := ws.out.Write(hdr); err != nil {
+		return err
+	}
+	if _, err := ws.out.Write(b); err != nil {
+		return err
+	}
+	return nil
+}
+
+func (ws *writerSink) Close() error { return nil }
+
+type bufWriteCloserSink struct {
+	mu     sync.Mutex
+	closer io.Closer
+	out    *writerSink   // out is built on buf.
+	buf    *bufio.Writer // buf is kept for flush.
+
+	writeStartOnce sync.Once
+	writeTicker    *time.Ticker
+}
+
+func (fs *bufWriteCloserSink) Write(e *pb.GrpcLogEntry) error {
+	// Start the write loop when Write is called.
+	fs.writeStartOnce.Do(fs.startFlushGoroutine)
+	fs.mu.Lock()
+	if err := fs.out.Write(e); err != nil {
+		fs.mu.Unlock()
+		return err
+	}
+	fs.mu.Unlock()
+	return nil
+}
+
+const (
+	bufFlushDuration = 60 * time.Second
+)
+
+func (fs *bufWriteCloserSink) startFlushGoroutine() {
+	fs.writeTicker = time.NewTicker(bufFlushDuration)
+	go func() {
+		for range fs.writeTicker.C {
+			fs.mu.Lock()
+			fs.buf.Flush()
+			fs.mu.Unlock()
+		}
+	}()
+}
+
+func (fs *bufWriteCloserSink) Close() error {
+	if fs.writeTicker != nil {
+		fs.writeTicker.Stop()
+	}
+	fs.mu.Lock()
+	fs.buf.Flush()
+	fs.closer.Close()
+	fs.out.Close()
+	fs.mu.Unlock()
+	return nil
+}
+
+func newBufWriteCloserSink(o io.WriteCloser) Sink {
+	bufW := bufio.NewWriter(o)
+	return &bufWriteCloserSink{
+		closer: o,
+		out:    newWriterSink(bufW),
+		buf:    bufW,
+	}
+}
+
+// NewTempFileSink creates a temp file and returns a Sink that writes to this
+// file.
+func NewTempFileSink() (Sink, error) {
+	tempFile, err := ioutil.TempFile("/tmp", "grpcgo_binarylog_*.txt")
+	if err != nil {
+		return nil, fmt.Errorf("failed to create temp file: %v", err)
+	}
+	return newBufWriteCloserSink(tempFile), nil
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/internal/binarylog/util.go b/demo_test/vendor/google.golang.org/grpc/internal/binarylog/util.go
new file mode 100644
index 0000000..15dc780
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/internal/binarylog/util.go
@@ -0,0 +1,41 @@
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package binarylog
+
+import (
+	"errors"
+	"strings"
+)
+
+// parseMethodName splits service and method from the input. It expects format
+// "/service/method".
+//
+// TODO: move to internal/grpcutil.
+func parseMethodName(methodName string) (service, method string, _ error) {
+	if !strings.HasPrefix(methodName, "/") {
+		return "", "", errors.New("invalid method name: should start with /")
+	}
+	methodName = methodName[1:]
+
+	pos := strings.LastIndex(methodName, "/")
+	if pos < 0 {
+		return "", "", errors.New("invalid method name: suffix /method is missing")
+	}
+	return methodName[:pos], methodName[pos+1:], nil
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/internal/buffer/unbounded.go b/demo_test/vendor/google.golang.org/grpc/internal/buffer/unbounded.go
new file mode 100644
index 0000000..9f6a0c1
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/internal/buffer/unbounded.go
@@ -0,0 +1,85 @@
+/*
+ * Copyright 2019 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+// Package buffer provides an implementation of an unbounded buffer.
+package buffer
+
+import "sync"
+
+// Unbounded is an implementation of an unbounded buffer which does not use
+// extra goroutines. This is typically used for passing updates from one entity
+// to another within gRPC.
+//
+// All methods on this type are thread-safe and don't block on anything except
+// the underlying mutex used for synchronization.
+//
+// Unbounded supports values of any type to be stored in it by using a channel
+// of `interface{}`. This means that a call to Put() incurs an extra memory
+// allocation, and also that users need a type assertion while reading. For
+// performance critical code paths, using Unbounded is strongly discouraged and
+// defining a new type specific implementation of this buffer is preferred. See
+// internal/transport/transport.go for an example of this.
+type Unbounded struct {
+	c       chan interface{}
+	mu      sync.Mutex
+	backlog []interface{}
+}
+
+// NewUnbounded returns a new instance of Unbounded.
+func NewUnbounded() *Unbounded {
+	return &Unbounded{c: make(chan interface{}, 1)}
+}
+
+// Put adds t to the unbounded buffer.
+func (b *Unbounded) Put(t interface{}) {
+	b.mu.Lock()
+	if len(b.backlog) == 0 {
+		select {
+		case b.c <- t:
+			b.mu.Unlock()
+			return
+		default:
+		}
+	}
+	b.backlog = append(b.backlog, t)
+	b.mu.Unlock()
+}
+
+// Load sends the earliest buffered data, if any, onto the read channel
+// returned by Get(). Users are expected to call this every time they read a
+// value from the read channel.
+func (b *Unbounded) Load() {
+	b.mu.Lock()
+	if len(b.backlog) > 0 {
+		select {
+		case b.c <- b.backlog[0]:
+			b.backlog[0] = nil
+			b.backlog = b.backlog[1:]
+		default:
+		}
+	}
+	b.mu.Unlock()
+}
+
+// Get returns a read channel on which values added to the buffer, via Put(),
+// are sent on.
+//
+// Upon reading a value from this channel, users are expected to call Load() to
+// send the next buffered value onto the channel if there is any.
+func (b *Unbounded) Get() <-chan interface{} {
+	return b.c
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/internal/channelz/funcs.go b/demo_test/vendor/google.golang.org/grpc/internal/channelz/funcs.go
new file mode 100644
index 0000000..e4252e5
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/internal/channelz/funcs.go
@@ -0,0 +1,739 @@
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+// Package channelz defines APIs for enabling channelz service, entry
+// registration/deletion, and accessing channelz data. It also defines channelz
+// metric struct formats.
+//
+// All APIs in this package are experimental.
+package channelz
+
+import (
+	"fmt"
+	"sort"
+	"sync"
+	"sync/atomic"
+	"time"
+
+	"google.golang.org/grpc/internal/grpclog"
+)
+
+const (
+	defaultMaxTraceEntry int32 = 30
+)
+
+var (
+	db    dbWrapper
+	idGen idGenerator
+	// EntryPerPage defines the number of channelz entries to be shown on a web page.
+	EntryPerPage  = int64(50)
+	curState      int32
+	maxTraceEntry = defaultMaxTraceEntry
+)
+
+// TurnOn turns on channelz data collection.
+func TurnOn() {
+	if !IsOn() {
+		NewChannelzStorage()
+		atomic.StoreInt32(&curState, 1)
+	}
+}
+
+// IsOn returns whether channelz data collection is on.
+func IsOn() bool {
+	return atomic.CompareAndSwapInt32(&curState, 1, 1)
+}
+
+// SetMaxTraceEntry sets maximum number of trace entry per entity (i.e. channel/subchannel).
+// Setting it to 0 will disable channel tracing.
+func SetMaxTraceEntry(i int32) {
+	atomic.StoreInt32(&maxTraceEntry, i)
+}
+
+// ResetMaxTraceEntryToDefault resets the maximum number of trace entry per entity to default.
+func ResetMaxTraceEntryToDefault() {
+	atomic.StoreInt32(&maxTraceEntry, defaultMaxTraceEntry)
+}
+
+func getMaxTraceEntry() int {
+	i := atomic.LoadInt32(&maxTraceEntry)
+	return int(i)
+}
+
+// dbWarpper wraps around a reference to internal channelz data storage, and
+// provide synchronized functionality to set and get the reference.
+type dbWrapper struct {
+	mu sync.RWMutex
+	DB *channelMap
+}
+
+func (d *dbWrapper) set(db *channelMap) {
+	d.mu.Lock()
+	d.DB = db
+	d.mu.Unlock()
+}
+
+func (d *dbWrapper) get() *channelMap {
+	d.mu.RLock()
+	defer d.mu.RUnlock()
+	return d.DB
+}
+
+// NewChannelzStorage initializes channelz data storage and id generator.
+//
+// This function returns a cleanup function to wait for all channelz state to be reset by the
+// grpc goroutines when those entities get closed. By using this cleanup function, we make sure tests
+// don't mess up each other, i.e. lingering goroutine from previous test doing entity removal happen
+// to remove some entity just register by the new test, since the id space is the same.
+//
+// Note: This function is exported for testing purpose only. User should not call
+// it in most cases.
+func NewChannelzStorage() (cleanup func() error) {
+	db.set(&channelMap{
+		topLevelChannels: make(map[int64]struct{}),
+		channels:         make(map[int64]*channel),
+		listenSockets:    make(map[int64]*listenSocket),
+		normalSockets:    make(map[int64]*normalSocket),
+		servers:          make(map[int64]*server),
+		subChannels:      make(map[int64]*subChannel),
+	})
+	idGen.reset()
+	return func() error {
+		var err error
+		cm := db.get()
+		if cm == nil {
+			return nil
+		}
+		for i := 0; i < 1000; i++ {
+			cm.mu.Lock()
+			if len(cm.topLevelChannels) == 0 && len(cm.servers) == 0 && len(cm.channels) == 0 && len(cm.subChannels) == 0 && len(cm.listenSockets) == 0 && len(cm.normalSockets) == 0 {
+				cm.mu.Unlock()
+				// all things stored in the channelz map have been cleared.
+				return nil
+			}
+			cm.mu.Unlock()
+			time.Sleep(10 * time.Millisecond)
+		}
+
+		cm.mu.Lock()
+		err = fmt.Errorf("after 10s the channelz map has not been cleaned up yet, topchannels: %d, servers: %d, channels: %d, subchannels: %d, listen sockets: %d, normal sockets: %d", len(cm.topLevelChannels), len(cm.servers), len(cm.channels), len(cm.subChannels), len(cm.listenSockets), len(cm.normalSockets))
+		cm.mu.Unlock()
+		return err
+	}
+}
+
+// GetTopChannels returns a slice of top channel's ChannelMetric, along with a
+// boolean indicating whether there's more top channels to be queried for.
+//
+// The arg id specifies that only top channel with id at or above it will be included
+// in the result. The returned slice is up to a length of the arg maxResults or
+// EntryPerPage if maxResults is zero, and is sorted in ascending id order.
+func GetTopChannels(id int64, maxResults int64) ([]*ChannelMetric, bool) {
+	return db.get().GetTopChannels(id, maxResults)
+}
+
+// GetServers returns a slice of server's ServerMetric, along with a
+// boolean indicating whether there's more servers to be queried for.
+//
+// The arg id specifies that only server with id at or above it will be included
+// in the result. The returned slice is up to a length of the arg maxResults or
+// EntryPerPage if maxResults is zero, and is sorted in ascending id order.
+func GetServers(id int64, maxResults int64) ([]*ServerMetric, bool) {
+	return db.get().GetServers(id, maxResults)
+}
+
+// GetServerSockets returns a slice of server's (identified by id) normal socket's
+// SocketMetric, along with a boolean indicating whether there's more sockets to
+// be queried for.
+//
+// The arg startID specifies that only sockets with id at or above it will be
+// included in the result. The returned slice is up to a length of the arg maxResults
+// or EntryPerPage if maxResults is zero, and is sorted in ascending id order.
+func GetServerSockets(id int64, startID int64, maxResults int64) ([]*SocketMetric, bool) {
+	return db.get().GetServerSockets(id, startID, maxResults)
+}
+
+// GetChannel returns the ChannelMetric for the channel (identified by id).
+func GetChannel(id int64) *ChannelMetric {
+	return db.get().GetChannel(id)
+}
+
+// GetSubChannel returns the SubChannelMetric for the subchannel (identified by id).
+func GetSubChannel(id int64) *SubChannelMetric {
+	return db.get().GetSubChannel(id)
+}
+
+// GetSocket returns the SocketInternalMetric for the socket (identified by id).
+func GetSocket(id int64) *SocketMetric {
+	return db.get().GetSocket(id)
+}
+
+// GetServer returns the ServerMetric for the server (identified by id).
+func GetServer(id int64) *ServerMetric {
+	return db.get().GetServer(id)
+}
+
+// RegisterChannel registers the given channel c in channelz database with ref
+// as its reference name, and add it to the child list of its parent (identified
+// by pid). pid = 0 means no parent. It returns the unique channelz tracking id
+// assigned to this channel.
+func RegisterChannel(c Channel, pid int64, ref string) int64 {
+	id := idGen.genID()
+	cn := &channel{
+		refName:     ref,
+		c:           c,
+		subChans:    make(map[int64]string),
+		nestedChans: make(map[int64]string),
+		id:          id,
+		pid:         pid,
+		trace:       &channelTrace{createdTime: time.Now(), events: make([]*TraceEvent, 0, getMaxTraceEntry())},
+	}
+	if pid == 0 {
+		db.get().addChannel(id, cn, true, pid, ref)
+	} else {
+		db.get().addChannel(id, cn, false, pid, ref)
+	}
+	return id
+}
+
+// RegisterSubChannel registers the given channel c in channelz database with ref
+// as its reference name, and add it to the child list of its parent (identified
+// by pid). It returns the unique channelz tracking id assigned to this subchannel.
+func RegisterSubChannel(c Channel, pid int64, ref string) int64 {
+	if pid == 0 {
+		grpclog.ErrorDepth(0, "a SubChannel's parent id cannot be 0")
+		return 0
+	}
+	id := idGen.genID()
+	sc := &subChannel{
+		refName: ref,
+		c:       c,
+		sockets: make(map[int64]string),
+		id:      id,
+		pid:     pid,
+		trace:   &channelTrace{createdTime: time.Now(), events: make([]*TraceEvent, 0, getMaxTraceEntry())},
+	}
+	db.get().addSubChannel(id, sc, pid, ref)
+	return id
+}
+
+// RegisterServer registers the given server s in channelz database. It returns
+// the unique channelz tracking id assigned to this server.
+func RegisterServer(s Server, ref string) int64 {
+	id := idGen.genID()
+	svr := &server{
+		refName:       ref,
+		s:             s,
+		sockets:       make(map[int64]string),
+		listenSockets: make(map[int64]string),
+		id:            id,
+	}
+	db.get().addServer(id, svr)
+	return id
+}
+
+// RegisterListenSocket registers the given listen socket s in channelz database
+// with ref as its reference name, and add it to the child list of its parent
+// (identified by pid). It returns the unique channelz tracking id assigned to
+// this listen socket.
+func RegisterListenSocket(s Socket, pid int64, ref string) int64 {
+	if pid == 0 {
+		grpclog.ErrorDepth(0, "a ListenSocket's parent id cannot be 0")
+		return 0
+	}
+	id := idGen.genID()
+	ls := &listenSocket{refName: ref, s: s, id: id, pid: pid}
+	db.get().addListenSocket(id, ls, pid, ref)
+	return id
+}
+
+// RegisterNormalSocket registers the given normal socket s in channelz database
+// with ref as its reference name, and add it to the child list of its parent
+// (identified by pid). It returns the unique channelz tracking id assigned to
+// this normal socket.
+func RegisterNormalSocket(s Socket, pid int64, ref string) int64 {
+	if pid == 0 {
+		grpclog.ErrorDepth(0, "a NormalSocket's parent id cannot be 0")
+		return 0
+	}
+	id := idGen.genID()
+	ns := &normalSocket{refName: ref, s: s, id: id, pid: pid}
+	db.get().addNormalSocket(id, ns, pid, ref)
+	return id
+}
+
+// RemoveEntry removes an entry with unique channelz trakcing id to be id from
+// channelz database.
+func RemoveEntry(id int64) {
+	db.get().removeEntry(id)
+}
+
+// TraceEventDesc is what the caller of AddTraceEvent should provide to describe the event to be added
+// to the channel trace.
+// The Parent field is optional. It is used for event that will be recorded in the entity's parent
+// trace also.
+type TraceEventDesc struct {
+	Desc     string
+	Severity Severity
+	Parent   *TraceEventDesc
+}
+
+// AddTraceEvent adds trace related to the entity with specified id, using the provided TraceEventDesc.
+func AddTraceEvent(id int64, depth int, desc *TraceEventDesc) {
+	for d := desc; d != nil; d = d.Parent {
+		switch d.Severity {
+		case CtUNKNOWN:
+			grpclog.InfoDepth(depth+1, d.Desc)
+		case CtINFO:
+			grpclog.InfoDepth(depth+1, d.Desc)
+		case CtWarning:
+			grpclog.WarningDepth(depth+1, d.Desc)
+		case CtError:
+			grpclog.ErrorDepth(depth+1, d.Desc)
+		}
+	}
+	if getMaxTraceEntry() == 0 {
+		return
+	}
+	db.get().traceEvent(id, desc)
+}
+
+// channelMap is the storage data structure for channelz.
+// Methods of channelMap can be divided in two two categories with respect to locking.
+// 1. Methods acquire the global lock.
+// 2. Methods that can only be called when global lock is held.
+// A second type of method need always to be called inside a first type of method.
+type channelMap struct {
+	mu               sync.RWMutex
+	topLevelChannels map[int64]struct{}
+	servers          map[int64]*server
+	channels         map[int64]*channel
+	subChannels      map[int64]*subChannel
+	listenSockets    map[int64]*listenSocket
+	normalSockets    map[int64]*normalSocket
+}
+
+func (c *channelMap) addServer(id int64, s *server) {
+	c.mu.Lock()
+	s.cm = c
+	c.servers[id] = s
+	c.mu.Unlock()
+}
+
+func (c *channelMap) addChannel(id int64, cn *channel, isTopChannel bool, pid int64, ref string) {
+	c.mu.Lock()
+	cn.cm = c
+	cn.trace.cm = c
+	c.channels[id] = cn
+	if isTopChannel {
+		c.topLevelChannels[id] = struct{}{}
+	} else {
+		c.findEntry(pid).addChild(id, cn)
+	}
+	c.mu.Unlock()
+}
+
+func (c *channelMap) addSubChannel(id int64, sc *subChannel, pid int64, ref string) {
+	c.mu.Lock()
+	sc.cm = c
+	sc.trace.cm = c
+	c.subChannels[id] = sc
+	c.findEntry(pid).addChild(id, sc)
+	c.mu.Unlock()
+}
+
+func (c *channelMap) addListenSocket(id int64, ls *listenSocket, pid int64, ref string) {
+	c.mu.Lock()
+	ls.cm = c
+	c.listenSockets[id] = ls
+	c.findEntry(pid).addChild(id, ls)
+	c.mu.Unlock()
+}
+
+func (c *channelMap) addNormalSocket(id int64, ns *normalSocket, pid int64, ref string) {
+	c.mu.Lock()
+	ns.cm = c
+	c.normalSockets[id] = ns
+	c.findEntry(pid).addChild(id, ns)
+	c.mu.Unlock()
+}
+
+// removeEntry triggers the removal of an entry, which may not indeed delete the entry, if it has to
+// wait on the deletion of its children and until no other entity's channel trace references it.
+// It may lead to a chain of entry deletion. For example, deleting the last socket of a gracefully
+// shutting down server will lead to the server being also deleted.
+func (c *channelMap) removeEntry(id int64) {
+	c.mu.Lock()
+	c.findEntry(id).triggerDelete()
+	c.mu.Unlock()
+}
+
+// c.mu must be held by the caller
+func (c *channelMap) decrTraceRefCount(id int64) {
+	e := c.findEntry(id)
+	if v, ok := e.(tracedChannel); ok {
+		v.decrTraceRefCount()
+		e.deleteSelfIfReady()
+	}
+}
+
+// c.mu must be held by the caller.
+func (c *channelMap) findEntry(id int64) entry {
+	var v entry
+	var ok bool
+	if v, ok = c.channels[id]; ok {
+		return v
+	}
+	if v, ok = c.subChannels[id]; ok {
+		return v
+	}
+	if v, ok = c.servers[id]; ok {
+		return v
+	}
+	if v, ok = c.listenSockets[id]; ok {
+		return v
+	}
+	if v, ok = c.normalSockets[id]; ok {
+		return v
+	}
+	return &dummyEntry{idNotFound: id}
+}
+
+// c.mu must be held by the caller
+// deleteEntry simply deletes an entry from the channelMap. Before calling this
+// method, caller must check this entry is ready to be deleted, i.e removeEntry()
+// has been called on it, and no children still exist.
+// Conditionals are ordered by the expected frequency of deletion of each entity
+// type, in order to optimize performance.
+func (c *channelMap) deleteEntry(id int64) {
+	var ok bool
+	if _, ok = c.normalSockets[id]; ok {
+		delete(c.normalSockets, id)
+		return
+	}
+	if _, ok = c.subChannels[id]; ok {
+		delete(c.subChannels, id)
+		return
+	}
+	if _, ok = c.channels[id]; ok {
+		delete(c.channels, id)
+		delete(c.topLevelChannels, id)
+		return
+	}
+	if _, ok = c.listenSockets[id]; ok {
+		delete(c.listenSockets, id)
+		return
+	}
+	if _, ok = c.servers[id]; ok {
+		delete(c.servers, id)
+		return
+	}
+}
+
+func (c *channelMap) traceEvent(id int64, desc *TraceEventDesc) {
+	c.mu.Lock()
+	child := c.findEntry(id)
+	childTC, ok := child.(tracedChannel)
+	if !ok {
+		c.mu.Unlock()
+		return
+	}
+	childTC.getChannelTrace().append(&TraceEvent{Desc: desc.Desc, Severity: desc.Severity, Timestamp: time.Now()})
+	if desc.Parent != nil {
+		parent := c.findEntry(child.getParentID())
+		var chanType RefChannelType
+		switch child.(type) {
+		case *channel:
+			chanType = RefChannel
+		case *subChannel:
+			chanType = RefSubChannel
+		}
+		if parentTC, ok := parent.(tracedChannel); ok {
+			parentTC.getChannelTrace().append(&TraceEvent{
+				Desc:      desc.Parent.Desc,
+				Severity:  desc.Parent.Severity,
+				Timestamp: time.Now(),
+				RefID:     id,
+				RefName:   childTC.getRefName(),
+				RefType:   chanType,
+			})
+			childTC.incrTraceRefCount()
+		}
+	}
+	c.mu.Unlock()
+}
+
+type int64Slice []int64
+
+func (s int64Slice) Len() int           { return len(s) }
+func (s int64Slice) Swap(i, j int)      { s[i], s[j] = s[j], s[i] }
+func (s int64Slice) Less(i, j int) bool { return s[i] < s[j] }
+
+func copyMap(m map[int64]string) map[int64]string {
+	n := make(map[int64]string)
+	for k, v := range m {
+		n[k] = v
+	}
+	return n
+}
+
+func min(a, b int64) int64 {
+	if a < b {
+		return a
+	}
+	return b
+}
+
+func (c *channelMap) GetTopChannels(id int64, maxResults int64) ([]*ChannelMetric, bool) {
+	if maxResults <= 0 {
+		maxResults = EntryPerPage
+	}
+	c.mu.RLock()
+	l := int64(len(c.topLevelChannels))
+	ids := make([]int64, 0, l)
+	cns := make([]*channel, 0, min(l, maxResults))
+
+	for k := range c.topLevelChannels {
+		ids = append(ids, k)
+	}
+	sort.Sort(int64Slice(ids))
+	idx := sort.Search(len(ids), func(i int) bool { return ids[i] >= id })
+	count := int64(0)
+	var end bool
+	var t []*ChannelMetric
+	for i, v := range ids[idx:] {
+		if count == maxResults {
+			break
+		}
+		if cn, ok := c.channels[v]; ok {
+			cns = append(cns, cn)
+			t = append(t, &ChannelMetric{
+				NestedChans: copyMap(cn.nestedChans),
+				SubChans:    copyMap(cn.subChans),
+			})
+			count++
+		}
+		if i == len(ids[idx:])-1 {
+			end = true
+			break
+		}
+	}
+	c.mu.RUnlock()
+	if count == 0 {
+		end = true
+	}
+
+	for i, cn := range cns {
+		t[i].ChannelData = cn.c.ChannelzMetric()
+		t[i].ID = cn.id
+		t[i].RefName = cn.refName
+		t[i].Trace = cn.trace.dumpData()
+	}
+	return t, end
+}
+
+func (c *channelMap) GetServers(id, maxResults int64) ([]*ServerMetric, bool) {
+	if maxResults <= 0 {
+		maxResults = EntryPerPage
+	}
+	c.mu.RLock()
+	l := int64(len(c.servers))
+	ids := make([]int64, 0, l)
+	ss := make([]*server, 0, min(l, maxResults))
+	for k := range c.servers {
+		ids = append(ids, k)
+	}
+	sort.Sort(int64Slice(ids))
+	idx := sort.Search(len(ids), func(i int) bool { return ids[i] >= id })
+	count := int64(0)
+	var end bool
+	var s []*ServerMetric
+	for i, v := range ids[idx:] {
+		if count == maxResults {
+			break
+		}
+		if svr, ok := c.servers[v]; ok {
+			ss = append(ss, svr)
+			s = append(s, &ServerMetric{
+				ListenSockets: copyMap(svr.listenSockets),
+			})
+			count++
+		}
+		if i == len(ids[idx:])-1 {
+			end = true
+			break
+		}
+	}
+	c.mu.RUnlock()
+	if count == 0 {
+		end = true
+	}
+
+	for i, svr := range ss {
+		s[i].ServerData = svr.s.ChannelzMetric()
+		s[i].ID = svr.id
+		s[i].RefName = svr.refName
+	}
+	return s, end
+}
+
+func (c *channelMap) GetServerSockets(id int64, startID int64, maxResults int64) ([]*SocketMetric, bool) {
+	if maxResults <= 0 {
+		maxResults = EntryPerPage
+	}
+	var svr *server
+	var ok bool
+	c.mu.RLock()
+	if svr, ok = c.servers[id]; !ok {
+		// server with id doesn't exist.
+		c.mu.RUnlock()
+		return nil, true
+	}
+	svrskts := svr.sockets
+	l := int64(len(svrskts))
+	ids := make([]int64, 0, l)
+	sks := make([]*normalSocket, 0, min(l, maxResults))
+	for k := range svrskts {
+		ids = append(ids, k)
+	}
+	sort.Sort(int64Slice(ids))
+	idx := sort.Search(len(ids), func(i int) bool { return ids[i] >= startID })
+	count := int64(0)
+	var end bool
+	for i, v := range ids[idx:] {
+		if count == maxResults {
+			break
+		}
+		if ns, ok := c.normalSockets[v]; ok {
+			sks = append(sks, ns)
+			count++
+		}
+		if i == len(ids[idx:])-1 {
+			end = true
+			break
+		}
+	}
+	c.mu.RUnlock()
+	if count == 0 {
+		end = true
+	}
+	var s []*SocketMetric
+	for _, ns := range sks {
+		sm := &SocketMetric{}
+		sm.SocketData = ns.s.ChannelzMetric()
+		sm.ID = ns.id
+		sm.RefName = ns.refName
+		s = append(s, sm)
+	}
+	return s, end
+}
+
+func (c *channelMap) GetChannel(id int64) *ChannelMetric {
+	cm := &ChannelMetric{}
+	var cn *channel
+	var ok bool
+	c.mu.RLock()
+	if cn, ok = c.channels[id]; !ok {
+		// channel with id doesn't exist.
+		c.mu.RUnlock()
+		return nil
+	}
+	cm.NestedChans = copyMap(cn.nestedChans)
+	cm.SubChans = copyMap(cn.subChans)
+	// cn.c can be set to &dummyChannel{} when deleteSelfFromMap is called. Save a copy of cn.c when
+	// holding the lock to prevent potential data race.
+	chanCopy := cn.c
+	c.mu.RUnlock()
+	cm.ChannelData = chanCopy.ChannelzMetric()
+	cm.ID = cn.id
+	cm.RefName = cn.refName
+	cm.Trace = cn.trace.dumpData()
+	return cm
+}
+
+func (c *channelMap) GetSubChannel(id int64) *SubChannelMetric {
+	cm := &SubChannelMetric{}
+	var sc *subChannel
+	var ok bool
+	c.mu.RLock()
+	if sc, ok = c.subChannels[id]; !ok {
+		// subchannel with id doesn't exist.
+		c.mu.RUnlock()
+		return nil
+	}
+	cm.Sockets = copyMap(sc.sockets)
+	// sc.c can be set to &dummyChannel{} when deleteSelfFromMap is called. Save a copy of sc.c when
+	// holding the lock to prevent potential data race.
+	chanCopy := sc.c
+	c.mu.RUnlock()
+	cm.ChannelData = chanCopy.ChannelzMetric()
+	cm.ID = sc.id
+	cm.RefName = sc.refName
+	cm.Trace = sc.trace.dumpData()
+	return cm
+}
+
+func (c *channelMap) GetSocket(id int64) *SocketMetric {
+	sm := &SocketMetric{}
+	c.mu.RLock()
+	if ls, ok := c.listenSockets[id]; ok {
+		c.mu.RUnlock()
+		sm.SocketData = ls.s.ChannelzMetric()
+		sm.ID = ls.id
+		sm.RefName = ls.refName
+		return sm
+	}
+	if ns, ok := c.normalSockets[id]; ok {
+		c.mu.RUnlock()
+		sm.SocketData = ns.s.ChannelzMetric()
+		sm.ID = ns.id
+		sm.RefName = ns.refName
+		return sm
+	}
+	c.mu.RUnlock()
+	return nil
+}
+
+func (c *channelMap) GetServer(id int64) *ServerMetric {
+	sm := &ServerMetric{}
+	var svr *server
+	var ok bool
+	c.mu.RLock()
+	if svr, ok = c.servers[id]; !ok {
+		c.mu.RUnlock()
+		return nil
+	}
+	sm.ListenSockets = copyMap(svr.listenSockets)
+	c.mu.RUnlock()
+	sm.ID = svr.id
+	sm.RefName = svr.refName
+	sm.ServerData = svr.s.ChannelzMetric()
+	return sm
+}
+
+type idGenerator struct {
+	id int64
+}
+
+func (i *idGenerator) reset() {
+	atomic.StoreInt64(&i.id, 0)
+}
+
+func (i *idGenerator) genID() int64 {
+	return atomic.AddInt64(&i.id, 1)
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/internal/channelz/logging.go b/demo_test/vendor/google.golang.org/grpc/internal/channelz/logging.go
new file mode 100644
index 0000000..59c7bed
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/internal/channelz/logging.go
@@ -0,0 +1,100 @@
+/*
+ *
+ * Copyright 2020 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package channelz
+
+import (
+	"fmt"
+
+	"google.golang.org/grpc/internal/grpclog"
+)
+
+// Info logs through grpclog.Info and adds a trace event if channelz is on.
+func Info(id int64, args ...interface{}) {
+	if IsOn() {
+		AddTraceEvent(id, 1, &TraceEventDesc{
+			Desc:     fmt.Sprint(args...),
+			Severity: CtINFO,
+		})
+	} else {
+		grpclog.InfoDepth(1, args...)
+	}
+}
+
+// Infof logs through grpclog.Infof and adds a trace event if channelz is on.
+func Infof(id int64, format string, args ...interface{}) {
+	msg := fmt.Sprintf(format, args...)
+	if IsOn() {
+		AddTraceEvent(id, 1, &TraceEventDesc{
+			Desc:     msg,
+			Severity: CtINFO,
+		})
+	} else {
+		grpclog.InfoDepth(1, msg)
+	}
+}
+
+// Warning logs through grpclog.Warning and adds a trace event if channelz is on.
+func Warning(id int64, args ...interface{}) {
+	if IsOn() {
+		AddTraceEvent(id, 1, &TraceEventDesc{
+			Desc:     fmt.Sprint(args...),
+			Severity: CtWarning,
+		})
+	} else {
+		grpclog.WarningDepth(1, args...)
+	}
+}
+
+// Warningf logs through grpclog.Warningf and adds a trace event if channelz is on.
+func Warningf(id int64, format string, args ...interface{}) {
+	msg := fmt.Sprintf(format, args...)
+	if IsOn() {
+		AddTraceEvent(id, 1, &TraceEventDesc{
+			Desc:     msg,
+			Severity: CtWarning,
+		})
+	} else {
+		grpclog.WarningDepth(1, msg)
+	}
+}
+
+// Error logs through grpclog.Error and adds a trace event if channelz is on.
+func Error(id int64, args ...interface{}) {
+	if IsOn() {
+		AddTraceEvent(id, 1, &TraceEventDesc{
+			Desc:     fmt.Sprint(args...),
+			Severity: CtError,
+		})
+	} else {
+		grpclog.ErrorDepth(1, args...)
+	}
+}
+
+// Errorf logs through grpclog.Errorf and adds a trace event if channelz is on.
+func Errorf(id int64, format string, args ...interface{}) {
+	msg := fmt.Sprintf(format, args...)
+	if IsOn() {
+		AddTraceEvent(id, 1, &TraceEventDesc{
+			Desc:     msg,
+			Severity: CtError,
+		})
+	} else {
+		grpclog.ErrorDepth(1, msg)
+	}
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/internal/channelz/types.go b/demo_test/vendor/google.golang.org/grpc/internal/channelz/types.go
new file mode 100644
index 0000000..17c2274
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/internal/channelz/types.go
@@ -0,0 +1,702 @@
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package channelz
+
+import (
+	"net"
+	"sync"
+	"sync/atomic"
+	"time"
+
+	"google.golang.org/grpc/connectivity"
+	"google.golang.org/grpc/credentials"
+	"google.golang.org/grpc/grpclog"
+)
+
+// entry represents a node in the channelz database.
+type entry interface {
+	// addChild adds a child e, whose channelz id is id to child list
+	addChild(id int64, e entry)
+	// deleteChild deletes a child with channelz id to be id from child list
+	deleteChild(id int64)
+	// triggerDelete tries to delete self from channelz database. However, if child
+	// list is not empty, then deletion from the database is on hold until the last
+	// child is deleted from database.
+	triggerDelete()
+	// deleteSelfIfReady check whether triggerDelete() has been called before, and whether child
+	// list is now empty. If both conditions are met, then delete self from database.
+	deleteSelfIfReady()
+	// getParentID returns parent ID of the entry. 0 value parent ID means no parent.
+	getParentID() int64
+}
+
+// dummyEntry is a fake entry to handle entry not found case.
+type dummyEntry struct {
+	idNotFound int64
+}
+
+func (d *dummyEntry) addChild(id int64, e entry) {
+	// Note: It is possible for a normal program to reach here under race condition.
+	// For example, there could be a race between ClientConn.Close() info being propagated
+	// to addrConn and http2Client. ClientConn.Close() cancel the context and result
+	// in http2Client to error. The error info is then caught by transport monitor
+	// and before addrConn.tearDown() is called in side ClientConn.Close(). Therefore,
+	// the addrConn will create a new transport. And when registering the new transport in
+	// channelz, its parent addrConn could have already been torn down and deleted
+	// from channelz tracking, and thus reach the code here.
+	grpclog.Infof("attempt to add child of type %T with id %d to a parent (id=%d) that doesn't currently exist", e, id, d.idNotFound)
+}
+
+func (d *dummyEntry) deleteChild(id int64) {
+	// It is possible for a normal program to reach here under race condition.
+	// Refer to the example described in addChild().
+	grpclog.Infof("attempt to delete child with id %d from a parent (id=%d) that doesn't currently exist", id, d.idNotFound)
+}
+
+func (d *dummyEntry) triggerDelete() {
+	grpclog.Warningf("attempt to delete an entry (id=%d) that doesn't currently exist", d.idNotFound)
+}
+
+func (*dummyEntry) deleteSelfIfReady() {
+	// code should not reach here. deleteSelfIfReady is always called on an existing entry.
+}
+
+func (*dummyEntry) getParentID() int64 {
+	return 0
+}
+
+// ChannelMetric defines the info channelz provides for a specific Channel, which
+// includes ChannelInternalMetric and channelz-specific data, such as channelz id,
+// child list, etc.
+type ChannelMetric struct {
+	// ID is the channelz id of this channel.
+	ID int64
+	// RefName is the human readable reference string of this channel.
+	RefName string
+	// ChannelData contains channel internal metric reported by the channel through
+	// ChannelzMetric().
+	ChannelData *ChannelInternalMetric
+	// NestedChans tracks the nested channel type children of this channel in the format of
+	// a map from nested channel channelz id to corresponding reference string.
+	NestedChans map[int64]string
+	// SubChans tracks the subchannel type children of this channel in the format of a
+	// map from subchannel channelz id to corresponding reference string.
+	SubChans map[int64]string
+	// Sockets tracks the socket type children of this channel in the format of a map
+	// from socket channelz id to corresponding reference string.
+	// Note current grpc implementation doesn't allow channel having sockets directly,
+	// therefore, this is field is unused.
+	Sockets map[int64]string
+	// Trace contains the most recent traced events.
+	Trace *ChannelTrace
+}
+
+// SubChannelMetric defines the info channelz provides for a specific SubChannel,
+// which includes ChannelInternalMetric and channelz-specific data, such as
+// channelz id, child list, etc.
+type SubChannelMetric struct {
+	// ID is the channelz id of this subchannel.
+	ID int64
+	// RefName is the human readable reference string of this subchannel.
+	RefName string
+	// ChannelData contains subchannel internal metric reported by the subchannel
+	// through ChannelzMetric().
+	ChannelData *ChannelInternalMetric
+	// NestedChans tracks the nested channel type children of this subchannel in the format of
+	// a map from nested channel channelz id to corresponding reference string.
+	// Note current grpc implementation doesn't allow subchannel to have nested channels
+	// as children, therefore, this field is unused.
+	NestedChans map[int64]string
+	// SubChans tracks the subchannel type children of this subchannel in the format of a
+	// map from subchannel channelz id to corresponding reference string.
+	// Note current grpc implementation doesn't allow subchannel to have subchannels
+	// as children, therefore, this field is unused.
+	SubChans map[int64]string
+	// Sockets tracks the socket type children of this subchannel in the format of a map
+	// from socket channelz id to corresponding reference string.
+	Sockets map[int64]string
+	// Trace contains the most recent traced events.
+	Trace *ChannelTrace
+}
+
+// ChannelInternalMetric defines the struct that the implementor of Channel interface
+// should return from ChannelzMetric().
+type ChannelInternalMetric struct {
+	// current connectivity state of the channel.
+	State connectivity.State
+	// The target this channel originally tried to connect to.  May be absent
+	Target string
+	// The number of calls started on the channel.
+	CallsStarted int64
+	// The number of calls that have completed with an OK status.
+	CallsSucceeded int64
+	// The number of calls that have a completed with a non-OK status.
+	CallsFailed int64
+	// The last time a call was started on the channel.
+	LastCallStartedTimestamp time.Time
+}
+
+// ChannelTrace stores traced events on a channel/subchannel and related info.
+type ChannelTrace struct {
+	// EventNum is the number of events that ever got traced (i.e. including those that have been deleted)
+	EventNum int64
+	// CreationTime is the creation time of the trace.
+	CreationTime time.Time
+	// Events stores the most recent trace events (up to $maxTraceEntry, newer event will overwrite the
+	// oldest one)
+	Events []*TraceEvent
+}
+
+// TraceEvent represent a single trace event
+type TraceEvent struct {
+	// Desc is a simple description of the trace event.
+	Desc string
+	// Severity states the severity of this trace event.
+	Severity Severity
+	// Timestamp is the event time.
+	Timestamp time.Time
+	// RefID is the id of the entity that gets referenced in the event. RefID is 0 if no other entity is
+	// involved in this event.
+	// e.g. SubChannel (id: 4[]) Created. --> RefID = 4, RefName = "" (inside [])
+	RefID int64
+	// RefName is the reference name for the entity that gets referenced in the event.
+	RefName string
+	// RefType indicates the referenced entity type, i.e Channel or SubChannel.
+	RefType RefChannelType
+}
+
+// Channel is the interface that should be satisfied in order to be tracked by
+// channelz as Channel or SubChannel.
+type Channel interface {
+	ChannelzMetric() *ChannelInternalMetric
+}
+
+type dummyChannel struct{}
+
+func (d *dummyChannel) ChannelzMetric() *ChannelInternalMetric {
+	return &ChannelInternalMetric{}
+}
+
+type channel struct {
+	refName     string
+	c           Channel
+	closeCalled bool
+	nestedChans map[int64]string
+	subChans    map[int64]string
+	id          int64
+	pid         int64
+	cm          *channelMap
+	trace       *channelTrace
+	// traceRefCount is the number of trace events that reference this channel.
+	// Non-zero traceRefCount means the trace of this channel cannot be deleted.
+	traceRefCount int32
+}
+
+func (c *channel) addChild(id int64, e entry) {
+	switch v := e.(type) {
+	case *subChannel:
+		c.subChans[id] = v.refName
+	case *channel:
+		c.nestedChans[id] = v.refName
+	default:
+		grpclog.Errorf("cannot add a child (id = %d) of type %T to a channel", id, e)
+	}
+}
+
+func (c *channel) deleteChild(id int64) {
+	delete(c.subChans, id)
+	delete(c.nestedChans, id)
+	c.deleteSelfIfReady()
+}
+
+func (c *channel) triggerDelete() {
+	c.closeCalled = true
+	c.deleteSelfIfReady()
+}
+
+func (c *channel) getParentID() int64 {
+	return c.pid
+}
+
+// deleteSelfFromTree tries to delete the channel from the channelz entry relation tree, which means
+// deleting the channel reference from its parent's child list.
+//
+// In order for a channel to be deleted from the tree, it must meet the criteria that, removal of the
+// corresponding grpc object has been invoked, and the channel does not have any children left.
+//
+// The returned boolean value indicates whether the channel has been successfully deleted from tree.
+func (c *channel) deleteSelfFromTree() (deleted bool) {
+	if !c.closeCalled || len(c.subChans)+len(c.nestedChans) != 0 {
+		return false
+	}
+	// not top channel
+	if c.pid != 0 {
+		c.cm.findEntry(c.pid).deleteChild(c.id)
+	}
+	return true
+}
+
+// deleteSelfFromMap checks whether it is valid to delete the channel from the map, which means
+// deleting the channel from channelz's tracking entirely. Users can no longer use id to query the
+// channel, and its memory will be garbage collected.
+//
+// The trace reference count of the channel must be 0 in order to be deleted from the map. This is
+// specified in the channel tracing gRFC that as long as some other trace has reference to an entity,
+// the trace of the referenced entity must not be deleted. In order to release the resource allocated
+// by grpc, the reference to the grpc object is reset to a dummy object.
+//
+// deleteSelfFromMap must be called after deleteSelfFromTree returns true.
+//
+// It returns a bool to indicate whether the channel can be safely deleted from map.
+func (c *channel) deleteSelfFromMap() (delete bool) {
+	if c.getTraceRefCount() != 0 {
+		c.c = &dummyChannel{}
+		return false
+	}
+	return true
+}
+
+// deleteSelfIfReady tries to delete the channel itself from the channelz database.
+// The delete process includes two steps:
+// 1. delete the channel from the entry relation tree, i.e. delete the channel reference from its
+//    parent's child list.
+// 2. delete the channel from the map, i.e. delete the channel entirely from channelz. Lookup by id
+//    will return entry not found error.
+func (c *channel) deleteSelfIfReady() {
+	if !c.deleteSelfFromTree() {
+		return
+	}
+	if !c.deleteSelfFromMap() {
+		return
+	}
+	c.cm.deleteEntry(c.id)
+	c.trace.clear()
+}
+
+func (c *channel) getChannelTrace() *channelTrace {
+	return c.trace
+}
+
+func (c *channel) incrTraceRefCount() {
+	atomic.AddInt32(&c.traceRefCount, 1)
+}
+
+func (c *channel) decrTraceRefCount() {
+	atomic.AddInt32(&c.traceRefCount, -1)
+}
+
+func (c *channel) getTraceRefCount() int {
+	i := atomic.LoadInt32(&c.traceRefCount)
+	return int(i)
+}
+
+func (c *channel) getRefName() string {
+	return c.refName
+}
+
+type subChannel struct {
+	refName       string
+	c             Channel
+	closeCalled   bool
+	sockets       map[int64]string
+	id            int64
+	pid           int64
+	cm            *channelMap
+	trace         *channelTrace
+	traceRefCount int32
+}
+
+func (sc *subChannel) addChild(id int64, e entry) {
+	if v, ok := e.(*normalSocket); ok {
+		sc.sockets[id] = v.refName
+	} else {
+		grpclog.Errorf("cannot add a child (id = %d) of type %T to a subChannel", id, e)
+	}
+}
+
+func (sc *subChannel) deleteChild(id int64) {
+	delete(sc.sockets, id)
+	sc.deleteSelfIfReady()
+}
+
+func (sc *subChannel) triggerDelete() {
+	sc.closeCalled = true
+	sc.deleteSelfIfReady()
+}
+
+func (sc *subChannel) getParentID() int64 {
+	return sc.pid
+}
+
+// deleteSelfFromTree tries to delete the subchannel from the channelz entry relation tree, which
+// means deleting the subchannel reference from its parent's child list.
+//
+// In order for a subchannel to be deleted from the tree, it must meet the criteria that, removal of
+// the corresponding grpc object has been invoked, and the subchannel does not have any children left.
+//
+// The returned boolean value indicates whether the channel has been successfully deleted from tree.
+func (sc *subChannel) deleteSelfFromTree() (deleted bool) {
+	if !sc.closeCalled || len(sc.sockets) != 0 {
+		return false
+	}
+	sc.cm.findEntry(sc.pid).deleteChild(sc.id)
+	return true
+}
+
+// deleteSelfFromMap checks whether it is valid to delete the subchannel from the map, which means
+// deleting the subchannel from channelz's tracking entirely. Users can no longer use id to query
+// the subchannel, and its memory will be garbage collected.
+//
+// The trace reference count of the subchannel must be 0 in order to be deleted from the map. This is
+// specified in the channel tracing gRFC that as long as some other trace has reference to an entity,
+// the trace of the referenced entity must not be deleted. In order to release the resource allocated
+// by grpc, the reference to the grpc object is reset to a dummy object.
+//
+// deleteSelfFromMap must be called after deleteSelfFromTree returns true.
+//
+// It returns a bool to indicate whether the channel can be safely deleted from map.
+func (sc *subChannel) deleteSelfFromMap() (delete bool) {
+	if sc.getTraceRefCount() != 0 {
+		// free the grpc struct (i.e. addrConn)
+		sc.c = &dummyChannel{}
+		return false
+	}
+	return true
+}
+
+// deleteSelfIfReady tries to delete the subchannel itself from the channelz database.
+// The delete process includes two steps:
+// 1. delete the subchannel from the entry relation tree, i.e. delete the subchannel reference from
+//    its parent's child list.
+// 2. delete the subchannel from the map, i.e. delete the subchannel entirely from channelz. Lookup
+//    by id will return entry not found error.
+func (sc *subChannel) deleteSelfIfReady() {
+	if !sc.deleteSelfFromTree() {
+		return
+	}
+	if !sc.deleteSelfFromMap() {
+		return
+	}
+	sc.cm.deleteEntry(sc.id)
+	sc.trace.clear()
+}
+
+func (sc *subChannel) getChannelTrace() *channelTrace {
+	return sc.trace
+}
+
+func (sc *subChannel) incrTraceRefCount() {
+	atomic.AddInt32(&sc.traceRefCount, 1)
+}
+
+func (sc *subChannel) decrTraceRefCount() {
+	atomic.AddInt32(&sc.traceRefCount, -1)
+}
+
+func (sc *subChannel) getTraceRefCount() int {
+	i := atomic.LoadInt32(&sc.traceRefCount)
+	return int(i)
+}
+
+func (sc *subChannel) getRefName() string {
+	return sc.refName
+}
+
+// SocketMetric defines the info channelz provides for a specific Socket, which
+// includes SocketInternalMetric and channelz-specific data, such as channelz id, etc.
+type SocketMetric struct {
+	// ID is the channelz id of this socket.
+	ID int64
+	// RefName is the human readable reference string of this socket.
+	RefName string
+	// SocketData contains socket internal metric reported by the socket through
+	// ChannelzMetric().
+	SocketData *SocketInternalMetric
+}
+
+// SocketInternalMetric defines the struct that the implementor of Socket interface
+// should return from ChannelzMetric().
+type SocketInternalMetric struct {
+	// The number of streams that have been started.
+	StreamsStarted int64
+	// The number of streams that have ended successfully:
+	// On client side, receiving frame with eos bit set.
+	// On server side, sending frame with eos bit set.
+	StreamsSucceeded int64
+	// The number of streams that have ended unsuccessfully:
+	// On client side, termination without receiving frame with eos bit set.
+	// On server side, termination without sending frame with eos bit set.
+	StreamsFailed int64
+	// The number of messages successfully sent on this socket.
+	MessagesSent     int64
+	MessagesReceived int64
+	// The number of keep alives sent.  This is typically implemented with HTTP/2
+	// ping messages.
+	KeepAlivesSent int64
+	// The last time a stream was created by this endpoint.  Usually unset for
+	// servers.
+	LastLocalStreamCreatedTimestamp time.Time
+	// The last time a stream was created by the remote endpoint.  Usually unset
+	// for clients.
+	LastRemoteStreamCreatedTimestamp time.Time
+	// The last time a message was sent by this endpoint.
+	LastMessageSentTimestamp time.Time
+	// The last time a message was received by this endpoint.
+	LastMessageReceivedTimestamp time.Time
+	// The amount of window, granted to the local endpoint by the remote endpoint.
+	// This may be slightly out of date due to network latency.  This does NOT
+	// include stream level or TCP level flow control info.
+	LocalFlowControlWindow int64
+	// The amount of window, granted to the remote endpoint by the local endpoint.
+	// This may be slightly out of date due to network latency.  This does NOT
+	// include stream level or TCP level flow control info.
+	RemoteFlowControlWindow int64
+	// The locally bound address.
+	LocalAddr net.Addr
+	// The remote bound address.  May be absent.
+	RemoteAddr net.Addr
+	// Optional, represents the name of the remote endpoint, if different than
+	// the original target name.
+	RemoteName    string
+	SocketOptions *SocketOptionData
+	Security      credentials.ChannelzSecurityValue
+}
+
+// Socket is the interface that should be satisfied in order to be tracked by
+// channelz as Socket.
+type Socket interface {
+	ChannelzMetric() *SocketInternalMetric
+}
+
+type listenSocket struct {
+	refName string
+	s       Socket
+	id      int64
+	pid     int64
+	cm      *channelMap
+}
+
+func (ls *listenSocket) addChild(id int64, e entry) {
+	grpclog.Errorf("cannot add a child (id = %d) of type %T to a listen socket", id, e)
+}
+
+func (ls *listenSocket) deleteChild(id int64) {
+	grpclog.Errorf("cannot delete a child (id = %d) from a listen socket", id)
+}
+
+func (ls *listenSocket) triggerDelete() {
+	ls.cm.deleteEntry(ls.id)
+	ls.cm.findEntry(ls.pid).deleteChild(ls.id)
+}
+
+func (ls *listenSocket) deleteSelfIfReady() {
+	grpclog.Errorf("cannot call deleteSelfIfReady on a listen socket")
+}
+
+func (ls *listenSocket) getParentID() int64 {
+	return ls.pid
+}
+
+type normalSocket struct {
+	refName string
+	s       Socket
+	id      int64
+	pid     int64
+	cm      *channelMap
+}
+
+func (ns *normalSocket) addChild(id int64, e entry) {
+	grpclog.Errorf("cannot add a child (id = %d) of type %T to a normal socket", id, e)
+}
+
+func (ns *normalSocket) deleteChild(id int64) {
+	grpclog.Errorf("cannot delete a child (id = %d) from a normal socket", id)
+}
+
+func (ns *normalSocket) triggerDelete() {
+	ns.cm.deleteEntry(ns.id)
+	ns.cm.findEntry(ns.pid).deleteChild(ns.id)
+}
+
+func (ns *normalSocket) deleteSelfIfReady() {
+	grpclog.Errorf("cannot call deleteSelfIfReady on a normal socket")
+}
+
+func (ns *normalSocket) getParentID() int64 {
+	return ns.pid
+}
+
+// ServerMetric defines the info channelz provides for a specific Server, which
+// includes ServerInternalMetric and channelz-specific data, such as channelz id,
+// child list, etc.
+type ServerMetric struct {
+	// ID is the channelz id of this server.
+	ID int64
+	// RefName is the human readable reference string of this server.
+	RefName string
+	// ServerData contains server internal metric reported by the server through
+	// ChannelzMetric().
+	ServerData *ServerInternalMetric
+	// ListenSockets tracks the listener socket type children of this server in the
+	// format of a map from socket channelz id to corresponding reference string.
+	ListenSockets map[int64]string
+}
+
+// ServerInternalMetric defines the struct that the implementor of Server interface
+// should return from ChannelzMetric().
+type ServerInternalMetric struct {
+	// The number of incoming calls started on the server.
+	CallsStarted int64
+	// The number of incoming calls that have completed with an OK status.
+	CallsSucceeded int64
+	// The number of incoming calls that have a completed with a non-OK status.
+	CallsFailed int64
+	// The last time a call was started on the server.
+	LastCallStartedTimestamp time.Time
+}
+
+// Server is the interface to be satisfied in order to be tracked by channelz as
+// Server.
+type Server interface {
+	ChannelzMetric() *ServerInternalMetric
+}
+
+type server struct {
+	refName       string
+	s             Server
+	closeCalled   bool
+	sockets       map[int64]string
+	listenSockets map[int64]string
+	id            int64
+	cm            *channelMap
+}
+
+func (s *server) addChild(id int64, e entry) {
+	switch v := e.(type) {
+	case *normalSocket:
+		s.sockets[id] = v.refName
+	case *listenSocket:
+		s.listenSockets[id] = v.refName
+	default:
+		grpclog.Errorf("cannot add a child (id = %d) of type %T to a server", id, e)
+	}
+}
+
+func (s *server) deleteChild(id int64) {
+	delete(s.sockets, id)
+	delete(s.listenSockets, id)
+	s.deleteSelfIfReady()
+}
+
+func (s *server) triggerDelete() {
+	s.closeCalled = true
+	s.deleteSelfIfReady()
+}
+
+func (s *server) deleteSelfIfReady() {
+	if !s.closeCalled || len(s.sockets)+len(s.listenSockets) != 0 {
+		return
+	}
+	s.cm.deleteEntry(s.id)
+}
+
+func (s *server) getParentID() int64 {
+	return 0
+}
+
+type tracedChannel interface {
+	getChannelTrace() *channelTrace
+	incrTraceRefCount()
+	decrTraceRefCount()
+	getRefName() string
+}
+
+type channelTrace struct {
+	cm          *channelMap
+	createdTime time.Time
+	eventCount  int64
+	mu          sync.Mutex
+	events      []*TraceEvent
+}
+
+func (c *channelTrace) append(e *TraceEvent) {
+	c.mu.Lock()
+	if len(c.events) == getMaxTraceEntry() {
+		del := c.events[0]
+		c.events = c.events[1:]
+		if del.RefID != 0 {
+			// start recursive cleanup in a goroutine to not block the call originated from grpc.
+			go func() {
+				// need to acquire c.cm.mu lock to call the unlocked attemptCleanup func.
+				c.cm.mu.Lock()
+				c.cm.decrTraceRefCount(del.RefID)
+				c.cm.mu.Unlock()
+			}()
+		}
+	}
+	e.Timestamp = time.Now()
+	c.events = append(c.events, e)
+	c.eventCount++
+	c.mu.Unlock()
+}
+
+func (c *channelTrace) clear() {
+	c.mu.Lock()
+	for _, e := range c.events {
+		if e.RefID != 0 {
+			// caller should have already held the c.cm.mu lock.
+			c.cm.decrTraceRefCount(e.RefID)
+		}
+	}
+	c.mu.Unlock()
+}
+
+// Severity is the severity level of a trace event.
+// The canonical enumeration of all valid values is here:
+// https://github.com/grpc/grpc-proto/blob/9b13d199cc0d4703c7ea26c9c330ba695866eb23/grpc/channelz/v1/channelz.proto#L126.
+type Severity int
+
+const (
+	// CtUNKNOWN indicates unknown severity of a trace event.
+	CtUNKNOWN Severity = iota
+	// CtINFO indicates info level severity of a trace event.
+	CtINFO
+	// CtWarning indicates warning level severity of a trace event.
+	CtWarning
+	// CtError indicates error level severity of a trace event.
+	CtError
+)
+
+// RefChannelType is the type of the entity being referenced in a trace event.
+type RefChannelType int
+
+const (
+	// RefChannel indicates the referenced entity is a Channel.
+	RefChannel RefChannelType = iota
+	// RefSubChannel indicates the referenced entity is a SubChannel.
+	RefSubChannel
+)
+
+func (c *channelTrace) dumpData() *ChannelTrace {
+	c.mu.Lock()
+	ct := &ChannelTrace{EventNum: c.eventCount, CreationTime: c.createdTime}
+	ct.Events = c.events[:len(c.events)]
+	c.mu.Unlock()
+	return ct
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/internal/channelz/types_linux.go b/demo_test/vendor/google.golang.org/grpc/internal/channelz/types_linux.go
new file mode 100644
index 0000000..692dd61
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/internal/channelz/types_linux.go
@@ -0,0 +1,53 @@
+// +build !appengine
+
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package channelz
+
+import (
+	"syscall"
+
+	"golang.org/x/sys/unix"
+)
+
+// SocketOptionData defines the struct to hold socket option data, and related
+// getter function to obtain info from fd.
+type SocketOptionData struct {
+	Linger      *unix.Linger
+	RecvTimeout *unix.Timeval
+	SendTimeout *unix.Timeval
+	TCPInfo     *unix.TCPInfo
+}
+
+// Getsockopt defines the function to get socket options requested by channelz.
+// It is to be passed to syscall.RawConn.Control().
+func (s *SocketOptionData) Getsockopt(fd uintptr) {
+	if v, err := unix.GetsockoptLinger(int(fd), syscall.SOL_SOCKET, syscall.SO_LINGER); err == nil {
+		s.Linger = v
+	}
+	if v, err := unix.GetsockoptTimeval(int(fd), syscall.SOL_SOCKET, syscall.SO_RCVTIMEO); err == nil {
+		s.RecvTimeout = v
+	}
+	if v, err := unix.GetsockoptTimeval(int(fd), syscall.SOL_SOCKET, syscall.SO_SNDTIMEO); err == nil {
+		s.SendTimeout = v
+	}
+	if v, err := unix.GetsockoptTCPInfo(int(fd), syscall.SOL_TCP, syscall.TCP_INFO); err == nil {
+		s.TCPInfo = v
+	}
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/internal/channelz/types_nonlinux.go b/demo_test/vendor/google.golang.org/grpc/internal/channelz/types_nonlinux.go
new file mode 100644
index 0000000..79edbef
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/internal/channelz/types_nonlinux.go
@@ -0,0 +1,44 @@
+// +build !linux appengine
+
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package channelz
+
+import (
+	"sync"
+
+	"google.golang.org/grpc/grpclog"
+)
+
+var once sync.Once
+
+// SocketOptionData defines the struct to hold socket option data, and related
+// getter function to obtain info from fd.
+// Windows OS doesn't support Socket Option
+type SocketOptionData struct {
+}
+
+// Getsockopt defines the function to get socket options requested by channelz.
+// It is to be passed to syscall.RawConn.Control().
+// Windows OS doesn't support Socket Option
+func (s *SocketOptionData) Getsockopt(fd uintptr) {
+	once.Do(func() {
+		grpclog.Warningln("Channelz: socket options are not supported on non-linux os and appengine.")
+	})
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/internal/channelz/util_linux.go b/demo_test/vendor/google.golang.org/grpc/internal/channelz/util_linux.go
new file mode 100644
index 0000000..fdf409d
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/internal/channelz/util_linux.go
@@ -0,0 +1,39 @@
+// +build linux,!appengine
+
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package channelz
+
+import (
+	"syscall"
+)
+
+// GetSocketOption gets the socket option info of the conn.
+func GetSocketOption(socket interface{}) *SocketOptionData {
+	c, ok := socket.(syscall.Conn)
+	if !ok {
+		return nil
+	}
+	data := &SocketOptionData{}
+	if rawConn, err := c.SyscallConn(); err == nil {
+		rawConn.Control(data.Getsockopt)
+		return data
+	}
+	return nil
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/internal/channelz/util_nonlinux.go b/demo_test/vendor/google.golang.org/grpc/internal/channelz/util_nonlinux.go
new file mode 100644
index 0000000..8864a08
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/internal/channelz/util_nonlinux.go
@@ -0,0 +1,26 @@
+// +build !linux appengine
+
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package channelz
+
+// GetSocketOption gets the socket option info of the conn.
+func GetSocketOption(c interface{}) *SocketOptionData {
+	return nil
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/internal/envconfig/envconfig.go b/demo_test/vendor/google.golang.org/grpc/internal/envconfig/envconfig.go
new file mode 100644
index 0000000..ae6c897
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/internal/envconfig/envconfig.go
@@ -0,0 +1,38 @@
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+// Package envconfig contains grpc settings configured by environment variables.
+package envconfig
+
+import (
+	"os"
+	"strings"
+)
+
+const (
+	prefix          = "GRPC_GO_"
+	retryStr        = prefix + "RETRY"
+	txtErrIgnoreStr = prefix + "IGNORE_TXT_ERRORS"
+)
+
+var (
+	// Retry is set if retry is explicitly enabled via "GRPC_GO_RETRY=on".
+	Retry = strings.EqualFold(os.Getenv(retryStr), "on")
+	// TXTErrIgnore is set if TXT errors should be ignored ("GRPC_GO_IGNORE_TXT_ERRORS" is not "false").
+	TXTErrIgnore = !strings.EqualFold(os.Getenv(retryStr), "false")
+)
diff --git a/demo_test/vendor/google.golang.org/grpc/internal/grpclog/grpclog.go b/demo_test/vendor/google.golang.org/grpc/internal/grpclog/grpclog.go
new file mode 100644
index 0000000..8c8e19f
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/internal/grpclog/grpclog.go
@@ -0,0 +1,118 @@
+/*
+ *
+ * Copyright 2020 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+// Package grpclog (internal) defines depth logging for grpc.
+package grpclog
+
+// Logger is the logger used for the non-depth log functions.
+var Logger LoggerV2
+
+// DepthLogger is the logger used for the depth log functions.
+var DepthLogger DepthLoggerV2
+
+// InfoDepth logs to the INFO log at the specified depth.
+func InfoDepth(depth int, args ...interface{}) {
+	if DepthLogger != nil {
+		DepthLogger.InfoDepth(depth, args...)
+	} else {
+		Logger.Info(args...)
+	}
+}
+
+// WarningDepth logs to the WARNING log at the specified depth.
+func WarningDepth(depth int, args ...interface{}) {
+	if DepthLogger != nil {
+		DepthLogger.WarningDepth(depth, args...)
+	} else {
+		Logger.Warning(args...)
+	}
+}
+
+// ErrorDepth logs to the ERROR log at the specified depth.
+func ErrorDepth(depth int, args ...interface{}) {
+	if DepthLogger != nil {
+		DepthLogger.ErrorDepth(depth, args...)
+	} else {
+		Logger.Error(args...)
+	}
+}
+
+// FatalDepth logs to the FATAL log at the specified depth.
+func FatalDepth(depth int, args ...interface{}) {
+	if DepthLogger != nil {
+		DepthLogger.FatalDepth(depth, args...)
+	} else {
+		Logger.Fatal(args...)
+	}
+}
+
+// LoggerV2 does underlying logging work for grpclog.
+// This is a copy of the LoggerV2 defined in the external grpclog package. It
+// is defined here to avoid a circular dependency.
+type LoggerV2 interface {
+	// Info logs to INFO log. Arguments are handled in the manner of fmt.Print.
+	Info(args ...interface{})
+	// Infoln logs to INFO log. Arguments are handled in the manner of fmt.Println.
+	Infoln(args ...interface{})
+	// Infof logs to INFO log. Arguments are handled in the manner of fmt.Printf.
+	Infof(format string, args ...interface{})
+	// Warning logs to WARNING log. Arguments are handled in the manner of fmt.Print.
+	Warning(args ...interface{})
+	// Warningln logs to WARNING log. Arguments are handled in the manner of fmt.Println.
+	Warningln(args ...interface{})
+	// Warningf logs to WARNING log. Arguments are handled in the manner of fmt.Printf.
+	Warningf(format string, args ...interface{})
+	// Error logs to ERROR log. Arguments are handled in the manner of fmt.Print.
+	Error(args ...interface{})
+	// Errorln logs to ERROR log. Arguments are handled in the manner of fmt.Println.
+	Errorln(args ...interface{})
+	// Errorf logs to ERROR log. Arguments are handled in the manner of fmt.Printf.
+	Errorf(format string, args ...interface{})
+	// Fatal logs to ERROR log. Arguments are handled in the manner of fmt.Print.
+	// gRPC ensures that all Fatal logs will exit with os.Exit(1).
+	// Implementations may also call os.Exit() with a non-zero exit code.
+	Fatal(args ...interface{})
+	// Fatalln logs to ERROR log. Arguments are handled in the manner of fmt.Println.
+	// gRPC ensures that all Fatal logs will exit with os.Exit(1).
+	// Implementations may also call os.Exit() with a non-zero exit code.
+	Fatalln(args ...interface{})
+	// Fatalf logs to ERROR log. Arguments are handled in the manner of fmt.Printf.
+	// gRPC ensures that all Fatal logs will exit with os.Exit(1).
+	// Implementations may also call os.Exit() with a non-zero exit code.
+	Fatalf(format string, args ...interface{})
+	// V reports whether verbosity level l is at least the requested verbose level.
+	V(l int) bool
+}
+
+// DepthLoggerV2 logs at a specified call frame. If a LoggerV2 also implements
+// DepthLoggerV2, the below functions will be called with the appropriate stack
+// depth set for trivial functions the logger may ignore.
+// This is a copy of the DepthLoggerV2 defined in the external grpclog package.
+// It is defined here to avoid a circular dependency.
+//
+// This API is EXPERIMENTAL.
+type DepthLoggerV2 interface {
+	// InfoDepth logs to INFO log at the specified depth. Arguments are handled in the manner of fmt.Print.
+	InfoDepth(depth int, args ...interface{})
+	// WarningDepth logs to WARNING log at the specified depth. Arguments are handled in the manner of fmt.Print.
+	WarningDepth(depth int, args ...interface{})
+	// ErrorDetph logs to ERROR log at the specified depth. Arguments are handled in the manner of fmt.Print.
+	ErrorDepth(depth int, args ...interface{})
+	// FatalDepth logs to FATAL log at the specified depth. Arguments are handled in the manner of fmt.Print.
+	FatalDepth(depth int, args ...interface{})
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/internal/grpclog/prefixLogger.go b/demo_test/vendor/google.golang.org/grpc/internal/grpclog/prefixLogger.go
new file mode 100644
index 0000000..f6e0dc1
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/internal/grpclog/prefixLogger.go
@@ -0,0 +1,63 @@
+/*
+ *
+ * Copyright 2020 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package grpclog
+
+// PrefixLogger does logging with a prefix.
+//
+// Logging method on a nil logs without any prefix.
+type PrefixLogger struct {
+	prefix string
+}
+
+// Infof does info logging.
+func (pl *PrefixLogger) Infof(format string, args ...interface{}) {
+	if pl != nil {
+		// Handle nil, so the tests can pass in a nil logger.
+		format = pl.prefix + format
+	}
+	Logger.Infof(format, args...)
+}
+
+// Warningf does warning logging.
+func (pl *PrefixLogger) Warningf(format string, args ...interface{}) {
+	if pl != nil {
+		format = pl.prefix + format
+	}
+	Logger.Warningf(format, args...)
+}
+
+// Errorf does error logging.
+func (pl *PrefixLogger) Errorf(format string, args ...interface{}) {
+	if pl != nil {
+		format = pl.prefix + format
+	}
+	Logger.Errorf(format, args...)
+}
+
+// Debugf does info logging at verbose level 2.
+func (pl *PrefixLogger) Debugf(format string, args ...interface{}) {
+	if Logger.V(2) {
+		pl.Infof(format, args...)
+	}
+}
+
+// NewPrefixLogger creates a prefix logger with the given prefix.
+func NewPrefixLogger(prefix string) *PrefixLogger {
+	return &PrefixLogger{prefix: prefix}
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/internal/grpcrand/grpcrand.go b/demo_test/vendor/google.golang.org/grpc/internal/grpcrand/grpcrand.go
new file mode 100644
index 0000000..200b115
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/internal/grpcrand/grpcrand.go
@@ -0,0 +1,56 @@
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+// Package grpcrand implements math/rand functions in a concurrent-safe way
+// with a global random source, independent of math/rand's global source.
+package grpcrand
+
+import (
+	"math/rand"
+	"sync"
+	"time"
+)
+
+var (
+	r  = rand.New(rand.NewSource(time.Now().UnixNano()))
+	mu sync.Mutex
+)
+
+// Int63n implements rand.Int63n on the grpcrand global source.
+func Int63n(n int64) int64 {
+	mu.Lock()
+	res := r.Int63n(n)
+	mu.Unlock()
+	return res
+}
+
+// Intn implements rand.Intn on the grpcrand global source.
+func Intn(n int) int {
+	mu.Lock()
+	res := r.Intn(n)
+	mu.Unlock()
+	return res
+}
+
+// Float64 implements rand.Float64 on the grpcrand global source.
+func Float64() float64 {
+	mu.Lock()
+	res := r.Float64()
+	mu.Unlock()
+	return res
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/internal/grpcsync/event.go b/demo_test/vendor/google.golang.org/grpc/internal/grpcsync/event.go
new file mode 100644
index 0000000..fbe697c
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/internal/grpcsync/event.go
@@ -0,0 +1,61 @@
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+// Package grpcsync implements additional synchronization primitives built upon
+// the sync package.
+package grpcsync
+
+import (
+	"sync"
+	"sync/atomic"
+)
+
+// Event represents a one-time event that may occur in the future.
+type Event struct {
+	fired int32
+	c     chan struct{}
+	o     sync.Once
+}
+
+// Fire causes e to complete.  It is safe to call multiple times, and
+// concurrently.  It returns true iff this call to Fire caused the signaling
+// channel returned by Done to close.
+func (e *Event) Fire() bool {
+	ret := false
+	e.o.Do(func() {
+		atomic.StoreInt32(&e.fired, 1)
+		close(e.c)
+		ret = true
+	})
+	return ret
+}
+
+// Done returns a channel that will be closed when Fire is called.
+func (e *Event) Done() <-chan struct{} {
+	return e.c
+}
+
+// HasFired returns true if Fire has been called.
+func (e *Event) HasFired() bool {
+	return atomic.LoadInt32(&e.fired) == 1
+}
+
+// NewEvent returns a new, ready-to-use Event.
+func NewEvent() *Event {
+	return &Event{c: make(chan struct{})}
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/internal/grpcutil/target.go b/demo_test/vendor/google.golang.org/grpc/internal/grpcutil/target.go
new file mode 100644
index 0000000..80b33cd
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/internal/grpcutil/target.go
@@ -0,0 +1,55 @@
+/*
+ *
+ * Copyright 2020 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+// Package grpcutil provides a bunch of utility functions to be used across the
+// gRPC codebase.
+package grpcutil
+
+import (
+	"strings"
+
+	"google.golang.org/grpc/resolver"
+)
+
+// split2 returns the values from strings.SplitN(s, sep, 2).
+// If sep is not found, it returns ("", "", false) instead.
+func split2(s, sep string) (string, string, bool) {
+	spl := strings.SplitN(s, sep, 2)
+	if len(spl) < 2 {
+		return "", "", false
+	}
+	return spl[0], spl[1], true
+}
+
+// ParseTarget splits target into a resolver.Target struct containing scheme,
+// authority and endpoint.
+//
+// If target is not a valid scheme://authority/endpoint, it returns {Endpoint:
+// target}.
+func ParseTarget(target string) (ret resolver.Target) {
+	var ok bool
+	ret.Scheme, ret.Endpoint, ok = split2(target, "://")
+	if !ok {
+		return resolver.Target{Endpoint: target}
+	}
+	ret.Authority, ret.Endpoint, ok = split2(ret.Endpoint, "/")
+	if !ok {
+		return resolver.Target{Endpoint: target}
+	}
+	return ret
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/internal/internal.go b/demo_test/vendor/google.golang.org/grpc/internal/internal.go
new file mode 100644
index 0000000..c6fbe8b
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/internal/internal.go
@@ -0,0 +1,67 @@
+/*
+ * Copyright 2016 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+// Package internal contains gRPC-internal code, to avoid polluting
+// the godoc of the top-level grpc package.  It must not import any grpc
+// symbols to avoid circular dependencies.
+package internal
+
+import (
+	"context"
+	"time"
+
+	"google.golang.org/grpc/connectivity"
+)
+
+var (
+	// WithHealthCheckFunc is set by dialoptions.go
+	WithHealthCheckFunc interface{} // func (HealthChecker) DialOption
+	// HealthCheckFunc is used to provide client-side LB channel health checking
+	HealthCheckFunc HealthChecker
+	// BalancerUnregister is exported by package balancer to unregister a balancer.
+	BalancerUnregister func(name string)
+	// KeepaliveMinPingTime is the minimum ping interval.  This must be 10s by
+	// default, but tests may wish to set it lower for convenience.
+	KeepaliveMinPingTime = 10 * time.Second
+	// NewRequestInfoContext creates a new context based on the argument context attaching
+	// the passed in RequestInfo to the new context.
+	NewRequestInfoContext interface{} // func(context.Context, credentials.RequestInfo) context.Context
+	// ParseServiceConfigForTesting is for creating a fake
+	// ClientConn for resolver testing only
+	ParseServiceConfigForTesting interface{} // func(string) *serviceconfig.ParseResult
+)
+
+// HealthChecker defines the signature of the client-side LB channel health checking function.
+//
+// The implementation is expected to create a health checking RPC stream by
+// calling newStream(), watch for the health status of serviceName, and report
+// it's health back by calling setConnectivityState().
+//
+// The health checking protocol is defined at:
+// https://github.com/grpc/grpc/blob/master/doc/health-checking.md
+type HealthChecker func(ctx context.Context, newStream func(string) (interface{}, error), setConnectivityState func(connectivity.State, error), serviceName string) error
+
+const (
+	// CredsBundleModeFallback switches GoogleDefaultCreds to fallback mode.
+	CredsBundleModeFallback = "fallback"
+	// CredsBundleModeBalancer switches GoogleDefaultCreds to grpclb balancer
+	// mode.
+	CredsBundleModeBalancer = "balancer"
+	// CredsBundleModeBackendFromBalancer switches GoogleDefaultCreds to mode
+	// that supports backend returned by grpclb balancer.
+	CredsBundleModeBackendFromBalancer = "backend-from-balancer"
+)
diff --git a/demo_test/vendor/google.golang.org/grpc/internal/resolver/dns/dns_resolver.go b/demo_test/vendor/google.golang.org/grpc/internal/resolver/dns/dns_resolver.go
new file mode 100644
index 0000000..c368db6
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/internal/resolver/dns/dns_resolver.go
@@ -0,0 +1,441 @@
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+// Package dns implements a dns resolver to be installed as the default resolver
+// in grpc.
+package dns
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"net"
+	"os"
+	"strconv"
+	"strings"
+	"sync"
+	"time"
+
+	"google.golang.org/grpc/grpclog"
+	"google.golang.org/grpc/internal/envconfig"
+	"google.golang.org/grpc/internal/grpcrand"
+	"google.golang.org/grpc/resolver"
+	"google.golang.org/grpc/serviceconfig"
+)
+
+// EnableSRVLookups controls whether the DNS resolver attempts to fetch gRPCLB
+// addresses from SRV records.  Must not be changed after init time.
+var EnableSRVLookups = false
+
+func init() {
+	resolver.Register(NewBuilder())
+}
+
+const (
+	defaultPort       = "443"
+	defaultDNSSvrPort = "53"
+	golang            = "GO"
+	// txtPrefix is the prefix string to be prepended to the host name for txt record lookup.
+	txtPrefix = "_grpc_config."
+	// In DNS, service config is encoded in a TXT record via the mechanism
+	// described in RFC-1464 using the attribute name grpc_config.
+	txtAttribute = "grpc_config="
+)
+
+var (
+	errMissingAddr = errors.New("dns resolver: missing address")
+
+	// Addresses ending with a colon that is supposed to be the separator
+	// between host and port is not allowed.  E.g. "::" is a valid address as
+	// it is an IPv6 address (host only) and "[::]:" is invalid as it ends with
+	// a colon as the host and port separator
+	errEndsWithColon = errors.New("dns resolver: missing port after port-separator colon")
+)
+
+var (
+	defaultResolver netResolver = net.DefaultResolver
+	// To prevent excessive re-resolution, we enforce a rate limit on DNS
+	// resolution requests.
+	minDNSResRate = 30 * time.Second
+)
+
+var customAuthorityDialler = func(authority string) func(ctx context.Context, network, address string) (net.Conn, error) {
+	return func(ctx context.Context, network, address string) (net.Conn, error) {
+		var dialer net.Dialer
+		return dialer.DialContext(ctx, network, authority)
+	}
+}
+
+var customAuthorityResolver = func(authority string) (netResolver, error) {
+	host, port, err := parseTarget(authority, defaultDNSSvrPort)
+	if err != nil {
+		return nil, err
+	}
+
+	authorityWithPort := net.JoinHostPort(host, port)
+
+	return &net.Resolver{
+		PreferGo: true,
+		Dial:     customAuthorityDialler(authorityWithPort),
+	}, nil
+}
+
+// NewBuilder creates a dnsBuilder which is used to factory DNS resolvers.
+func NewBuilder() resolver.Builder {
+	return &dnsBuilder{}
+}
+
+type dnsBuilder struct{}
+
+// Build creates and starts a DNS resolver that watches the name resolution of the target.
+func (b *dnsBuilder) Build(target resolver.Target, cc resolver.ClientConn, opts resolver.BuildOptions) (resolver.Resolver, error) {
+	host, port, err := parseTarget(target.Endpoint, defaultPort)
+	if err != nil {
+		return nil, err
+	}
+
+	// IP address.
+	if ipAddr, ok := formatIP(host); ok {
+		addr := []resolver.Address{{Addr: ipAddr + ":" + port}}
+		cc.UpdateState(resolver.State{Addresses: addr})
+		return deadResolver{}, nil
+	}
+
+	// DNS address (non-IP).
+	ctx, cancel := context.WithCancel(context.Background())
+	d := &dnsResolver{
+		host:                 host,
+		port:                 port,
+		ctx:                  ctx,
+		cancel:               cancel,
+		cc:                   cc,
+		rn:                   make(chan struct{}, 1),
+		disableServiceConfig: opts.DisableServiceConfig,
+	}
+
+	if target.Authority == "" {
+		d.resolver = defaultResolver
+	} else {
+		d.resolver, err = customAuthorityResolver(target.Authority)
+		if err != nil {
+			return nil, err
+		}
+	}
+
+	d.wg.Add(1)
+	go d.watcher()
+	d.ResolveNow(resolver.ResolveNowOptions{})
+	return d, nil
+}
+
+// Scheme returns the naming scheme of this resolver builder, which is "dns".
+func (b *dnsBuilder) Scheme() string {
+	return "dns"
+}
+
+type netResolver interface {
+	LookupHost(ctx context.Context, host string) (addrs []string, err error)
+	LookupSRV(ctx context.Context, service, proto, name string) (cname string, addrs []*net.SRV, err error)
+	LookupTXT(ctx context.Context, name string) (txts []string, err error)
+}
+
+// deadResolver is a resolver that does nothing.
+type deadResolver struct{}
+
+func (deadResolver) ResolveNow(resolver.ResolveNowOptions) {}
+
+func (deadResolver) Close() {}
+
+// dnsResolver watches for the name resolution update for a non-IP target.
+type dnsResolver struct {
+	host     string
+	port     string
+	resolver netResolver
+	ctx      context.Context
+	cancel   context.CancelFunc
+	cc       resolver.ClientConn
+	// rn channel is used by ResolveNow() to force an immediate resolution of the target.
+	rn chan struct{}
+	// wg is used to enforce Close() to return after the watcher() goroutine has finished.
+	// Otherwise, data race will be possible. [Race Example] in dns_resolver_test we
+	// replace the real lookup functions with mocked ones to facilitate testing.
+	// If Close() doesn't wait for watcher() goroutine finishes, race detector sometimes
+	// will warns lookup (READ the lookup function pointers) inside watcher() goroutine
+	// has data race with replaceNetFunc (WRITE the lookup function pointers).
+	wg                   sync.WaitGroup
+	disableServiceConfig bool
+}
+
+// ResolveNow invoke an immediate resolution of the target that this dnsResolver watches.
+func (d *dnsResolver) ResolveNow(resolver.ResolveNowOptions) {
+	select {
+	case d.rn <- struct{}{}:
+	default:
+	}
+}
+
+// Close closes the dnsResolver.
+func (d *dnsResolver) Close() {
+	d.cancel()
+	d.wg.Wait()
+}
+
+func (d *dnsResolver) watcher() {
+	defer d.wg.Done()
+	for {
+		select {
+		case <-d.ctx.Done():
+			return
+		case <-d.rn:
+		}
+
+		state, err := d.lookup()
+		if err != nil {
+			d.cc.ReportError(err)
+		} else {
+			d.cc.UpdateState(*state)
+		}
+
+		// Sleep to prevent excessive re-resolutions. Incoming resolution requests
+		// will be queued in d.rn.
+		t := time.NewTimer(minDNSResRate)
+		select {
+		case <-t.C:
+		case <-d.ctx.Done():
+			t.Stop()
+			return
+		}
+	}
+}
+
+func (d *dnsResolver) lookupSRV() ([]resolver.Address, error) {
+	if !EnableSRVLookups {
+		return nil, nil
+	}
+	var newAddrs []resolver.Address
+	_, srvs, err := d.resolver.LookupSRV(d.ctx, "grpclb", "tcp", d.host)
+	if err != nil {
+		err = handleDNSError(err, "SRV") // may become nil
+		return nil, err
+	}
+	for _, s := range srvs {
+		lbAddrs, err := d.resolver.LookupHost(d.ctx, s.Target)
+		if err != nil {
+			err = handleDNSError(err, "A") // may become nil
+			if err == nil {
+				// If there are other SRV records, look them up and ignore this
+				// one that does not exist.
+				continue
+			}
+			return nil, err
+		}
+		for _, a := range lbAddrs {
+			ip, ok := formatIP(a)
+			if !ok {
+				return nil, fmt.Errorf("dns: error parsing A record IP address %v", a)
+			}
+			addr := ip + ":" + strconv.Itoa(int(s.Port))
+			newAddrs = append(newAddrs, resolver.Address{Addr: addr, Type: resolver.GRPCLB, ServerName: s.Target})
+		}
+	}
+	return newAddrs, nil
+}
+
+var filterError = func(err error) error {
+	if dnsErr, ok := err.(*net.DNSError); ok && !dnsErr.IsTimeout && !dnsErr.IsTemporary {
+		// Timeouts and temporary errors should be communicated to gRPC to
+		// attempt another DNS query (with backoff).  Other errors should be
+		// suppressed (they may represent the absence of a TXT record).
+		return nil
+	}
+	return err
+}
+
+func handleDNSError(err error, lookupType string) error {
+	err = filterError(err)
+	if err != nil {
+		err = fmt.Errorf("dns: %v record lookup error: %v", lookupType, err)
+		grpclog.Infoln(err)
+	}
+	return err
+}
+
+func (d *dnsResolver) lookupTXT() *serviceconfig.ParseResult {
+	ss, err := d.resolver.LookupTXT(d.ctx, txtPrefix+d.host)
+	if err != nil {
+		if envconfig.TXTErrIgnore {
+			return nil
+		}
+		if err = handleDNSError(err, "TXT"); err != nil {
+			return &serviceconfig.ParseResult{Err: err}
+		}
+		return nil
+	}
+	var res string
+	for _, s := range ss {
+		res += s
+	}
+
+	// TXT record must have "grpc_config=" attribute in order to be used as service config.
+	if !strings.HasPrefix(res, txtAttribute) {
+		grpclog.Warningf("dns: TXT record %v missing %v attribute", res, txtAttribute)
+		// This is not an error; it is the equivalent of not having a service config.
+		return nil
+	}
+	sc := canaryingSC(strings.TrimPrefix(res, txtAttribute))
+	return d.cc.ParseServiceConfig(sc)
+}
+
+func (d *dnsResolver) lookupHost() ([]resolver.Address, error) {
+	var newAddrs []resolver.Address
+	addrs, err := d.resolver.LookupHost(d.ctx, d.host)
+	if err != nil {
+		err = handleDNSError(err, "A")
+		return nil, err
+	}
+	for _, a := range addrs {
+		ip, ok := formatIP(a)
+		if !ok {
+			return nil, fmt.Errorf("dns: error parsing A record IP address %v", a)
+		}
+		addr := ip + ":" + d.port
+		newAddrs = append(newAddrs, resolver.Address{Addr: addr})
+	}
+	return newAddrs, nil
+}
+
+func (d *dnsResolver) lookup() (*resolver.State, error) {
+	srv, srvErr := d.lookupSRV()
+	addrs, hostErr := d.lookupHost()
+	if hostErr != nil && (srvErr != nil || len(srv) == 0) {
+		return nil, hostErr
+	}
+	state := &resolver.State{
+		Addresses: append(addrs, srv...),
+	}
+	if !d.disableServiceConfig {
+		state.ServiceConfig = d.lookupTXT()
+	}
+	return state, nil
+}
+
+// formatIP returns ok = false if addr is not a valid textual representation of an IP address.
+// If addr is an IPv4 address, return the addr and ok = true.
+// If addr is an IPv6 address, return the addr enclosed in square brackets and ok = true.
+func formatIP(addr string) (addrIP string, ok bool) {
+	ip := net.ParseIP(addr)
+	if ip == nil {
+		return "", false
+	}
+	if ip.To4() != nil {
+		return addr, true
+	}
+	return "[" + addr + "]", true
+}
+
+// parseTarget takes the user input target string and default port, returns formatted host and port info.
+// If target doesn't specify a port, set the port to be the defaultPort.
+// If target is in IPv6 format and host-name is enclosed in square brackets, brackets
+// are stripped when setting the host.
+// examples:
+// target: "www.google.com" defaultPort: "443" returns host: "www.google.com", port: "443"
+// target: "ipv4-host:80" defaultPort: "443" returns host: "ipv4-host", port: "80"
+// target: "[ipv6-host]" defaultPort: "443" returns host: "ipv6-host", port: "443"
+// target: ":80" defaultPort: "443" returns host: "localhost", port: "80"
+func parseTarget(target, defaultPort string) (host, port string, err error) {
+	if target == "" {
+		return "", "", errMissingAddr
+	}
+	if ip := net.ParseIP(target); ip != nil {
+		// target is an IPv4 or IPv6(without brackets) address
+		return target, defaultPort, nil
+	}
+	if host, port, err = net.SplitHostPort(target); err == nil {
+		if port == "" {
+			// If the port field is empty (target ends with colon), e.g. "[::1]:", this is an error.
+			return "", "", errEndsWithColon
+		}
+		// target has port, i.e ipv4-host:port, [ipv6-host]:port, host-name:port
+		if host == "" {
+			// Keep consistent with net.Dial(): If the host is empty, as in ":80", the local system is assumed.
+			host = "localhost"
+		}
+		return host, port, nil
+	}
+	if host, port, err = net.SplitHostPort(target + ":" + defaultPort); err == nil {
+		// target doesn't have port
+		return host, port, nil
+	}
+	return "", "", fmt.Errorf("invalid target address %v, error info: %v", target, err)
+}
+
+type rawChoice struct {
+	ClientLanguage *[]string        `json:"clientLanguage,omitempty"`
+	Percentage     *int             `json:"percentage,omitempty"`
+	ClientHostName *[]string        `json:"clientHostName,omitempty"`
+	ServiceConfig  *json.RawMessage `json:"serviceConfig,omitempty"`
+}
+
+func containsString(a *[]string, b string) bool {
+	if a == nil {
+		return true
+	}
+	for _, c := range *a {
+		if c == b {
+			return true
+		}
+	}
+	return false
+}
+
+func chosenByPercentage(a *int) bool {
+	if a == nil {
+		return true
+	}
+	return grpcrand.Intn(100)+1 <= *a
+}
+
+func canaryingSC(js string) string {
+	if js == "" {
+		return ""
+	}
+	var rcs []rawChoice
+	err := json.Unmarshal([]byte(js), &rcs)
+	if err != nil {
+		grpclog.Warningf("dns: error parsing service config json: %v", err)
+		return ""
+	}
+	cliHostname, err := os.Hostname()
+	if err != nil {
+		grpclog.Warningf("dns: error getting client hostname: %v", err)
+		return ""
+	}
+	var sc string
+	for _, c := range rcs {
+		if !containsString(c.ClientLanguage, golang) ||
+			!chosenByPercentage(c.Percentage) ||
+			!containsString(c.ClientHostName, cliHostname) ||
+			c.ServiceConfig == nil {
+			continue
+		}
+		sc = string(*c.ServiceConfig)
+		break
+	}
+	return sc
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/internal/resolver/dns/go113.go b/demo_test/vendor/google.golang.org/grpc/internal/resolver/dns/go113.go
new file mode 100644
index 0000000..8783a8c
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/internal/resolver/dns/go113.go
@@ -0,0 +1,33 @@
+// +build go1.13
+
+/*
+ *
+ * Copyright 2019 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package dns
+
+import "net"
+
+func init() {
+	filterError = func(err error) error {
+		if dnsErr, ok := err.(*net.DNSError); ok && dnsErr.IsNotFound {
+			// The name does not exist; not an error.
+			return nil
+		}
+		return err
+	}
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/internal/resolver/passthrough/passthrough.go b/demo_test/vendor/google.golang.org/grpc/internal/resolver/passthrough/passthrough.go
new file mode 100644
index 0000000..520d922
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/internal/resolver/passthrough/passthrough.go
@@ -0,0 +1,57 @@
+/*
+ *
+ * Copyright 2017 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+// Package passthrough implements a pass-through resolver. It sends the target
+// name without scheme back to gRPC as resolved address.
+package passthrough
+
+import "google.golang.org/grpc/resolver"
+
+const scheme = "passthrough"
+
+type passthroughBuilder struct{}
+
+func (*passthroughBuilder) Build(target resolver.Target, cc resolver.ClientConn, opts resolver.BuildOptions) (resolver.Resolver, error) {
+	r := &passthroughResolver{
+		target: target,
+		cc:     cc,
+	}
+	r.start()
+	return r, nil
+}
+
+func (*passthroughBuilder) Scheme() string {
+	return scheme
+}
+
+type passthroughResolver struct {
+	target resolver.Target
+	cc     resolver.ClientConn
+}
+
+func (r *passthroughResolver) start() {
+	r.cc.UpdateState(resolver.State{Addresses: []resolver.Address{{Addr: r.target.Endpoint}}})
+}
+
+func (*passthroughResolver) ResolveNow(o resolver.ResolveNowOptions) {}
+
+func (*passthroughResolver) Close() {}
+
+func init() {
+	resolver.Register(&passthroughBuilder{})
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/internal/status/status.go b/demo_test/vendor/google.golang.org/grpc/internal/status/status.go
new file mode 100644
index 0000000..6812606
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/internal/status/status.go
@@ -0,0 +1,161 @@
+/*
+ *
+ * Copyright 2020 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+// Package status implements errors returned by gRPC.  These errors are
+// serialized and transmitted on the wire between server and client, and allow
+// for additional data to be transmitted via the Details field in the status
+// proto.  gRPC service handlers should return an error created by this
+// package, and gRPC clients should expect a corresponding error to be
+// returned from the RPC call.
+//
+// This package upholds the invariants that a non-nil error may not
+// contain an OK code, and an OK code must result in a nil error.
+package status
+
+import (
+	"errors"
+	"fmt"
+
+	"github.com/golang/protobuf/proto"
+	"github.com/golang/protobuf/ptypes"
+	spb "google.golang.org/genproto/googleapis/rpc/status"
+	"google.golang.org/grpc/codes"
+)
+
+// Status represents an RPC status code, message, and details.  It is immutable
+// and should be created with New, Newf, or FromProto.
+type Status struct {
+	s *spb.Status
+}
+
+// New returns a Status representing c and msg.
+func New(c codes.Code, msg string) *Status {
+	return &Status{s: &spb.Status{Code: int32(c), Message: msg}}
+}
+
+// Newf returns New(c, fmt.Sprintf(format, a...)).
+func Newf(c codes.Code, format string, a ...interface{}) *Status {
+	return New(c, fmt.Sprintf(format, a...))
+}
+
+// FromProto returns a Status representing s.
+func FromProto(s *spb.Status) *Status {
+	return &Status{s: proto.Clone(s).(*spb.Status)}
+}
+
+// Err returns an error representing c and msg.  If c is OK, returns nil.
+func Err(c codes.Code, msg string) error {
+	return New(c, msg).Err()
+}
+
+// Errorf returns Error(c, fmt.Sprintf(format, a...)).
+func Errorf(c codes.Code, format string, a ...interface{}) error {
+	return Err(c, fmt.Sprintf(format, a...))
+}
+
+// Code returns the status code contained in s.
+func (s *Status) Code() codes.Code {
+	if s == nil || s.s == nil {
+		return codes.OK
+	}
+	return codes.Code(s.s.Code)
+}
+
+// Message returns the message contained in s.
+func (s *Status) Message() string {
+	if s == nil || s.s == nil {
+		return ""
+	}
+	return s.s.Message
+}
+
+// Proto returns s's status as an spb.Status proto message.
+func (s *Status) Proto() *spb.Status {
+	if s == nil {
+		return nil
+	}
+	return proto.Clone(s.s).(*spb.Status)
+}
+
+// Err returns an immutable error representing s; returns nil if s.Code() is OK.
+func (s *Status) Err() error {
+	if s.Code() == codes.OK {
+		return nil
+	}
+	return (*Error)(s.Proto())
+}
+
+// WithDetails returns a new status with the provided details messages appended to the status.
+// If any errors are encountered, it returns nil and the first error encountered.
+func (s *Status) WithDetails(details ...proto.Message) (*Status, error) {
+	if s.Code() == codes.OK {
+		return nil, errors.New("no error details for status with code OK")
+	}
+	// s.Code() != OK implies that s.Proto() != nil.
+	p := s.Proto()
+	for _, detail := range details {
+		any, err := ptypes.MarshalAny(detail)
+		if err != nil {
+			return nil, err
+		}
+		p.Details = append(p.Details, any)
+	}
+	return &Status{s: p}, nil
+}
+
+// Details returns a slice of details messages attached to the status.
+// If a detail cannot be decoded, the error is returned in place of the detail.
+func (s *Status) Details() []interface{} {
+	if s == nil || s.s == nil {
+		return nil
+	}
+	details := make([]interface{}, 0, len(s.s.Details))
+	for _, any := range s.s.Details {
+		detail := &ptypes.DynamicAny{}
+		if err := ptypes.UnmarshalAny(any, detail); err != nil {
+			details = append(details, err)
+			continue
+		}
+		details = append(details, detail.Message)
+	}
+	return details
+}
+
+// Error is an alias of a status proto. It implements error and Status,
+// and a nil Error should never be returned by this package.
+type Error spb.Status
+
+func (se *Error) Error() string {
+	p := (*spb.Status)(se)
+	return fmt.Sprintf("rpc error: code = %s desc = %s", codes.Code(p.GetCode()), p.GetMessage())
+}
+
+// GRPCStatus returns the Status represented by se.
+func (se *Error) GRPCStatus() *Status {
+	return FromProto((*spb.Status)(se))
+}
+
+// Is implements future error.Is functionality.
+// A Error is equivalent if the code and message are identical.
+func (se *Error) Is(target error) bool {
+	tse, ok := target.(*Error)
+	if !ok {
+		return false
+	}
+	return proto.Equal((*spb.Status)(se), (*spb.Status)(tse))
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/internal/syscall/syscall_linux.go b/demo_test/vendor/google.golang.org/grpc/internal/syscall/syscall_linux.go
new file mode 100644
index 0000000..43281a3
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/internal/syscall/syscall_linux.go
@@ -0,0 +1,114 @@
+// +build !appengine
+
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+// Package syscall provides functionalities that grpc uses to get low-level operating system
+// stats/info.
+package syscall
+
+import (
+	"fmt"
+	"net"
+	"syscall"
+	"time"
+
+	"golang.org/x/sys/unix"
+	"google.golang.org/grpc/grpclog"
+)
+
+// GetCPUTime returns the how much CPU time has passed since the start of this process.
+func GetCPUTime() int64 {
+	var ts unix.Timespec
+	if err := unix.ClockGettime(unix.CLOCK_PROCESS_CPUTIME_ID, &ts); err != nil {
+		grpclog.Fatal(err)
+	}
+	return ts.Nano()
+}
+
+// Rusage is an alias for syscall.Rusage under linux non-appengine environment.
+type Rusage syscall.Rusage
+
+// GetRusage returns the resource usage of current process.
+func GetRusage() (rusage *Rusage) {
+	rusage = new(Rusage)
+	syscall.Getrusage(syscall.RUSAGE_SELF, (*syscall.Rusage)(rusage))
+	return
+}
+
+// CPUTimeDiff returns the differences of user CPU time and system CPU time used
+// between two Rusage structs.
+func CPUTimeDiff(first *Rusage, latest *Rusage) (float64, float64) {
+	f := (*syscall.Rusage)(first)
+	l := (*syscall.Rusage)(latest)
+	var (
+		utimeDiffs  = l.Utime.Sec - f.Utime.Sec
+		utimeDiffus = l.Utime.Usec - f.Utime.Usec
+		stimeDiffs  = l.Stime.Sec - f.Stime.Sec
+		stimeDiffus = l.Stime.Usec - f.Stime.Usec
+	)
+
+	uTimeElapsed := float64(utimeDiffs) + float64(utimeDiffus)*1.0e-6
+	sTimeElapsed := float64(stimeDiffs) + float64(stimeDiffus)*1.0e-6
+
+	return uTimeElapsed, sTimeElapsed
+}
+
+// SetTCPUserTimeout sets the TCP user timeout on a connection's socket
+func SetTCPUserTimeout(conn net.Conn, timeout time.Duration) error {
+	tcpconn, ok := conn.(*net.TCPConn)
+	if !ok {
+		// not a TCP connection. exit early
+		return nil
+	}
+	rawConn, err := tcpconn.SyscallConn()
+	if err != nil {
+		return fmt.Errorf("error getting raw connection: %v", err)
+	}
+	err = rawConn.Control(func(fd uintptr) {
+		err = syscall.SetsockoptInt(int(fd), syscall.IPPROTO_TCP, unix.TCP_USER_TIMEOUT, int(timeout/time.Millisecond))
+	})
+	if err != nil {
+		return fmt.Errorf("error setting option on socket: %v", err)
+	}
+
+	return nil
+}
+
+// GetTCPUserTimeout gets the TCP user timeout on a connection's socket
+func GetTCPUserTimeout(conn net.Conn) (opt int, err error) {
+	tcpconn, ok := conn.(*net.TCPConn)
+	if !ok {
+		err = fmt.Errorf("conn is not *net.TCPConn. got %T", conn)
+		return
+	}
+	rawConn, err := tcpconn.SyscallConn()
+	if err != nil {
+		err = fmt.Errorf("error getting raw connection: %v", err)
+		return
+	}
+	err = rawConn.Control(func(fd uintptr) {
+		opt, err = syscall.GetsockoptInt(int(fd), syscall.IPPROTO_TCP, unix.TCP_USER_TIMEOUT)
+	})
+	if err != nil {
+		err = fmt.Errorf("error getting option on socket: %v", err)
+		return
+	}
+
+	return
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/internal/syscall/syscall_nonlinux.go b/demo_test/vendor/google.golang.org/grpc/internal/syscall/syscall_nonlinux.go
new file mode 100644
index 0000000..d3fd9da
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/internal/syscall/syscall_nonlinux.go
@@ -0,0 +1,73 @@
+// +build !linux appengine
+
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package syscall
+
+import (
+	"net"
+	"sync"
+	"time"
+
+	"google.golang.org/grpc/grpclog"
+)
+
+var once sync.Once
+
+func log() {
+	once.Do(func() {
+		grpclog.Info("CPU time info is unavailable on non-linux or appengine environment.")
+	})
+}
+
+// GetCPUTime returns the how much CPU time has passed since the start of this process.
+// It always returns 0 under non-linux or appengine environment.
+func GetCPUTime() int64 {
+	log()
+	return 0
+}
+
+// Rusage is an empty struct under non-linux or appengine environment.
+type Rusage struct{}
+
+// GetRusage is a no-op function under non-linux or appengine environment.
+func GetRusage() (rusage *Rusage) {
+	log()
+	return nil
+}
+
+// CPUTimeDiff returns the differences of user CPU time and system CPU time used
+// between two Rusage structs. It a no-op function for non-linux or appengine environment.
+func CPUTimeDiff(first *Rusage, latest *Rusage) (float64, float64) {
+	log()
+	return 0, 0
+}
+
+// SetTCPUserTimeout is a no-op function under non-linux or appengine environments
+func SetTCPUserTimeout(conn net.Conn, timeout time.Duration) error {
+	log()
+	return nil
+}
+
+// GetTCPUserTimeout is a no-op function under non-linux or appengine environments
+// a negative return value indicates the operation is not supported
+func GetTCPUserTimeout(conn net.Conn) (int, error) {
+	log()
+	return -1, nil
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/internal/transport/bdp_estimator.go b/demo_test/vendor/google.golang.org/grpc/internal/transport/bdp_estimator.go
new file mode 100644
index 0000000..070680e
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/internal/transport/bdp_estimator.go
@@ -0,0 +1,141 @@
+/*
+ *
+ * Copyright 2017 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package transport
+
+import (
+	"sync"
+	"time"
+)
+
+const (
+	// bdpLimit is the maximum value the flow control windows will be increased
+	// to.  TCP typically limits this to 4MB, but some systems go up to 16MB.
+	// Since this is only a limit, it is safe to make it optimistic.
+	bdpLimit = (1 << 20) * 16
+	// alpha is a constant factor used to keep a moving average
+	// of RTTs.
+	alpha = 0.9
+	// If the current bdp sample is greater than or equal to
+	// our beta * our estimated bdp and the current bandwidth
+	// sample is the maximum bandwidth observed so far, we
+	// increase our bbp estimate by a factor of gamma.
+	beta = 0.66
+	// To put our bdp to be smaller than or equal to twice the real BDP,
+	// we should multiply our current sample with 4/3, however to round things out
+	// we use 2 as the multiplication factor.
+	gamma = 2
+)
+
+// Adding arbitrary data to ping so that its ack can be identified.
+// Easter-egg: what does the ping message say?
+var bdpPing = &ping{data: [8]byte{2, 4, 16, 16, 9, 14, 7, 7}}
+
+type bdpEstimator struct {
+	// sentAt is the time when the ping was sent.
+	sentAt time.Time
+
+	mu sync.Mutex
+	// bdp is the current bdp estimate.
+	bdp uint32
+	// sample is the number of bytes received in one measurement cycle.
+	sample uint32
+	// bwMax is the maximum bandwidth noted so far (bytes/sec).
+	bwMax float64
+	// bool to keep track of the beginning of a new measurement cycle.
+	isSent bool
+	// Callback to update the window sizes.
+	updateFlowControl func(n uint32)
+	// sampleCount is the number of samples taken so far.
+	sampleCount uint64
+	// round trip time (seconds)
+	rtt float64
+}
+
+// timesnap registers the time bdp ping was sent out so that
+// network rtt can be calculated when its ack is received.
+// It is called (by controller) when the bdpPing is
+// being written on the wire.
+func (b *bdpEstimator) timesnap(d [8]byte) {
+	if bdpPing.data != d {
+		return
+	}
+	b.sentAt = time.Now()
+}
+
+// add adds bytes to the current sample for calculating bdp.
+// It returns true only if a ping must be sent. This can be used
+// by the caller (handleData) to make decision about batching
+// a window update with it.
+func (b *bdpEstimator) add(n uint32) bool {
+	b.mu.Lock()
+	defer b.mu.Unlock()
+	if b.bdp == bdpLimit {
+		return false
+	}
+	if !b.isSent {
+		b.isSent = true
+		b.sample = n
+		b.sentAt = time.Time{}
+		b.sampleCount++
+		return true
+	}
+	b.sample += n
+	return false
+}
+
+// calculate is called when an ack for a bdp ping is received.
+// Here we calculate the current bdp and bandwidth sample and
+// decide if the flow control windows should go up.
+func (b *bdpEstimator) calculate(d [8]byte) {
+	// Check if the ping acked for was the bdp ping.
+	if bdpPing.data != d {
+		return
+	}
+	b.mu.Lock()
+	rttSample := time.Since(b.sentAt).Seconds()
+	if b.sampleCount < 10 {
+		// Bootstrap rtt with an average of first 10 rtt samples.
+		b.rtt += (rttSample - b.rtt) / float64(b.sampleCount)
+	} else {
+		// Heed to the recent past more.
+		b.rtt += (rttSample - b.rtt) * float64(alpha)
+	}
+	b.isSent = false
+	// The number of bytes accumulated so far in the sample is smaller
+	// than or equal to 1.5 times the real BDP on a saturated connection.
+	bwCurrent := float64(b.sample) / (b.rtt * float64(1.5))
+	if bwCurrent > b.bwMax {
+		b.bwMax = bwCurrent
+	}
+	// If the current sample (which is smaller than or equal to the 1.5 times the real BDP) is
+	// greater than or equal to 2/3rd our perceived bdp AND this is the maximum bandwidth seen so far, we
+	// should update our perception of the network BDP.
+	if float64(b.sample) >= beta*float64(b.bdp) && bwCurrent == b.bwMax && b.bdp != bdpLimit {
+		sampleFloat := float64(b.sample)
+		b.bdp = uint32(gamma * sampleFloat)
+		if b.bdp > bdpLimit {
+			b.bdp = bdpLimit
+		}
+		bdp := b.bdp
+		b.mu.Unlock()
+		b.updateFlowControl(bdp)
+		return
+	}
+	b.mu.Unlock()
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/internal/transport/controlbuf.go b/demo_test/vendor/google.golang.org/grpc/internal/transport/controlbuf.go
new file mode 100644
index 0000000..ddee20b
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/internal/transport/controlbuf.go
@@ -0,0 +1,926 @@
+/*
+ *
+ * Copyright 2014 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package transport
+
+import (
+	"bytes"
+	"fmt"
+	"runtime"
+	"sync"
+	"sync/atomic"
+
+	"golang.org/x/net/http2"
+	"golang.org/x/net/http2/hpack"
+)
+
+var updateHeaderTblSize = func(e *hpack.Encoder, v uint32) {
+	e.SetMaxDynamicTableSizeLimit(v)
+}
+
+type itemNode struct {
+	it   interface{}
+	next *itemNode
+}
+
+type itemList struct {
+	head *itemNode
+	tail *itemNode
+}
+
+func (il *itemList) enqueue(i interface{}) {
+	n := &itemNode{it: i}
+	if il.tail == nil {
+		il.head, il.tail = n, n
+		return
+	}
+	il.tail.next = n
+	il.tail = n
+}
+
+// peek returns the first item in the list without removing it from the
+// list.
+func (il *itemList) peek() interface{} {
+	return il.head.it
+}
+
+func (il *itemList) dequeue() interface{} {
+	if il.head == nil {
+		return nil
+	}
+	i := il.head.it
+	il.head = il.head.next
+	if il.head == nil {
+		il.tail = nil
+	}
+	return i
+}
+
+func (il *itemList) dequeueAll() *itemNode {
+	h := il.head
+	il.head, il.tail = nil, nil
+	return h
+}
+
+func (il *itemList) isEmpty() bool {
+	return il.head == nil
+}
+
+// The following defines various control items which could flow through
+// the control buffer of transport. They represent different aspects of
+// control tasks, e.g., flow control, settings, streaming resetting, etc.
+
+// maxQueuedTransportResponseFrames is the most queued "transport response"
+// frames we will buffer before preventing new reads from occurring on the
+// transport.  These are control frames sent in response to client requests,
+// such as RST_STREAM due to bad headers or settings acks.
+const maxQueuedTransportResponseFrames = 50
+
+type cbItem interface {
+	isTransportResponseFrame() bool
+}
+
+// registerStream is used to register an incoming stream with loopy writer.
+type registerStream struct {
+	streamID uint32
+	wq       *writeQuota
+}
+
+func (*registerStream) isTransportResponseFrame() bool { return false }
+
+// headerFrame is also used to register stream on the client-side.
+type headerFrame struct {
+	streamID   uint32
+	hf         []hpack.HeaderField
+	endStream  bool               // Valid on server side.
+	initStream func(uint32) error // Used only on the client side.
+	onWrite    func()
+	wq         *writeQuota    // write quota for the stream created.
+	cleanup    *cleanupStream // Valid on the server side.
+	onOrphaned func(error)    // Valid on client-side
+}
+
+func (h *headerFrame) isTransportResponseFrame() bool {
+	return h.cleanup != nil && h.cleanup.rst // Results in a RST_STREAM
+}
+
+type cleanupStream struct {
+	streamID uint32
+	rst      bool
+	rstCode  http2.ErrCode
+	onWrite  func()
+}
+
+func (c *cleanupStream) isTransportResponseFrame() bool { return c.rst } // Results in a RST_STREAM
+
+type dataFrame struct {
+	streamID  uint32
+	endStream bool
+	h         []byte
+	d         []byte
+	// onEachWrite is called every time
+	// a part of d is written out.
+	onEachWrite func()
+}
+
+func (*dataFrame) isTransportResponseFrame() bool { return false }
+
+type incomingWindowUpdate struct {
+	streamID  uint32
+	increment uint32
+}
+
+func (*incomingWindowUpdate) isTransportResponseFrame() bool { return false }
+
+type outgoingWindowUpdate struct {
+	streamID  uint32
+	increment uint32
+}
+
+func (*outgoingWindowUpdate) isTransportResponseFrame() bool {
+	return false // window updates are throttled by thresholds
+}
+
+type incomingSettings struct {
+	ss []http2.Setting
+}
+
+func (*incomingSettings) isTransportResponseFrame() bool { return true } // Results in a settings ACK
+
+type outgoingSettings struct {
+	ss []http2.Setting
+}
+
+func (*outgoingSettings) isTransportResponseFrame() bool { return false }
+
+type incomingGoAway struct {
+}
+
+func (*incomingGoAway) isTransportResponseFrame() bool { return false }
+
+type goAway struct {
+	code      http2.ErrCode
+	debugData []byte
+	headsUp   bool
+	closeConn bool
+}
+
+func (*goAway) isTransportResponseFrame() bool { return false }
+
+type ping struct {
+	ack  bool
+	data [8]byte
+}
+
+func (*ping) isTransportResponseFrame() bool { return true }
+
+type outFlowControlSizeRequest struct {
+	resp chan uint32
+}
+
+func (*outFlowControlSizeRequest) isTransportResponseFrame() bool { return false }
+
+type outStreamState int
+
+const (
+	active outStreamState = iota
+	empty
+	waitingOnStreamQuota
+)
+
+type outStream struct {
+	id               uint32
+	state            outStreamState
+	itl              *itemList
+	bytesOutStanding int
+	wq               *writeQuota
+
+	next *outStream
+	prev *outStream
+}
+
+func (s *outStream) deleteSelf() {
+	if s.prev != nil {
+		s.prev.next = s.next
+	}
+	if s.next != nil {
+		s.next.prev = s.prev
+	}
+	s.next, s.prev = nil, nil
+}
+
+type outStreamList struct {
+	// Following are sentinel objects that mark the
+	// beginning and end of the list. They do not
+	// contain any item lists. All valid objects are
+	// inserted in between them.
+	// This is needed so that an outStream object can
+	// deleteSelf() in O(1) time without knowing which
+	// list it belongs to.
+	head *outStream
+	tail *outStream
+}
+
+func newOutStreamList() *outStreamList {
+	head, tail := new(outStream), new(outStream)
+	head.next = tail
+	tail.prev = head
+	return &outStreamList{
+		head: head,
+		tail: tail,
+	}
+}
+
+func (l *outStreamList) enqueue(s *outStream) {
+	e := l.tail.prev
+	e.next = s
+	s.prev = e
+	s.next = l.tail
+	l.tail.prev = s
+}
+
+// remove from the beginning of the list.
+func (l *outStreamList) dequeue() *outStream {
+	b := l.head.next
+	if b == l.tail {
+		return nil
+	}
+	b.deleteSelf()
+	return b
+}
+
+// controlBuffer is a way to pass information to loopy.
+// Information is passed as specific struct types called control frames.
+// A control frame not only represents data, messages or headers to be sent out
+// but can also be used to instruct loopy to update its internal state.
+// It shouldn't be confused with an HTTP2 frame, although some of the control frames
+// like dataFrame and headerFrame do go out on wire as HTTP2 frames.
+type controlBuffer struct {
+	ch              chan struct{}
+	done            <-chan struct{}
+	mu              sync.Mutex
+	consumerWaiting bool
+	list            *itemList
+	err             error
+
+	// transportResponseFrames counts the number of queued items that represent
+	// the response of an action initiated by the peer.  trfChan is created
+	// when transportResponseFrames >= maxQueuedTransportResponseFrames and is
+	// closed and nilled when transportResponseFrames drops below the
+	// threshold.  Both fields are protected by mu.
+	transportResponseFrames int
+	trfChan                 atomic.Value // *chan struct{}
+}
+
+func newControlBuffer(done <-chan struct{}) *controlBuffer {
+	return &controlBuffer{
+		ch:   make(chan struct{}, 1),
+		list: &itemList{},
+		done: done,
+	}
+}
+
+// throttle blocks if there are too many incomingSettings/cleanupStreams in the
+// controlbuf.
+func (c *controlBuffer) throttle() {
+	ch, _ := c.trfChan.Load().(*chan struct{})
+	if ch != nil {
+		select {
+		case <-*ch:
+		case <-c.done:
+		}
+	}
+}
+
+func (c *controlBuffer) put(it cbItem) error {
+	_, err := c.executeAndPut(nil, it)
+	return err
+}
+
+func (c *controlBuffer) executeAndPut(f func(it interface{}) bool, it cbItem) (bool, error) {
+	var wakeUp bool
+	c.mu.Lock()
+	if c.err != nil {
+		c.mu.Unlock()
+		return false, c.err
+	}
+	if f != nil {
+		if !f(it) { // f wasn't successful
+			c.mu.Unlock()
+			return false, nil
+		}
+	}
+	if c.consumerWaiting {
+		wakeUp = true
+		c.consumerWaiting = false
+	}
+	c.list.enqueue(it)
+	if it.isTransportResponseFrame() {
+		c.transportResponseFrames++
+		if c.transportResponseFrames == maxQueuedTransportResponseFrames {
+			// We are adding the frame that puts us over the threshold; create
+			// a throttling channel.
+			ch := make(chan struct{})
+			c.trfChan.Store(&ch)
+		}
+	}
+	c.mu.Unlock()
+	if wakeUp {
+		select {
+		case c.ch <- struct{}{}:
+		default:
+		}
+	}
+	return true, nil
+}
+
+// Note argument f should never be nil.
+func (c *controlBuffer) execute(f func(it interface{}) bool, it interface{}) (bool, error) {
+	c.mu.Lock()
+	if c.err != nil {
+		c.mu.Unlock()
+		return false, c.err
+	}
+	if !f(it) { // f wasn't successful
+		c.mu.Unlock()
+		return false, nil
+	}
+	c.mu.Unlock()
+	return true, nil
+}
+
+func (c *controlBuffer) get(block bool) (interface{}, error) {
+	for {
+		c.mu.Lock()
+		if c.err != nil {
+			c.mu.Unlock()
+			return nil, c.err
+		}
+		if !c.list.isEmpty() {
+			h := c.list.dequeue().(cbItem)
+			if h.isTransportResponseFrame() {
+				if c.transportResponseFrames == maxQueuedTransportResponseFrames {
+					// We are removing the frame that put us over the
+					// threshold; close and clear the throttling channel.
+					ch := c.trfChan.Load().(*chan struct{})
+					close(*ch)
+					c.trfChan.Store((*chan struct{})(nil))
+				}
+				c.transportResponseFrames--
+			}
+			c.mu.Unlock()
+			return h, nil
+		}
+		if !block {
+			c.mu.Unlock()
+			return nil, nil
+		}
+		c.consumerWaiting = true
+		c.mu.Unlock()
+		select {
+		case <-c.ch:
+		case <-c.done:
+			c.finish()
+			return nil, ErrConnClosing
+		}
+	}
+}
+
+func (c *controlBuffer) finish() {
+	c.mu.Lock()
+	if c.err != nil {
+		c.mu.Unlock()
+		return
+	}
+	c.err = ErrConnClosing
+	// There may be headers for streams in the control buffer.
+	// These streams need to be cleaned out since the transport
+	// is still not aware of these yet.
+	for head := c.list.dequeueAll(); head != nil; head = head.next {
+		hdr, ok := head.it.(*headerFrame)
+		if !ok {
+			continue
+		}
+		if hdr.onOrphaned != nil { // It will be nil on the server-side.
+			hdr.onOrphaned(ErrConnClosing)
+		}
+	}
+	c.mu.Unlock()
+}
+
+type side int
+
+const (
+	clientSide side = iota
+	serverSide
+)
+
+// Loopy receives frames from the control buffer.
+// Each frame is handled individually; most of the work done by loopy goes
+// into handling data frames. Loopy maintains a queue of active streams, and each
+// stream maintains a queue of data frames; as loopy receives data frames
+// it gets added to the queue of the relevant stream.
+// Loopy goes over this list of active streams by processing one node every iteration,
+// thereby closely resemebling to a round-robin scheduling over all streams. While
+// processing a stream, loopy writes out data bytes from this stream capped by the min
+// of http2MaxFrameLen, connection-level flow control and stream-level flow control.
+type loopyWriter struct {
+	side      side
+	cbuf      *controlBuffer
+	sendQuota uint32
+	oiws      uint32 // outbound initial window size.
+	// estdStreams is map of all established streams that are not cleaned-up yet.
+	// On client-side, this is all streams whose headers were sent out.
+	// On server-side, this is all streams whose headers were received.
+	estdStreams map[uint32]*outStream // Established streams.
+	// activeStreams is a linked-list of all streams that have data to send and some
+	// stream-level flow control quota.
+	// Each of these streams internally have a list of data items(and perhaps trailers
+	// on the server-side) to be sent out.
+	activeStreams *outStreamList
+	framer        *framer
+	hBuf          *bytes.Buffer  // The buffer for HPACK encoding.
+	hEnc          *hpack.Encoder // HPACK encoder.
+	bdpEst        *bdpEstimator
+	draining      bool
+
+	// Side-specific handlers
+	ssGoAwayHandler func(*goAway) (bool, error)
+}
+
+func newLoopyWriter(s side, fr *framer, cbuf *controlBuffer, bdpEst *bdpEstimator) *loopyWriter {
+	var buf bytes.Buffer
+	l := &loopyWriter{
+		side:          s,
+		cbuf:          cbuf,
+		sendQuota:     defaultWindowSize,
+		oiws:          defaultWindowSize,
+		estdStreams:   make(map[uint32]*outStream),
+		activeStreams: newOutStreamList(),
+		framer:        fr,
+		hBuf:          &buf,
+		hEnc:          hpack.NewEncoder(&buf),
+		bdpEst:        bdpEst,
+	}
+	return l
+}
+
+const minBatchSize = 1000
+
+// run should be run in a separate goroutine.
+// It reads control frames from controlBuf and processes them by:
+// 1. Updating loopy's internal state, or/and
+// 2. Writing out HTTP2 frames on the wire.
+//
+// Loopy keeps all active streams with data to send in a linked-list.
+// All streams in the activeStreams linked-list must have both:
+// 1. Data to send, and
+// 2. Stream level flow control quota available.
+//
+// In each iteration of run loop, other than processing the incoming control
+// frame, loopy calls processData, which processes one node from the activeStreams linked-list.
+// This results in writing of HTTP2 frames into an underlying write buffer.
+// When there's no more control frames to read from controlBuf, loopy flushes the write buffer.
+// As an optimization, to increase the batch size for each flush, loopy yields the processor, once
+// if the batch size is too low to give stream goroutines a chance to fill it up.
+func (l *loopyWriter) run() (err error) {
+	defer func() {
+		if err == ErrConnClosing {
+			// Don't log ErrConnClosing as error since it happens
+			// 1. When the connection is closed by some other known issue.
+			// 2. User closed the connection.
+			// 3. A graceful close of connection.
+			infof("transport: loopyWriter.run returning. %v", err)
+			err = nil
+		}
+	}()
+	for {
+		it, err := l.cbuf.get(true)
+		if err != nil {
+			return err
+		}
+		if err = l.handle(it); err != nil {
+			return err
+		}
+		if _, err = l.processData(); err != nil {
+			return err
+		}
+		gosched := true
+	hasdata:
+		for {
+			it, err := l.cbuf.get(false)
+			if err != nil {
+				return err
+			}
+			if it != nil {
+				if err = l.handle(it); err != nil {
+					return err
+				}
+				if _, err = l.processData(); err != nil {
+					return err
+				}
+				continue hasdata
+			}
+			isEmpty, err := l.processData()
+			if err != nil {
+				return err
+			}
+			if !isEmpty {
+				continue hasdata
+			}
+			if gosched {
+				gosched = false
+				if l.framer.writer.offset < minBatchSize {
+					runtime.Gosched()
+					continue hasdata
+				}
+			}
+			l.framer.writer.Flush()
+			break hasdata
+
+		}
+	}
+}
+
+func (l *loopyWriter) outgoingWindowUpdateHandler(w *outgoingWindowUpdate) error {
+	return l.framer.fr.WriteWindowUpdate(w.streamID, w.increment)
+}
+
+func (l *loopyWriter) incomingWindowUpdateHandler(w *incomingWindowUpdate) error {
+	// Otherwise update the quota.
+	if w.streamID == 0 {
+		l.sendQuota += w.increment
+		return nil
+	}
+	// Find the stream and update it.
+	if str, ok := l.estdStreams[w.streamID]; ok {
+		str.bytesOutStanding -= int(w.increment)
+		if strQuota := int(l.oiws) - str.bytesOutStanding; strQuota > 0 && str.state == waitingOnStreamQuota {
+			str.state = active
+			l.activeStreams.enqueue(str)
+			return nil
+		}
+	}
+	return nil
+}
+
+func (l *loopyWriter) outgoingSettingsHandler(s *outgoingSettings) error {
+	return l.framer.fr.WriteSettings(s.ss...)
+}
+
+func (l *loopyWriter) incomingSettingsHandler(s *incomingSettings) error {
+	if err := l.applySettings(s.ss); err != nil {
+		return err
+	}
+	return l.framer.fr.WriteSettingsAck()
+}
+
+func (l *loopyWriter) registerStreamHandler(h *registerStream) error {
+	str := &outStream{
+		id:    h.streamID,
+		state: empty,
+		itl:   &itemList{},
+		wq:    h.wq,
+	}
+	l.estdStreams[h.streamID] = str
+	return nil
+}
+
+func (l *loopyWriter) headerHandler(h *headerFrame) error {
+	if l.side == serverSide {
+		str, ok := l.estdStreams[h.streamID]
+		if !ok {
+			warningf("transport: loopy doesn't recognize the stream: %d", h.streamID)
+			return nil
+		}
+		// Case 1.A: Server is responding back with headers.
+		if !h.endStream {
+			return l.writeHeader(h.streamID, h.endStream, h.hf, h.onWrite)
+		}
+		// else:  Case 1.B: Server wants to close stream.
+
+		if str.state != empty { // either active or waiting on stream quota.
+			// add it str's list of items.
+			str.itl.enqueue(h)
+			return nil
+		}
+		if err := l.writeHeader(h.streamID, h.endStream, h.hf, h.onWrite); err != nil {
+			return err
+		}
+		return l.cleanupStreamHandler(h.cleanup)
+	}
+	// Case 2: Client wants to originate stream.
+	str := &outStream{
+		id:    h.streamID,
+		state: empty,
+		itl:   &itemList{},
+		wq:    h.wq,
+	}
+	str.itl.enqueue(h)
+	return l.originateStream(str)
+}
+
+func (l *loopyWriter) originateStream(str *outStream) error {
+	hdr := str.itl.dequeue().(*headerFrame)
+	if err := hdr.initStream(str.id); err != nil {
+		if err == ErrConnClosing {
+			return err
+		}
+		// Other errors(errStreamDrain) need not close transport.
+		return nil
+	}
+	if err := l.writeHeader(str.id, hdr.endStream, hdr.hf, hdr.onWrite); err != nil {
+		return err
+	}
+	l.estdStreams[str.id] = str
+	return nil
+}
+
+func (l *loopyWriter) writeHeader(streamID uint32, endStream bool, hf []hpack.HeaderField, onWrite func()) error {
+	if onWrite != nil {
+		onWrite()
+	}
+	l.hBuf.Reset()
+	for _, f := range hf {
+		if err := l.hEnc.WriteField(f); err != nil {
+			warningf("transport: loopyWriter.writeHeader encountered error while encoding headers:", err)
+		}
+	}
+	var (
+		err               error
+		endHeaders, first bool
+	)
+	first = true
+	for !endHeaders {
+		size := l.hBuf.Len()
+		if size > http2MaxFrameLen {
+			size = http2MaxFrameLen
+		} else {
+			endHeaders = true
+		}
+		if first {
+			first = false
+			err = l.framer.fr.WriteHeaders(http2.HeadersFrameParam{
+				StreamID:      streamID,
+				BlockFragment: l.hBuf.Next(size),
+				EndStream:     endStream,
+				EndHeaders:    endHeaders,
+			})
+		} else {
+			err = l.framer.fr.WriteContinuation(
+				streamID,
+				endHeaders,
+				l.hBuf.Next(size),
+			)
+		}
+		if err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+func (l *loopyWriter) preprocessData(df *dataFrame) error {
+	str, ok := l.estdStreams[df.streamID]
+	if !ok {
+		return nil
+	}
+	// If we got data for a stream it means that
+	// stream was originated and the headers were sent out.
+	str.itl.enqueue(df)
+	if str.state == empty {
+		str.state = active
+		l.activeStreams.enqueue(str)
+	}
+	return nil
+}
+
+func (l *loopyWriter) pingHandler(p *ping) error {
+	if !p.ack {
+		l.bdpEst.timesnap(p.data)
+	}
+	return l.framer.fr.WritePing(p.ack, p.data)
+
+}
+
+func (l *loopyWriter) outFlowControlSizeRequestHandler(o *outFlowControlSizeRequest) error {
+	o.resp <- l.sendQuota
+	return nil
+}
+
+func (l *loopyWriter) cleanupStreamHandler(c *cleanupStream) error {
+	c.onWrite()
+	if str, ok := l.estdStreams[c.streamID]; ok {
+		// On the server side it could be a trailers-only response or
+		// a RST_STREAM before stream initialization thus the stream might
+		// not be established yet.
+		delete(l.estdStreams, c.streamID)
+		str.deleteSelf()
+	}
+	if c.rst { // If RST_STREAM needs to be sent.
+		if err := l.framer.fr.WriteRSTStream(c.streamID, c.rstCode); err != nil {
+			return err
+		}
+	}
+	if l.side == clientSide && l.draining && len(l.estdStreams) == 0 {
+		return ErrConnClosing
+	}
+	return nil
+}
+
+func (l *loopyWriter) incomingGoAwayHandler(*incomingGoAway) error {
+	if l.side == clientSide {
+		l.draining = true
+		if len(l.estdStreams) == 0 {
+			return ErrConnClosing
+		}
+	}
+	return nil
+}
+
+func (l *loopyWriter) goAwayHandler(g *goAway) error {
+	// Handling of outgoing GoAway is very specific to side.
+	if l.ssGoAwayHandler != nil {
+		draining, err := l.ssGoAwayHandler(g)
+		if err != nil {
+			return err
+		}
+		l.draining = draining
+	}
+	return nil
+}
+
+func (l *loopyWriter) handle(i interface{}) error {
+	switch i := i.(type) {
+	case *incomingWindowUpdate:
+		return l.incomingWindowUpdateHandler(i)
+	case *outgoingWindowUpdate:
+		return l.outgoingWindowUpdateHandler(i)
+	case *incomingSettings:
+		return l.incomingSettingsHandler(i)
+	case *outgoingSettings:
+		return l.outgoingSettingsHandler(i)
+	case *headerFrame:
+		return l.headerHandler(i)
+	case *registerStream:
+		return l.registerStreamHandler(i)
+	case *cleanupStream:
+		return l.cleanupStreamHandler(i)
+	case *incomingGoAway:
+		return l.incomingGoAwayHandler(i)
+	case *dataFrame:
+		return l.preprocessData(i)
+	case *ping:
+		return l.pingHandler(i)
+	case *goAway:
+		return l.goAwayHandler(i)
+	case *outFlowControlSizeRequest:
+		return l.outFlowControlSizeRequestHandler(i)
+	default:
+		return fmt.Errorf("transport: unknown control message type %T", i)
+	}
+}
+
+func (l *loopyWriter) applySettings(ss []http2.Setting) error {
+	for _, s := range ss {
+		switch s.ID {
+		case http2.SettingInitialWindowSize:
+			o := l.oiws
+			l.oiws = s.Val
+			if o < l.oiws {
+				// If the new limit is greater make all depleted streams active.
+				for _, stream := range l.estdStreams {
+					if stream.state == waitingOnStreamQuota {
+						stream.state = active
+						l.activeStreams.enqueue(stream)
+					}
+				}
+			}
+		case http2.SettingHeaderTableSize:
+			updateHeaderTblSize(l.hEnc, s.Val)
+		}
+	}
+	return nil
+}
+
+// processData removes the first stream from active streams, writes out at most 16KB
+// of its data and then puts it at the end of activeStreams if there's still more data
+// to be sent and stream has some stream-level flow control.
+func (l *loopyWriter) processData() (bool, error) {
+	if l.sendQuota == 0 {
+		return true, nil
+	}
+	str := l.activeStreams.dequeue() // Remove the first stream.
+	if str == nil {
+		return true, nil
+	}
+	dataItem := str.itl.peek().(*dataFrame) // Peek at the first data item this stream.
+	// A data item is represented by a dataFrame, since it later translates into
+	// multiple HTTP2 data frames.
+	// Every dataFrame has two buffers; h that keeps grpc-message header and d that is acutal data.
+	// As an optimization to keep wire traffic low, data from d is copied to h to make as big as the
+	// maximum possilbe HTTP2 frame size.
+
+	if len(dataItem.h) == 0 && len(dataItem.d) == 0 { // Empty data frame
+		// Client sends out empty data frame with endStream = true
+		if err := l.framer.fr.WriteData(dataItem.streamID, dataItem.endStream, nil); err != nil {
+			return false, err
+		}
+		str.itl.dequeue() // remove the empty data item from stream
+		if str.itl.isEmpty() {
+			str.state = empty
+		} else if trailer, ok := str.itl.peek().(*headerFrame); ok { // the next item is trailers.
+			if err := l.writeHeader(trailer.streamID, trailer.endStream, trailer.hf, trailer.onWrite); err != nil {
+				return false, err
+			}
+			if err := l.cleanupStreamHandler(trailer.cleanup); err != nil {
+				return false, nil
+			}
+		} else {
+			l.activeStreams.enqueue(str)
+		}
+		return false, nil
+	}
+	var (
+		idx int
+		buf []byte
+	)
+	if len(dataItem.h) != 0 { // data header has not been written out yet.
+		buf = dataItem.h
+	} else {
+		idx = 1
+		buf = dataItem.d
+	}
+	size := http2MaxFrameLen
+	if len(buf) < size {
+		size = len(buf)
+	}
+	if strQuota := int(l.oiws) - str.bytesOutStanding; strQuota <= 0 { // stream-level flow control.
+		str.state = waitingOnStreamQuota
+		return false, nil
+	} else if strQuota < size {
+		size = strQuota
+	}
+
+	if l.sendQuota < uint32(size) { // connection-level flow control.
+		size = int(l.sendQuota)
+	}
+	// Now that outgoing flow controls are checked we can replenish str's write quota
+	str.wq.replenish(size)
+	var endStream bool
+	// If this is the last data message on this stream and all of it can be written in this iteration.
+	if dataItem.endStream && size == len(buf) {
+		// buf contains either data or it contains header but data is empty.
+		if idx == 1 || len(dataItem.d) == 0 {
+			endStream = true
+		}
+	}
+	if dataItem.onEachWrite != nil {
+		dataItem.onEachWrite()
+	}
+	if err := l.framer.fr.WriteData(dataItem.streamID, endStream, buf[:size]); err != nil {
+		return false, err
+	}
+	buf = buf[size:]
+	str.bytesOutStanding += size
+	l.sendQuota -= uint32(size)
+	if idx == 0 {
+		dataItem.h = buf
+	} else {
+		dataItem.d = buf
+	}
+
+	if len(dataItem.h) == 0 && len(dataItem.d) == 0 { // All the data from that message was written out.
+		str.itl.dequeue()
+	}
+	if str.itl.isEmpty() {
+		str.state = empty
+	} else if trailer, ok := str.itl.peek().(*headerFrame); ok { // The next item is trailers.
+		if err := l.writeHeader(trailer.streamID, trailer.endStream, trailer.hf, trailer.onWrite); err != nil {
+			return false, err
+		}
+		if err := l.cleanupStreamHandler(trailer.cleanup); err != nil {
+			return false, err
+		}
+	} else if int(l.oiws)-str.bytesOutStanding <= 0 { // Ran out of stream quota.
+		str.state = waitingOnStreamQuota
+	} else { // Otherwise add it back to the list of active streams.
+		l.activeStreams.enqueue(str)
+	}
+	return false, nil
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/internal/transport/defaults.go b/demo_test/vendor/google.golang.org/grpc/internal/transport/defaults.go
new file mode 100644
index 0000000..9fa306b
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/internal/transport/defaults.go
@@ -0,0 +1,49 @@
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package transport
+
+import (
+	"math"
+	"time"
+)
+
+const (
+	// The default value of flow control window size in HTTP2 spec.
+	defaultWindowSize = 65535
+	// The initial window size for flow control.
+	initialWindowSize             = defaultWindowSize // for an RPC
+	infinity                      = time.Duration(math.MaxInt64)
+	defaultClientKeepaliveTime    = infinity
+	defaultClientKeepaliveTimeout = 20 * time.Second
+	defaultMaxStreamsClient       = 100
+	defaultMaxConnectionIdle      = infinity
+	defaultMaxConnectionAge       = infinity
+	defaultMaxConnectionAgeGrace  = infinity
+	defaultServerKeepaliveTime    = 2 * time.Hour
+	defaultServerKeepaliveTimeout = 20 * time.Second
+	defaultKeepalivePolicyMinTime = 5 * time.Minute
+	// max window limit set by HTTP2 Specs.
+	maxWindowSize = math.MaxInt32
+	// defaultWriteQuota is the default value for number of data
+	// bytes that each stream can schedule before some of it being
+	// flushed out.
+	defaultWriteQuota              = 64 * 1024
+	defaultClientMaxHeaderListSize = uint32(16 << 20)
+	defaultServerMaxHeaderListSize = uint32(16 << 20)
+)
diff --git a/demo_test/vendor/google.golang.org/grpc/internal/transport/flowcontrol.go b/demo_test/vendor/google.golang.org/grpc/internal/transport/flowcontrol.go
new file mode 100644
index 0000000..f262edd
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/internal/transport/flowcontrol.go
@@ -0,0 +1,217 @@
+/*
+ *
+ * Copyright 2014 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package transport
+
+import (
+	"fmt"
+	"math"
+	"sync"
+	"sync/atomic"
+)
+
+// writeQuota is a soft limit on the amount of data a stream can
+// schedule before some of it is written out.
+type writeQuota struct {
+	quota int32
+	// get waits on read from when quota goes less than or equal to zero.
+	// replenish writes on it when quota goes positive again.
+	ch chan struct{}
+	// done is triggered in error case.
+	done <-chan struct{}
+	// replenish is called by loopyWriter to give quota back to.
+	// It is implemented as a field so that it can be updated
+	// by tests.
+	replenish func(n int)
+}
+
+func newWriteQuota(sz int32, done <-chan struct{}) *writeQuota {
+	w := &writeQuota{
+		quota: sz,
+		ch:    make(chan struct{}, 1),
+		done:  done,
+	}
+	w.replenish = w.realReplenish
+	return w
+}
+
+func (w *writeQuota) get(sz int32) error {
+	for {
+		if atomic.LoadInt32(&w.quota) > 0 {
+			atomic.AddInt32(&w.quota, -sz)
+			return nil
+		}
+		select {
+		case <-w.ch:
+			continue
+		case <-w.done:
+			return errStreamDone
+		}
+	}
+}
+
+func (w *writeQuota) realReplenish(n int) {
+	sz := int32(n)
+	a := atomic.AddInt32(&w.quota, sz)
+	b := a - sz
+	if b <= 0 && a > 0 {
+		select {
+		case w.ch <- struct{}{}:
+		default:
+		}
+	}
+}
+
+type trInFlow struct {
+	limit               uint32
+	unacked             uint32
+	effectiveWindowSize uint32
+}
+
+func (f *trInFlow) newLimit(n uint32) uint32 {
+	d := n - f.limit
+	f.limit = n
+	f.updateEffectiveWindowSize()
+	return d
+}
+
+func (f *trInFlow) onData(n uint32) uint32 {
+	f.unacked += n
+	if f.unacked >= f.limit/4 {
+		w := f.unacked
+		f.unacked = 0
+		f.updateEffectiveWindowSize()
+		return w
+	}
+	f.updateEffectiveWindowSize()
+	return 0
+}
+
+func (f *trInFlow) reset() uint32 {
+	w := f.unacked
+	f.unacked = 0
+	f.updateEffectiveWindowSize()
+	return w
+}
+
+func (f *trInFlow) updateEffectiveWindowSize() {
+	atomic.StoreUint32(&f.effectiveWindowSize, f.limit-f.unacked)
+}
+
+func (f *trInFlow) getSize() uint32 {
+	return atomic.LoadUint32(&f.effectiveWindowSize)
+}
+
+// TODO(mmukhi): Simplify this code.
+// inFlow deals with inbound flow control
+type inFlow struct {
+	mu sync.Mutex
+	// The inbound flow control limit for pending data.
+	limit uint32
+	// pendingData is the overall data which have been received but not been
+	// consumed by applications.
+	pendingData uint32
+	// The amount of data the application has consumed but grpc has not sent
+	// window update for them. Used to reduce window update frequency.
+	pendingUpdate uint32
+	// delta is the extra window update given by receiver when an application
+	// is reading data bigger in size than the inFlow limit.
+	delta uint32
+}
+
+// newLimit updates the inflow window to a new value n.
+// It assumes that n is always greater than the old limit.
+func (f *inFlow) newLimit(n uint32) uint32 {
+	f.mu.Lock()
+	d := n - f.limit
+	f.limit = n
+	f.mu.Unlock()
+	return d
+}
+
+func (f *inFlow) maybeAdjust(n uint32) uint32 {
+	if n > uint32(math.MaxInt32) {
+		n = uint32(math.MaxInt32)
+	}
+	f.mu.Lock()
+	defer f.mu.Unlock()
+	// estSenderQuota is the receiver's view of the maximum number of bytes the sender
+	// can send without a window update.
+	estSenderQuota := int32(f.limit - (f.pendingData + f.pendingUpdate))
+	// estUntransmittedData is the maximum number of bytes the sends might not have put
+	// on the wire yet. A value of 0 or less means that we have already received all or
+	// more bytes than the application is requesting to read.
+	estUntransmittedData := int32(n - f.pendingData) // Casting into int32 since it could be negative.
+	// This implies that unless we send a window update, the sender won't be able to send all the bytes
+	// for this message. Therefore we must send an update over the limit since there's an active read
+	// request from the application.
+	if estUntransmittedData > estSenderQuota {
+		// Sender's window shouldn't go more than 2^31 - 1 as specified in the HTTP spec.
+		if f.limit+n > maxWindowSize {
+			f.delta = maxWindowSize - f.limit
+		} else {
+			// Send a window update for the whole message and not just the difference between
+			// estUntransmittedData and estSenderQuota. This will be helpful in case the message
+			// is padded; We will fallback on the current available window(at least a 1/4th of the limit).
+			f.delta = n
+		}
+		return f.delta
+	}
+	return 0
+}
+
+// onData is invoked when some data frame is received. It updates pendingData.
+func (f *inFlow) onData(n uint32) error {
+	f.mu.Lock()
+	f.pendingData += n
+	if f.pendingData+f.pendingUpdate > f.limit+f.delta {
+		limit := f.limit
+		rcvd := f.pendingData + f.pendingUpdate
+		f.mu.Unlock()
+		return fmt.Errorf("received %d-bytes data exceeding the limit %d bytes", rcvd, limit)
+	}
+	f.mu.Unlock()
+	return nil
+}
+
+// onRead is invoked when the application reads the data. It returns the window size
+// to be sent to the peer.
+func (f *inFlow) onRead(n uint32) uint32 {
+	f.mu.Lock()
+	if f.pendingData == 0 {
+		f.mu.Unlock()
+		return 0
+	}
+	f.pendingData -= n
+	if n > f.delta {
+		n -= f.delta
+		f.delta = 0
+	} else {
+		f.delta -= n
+		n = 0
+	}
+	f.pendingUpdate += n
+	if f.pendingUpdate >= f.limit/4 {
+		wu := f.pendingUpdate
+		f.pendingUpdate = 0
+		f.mu.Unlock()
+		return wu
+	}
+	f.mu.Unlock()
+	return 0
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/internal/transport/handler_server.go b/demo_test/vendor/google.golang.org/grpc/internal/transport/handler_server.go
new file mode 100644
index 0000000..fc44e97
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/internal/transport/handler_server.go
@@ -0,0 +1,462 @@
+/*
+ *
+ * Copyright 2016 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+// This file is the implementation of a gRPC server using HTTP/2 which
+// uses the standard Go http2 Server implementation (via the
+// http.Handler interface), rather than speaking low-level HTTP/2
+// frames itself. It is the implementation of *grpc.Server.ServeHTTP.
+
+package transport
+
+import (
+	"bytes"
+	"context"
+	"errors"
+	"fmt"
+	"io"
+	"net"
+	"net/http"
+	"strings"
+	"sync"
+	"time"
+
+	"github.com/golang/protobuf/proto"
+	"golang.org/x/net/http2"
+	"google.golang.org/grpc/codes"
+	"google.golang.org/grpc/credentials"
+	"google.golang.org/grpc/metadata"
+	"google.golang.org/grpc/peer"
+	"google.golang.org/grpc/stats"
+	"google.golang.org/grpc/status"
+)
+
+// NewServerHandlerTransport returns a ServerTransport handling gRPC
+// from inside an http.Handler. It requires that the http Server
+// supports HTTP/2.
+func NewServerHandlerTransport(w http.ResponseWriter, r *http.Request, stats stats.Handler) (ServerTransport, error) {
+	if r.ProtoMajor != 2 {
+		return nil, errors.New("gRPC requires HTTP/2")
+	}
+	if r.Method != "POST" {
+		return nil, errors.New("invalid gRPC request method")
+	}
+	contentType := r.Header.Get("Content-Type")
+	// TODO: do we assume contentType is lowercase? we did before
+	contentSubtype, validContentType := contentSubtype(contentType)
+	if !validContentType {
+		return nil, errors.New("invalid gRPC request content-type")
+	}
+	if _, ok := w.(http.Flusher); !ok {
+		return nil, errors.New("gRPC requires a ResponseWriter supporting http.Flusher")
+	}
+
+	st := &serverHandlerTransport{
+		rw:             w,
+		req:            r,
+		closedCh:       make(chan struct{}),
+		writes:         make(chan func()),
+		contentType:    contentType,
+		contentSubtype: contentSubtype,
+		stats:          stats,
+	}
+
+	if v := r.Header.Get("grpc-timeout"); v != "" {
+		to, err := decodeTimeout(v)
+		if err != nil {
+			return nil, status.Errorf(codes.Internal, "malformed time-out: %v", err)
+		}
+		st.timeoutSet = true
+		st.timeout = to
+	}
+
+	metakv := []string{"content-type", contentType}
+	if r.Host != "" {
+		metakv = append(metakv, ":authority", r.Host)
+	}
+	for k, vv := range r.Header {
+		k = strings.ToLower(k)
+		if isReservedHeader(k) && !isWhitelistedHeader(k) {
+			continue
+		}
+		for _, v := range vv {
+			v, err := decodeMetadataHeader(k, v)
+			if err != nil {
+				return nil, status.Errorf(codes.Internal, "malformed binary metadata: %v", err)
+			}
+			metakv = append(metakv, k, v)
+		}
+	}
+	st.headerMD = metadata.Pairs(metakv...)
+
+	return st, nil
+}
+
+// serverHandlerTransport is an implementation of ServerTransport
+// which replies to exactly one gRPC request (exactly one HTTP request),
+// using the net/http.Handler interface. This http.Handler is guaranteed
+// at this point to be speaking over HTTP/2, so it's able to speak valid
+// gRPC.
+type serverHandlerTransport struct {
+	rw         http.ResponseWriter
+	req        *http.Request
+	timeoutSet bool
+	timeout    time.Duration
+
+	headerMD metadata.MD
+
+	closeOnce sync.Once
+	closedCh  chan struct{} // closed on Close
+
+	// writes is a channel of code to run serialized in the
+	// ServeHTTP (HandleStreams) goroutine. The channel is closed
+	// when WriteStatus is called.
+	writes chan func()
+
+	// block concurrent WriteStatus calls
+	// e.g. grpc/(*serverStream).SendMsg/RecvMsg
+	writeStatusMu sync.Mutex
+
+	// we just mirror the request content-type
+	contentType string
+	// we store both contentType and contentSubtype so we don't keep recreating them
+	// TODO make sure this is consistent across handler_server and http2_server
+	contentSubtype string
+
+	stats stats.Handler
+}
+
+func (ht *serverHandlerTransport) Close() error {
+	ht.closeOnce.Do(ht.closeCloseChanOnce)
+	return nil
+}
+
+func (ht *serverHandlerTransport) closeCloseChanOnce() { close(ht.closedCh) }
+
+func (ht *serverHandlerTransport) RemoteAddr() net.Addr { return strAddr(ht.req.RemoteAddr) }
+
+// strAddr is a net.Addr backed by either a TCP "ip:port" string, or
+// the empty string if unknown.
+type strAddr string
+
+func (a strAddr) Network() string {
+	if a != "" {
+		// Per the documentation on net/http.Request.RemoteAddr, if this is
+		// set, it's set to the IP:port of the peer (hence, TCP):
+		// https://golang.org/pkg/net/http/#Request
+		//
+		// If we want to support Unix sockets later, we can
+		// add our own grpc-specific convention within the
+		// grpc codebase to set RemoteAddr to a different
+		// format, or probably better: we can attach it to the
+		// context and use that from serverHandlerTransport.RemoteAddr.
+		return "tcp"
+	}
+	return ""
+}
+
+func (a strAddr) String() string { return string(a) }
+
+// do runs fn in the ServeHTTP goroutine.
+func (ht *serverHandlerTransport) do(fn func()) error {
+	select {
+	case <-ht.closedCh:
+		return ErrConnClosing
+	case ht.writes <- fn:
+		return nil
+	}
+}
+
+func (ht *serverHandlerTransport) WriteStatus(s *Stream, st *status.Status) error {
+	ht.writeStatusMu.Lock()
+	defer ht.writeStatusMu.Unlock()
+
+	headersWritten := s.updateHeaderSent()
+	err := ht.do(func() {
+		if !headersWritten {
+			ht.writePendingHeaders(s)
+		}
+
+		// And flush, in case no header or body has been sent yet.
+		// This forces a separation of headers and trailers if this is the
+		// first call (for example, in end2end tests's TestNoService).
+		ht.rw.(http.Flusher).Flush()
+
+		h := ht.rw.Header()
+		h.Set("Grpc-Status", fmt.Sprintf("%d", st.Code()))
+		if m := st.Message(); m != "" {
+			h.Set("Grpc-Message", encodeGrpcMessage(m))
+		}
+
+		if p := st.Proto(); p != nil && len(p.Details) > 0 {
+			stBytes, err := proto.Marshal(p)
+			if err != nil {
+				// TODO: return error instead, when callers are able to handle it.
+				panic(err)
+			}
+
+			h.Set("Grpc-Status-Details-Bin", encodeBinHeader(stBytes))
+		}
+
+		if md := s.Trailer(); len(md) > 0 {
+			for k, vv := range md {
+				// Clients don't tolerate reading restricted headers after some non restricted ones were sent.
+				if isReservedHeader(k) {
+					continue
+				}
+				for _, v := range vv {
+					// http2 ResponseWriter mechanism to send undeclared Trailers after
+					// the headers have possibly been written.
+					h.Add(http2.TrailerPrefix+k, encodeMetadataHeader(k, v))
+				}
+			}
+		}
+	})
+
+	if err == nil { // transport has not been closed
+		if ht.stats != nil {
+			// Note: The trailer fields are compressed with hpack after this call returns.
+			// No WireLength field is set here.
+			ht.stats.HandleRPC(s.Context(), &stats.OutTrailer{
+				Trailer: s.trailer.Copy(),
+			})
+		}
+	}
+	ht.Close()
+	return err
+}
+
+// writePendingHeaders sets common and custom headers on the first
+// write call (Write, WriteHeader, or WriteStatus)
+func (ht *serverHandlerTransport) writePendingHeaders(s *Stream) {
+	ht.writeCommonHeaders(s)
+	ht.writeCustomHeaders(s)
+}
+
+// writeCommonHeaders sets common headers on the first write
+// call (Write, WriteHeader, or WriteStatus).
+func (ht *serverHandlerTransport) writeCommonHeaders(s *Stream) {
+	h := ht.rw.Header()
+	h["Date"] = nil // suppress Date to make tests happy; TODO: restore
+	h.Set("Content-Type", ht.contentType)
+
+	// Predeclare trailers we'll set later in WriteStatus (after the body).
+	// This is a SHOULD in the HTTP RFC, and the way you add (known)
+	// Trailers per the net/http.ResponseWriter contract.
+	// See https://golang.org/pkg/net/http/#ResponseWriter
+	// and https://golang.org/pkg/net/http/#example_ResponseWriter_trailers
+	h.Add("Trailer", "Grpc-Status")
+	h.Add("Trailer", "Grpc-Message")
+	h.Add("Trailer", "Grpc-Status-Details-Bin")
+
+	if s.sendCompress != "" {
+		h.Set("Grpc-Encoding", s.sendCompress)
+	}
+}
+
+// writeCustomHeaders sets custom headers set on the stream via SetHeader
+// on the first write call (Write, WriteHeader, or WriteStatus).
+func (ht *serverHandlerTransport) writeCustomHeaders(s *Stream) {
+	h := ht.rw.Header()
+
+	s.hdrMu.Lock()
+	for k, vv := range s.header {
+		if isReservedHeader(k) {
+			continue
+		}
+		for _, v := range vv {
+			h.Add(k, encodeMetadataHeader(k, v))
+		}
+	}
+
+	s.hdrMu.Unlock()
+}
+
+func (ht *serverHandlerTransport) Write(s *Stream, hdr []byte, data []byte, opts *Options) error {
+	headersWritten := s.updateHeaderSent()
+	return ht.do(func() {
+		if !headersWritten {
+			ht.writePendingHeaders(s)
+		}
+		ht.rw.Write(hdr)
+		ht.rw.Write(data)
+		ht.rw.(http.Flusher).Flush()
+	})
+}
+
+func (ht *serverHandlerTransport) WriteHeader(s *Stream, md metadata.MD) error {
+	if err := s.SetHeader(md); err != nil {
+		return err
+	}
+
+	headersWritten := s.updateHeaderSent()
+	err := ht.do(func() {
+		if !headersWritten {
+			ht.writePendingHeaders(s)
+		}
+
+		ht.rw.WriteHeader(200)
+		ht.rw.(http.Flusher).Flush()
+	})
+
+	if err == nil {
+		if ht.stats != nil {
+			// Note: The header fields are compressed with hpack after this call returns.
+			// No WireLength field is set here.
+			ht.stats.HandleRPC(s.Context(), &stats.OutHeader{
+				Header:      md.Copy(),
+				Compression: s.sendCompress,
+			})
+		}
+	}
+	return err
+}
+
+func (ht *serverHandlerTransport) HandleStreams(startStream func(*Stream), traceCtx func(context.Context, string) context.Context) {
+	// With this transport type there will be exactly 1 stream: this HTTP request.
+
+	ctx := ht.req.Context()
+	var cancel context.CancelFunc
+	if ht.timeoutSet {
+		ctx, cancel = context.WithTimeout(ctx, ht.timeout)
+	} else {
+		ctx, cancel = context.WithCancel(ctx)
+	}
+
+	// requestOver is closed when the status has been written via WriteStatus.
+	requestOver := make(chan struct{})
+	go func() {
+		select {
+		case <-requestOver:
+		case <-ht.closedCh:
+		case <-ht.req.Context().Done():
+		}
+		cancel()
+		ht.Close()
+	}()
+
+	req := ht.req
+
+	s := &Stream{
+		id:             0, // irrelevant
+		requestRead:    func(int) {},
+		cancel:         cancel,
+		buf:            newRecvBuffer(),
+		st:             ht,
+		method:         req.URL.Path,
+		recvCompress:   req.Header.Get("grpc-encoding"),
+		contentSubtype: ht.contentSubtype,
+	}
+	pr := &peer.Peer{
+		Addr: ht.RemoteAddr(),
+	}
+	if req.TLS != nil {
+		pr.AuthInfo = credentials.TLSInfo{State: *req.TLS, CommonAuthInfo: credentials.CommonAuthInfo{SecurityLevel: credentials.PrivacyAndIntegrity}}
+	}
+	ctx = metadata.NewIncomingContext(ctx, ht.headerMD)
+	s.ctx = peer.NewContext(ctx, pr)
+	if ht.stats != nil {
+		s.ctx = ht.stats.TagRPC(s.ctx, &stats.RPCTagInfo{FullMethodName: s.method})
+		inHeader := &stats.InHeader{
+			FullMethod:  s.method,
+			RemoteAddr:  ht.RemoteAddr(),
+			Compression: s.recvCompress,
+		}
+		ht.stats.HandleRPC(s.ctx, inHeader)
+	}
+	s.trReader = &transportReader{
+		reader:        &recvBufferReader{ctx: s.ctx, ctxDone: s.ctx.Done(), recv: s.buf, freeBuffer: func(*bytes.Buffer) {}},
+		windowHandler: func(int) {},
+	}
+
+	// readerDone is closed when the Body.Read-ing goroutine exits.
+	readerDone := make(chan struct{})
+	go func() {
+		defer close(readerDone)
+
+		// TODO: minimize garbage, optimize recvBuffer code/ownership
+		const readSize = 8196
+		for buf := make([]byte, readSize); ; {
+			n, err := req.Body.Read(buf)
+			if n > 0 {
+				s.buf.put(recvMsg{buffer: bytes.NewBuffer(buf[:n:n])})
+				buf = buf[n:]
+			}
+			if err != nil {
+				s.buf.put(recvMsg{err: mapRecvMsgError(err)})
+				return
+			}
+			if len(buf) == 0 {
+				buf = make([]byte, readSize)
+			}
+		}
+	}()
+
+	// startStream is provided by the *grpc.Server's serveStreams.
+	// It starts a goroutine serving s and exits immediately.
+	// The goroutine that is started is the one that then calls
+	// into ht, calling WriteHeader, Write, WriteStatus, Close, etc.
+	startStream(s)
+
+	ht.runStream()
+	close(requestOver)
+
+	// Wait for reading goroutine to finish.
+	req.Body.Close()
+	<-readerDone
+}
+
+func (ht *serverHandlerTransport) runStream() {
+	for {
+		select {
+		case fn := <-ht.writes:
+			fn()
+		case <-ht.closedCh:
+			return
+		}
+	}
+}
+
+func (ht *serverHandlerTransport) IncrMsgSent() {}
+
+func (ht *serverHandlerTransport) IncrMsgRecv() {}
+
+func (ht *serverHandlerTransport) Drain() {
+	panic("Drain() is not implemented")
+}
+
+// mapRecvMsgError returns the non-nil err into the appropriate
+// error value as expected by callers of *grpc.parser.recvMsg.
+// In particular, in can only be:
+//   * io.EOF
+//   * io.ErrUnexpectedEOF
+//   * of type transport.ConnectionError
+//   * an error from the status package
+func mapRecvMsgError(err error) error {
+	if err == io.EOF || err == io.ErrUnexpectedEOF {
+		return err
+	}
+	if se, ok := err.(http2.StreamError); ok {
+		if code, ok := http2ErrConvTab[se.Code]; ok {
+			return status.Error(code, se.Error())
+		}
+	}
+	if strings.Contains(err.Error(), "body closed by handler") {
+		return status.Error(codes.Canceled, err.Error())
+	}
+	return connectionErrorf(true, err, err.Error())
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/internal/transport/http2_client.go b/demo_test/vendor/google.golang.org/grpc/internal/transport/http2_client.go
new file mode 100644
index 0000000..1cc586f
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/internal/transport/http2_client.go
@@ -0,0 +1,1462 @@
+/*
+ *
+ * Copyright 2014 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package transport
+
+import (
+	"context"
+	"fmt"
+	"io"
+	"math"
+	"net"
+	"strconv"
+	"strings"
+	"sync"
+	"sync/atomic"
+	"time"
+
+	"golang.org/x/net/http2"
+	"golang.org/x/net/http2/hpack"
+
+	"google.golang.org/grpc/codes"
+	"google.golang.org/grpc/credentials"
+	"google.golang.org/grpc/internal"
+	"google.golang.org/grpc/internal/channelz"
+	"google.golang.org/grpc/internal/syscall"
+	"google.golang.org/grpc/keepalive"
+	"google.golang.org/grpc/metadata"
+	"google.golang.org/grpc/peer"
+	"google.golang.org/grpc/stats"
+	"google.golang.org/grpc/status"
+)
+
+// clientConnectionCounter counts the number of connections a client has
+// initiated (equal to the number of http2Clients created). Must be accessed
+// atomically.
+var clientConnectionCounter uint64
+
+// http2Client implements the ClientTransport interface with HTTP2.
+type http2Client struct {
+	lastRead   int64 // Keep this field 64-bit aligned. Accessed atomically.
+	ctx        context.Context
+	cancel     context.CancelFunc
+	ctxDone    <-chan struct{} // Cache the ctx.Done() chan.
+	userAgent  string
+	md         interface{}
+	conn       net.Conn // underlying communication channel
+	loopy      *loopyWriter
+	remoteAddr net.Addr
+	localAddr  net.Addr
+	authInfo   credentials.AuthInfo // auth info about the connection
+
+	readerDone chan struct{} // sync point to enable testing.
+	writerDone chan struct{} // sync point to enable testing.
+	// goAway is closed to notify the upper layer (i.e., addrConn.transportMonitor)
+	// that the server sent GoAway on this transport.
+	goAway chan struct{}
+
+	framer *framer
+	// controlBuf delivers all the control related tasks (e.g., window
+	// updates, reset streams, and various settings) to the controller.
+	controlBuf *controlBuffer
+	fc         *trInFlow
+	// The scheme used: https if TLS is on, http otherwise.
+	scheme string
+
+	isSecure bool
+
+	perRPCCreds []credentials.PerRPCCredentials
+
+	kp               keepalive.ClientParameters
+	keepaliveEnabled bool
+
+	statsHandler stats.Handler
+
+	initialWindowSize int32
+
+	// configured by peer through SETTINGS_MAX_HEADER_LIST_SIZE
+	maxSendHeaderListSize *uint32
+
+	bdpEst *bdpEstimator
+	// onPrefaceReceipt is a callback that client transport calls upon
+	// receiving server preface to signal that a succefull HTTP2
+	// connection was established.
+	onPrefaceReceipt func()
+
+	maxConcurrentStreams  uint32
+	streamQuota           int64
+	streamsQuotaAvailable chan struct{}
+	waitingStreams        uint32
+	nextID                uint32
+
+	mu            sync.Mutex // guard the following variables
+	state         transportState
+	activeStreams map[uint32]*Stream
+	// prevGoAway ID records the Last-Stream-ID in the previous GOAway frame.
+	prevGoAwayID uint32
+	// goAwayReason records the http2.ErrCode and debug data received with the
+	// GoAway frame.
+	goAwayReason GoAwayReason
+	// A condition variable used to signal when the keepalive goroutine should
+	// go dormant. The condition for dormancy is based on the number of active
+	// streams and the `PermitWithoutStream` keepalive client parameter. And
+	// since the number of active streams is guarded by the above mutex, we use
+	// the same for this condition variable as well.
+	kpDormancyCond *sync.Cond
+	// A boolean to track whether the keepalive goroutine is dormant or not.
+	// This is checked before attempting to signal the above condition
+	// variable.
+	kpDormant bool
+
+	// Fields below are for channelz metric collection.
+	channelzID int64 // channelz unique identification number
+	czData     *channelzData
+
+	onGoAway func(GoAwayReason)
+	onClose  func()
+
+	bufferPool *bufferPool
+
+	connectionID uint64
+}
+
+func dial(ctx context.Context, fn func(context.Context, string) (net.Conn, error), addr string) (net.Conn, error) {
+	if fn != nil {
+		return fn(ctx, addr)
+	}
+	return (&net.Dialer{}).DialContext(ctx, "tcp", addr)
+}
+
+func isTemporary(err error) bool {
+	switch err := err.(type) {
+	case interface {
+		Temporary() bool
+	}:
+		return err.Temporary()
+	case interface {
+		Timeout() bool
+	}:
+		// Timeouts may be resolved upon retry, and are thus treated as
+		// temporary.
+		return err.Timeout()
+	}
+	return true
+}
+
+// newHTTP2Client constructs a connected ClientTransport to addr based on HTTP2
+// and starts to receive messages on it. Non-nil error returns if construction
+// fails.
+func newHTTP2Client(connectCtx, ctx context.Context, addr TargetInfo, opts ConnectOptions, onPrefaceReceipt func(), onGoAway func(GoAwayReason), onClose func()) (_ *http2Client, err error) {
+	scheme := "http"
+	ctx, cancel := context.WithCancel(ctx)
+	defer func() {
+		if err != nil {
+			cancel()
+		}
+	}()
+
+	conn, err := dial(connectCtx, opts.Dialer, addr.Addr)
+	if err != nil {
+		if opts.FailOnNonTempDialError {
+			return nil, connectionErrorf(isTemporary(err), err, "transport: error while dialing: %v", err)
+		}
+		return nil, connectionErrorf(true, err, "transport: Error while dialing %v", err)
+	}
+	// Any further errors will close the underlying connection
+	defer func(conn net.Conn) {
+		if err != nil {
+			conn.Close()
+		}
+	}(conn)
+	kp := opts.KeepaliveParams
+	// Validate keepalive parameters.
+	if kp.Time == 0 {
+		kp.Time = defaultClientKeepaliveTime
+	}
+	if kp.Timeout == 0 {
+		kp.Timeout = defaultClientKeepaliveTimeout
+	}
+	keepaliveEnabled := false
+	if kp.Time != infinity {
+		if err = syscall.SetTCPUserTimeout(conn, kp.Timeout); err != nil {
+			return nil, connectionErrorf(false, err, "transport: failed to set TCP_USER_TIMEOUT: %v", err)
+		}
+		keepaliveEnabled = true
+	}
+	var (
+		isSecure bool
+		authInfo credentials.AuthInfo
+	)
+	transportCreds := opts.TransportCredentials
+	perRPCCreds := opts.PerRPCCredentials
+
+	if b := opts.CredsBundle; b != nil {
+		if t := b.TransportCredentials(); t != nil {
+			transportCreds = t
+		}
+		if t := b.PerRPCCredentials(); t != nil {
+			perRPCCreds = append(perRPCCreds, t)
+		}
+	}
+	if transportCreds != nil {
+		scheme = "https"
+		conn, authInfo, err = transportCreds.ClientHandshake(connectCtx, addr.Authority, conn)
+		if err != nil {
+			return nil, connectionErrorf(isTemporary(err), err, "transport: authentication handshake failed: %v", err)
+		}
+		isSecure = true
+	}
+	dynamicWindow := true
+	icwz := int32(initialWindowSize)
+	if opts.InitialConnWindowSize >= defaultWindowSize {
+		icwz = opts.InitialConnWindowSize
+		dynamicWindow = false
+	}
+	writeBufSize := opts.WriteBufferSize
+	readBufSize := opts.ReadBufferSize
+	maxHeaderListSize := defaultClientMaxHeaderListSize
+	if opts.MaxHeaderListSize != nil {
+		maxHeaderListSize = *opts.MaxHeaderListSize
+	}
+	t := &http2Client{
+		ctx:                   ctx,
+		ctxDone:               ctx.Done(), // Cache Done chan.
+		cancel:                cancel,
+		userAgent:             opts.UserAgent,
+		md:                    addr.Metadata,
+		conn:                  conn,
+		remoteAddr:            conn.RemoteAddr(),
+		localAddr:             conn.LocalAddr(),
+		authInfo:              authInfo,
+		readerDone:            make(chan struct{}),
+		writerDone:            make(chan struct{}),
+		goAway:                make(chan struct{}),
+		framer:                newFramer(conn, writeBufSize, readBufSize, maxHeaderListSize),
+		fc:                    &trInFlow{limit: uint32(icwz)},
+		scheme:                scheme,
+		activeStreams:         make(map[uint32]*Stream),
+		isSecure:              isSecure,
+		perRPCCreds:           perRPCCreds,
+		kp:                    kp,
+		statsHandler:          opts.StatsHandler,
+		initialWindowSize:     initialWindowSize,
+		onPrefaceReceipt:      onPrefaceReceipt,
+		nextID:                1,
+		maxConcurrentStreams:  defaultMaxStreamsClient,
+		streamQuota:           defaultMaxStreamsClient,
+		streamsQuotaAvailable: make(chan struct{}, 1),
+		czData:                new(channelzData),
+		onGoAway:              onGoAway,
+		onClose:               onClose,
+		keepaliveEnabled:      keepaliveEnabled,
+		bufferPool:            newBufferPool(),
+	}
+	t.controlBuf = newControlBuffer(t.ctxDone)
+	if opts.InitialWindowSize >= defaultWindowSize {
+		t.initialWindowSize = opts.InitialWindowSize
+		dynamicWindow = false
+	}
+	if dynamicWindow {
+		t.bdpEst = &bdpEstimator{
+			bdp:               initialWindowSize,
+			updateFlowControl: t.updateFlowControl,
+		}
+	}
+	if t.statsHandler != nil {
+		t.ctx = t.statsHandler.TagConn(t.ctx, &stats.ConnTagInfo{
+			RemoteAddr: t.remoteAddr,
+			LocalAddr:  t.localAddr,
+		})
+		connBegin := &stats.ConnBegin{
+			Client: true,
+		}
+		t.statsHandler.HandleConn(t.ctx, connBegin)
+	}
+	if channelz.IsOn() {
+		t.channelzID = channelz.RegisterNormalSocket(t, opts.ChannelzParentID, fmt.Sprintf("%s -> %s", t.localAddr, t.remoteAddr))
+	}
+	if t.keepaliveEnabled {
+		t.kpDormancyCond = sync.NewCond(&t.mu)
+		go t.keepalive()
+	}
+	// Start the reader goroutine for incoming message. Each transport has
+	// a dedicated goroutine which reads HTTP2 frame from network. Then it
+	// dispatches the frame to the corresponding stream entity.
+	go t.reader()
+
+	// Send connection preface to server.
+	n, err := t.conn.Write(clientPreface)
+	if err != nil {
+		t.Close()
+		return nil, connectionErrorf(true, err, "transport: failed to write client preface: %v", err)
+	}
+	if n != len(clientPreface) {
+		t.Close()
+		return nil, connectionErrorf(true, err, "transport: preface mismatch, wrote %d bytes; want %d", n, len(clientPreface))
+	}
+	var ss []http2.Setting
+
+	if t.initialWindowSize != defaultWindowSize {
+		ss = append(ss, http2.Setting{
+			ID:  http2.SettingInitialWindowSize,
+			Val: uint32(t.initialWindowSize),
+		})
+	}
+	if opts.MaxHeaderListSize != nil {
+		ss = append(ss, http2.Setting{
+			ID:  http2.SettingMaxHeaderListSize,
+			Val: *opts.MaxHeaderListSize,
+		})
+	}
+	err = t.framer.fr.WriteSettings(ss...)
+	if err != nil {
+		t.Close()
+		return nil, connectionErrorf(true, err, "transport: failed to write initial settings frame: %v", err)
+	}
+	// Adjust the connection flow control window if needed.
+	if delta := uint32(icwz - defaultWindowSize); delta > 0 {
+		if err := t.framer.fr.WriteWindowUpdate(0, delta); err != nil {
+			t.Close()
+			return nil, connectionErrorf(true, err, "transport: failed to write window update: %v", err)
+		}
+	}
+
+	t.connectionID = atomic.AddUint64(&clientConnectionCounter, 1)
+
+	if err := t.framer.writer.Flush(); err != nil {
+		return nil, err
+	}
+	go func() {
+		t.loopy = newLoopyWriter(clientSide, t.framer, t.controlBuf, t.bdpEst)
+		err := t.loopy.run()
+		if err != nil {
+			errorf("transport: loopyWriter.run returning. Err: %v", err)
+		}
+		// If it's a connection error, let reader goroutine handle it
+		// since there might be data in the buffers.
+		if _, ok := err.(net.Error); !ok {
+			t.conn.Close()
+		}
+		close(t.writerDone)
+	}()
+	return t, nil
+}
+
+func (t *http2Client) newStream(ctx context.Context, callHdr *CallHdr) *Stream {
+	// TODO(zhaoq): Handle uint32 overflow of Stream.id.
+	s := &Stream{
+		ct:             t,
+		done:           make(chan struct{}),
+		method:         callHdr.Method,
+		sendCompress:   callHdr.SendCompress,
+		buf:            newRecvBuffer(),
+		headerChan:     make(chan struct{}),
+		contentSubtype: callHdr.ContentSubtype,
+	}
+	s.wq = newWriteQuota(defaultWriteQuota, s.done)
+	s.requestRead = func(n int) {
+		t.adjustWindow(s, uint32(n))
+	}
+	// The client side stream context should have exactly the same life cycle with the user provided context.
+	// That means, s.ctx should be read-only. And s.ctx is done iff ctx is done.
+	// So we use the original context here instead of creating a copy.
+	s.ctx = ctx
+	s.trReader = &transportReader{
+		reader: &recvBufferReader{
+			ctx:     s.ctx,
+			ctxDone: s.ctx.Done(),
+			recv:    s.buf,
+			closeStream: func(err error) {
+				t.CloseStream(s, err)
+			},
+			freeBuffer: t.bufferPool.put,
+		},
+		windowHandler: func(n int) {
+			t.updateWindow(s, uint32(n))
+		},
+	}
+	return s
+}
+
+func (t *http2Client) getPeer() *peer.Peer {
+	return &peer.Peer{
+		Addr:     t.remoteAddr,
+		AuthInfo: t.authInfo,
+	}
+}
+
+func (t *http2Client) createHeaderFields(ctx context.Context, callHdr *CallHdr) ([]hpack.HeaderField, error) {
+	aud := t.createAudience(callHdr)
+	ri := credentials.RequestInfo{
+		Method:   callHdr.Method,
+		AuthInfo: t.authInfo,
+	}
+	ctxWithRequestInfo := internal.NewRequestInfoContext.(func(context.Context, credentials.RequestInfo) context.Context)(ctx, ri)
+	authData, err := t.getTrAuthData(ctxWithRequestInfo, aud)
+	if err != nil {
+		return nil, err
+	}
+	callAuthData, err := t.getCallAuthData(ctxWithRequestInfo, aud, callHdr)
+	if err != nil {
+		return nil, err
+	}
+	// TODO(mmukhi): Benchmark if the performance gets better if count the metadata and other header fields
+	// first and create a slice of that exact size.
+	// Make the slice of certain predictable size to reduce allocations made by append.
+	hfLen := 7 // :method, :scheme, :path, :authority, content-type, user-agent, te
+	hfLen += len(authData) + len(callAuthData)
+	headerFields := make([]hpack.HeaderField, 0, hfLen)
+	headerFields = append(headerFields, hpack.HeaderField{Name: ":method", Value: "POST"})
+	headerFields = append(headerFields, hpack.HeaderField{Name: ":scheme", Value: t.scheme})
+	headerFields = append(headerFields, hpack.HeaderField{Name: ":path", Value: callHdr.Method})
+	headerFields = append(headerFields, hpack.HeaderField{Name: ":authority", Value: callHdr.Host})
+	headerFields = append(headerFields, hpack.HeaderField{Name: "content-type", Value: contentType(callHdr.ContentSubtype)})
+	headerFields = append(headerFields, hpack.HeaderField{Name: "user-agent", Value: t.userAgent})
+	headerFields = append(headerFields, hpack.HeaderField{Name: "te", Value: "trailers"})
+	if callHdr.PreviousAttempts > 0 {
+		headerFields = append(headerFields, hpack.HeaderField{Name: "grpc-previous-rpc-attempts", Value: strconv.Itoa(callHdr.PreviousAttempts)})
+	}
+
+	if callHdr.SendCompress != "" {
+		headerFields = append(headerFields, hpack.HeaderField{Name: "grpc-encoding", Value: callHdr.SendCompress})
+		headerFields = append(headerFields, hpack.HeaderField{Name: "grpc-accept-encoding", Value: callHdr.SendCompress})
+	}
+	if dl, ok := ctx.Deadline(); ok {
+		// Send out timeout regardless its value. The server can detect timeout context by itself.
+		// TODO(mmukhi): Perhaps this field should be updated when actually writing out to the wire.
+		timeout := time.Until(dl)
+		headerFields = append(headerFields, hpack.HeaderField{Name: "grpc-timeout", Value: encodeTimeout(timeout)})
+	}
+	for k, v := range authData {
+		headerFields = append(headerFields, hpack.HeaderField{Name: k, Value: encodeMetadataHeader(k, v)})
+	}
+	for k, v := range callAuthData {
+		headerFields = append(headerFields, hpack.HeaderField{Name: k, Value: encodeMetadataHeader(k, v)})
+	}
+	if b := stats.OutgoingTags(ctx); b != nil {
+		headerFields = append(headerFields, hpack.HeaderField{Name: "grpc-tags-bin", Value: encodeBinHeader(b)})
+	}
+	if b := stats.OutgoingTrace(ctx); b != nil {
+		headerFields = append(headerFields, hpack.HeaderField{Name: "grpc-trace-bin", Value: encodeBinHeader(b)})
+	}
+
+	if md, added, ok := metadata.FromOutgoingContextRaw(ctx); ok {
+		var k string
+		for k, vv := range md {
+			// HTTP doesn't allow you to set pseudoheaders after non pseudoheaders were set.
+			if isReservedHeader(k) {
+				continue
+			}
+			for _, v := range vv {
+				headerFields = append(headerFields, hpack.HeaderField{Name: k, Value: encodeMetadataHeader(k, v)})
+			}
+		}
+		for _, vv := range added {
+			for i, v := range vv {
+				if i%2 == 0 {
+					k = v
+					continue
+				}
+				// HTTP doesn't allow you to set pseudoheaders after non pseudoheaders were set.
+				if isReservedHeader(k) {
+					continue
+				}
+				headerFields = append(headerFields, hpack.HeaderField{Name: strings.ToLower(k), Value: encodeMetadataHeader(k, v)})
+			}
+		}
+	}
+	if md, ok := t.md.(*metadata.MD); ok {
+		for k, vv := range *md {
+			if isReservedHeader(k) {
+				continue
+			}
+			for _, v := range vv {
+				headerFields = append(headerFields, hpack.HeaderField{Name: k, Value: encodeMetadataHeader(k, v)})
+			}
+		}
+	}
+	return headerFields, nil
+}
+
+func (t *http2Client) createAudience(callHdr *CallHdr) string {
+	// Create an audience string only if needed.
+	if len(t.perRPCCreds) == 0 && callHdr.Creds == nil {
+		return ""
+	}
+	// Construct URI required to get auth request metadata.
+	// Omit port if it is the default one.
+	host := strings.TrimSuffix(callHdr.Host, ":443")
+	pos := strings.LastIndex(callHdr.Method, "/")
+	if pos == -1 {
+		pos = len(callHdr.Method)
+	}
+	return "https://" + host + callHdr.Method[:pos]
+}
+
+func (t *http2Client) getTrAuthData(ctx context.Context, audience string) (map[string]string, error) {
+	if len(t.perRPCCreds) == 0 {
+		return nil, nil
+	}
+	authData := map[string]string{}
+	for _, c := range t.perRPCCreds {
+		data, err := c.GetRequestMetadata(ctx, audience)
+		if err != nil {
+			if _, ok := status.FromError(err); ok {
+				return nil, err
+			}
+
+			return nil, status.Errorf(codes.Unauthenticated, "transport: %v", err)
+		}
+		for k, v := range data {
+			// Capital header names are illegal in HTTP/2.
+			k = strings.ToLower(k)
+			authData[k] = v
+		}
+	}
+	return authData, nil
+}
+
+func (t *http2Client) getCallAuthData(ctx context.Context, audience string, callHdr *CallHdr) (map[string]string, error) {
+	var callAuthData map[string]string
+	// Check if credentials.PerRPCCredentials were provided via call options.
+	// Note: if these credentials are provided both via dial options and call
+	// options, then both sets of credentials will be applied.
+	if callCreds := callHdr.Creds; callCreds != nil {
+		if !t.isSecure && callCreds.RequireTransportSecurity() {
+			return nil, status.Error(codes.Unauthenticated, "transport: cannot send secure credentials on an insecure connection")
+		}
+		data, err := callCreds.GetRequestMetadata(ctx, audience)
+		if err != nil {
+			return nil, status.Errorf(codes.Internal, "transport: %v", err)
+		}
+		callAuthData = make(map[string]string, len(data))
+		for k, v := range data {
+			// Capital header names are illegal in HTTP/2
+			k = strings.ToLower(k)
+			callAuthData[k] = v
+		}
+	}
+	return callAuthData, nil
+}
+
+// NewStream creates a stream and registers it into the transport as "active"
+// streams.
+func (t *http2Client) NewStream(ctx context.Context, callHdr *CallHdr) (_ *Stream, err error) {
+	ctx = peer.NewContext(ctx, t.getPeer())
+	headerFields, err := t.createHeaderFields(ctx, callHdr)
+	if err != nil {
+		return nil, err
+	}
+	s := t.newStream(ctx, callHdr)
+	cleanup := func(err error) {
+		if s.swapState(streamDone) == streamDone {
+			// If it was already done, return.
+			return
+		}
+		// The stream was unprocessed by the server.
+		atomic.StoreUint32(&s.unprocessed, 1)
+		s.write(recvMsg{err: err})
+		close(s.done)
+		// If headerChan isn't closed, then close it.
+		if atomic.CompareAndSwapUint32(&s.headerChanClosed, 0, 1) {
+			close(s.headerChan)
+		}
+	}
+	hdr := &headerFrame{
+		hf:        headerFields,
+		endStream: false,
+		initStream: func(id uint32) error {
+			t.mu.Lock()
+			if state := t.state; state != reachable {
+				t.mu.Unlock()
+				// Do a quick cleanup.
+				err := error(errStreamDrain)
+				if state == closing {
+					err = ErrConnClosing
+				}
+				cleanup(err)
+				return err
+			}
+			t.activeStreams[id] = s
+			if channelz.IsOn() {
+				atomic.AddInt64(&t.czData.streamsStarted, 1)
+				atomic.StoreInt64(&t.czData.lastStreamCreatedTime, time.Now().UnixNano())
+			}
+			// If the keepalive goroutine has gone dormant, wake it up.
+			if t.kpDormant {
+				t.kpDormancyCond.Signal()
+			}
+			t.mu.Unlock()
+			return nil
+		},
+		onOrphaned: cleanup,
+		wq:         s.wq,
+	}
+	firstTry := true
+	var ch chan struct{}
+	checkForStreamQuota := func(it interface{}) bool {
+		if t.streamQuota <= 0 { // Can go negative if server decreases it.
+			if firstTry {
+				t.waitingStreams++
+			}
+			ch = t.streamsQuotaAvailable
+			return false
+		}
+		if !firstTry {
+			t.waitingStreams--
+		}
+		t.streamQuota--
+		h := it.(*headerFrame)
+		h.streamID = t.nextID
+		t.nextID += 2
+		s.id = h.streamID
+		s.fc = &inFlow{limit: uint32(t.initialWindowSize)}
+		if t.streamQuota > 0 && t.waitingStreams > 0 {
+			select {
+			case t.streamsQuotaAvailable <- struct{}{}:
+			default:
+			}
+		}
+		return true
+	}
+	var hdrListSizeErr error
+	checkForHeaderListSize := func(it interface{}) bool {
+		if t.maxSendHeaderListSize == nil {
+			return true
+		}
+		hdrFrame := it.(*headerFrame)
+		var sz int64
+		for _, f := range hdrFrame.hf {
+			if sz += int64(f.Size()); sz > int64(*t.maxSendHeaderListSize) {
+				hdrListSizeErr = status.Errorf(codes.Internal, "header list size to send violates the maximum size (%d bytes) set by server", *t.maxSendHeaderListSize)
+				return false
+			}
+		}
+		return true
+	}
+	for {
+		success, err := t.controlBuf.executeAndPut(func(it interface{}) bool {
+			if !checkForStreamQuota(it) {
+				return false
+			}
+			if !checkForHeaderListSize(it) {
+				return false
+			}
+			return true
+		}, hdr)
+		if err != nil {
+			return nil, err
+		}
+		if success {
+			break
+		}
+		if hdrListSizeErr != nil {
+			return nil, hdrListSizeErr
+		}
+		firstTry = false
+		select {
+		case <-ch:
+		case <-s.ctx.Done():
+			return nil, ContextErr(s.ctx.Err())
+		case <-t.goAway:
+			return nil, errStreamDrain
+		case <-t.ctx.Done():
+			return nil, ErrConnClosing
+		}
+	}
+	if t.statsHandler != nil {
+		header, ok := metadata.FromOutgoingContext(ctx)
+		if ok {
+			header.Set("user-agent", t.userAgent)
+		} else {
+			header = metadata.Pairs("user-agent", t.userAgent)
+		}
+		// Note: The header fields are compressed with hpack after this call returns.
+		// No WireLength field is set here.
+		outHeader := &stats.OutHeader{
+			Client:      true,
+			FullMethod:  callHdr.Method,
+			RemoteAddr:  t.remoteAddr,
+			LocalAddr:   t.localAddr,
+			Compression: callHdr.SendCompress,
+			Header:      header,
+		}
+		t.statsHandler.HandleRPC(s.ctx, outHeader)
+	}
+	return s, nil
+}
+
+// CloseStream clears the footprint of a stream when the stream is not needed any more.
+// This must not be executed in reader's goroutine.
+func (t *http2Client) CloseStream(s *Stream, err error) {
+	var (
+		rst     bool
+		rstCode http2.ErrCode
+	)
+	if err != nil {
+		rst = true
+		rstCode = http2.ErrCodeCancel
+	}
+	t.closeStream(s, err, rst, rstCode, status.Convert(err), nil, false)
+}
+
+func (t *http2Client) closeStream(s *Stream, err error, rst bool, rstCode http2.ErrCode, st *status.Status, mdata map[string][]string, eosReceived bool) {
+	// Set stream status to done.
+	if s.swapState(streamDone) == streamDone {
+		// If it was already done, return.  If multiple closeStream calls
+		// happen simultaneously, wait for the first to finish.
+		<-s.done
+		return
+	}
+	// status and trailers can be updated here without any synchronization because the stream goroutine will
+	// only read it after it sees an io.EOF error from read or write and we'll write those errors
+	// only after updating this.
+	s.status = st
+	if len(mdata) > 0 {
+		s.trailer = mdata
+	}
+	if err != nil {
+		// This will unblock reads eventually.
+		s.write(recvMsg{err: err})
+	}
+	// If headerChan isn't closed, then close it.
+	if atomic.CompareAndSwapUint32(&s.headerChanClosed, 0, 1) {
+		s.noHeaders = true
+		close(s.headerChan)
+	}
+	cleanup := &cleanupStream{
+		streamID: s.id,
+		onWrite: func() {
+			t.mu.Lock()
+			if t.activeStreams != nil {
+				delete(t.activeStreams, s.id)
+			}
+			t.mu.Unlock()
+			if channelz.IsOn() {
+				if eosReceived {
+					atomic.AddInt64(&t.czData.streamsSucceeded, 1)
+				} else {
+					atomic.AddInt64(&t.czData.streamsFailed, 1)
+				}
+			}
+		},
+		rst:     rst,
+		rstCode: rstCode,
+	}
+	addBackStreamQuota := func(interface{}) bool {
+		t.streamQuota++
+		if t.streamQuota > 0 && t.waitingStreams > 0 {
+			select {
+			case t.streamsQuotaAvailable <- struct{}{}:
+			default:
+			}
+		}
+		return true
+	}
+	t.controlBuf.executeAndPut(addBackStreamQuota, cleanup)
+	// This will unblock write.
+	close(s.done)
+}
+
+// Close kicks off the shutdown process of the transport. This should be called
+// only once on a transport. Once it is called, the transport should not be
+// accessed any more.
+//
+// This method blocks until the addrConn that initiated this transport is
+// re-connected. This happens because t.onClose() begins reconnect logic at the
+// addrConn level and blocks until the addrConn is successfully connected.
+func (t *http2Client) Close() error {
+	t.mu.Lock()
+	// Make sure we only Close once.
+	if t.state == closing {
+		t.mu.Unlock()
+		return nil
+	}
+	// Call t.onClose before setting the state to closing to prevent the client
+	// from attempting to create new streams ASAP.
+	t.onClose()
+	t.state = closing
+	streams := t.activeStreams
+	t.activeStreams = nil
+	if t.kpDormant {
+		// If the keepalive goroutine is blocked on this condition variable, we
+		// should unblock it so that the goroutine eventually exits.
+		t.kpDormancyCond.Signal()
+	}
+	t.mu.Unlock()
+	t.controlBuf.finish()
+	t.cancel()
+	err := t.conn.Close()
+	if channelz.IsOn() {
+		channelz.RemoveEntry(t.channelzID)
+	}
+	// Notify all active streams.
+	for _, s := range streams {
+		t.closeStream(s, ErrConnClosing, false, http2.ErrCodeNo, status.New(codes.Unavailable, ErrConnClosing.Desc), nil, false)
+	}
+	if t.statsHandler != nil {
+		connEnd := &stats.ConnEnd{
+			Client: true,
+		}
+		t.statsHandler.HandleConn(t.ctx, connEnd)
+	}
+	return err
+}
+
+// GracefulClose sets the state to draining, which prevents new streams from
+// being created and causes the transport to be closed when the last active
+// stream is closed.  If there are no active streams, the transport is closed
+// immediately.  This does nothing if the transport is already draining or
+// closing.
+func (t *http2Client) GracefulClose() {
+	t.mu.Lock()
+	// Make sure we move to draining only from active.
+	if t.state == draining || t.state == closing {
+		t.mu.Unlock()
+		return
+	}
+	t.state = draining
+	active := len(t.activeStreams)
+	t.mu.Unlock()
+	if active == 0 {
+		t.Close()
+		return
+	}
+	t.controlBuf.put(&incomingGoAway{})
+}
+
+// Write formats the data into HTTP2 data frame(s) and sends it out. The caller
+// should proceed only if Write returns nil.
+func (t *http2Client) Write(s *Stream, hdr []byte, data []byte, opts *Options) error {
+	if opts.Last {
+		// If it's the last message, update stream state.
+		if !s.compareAndSwapState(streamActive, streamWriteDone) {
+			return errStreamDone
+		}
+	} else if s.getState() != streamActive {
+		return errStreamDone
+	}
+	df := &dataFrame{
+		streamID:  s.id,
+		endStream: opts.Last,
+	}
+	if hdr != nil || data != nil { // If it's not an empty data frame.
+		// Add some data to grpc message header so that we can equally
+		// distribute bytes across frames.
+		emptyLen := http2MaxFrameLen - len(hdr)
+		if emptyLen > len(data) {
+			emptyLen = len(data)
+		}
+		hdr = append(hdr, data[:emptyLen]...)
+		data = data[emptyLen:]
+		df.h, df.d = hdr, data
+		// TODO(mmukhi): The above logic in this if can be moved to loopyWriter's data handler.
+		if err := s.wq.get(int32(len(hdr) + len(data))); err != nil {
+			return err
+		}
+	}
+	return t.controlBuf.put(df)
+}
+
+func (t *http2Client) getStream(f http2.Frame) *Stream {
+	t.mu.Lock()
+	s := t.activeStreams[f.Header().StreamID]
+	t.mu.Unlock()
+	return s
+}
+
+// adjustWindow sends out extra window update over the initial window size
+// of stream if the application is requesting data larger in size than
+// the window.
+func (t *http2Client) adjustWindow(s *Stream, n uint32) {
+	if w := s.fc.maybeAdjust(n); w > 0 {
+		t.controlBuf.put(&outgoingWindowUpdate{streamID: s.id, increment: w})
+	}
+}
+
+// updateWindow adjusts the inbound quota for the stream.
+// Window updates will be sent out when the cumulative quota
+// exceeds the corresponding threshold.
+func (t *http2Client) updateWindow(s *Stream, n uint32) {
+	if w := s.fc.onRead(n); w > 0 {
+		t.controlBuf.put(&outgoingWindowUpdate{streamID: s.id, increment: w})
+	}
+}
+
+// updateFlowControl updates the incoming flow control windows
+// for the transport and the stream based on the current bdp
+// estimation.
+func (t *http2Client) updateFlowControl(n uint32) {
+	t.mu.Lock()
+	for _, s := range t.activeStreams {
+		s.fc.newLimit(n)
+	}
+	t.mu.Unlock()
+	updateIWS := func(interface{}) bool {
+		t.initialWindowSize = int32(n)
+		return true
+	}
+	t.controlBuf.executeAndPut(updateIWS, &outgoingWindowUpdate{streamID: 0, increment: t.fc.newLimit(n)})
+	t.controlBuf.put(&outgoingSettings{
+		ss: []http2.Setting{
+			{
+				ID:  http2.SettingInitialWindowSize,
+				Val: n,
+			},
+		},
+	})
+}
+
+func (t *http2Client) handleData(f *http2.DataFrame) {
+	size := f.Header().Length
+	var sendBDPPing bool
+	if t.bdpEst != nil {
+		sendBDPPing = t.bdpEst.add(size)
+	}
+	// Decouple connection's flow control from application's read.
+	// An update on connection's flow control should not depend on
+	// whether user application has read the data or not. Such a
+	// restriction is already imposed on the stream's flow control,
+	// and therefore the sender will be blocked anyways.
+	// Decoupling the connection flow control will prevent other
+	// active(fast) streams from starving in presence of slow or
+	// inactive streams.
+	//
+	if w := t.fc.onData(size); w > 0 {
+		t.controlBuf.put(&outgoingWindowUpdate{
+			streamID:  0,
+			increment: w,
+		})
+	}
+	if sendBDPPing {
+		// Avoid excessive ping detection (e.g. in an L7 proxy)
+		// by sending a window update prior to the BDP ping.
+
+		if w := t.fc.reset(); w > 0 {
+			t.controlBuf.put(&outgoingWindowUpdate{
+				streamID:  0,
+				increment: w,
+			})
+		}
+
+		t.controlBuf.put(bdpPing)
+	}
+	// Select the right stream to dispatch.
+	s := t.getStream(f)
+	if s == nil {
+		return
+	}
+	if size > 0 {
+		if err := s.fc.onData(size); err != nil {
+			t.closeStream(s, io.EOF, true, http2.ErrCodeFlowControl, status.New(codes.Internal, err.Error()), nil, false)
+			return
+		}
+		if f.Header().Flags.Has(http2.FlagDataPadded) {
+			if w := s.fc.onRead(size - uint32(len(f.Data()))); w > 0 {
+				t.controlBuf.put(&outgoingWindowUpdate{s.id, w})
+			}
+		}
+		// TODO(bradfitz, zhaoq): A copy is required here because there is no
+		// guarantee f.Data() is consumed before the arrival of next frame.
+		// Can this copy be eliminated?
+		if len(f.Data()) > 0 {
+			buffer := t.bufferPool.get()
+			buffer.Reset()
+			buffer.Write(f.Data())
+			s.write(recvMsg{buffer: buffer})
+		}
+	}
+	// The server has closed the stream without sending trailers.  Record that
+	// the read direction is closed, and set the status appropriately.
+	if f.FrameHeader.Flags.Has(http2.FlagDataEndStream) {
+		t.closeStream(s, io.EOF, false, http2.ErrCodeNo, status.New(codes.Internal, "server closed the stream without sending trailers"), nil, true)
+	}
+}
+
+func (t *http2Client) handleRSTStream(f *http2.RSTStreamFrame) {
+	s := t.getStream(f)
+	if s == nil {
+		return
+	}
+	if f.ErrCode == http2.ErrCodeRefusedStream {
+		// The stream was unprocessed by the server.
+		atomic.StoreUint32(&s.unprocessed, 1)
+	}
+	statusCode, ok := http2ErrConvTab[f.ErrCode]
+	if !ok {
+		warningf("transport: http2Client.handleRSTStream found no mapped gRPC status for the received http2 error %v", f.ErrCode)
+		statusCode = codes.Unknown
+	}
+	if statusCode == codes.Canceled {
+		if d, ok := s.ctx.Deadline(); ok && !d.After(time.Now()) {
+			// Our deadline was already exceeded, and that was likely the cause
+			// of this cancelation.  Alter the status code accordingly.
+			statusCode = codes.DeadlineExceeded
+		}
+	}
+	t.closeStream(s, io.EOF, false, http2.ErrCodeNo, status.Newf(statusCode, "stream terminated by RST_STREAM with error code: %v", f.ErrCode), nil, false)
+}
+
+func (t *http2Client) handleSettings(f *http2.SettingsFrame, isFirst bool) {
+	if f.IsAck() {
+		return
+	}
+	var maxStreams *uint32
+	var ss []http2.Setting
+	var updateFuncs []func()
+	f.ForeachSetting(func(s http2.Setting) error {
+		switch s.ID {
+		case http2.SettingMaxConcurrentStreams:
+			maxStreams = new(uint32)
+			*maxStreams = s.Val
+		case http2.SettingMaxHeaderListSize:
+			updateFuncs = append(updateFuncs, func() {
+				t.maxSendHeaderListSize = new(uint32)
+				*t.maxSendHeaderListSize = s.Val
+			})
+		default:
+			ss = append(ss, s)
+		}
+		return nil
+	})
+	if isFirst && maxStreams == nil {
+		maxStreams = new(uint32)
+		*maxStreams = math.MaxUint32
+	}
+	sf := &incomingSettings{
+		ss: ss,
+	}
+	if maxStreams != nil {
+		updateStreamQuota := func() {
+			delta := int64(*maxStreams) - int64(t.maxConcurrentStreams)
+			t.maxConcurrentStreams = *maxStreams
+			t.streamQuota += delta
+			if delta > 0 && t.waitingStreams > 0 {
+				close(t.streamsQuotaAvailable) // wake all of them up.
+				t.streamsQuotaAvailable = make(chan struct{}, 1)
+			}
+		}
+		updateFuncs = append(updateFuncs, updateStreamQuota)
+	}
+	t.controlBuf.executeAndPut(func(interface{}) bool {
+		for _, f := range updateFuncs {
+			f()
+		}
+		return true
+	}, sf)
+}
+
+func (t *http2Client) handlePing(f *http2.PingFrame) {
+	if f.IsAck() {
+		// Maybe it's a BDP ping.
+		if t.bdpEst != nil {
+			t.bdpEst.calculate(f.Data)
+		}
+		return
+	}
+	pingAck := &ping{ack: true}
+	copy(pingAck.data[:], f.Data[:])
+	t.controlBuf.put(pingAck)
+}
+
+func (t *http2Client) handleGoAway(f *http2.GoAwayFrame) {
+	t.mu.Lock()
+	if t.state == closing {
+		t.mu.Unlock()
+		return
+	}
+	if f.ErrCode == http2.ErrCodeEnhanceYourCalm {
+		infof("Client received GoAway with http2.ErrCodeEnhanceYourCalm.")
+	}
+	id := f.LastStreamID
+	if id > 0 && id%2 != 1 {
+		t.mu.Unlock()
+		t.Close()
+		return
+	}
+	// A client can receive multiple GoAways from the server (see
+	// https://github.com/grpc/grpc-go/issues/1387).  The idea is that the first
+	// GoAway will be sent with an ID of MaxInt32 and the second GoAway will be
+	// sent after an RTT delay with the ID of the last stream the server will
+	// process.
+	//
+	// Therefore, when we get the first GoAway we don't necessarily close any
+	// streams. While in case of second GoAway we close all streams created after
+	// the GoAwayId. This way streams that were in-flight while the GoAway from
+	// server was being sent don't get killed.
+	select {
+	case <-t.goAway: // t.goAway has been closed (i.e.,multiple GoAways).
+		// If there are multiple GoAways the first one should always have an ID greater than the following ones.
+		if id > t.prevGoAwayID {
+			t.mu.Unlock()
+			t.Close()
+			return
+		}
+	default:
+		t.setGoAwayReason(f)
+		close(t.goAway)
+		t.controlBuf.put(&incomingGoAway{})
+		// Notify the clientconn about the GOAWAY before we set the state to
+		// draining, to allow the client to stop attempting to create streams
+		// before disallowing new streams on this connection.
+		t.onGoAway(t.goAwayReason)
+		t.state = draining
+	}
+	// All streams with IDs greater than the GoAwayId
+	// and smaller than the previous GoAway ID should be killed.
+	upperLimit := t.prevGoAwayID
+	if upperLimit == 0 { // This is the first GoAway Frame.
+		upperLimit = math.MaxUint32 // Kill all streams after the GoAway ID.
+	}
+	for streamID, stream := range t.activeStreams {
+		if streamID > id && streamID <= upperLimit {
+			// The stream was unprocessed by the server.
+			atomic.StoreUint32(&stream.unprocessed, 1)
+			t.closeStream(stream, errStreamDrain, false, http2.ErrCodeNo, statusGoAway, nil, false)
+		}
+	}
+	t.prevGoAwayID = id
+	active := len(t.activeStreams)
+	t.mu.Unlock()
+	if active == 0 {
+		t.Close()
+	}
+}
+
+// setGoAwayReason sets the value of t.goAwayReason based
+// on the GoAway frame received.
+// It expects a lock on transport's mutext to be held by
+// the caller.
+func (t *http2Client) setGoAwayReason(f *http2.GoAwayFrame) {
+	t.goAwayReason = GoAwayNoReason
+	switch f.ErrCode {
+	case http2.ErrCodeEnhanceYourCalm:
+		if string(f.DebugData()) == "too_many_pings" {
+			t.goAwayReason = GoAwayTooManyPings
+		}
+	}
+}
+
+func (t *http2Client) GetGoAwayReason() GoAwayReason {
+	t.mu.Lock()
+	defer t.mu.Unlock()
+	return t.goAwayReason
+}
+
+func (t *http2Client) handleWindowUpdate(f *http2.WindowUpdateFrame) {
+	t.controlBuf.put(&incomingWindowUpdate{
+		streamID:  f.Header().StreamID,
+		increment: f.Increment,
+	})
+}
+
+// operateHeaders takes action on the decoded headers.
+func (t *http2Client) operateHeaders(frame *http2.MetaHeadersFrame) {
+	s := t.getStream(frame)
+	if s == nil {
+		return
+	}
+	endStream := frame.StreamEnded()
+	atomic.StoreUint32(&s.bytesReceived, 1)
+	initialHeader := atomic.LoadUint32(&s.headerChanClosed) == 0
+
+	if !initialHeader && !endStream {
+		// As specified by gRPC over HTTP2, a HEADERS frame (and associated CONTINUATION frames) can only appear at the start or end of a stream. Therefore, second HEADERS frame must have EOS bit set.
+		st := status.New(codes.Internal, "a HEADERS frame cannot appear in the middle of a stream")
+		t.closeStream(s, st.Err(), true, http2.ErrCodeProtocol, st, nil, false)
+		return
+	}
+
+	state := &decodeState{}
+	// Initialize isGRPC value to be !initialHeader, since if a gRPC Response-Headers has already been received, then it means that the peer is speaking gRPC and we are in gRPC mode.
+	state.data.isGRPC = !initialHeader
+	if err := state.decodeHeader(frame); err != nil {
+		t.closeStream(s, err, true, http2.ErrCodeProtocol, status.Convert(err), nil, endStream)
+		return
+	}
+
+	isHeader := false
+	defer func() {
+		if t.statsHandler != nil {
+			if isHeader {
+				inHeader := &stats.InHeader{
+					Client:      true,
+					WireLength:  int(frame.Header().Length),
+					Header:      s.header.Copy(),
+					Compression: s.recvCompress,
+				}
+				t.statsHandler.HandleRPC(s.ctx, inHeader)
+			} else {
+				inTrailer := &stats.InTrailer{
+					Client:     true,
+					WireLength: int(frame.Header().Length),
+					Trailer:    s.trailer.Copy(),
+				}
+				t.statsHandler.HandleRPC(s.ctx, inTrailer)
+			}
+		}
+	}()
+
+	// If headerChan hasn't been closed yet
+	if atomic.CompareAndSwapUint32(&s.headerChanClosed, 0, 1) {
+		s.headerValid = true
+		if !endStream {
+			// HEADERS frame block carries a Response-Headers.
+			isHeader = true
+			// These values can be set without any synchronization because
+			// stream goroutine will read it only after seeing a closed
+			// headerChan which we'll close after setting this.
+			s.recvCompress = state.data.encoding
+			if len(state.data.mdata) > 0 {
+				s.header = state.data.mdata
+			}
+		} else {
+			// HEADERS frame block carries a Trailers-Only.
+			s.noHeaders = true
+		}
+		close(s.headerChan)
+	}
+
+	if !endStream {
+		return
+	}
+
+	// if client received END_STREAM from server while stream was still active, send RST_STREAM
+	rst := s.getState() == streamActive
+	t.closeStream(s, io.EOF, rst, http2.ErrCodeNo, state.status(), state.data.mdata, true)
+}
+
+// reader runs as a separate goroutine in charge of reading data from network
+// connection.
+//
+// TODO(zhaoq): currently one reader per transport. Investigate whether this is
+// optimal.
+// TODO(zhaoq): Check the validity of the incoming frame sequence.
+func (t *http2Client) reader() {
+	defer close(t.readerDone)
+	// Check the validity of server preface.
+	frame, err := t.framer.fr.ReadFrame()
+	if err != nil {
+		t.Close() // this kicks off resetTransport, so must be last before return
+		return
+	}
+	t.conn.SetReadDeadline(time.Time{}) // reset deadline once we get the settings frame (we didn't time out, yay!)
+	if t.keepaliveEnabled {
+		atomic.StoreInt64(&t.lastRead, time.Now().UnixNano())
+	}
+	sf, ok := frame.(*http2.SettingsFrame)
+	if !ok {
+		t.Close() // this kicks off resetTransport, so must be last before return
+		return
+	}
+	t.onPrefaceReceipt()
+	t.handleSettings(sf, true)
+
+	// loop to keep reading incoming messages on this transport.
+	for {
+		t.controlBuf.throttle()
+		frame, err := t.framer.fr.ReadFrame()
+		if t.keepaliveEnabled {
+			atomic.StoreInt64(&t.lastRead, time.Now().UnixNano())
+		}
+		if err != nil {
+			// Abort an active stream if the http2.Framer returns a
+			// http2.StreamError. This can happen only if the server's response
+			// is malformed http2.
+			if se, ok := err.(http2.StreamError); ok {
+				t.mu.Lock()
+				s := t.activeStreams[se.StreamID]
+				t.mu.Unlock()
+				if s != nil {
+					// use error detail to provide better err message
+					code := http2ErrConvTab[se.Code]
+					msg := t.framer.fr.ErrorDetail().Error()
+					t.closeStream(s, status.Error(code, msg), true, http2.ErrCodeProtocol, status.New(code, msg), nil, false)
+				}
+				continue
+			} else {
+				// Transport error.
+				t.Close()
+				return
+			}
+		}
+		switch frame := frame.(type) {
+		case *http2.MetaHeadersFrame:
+			t.operateHeaders(frame)
+		case *http2.DataFrame:
+			t.handleData(frame)
+		case *http2.RSTStreamFrame:
+			t.handleRSTStream(frame)
+		case *http2.SettingsFrame:
+			t.handleSettings(frame, false)
+		case *http2.PingFrame:
+			t.handlePing(frame)
+		case *http2.GoAwayFrame:
+			t.handleGoAway(frame)
+		case *http2.WindowUpdateFrame:
+			t.handleWindowUpdate(frame)
+		default:
+			errorf("transport: http2Client.reader got unhandled frame type %v.", frame)
+		}
+	}
+}
+
+func minTime(a, b time.Duration) time.Duration {
+	if a < b {
+		return a
+	}
+	return b
+}
+
+// keepalive running in a separate goroutune makes sure the connection is alive by sending pings.
+func (t *http2Client) keepalive() {
+	p := &ping{data: [8]byte{}}
+	// True iff a ping has been sent, and no data has been received since then.
+	outstandingPing := false
+	// Amount of time remaining before which we should receive an ACK for the
+	// last sent ping.
+	timeoutLeft := time.Duration(0)
+	// Records the last value of t.lastRead before we go block on the timer.
+	// This is required to check for read activity since then.
+	prevNano := time.Now().UnixNano()
+	timer := time.NewTimer(t.kp.Time)
+	for {
+		select {
+		case <-timer.C:
+			lastRead := atomic.LoadInt64(&t.lastRead)
+			if lastRead > prevNano {
+				// There has been read activity since the last time we were here.
+				outstandingPing = false
+				// Next timer should fire at kp.Time seconds from lastRead time.
+				timer.Reset(time.Duration(lastRead) + t.kp.Time - time.Duration(time.Now().UnixNano()))
+				prevNano = lastRead
+				continue
+			}
+			if outstandingPing && timeoutLeft <= 0 {
+				t.Close()
+				return
+			}
+			t.mu.Lock()
+			if t.state == closing {
+				// If the transport is closing, we should exit from the
+				// keepalive goroutine here. If not, we could have a race
+				// between the call to Signal() from Close() and the call to
+				// Wait() here, whereby the keepalive goroutine ends up
+				// blocking on the condition variable which will never be
+				// signalled again.
+				t.mu.Unlock()
+				return
+			}
+			if len(t.activeStreams) < 1 && !t.kp.PermitWithoutStream {
+				// If a ping was sent out previously (because there were active
+				// streams at that point) which wasn't acked and its timeout
+				// hadn't fired, but we got here and are about to go dormant,
+				// we should make sure that we unconditionally send a ping once
+				// we awaken.
+				outstandingPing = false
+				t.kpDormant = true
+				t.kpDormancyCond.Wait()
+			}
+			t.kpDormant = false
+			t.mu.Unlock()
+
+			// We get here either because we were dormant and a new stream was
+			// created which unblocked the Wait() call, or because the
+			// keepalive timer expired. In both cases, we need to send a ping.
+			if !outstandingPing {
+				if channelz.IsOn() {
+					atomic.AddInt64(&t.czData.kpCount, 1)
+				}
+				t.controlBuf.put(p)
+				timeoutLeft = t.kp.Timeout
+				outstandingPing = true
+			}
+			// The amount of time to sleep here is the minimum of kp.Time and
+			// timeoutLeft. This will ensure that we wait only for kp.Time
+			// before sending out the next ping (for cases where the ping is
+			// acked).
+			sleepDuration := minTime(t.kp.Time, timeoutLeft)
+			timeoutLeft -= sleepDuration
+			timer.Reset(sleepDuration)
+		case <-t.ctx.Done():
+			if !timer.Stop() {
+				<-timer.C
+			}
+			return
+		}
+	}
+}
+
+func (t *http2Client) Error() <-chan struct{} {
+	return t.ctx.Done()
+}
+
+func (t *http2Client) GoAway() <-chan struct{} {
+	return t.goAway
+}
+
+func (t *http2Client) ChannelzMetric() *channelz.SocketInternalMetric {
+	s := channelz.SocketInternalMetric{
+		StreamsStarted:                  atomic.LoadInt64(&t.czData.streamsStarted),
+		StreamsSucceeded:                atomic.LoadInt64(&t.czData.streamsSucceeded),
+		StreamsFailed:                   atomic.LoadInt64(&t.czData.streamsFailed),
+		MessagesSent:                    atomic.LoadInt64(&t.czData.msgSent),
+		MessagesReceived:                atomic.LoadInt64(&t.czData.msgRecv),
+		KeepAlivesSent:                  atomic.LoadInt64(&t.czData.kpCount),
+		LastLocalStreamCreatedTimestamp: time.Unix(0, atomic.LoadInt64(&t.czData.lastStreamCreatedTime)),
+		LastMessageSentTimestamp:        time.Unix(0, atomic.LoadInt64(&t.czData.lastMsgSentTime)),
+		LastMessageReceivedTimestamp:    time.Unix(0, atomic.LoadInt64(&t.czData.lastMsgRecvTime)),
+		LocalFlowControlWindow:          int64(t.fc.getSize()),
+		SocketOptions:                   channelz.GetSocketOption(t.conn),
+		LocalAddr:                       t.localAddr,
+		RemoteAddr:                      t.remoteAddr,
+		// RemoteName :
+	}
+	if au, ok := t.authInfo.(credentials.ChannelzSecurityInfo); ok {
+		s.Security = au.GetSecurityValue()
+	}
+	s.RemoteFlowControlWindow = t.getOutFlowWindow()
+	return &s
+}
+
+func (t *http2Client) RemoteAddr() net.Addr { return t.remoteAddr }
+
+func (t *http2Client) IncrMsgSent() {
+	atomic.AddInt64(&t.czData.msgSent, 1)
+	atomic.StoreInt64(&t.czData.lastMsgSentTime, time.Now().UnixNano())
+}
+
+func (t *http2Client) IncrMsgRecv() {
+	atomic.AddInt64(&t.czData.msgRecv, 1)
+	atomic.StoreInt64(&t.czData.lastMsgRecvTime, time.Now().UnixNano())
+}
+
+func (t *http2Client) getOutFlowWindow() int64 {
+	resp := make(chan uint32, 1)
+	timer := time.NewTimer(time.Second)
+	defer timer.Stop()
+	t.controlBuf.put(&outFlowControlSizeRequest{resp})
+	select {
+	case sz := <-resp:
+		return int64(sz)
+	case <-t.ctxDone:
+		return -1
+	case <-timer.C:
+		return -2
+	}
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/internal/transport/http2_server.go b/demo_test/vendor/google.golang.org/grpc/internal/transport/http2_server.go
new file mode 100644
index 0000000..fa33ffb
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/internal/transport/http2_server.go
@@ -0,0 +1,1251 @@
+/*
+ *
+ * Copyright 2014 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package transport
+
+import (
+	"bytes"
+	"context"
+	"errors"
+	"fmt"
+	"io"
+	"math"
+	"net"
+	"strconv"
+	"sync"
+	"sync/atomic"
+	"time"
+
+	"github.com/golang/protobuf/proto"
+	"golang.org/x/net/http2"
+	"golang.org/x/net/http2/hpack"
+
+	"google.golang.org/grpc/codes"
+	"google.golang.org/grpc/credentials"
+	"google.golang.org/grpc/grpclog"
+	"google.golang.org/grpc/internal/channelz"
+	"google.golang.org/grpc/internal/grpcrand"
+	"google.golang.org/grpc/keepalive"
+	"google.golang.org/grpc/metadata"
+	"google.golang.org/grpc/peer"
+	"google.golang.org/grpc/stats"
+	"google.golang.org/grpc/status"
+	"google.golang.org/grpc/tap"
+)
+
+var (
+	// ErrIllegalHeaderWrite indicates that setting header is illegal because of
+	// the stream's state.
+	ErrIllegalHeaderWrite = errors.New("transport: the stream is done or WriteHeader was already called")
+	// ErrHeaderListSizeLimitViolation indicates that the header list size is larger
+	// than the limit set by peer.
+	ErrHeaderListSizeLimitViolation = errors.New("transport: trying to send header list size larger than the limit set by peer")
+)
+
+// serverConnectionCounter counts the number of connections a server has seen
+// (equal to the number of http2Servers created). Must be accessed atomically.
+var serverConnectionCounter uint64
+
+// http2Server implements the ServerTransport interface with HTTP2.
+type http2Server struct {
+	lastRead    int64 // Keep this field 64-bit aligned. Accessed atomically.
+	ctx         context.Context
+	done        chan struct{}
+	conn        net.Conn
+	loopy       *loopyWriter
+	readerDone  chan struct{} // sync point to enable testing.
+	writerDone  chan struct{} // sync point to enable testing.
+	remoteAddr  net.Addr
+	localAddr   net.Addr
+	maxStreamID uint32               // max stream ID ever seen
+	authInfo    credentials.AuthInfo // auth info about the connection
+	inTapHandle tap.ServerInHandle
+	framer      *framer
+	// The max number of concurrent streams.
+	maxStreams uint32
+	// controlBuf delivers all the control related tasks (e.g., window
+	// updates, reset streams, and various settings) to the controller.
+	controlBuf *controlBuffer
+	fc         *trInFlow
+	stats      stats.Handler
+	// Keepalive and max-age parameters for the server.
+	kp keepalive.ServerParameters
+	// Keepalive enforcement policy.
+	kep keepalive.EnforcementPolicy
+	// The time instance last ping was received.
+	lastPingAt time.Time
+	// Number of times the client has violated keepalive ping policy so far.
+	pingStrikes uint8
+	// Flag to signify that number of ping strikes should be reset to 0.
+	// This is set whenever data or header frames are sent.
+	// 1 means yes.
+	resetPingStrikes      uint32 // Accessed atomically.
+	initialWindowSize     int32
+	bdpEst                *bdpEstimator
+	maxSendHeaderListSize *uint32
+
+	mu sync.Mutex // guard the following
+
+	// drainChan is initialized when drain(...) is called the first time.
+	// After which the server writes out the first GoAway(with ID 2^31-1) frame.
+	// Then an independent goroutine will be launched to later send the second GoAway.
+	// During this time we don't want to write another first GoAway(with ID 2^31 -1) frame.
+	// Thus call to drain(...) will be a no-op if drainChan is already initialized since draining is
+	// already underway.
+	drainChan     chan struct{}
+	state         transportState
+	activeStreams map[uint32]*Stream
+	// idle is the time instant when the connection went idle.
+	// This is either the beginning of the connection or when the number of
+	// RPCs go down to 0.
+	// When the connection is busy, this value is set to 0.
+	idle time.Time
+
+	// Fields below are for channelz metric collection.
+	channelzID int64 // channelz unique identification number
+	czData     *channelzData
+	bufferPool *bufferPool
+
+	connectionID uint64
+}
+
+// newHTTP2Server constructs a ServerTransport based on HTTP2. ConnectionError is
+// returned if something goes wrong.
+func newHTTP2Server(conn net.Conn, config *ServerConfig) (_ ServerTransport, err error) {
+	writeBufSize := config.WriteBufferSize
+	readBufSize := config.ReadBufferSize
+	maxHeaderListSize := defaultServerMaxHeaderListSize
+	if config.MaxHeaderListSize != nil {
+		maxHeaderListSize = *config.MaxHeaderListSize
+	}
+	framer := newFramer(conn, writeBufSize, readBufSize, maxHeaderListSize)
+	// Send initial settings as connection preface to client.
+	isettings := []http2.Setting{{
+		ID:  http2.SettingMaxFrameSize,
+		Val: http2MaxFrameLen,
+	}}
+	// TODO(zhaoq): Have a better way to signal "no limit" because 0 is
+	// permitted in the HTTP2 spec.
+	maxStreams := config.MaxStreams
+	if maxStreams == 0 {
+		maxStreams = math.MaxUint32
+	} else {
+		isettings = append(isettings, http2.Setting{
+			ID:  http2.SettingMaxConcurrentStreams,
+			Val: maxStreams,
+		})
+	}
+	dynamicWindow := true
+	iwz := int32(initialWindowSize)
+	if config.InitialWindowSize >= defaultWindowSize {
+		iwz = config.InitialWindowSize
+		dynamicWindow = false
+	}
+	icwz := int32(initialWindowSize)
+	if config.InitialConnWindowSize >= defaultWindowSize {
+		icwz = config.InitialConnWindowSize
+		dynamicWindow = false
+	}
+	if iwz != defaultWindowSize {
+		isettings = append(isettings, http2.Setting{
+			ID:  http2.SettingInitialWindowSize,
+			Val: uint32(iwz)})
+	}
+	if config.MaxHeaderListSize != nil {
+		isettings = append(isettings, http2.Setting{
+			ID:  http2.SettingMaxHeaderListSize,
+			Val: *config.MaxHeaderListSize,
+		})
+	}
+	if config.HeaderTableSize != nil {
+		isettings = append(isettings, http2.Setting{
+			ID:  http2.SettingHeaderTableSize,
+			Val: *config.HeaderTableSize,
+		})
+	}
+	if err := framer.fr.WriteSettings(isettings...); err != nil {
+		return nil, connectionErrorf(false, err, "transport: %v", err)
+	}
+	// Adjust the connection flow control window if needed.
+	if delta := uint32(icwz - defaultWindowSize); delta > 0 {
+		if err := framer.fr.WriteWindowUpdate(0, delta); err != nil {
+			return nil, connectionErrorf(false, err, "transport: %v", err)
+		}
+	}
+	kp := config.KeepaliveParams
+	if kp.MaxConnectionIdle == 0 {
+		kp.MaxConnectionIdle = defaultMaxConnectionIdle
+	}
+	if kp.MaxConnectionAge == 0 {
+		kp.MaxConnectionAge = defaultMaxConnectionAge
+	}
+	// Add a jitter to MaxConnectionAge.
+	kp.MaxConnectionAge += getJitter(kp.MaxConnectionAge)
+	if kp.MaxConnectionAgeGrace == 0 {
+		kp.MaxConnectionAgeGrace = defaultMaxConnectionAgeGrace
+	}
+	if kp.Time == 0 {
+		kp.Time = defaultServerKeepaliveTime
+	}
+	if kp.Timeout == 0 {
+		kp.Timeout = defaultServerKeepaliveTimeout
+	}
+	kep := config.KeepalivePolicy
+	if kep.MinTime == 0 {
+		kep.MinTime = defaultKeepalivePolicyMinTime
+	}
+	done := make(chan struct{})
+	t := &http2Server{
+		ctx:               context.Background(),
+		done:              done,
+		conn:              conn,
+		remoteAddr:        conn.RemoteAddr(),
+		localAddr:         conn.LocalAddr(),
+		authInfo:          config.AuthInfo,
+		framer:            framer,
+		readerDone:        make(chan struct{}),
+		writerDone:        make(chan struct{}),
+		maxStreams:        maxStreams,
+		inTapHandle:       config.InTapHandle,
+		fc:                &trInFlow{limit: uint32(icwz)},
+		state:             reachable,
+		activeStreams:     make(map[uint32]*Stream),
+		stats:             config.StatsHandler,
+		kp:                kp,
+		idle:              time.Now(),
+		kep:               kep,
+		initialWindowSize: iwz,
+		czData:            new(channelzData),
+		bufferPool:        newBufferPool(),
+	}
+	t.controlBuf = newControlBuffer(t.done)
+	if dynamicWindow {
+		t.bdpEst = &bdpEstimator{
+			bdp:               initialWindowSize,
+			updateFlowControl: t.updateFlowControl,
+		}
+	}
+	if t.stats != nil {
+		t.ctx = t.stats.TagConn(t.ctx, &stats.ConnTagInfo{
+			RemoteAddr: t.remoteAddr,
+			LocalAddr:  t.localAddr,
+		})
+		connBegin := &stats.ConnBegin{}
+		t.stats.HandleConn(t.ctx, connBegin)
+	}
+	if channelz.IsOn() {
+		t.channelzID = channelz.RegisterNormalSocket(t, config.ChannelzParentID, fmt.Sprintf("%s -> %s", t.remoteAddr, t.localAddr))
+	}
+
+	t.connectionID = atomic.AddUint64(&serverConnectionCounter, 1)
+
+	t.framer.writer.Flush()
+
+	defer func() {
+		if err != nil {
+			t.Close()
+		}
+	}()
+
+	// Check the validity of client preface.
+	preface := make([]byte, len(clientPreface))
+	if _, err := io.ReadFull(t.conn, preface); err != nil {
+		return nil, connectionErrorf(false, err, "transport: http2Server.HandleStreams failed to receive the preface from client: %v", err)
+	}
+	if !bytes.Equal(preface, clientPreface) {
+		return nil, connectionErrorf(false, nil, "transport: http2Server.HandleStreams received bogus greeting from client: %q", preface)
+	}
+
+	frame, err := t.framer.fr.ReadFrame()
+	if err == io.EOF || err == io.ErrUnexpectedEOF {
+		return nil, err
+	}
+	if err != nil {
+		return nil, connectionErrorf(false, err, "transport: http2Server.HandleStreams failed to read initial settings frame: %v", err)
+	}
+	atomic.StoreInt64(&t.lastRead, time.Now().UnixNano())
+	sf, ok := frame.(*http2.SettingsFrame)
+	if !ok {
+		return nil, connectionErrorf(false, nil, "transport: http2Server.HandleStreams saw invalid preface type %T from client", frame)
+	}
+	t.handleSettings(sf)
+
+	go func() {
+		t.loopy = newLoopyWriter(serverSide, t.framer, t.controlBuf, t.bdpEst)
+		t.loopy.ssGoAwayHandler = t.outgoingGoAwayHandler
+		if err := t.loopy.run(); err != nil {
+			errorf("transport: loopyWriter.run returning. Err: %v", err)
+		}
+		t.conn.Close()
+		close(t.writerDone)
+	}()
+	go t.keepalive()
+	return t, nil
+}
+
+// operateHeader takes action on the decoded headers.
+func (t *http2Server) operateHeaders(frame *http2.MetaHeadersFrame, handle func(*Stream), traceCtx func(context.Context, string) context.Context) (fatal bool) {
+	streamID := frame.Header().StreamID
+	state := &decodeState{
+		serverSide: true,
+	}
+	if err := state.decodeHeader(frame); err != nil {
+		if se, ok := status.FromError(err); ok {
+			t.controlBuf.put(&cleanupStream{
+				streamID: streamID,
+				rst:      true,
+				rstCode:  statusCodeConvTab[se.Code()],
+				onWrite:  func() {},
+			})
+		}
+		return false
+	}
+
+	buf := newRecvBuffer()
+	s := &Stream{
+		id:             streamID,
+		st:             t,
+		buf:            buf,
+		fc:             &inFlow{limit: uint32(t.initialWindowSize)},
+		recvCompress:   state.data.encoding,
+		method:         state.data.method,
+		contentSubtype: state.data.contentSubtype,
+	}
+	if frame.StreamEnded() {
+		// s is just created by the caller. No lock needed.
+		s.state = streamReadDone
+	}
+	if state.data.timeoutSet {
+		s.ctx, s.cancel = context.WithTimeout(t.ctx, state.data.timeout)
+	} else {
+		s.ctx, s.cancel = context.WithCancel(t.ctx)
+	}
+	pr := &peer.Peer{
+		Addr: t.remoteAddr,
+	}
+	// Attach Auth info if there is any.
+	if t.authInfo != nil {
+		pr.AuthInfo = t.authInfo
+	}
+	s.ctx = peer.NewContext(s.ctx, pr)
+	// Attach the received metadata to the context.
+	if len(state.data.mdata) > 0 {
+		s.ctx = metadata.NewIncomingContext(s.ctx, state.data.mdata)
+	}
+	if state.data.statsTags != nil {
+		s.ctx = stats.SetIncomingTags(s.ctx, state.data.statsTags)
+	}
+	if state.data.statsTrace != nil {
+		s.ctx = stats.SetIncomingTrace(s.ctx, state.data.statsTrace)
+	}
+	if t.inTapHandle != nil {
+		var err error
+		info := &tap.Info{
+			FullMethodName: state.data.method,
+		}
+		s.ctx, err = t.inTapHandle(s.ctx, info)
+		if err != nil {
+			warningf("transport: http2Server.operateHeaders got an error from InTapHandle: %v", err)
+			t.controlBuf.put(&cleanupStream{
+				streamID: s.id,
+				rst:      true,
+				rstCode:  http2.ErrCodeRefusedStream,
+				onWrite:  func() {},
+			})
+			s.cancel()
+			return false
+		}
+	}
+	t.mu.Lock()
+	if t.state != reachable {
+		t.mu.Unlock()
+		s.cancel()
+		return false
+	}
+	if uint32(len(t.activeStreams)) >= t.maxStreams {
+		t.mu.Unlock()
+		t.controlBuf.put(&cleanupStream{
+			streamID: streamID,
+			rst:      true,
+			rstCode:  http2.ErrCodeRefusedStream,
+			onWrite:  func() {},
+		})
+		s.cancel()
+		return false
+	}
+	if streamID%2 != 1 || streamID <= t.maxStreamID {
+		t.mu.Unlock()
+		// illegal gRPC stream id.
+		errorf("transport: http2Server.HandleStreams received an illegal stream id: %v", streamID)
+		s.cancel()
+		return true
+	}
+	t.maxStreamID = streamID
+	t.activeStreams[streamID] = s
+	if len(t.activeStreams) == 1 {
+		t.idle = time.Time{}
+	}
+	t.mu.Unlock()
+	if channelz.IsOn() {
+		atomic.AddInt64(&t.czData.streamsStarted, 1)
+		atomic.StoreInt64(&t.czData.lastStreamCreatedTime, time.Now().UnixNano())
+	}
+	s.requestRead = func(n int) {
+		t.adjustWindow(s, uint32(n))
+	}
+	s.ctx = traceCtx(s.ctx, s.method)
+	if t.stats != nil {
+		s.ctx = t.stats.TagRPC(s.ctx, &stats.RPCTagInfo{FullMethodName: s.method})
+		inHeader := &stats.InHeader{
+			FullMethod:  s.method,
+			RemoteAddr:  t.remoteAddr,
+			LocalAddr:   t.localAddr,
+			Compression: s.recvCompress,
+			WireLength:  int(frame.Header().Length),
+			Header:      metadata.MD(state.data.mdata).Copy(),
+		}
+		t.stats.HandleRPC(s.ctx, inHeader)
+	}
+	s.ctxDone = s.ctx.Done()
+	s.wq = newWriteQuota(defaultWriteQuota, s.ctxDone)
+	s.trReader = &transportReader{
+		reader: &recvBufferReader{
+			ctx:        s.ctx,
+			ctxDone:    s.ctxDone,
+			recv:       s.buf,
+			freeBuffer: t.bufferPool.put,
+		},
+		windowHandler: func(n int) {
+			t.updateWindow(s, uint32(n))
+		},
+	}
+	// Register the stream with loopy.
+	t.controlBuf.put(&registerStream{
+		streamID: s.id,
+		wq:       s.wq,
+	})
+	handle(s)
+	return false
+}
+
+// HandleStreams receives incoming streams using the given handler. This is
+// typically run in a separate goroutine.
+// traceCtx attaches trace to ctx and returns the new context.
+func (t *http2Server) HandleStreams(handle func(*Stream), traceCtx func(context.Context, string) context.Context) {
+	defer close(t.readerDone)
+	for {
+		t.controlBuf.throttle()
+		frame, err := t.framer.fr.ReadFrame()
+		atomic.StoreInt64(&t.lastRead, time.Now().UnixNano())
+		if err != nil {
+			if se, ok := err.(http2.StreamError); ok {
+				warningf("transport: http2Server.HandleStreams encountered http2.StreamError: %v", se)
+				t.mu.Lock()
+				s := t.activeStreams[se.StreamID]
+				t.mu.Unlock()
+				if s != nil {
+					t.closeStream(s, true, se.Code, false)
+				} else {
+					t.controlBuf.put(&cleanupStream{
+						streamID: se.StreamID,
+						rst:      true,
+						rstCode:  se.Code,
+						onWrite:  func() {},
+					})
+				}
+				continue
+			}
+			if err == io.EOF || err == io.ErrUnexpectedEOF {
+				t.Close()
+				return
+			}
+			warningf("transport: http2Server.HandleStreams failed to read frame: %v", err)
+			t.Close()
+			return
+		}
+		switch frame := frame.(type) {
+		case *http2.MetaHeadersFrame:
+			if t.operateHeaders(frame, handle, traceCtx) {
+				t.Close()
+				break
+			}
+		case *http2.DataFrame:
+			t.handleData(frame)
+		case *http2.RSTStreamFrame:
+			t.handleRSTStream(frame)
+		case *http2.SettingsFrame:
+			t.handleSettings(frame)
+		case *http2.PingFrame:
+			t.handlePing(frame)
+		case *http2.WindowUpdateFrame:
+			t.handleWindowUpdate(frame)
+		case *http2.GoAwayFrame:
+			// TODO: Handle GoAway from the client appropriately.
+		default:
+			errorf("transport: http2Server.HandleStreams found unhandled frame type %v.", frame)
+		}
+	}
+}
+
+func (t *http2Server) getStream(f http2.Frame) (*Stream, bool) {
+	t.mu.Lock()
+	defer t.mu.Unlock()
+	if t.activeStreams == nil {
+		// The transport is closing.
+		return nil, false
+	}
+	s, ok := t.activeStreams[f.Header().StreamID]
+	if !ok {
+		// The stream is already done.
+		return nil, false
+	}
+	return s, true
+}
+
+// adjustWindow sends out extra window update over the initial window size
+// of stream if the application is requesting data larger in size than
+// the window.
+func (t *http2Server) adjustWindow(s *Stream, n uint32) {
+	if w := s.fc.maybeAdjust(n); w > 0 {
+		t.controlBuf.put(&outgoingWindowUpdate{streamID: s.id, increment: w})
+	}
+
+}
+
+// updateWindow adjusts the inbound quota for the stream and the transport.
+// Window updates will deliver to the controller for sending when
+// the cumulative quota exceeds the corresponding threshold.
+func (t *http2Server) updateWindow(s *Stream, n uint32) {
+	if w := s.fc.onRead(n); w > 0 {
+		t.controlBuf.put(&outgoingWindowUpdate{streamID: s.id,
+			increment: w,
+		})
+	}
+}
+
+// updateFlowControl updates the incoming flow control windows
+// for the transport and the stream based on the current bdp
+// estimation.
+func (t *http2Server) updateFlowControl(n uint32) {
+	t.mu.Lock()
+	for _, s := range t.activeStreams {
+		s.fc.newLimit(n)
+	}
+	t.initialWindowSize = int32(n)
+	t.mu.Unlock()
+	t.controlBuf.put(&outgoingWindowUpdate{
+		streamID:  0,
+		increment: t.fc.newLimit(n),
+	})
+	t.controlBuf.put(&outgoingSettings{
+		ss: []http2.Setting{
+			{
+				ID:  http2.SettingInitialWindowSize,
+				Val: n,
+			},
+		},
+	})
+
+}
+
+func (t *http2Server) handleData(f *http2.DataFrame) {
+	size := f.Header().Length
+	var sendBDPPing bool
+	if t.bdpEst != nil {
+		sendBDPPing = t.bdpEst.add(size)
+	}
+	// Decouple connection's flow control from application's read.
+	// An update on connection's flow control should not depend on
+	// whether user application has read the data or not. Such a
+	// restriction is already imposed on the stream's flow control,
+	// and therefore the sender will be blocked anyways.
+	// Decoupling the connection flow control will prevent other
+	// active(fast) streams from starving in presence of slow or
+	// inactive streams.
+	if w := t.fc.onData(size); w > 0 {
+		t.controlBuf.put(&outgoingWindowUpdate{
+			streamID:  0,
+			increment: w,
+		})
+	}
+	if sendBDPPing {
+		// Avoid excessive ping detection (e.g. in an L7 proxy)
+		// by sending a window update prior to the BDP ping.
+		if w := t.fc.reset(); w > 0 {
+			t.controlBuf.put(&outgoingWindowUpdate{
+				streamID:  0,
+				increment: w,
+			})
+		}
+		t.controlBuf.put(bdpPing)
+	}
+	// Select the right stream to dispatch.
+	s, ok := t.getStream(f)
+	if !ok {
+		return
+	}
+	if size > 0 {
+		if err := s.fc.onData(size); err != nil {
+			t.closeStream(s, true, http2.ErrCodeFlowControl, false)
+			return
+		}
+		if f.Header().Flags.Has(http2.FlagDataPadded) {
+			if w := s.fc.onRead(size - uint32(len(f.Data()))); w > 0 {
+				t.controlBuf.put(&outgoingWindowUpdate{s.id, w})
+			}
+		}
+		// TODO(bradfitz, zhaoq): A copy is required here because there is no
+		// guarantee f.Data() is consumed before the arrival of next frame.
+		// Can this copy be eliminated?
+		if len(f.Data()) > 0 {
+			buffer := t.bufferPool.get()
+			buffer.Reset()
+			buffer.Write(f.Data())
+			s.write(recvMsg{buffer: buffer})
+		}
+	}
+	if f.Header().Flags.Has(http2.FlagDataEndStream) {
+		// Received the end of stream from the client.
+		s.compareAndSwapState(streamActive, streamReadDone)
+		s.write(recvMsg{err: io.EOF})
+	}
+}
+
+func (t *http2Server) handleRSTStream(f *http2.RSTStreamFrame) {
+	// If the stream is not deleted from the transport's active streams map, then do a regular close stream.
+	if s, ok := t.getStream(f); ok {
+		t.closeStream(s, false, 0, false)
+		return
+	}
+	// If the stream is already deleted from the active streams map, then put a cleanupStream item into controlbuf to delete the stream from loopy writer's established streams map.
+	t.controlBuf.put(&cleanupStream{
+		streamID: f.Header().StreamID,
+		rst:      false,
+		rstCode:  0,
+		onWrite:  func() {},
+	})
+}
+
+func (t *http2Server) handleSettings(f *http2.SettingsFrame) {
+	if f.IsAck() {
+		return
+	}
+	var ss []http2.Setting
+	var updateFuncs []func()
+	f.ForeachSetting(func(s http2.Setting) error {
+		switch s.ID {
+		case http2.SettingMaxHeaderListSize:
+			updateFuncs = append(updateFuncs, func() {
+				t.maxSendHeaderListSize = new(uint32)
+				*t.maxSendHeaderListSize = s.Val
+			})
+		default:
+			ss = append(ss, s)
+		}
+		return nil
+	})
+	t.controlBuf.executeAndPut(func(interface{}) bool {
+		for _, f := range updateFuncs {
+			f()
+		}
+		return true
+	}, &incomingSettings{
+		ss: ss,
+	})
+}
+
+const (
+	maxPingStrikes     = 2
+	defaultPingTimeout = 2 * time.Hour
+)
+
+func (t *http2Server) handlePing(f *http2.PingFrame) {
+	if f.IsAck() {
+		if f.Data == goAwayPing.data && t.drainChan != nil {
+			close(t.drainChan)
+			return
+		}
+		// Maybe it's a BDP ping.
+		if t.bdpEst != nil {
+			t.bdpEst.calculate(f.Data)
+		}
+		return
+	}
+	pingAck := &ping{ack: true}
+	copy(pingAck.data[:], f.Data[:])
+	t.controlBuf.put(pingAck)
+
+	now := time.Now()
+	defer func() {
+		t.lastPingAt = now
+	}()
+	// A reset ping strikes means that we don't need to check for policy
+	// violation for this ping and the pingStrikes counter should be set
+	// to 0.
+	if atomic.CompareAndSwapUint32(&t.resetPingStrikes, 1, 0) {
+		t.pingStrikes = 0
+		return
+	}
+	t.mu.Lock()
+	ns := len(t.activeStreams)
+	t.mu.Unlock()
+	if ns < 1 && !t.kep.PermitWithoutStream {
+		// Keepalive shouldn't be active thus, this new ping should
+		// have come after at least defaultPingTimeout.
+		if t.lastPingAt.Add(defaultPingTimeout).After(now) {
+			t.pingStrikes++
+		}
+	} else {
+		// Check if keepalive policy is respected.
+		if t.lastPingAt.Add(t.kep.MinTime).After(now) {
+			t.pingStrikes++
+		}
+	}
+
+	if t.pingStrikes > maxPingStrikes {
+		// Send goaway and close the connection.
+		errorf("transport: Got too many pings from the client, closing the connection.")
+		t.controlBuf.put(&goAway{code: http2.ErrCodeEnhanceYourCalm, debugData: []byte("too_many_pings"), closeConn: true})
+	}
+}
+
+func (t *http2Server) handleWindowUpdate(f *http2.WindowUpdateFrame) {
+	t.controlBuf.put(&incomingWindowUpdate{
+		streamID:  f.Header().StreamID,
+		increment: f.Increment,
+	})
+}
+
+func appendHeaderFieldsFromMD(headerFields []hpack.HeaderField, md metadata.MD) []hpack.HeaderField {
+	for k, vv := range md {
+		if isReservedHeader(k) {
+			// Clients don't tolerate reading restricted headers after some non restricted ones were sent.
+			continue
+		}
+		for _, v := range vv {
+			headerFields = append(headerFields, hpack.HeaderField{Name: k, Value: encodeMetadataHeader(k, v)})
+		}
+	}
+	return headerFields
+}
+
+func (t *http2Server) checkForHeaderListSize(it interface{}) bool {
+	if t.maxSendHeaderListSize == nil {
+		return true
+	}
+	hdrFrame := it.(*headerFrame)
+	var sz int64
+	for _, f := range hdrFrame.hf {
+		if sz += int64(f.Size()); sz > int64(*t.maxSendHeaderListSize) {
+			errorf("header list size to send violates the maximum size (%d bytes) set by client", *t.maxSendHeaderListSize)
+			return false
+		}
+	}
+	return true
+}
+
+// WriteHeader sends the header metadata md back to the client.
+func (t *http2Server) WriteHeader(s *Stream, md metadata.MD) error {
+	if s.updateHeaderSent() || s.getState() == streamDone {
+		return ErrIllegalHeaderWrite
+	}
+	s.hdrMu.Lock()
+	if md.Len() > 0 {
+		if s.header.Len() > 0 {
+			s.header = metadata.Join(s.header, md)
+		} else {
+			s.header = md
+		}
+	}
+	if err := t.writeHeaderLocked(s); err != nil {
+		s.hdrMu.Unlock()
+		return err
+	}
+	s.hdrMu.Unlock()
+	return nil
+}
+
+func (t *http2Server) setResetPingStrikes() {
+	atomic.StoreUint32(&t.resetPingStrikes, 1)
+}
+
+func (t *http2Server) writeHeaderLocked(s *Stream) error {
+	// TODO(mmukhi): Benchmark if the performance gets better if count the metadata and other header fields
+	// first and create a slice of that exact size.
+	headerFields := make([]hpack.HeaderField, 0, 2) // at least :status, content-type will be there if none else.
+	headerFields = append(headerFields, hpack.HeaderField{Name: ":status", Value: "200"})
+	headerFields = append(headerFields, hpack.HeaderField{Name: "content-type", Value: contentType(s.contentSubtype)})
+	if s.sendCompress != "" {
+		headerFields = append(headerFields, hpack.HeaderField{Name: "grpc-encoding", Value: s.sendCompress})
+	}
+	headerFields = appendHeaderFieldsFromMD(headerFields, s.header)
+	success, err := t.controlBuf.executeAndPut(t.checkForHeaderListSize, &headerFrame{
+		streamID:  s.id,
+		hf:        headerFields,
+		endStream: false,
+		onWrite:   t.setResetPingStrikes,
+	})
+	if !success {
+		if err != nil {
+			return err
+		}
+		t.closeStream(s, true, http2.ErrCodeInternal, false)
+		return ErrHeaderListSizeLimitViolation
+	}
+	if t.stats != nil {
+		// Note: Headers are compressed with hpack after this call returns.
+		// No WireLength field is set here.
+		outHeader := &stats.OutHeader{
+			Header:      s.header.Copy(),
+			Compression: s.sendCompress,
+		}
+		t.stats.HandleRPC(s.Context(), outHeader)
+	}
+	return nil
+}
+
+// WriteStatus sends stream status to the client and terminates the stream.
+// There is no further I/O operations being able to perform on this stream.
+// TODO(zhaoq): Now it indicates the end of entire stream. Revisit if early
+// OK is adopted.
+func (t *http2Server) WriteStatus(s *Stream, st *status.Status) error {
+	if s.getState() == streamDone {
+		return nil
+	}
+	s.hdrMu.Lock()
+	// TODO(mmukhi): Benchmark if the performance gets better if count the metadata and other header fields
+	// first and create a slice of that exact size.
+	headerFields := make([]hpack.HeaderField, 0, 2) // grpc-status and grpc-message will be there if none else.
+	if !s.updateHeaderSent() {                      // No headers have been sent.
+		if len(s.header) > 0 { // Send a separate header frame.
+			if err := t.writeHeaderLocked(s); err != nil {
+				s.hdrMu.Unlock()
+				return err
+			}
+		} else { // Send a trailer only response.
+			headerFields = append(headerFields, hpack.HeaderField{Name: ":status", Value: "200"})
+			headerFields = append(headerFields, hpack.HeaderField{Name: "content-type", Value: contentType(s.contentSubtype)})
+		}
+	}
+	headerFields = append(headerFields, hpack.HeaderField{Name: "grpc-status", Value: strconv.Itoa(int(st.Code()))})
+	headerFields = append(headerFields, hpack.HeaderField{Name: "grpc-message", Value: encodeGrpcMessage(st.Message())})
+
+	if p := st.Proto(); p != nil && len(p.Details) > 0 {
+		stBytes, err := proto.Marshal(p)
+		if err != nil {
+			// TODO: return error instead, when callers are able to handle it.
+			grpclog.Errorf("transport: failed to marshal rpc status: %v, error: %v", p, err)
+		} else {
+			headerFields = append(headerFields, hpack.HeaderField{Name: "grpc-status-details-bin", Value: encodeBinHeader(stBytes)})
+		}
+	}
+
+	// Attach the trailer metadata.
+	headerFields = appendHeaderFieldsFromMD(headerFields, s.trailer)
+	trailingHeader := &headerFrame{
+		streamID:  s.id,
+		hf:        headerFields,
+		endStream: true,
+		onWrite:   t.setResetPingStrikes,
+	}
+	s.hdrMu.Unlock()
+	success, err := t.controlBuf.execute(t.checkForHeaderListSize, trailingHeader)
+	if !success {
+		if err != nil {
+			return err
+		}
+		t.closeStream(s, true, http2.ErrCodeInternal, false)
+		return ErrHeaderListSizeLimitViolation
+	}
+	// Send a RST_STREAM after the trailers if the client has not already half-closed.
+	rst := s.getState() == streamActive
+	t.finishStream(s, rst, http2.ErrCodeNo, trailingHeader, true)
+	if t.stats != nil {
+		// Note: The trailer fields are compressed with hpack after this call returns.
+		// No WireLength field is set here.
+		t.stats.HandleRPC(s.Context(), &stats.OutTrailer{
+			Trailer: s.trailer.Copy(),
+		})
+	}
+	return nil
+}
+
+// Write converts the data into HTTP2 data frame and sends it out. Non-nil error
+// is returns if it fails (e.g., framing error, transport error).
+func (t *http2Server) Write(s *Stream, hdr []byte, data []byte, opts *Options) error {
+	if !s.isHeaderSent() { // Headers haven't been written yet.
+		if err := t.WriteHeader(s, nil); err != nil {
+			if _, ok := err.(ConnectionError); ok {
+				return err
+			}
+			// TODO(mmukhi, dfawley): Make sure this is the right code to return.
+			return status.Errorf(codes.Internal, "transport: %v", err)
+		}
+	} else {
+		// Writing headers checks for this condition.
+		if s.getState() == streamDone {
+			// TODO(mmukhi, dfawley): Should the server write also return io.EOF?
+			s.cancel()
+			select {
+			case <-t.done:
+				return ErrConnClosing
+			default:
+			}
+			return ContextErr(s.ctx.Err())
+		}
+	}
+	// Add some data to header frame so that we can equally distribute bytes across frames.
+	emptyLen := http2MaxFrameLen - len(hdr)
+	if emptyLen > len(data) {
+		emptyLen = len(data)
+	}
+	hdr = append(hdr, data[:emptyLen]...)
+	data = data[emptyLen:]
+	df := &dataFrame{
+		streamID:    s.id,
+		h:           hdr,
+		d:           data,
+		onEachWrite: t.setResetPingStrikes,
+	}
+	if err := s.wq.get(int32(len(hdr) + len(data))); err != nil {
+		select {
+		case <-t.done:
+			return ErrConnClosing
+		default:
+		}
+		return ContextErr(s.ctx.Err())
+	}
+	return t.controlBuf.put(df)
+}
+
+// keepalive running in a separate goroutine does the following:
+// 1. Gracefully closes an idle connection after a duration of keepalive.MaxConnectionIdle.
+// 2. Gracefully closes any connection after a duration of keepalive.MaxConnectionAge.
+// 3. Forcibly closes a connection after an additive period of keepalive.MaxConnectionAgeGrace over keepalive.MaxConnectionAge.
+// 4. Makes sure a connection is alive by sending pings with a frequency of keepalive.Time and closes a non-responsive connection
+// after an additional duration of keepalive.Timeout.
+func (t *http2Server) keepalive() {
+	p := &ping{}
+	// True iff a ping has been sent, and no data has been received since then.
+	outstandingPing := false
+	// Amount of time remaining before which we should receive an ACK for the
+	// last sent ping.
+	kpTimeoutLeft := time.Duration(0)
+	// Records the last value of t.lastRead before we go block on the timer.
+	// This is required to check for read activity since then.
+	prevNano := time.Now().UnixNano()
+	// Initialize the different timers to their default values.
+	idleTimer := time.NewTimer(t.kp.MaxConnectionIdle)
+	ageTimer := time.NewTimer(t.kp.MaxConnectionAge)
+	kpTimer := time.NewTimer(t.kp.Time)
+	defer func() {
+		// We need to drain the underlying channel in these timers after a call
+		// to Stop(), only if we are interested in resetting them. Clearly we
+		// are not interested in resetting them here.
+		idleTimer.Stop()
+		ageTimer.Stop()
+		kpTimer.Stop()
+	}()
+
+	for {
+		select {
+		case <-idleTimer.C:
+			t.mu.Lock()
+			idle := t.idle
+			if idle.IsZero() { // The connection is non-idle.
+				t.mu.Unlock()
+				idleTimer.Reset(t.kp.MaxConnectionIdle)
+				continue
+			}
+			val := t.kp.MaxConnectionIdle - time.Since(idle)
+			t.mu.Unlock()
+			if val <= 0 {
+				// The connection has been idle for a duration of keepalive.MaxConnectionIdle or more.
+				// Gracefully close the connection.
+				t.drain(http2.ErrCodeNo, []byte{})
+				return
+			}
+			idleTimer.Reset(val)
+		case <-ageTimer.C:
+			t.drain(http2.ErrCodeNo, []byte{})
+			ageTimer.Reset(t.kp.MaxConnectionAgeGrace)
+			select {
+			case <-ageTimer.C:
+				// Close the connection after grace period.
+				infof("transport: closing server transport due to maximum connection age.")
+				t.Close()
+			case <-t.done:
+			}
+			return
+		case <-kpTimer.C:
+			lastRead := atomic.LoadInt64(&t.lastRead)
+			if lastRead > prevNano {
+				// There has been read activity since the last time we were
+				// here. Setup the timer to fire at kp.Time seconds from
+				// lastRead time and continue.
+				outstandingPing = false
+				kpTimer.Reset(time.Duration(lastRead) + t.kp.Time - time.Duration(time.Now().UnixNano()))
+				prevNano = lastRead
+				continue
+			}
+			if outstandingPing && kpTimeoutLeft <= 0 {
+				infof("transport: closing server transport due to idleness.")
+				t.Close()
+				return
+			}
+			if !outstandingPing {
+				if channelz.IsOn() {
+					atomic.AddInt64(&t.czData.kpCount, 1)
+				}
+				t.controlBuf.put(p)
+				kpTimeoutLeft = t.kp.Timeout
+				outstandingPing = true
+			}
+			// The amount of time to sleep here is the minimum of kp.Time and
+			// timeoutLeft. This will ensure that we wait only for kp.Time
+			// before sending out the next ping (for cases where the ping is
+			// acked).
+			sleepDuration := minTime(t.kp.Time, kpTimeoutLeft)
+			kpTimeoutLeft -= sleepDuration
+			kpTimer.Reset(sleepDuration)
+		case <-t.done:
+			return
+		}
+	}
+}
+
+// Close starts shutting down the http2Server transport.
+// TODO(zhaoq): Now the destruction is not blocked on any pending streams. This
+// could cause some resource issue. Revisit this later.
+func (t *http2Server) Close() error {
+	t.mu.Lock()
+	if t.state == closing {
+		t.mu.Unlock()
+		return errors.New("transport: Close() was already called")
+	}
+	t.state = closing
+	streams := t.activeStreams
+	t.activeStreams = nil
+	t.mu.Unlock()
+	t.controlBuf.finish()
+	close(t.done)
+	err := t.conn.Close()
+	if channelz.IsOn() {
+		channelz.RemoveEntry(t.channelzID)
+	}
+	// Cancel all active streams.
+	for _, s := range streams {
+		s.cancel()
+	}
+	if t.stats != nil {
+		connEnd := &stats.ConnEnd{}
+		t.stats.HandleConn(t.ctx, connEnd)
+	}
+	return err
+}
+
+// deleteStream deletes the stream s from transport's active streams.
+func (t *http2Server) deleteStream(s *Stream, eosReceived bool) {
+	// In case stream sending and receiving are invoked in separate
+	// goroutines (e.g., bi-directional streaming), cancel needs to be
+	// called to interrupt the potential blocking on other goroutines.
+	s.cancel()
+
+	t.mu.Lock()
+	if _, ok := t.activeStreams[s.id]; ok {
+		delete(t.activeStreams, s.id)
+		if len(t.activeStreams) == 0 {
+			t.idle = time.Now()
+		}
+	}
+	t.mu.Unlock()
+
+	if channelz.IsOn() {
+		if eosReceived {
+			atomic.AddInt64(&t.czData.streamsSucceeded, 1)
+		} else {
+			atomic.AddInt64(&t.czData.streamsFailed, 1)
+		}
+	}
+}
+
+// finishStream closes the stream and puts the trailing headerFrame into controlbuf.
+func (t *http2Server) finishStream(s *Stream, rst bool, rstCode http2.ErrCode, hdr *headerFrame, eosReceived bool) {
+	oldState := s.swapState(streamDone)
+	if oldState == streamDone {
+		// If the stream was already done, return.
+		return
+	}
+
+	hdr.cleanup = &cleanupStream{
+		streamID: s.id,
+		rst:      rst,
+		rstCode:  rstCode,
+		onWrite: func() {
+			t.deleteStream(s, eosReceived)
+		},
+	}
+	t.controlBuf.put(hdr)
+}
+
+// closeStream clears the footprint of a stream when the stream is not needed any more.
+func (t *http2Server) closeStream(s *Stream, rst bool, rstCode http2.ErrCode, eosReceived bool) {
+	s.swapState(streamDone)
+	t.deleteStream(s, eosReceived)
+
+	t.controlBuf.put(&cleanupStream{
+		streamID: s.id,
+		rst:      rst,
+		rstCode:  rstCode,
+		onWrite:  func() {},
+	})
+}
+
+func (t *http2Server) RemoteAddr() net.Addr {
+	return t.remoteAddr
+}
+
+func (t *http2Server) Drain() {
+	t.drain(http2.ErrCodeNo, []byte{})
+}
+
+func (t *http2Server) drain(code http2.ErrCode, debugData []byte) {
+	t.mu.Lock()
+	defer t.mu.Unlock()
+	if t.drainChan != nil {
+		return
+	}
+	t.drainChan = make(chan struct{})
+	t.controlBuf.put(&goAway{code: code, debugData: debugData, headsUp: true})
+}
+
+var goAwayPing = &ping{data: [8]byte{1, 6, 1, 8, 0, 3, 3, 9}}
+
+// Handles outgoing GoAway and returns true if loopy needs to put itself
+// in draining mode.
+func (t *http2Server) outgoingGoAwayHandler(g *goAway) (bool, error) {
+	t.mu.Lock()
+	if t.state == closing { // TODO(mmukhi): This seems unnecessary.
+		t.mu.Unlock()
+		// The transport is closing.
+		return false, ErrConnClosing
+	}
+	sid := t.maxStreamID
+	if !g.headsUp {
+		// Stop accepting more streams now.
+		t.state = draining
+		if len(t.activeStreams) == 0 {
+			g.closeConn = true
+		}
+		t.mu.Unlock()
+		if err := t.framer.fr.WriteGoAway(sid, g.code, g.debugData); err != nil {
+			return false, err
+		}
+		if g.closeConn {
+			// Abruptly close the connection following the GoAway (via
+			// loopywriter).  But flush out what's inside the buffer first.
+			t.framer.writer.Flush()
+			return false, fmt.Errorf("transport: Connection closing")
+		}
+		return true, nil
+	}
+	t.mu.Unlock()
+	// For a graceful close, send out a GoAway with stream ID of MaxUInt32,
+	// Follow that with a ping and wait for the ack to come back or a timer
+	// to expire. During this time accept new streams since they might have
+	// originated before the GoAway reaches the client.
+	// After getting the ack or timer expiration send out another GoAway this
+	// time with an ID of the max stream server intends to process.
+	if err := t.framer.fr.WriteGoAway(math.MaxUint32, http2.ErrCodeNo, []byte{}); err != nil {
+		return false, err
+	}
+	if err := t.framer.fr.WritePing(false, goAwayPing.data); err != nil {
+		return false, err
+	}
+	go func() {
+		timer := time.NewTimer(time.Minute)
+		defer timer.Stop()
+		select {
+		case <-t.drainChan:
+		case <-timer.C:
+		case <-t.done:
+			return
+		}
+		t.controlBuf.put(&goAway{code: g.code, debugData: g.debugData})
+	}()
+	return false, nil
+}
+
+func (t *http2Server) ChannelzMetric() *channelz.SocketInternalMetric {
+	s := channelz.SocketInternalMetric{
+		StreamsStarted:                   atomic.LoadInt64(&t.czData.streamsStarted),
+		StreamsSucceeded:                 atomic.LoadInt64(&t.czData.streamsSucceeded),
+		StreamsFailed:                    atomic.LoadInt64(&t.czData.streamsFailed),
+		MessagesSent:                     atomic.LoadInt64(&t.czData.msgSent),
+		MessagesReceived:                 atomic.LoadInt64(&t.czData.msgRecv),
+		KeepAlivesSent:                   atomic.LoadInt64(&t.czData.kpCount),
+		LastRemoteStreamCreatedTimestamp: time.Unix(0, atomic.LoadInt64(&t.czData.lastStreamCreatedTime)),
+		LastMessageSentTimestamp:         time.Unix(0, atomic.LoadInt64(&t.czData.lastMsgSentTime)),
+		LastMessageReceivedTimestamp:     time.Unix(0, atomic.LoadInt64(&t.czData.lastMsgRecvTime)),
+		LocalFlowControlWindow:           int64(t.fc.getSize()),
+		SocketOptions:                    channelz.GetSocketOption(t.conn),
+		LocalAddr:                        t.localAddr,
+		RemoteAddr:                       t.remoteAddr,
+		// RemoteName :
+	}
+	if au, ok := t.authInfo.(credentials.ChannelzSecurityInfo); ok {
+		s.Security = au.GetSecurityValue()
+	}
+	s.RemoteFlowControlWindow = t.getOutFlowWindow()
+	return &s
+}
+
+func (t *http2Server) IncrMsgSent() {
+	atomic.AddInt64(&t.czData.msgSent, 1)
+	atomic.StoreInt64(&t.czData.lastMsgSentTime, time.Now().UnixNano())
+}
+
+func (t *http2Server) IncrMsgRecv() {
+	atomic.AddInt64(&t.czData.msgRecv, 1)
+	atomic.StoreInt64(&t.czData.lastMsgRecvTime, time.Now().UnixNano())
+}
+
+func (t *http2Server) getOutFlowWindow() int64 {
+	resp := make(chan uint32, 1)
+	timer := time.NewTimer(time.Second)
+	defer timer.Stop()
+	t.controlBuf.put(&outFlowControlSizeRequest{resp})
+	select {
+	case sz := <-resp:
+		return int64(sz)
+	case <-t.done:
+		return -1
+	case <-timer.C:
+		return -2
+	}
+}
+
+func getJitter(v time.Duration) time.Duration {
+	if v == infinity {
+		return 0
+	}
+	// Generate a jitter between +/- 10% of the value.
+	r := int64(v / 10)
+	j := grpcrand.Int63n(2*r) - r
+	return time.Duration(j)
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/internal/transport/http_util.go b/demo_test/vendor/google.golang.org/grpc/internal/transport/http_util.go
new file mode 100644
index 0000000..8f5f334
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/internal/transport/http_util.go
@@ -0,0 +1,677 @@
+/*
+ *
+ * Copyright 2014 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package transport
+
+import (
+	"bufio"
+	"bytes"
+	"encoding/base64"
+	"fmt"
+	"io"
+	"math"
+	"net"
+	"net/http"
+	"strconv"
+	"strings"
+	"time"
+	"unicode/utf8"
+
+	"github.com/golang/protobuf/proto"
+	"golang.org/x/net/http2"
+	"golang.org/x/net/http2/hpack"
+	spb "google.golang.org/genproto/googleapis/rpc/status"
+	"google.golang.org/grpc/codes"
+	"google.golang.org/grpc/status"
+)
+
+const (
+	// http2MaxFrameLen specifies the max length of a HTTP2 frame.
+	http2MaxFrameLen = 16384 // 16KB frame
+	// http://http2.github.io/http2-spec/#SettingValues
+	http2InitHeaderTableSize = 4096
+	// baseContentType is the base content-type for gRPC.  This is a valid
+	// content-type on it's own, but can also include a content-subtype such as
+	// "proto" as a suffix after "+" or ";".  See
+	// https://github.com/grpc/grpc/blob/master/doc/PROTOCOL-HTTP2.md#requests
+	// for more details.
+	baseContentType = "application/grpc"
+)
+
+var (
+	clientPreface   = []byte(http2.ClientPreface)
+	http2ErrConvTab = map[http2.ErrCode]codes.Code{
+		http2.ErrCodeNo:                 codes.Internal,
+		http2.ErrCodeProtocol:           codes.Internal,
+		http2.ErrCodeInternal:           codes.Internal,
+		http2.ErrCodeFlowControl:        codes.ResourceExhausted,
+		http2.ErrCodeSettingsTimeout:    codes.Internal,
+		http2.ErrCodeStreamClosed:       codes.Internal,
+		http2.ErrCodeFrameSize:          codes.Internal,
+		http2.ErrCodeRefusedStream:      codes.Unavailable,
+		http2.ErrCodeCancel:             codes.Canceled,
+		http2.ErrCodeCompression:        codes.Internal,
+		http2.ErrCodeConnect:            codes.Internal,
+		http2.ErrCodeEnhanceYourCalm:    codes.ResourceExhausted,
+		http2.ErrCodeInadequateSecurity: codes.PermissionDenied,
+		http2.ErrCodeHTTP11Required:     codes.Internal,
+	}
+	statusCodeConvTab = map[codes.Code]http2.ErrCode{
+		codes.Internal:          http2.ErrCodeInternal,
+		codes.Canceled:          http2.ErrCodeCancel,
+		codes.Unavailable:       http2.ErrCodeRefusedStream,
+		codes.ResourceExhausted: http2.ErrCodeEnhanceYourCalm,
+		codes.PermissionDenied:  http2.ErrCodeInadequateSecurity,
+	}
+	// HTTPStatusConvTab is the HTTP status code to gRPC error code conversion table.
+	HTTPStatusConvTab = map[int]codes.Code{
+		// 400 Bad Request - INTERNAL.
+		http.StatusBadRequest: codes.Internal,
+		// 401 Unauthorized  - UNAUTHENTICATED.
+		http.StatusUnauthorized: codes.Unauthenticated,
+		// 403 Forbidden - PERMISSION_DENIED.
+		http.StatusForbidden: codes.PermissionDenied,
+		// 404 Not Found - UNIMPLEMENTED.
+		http.StatusNotFound: codes.Unimplemented,
+		// 429 Too Many Requests - UNAVAILABLE.
+		http.StatusTooManyRequests: codes.Unavailable,
+		// 502 Bad Gateway - UNAVAILABLE.
+		http.StatusBadGateway: codes.Unavailable,
+		// 503 Service Unavailable - UNAVAILABLE.
+		http.StatusServiceUnavailable: codes.Unavailable,
+		// 504 Gateway timeout - UNAVAILABLE.
+		http.StatusGatewayTimeout: codes.Unavailable,
+	}
+)
+
+type parsedHeaderData struct {
+	encoding string
+	// statusGen caches the stream status received from the trailer the server
+	// sent.  Client side only.  Do not access directly.  After all trailers are
+	// parsed, use the status method to retrieve the status.
+	statusGen *status.Status
+	// rawStatusCode and rawStatusMsg are set from the raw trailer fields and are not
+	// intended for direct access outside of parsing.
+	rawStatusCode *int
+	rawStatusMsg  string
+	httpStatus    *int
+	// Server side only fields.
+	timeoutSet bool
+	timeout    time.Duration
+	method     string
+	// key-value metadata map from the peer.
+	mdata          map[string][]string
+	statsTags      []byte
+	statsTrace     []byte
+	contentSubtype string
+
+	// isGRPC field indicates whether the peer is speaking gRPC (otherwise HTTP).
+	//
+	// We are in gRPC mode (peer speaking gRPC) if:
+	// 	* We are client side and have already received a HEADER frame that indicates gRPC peer.
+	//  * The header contains valid  a content-type, i.e. a string starts with "application/grpc"
+	// And we should handle error specific to gRPC.
+	//
+	// Otherwise (i.e. a content-type string starts without "application/grpc", or does not exist), we
+	// are in HTTP fallback mode, and should handle error specific to HTTP.
+	isGRPC         bool
+	grpcErr        error
+	httpErr        error
+	contentTypeErr string
+}
+
+// decodeState configures decoding criteria and records the decoded data.
+type decodeState struct {
+	// whether decoding on server side or not
+	serverSide bool
+
+	// Records the states during HPACK decoding. It will be filled with info parsed from HTTP HEADERS
+	// frame once decodeHeader function has been invoked and returned.
+	data parsedHeaderData
+}
+
+// isReservedHeader checks whether hdr belongs to HTTP2 headers
+// reserved by gRPC protocol. Any other headers are classified as the
+// user-specified metadata.
+func isReservedHeader(hdr string) bool {
+	if hdr != "" && hdr[0] == ':' {
+		return true
+	}
+	switch hdr {
+	case "content-type",
+		"user-agent",
+		"grpc-message-type",
+		"grpc-encoding",
+		"grpc-message",
+		"grpc-status",
+		"grpc-timeout",
+		"grpc-status-details-bin",
+		// Intentionally exclude grpc-previous-rpc-attempts and
+		// grpc-retry-pushback-ms, which are "reserved", but their API
+		// intentionally works via metadata.
+		"te":
+		return true
+	default:
+		return false
+	}
+}
+
+// isWhitelistedHeader checks whether hdr should be propagated into metadata
+// visible to users, even though it is classified as "reserved", above.
+func isWhitelistedHeader(hdr string) bool {
+	switch hdr {
+	case ":authority", "user-agent":
+		return true
+	default:
+		return false
+	}
+}
+
+// contentSubtype returns the content-subtype for the given content-type.  The
+// given content-type must be a valid content-type that starts with
+// "application/grpc". A content-subtype will follow "application/grpc" after a
+// "+" or ";". See
+// https://github.com/grpc/grpc/blob/master/doc/PROTOCOL-HTTP2.md#requests for
+// more details.
+//
+// If contentType is not a valid content-type for gRPC, the boolean
+// will be false, otherwise true. If content-type == "application/grpc",
+// "application/grpc+", or "application/grpc;", the boolean will be true,
+// but no content-subtype will be returned.
+//
+// contentType is assumed to be lowercase already.
+func contentSubtype(contentType string) (string, bool) {
+	if contentType == baseContentType {
+		return "", true
+	}
+	if !strings.HasPrefix(contentType, baseContentType) {
+		return "", false
+	}
+	// guaranteed since != baseContentType and has baseContentType prefix
+	switch contentType[len(baseContentType)] {
+	case '+', ';':
+		// this will return true for "application/grpc+" or "application/grpc;"
+		// which the previous validContentType function tested to be valid, so we
+		// just say that no content-subtype is specified in this case
+		return contentType[len(baseContentType)+1:], true
+	default:
+		return "", false
+	}
+}
+
+// contentSubtype is assumed to be lowercase
+func contentType(contentSubtype string) string {
+	if contentSubtype == "" {
+		return baseContentType
+	}
+	return baseContentType + "+" + contentSubtype
+}
+
+func (d *decodeState) status() *status.Status {
+	if d.data.statusGen == nil {
+		// No status-details were provided; generate status using code/msg.
+		d.data.statusGen = status.New(codes.Code(int32(*(d.data.rawStatusCode))), d.data.rawStatusMsg)
+	}
+	return d.data.statusGen
+}
+
+const binHdrSuffix = "-bin"
+
+func encodeBinHeader(v []byte) string {
+	return base64.RawStdEncoding.EncodeToString(v)
+}
+
+func decodeBinHeader(v string) ([]byte, error) {
+	if len(v)%4 == 0 {
+		// Input was padded, or padding was not necessary.
+		return base64.StdEncoding.DecodeString(v)
+	}
+	return base64.RawStdEncoding.DecodeString(v)
+}
+
+func encodeMetadataHeader(k, v string) string {
+	if strings.HasSuffix(k, binHdrSuffix) {
+		return encodeBinHeader(([]byte)(v))
+	}
+	return v
+}
+
+func decodeMetadataHeader(k, v string) (string, error) {
+	if strings.HasSuffix(k, binHdrSuffix) {
+		b, err := decodeBinHeader(v)
+		return string(b), err
+	}
+	return v, nil
+}
+
+func (d *decodeState) decodeHeader(frame *http2.MetaHeadersFrame) error {
+	// frame.Truncated is set to true when framer detects that the current header
+	// list size hits MaxHeaderListSize limit.
+	if frame.Truncated {
+		return status.Error(codes.Internal, "peer header list size exceeded limit")
+	}
+
+	for _, hf := range frame.Fields {
+		d.processHeaderField(hf)
+	}
+
+	if d.data.isGRPC {
+		if d.data.grpcErr != nil {
+			return d.data.grpcErr
+		}
+		if d.serverSide {
+			return nil
+		}
+		if d.data.rawStatusCode == nil && d.data.statusGen == nil {
+			// gRPC status doesn't exist.
+			// Set rawStatusCode to be unknown and return nil error.
+			// So that, if the stream has ended this Unknown status
+			// will be propagated to the user.
+			// Otherwise, it will be ignored. In which case, status from
+			// a later trailer, that has StreamEnded flag set, is propagated.
+			code := int(codes.Unknown)
+			d.data.rawStatusCode = &code
+		}
+		return nil
+	}
+
+	// HTTP fallback mode
+	if d.data.httpErr != nil {
+		return d.data.httpErr
+	}
+
+	var (
+		code = codes.Internal // when header does not include HTTP status, return INTERNAL
+		ok   bool
+	)
+
+	if d.data.httpStatus != nil {
+		code, ok = HTTPStatusConvTab[*(d.data.httpStatus)]
+		if !ok {
+			code = codes.Unknown
+		}
+	}
+
+	return status.Error(code, d.constructHTTPErrMsg())
+}
+
+// constructErrMsg constructs error message to be returned in HTTP fallback mode.
+// Format: HTTP status code and its corresponding message + content-type error message.
+func (d *decodeState) constructHTTPErrMsg() string {
+	var errMsgs []string
+
+	if d.data.httpStatus == nil {
+		errMsgs = append(errMsgs, "malformed header: missing HTTP status")
+	} else {
+		errMsgs = append(errMsgs, fmt.Sprintf("%s: HTTP status code %d", http.StatusText(*(d.data.httpStatus)), *d.data.httpStatus))
+	}
+
+	if d.data.contentTypeErr == "" {
+		errMsgs = append(errMsgs, "transport: missing content-type field")
+	} else {
+		errMsgs = append(errMsgs, d.data.contentTypeErr)
+	}
+
+	return strings.Join(errMsgs, "; ")
+}
+
+func (d *decodeState) addMetadata(k, v string) {
+	if d.data.mdata == nil {
+		d.data.mdata = make(map[string][]string)
+	}
+	d.data.mdata[k] = append(d.data.mdata[k], v)
+}
+
+func (d *decodeState) processHeaderField(f hpack.HeaderField) {
+	switch f.Name {
+	case "content-type":
+		contentSubtype, validContentType := contentSubtype(f.Value)
+		if !validContentType {
+			d.data.contentTypeErr = fmt.Sprintf("transport: received the unexpected content-type %q", f.Value)
+			return
+		}
+		d.data.contentSubtype = contentSubtype
+		// TODO: do we want to propagate the whole content-type in the metadata,
+		// or come up with a way to just propagate the content-subtype if it was set?
+		// ie {"content-type": "application/grpc+proto"} or {"content-subtype": "proto"}
+		// in the metadata?
+		d.addMetadata(f.Name, f.Value)
+		d.data.isGRPC = true
+	case "grpc-encoding":
+		d.data.encoding = f.Value
+	case "grpc-status":
+		code, err := strconv.Atoi(f.Value)
+		if err != nil {
+			d.data.grpcErr = status.Errorf(codes.Internal, "transport: malformed grpc-status: %v", err)
+			return
+		}
+		d.data.rawStatusCode = &code
+	case "grpc-message":
+		d.data.rawStatusMsg = decodeGrpcMessage(f.Value)
+	case "grpc-status-details-bin":
+		v, err := decodeBinHeader(f.Value)
+		if err != nil {
+			d.data.grpcErr = status.Errorf(codes.Internal, "transport: malformed grpc-status-details-bin: %v", err)
+			return
+		}
+		s := &spb.Status{}
+		if err := proto.Unmarshal(v, s); err != nil {
+			d.data.grpcErr = status.Errorf(codes.Internal, "transport: malformed grpc-status-details-bin: %v", err)
+			return
+		}
+		d.data.statusGen = status.FromProto(s)
+	case "grpc-timeout":
+		d.data.timeoutSet = true
+		var err error
+		if d.data.timeout, err = decodeTimeout(f.Value); err != nil {
+			d.data.grpcErr = status.Errorf(codes.Internal, "transport: malformed time-out: %v", err)
+		}
+	case ":path":
+		d.data.method = f.Value
+	case ":status":
+		code, err := strconv.Atoi(f.Value)
+		if err != nil {
+			d.data.httpErr = status.Errorf(codes.Internal, "transport: malformed http-status: %v", err)
+			return
+		}
+		d.data.httpStatus = &code
+	case "grpc-tags-bin":
+		v, err := decodeBinHeader(f.Value)
+		if err != nil {
+			d.data.grpcErr = status.Errorf(codes.Internal, "transport: malformed grpc-tags-bin: %v", err)
+			return
+		}
+		d.data.statsTags = v
+		d.addMetadata(f.Name, string(v))
+	case "grpc-trace-bin":
+		v, err := decodeBinHeader(f.Value)
+		if err != nil {
+			d.data.grpcErr = status.Errorf(codes.Internal, "transport: malformed grpc-trace-bin: %v", err)
+			return
+		}
+		d.data.statsTrace = v
+		d.addMetadata(f.Name, string(v))
+	default:
+		if isReservedHeader(f.Name) && !isWhitelistedHeader(f.Name) {
+			break
+		}
+		v, err := decodeMetadataHeader(f.Name, f.Value)
+		if err != nil {
+			errorf("Failed to decode metadata header (%q, %q): %v", f.Name, f.Value, err)
+			return
+		}
+		d.addMetadata(f.Name, v)
+	}
+}
+
+type timeoutUnit uint8
+
+const (
+	hour        timeoutUnit = 'H'
+	minute      timeoutUnit = 'M'
+	second      timeoutUnit = 'S'
+	millisecond timeoutUnit = 'm'
+	microsecond timeoutUnit = 'u'
+	nanosecond  timeoutUnit = 'n'
+)
+
+func timeoutUnitToDuration(u timeoutUnit) (d time.Duration, ok bool) {
+	switch u {
+	case hour:
+		return time.Hour, true
+	case minute:
+		return time.Minute, true
+	case second:
+		return time.Second, true
+	case millisecond:
+		return time.Millisecond, true
+	case microsecond:
+		return time.Microsecond, true
+	case nanosecond:
+		return time.Nanosecond, true
+	default:
+	}
+	return
+}
+
+const maxTimeoutValue int64 = 100000000 - 1
+
+// div does integer division and round-up the result. Note that this is
+// equivalent to (d+r-1)/r but has less chance to overflow.
+func div(d, r time.Duration) int64 {
+	if m := d % r; m > 0 {
+		return int64(d/r + 1)
+	}
+	return int64(d / r)
+}
+
+// TODO(zhaoq): It is the simplistic and not bandwidth efficient. Improve it.
+func encodeTimeout(t time.Duration) string {
+	if t <= 0 {
+		return "0n"
+	}
+	if d := div(t, time.Nanosecond); d <= maxTimeoutValue {
+		return strconv.FormatInt(d, 10) + "n"
+	}
+	if d := div(t, time.Microsecond); d <= maxTimeoutValue {
+		return strconv.FormatInt(d, 10) + "u"
+	}
+	if d := div(t, time.Millisecond); d <= maxTimeoutValue {
+		return strconv.FormatInt(d, 10) + "m"
+	}
+	if d := div(t, time.Second); d <= maxTimeoutValue {
+		return strconv.FormatInt(d, 10) + "S"
+	}
+	if d := div(t, time.Minute); d <= maxTimeoutValue {
+		return strconv.FormatInt(d, 10) + "M"
+	}
+	// Note that maxTimeoutValue * time.Hour > MaxInt64.
+	return strconv.FormatInt(div(t, time.Hour), 10) + "H"
+}
+
+func decodeTimeout(s string) (time.Duration, error) {
+	size := len(s)
+	if size < 2 {
+		return 0, fmt.Errorf("transport: timeout string is too short: %q", s)
+	}
+	if size > 9 {
+		// Spec allows for 8 digits plus the unit.
+		return 0, fmt.Errorf("transport: timeout string is too long: %q", s)
+	}
+	unit := timeoutUnit(s[size-1])
+	d, ok := timeoutUnitToDuration(unit)
+	if !ok {
+		return 0, fmt.Errorf("transport: timeout unit is not recognized: %q", s)
+	}
+	t, err := strconv.ParseInt(s[:size-1], 10, 64)
+	if err != nil {
+		return 0, err
+	}
+	const maxHours = math.MaxInt64 / int64(time.Hour)
+	if d == time.Hour && t > maxHours {
+		// This timeout would overflow math.MaxInt64; clamp it.
+		return time.Duration(math.MaxInt64), nil
+	}
+	return d * time.Duration(t), nil
+}
+
+const (
+	spaceByte   = ' '
+	tildeByte   = '~'
+	percentByte = '%'
+)
+
+// encodeGrpcMessage is used to encode status code in header field
+// "grpc-message". It does percent encoding and also replaces invalid utf-8
+// characters with Unicode replacement character.
+//
+// It checks to see if each individual byte in msg is an allowable byte, and
+// then either percent encoding or passing it through. When percent encoding,
+// the byte is converted into hexadecimal notation with a '%' prepended.
+func encodeGrpcMessage(msg string) string {
+	if msg == "" {
+		return ""
+	}
+	lenMsg := len(msg)
+	for i := 0; i < lenMsg; i++ {
+		c := msg[i]
+		if !(c >= spaceByte && c <= tildeByte && c != percentByte) {
+			return encodeGrpcMessageUnchecked(msg)
+		}
+	}
+	return msg
+}
+
+func encodeGrpcMessageUnchecked(msg string) string {
+	var buf bytes.Buffer
+	for len(msg) > 0 {
+		r, size := utf8.DecodeRuneInString(msg)
+		for _, b := range []byte(string(r)) {
+			if size > 1 {
+				// If size > 1, r is not ascii. Always do percent encoding.
+				buf.WriteString(fmt.Sprintf("%%%02X", b))
+				continue
+			}
+
+			// The for loop is necessary even if size == 1. r could be
+			// utf8.RuneError.
+			//
+			// fmt.Sprintf("%%%02X", utf8.RuneError) gives "%FFFD".
+			if b >= spaceByte && b <= tildeByte && b != percentByte {
+				buf.WriteByte(b)
+			} else {
+				buf.WriteString(fmt.Sprintf("%%%02X", b))
+			}
+		}
+		msg = msg[size:]
+	}
+	return buf.String()
+}
+
+// decodeGrpcMessage decodes the msg encoded by encodeGrpcMessage.
+func decodeGrpcMessage(msg string) string {
+	if msg == "" {
+		return ""
+	}
+	lenMsg := len(msg)
+	for i := 0; i < lenMsg; i++ {
+		if msg[i] == percentByte && i+2 < lenMsg {
+			return decodeGrpcMessageUnchecked(msg)
+		}
+	}
+	return msg
+}
+
+func decodeGrpcMessageUnchecked(msg string) string {
+	var buf bytes.Buffer
+	lenMsg := len(msg)
+	for i := 0; i < lenMsg; i++ {
+		c := msg[i]
+		if c == percentByte && i+2 < lenMsg {
+			parsed, err := strconv.ParseUint(msg[i+1:i+3], 16, 8)
+			if err != nil {
+				buf.WriteByte(c)
+			} else {
+				buf.WriteByte(byte(parsed))
+				i += 2
+			}
+		} else {
+			buf.WriteByte(c)
+		}
+	}
+	return buf.String()
+}
+
+type bufWriter struct {
+	buf       []byte
+	offset    int
+	batchSize int
+	conn      net.Conn
+	err       error
+
+	onFlush func()
+}
+
+func newBufWriter(conn net.Conn, batchSize int) *bufWriter {
+	return &bufWriter{
+		buf:       make([]byte, batchSize*2),
+		batchSize: batchSize,
+		conn:      conn,
+	}
+}
+
+func (w *bufWriter) Write(b []byte) (n int, err error) {
+	if w.err != nil {
+		return 0, w.err
+	}
+	if w.batchSize == 0 { // Buffer has been disabled.
+		return w.conn.Write(b)
+	}
+	for len(b) > 0 {
+		nn := copy(w.buf[w.offset:], b)
+		b = b[nn:]
+		w.offset += nn
+		n += nn
+		if w.offset >= w.batchSize {
+			err = w.Flush()
+		}
+	}
+	return n, err
+}
+
+func (w *bufWriter) Flush() error {
+	if w.err != nil {
+		return w.err
+	}
+	if w.offset == 0 {
+		return nil
+	}
+	if w.onFlush != nil {
+		w.onFlush()
+	}
+	_, w.err = w.conn.Write(w.buf[:w.offset])
+	w.offset = 0
+	return w.err
+}
+
+type framer struct {
+	writer *bufWriter
+	fr     *http2.Framer
+}
+
+func newFramer(conn net.Conn, writeBufferSize, readBufferSize int, maxHeaderListSize uint32) *framer {
+	if writeBufferSize < 0 {
+		writeBufferSize = 0
+	}
+	var r io.Reader = conn
+	if readBufferSize > 0 {
+		r = bufio.NewReaderSize(r, readBufferSize)
+	}
+	w := newBufWriter(conn, writeBufferSize)
+	f := &framer{
+		writer: w,
+		fr:     http2.NewFramer(w, r),
+	}
+	f.fr.SetMaxReadFrameSize(http2MaxFrameLen)
+	// Opt-in to Frame reuse API on framer to reduce garbage.
+	// Frames aren't safe to read from after a subsequent call to ReadFrame.
+	f.fr.SetReuseFrames()
+	f.fr.MaxHeaderListSize = maxHeaderListSize
+	f.fr.ReadMetaHeaders = hpack.NewDecoder(http2InitHeaderTableSize, nil)
+	return f
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/internal/transport/log.go b/demo_test/vendor/google.golang.org/grpc/internal/transport/log.go
new file mode 100644
index 0000000..879df80
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/internal/transport/log.go
@@ -0,0 +1,44 @@
+/*
+ *
+ * Copyright 2017 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+// This file contains wrappers for grpclog functions.
+// The transport package only logs to verbose level 2 by default.
+
+package transport
+
+import "google.golang.org/grpc/grpclog"
+
+const logLevel = 2
+
+func infof(format string, args ...interface{}) {
+	if grpclog.V(logLevel) {
+		grpclog.Infof(format, args...)
+	}
+}
+
+func warningf(format string, args ...interface{}) {
+	if grpclog.V(logLevel) {
+		grpclog.Warningf(format, args...)
+	}
+}
+
+func errorf(format string, args ...interface{}) {
+	if grpclog.V(logLevel) {
+		grpclog.Errorf(format, args...)
+	}
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/internal/transport/transport.go b/demo_test/vendor/google.golang.org/grpc/internal/transport/transport.go
new file mode 100644
index 0000000..a30da9e
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/internal/transport/transport.go
@@ -0,0 +1,808 @@
+/*
+ *
+ * Copyright 2014 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+// Package transport defines and implements message oriented communication
+// channel to complete various transactions (e.g., an RPC).  It is meant for
+// grpc-internal usage and is not intended to be imported directly by users.
+package transport
+
+import (
+	"bytes"
+	"context"
+	"errors"
+	"fmt"
+	"io"
+	"net"
+	"sync"
+	"sync/atomic"
+
+	"google.golang.org/grpc/codes"
+	"google.golang.org/grpc/credentials"
+	"google.golang.org/grpc/keepalive"
+	"google.golang.org/grpc/metadata"
+	"google.golang.org/grpc/stats"
+	"google.golang.org/grpc/status"
+	"google.golang.org/grpc/tap"
+)
+
+type bufferPool struct {
+	pool sync.Pool
+}
+
+func newBufferPool() *bufferPool {
+	return &bufferPool{
+		pool: sync.Pool{
+			New: func() interface{} {
+				return new(bytes.Buffer)
+			},
+		},
+	}
+}
+
+func (p *bufferPool) get() *bytes.Buffer {
+	return p.pool.Get().(*bytes.Buffer)
+}
+
+func (p *bufferPool) put(b *bytes.Buffer) {
+	p.pool.Put(b)
+}
+
+// recvMsg represents the received msg from the transport. All transport
+// protocol specific info has been removed.
+type recvMsg struct {
+	buffer *bytes.Buffer
+	// nil: received some data
+	// io.EOF: stream is completed. data is nil.
+	// other non-nil error: transport failure. data is nil.
+	err error
+}
+
+// recvBuffer is an unbounded channel of recvMsg structs.
+//
+// Note: recvBuffer differs from buffer.Unbounded only in the fact that it
+// holds a channel of recvMsg structs instead of objects implementing "item"
+// interface. recvBuffer is written to much more often and using strict recvMsg
+// structs helps avoid allocation in "recvBuffer.put"
+type recvBuffer struct {
+	c       chan recvMsg
+	mu      sync.Mutex
+	backlog []recvMsg
+	err     error
+}
+
+func newRecvBuffer() *recvBuffer {
+	b := &recvBuffer{
+		c: make(chan recvMsg, 1),
+	}
+	return b
+}
+
+func (b *recvBuffer) put(r recvMsg) {
+	b.mu.Lock()
+	if b.err != nil {
+		b.mu.Unlock()
+		// An error had occurred earlier, don't accept more
+		// data or errors.
+		return
+	}
+	b.err = r.err
+	if len(b.backlog) == 0 {
+		select {
+		case b.c <- r:
+			b.mu.Unlock()
+			return
+		default:
+		}
+	}
+	b.backlog = append(b.backlog, r)
+	b.mu.Unlock()
+}
+
+func (b *recvBuffer) load() {
+	b.mu.Lock()
+	if len(b.backlog) > 0 {
+		select {
+		case b.c <- b.backlog[0]:
+			b.backlog[0] = recvMsg{}
+			b.backlog = b.backlog[1:]
+		default:
+		}
+	}
+	b.mu.Unlock()
+}
+
+// get returns the channel that receives a recvMsg in the buffer.
+//
+// Upon receipt of a recvMsg, the caller should call load to send another
+// recvMsg onto the channel if there is any.
+func (b *recvBuffer) get() <-chan recvMsg {
+	return b.c
+}
+
+// recvBufferReader implements io.Reader interface to read the data from
+// recvBuffer.
+type recvBufferReader struct {
+	closeStream func(error) // Closes the client transport stream with the given error and nil trailer metadata.
+	ctx         context.Context
+	ctxDone     <-chan struct{} // cache of ctx.Done() (for performance).
+	recv        *recvBuffer
+	last        *bytes.Buffer // Stores the remaining data in the previous calls.
+	err         error
+	freeBuffer  func(*bytes.Buffer)
+}
+
+// Read reads the next len(p) bytes from last. If last is drained, it tries to
+// read additional data from recv. It blocks if there no additional data available
+// in recv. If Read returns any non-nil error, it will continue to return that error.
+func (r *recvBufferReader) Read(p []byte) (n int, err error) {
+	if r.err != nil {
+		return 0, r.err
+	}
+	if r.last != nil {
+		// Read remaining data left in last call.
+		copied, _ := r.last.Read(p)
+		if r.last.Len() == 0 {
+			r.freeBuffer(r.last)
+			r.last = nil
+		}
+		return copied, nil
+	}
+	if r.closeStream != nil {
+		n, r.err = r.readClient(p)
+	} else {
+		n, r.err = r.read(p)
+	}
+	return n, r.err
+}
+
+func (r *recvBufferReader) read(p []byte) (n int, err error) {
+	select {
+	case <-r.ctxDone:
+		return 0, ContextErr(r.ctx.Err())
+	case m := <-r.recv.get():
+		return r.readAdditional(m, p)
+	}
+}
+
+func (r *recvBufferReader) readClient(p []byte) (n int, err error) {
+	// If the context is canceled, then closes the stream with nil metadata.
+	// closeStream writes its error parameter to r.recv as a recvMsg.
+	// r.readAdditional acts on that message and returns the necessary error.
+	select {
+	case <-r.ctxDone:
+		// Note that this adds the ctx error to the end of recv buffer, and
+		// reads from the head. This will delay the error until recv buffer is
+		// empty, thus will delay ctx cancellation in Recv().
+		//
+		// It's done this way to fix a race between ctx cancel and trailer. The
+		// race was, stream.Recv() may return ctx error if ctxDone wins the
+		// race, but stream.Trailer() may return a non-nil md because the stream
+		// was not marked as done when trailer is received. This closeStream
+		// call will mark stream as done, thus fix the race.
+		//
+		// TODO: delaying ctx error seems like a unnecessary side effect. What
+		// we really want is to mark the stream as done, and return ctx error
+		// faster.
+		r.closeStream(ContextErr(r.ctx.Err()))
+		m := <-r.recv.get()
+		return r.readAdditional(m, p)
+	case m := <-r.recv.get():
+		return r.readAdditional(m, p)
+	}
+}
+
+func (r *recvBufferReader) readAdditional(m recvMsg, p []byte) (n int, err error) {
+	r.recv.load()
+	if m.err != nil {
+		return 0, m.err
+	}
+	copied, _ := m.buffer.Read(p)
+	if m.buffer.Len() == 0 {
+		r.freeBuffer(m.buffer)
+		r.last = nil
+	} else {
+		r.last = m.buffer
+	}
+	return copied, nil
+}
+
+type streamState uint32
+
+const (
+	streamActive    streamState = iota
+	streamWriteDone             // EndStream sent
+	streamReadDone              // EndStream received
+	streamDone                  // the entire stream is finished.
+)
+
+// Stream represents an RPC in the transport layer.
+type Stream struct {
+	id           uint32
+	st           ServerTransport    // nil for client side Stream
+	ct           *http2Client       // nil for server side Stream
+	ctx          context.Context    // the associated context of the stream
+	cancel       context.CancelFunc // always nil for client side Stream
+	done         chan struct{}      // closed at the end of stream to unblock writers. On the client side.
+	ctxDone      <-chan struct{}    // same as done chan but for server side. Cache of ctx.Done() (for performance)
+	method       string             // the associated RPC method of the stream
+	recvCompress string
+	sendCompress string
+	buf          *recvBuffer
+	trReader     io.Reader
+	fc           *inFlow
+	wq           *writeQuota
+
+	// Callback to state application's intentions to read data. This
+	// is used to adjust flow control, if needed.
+	requestRead func(int)
+
+	headerChan       chan struct{} // closed to indicate the end of header metadata.
+	headerChanClosed uint32        // set when headerChan is closed. Used to avoid closing headerChan multiple times.
+	// headerValid indicates whether a valid header was received.  Only
+	// meaningful after headerChan is closed (always call waitOnHeader() before
+	// reading its value).  Not valid on server side.
+	headerValid bool
+
+	// hdrMu protects header and trailer metadata on the server-side.
+	hdrMu sync.Mutex
+	// On client side, header keeps the received header metadata.
+	//
+	// On server side, header keeps the header set by SetHeader(). The complete
+	// header will merged into this after t.WriteHeader() is called.
+	header  metadata.MD
+	trailer metadata.MD // the key-value map of trailer metadata.
+
+	noHeaders bool // set if the client never received headers (set only after the stream is done).
+
+	// On the server-side, headerSent is atomically set to 1 when the headers are sent out.
+	headerSent uint32
+
+	state streamState
+
+	// On client-side it is the status error received from the server.
+	// On server-side it is unused.
+	status *status.Status
+
+	bytesReceived uint32 // indicates whether any bytes have been received on this stream
+	unprocessed   uint32 // set if the server sends a refused stream or GOAWAY including this stream
+
+	// contentSubtype is the content-subtype for requests.
+	// this must be lowercase or the behavior is undefined.
+	contentSubtype string
+}
+
+// isHeaderSent is only valid on the server-side.
+func (s *Stream) isHeaderSent() bool {
+	return atomic.LoadUint32(&s.headerSent) == 1
+}
+
+// updateHeaderSent updates headerSent and returns true
+// if it was alreay set. It is valid only on server-side.
+func (s *Stream) updateHeaderSent() bool {
+	return atomic.SwapUint32(&s.headerSent, 1) == 1
+}
+
+func (s *Stream) swapState(st streamState) streamState {
+	return streamState(atomic.SwapUint32((*uint32)(&s.state), uint32(st)))
+}
+
+func (s *Stream) compareAndSwapState(oldState, newState streamState) bool {
+	return atomic.CompareAndSwapUint32((*uint32)(&s.state), uint32(oldState), uint32(newState))
+}
+
+func (s *Stream) getState() streamState {
+	return streamState(atomic.LoadUint32((*uint32)(&s.state)))
+}
+
+func (s *Stream) waitOnHeader() {
+	if s.headerChan == nil {
+		// On the server headerChan is always nil since a stream originates
+		// only after having received headers.
+		return
+	}
+	select {
+	case <-s.ctx.Done():
+		// Close the stream to prevent headers/trailers from changing after
+		// this function returns.
+		s.ct.CloseStream(s, ContextErr(s.ctx.Err()))
+		// headerChan could possibly not be closed yet if closeStream raced
+		// with operateHeaders; wait until it is closed explicitly here.
+		<-s.headerChan
+	case <-s.headerChan:
+	}
+}
+
+// RecvCompress returns the compression algorithm applied to the inbound
+// message. It is empty string if there is no compression applied.
+func (s *Stream) RecvCompress() string {
+	s.waitOnHeader()
+	return s.recvCompress
+}
+
+// SetSendCompress sets the compression algorithm to the stream.
+func (s *Stream) SetSendCompress(str string) {
+	s.sendCompress = str
+}
+
+// Done returns a channel which is closed when it receives the final status
+// from the server.
+func (s *Stream) Done() <-chan struct{} {
+	return s.done
+}
+
+// Header returns the header metadata of the stream.
+//
+// On client side, it acquires the key-value pairs of header metadata once it is
+// available. It blocks until i) the metadata is ready or ii) there is no header
+// metadata or iii) the stream is canceled/expired.
+//
+// On server side, it returns the out header after t.WriteHeader is called.  It
+// does not block and must not be called until after WriteHeader.
+func (s *Stream) Header() (metadata.MD, error) {
+	if s.headerChan == nil {
+		// On server side, return the header in stream. It will be the out
+		// header after t.WriteHeader is called.
+		return s.header.Copy(), nil
+	}
+	s.waitOnHeader()
+	if !s.headerValid {
+		return nil, s.status.Err()
+	}
+	return s.header.Copy(), nil
+}
+
+// TrailersOnly blocks until a header or trailers-only frame is received and
+// then returns true if the stream was trailers-only.  If the stream ends
+// before headers are received, returns true, nil.  Client-side only.
+func (s *Stream) TrailersOnly() bool {
+	s.waitOnHeader()
+	return s.noHeaders
+}
+
+// Trailer returns the cached trailer metedata. Note that if it is not called
+// after the entire stream is done, it could return an empty MD. Client
+// side only.
+// It can be safely read only after stream has ended that is either read
+// or write have returned io.EOF.
+func (s *Stream) Trailer() metadata.MD {
+	c := s.trailer.Copy()
+	return c
+}
+
+// ContentSubtype returns the content-subtype for a request. For example, a
+// content-subtype of "proto" will result in a content-type of
+// "application/grpc+proto". This will always be lowercase.  See
+// https://github.com/grpc/grpc/blob/master/doc/PROTOCOL-HTTP2.md#requests for
+// more details.
+func (s *Stream) ContentSubtype() string {
+	return s.contentSubtype
+}
+
+// Context returns the context of the stream.
+func (s *Stream) Context() context.Context {
+	return s.ctx
+}
+
+// Method returns the method for the stream.
+func (s *Stream) Method() string {
+	return s.method
+}
+
+// Status returns the status received from the server.
+// Status can be read safely only after the stream has ended,
+// that is, after Done() is closed.
+func (s *Stream) Status() *status.Status {
+	return s.status
+}
+
+// SetHeader sets the header metadata. This can be called multiple times.
+// Server side only.
+// This should not be called in parallel to other data writes.
+func (s *Stream) SetHeader(md metadata.MD) error {
+	if md.Len() == 0 {
+		return nil
+	}
+	if s.isHeaderSent() || s.getState() == streamDone {
+		return ErrIllegalHeaderWrite
+	}
+	s.hdrMu.Lock()
+	s.header = metadata.Join(s.header, md)
+	s.hdrMu.Unlock()
+	return nil
+}
+
+// SendHeader sends the given header metadata. The given metadata is
+// combined with any metadata set by previous calls to SetHeader and
+// then written to the transport stream.
+func (s *Stream) SendHeader(md metadata.MD) error {
+	return s.st.WriteHeader(s, md)
+}
+
+// SetTrailer sets the trailer metadata which will be sent with the RPC status
+// by the server. This can be called multiple times. Server side only.
+// This should not be called parallel to other data writes.
+func (s *Stream) SetTrailer(md metadata.MD) error {
+	if md.Len() == 0 {
+		return nil
+	}
+	if s.getState() == streamDone {
+		return ErrIllegalHeaderWrite
+	}
+	s.hdrMu.Lock()
+	s.trailer = metadata.Join(s.trailer, md)
+	s.hdrMu.Unlock()
+	return nil
+}
+
+func (s *Stream) write(m recvMsg) {
+	s.buf.put(m)
+}
+
+// Read reads all p bytes from the wire for this stream.
+func (s *Stream) Read(p []byte) (n int, err error) {
+	// Don't request a read if there was an error earlier
+	if er := s.trReader.(*transportReader).er; er != nil {
+		return 0, er
+	}
+	s.requestRead(len(p))
+	return io.ReadFull(s.trReader, p)
+}
+
+// tranportReader reads all the data available for this Stream from the transport and
+// passes them into the decoder, which converts them into a gRPC message stream.
+// The error is io.EOF when the stream is done or another non-nil error if
+// the stream broke.
+type transportReader struct {
+	reader io.Reader
+	// The handler to control the window update procedure for both this
+	// particular stream and the associated transport.
+	windowHandler func(int)
+	er            error
+}
+
+func (t *transportReader) Read(p []byte) (n int, err error) {
+	n, err = t.reader.Read(p)
+	if err != nil {
+		t.er = err
+		return
+	}
+	t.windowHandler(n)
+	return
+}
+
+// BytesReceived indicates whether any bytes have been received on this stream.
+func (s *Stream) BytesReceived() bool {
+	return atomic.LoadUint32(&s.bytesReceived) == 1
+}
+
+// Unprocessed indicates whether the server did not process this stream --
+// i.e. it sent a refused stream or GOAWAY including this stream ID.
+func (s *Stream) Unprocessed() bool {
+	return atomic.LoadUint32(&s.unprocessed) == 1
+}
+
+// GoString is implemented by Stream so context.String() won't
+// race when printing %#v.
+func (s *Stream) GoString() string {
+	return fmt.Sprintf("<stream: %p, %v>", s, s.method)
+}
+
+// state of transport
+type transportState int
+
+const (
+	reachable transportState = iota
+	closing
+	draining
+)
+
+// ServerConfig consists of all the configurations to establish a server transport.
+type ServerConfig struct {
+	MaxStreams            uint32
+	AuthInfo              credentials.AuthInfo
+	InTapHandle           tap.ServerInHandle
+	StatsHandler          stats.Handler
+	KeepaliveParams       keepalive.ServerParameters
+	KeepalivePolicy       keepalive.EnforcementPolicy
+	InitialWindowSize     int32
+	InitialConnWindowSize int32
+	WriteBufferSize       int
+	ReadBufferSize        int
+	ChannelzParentID      int64
+	MaxHeaderListSize     *uint32
+	HeaderTableSize       *uint32
+}
+
+// NewServerTransport creates a ServerTransport with conn or non-nil error
+// if it fails.
+func NewServerTransport(protocol string, conn net.Conn, config *ServerConfig) (ServerTransport, error) {
+	return newHTTP2Server(conn, config)
+}
+
+// ConnectOptions covers all relevant options for communicating with the server.
+type ConnectOptions struct {
+	// UserAgent is the application user agent.
+	UserAgent string
+	// Dialer specifies how to dial a network address.
+	Dialer func(context.Context, string) (net.Conn, error)
+	// FailOnNonTempDialError specifies if gRPC fails on non-temporary dial errors.
+	FailOnNonTempDialError bool
+	// PerRPCCredentials stores the PerRPCCredentials required to issue RPCs.
+	PerRPCCredentials []credentials.PerRPCCredentials
+	// TransportCredentials stores the Authenticator required to setup a client
+	// connection. Only one of TransportCredentials and CredsBundle is non-nil.
+	TransportCredentials credentials.TransportCredentials
+	// CredsBundle is the credentials bundle to be used. Only one of
+	// TransportCredentials and CredsBundle is non-nil.
+	CredsBundle credentials.Bundle
+	// KeepaliveParams stores the keepalive parameters.
+	KeepaliveParams keepalive.ClientParameters
+	// StatsHandler stores the handler for stats.
+	StatsHandler stats.Handler
+	// InitialWindowSize sets the initial window size for a stream.
+	InitialWindowSize int32
+	// InitialConnWindowSize sets the initial window size for a connection.
+	InitialConnWindowSize int32
+	// WriteBufferSize sets the size of write buffer which in turn determines how much data can be batched before it's written on the wire.
+	WriteBufferSize int
+	// ReadBufferSize sets the size of read buffer, which in turn determines how much data can be read at most for one read syscall.
+	ReadBufferSize int
+	// ChannelzParentID sets the addrConn id which initiate the creation of this client transport.
+	ChannelzParentID int64
+	// MaxHeaderListSize sets the max (uncompressed) size of header list that is prepared to be received.
+	MaxHeaderListSize *uint32
+}
+
+// TargetInfo contains the information of the target such as network address and metadata.
+type TargetInfo struct {
+	Addr      string
+	Metadata  interface{}
+	Authority string
+}
+
+// NewClientTransport establishes the transport with the required ConnectOptions
+// and returns it to the caller.
+func NewClientTransport(connectCtx, ctx context.Context, target TargetInfo, opts ConnectOptions, onPrefaceReceipt func(), onGoAway func(GoAwayReason), onClose func()) (ClientTransport, error) {
+	return newHTTP2Client(connectCtx, ctx, target, opts, onPrefaceReceipt, onGoAway, onClose)
+}
+
+// Options provides additional hints and information for message
+// transmission.
+type Options struct {
+	// Last indicates whether this write is the last piece for
+	// this stream.
+	Last bool
+}
+
+// CallHdr carries the information of a particular RPC.
+type CallHdr struct {
+	// Host specifies the peer's host.
+	Host string
+
+	// Method specifies the operation to perform.
+	Method string
+
+	// SendCompress specifies the compression algorithm applied on
+	// outbound message.
+	SendCompress string
+
+	// Creds specifies credentials.PerRPCCredentials for a call.
+	Creds credentials.PerRPCCredentials
+
+	// ContentSubtype specifies the content-subtype for a request. For example, a
+	// content-subtype of "proto" will result in a content-type of
+	// "application/grpc+proto". The value of ContentSubtype must be all
+	// lowercase, otherwise the behavior is undefined. See
+	// https://github.com/grpc/grpc/blob/master/doc/PROTOCOL-HTTP2.md#requests
+	// for more details.
+	ContentSubtype string
+
+	PreviousAttempts int // value of grpc-previous-rpc-attempts header to set
+}
+
+// ClientTransport is the common interface for all gRPC client-side transport
+// implementations.
+type ClientTransport interface {
+	// Close tears down this transport. Once it returns, the transport
+	// should not be accessed any more. The caller must make sure this
+	// is called only once.
+	Close() error
+
+	// GracefulClose starts to tear down the transport: the transport will stop
+	// accepting new RPCs and NewStream will return error. Once all streams are
+	// finished, the transport will close.
+	//
+	// It does not block.
+	GracefulClose()
+
+	// Write sends the data for the given stream. A nil stream indicates
+	// the write is to be performed on the transport as a whole.
+	Write(s *Stream, hdr []byte, data []byte, opts *Options) error
+
+	// NewStream creates a Stream for an RPC.
+	NewStream(ctx context.Context, callHdr *CallHdr) (*Stream, error)
+
+	// CloseStream clears the footprint of a stream when the stream is
+	// not needed any more. The err indicates the error incurred when
+	// CloseStream is called. Must be called when a stream is finished
+	// unless the associated transport is closing.
+	CloseStream(stream *Stream, err error)
+
+	// Error returns a channel that is closed when some I/O error
+	// happens. Typically the caller should have a goroutine to monitor
+	// this in order to take action (e.g., close the current transport
+	// and create a new one) in error case. It should not return nil
+	// once the transport is initiated.
+	Error() <-chan struct{}
+
+	// GoAway returns a channel that is closed when ClientTransport
+	// receives the draining signal from the server (e.g., GOAWAY frame in
+	// HTTP/2).
+	GoAway() <-chan struct{}
+
+	// GetGoAwayReason returns the reason why GoAway frame was received.
+	GetGoAwayReason() GoAwayReason
+
+	// RemoteAddr returns the remote network address.
+	RemoteAddr() net.Addr
+
+	// IncrMsgSent increments the number of message sent through this transport.
+	IncrMsgSent()
+
+	// IncrMsgRecv increments the number of message received through this transport.
+	IncrMsgRecv()
+}
+
+// ServerTransport is the common interface for all gRPC server-side transport
+// implementations.
+//
+// Methods may be called concurrently from multiple goroutines, but
+// Write methods for a given Stream will be called serially.
+type ServerTransport interface {
+	// HandleStreams receives incoming streams using the given handler.
+	HandleStreams(func(*Stream), func(context.Context, string) context.Context)
+
+	// WriteHeader sends the header metadata for the given stream.
+	// WriteHeader may not be called on all streams.
+	WriteHeader(s *Stream, md metadata.MD) error
+
+	// Write sends the data for the given stream.
+	// Write may not be called on all streams.
+	Write(s *Stream, hdr []byte, data []byte, opts *Options) error
+
+	// WriteStatus sends the status of a stream to the client.  WriteStatus is
+	// the final call made on a stream and always occurs.
+	WriteStatus(s *Stream, st *status.Status) error
+
+	// Close tears down the transport. Once it is called, the transport
+	// should not be accessed any more. All the pending streams and their
+	// handlers will be terminated asynchronously.
+	Close() error
+
+	// RemoteAddr returns the remote network address.
+	RemoteAddr() net.Addr
+
+	// Drain notifies the client this ServerTransport stops accepting new RPCs.
+	Drain()
+
+	// IncrMsgSent increments the number of message sent through this transport.
+	IncrMsgSent()
+
+	// IncrMsgRecv increments the number of message received through this transport.
+	IncrMsgRecv()
+}
+
+// connectionErrorf creates an ConnectionError with the specified error description.
+func connectionErrorf(temp bool, e error, format string, a ...interface{}) ConnectionError {
+	return ConnectionError{
+		Desc: fmt.Sprintf(format, a...),
+		temp: temp,
+		err:  e,
+	}
+}
+
+// ConnectionError is an error that results in the termination of the
+// entire connection and the retry of all the active streams.
+type ConnectionError struct {
+	Desc string
+	temp bool
+	err  error
+}
+
+func (e ConnectionError) Error() string {
+	return fmt.Sprintf("connection error: desc = %q", e.Desc)
+}
+
+// Temporary indicates if this connection error is temporary or fatal.
+func (e ConnectionError) Temporary() bool {
+	return e.temp
+}
+
+// Origin returns the original error of this connection error.
+func (e ConnectionError) Origin() error {
+	// Never return nil error here.
+	// If the original error is nil, return itself.
+	if e.err == nil {
+		return e
+	}
+	return e.err
+}
+
+var (
+	// ErrConnClosing indicates that the transport is closing.
+	ErrConnClosing = connectionErrorf(true, nil, "transport is closing")
+	// errStreamDrain indicates that the stream is rejected because the
+	// connection is draining. This could be caused by goaway or balancer
+	// removing the address.
+	errStreamDrain = status.Error(codes.Unavailable, "the connection is draining")
+	// errStreamDone is returned from write at the client side to indiacte application
+	// layer of an error.
+	errStreamDone = errors.New("the stream is done")
+	// StatusGoAway indicates that the server sent a GOAWAY that included this
+	// stream's ID in unprocessed RPCs.
+	statusGoAway = status.New(codes.Unavailable, "the stream is rejected because server is draining the connection")
+)
+
+// GoAwayReason contains the reason for the GoAway frame received.
+type GoAwayReason uint8
+
+const (
+	// GoAwayInvalid indicates that no GoAway frame is received.
+	GoAwayInvalid GoAwayReason = 0
+	// GoAwayNoReason is the default value when GoAway frame is received.
+	GoAwayNoReason GoAwayReason = 1
+	// GoAwayTooManyPings indicates that a GoAway frame with
+	// ErrCodeEnhanceYourCalm was received and that the debug data said
+	// "too_many_pings".
+	GoAwayTooManyPings GoAwayReason = 2
+)
+
+// channelzData is used to store channelz related data for http2Client and http2Server.
+// These fields cannot be embedded in the original structs (e.g. http2Client), since to do atomic
+// operation on int64 variable on 32-bit machine, user is responsible to enforce memory alignment.
+// Here, by grouping those int64 fields inside a struct, we are enforcing the alignment.
+type channelzData struct {
+	kpCount int64
+	// The number of streams that have started, including already finished ones.
+	streamsStarted int64
+	// Client side: The number of streams that have ended successfully by receiving
+	// EoS bit set frame from server.
+	// Server side: The number of streams that have ended successfully by sending
+	// frame with EoS bit set.
+	streamsSucceeded int64
+	streamsFailed    int64
+	// lastStreamCreatedTime stores the timestamp that the last stream gets created. It is of int64 type
+	// instead of time.Time since it's more costly to atomically update time.Time variable than int64
+	// variable. The same goes for lastMsgSentTime and lastMsgRecvTime.
+	lastStreamCreatedTime int64
+	msgSent               int64
+	msgRecv               int64
+	lastMsgSentTime       int64
+	lastMsgRecvTime       int64
+}
+
+// ContextErr converts the error from context package into a status error.
+func ContextErr(err error) error {
+	switch err {
+	case context.DeadlineExceeded:
+		return status.Error(codes.DeadlineExceeded, err.Error())
+	case context.Canceled:
+		return status.Error(codes.Canceled, err.Error())
+	}
+	return status.Errorf(codes.Internal, "Unexpected error from context packet: %v", err)
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/keepalive/keepalive.go b/demo_test/vendor/google.golang.org/grpc/keepalive/keepalive.go
new file mode 100644
index 0000000..34d31b5
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/keepalive/keepalive.go
@@ -0,0 +1,85 @@
+/*
+ *
+ * Copyright 2017 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+// Package keepalive defines configurable parameters for point-to-point
+// healthcheck.
+package keepalive
+
+import (
+	"time"
+)
+
+// ClientParameters is used to set keepalive parameters on the client-side.
+// These configure how the client will actively probe to notice when a
+// connection is broken and send pings so intermediaries will be aware of the
+// liveness of the connection. Make sure these parameters are set in
+// coordination with the keepalive policy on the server, as incompatible
+// settings can result in closing of connection.
+type ClientParameters struct {
+	// After a duration of this time if the client doesn't see any activity it
+	// pings the server to see if the transport is still alive.
+	// If set below 10s, a minimum value of 10s will be used instead.
+	Time time.Duration // The current default value is infinity.
+	// After having pinged for keepalive check, the client waits for a duration
+	// of Timeout and if no activity is seen even after that the connection is
+	// closed.
+	Timeout time.Duration // The current default value is 20 seconds.
+	// If true, client sends keepalive pings even with no active RPCs. If false,
+	// when there are no active RPCs, Time and Timeout will be ignored and no
+	// keepalive pings will be sent.
+	PermitWithoutStream bool // false by default.
+}
+
+// ServerParameters is used to set keepalive and max-age parameters on the
+// server-side.
+type ServerParameters struct {
+	// MaxConnectionIdle is a duration for the amount of time after which an
+	// idle connection would be closed by sending a GoAway. Idleness duration is
+	// defined since the most recent time the number of outstanding RPCs became
+	// zero or the connection establishment.
+	MaxConnectionIdle time.Duration // The current default value is infinity.
+	// MaxConnectionAge is a duration for the maximum amount of time a
+	// connection may exist before it will be closed by sending a GoAway. A
+	// random jitter of +/-10% will be added to MaxConnectionAge to spread out
+	// connection storms.
+	MaxConnectionAge time.Duration // The current default value is infinity.
+	// MaxConnectionAgeGrace is an additive period after MaxConnectionAge after
+	// which the connection will be forcibly closed.
+	MaxConnectionAgeGrace time.Duration // The current default value is infinity.
+	// After a duration of this time if the server doesn't see any activity it
+	// pings the client to see if the transport is still alive.
+	// If set below 1s, a minimum value of 1s will be used instead.
+	Time time.Duration // The current default value is 2 hours.
+	// After having pinged for keepalive check, the server waits for a duration
+	// of Timeout and if no activity is seen even after that the connection is
+	// closed.
+	Timeout time.Duration // The current default value is 20 seconds.
+}
+
+// EnforcementPolicy is used to set keepalive enforcement policy on the
+// server-side. Server will close connection with a client that violates this
+// policy.
+type EnforcementPolicy struct {
+	// MinTime is the minimum amount of time a client should wait before sending
+	// a keepalive ping.
+	MinTime time.Duration // The current default value is 5 minutes.
+	// If true, server allows keepalive pings even when there are no active
+	// streams(RPCs). If false, and client sends ping when there are no active
+	// streams, server will send GOAWAY and close the connection.
+	PermitWithoutStream bool // false by default.
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/metadata/metadata.go b/demo_test/vendor/google.golang.org/grpc/metadata/metadata.go
new file mode 100644
index 0000000..cf6d1b9
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/metadata/metadata.go
@@ -0,0 +1,209 @@
+/*
+ *
+ * Copyright 2014 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+// Package metadata define the structure of the metadata supported by gRPC library.
+// Please refer to https://github.com/grpc/grpc/blob/master/doc/PROTOCOL-HTTP2.md
+// for more information about custom-metadata.
+package metadata // import "google.golang.org/grpc/metadata"
+
+import (
+	"context"
+	"fmt"
+	"strings"
+)
+
+// DecodeKeyValue returns k, v, nil.
+//
+// Deprecated: use k and v directly instead.
+func DecodeKeyValue(k, v string) (string, string, error) {
+	return k, v, nil
+}
+
+// MD is a mapping from metadata keys to values. Users should use the following
+// two convenience functions New and Pairs to generate MD.
+type MD map[string][]string
+
+// New creates an MD from a given key-value map.
+//
+// Only the following ASCII characters are allowed in keys:
+//  - digits: 0-9
+//  - uppercase letters: A-Z (normalized to lower)
+//  - lowercase letters: a-z
+//  - special characters: -_.
+// Uppercase letters are automatically converted to lowercase.
+//
+// Keys beginning with "grpc-" are reserved for grpc-internal use only and may
+// result in errors if set in metadata.
+func New(m map[string]string) MD {
+	md := MD{}
+	for k, val := range m {
+		key := strings.ToLower(k)
+		md[key] = append(md[key], val)
+	}
+	return md
+}
+
+// Pairs returns an MD formed by the mapping of key, value ...
+// Pairs panics if len(kv) is odd.
+//
+// Only the following ASCII characters are allowed in keys:
+//  - digits: 0-9
+//  - uppercase letters: A-Z (normalized to lower)
+//  - lowercase letters: a-z
+//  - special characters: -_.
+// Uppercase letters are automatically converted to lowercase.
+//
+// Keys beginning with "grpc-" are reserved for grpc-internal use only and may
+// result in errors if set in metadata.
+func Pairs(kv ...string) MD {
+	if len(kv)%2 == 1 {
+		panic(fmt.Sprintf("metadata: Pairs got the odd number of input pairs for metadata: %d", len(kv)))
+	}
+	md := MD{}
+	var key string
+	for i, s := range kv {
+		if i%2 == 0 {
+			key = strings.ToLower(s)
+			continue
+		}
+		md[key] = append(md[key], s)
+	}
+	return md
+}
+
+// Len returns the number of items in md.
+func (md MD) Len() int {
+	return len(md)
+}
+
+// Copy returns a copy of md.
+func (md MD) Copy() MD {
+	return Join(md)
+}
+
+// Get obtains the values for a given key.
+func (md MD) Get(k string) []string {
+	k = strings.ToLower(k)
+	return md[k]
+}
+
+// Set sets the value of a given key with a slice of values.
+func (md MD) Set(k string, vals ...string) {
+	if len(vals) == 0 {
+		return
+	}
+	k = strings.ToLower(k)
+	md[k] = vals
+}
+
+// Append adds the values to key k, not overwriting what was already stored at that key.
+func (md MD) Append(k string, vals ...string) {
+	if len(vals) == 0 {
+		return
+	}
+	k = strings.ToLower(k)
+	md[k] = append(md[k], vals...)
+}
+
+// Join joins any number of mds into a single MD.
+// The order of values for each key is determined by the order in which
+// the mds containing those values are presented to Join.
+func Join(mds ...MD) MD {
+	out := MD{}
+	for _, md := range mds {
+		for k, v := range md {
+			out[k] = append(out[k], v...)
+		}
+	}
+	return out
+}
+
+type mdIncomingKey struct{}
+type mdOutgoingKey struct{}
+
+// NewIncomingContext creates a new context with incoming md attached.
+func NewIncomingContext(ctx context.Context, md MD) context.Context {
+	return context.WithValue(ctx, mdIncomingKey{}, md)
+}
+
+// NewOutgoingContext creates a new context with outgoing md attached. If used
+// in conjunction with AppendToOutgoingContext, NewOutgoingContext will
+// overwrite any previously-appended metadata.
+func NewOutgoingContext(ctx context.Context, md MD) context.Context {
+	return context.WithValue(ctx, mdOutgoingKey{}, rawMD{md: md})
+}
+
+// AppendToOutgoingContext returns a new context with the provided kv merged
+// with any existing metadata in the context. Please refer to the
+// documentation of Pairs for a description of kv.
+func AppendToOutgoingContext(ctx context.Context, kv ...string) context.Context {
+	if len(kv)%2 == 1 {
+		panic(fmt.Sprintf("metadata: AppendToOutgoingContext got an odd number of input pairs for metadata: %d", len(kv)))
+	}
+	md, _ := ctx.Value(mdOutgoingKey{}).(rawMD)
+	added := make([][]string, len(md.added)+1)
+	copy(added, md.added)
+	added[len(added)-1] = make([]string, len(kv))
+	copy(added[len(added)-1], kv)
+	return context.WithValue(ctx, mdOutgoingKey{}, rawMD{md: md.md, added: added})
+}
+
+// FromIncomingContext returns the incoming metadata in ctx if it exists.  The
+// returned MD should not be modified. Writing to it may cause races.
+// Modification should be made to copies of the returned MD.
+func FromIncomingContext(ctx context.Context) (md MD, ok bool) {
+	md, ok = ctx.Value(mdIncomingKey{}).(MD)
+	return
+}
+
+// FromOutgoingContextRaw returns the un-merged, intermediary contents
+// of rawMD. Remember to perform strings.ToLower on the keys. The returned
+// MD should not be modified. Writing to it may cause races. Modification
+// should be made to copies of the returned MD.
+//
+// This is intended for gRPC-internal use ONLY.
+func FromOutgoingContextRaw(ctx context.Context) (MD, [][]string, bool) {
+	raw, ok := ctx.Value(mdOutgoingKey{}).(rawMD)
+	if !ok {
+		return nil, nil, false
+	}
+
+	return raw.md, raw.added, true
+}
+
+// FromOutgoingContext returns the outgoing metadata in ctx if it exists.  The
+// returned MD should not be modified. Writing to it may cause races.
+// Modification should be made to copies of the returned MD.
+func FromOutgoingContext(ctx context.Context) (MD, bool) {
+	raw, ok := ctx.Value(mdOutgoingKey{}).(rawMD)
+	if !ok {
+		return nil, false
+	}
+
+	mds := make([]MD, 0, len(raw.added)+1)
+	mds = append(mds, raw.md)
+	for _, vv := range raw.added {
+		mds = append(mds, Pairs(vv...))
+	}
+	return Join(mds...), ok
+}
+
+type rawMD struct {
+	md    MD
+	added [][]string
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/naming/dns_resolver.go b/demo_test/vendor/google.golang.org/grpc/naming/dns_resolver.go
new file mode 100644
index 0000000..c9f79dc
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/naming/dns_resolver.go
@@ -0,0 +1,293 @@
+/*
+ *
+ * Copyright 2017 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package naming
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"net"
+	"strconv"
+	"time"
+
+	"google.golang.org/grpc/grpclog"
+)
+
+const (
+	defaultPort = "443"
+	defaultFreq = time.Minute * 30
+)
+
+var (
+	errMissingAddr  = errors.New("missing address")
+	errWatcherClose = errors.New("watcher has been closed")
+
+	lookupHost = net.DefaultResolver.LookupHost
+	lookupSRV  = net.DefaultResolver.LookupSRV
+)
+
+// NewDNSResolverWithFreq creates a DNS Resolver that can resolve DNS names, and
+// create watchers that poll the DNS server using the frequency set by freq.
+func NewDNSResolverWithFreq(freq time.Duration) (Resolver, error) {
+	return &dnsResolver{freq: freq}, nil
+}
+
+// NewDNSResolver creates a DNS Resolver that can resolve DNS names, and create
+// watchers that poll the DNS server using the default frequency defined by defaultFreq.
+func NewDNSResolver() (Resolver, error) {
+	return NewDNSResolverWithFreq(defaultFreq)
+}
+
+// dnsResolver handles name resolution for names following the DNS scheme
+type dnsResolver struct {
+	// frequency of polling the DNS server that the watchers created by this resolver will use.
+	freq time.Duration
+}
+
+// formatIP returns ok = false if addr is not a valid textual representation of an IP address.
+// If addr is an IPv4 address, return the addr and ok = true.
+// If addr is an IPv6 address, return the addr enclosed in square brackets and ok = true.
+func formatIP(addr string) (addrIP string, ok bool) {
+	ip := net.ParseIP(addr)
+	if ip == nil {
+		return "", false
+	}
+	if ip.To4() != nil {
+		return addr, true
+	}
+	return "[" + addr + "]", true
+}
+
+// parseTarget takes the user input target string, returns formatted host and port info.
+// If target doesn't specify a port, set the port to be the defaultPort.
+// If target is in IPv6 format and host-name is enclosed in square brackets, brackets
+// are stripped when setting the host.
+// examples:
+// target: "www.google.com" returns host: "www.google.com", port: "443"
+// target: "ipv4-host:80" returns host: "ipv4-host", port: "80"
+// target: "[ipv6-host]" returns host: "ipv6-host", port: "443"
+// target: ":80" returns host: "localhost", port: "80"
+// target: ":" returns host: "localhost", port: "443"
+func parseTarget(target string) (host, port string, err error) {
+	if target == "" {
+		return "", "", errMissingAddr
+	}
+
+	if ip := net.ParseIP(target); ip != nil {
+		// target is an IPv4 or IPv6(without brackets) address
+		return target, defaultPort, nil
+	}
+	if host, port, err := net.SplitHostPort(target); err == nil {
+		// target has port, i.e ipv4-host:port, [ipv6-host]:port, host-name:port
+		if host == "" {
+			// Keep consistent with net.Dial(): If the host is empty, as in ":80", the local system is assumed.
+			host = "localhost"
+		}
+		if port == "" {
+			// If the port field is empty(target ends with colon), e.g. "[::1]:", defaultPort is used.
+			port = defaultPort
+		}
+		return host, port, nil
+	}
+	if host, port, err := net.SplitHostPort(target + ":" + defaultPort); err == nil {
+		// target doesn't have port
+		return host, port, nil
+	}
+	return "", "", fmt.Errorf("invalid target address %v", target)
+}
+
+// Resolve creates a watcher that watches the name resolution of the target.
+func (r *dnsResolver) Resolve(target string) (Watcher, error) {
+	host, port, err := parseTarget(target)
+	if err != nil {
+		return nil, err
+	}
+
+	if net.ParseIP(host) != nil {
+		ipWatcher := &ipWatcher{
+			updateChan: make(chan *Update, 1),
+		}
+		host, _ = formatIP(host)
+		ipWatcher.updateChan <- &Update{Op: Add, Addr: host + ":" + port}
+		return ipWatcher, nil
+	}
+
+	ctx, cancel := context.WithCancel(context.Background())
+	return &dnsWatcher{
+		r:      r,
+		host:   host,
+		port:   port,
+		ctx:    ctx,
+		cancel: cancel,
+		t:      time.NewTimer(0),
+	}, nil
+}
+
+// dnsWatcher watches for the name resolution update for a specific target
+type dnsWatcher struct {
+	r    *dnsResolver
+	host string
+	port string
+	// The latest resolved address set
+	curAddrs map[string]*Update
+	ctx      context.Context
+	cancel   context.CancelFunc
+	t        *time.Timer
+}
+
+// ipWatcher watches for the name resolution update for an IP address.
+type ipWatcher struct {
+	updateChan chan *Update
+}
+
+// Next returns the address resolution Update for the target. For IP address,
+// the resolution is itself, thus polling name server is unnecessary. Therefore,
+// Next() will return an Update the first time it is called, and will be blocked
+// for all following calls as no Update exists until watcher is closed.
+func (i *ipWatcher) Next() ([]*Update, error) {
+	u, ok := <-i.updateChan
+	if !ok {
+		return nil, errWatcherClose
+	}
+	return []*Update{u}, nil
+}
+
+// Close closes the ipWatcher.
+func (i *ipWatcher) Close() {
+	close(i.updateChan)
+}
+
+// AddressType indicates the address type returned by name resolution.
+type AddressType uint8
+
+const (
+	// Backend indicates the server is a backend server.
+	Backend AddressType = iota
+	// GRPCLB indicates the server is a grpclb load balancer.
+	GRPCLB
+)
+
+// AddrMetadataGRPCLB contains the information the name resolver for grpclb should provide. The
+// name resolver used by the grpclb balancer is required to provide this type of metadata in
+// its address updates.
+type AddrMetadataGRPCLB struct {
+	// AddrType is the type of server (grpc load balancer or backend).
+	AddrType AddressType
+	// ServerName is the name of the grpc load balancer. Used for authentication.
+	ServerName string
+}
+
+// compileUpdate compares the old resolved addresses and newly resolved addresses,
+// and generates an update list
+func (w *dnsWatcher) compileUpdate(newAddrs map[string]*Update) []*Update {
+	var res []*Update
+	for a, u := range w.curAddrs {
+		if _, ok := newAddrs[a]; !ok {
+			u.Op = Delete
+			res = append(res, u)
+		}
+	}
+	for a, u := range newAddrs {
+		if _, ok := w.curAddrs[a]; !ok {
+			res = append(res, u)
+		}
+	}
+	return res
+}
+
+func (w *dnsWatcher) lookupSRV() map[string]*Update {
+	newAddrs := make(map[string]*Update)
+	_, srvs, err := lookupSRV(w.ctx, "grpclb", "tcp", w.host)
+	if err != nil {
+		grpclog.Infof("grpc: failed dns SRV record lookup due to %v.\n", err)
+		return nil
+	}
+	for _, s := range srvs {
+		lbAddrs, err := lookupHost(w.ctx, s.Target)
+		if err != nil {
+			grpclog.Warningf("grpc: failed load balancer address dns lookup due to %v.\n", err)
+			continue
+		}
+		for _, a := range lbAddrs {
+			a, ok := formatIP(a)
+			if !ok {
+				grpclog.Errorf("grpc: failed IP parsing due to %v.\n", err)
+				continue
+			}
+			addr := a + ":" + strconv.Itoa(int(s.Port))
+			newAddrs[addr] = &Update{Addr: addr,
+				Metadata: AddrMetadataGRPCLB{AddrType: GRPCLB, ServerName: s.Target}}
+		}
+	}
+	return newAddrs
+}
+
+func (w *dnsWatcher) lookupHost() map[string]*Update {
+	newAddrs := make(map[string]*Update)
+	addrs, err := lookupHost(w.ctx, w.host)
+	if err != nil {
+		grpclog.Warningf("grpc: failed dns A record lookup due to %v.\n", err)
+		return nil
+	}
+	for _, a := range addrs {
+		a, ok := formatIP(a)
+		if !ok {
+			grpclog.Errorf("grpc: failed IP parsing due to %v.\n", err)
+			continue
+		}
+		addr := a + ":" + w.port
+		newAddrs[addr] = &Update{Addr: addr}
+	}
+	return newAddrs
+}
+
+func (w *dnsWatcher) lookup() []*Update {
+	newAddrs := w.lookupSRV()
+	if newAddrs == nil {
+		// If failed to get any balancer address (either no corresponding SRV for the
+		// target, or caused by failure during resolution/parsing of the balancer target),
+		// return any A record info available.
+		newAddrs = w.lookupHost()
+	}
+	result := w.compileUpdate(newAddrs)
+	w.curAddrs = newAddrs
+	return result
+}
+
+// Next returns the resolved address update(delta) for the target. If there's no
+// change, it will sleep for 30 mins and try to resolve again after that.
+func (w *dnsWatcher) Next() ([]*Update, error) {
+	for {
+		select {
+		case <-w.ctx.Done():
+			return nil, errWatcherClose
+		case <-w.t.C:
+		}
+		result := w.lookup()
+		// Next lookup should happen after an interval defined by w.r.freq.
+		w.t.Reset(w.r.freq)
+		if len(result) > 0 {
+			return result, nil
+		}
+	}
+}
+
+func (w *dnsWatcher) Close() {
+	w.cancel()
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/naming/naming.go b/demo_test/vendor/google.golang.org/grpc/naming/naming.go
new file mode 100644
index 0000000..f4c1c8b
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/naming/naming.go
@@ -0,0 +1,68 @@
+/*
+ *
+ * Copyright 2014 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+// Package naming defines the naming API and related data structures for gRPC.
+//
+// This package is deprecated: please use package resolver instead.
+package naming
+
+// Operation defines the corresponding operations for a name resolution change.
+//
+// Deprecated: please use package resolver.
+type Operation uint8
+
+const (
+	// Add indicates a new address is added.
+	Add Operation = iota
+	// Delete indicates an existing address is deleted.
+	Delete
+)
+
+// Update defines a name resolution update. Notice that it is not valid having both
+// empty string Addr and nil Metadata in an Update.
+//
+// Deprecated: please use package resolver.
+type Update struct {
+	// Op indicates the operation of the update.
+	Op Operation
+	// Addr is the updated address. It is empty string if there is no address update.
+	Addr string
+	// Metadata is the updated metadata. It is nil if there is no metadata update.
+	// Metadata is not required for a custom naming implementation.
+	Metadata interface{}
+}
+
+// Resolver creates a Watcher for a target to track its resolution changes.
+//
+// Deprecated: please use package resolver.
+type Resolver interface {
+	// Resolve creates a Watcher for target.
+	Resolve(target string) (Watcher, error)
+}
+
+// Watcher watches for the updates on the specified target.
+//
+// Deprecated: please use package resolver.
+type Watcher interface {
+	// Next blocks until an update or error happens. It may return one or more
+	// updates. The first call should get the full set of the results. It should
+	// return an error if and only if Watcher cannot recover.
+	Next() ([]*Update, error)
+	// Close closes the Watcher.
+	Close()
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/peer/peer.go b/demo_test/vendor/google.golang.org/grpc/peer/peer.go
new file mode 100644
index 0000000..e01d219
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/peer/peer.go
@@ -0,0 +1,51 @@
+/*
+ *
+ * Copyright 2014 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+// Package peer defines various peer information associated with RPCs and
+// corresponding utils.
+package peer
+
+import (
+	"context"
+	"net"
+
+	"google.golang.org/grpc/credentials"
+)
+
+// Peer contains the information of the peer for an RPC, such as the address
+// and authentication information.
+type Peer struct {
+	// Addr is the peer address.
+	Addr net.Addr
+	// AuthInfo is the authentication information of the transport.
+	// It is nil if there is no transport security being used.
+	AuthInfo credentials.AuthInfo
+}
+
+type peerKey struct{}
+
+// NewContext creates a new context with peer information attached.
+func NewContext(ctx context.Context, p *Peer) context.Context {
+	return context.WithValue(ctx, peerKey{}, p)
+}
+
+// FromContext returns the peer information in ctx if it exists.
+func FromContext(ctx context.Context) (p *Peer, ok bool) {
+	p, ok = ctx.Value(peerKey{}).(*Peer)
+	return
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/picker_wrapper.go b/demo_test/vendor/google.golang.org/grpc/picker_wrapper.go
new file mode 100644
index 0000000..0044789
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/picker_wrapper.go
@@ -0,0 +1,229 @@
+/*
+ *
+ * Copyright 2017 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package grpc
+
+import (
+	"context"
+	"fmt"
+	"io"
+	"sync"
+
+	"google.golang.org/grpc/balancer"
+	"google.golang.org/grpc/codes"
+	"google.golang.org/grpc/grpclog"
+	"google.golang.org/grpc/internal/channelz"
+	"google.golang.org/grpc/internal/transport"
+	"google.golang.org/grpc/status"
+)
+
+// v2PickerWrapper wraps a balancer.Picker while providing the
+// balancer.V2Picker API.  It requires a pickerWrapper to generate errors
+// including the latest connectionError.  To be deleted when balancer.Picker is
+// updated to the balancer.V2Picker API.
+type v2PickerWrapper struct {
+	picker  balancer.Picker
+	connErr *connErr
+}
+
+func (v *v2PickerWrapper) Pick(info balancer.PickInfo) (balancer.PickResult, error) {
+	sc, done, err := v.picker.Pick(info.Ctx, info)
+	if err != nil {
+		if err == balancer.ErrTransientFailure {
+			return balancer.PickResult{}, balancer.TransientFailureError(fmt.Errorf("%v, latest connection error: %v", err, v.connErr.connectionError()))
+		}
+		return balancer.PickResult{}, err
+	}
+	return balancer.PickResult{SubConn: sc, Done: done}, nil
+}
+
+// pickerWrapper is a wrapper of balancer.Picker. It blocks on certain pick
+// actions and unblock when there's a picker update.
+type pickerWrapper struct {
+	mu         sync.Mutex
+	done       bool
+	blockingCh chan struct{}
+	picker     balancer.V2Picker
+
+	// The latest connection error.  TODO: remove when V1 picker is deprecated;
+	// balancer should be responsible for providing the error.
+	*connErr
+}
+
+type connErr struct {
+	mu  sync.Mutex
+	err error
+}
+
+func (c *connErr) updateConnectionError(err error) {
+	c.mu.Lock()
+	c.err = err
+	c.mu.Unlock()
+}
+
+func (c *connErr) connectionError() error {
+	c.mu.Lock()
+	err := c.err
+	c.mu.Unlock()
+	return err
+}
+
+func newPickerWrapper() *pickerWrapper {
+	return &pickerWrapper{blockingCh: make(chan struct{}), connErr: &connErr{}}
+}
+
+// updatePicker is called by UpdateBalancerState. It unblocks all blocked pick.
+func (pw *pickerWrapper) updatePicker(p balancer.Picker) {
+	pw.updatePickerV2(&v2PickerWrapper{picker: p, connErr: pw.connErr})
+}
+
+// updatePicker is called by UpdateBalancerState. It unblocks all blocked pick.
+func (pw *pickerWrapper) updatePickerV2(p balancer.V2Picker) {
+	pw.mu.Lock()
+	if pw.done {
+		pw.mu.Unlock()
+		return
+	}
+	pw.picker = p
+	// pw.blockingCh should never be nil.
+	close(pw.blockingCh)
+	pw.blockingCh = make(chan struct{})
+	pw.mu.Unlock()
+}
+
+func doneChannelzWrapper(acw *acBalancerWrapper, done func(balancer.DoneInfo)) func(balancer.DoneInfo) {
+	acw.mu.Lock()
+	ac := acw.ac
+	acw.mu.Unlock()
+	ac.incrCallsStarted()
+	return func(b balancer.DoneInfo) {
+		if b.Err != nil && b.Err != io.EOF {
+			ac.incrCallsFailed()
+		} else {
+			ac.incrCallsSucceeded()
+		}
+		if done != nil {
+			done(b)
+		}
+	}
+}
+
+// pick returns the transport that will be used for the RPC.
+// It may block in the following cases:
+// - there's no picker
+// - the current picker returns ErrNoSubConnAvailable
+// - the current picker returns other errors and failfast is false.
+// - the subConn returned by the current picker is not READY
+// When one of these situations happens, pick blocks until the picker gets updated.
+func (pw *pickerWrapper) pick(ctx context.Context, failfast bool, info balancer.PickInfo) (transport.ClientTransport, func(balancer.DoneInfo), error) {
+	var ch chan struct{}
+
+	var lastPickErr error
+	for {
+		pw.mu.Lock()
+		if pw.done {
+			pw.mu.Unlock()
+			return nil, nil, ErrClientConnClosing
+		}
+
+		if pw.picker == nil {
+			ch = pw.blockingCh
+		}
+		if ch == pw.blockingCh {
+			// This could happen when either:
+			// - pw.picker is nil (the previous if condition), or
+			// - has called pick on the current picker.
+			pw.mu.Unlock()
+			select {
+			case <-ctx.Done():
+				var errStr string
+				if lastPickErr != nil {
+					errStr = "latest balancer error: " + lastPickErr.Error()
+				} else if connectionErr := pw.connectionError(); connectionErr != nil {
+					errStr = "latest connection error: " + connectionErr.Error()
+				} else {
+					errStr = ctx.Err().Error()
+				}
+				switch ctx.Err() {
+				case context.DeadlineExceeded:
+					return nil, nil, status.Error(codes.DeadlineExceeded, errStr)
+				case context.Canceled:
+					return nil, nil, status.Error(codes.Canceled, errStr)
+				}
+			case <-ch:
+			}
+			continue
+		}
+
+		ch = pw.blockingCh
+		p := pw.picker
+		pw.mu.Unlock()
+
+		pickResult, err := p.Pick(info)
+
+		if err != nil {
+			if err == balancer.ErrNoSubConnAvailable {
+				continue
+			}
+			if tfe, ok := err.(interface{ IsTransientFailure() bool }); ok && tfe.IsTransientFailure() {
+				if !failfast {
+					lastPickErr = err
+					continue
+				}
+				return nil, nil, status.Error(codes.Unavailable, err.Error())
+			}
+			if _, ok := status.FromError(err); ok {
+				return nil, nil, err
+			}
+			// err is some other error.
+			return nil, nil, status.Error(codes.Unknown, err.Error())
+		}
+
+		acw, ok := pickResult.SubConn.(*acBalancerWrapper)
+		if !ok {
+			grpclog.Error("subconn returned from pick is not *acBalancerWrapper")
+			continue
+		}
+		if t, ok := acw.getAddrConn().getReadyTransport(); ok {
+			if channelz.IsOn() {
+				return t, doneChannelzWrapper(acw, pickResult.Done), nil
+			}
+			return t, pickResult.Done, nil
+		}
+		if pickResult.Done != nil {
+			// Calling done with nil error, no bytes sent and no bytes received.
+			// DoneInfo with default value works.
+			pickResult.Done(balancer.DoneInfo{})
+		}
+		grpclog.Infof("blockingPicker: the picked transport is not ready, loop back to repick")
+		// If ok == false, ac.state is not READY.
+		// A valid picker always returns READY subConn. This means the state of ac
+		// just changed, and picker will be updated shortly.
+		// continue back to the beginning of the for loop to repick.
+	}
+}
+
+func (pw *pickerWrapper) close() {
+	pw.mu.Lock()
+	defer pw.mu.Unlock()
+	if pw.done {
+		return
+	}
+	pw.done = true
+	close(pw.blockingCh)
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/pickfirst.go b/demo_test/vendor/google.golang.org/grpc/pickfirst.go
new file mode 100644
index 0000000..c43dac9
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/pickfirst.go
@@ -0,0 +1,159 @@
+/*
+ *
+ * Copyright 2017 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package grpc
+
+import (
+	"errors"
+
+	"google.golang.org/grpc/balancer"
+	"google.golang.org/grpc/codes"
+	"google.golang.org/grpc/connectivity"
+	"google.golang.org/grpc/grpclog"
+	"google.golang.org/grpc/resolver"
+	"google.golang.org/grpc/status"
+)
+
+// PickFirstBalancerName is the name of the pick_first balancer.
+const PickFirstBalancerName = "pick_first"
+
+func newPickfirstBuilder() balancer.Builder {
+	return &pickfirstBuilder{}
+}
+
+type pickfirstBuilder struct{}
+
+func (*pickfirstBuilder) Build(cc balancer.ClientConn, opt balancer.BuildOptions) balancer.Balancer {
+	return &pickfirstBalancer{cc: cc}
+}
+
+func (*pickfirstBuilder) Name() string {
+	return PickFirstBalancerName
+}
+
+type pickfirstBalancer struct {
+	state connectivity.State
+	cc    balancer.ClientConn
+	sc    balancer.SubConn
+}
+
+var _ balancer.V2Balancer = &pickfirstBalancer{} // Assert we implement v2
+
+func (b *pickfirstBalancer) HandleResolvedAddrs(addrs []resolver.Address, err error) {
+	if err != nil {
+		b.ResolverError(err)
+		return
+	}
+	b.UpdateClientConnState(balancer.ClientConnState{ResolverState: resolver.State{Addresses: addrs}}) // Ignore error
+}
+
+func (b *pickfirstBalancer) HandleSubConnStateChange(sc balancer.SubConn, s connectivity.State) {
+	b.UpdateSubConnState(sc, balancer.SubConnState{ConnectivityState: s})
+}
+
+func (b *pickfirstBalancer) ResolverError(err error) {
+	switch b.state {
+	case connectivity.TransientFailure, connectivity.Idle, connectivity.Connecting:
+		// Set a failing picker if we don't have a good picker.
+		b.cc.UpdateState(balancer.State{ConnectivityState: connectivity.TransientFailure,
+			Picker: &picker{err: status.Errorf(codes.Unavailable, "name resolver error: %v", err)}},
+		)
+	}
+	if grpclog.V(2) {
+		grpclog.Infof("pickfirstBalancer: ResolverError called with error %v", err)
+	}
+}
+
+func (b *pickfirstBalancer) UpdateClientConnState(cs balancer.ClientConnState) error {
+	if len(cs.ResolverState.Addresses) == 0 {
+		b.ResolverError(errors.New("produced zero addresses"))
+		return balancer.ErrBadResolverState
+	}
+	if b.sc == nil {
+		var err error
+		b.sc, err = b.cc.NewSubConn(cs.ResolverState.Addresses, balancer.NewSubConnOptions{})
+		if err != nil {
+			if grpclog.V(2) {
+				grpclog.Errorf("pickfirstBalancer: failed to NewSubConn: %v", err)
+			}
+			b.state = connectivity.TransientFailure
+			b.cc.UpdateState(balancer.State{ConnectivityState: connectivity.TransientFailure,
+				Picker: &picker{err: status.Errorf(codes.Unavailable, "error creating connection: %v", err)}},
+			)
+			return balancer.ErrBadResolverState
+		}
+		b.state = connectivity.Idle
+		b.cc.UpdateState(balancer.State{ConnectivityState: connectivity.Idle, Picker: &picker{result: balancer.PickResult{SubConn: b.sc}}})
+		b.sc.Connect()
+	} else {
+		b.sc.UpdateAddresses(cs.ResolverState.Addresses)
+		b.sc.Connect()
+	}
+	return nil
+}
+
+func (b *pickfirstBalancer) UpdateSubConnState(sc balancer.SubConn, s balancer.SubConnState) {
+	if grpclog.V(2) {
+		grpclog.Infof("pickfirstBalancer: HandleSubConnStateChange: %p, %v", sc, s)
+	}
+	if b.sc != sc {
+		if grpclog.V(2) {
+			grpclog.Infof("pickfirstBalancer: ignored state change because sc is not recognized")
+		}
+		return
+	}
+	b.state = s.ConnectivityState
+	if s.ConnectivityState == connectivity.Shutdown {
+		b.sc = nil
+		return
+	}
+
+	switch s.ConnectivityState {
+	case connectivity.Ready, connectivity.Idle:
+		b.cc.UpdateState(balancer.State{ConnectivityState: s.ConnectivityState, Picker: &picker{result: balancer.PickResult{SubConn: sc}}})
+	case connectivity.Connecting:
+		b.cc.UpdateState(balancer.State{ConnectivityState: s.ConnectivityState, Picker: &picker{err: balancer.ErrNoSubConnAvailable}})
+	case connectivity.TransientFailure:
+		err := balancer.ErrTransientFailure
+		// TODO: this can be unconditional after the V1 API is removed, as
+		// SubConnState will always contain a connection error.
+		if s.ConnectionError != nil {
+			err = balancer.TransientFailureError(s.ConnectionError)
+		}
+		b.cc.UpdateState(balancer.State{
+			ConnectivityState: s.ConnectivityState,
+			Picker:            &picker{err: err},
+		})
+	}
+}
+
+func (b *pickfirstBalancer) Close() {
+}
+
+type picker struct {
+	result balancer.PickResult
+	err    error
+}
+
+func (p *picker) Pick(info balancer.PickInfo) (balancer.PickResult, error) {
+	return p.result, p.err
+}
+
+func init() {
+	balancer.Register(newPickfirstBuilder())
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/preloader.go b/demo_test/vendor/google.golang.org/grpc/preloader.go
new file mode 100644
index 0000000..76acbbc
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/preloader.go
@@ -0,0 +1,64 @@
+/*
+ *
+ * Copyright 2019 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package grpc
+
+import (
+	"google.golang.org/grpc/codes"
+	"google.golang.org/grpc/status"
+)
+
+// PreparedMsg is responsible for creating a Marshalled and Compressed object.
+//
+// This API is EXPERIMENTAL.
+type PreparedMsg struct {
+	// Struct for preparing msg before sending them
+	encodedData []byte
+	hdr         []byte
+	payload     []byte
+}
+
+// Encode marshalls and compresses the message using the codec and compressor for the stream.
+func (p *PreparedMsg) Encode(s Stream, msg interface{}) error {
+	ctx := s.Context()
+	rpcInfo, ok := rpcInfoFromContext(ctx)
+	if !ok {
+		return status.Errorf(codes.Internal, "grpc: unable to get rpcInfo")
+	}
+
+	// check if the context has the relevant information to prepareMsg
+	if rpcInfo.preloaderInfo == nil {
+		return status.Errorf(codes.Internal, "grpc: rpcInfo.preloaderInfo is nil")
+	}
+	if rpcInfo.preloaderInfo.codec == nil {
+		return status.Errorf(codes.Internal, "grpc: rpcInfo.preloaderInfo.codec is nil")
+	}
+
+	// prepare the msg
+	data, err := encode(rpcInfo.preloaderInfo.codec, msg)
+	if err != nil {
+		return err
+	}
+	p.encodedData = data
+	compData, err := compress(data, rpcInfo.preloaderInfo.cp, rpcInfo.preloaderInfo.comp)
+	if err != nil {
+		return err
+	}
+	p.hdr, p.payload = msgHeader(data, compData)
+	return nil
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/proxy.go b/demo_test/vendor/google.golang.org/grpc/proxy.go
new file mode 100644
index 0000000..f8f69bf
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/proxy.go
@@ -0,0 +1,152 @@
+/*
+ *
+ * Copyright 2017 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package grpc
+
+import (
+	"bufio"
+	"context"
+	"encoding/base64"
+	"errors"
+	"fmt"
+	"io"
+	"net"
+	"net/http"
+	"net/http/httputil"
+	"net/url"
+)
+
+const proxyAuthHeaderKey = "Proxy-Authorization"
+
+var (
+	// errDisabled indicates that proxy is disabled for the address.
+	errDisabled = errors.New("proxy is disabled for the address")
+	// The following variable will be overwritten in the tests.
+	httpProxyFromEnvironment = http.ProxyFromEnvironment
+)
+
+func mapAddress(ctx context.Context, address string) (*url.URL, error) {
+	req := &http.Request{
+		URL: &url.URL{
+			Scheme: "https",
+			Host:   address,
+		},
+	}
+	url, err := httpProxyFromEnvironment(req)
+	if err != nil {
+		return nil, err
+	}
+	if url == nil {
+		return nil, errDisabled
+	}
+	return url, nil
+}
+
+// To read a response from a net.Conn, http.ReadResponse() takes a bufio.Reader.
+// It's possible that this reader reads more than what's need for the response and stores
+// those bytes in the buffer.
+// bufConn wraps the original net.Conn and the bufio.Reader to make sure we don't lose the
+// bytes in the buffer.
+type bufConn struct {
+	net.Conn
+	r io.Reader
+}
+
+func (c *bufConn) Read(b []byte) (int, error) {
+	return c.r.Read(b)
+}
+
+func basicAuth(username, password string) string {
+	auth := username + ":" + password
+	return base64.StdEncoding.EncodeToString([]byte(auth))
+}
+
+func doHTTPConnectHandshake(ctx context.Context, conn net.Conn, backendAddr string, proxyURL *url.URL) (_ net.Conn, err error) {
+	defer func() {
+		if err != nil {
+			conn.Close()
+		}
+	}()
+
+	req := &http.Request{
+		Method: http.MethodConnect,
+		URL:    &url.URL{Host: backendAddr},
+		Header: map[string][]string{"User-Agent": {grpcUA}},
+	}
+	if t := proxyURL.User; t != nil {
+		u := t.Username()
+		p, _ := t.Password()
+		req.Header.Add(proxyAuthHeaderKey, "Basic "+basicAuth(u, p))
+	}
+
+	if err := sendHTTPRequest(ctx, req, conn); err != nil {
+		return nil, fmt.Errorf("failed to write the HTTP request: %v", err)
+	}
+
+	r := bufio.NewReader(conn)
+	resp, err := http.ReadResponse(r, req)
+	if err != nil {
+		return nil, fmt.Errorf("reading server HTTP response: %v", err)
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode != http.StatusOK {
+		dump, err := httputil.DumpResponse(resp, true)
+		if err != nil {
+			return nil, fmt.Errorf("failed to do connect handshake, status code: %s", resp.Status)
+		}
+		return nil, fmt.Errorf("failed to do connect handshake, response: %q", dump)
+	}
+
+	return &bufConn{Conn: conn, r: r}, nil
+}
+
+// newProxyDialer returns a dialer that connects to proxy first if necessary.
+// The returned dialer checks if a proxy is necessary, dial to the proxy with the
+// provided dialer, does HTTP CONNECT handshake and returns the connection.
+func newProxyDialer(dialer func(context.Context, string) (net.Conn, error)) func(context.Context, string) (net.Conn, error) {
+	return func(ctx context.Context, addr string) (conn net.Conn, err error) {
+		var newAddr string
+		proxyURL, err := mapAddress(ctx, addr)
+		if err != nil {
+			if err != errDisabled {
+				return nil, err
+			}
+			newAddr = addr
+		} else {
+			newAddr = proxyURL.Host
+		}
+
+		conn, err = dialer(ctx, newAddr)
+		if err != nil {
+			return
+		}
+		if proxyURL != nil {
+			// proxy is disabled if proxyURL is nil.
+			conn, err = doHTTPConnectHandshake(ctx, conn, addr, proxyURL)
+		}
+		return
+	}
+}
+
+func sendHTTPRequest(ctx context.Context, req *http.Request, conn net.Conn) error {
+	req = req.WithContext(ctx)
+	if err := req.Write(conn); err != nil {
+		return fmt.Errorf("failed to write the HTTP request: %v", err)
+	}
+	return nil
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/resolver/resolver.go b/demo_test/vendor/google.golang.org/grpc/resolver/resolver.go
new file mode 100644
index 0000000..fe14b2f
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/resolver/resolver.go
@@ -0,0 +1,253 @@
+/*
+ *
+ * Copyright 2017 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+// Package resolver defines APIs for name resolution in gRPC.
+// All APIs in this package are experimental.
+package resolver
+
+import (
+	"context"
+	"net"
+
+	"google.golang.org/grpc/attributes"
+	"google.golang.org/grpc/credentials"
+	"google.golang.org/grpc/serviceconfig"
+)
+
+var (
+	// m is a map from scheme to resolver builder.
+	m = make(map[string]Builder)
+	// defaultScheme is the default scheme to use.
+	defaultScheme = "passthrough"
+)
+
+// TODO(bar) install dns resolver in init(){}.
+
+// Register registers the resolver builder to the resolver map. b.Scheme will be
+// used as the scheme registered with this builder.
+//
+// NOTE: this function must only be called during initialization time (i.e. in
+// an init() function), and is not thread-safe. If multiple Resolvers are
+// registered with the same name, the one registered last will take effect.
+func Register(b Builder) {
+	m[b.Scheme()] = b
+}
+
+// Get returns the resolver builder registered with the given scheme.
+//
+// If no builder is register with the scheme, nil will be returned.
+func Get(scheme string) Builder {
+	if b, ok := m[scheme]; ok {
+		return b
+	}
+	return nil
+}
+
+// SetDefaultScheme sets the default scheme that will be used. The default
+// default scheme is "passthrough".
+//
+// NOTE: this function must only be called during initialization time (i.e. in
+// an init() function), and is not thread-safe. The scheme set last overrides
+// previously set values.
+func SetDefaultScheme(scheme string) {
+	defaultScheme = scheme
+}
+
+// GetDefaultScheme gets the default scheme that will be used.
+func GetDefaultScheme() string {
+	return defaultScheme
+}
+
+// AddressType indicates the address type returned by name resolution.
+//
+// Deprecated: use Attributes in Address instead.
+type AddressType uint8
+
+const (
+	// Backend indicates the address is for a backend server.
+	//
+	// Deprecated: use Attributes in Address instead.
+	Backend AddressType = iota
+	// GRPCLB indicates the address is for a grpclb load balancer.
+	//
+	// Deprecated: use Attributes in Address instead.
+	GRPCLB
+)
+
+// Address represents a server the client connects to.
+// This is the EXPERIMENTAL API and may be changed or extended in the future.
+type Address struct {
+	// Addr is the server address on which a connection will be established.
+	Addr string
+
+	// ServerName is the name of this address.
+	// If non-empty, the ServerName is used as the transport certification authority for
+	// the address, instead of the hostname from the Dial target string. In most cases,
+	// this should not be set.
+	//
+	// If Type is GRPCLB, ServerName should be the name of the remote load
+	// balancer, not the name of the backend.
+	//
+	// WARNING: ServerName must only be populated with trusted values. It
+	// is insecure to populate it with data from untrusted inputs since untrusted
+	// values could be used to bypass the authority checks performed by TLS.
+	ServerName string
+
+	// Attributes contains arbitrary data about this address intended for
+	// consumption by the load balancing policy.
+	Attributes *attributes.Attributes
+
+	// Type is the type of this address.
+	//
+	// Deprecated: use Attributes instead.
+	Type AddressType
+
+	// Metadata is the information associated with Addr, which may be used
+	// to make load balancing decision.
+	//
+	// Deprecated: use Attributes instead.
+	Metadata interface{}
+}
+
+// BuildOptions includes additional information for the builder to create
+// the resolver.
+type BuildOptions struct {
+	// DisableServiceConfig indicates whether a resolver implementation should
+	// fetch service config data.
+	DisableServiceConfig bool
+	// DialCreds is the transport credentials used by the ClientConn for
+	// communicating with the target gRPC service (set via
+	// WithTransportCredentials). In cases where a name resolution service
+	// requires the same credentials, the resolver may use this field. In most
+	// cases though, it is not appropriate, and this field may be ignored.
+	DialCreds credentials.TransportCredentials
+	// CredsBundle is the credentials bundle used by the ClientConn for
+	// communicating with the target gRPC service (set via
+	// WithCredentialsBundle). In cases where a name resolution service
+	// requires the same credentials, the resolver may use this field. In most
+	// cases though, it is not appropriate, and this field may be ignored.
+	CredsBundle credentials.Bundle
+	// Dialer is the custom dialer used by the ClientConn for dialling the
+	// target gRPC service (set via WithDialer). In cases where a name
+	// resolution service requires the same dialer, the resolver may use this
+	// field. In most cases though, it is not appropriate, and this field may
+	// be ignored.
+	Dialer func(context.Context, string) (net.Conn, error)
+}
+
+// State contains the current Resolver state relevant to the ClientConn.
+type State struct {
+	// Addresses is the latest set of resolved addresses for the target.
+	Addresses []Address
+
+	// ServiceConfig contains the result from parsing the latest service
+	// config.  If it is nil, it indicates no service config is present or the
+	// resolver does not provide service configs.
+	ServiceConfig *serviceconfig.ParseResult
+
+	// Attributes contains arbitrary data about the resolver intended for
+	// consumption by the load balancing policy.
+	Attributes *attributes.Attributes
+}
+
+// ClientConn contains the callbacks for resolver to notify any updates
+// to the gRPC ClientConn.
+//
+// This interface is to be implemented by gRPC. Users should not need a
+// brand new implementation of this interface. For the situations like
+// testing, the new implementation should embed this interface. This allows
+// gRPC to add new methods to this interface.
+type ClientConn interface {
+	// UpdateState updates the state of the ClientConn appropriately.
+	UpdateState(State)
+	// ReportError notifies the ClientConn that the Resolver encountered an
+	// error.  The ClientConn will notify the load balancer and begin calling
+	// ResolveNow on the Resolver with exponential backoff.
+	ReportError(error)
+	// NewAddress is called by resolver to notify ClientConn a new list
+	// of resolved addresses.
+	// The address list should be the complete list of resolved addresses.
+	//
+	// Deprecated: Use UpdateState instead.
+	NewAddress(addresses []Address)
+	// NewServiceConfig is called by resolver to notify ClientConn a new
+	// service config. The service config should be provided as a json string.
+	//
+	// Deprecated: Use UpdateState instead.
+	NewServiceConfig(serviceConfig string)
+	// ParseServiceConfig parses the provided service config and returns an
+	// object that provides the parsed config.
+	ParseServiceConfig(serviceConfigJSON string) *serviceconfig.ParseResult
+}
+
+// Target represents a target for gRPC, as specified in:
+// https://github.com/grpc/grpc/blob/master/doc/naming.md.
+// It is parsed from the target string that gets passed into Dial or DialContext by the user. And
+// grpc passes it to the resolver and the balancer.
+//
+// If the target follows the naming spec, and the parsed scheme is registered with grpc, we will
+// parse the target string according to the spec. e.g. "dns://some_authority/foo.bar" will be parsed
+// into &Target{Scheme: "dns", Authority: "some_authority", Endpoint: "foo.bar"}
+//
+// If the target does not contain a scheme, we will apply the default scheme, and set the Target to
+// be the full target string. e.g. "foo.bar" will be parsed into
+// &Target{Scheme: resolver.GetDefaultScheme(), Endpoint: "foo.bar"}.
+//
+// If the parsed scheme is not registered (i.e. no corresponding resolver available to resolve the
+// endpoint), we set the Scheme to be the default scheme, and set the Endpoint to be the full target
+// string. e.g. target string "unknown_scheme://authority/endpoint" will be parsed into
+// &Target{Scheme: resolver.GetDefaultScheme(), Endpoint: "unknown_scheme://authority/endpoint"}.
+type Target struct {
+	Scheme    string
+	Authority string
+	Endpoint  string
+}
+
+// Builder creates a resolver that will be used to watch name resolution updates.
+type Builder interface {
+	// Build creates a new resolver for the given target.
+	//
+	// gRPC dial calls Build synchronously, and fails if the returned error is
+	// not nil.
+	Build(target Target, cc ClientConn, opts BuildOptions) (Resolver, error)
+	// Scheme returns the scheme supported by this resolver.
+	// Scheme is defined at https://github.com/grpc/grpc/blob/master/doc/naming.md.
+	Scheme() string
+}
+
+// ResolveNowOptions includes additional information for ResolveNow.
+type ResolveNowOptions struct{}
+
+// Resolver watches for the updates on the specified target.
+// Updates include address updates and service config updates.
+type Resolver interface {
+	// ResolveNow will be called by gRPC to try to resolve the target name
+	// again. It's just a hint, resolver can ignore this if it's not necessary.
+	//
+	// It could be called multiple times concurrently.
+	ResolveNow(ResolveNowOptions)
+	// Close closes the resolver.
+	Close()
+}
+
+// UnregisterForTesting removes the resolver builder with the given scheme from the
+// resolver map.
+// This function is for testing only.
+func UnregisterForTesting(scheme string) {
+	delete(m, scheme)
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/resolver_conn_wrapper.go b/demo_test/vendor/google.golang.org/grpc/resolver_conn_wrapper.go
new file mode 100644
index 0000000..edfda86
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/resolver_conn_wrapper.go
@@ -0,0 +1,222 @@
+/*
+ *
+ * Copyright 2017 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package grpc
+
+import (
+	"fmt"
+	"strings"
+	"sync"
+	"time"
+
+	"google.golang.org/grpc/balancer"
+	"google.golang.org/grpc/credentials"
+	"google.golang.org/grpc/internal/channelz"
+	"google.golang.org/grpc/internal/grpcsync"
+	"google.golang.org/grpc/resolver"
+	"google.golang.org/grpc/serviceconfig"
+)
+
+// ccResolverWrapper is a wrapper on top of cc for resolvers.
+// It implements resolver.ClientConn interface.
+type ccResolverWrapper struct {
+	cc         *ClientConn
+	resolverMu sync.Mutex
+	resolver   resolver.Resolver
+	done       *grpcsync.Event
+	curState   resolver.State
+
+	pollingMu sync.Mutex
+	polling   chan struct{}
+}
+
+// newCCResolverWrapper uses the resolver.Builder to build a Resolver and
+// returns a ccResolverWrapper object which wraps the newly built resolver.
+func newCCResolverWrapper(cc *ClientConn, rb resolver.Builder) (*ccResolverWrapper, error) {
+	ccr := &ccResolverWrapper{
+		cc:   cc,
+		done: grpcsync.NewEvent(),
+	}
+
+	var credsClone credentials.TransportCredentials
+	if creds := cc.dopts.copts.TransportCredentials; creds != nil {
+		credsClone = creds.Clone()
+	}
+	rbo := resolver.BuildOptions{
+		DisableServiceConfig: cc.dopts.disableServiceConfig,
+		DialCreds:            credsClone,
+		CredsBundle:          cc.dopts.copts.CredsBundle,
+		Dialer:               cc.dopts.copts.Dialer,
+	}
+
+	var err error
+	// We need to hold the lock here while we assign to the ccr.resolver field
+	// to guard against a data race caused by the following code path,
+	// rb.Build-->ccr.ReportError-->ccr.poll-->ccr.resolveNow, would end up
+	// accessing ccr.resolver which is being assigned here.
+	ccr.resolverMu.Lock()
+	defer ccr.resolverMu.Unlock()
+	ccr.resolver, err = rb.Build(cc.parsedTarget, ccr, rbo)
+	if err != nil {
+		return nil, err
+	}
+	return ccr, nil
+}
+
+func (ccr *ccResolverWrapper) resolveNow(o resolver.ResolveNowOptions) {
+	ccr.resolverMu.Lock()
+	if !ccr.done.HasFired() {
+		ccr.resolver.ResolveNow(o)
+	}
+	ccr.resolverMu.Unlock()
+}
+
+func (ccr *ccResolverWrapper) close() {
+	ccr.resolverMu.Lock()
+	ccr.resolver.Close()
+	ccr.done.Fire()
+	ccr.resolverMu.Unlock()
+}
+
+// poll begins or ends asynchronous polling of the resolver based on whether
+// err is ErrBadResolverState.
+func (ccr *ccResolverWrapper) poll(err error) {
+	ccr.pollingMu.Lock()
+	defer ccr.pollingMu.Unlock()
+	if err != balancer.ErrBadResolverState {
+		// stop polling
+		if ccr.polling != nil {
+			close(ccr.polling)
+			ccr.polling = nil
+		}
+		return
+	}
+	if ccr.polling != nil {
+		// already polling
+		return
+	}
+	p := make(chan struct{})
+	ccr.polling = p
+	go func() {
+		for i := 0; ; i++ {
+			ccr.resolveNow(resolver.ResolveNowOptions{})
+			t := time.NewTimer(ccr.cc.dopts.resolveNowBackoff(i))
+			select {
+			case <-p:
+				t.Stop()
+				return
+			case <-ccr.done.Done():
+				// Resolver has been closed.
+				t.Stop()
+				return
+			case <-t.C:
+				select {
+				case <-p:
+					return
+				default:
+				}
+				// Timer expired; re-resolve.
+			}
+		}
+	}()
+}
+
+func (ccr *ccResolverWrapper) UpdateState(s resolver.State) {
+	if ccr.done.HasFired() {
+		return
+	}
+	channelz.Infof(ccr.cc.channelzID, "ccResolverWrapper: sending update to cc: %v", s)
+	if channelz.IsOn() {
+		ccr.addChannelzTraceEvent(s)
+	}
+	ccr.curState = s
+	ccr.poll(ccr.cc.updateResolverState(ccr.curState, nil))
+}
+
+func (ccr *ccResolverWrapper) ReportError(err error) {
+	if ccr.done.HasFired() {
+		return
+	}
+	channelz.Warningf(ccr.cc.channelzID, "ccResolverWrapper: reporting error to cc: %v", err)
+	ccr.poll(ccr.cc.updateResolverState(resolver.State{}, err))
+}
+
+// NewAddress is called by the resolver implementation to send addresses to gRPC.
+func (ccr *ccResolverWrapper) NewAddress(addrs []resolver.Address) {
+	if ccr.done.HasFired() {
+		return
+	}
+	channelz.Infof(ccr.cc.channelzID, "ccResolverWrapper: sending new addresses to cc: %v", addrs)
+	if channelz.IsOn() {
+		ccr.addChannelzTraceEvent(resolver.State{Addresses: addrs, ServiceConfig: ccr.curState.ServiceConfig})
+	}
+	ccr.curState.Addresses = addrs
+	ccr.poll(ccr.cc.updateResolverState(ccr.curState, nil))
+}
+
+// NewServiceConfig is called by the resolver implementation to send service
+// configs to gRPC.
+func (ccr *ccResolverWrapper) NewServiceConfig(sc string) {
+	if ccr.done.HasFired() {
+		return
+	}
+	channelz.Infof(ccr.cc.channelzID, "ccResolverWrapper: got new service config: %v", sc)
+	if ccr.cc.dopts.disableServiceConfig {
+		channelz.Info(ccr.cc.channelzID, "Service config lookups disabled; ignoring config")
+		return
+	}
+	scpr := parseServiceConfig(sc)
+	if scpr.Err != nil {
+		channelz.Warningf(ccr.cc.channelzID, "ccResolverWrapper: error parsing service config: %v", scpr.Err)
+		ccr.poll(balancer.ErrBadResolverState)
+		return
+	}
+	if channelz.IsOn() {
+		ccr.addChannelzTraceEvent(resolver.State{Addresses: ccr.curState.Addresses, ServiceConfig: scpr})
+	}
+	ccr.curState.ServiceConfig = scpr
+	ccr.poll(ccr.cc.updateResolverState(ccr.curState, nil))
+}
+
+func (ccr *ccResolverWrapper) ParseServiceConfig(scJSON string) *serviceconfig.ParseResult {
+	return parseServiceConfig(scJSON)
+}
+
+func (ccr *ccResolverWrapper) addChannelzTraceEvent(s resolver.State) {
+	var updates []string
+	var oldSC, newSC *ServiceConfig
+	var oldOK, newOK bool
+	if ccr.curState.ServiceConfig != nil {
+		oldSC, oldOK = ccr.curState.ServiceConfig.Config.(*ServiceConfig)
+	}
+	if s.ServiceConfig != nil {
+		newSC, newOK = s.ServiceConfig.Config.(*ServiceConfig)
+	}
+	if oldOK != newOK || (oldOK && newOK && oldSC.rawJSONString != newSC.rawJSONString) {
+		updates = append(updates, "service config updated")
+	}
+	if len(ccr.curState.Addresses) > 0 && len(s.Addresses) == 0 {
+		updates = append(updates, "resolver returned an empty address list")
+	} else if len(ccr.curState.Addresses) == 0 && len(s.Addresses) > 0 {
+		updates = append(updates, "resolver returned new addresses")
+	}
+	channelz.AddTraceEvent(ccr.cc.channelzID, 0, &channelz.TraceEventDesc{
+		Desc:     fmt.Sprintf("Resolver state updated: %+v (%v)", s, strings.Join(updates, "; ")),
+		Severity: channelz.CtINFO,
+	})
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/rpc_util.go b/demo_test/vendor/google.golang.org/grpc/rpc_util.go
new file mode 100644
index 0000000..cf9dbe7
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/rpc_util.go
@@ -0,0 +1,889 @@
+/*
+ *
+ * Copyright 2014 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package grpc
+
+import (
+	"bytes"
+	"compress/gzip"
+	"context"
+	"encoding/binary"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"math"
+	"net/url"
+	"strings"
+	"sync"
+	"time"
+
+	"google.golang.org/grpc/codes"
+	"google.golang.org/grpc/credentials"
+	"google.golang.org/grpc/encoding"
+	"google.golang.org/grpc/encoding/proto"
+	"google.golang.org/grpc/internal/transport"
+	"google.golang.org/grpc/metadata"
+	"google.golang.org/grpc/peer"
+	"google.golang.org/grpc/stats"
+	"google.golang.org/grpc/status"
+)
+
+// Compressor defines the interface gRPC uses to compress a message.
+//
+// Deprecated: use package encoding.
+type Compressor interface {
+	// Do compresses p into w.
+	Do(w io.Writer, p []byte) error
+	// Type returns the compression algorithm the Compressor uses.
+	Type() string
+}
+
+type gzipCompressor struct {
+	pool sync.Pool
+}
+
+// NewGZIPCompressor creates a Compressor based on GZIP.
+//
+// Deprecated: use package encoding/gzip.
+func NewGZIPCompressor() Compressor {
+	c, _ := NewGZIPCompressorWithLevel(gzip.DefaultCompression)
+	return c
+}
+
+// NewGZIPCompressorWithLevel is like NewGZIPCompressor but specifies the gzip compression level instead
+// of assuming DefaultCompression.
+//
+// The error returned will be nil if the level is valid.
+//
+// Deprecated: use package encoding/gzip.
+func NewGZIPCompressorWithLevel(level int) (Compressor, error) {
+	if level < gzip.DefaultCompression || level > gzip.BestCompression {
+		return nil, fmt.Errorf("grpc: invalid compression level: %d", level)
+	}
+	return &gzipCompressor{
+		pool: sync.Pool{
+			New: func() interface{} {
+				w, err := gzip.NewWriterLevel(ioutil.Discard, level)
+				if err != nil {
+					panic(err)
+				}
+				return w
+			},
+		},
+	}, nil
+}
+
+func (c *gzipCompressor) Do(w io.Writer, p []byte) error {
+	z := c.pool.Get().(*gzip.Writer)
+	defer c.pool.Put(z)
+	z.Reset(w)
+	if _, err := z.Write(p); err != nil {
+		return err
+	}
+	return z.Close()
+}
+
+func (c *gzipCompressor) Type() string {
+	return "gzip"
+}
+
+// Decompressor defines the interface gRPC uses to decompress a message.
+//
+// Deprecated: use package encoding.
+type Decompressor interface {
+	// Do reads the data from r and uncompress them.
+	Do(r io.Reader) ([]byte, error)
+	// Type returns the compression algorithm the Decompressor uses.
+	Type() string
+}
+
+type gzipDecompressor struct {
+	pool sync.Pool
+}
+
+// NewGZIPDecompressor creates a Decompressor based on GZIP.
+//
+// Deprecated: use package encoding/gzip.
+func NewGZIPDecompressor() Decompressor {
+	return &gzipDecompressor{}
+}
+
+func (d *gzipDecompressor) Do(r io.Reader) ([]byte, error) {
+	var z *gzip.Reader
+	switch maybeZ := d.pool.Get().(type) {
+	case nil:
+		newZ, err := gzip.NewReader(r)
+		if err != nil {
+			return nil, err
+		}
+		z = newZ
+	case *gzip.Reader:
+		z = maybeZ
+		if err := z.Reset(r); err != nil {
+			d.pool.Put(z)
+			return nil, err
+		}
+	}
+
+	defer func() {
+		z.Close()
+		d.pool.Put(z)
+	}()
+	return ioutil.ReadAll(z)
+}
+
+func (d *gzipDecompressor) Type() string {
+	return "gzip"
+}
+
+// callInfo contains all related configuration and information about an RPC.
+type callInfo struct {
+	compressorType        string
+	failFast              bool
+	stream                ClientStream
+	maxReceiveMessageSize *int
+	maxSendMessageSize    *int
+	creds                 credentials.PerRPCCredentials
+	contentSubtype        string
+	codec                 baseCodec
+	maxRetryRPCBufferSize int
+}
+
+func defaultCallInfo() *callInfo {
+	return &callInfo{
+		failFast:              true,
+		maxRetryRPCBufferSize: 256 * 1024, // 256KB
+	}
+}
+
+// CallOption configures a Call before it starts or extracts information from
+// a Call after it completes.
+type CallOption interface {
+	// before is called before the call is sent to any server.  If before
+	// returns a non-nil error, the RPC fails with that error.
+	before(*callInfo) error
+
+	// after is called after the call has completed.  after cannot return an
+	// error, so any failures should be reported via output parameters.
+	after(*callInfo)
+}
+
+// EmptyCallOption does not alter the Call configuration.
+// It can be embedded in another structure to carry satellite data for use
+// by interceptors.
+type EmptyCallOption struct{}
+
+func (EmptyCallOption) before(*callInfo) error { return nil }
+func (EmptyCallOption) after(*callInfo)        {}
+
+// Header returns a CallOptions that retrieves the header metadata
+// for a unary RPC.
+func Header(md *metadata.MD) CallOption {
+	return HeaderCallOption{HeaderAddr: md}
+}
+
+// HeaderCallOption is a CallOption for collecting response header metadata.
+// The metadata field will be populated *after* the RPC completes.
+// This is an EXPERIMENTAL API.
+type HeaderCallOption struct {
+	HeaderAddr *metadata.MD
+}
+
+func (o HeaderCallOption) before(c *callInfo) error { return nil }
+func (o HeaderCallOption) after(c *callInfo) {
+	if c.stream != nil {
+		*o.HeaderAddr, _ = c.stream.Header()
+	}
+}
+
+// Trailer returns a CallOptions that retrieves the trailer metadata
+// for a unary RPC.
+func Trailer(md *metadata.MD) CallOption {
+	return TrailerCallOption{TrailerAddr: md}
+}
+
+// TrailerCallOption is a CallOption for collecting response trailer metadata.
+// The metadata field will be populated *after* the RPC completes.
+// This is an EXPERIMENTAL API.
+type TrailerCallOption struct {
+	TrailerAddr *metadata.MD
+}
+
+func (o TrailerCallOption) before(c *callInfo) error { return nil }
+func (o TrailerCallOption) after(c *callInfo) {
+	if c.stream != nil {
+		*o.TrailerAddr = c.stream.Trailer()
+	}
+}
+
+// Peer returns a CallOption that retrieves peer information for a unary RPC.
+// The peer field will be populated *after* the RPC completes.
+func Peer(p *peer.Peer) CallOption {
+	return PeerCallOption{PeerAddr: p}
+}
+
+// PeerCallOption is a CallOption for collecting the identity of the remote
+// peer. The peer field will be populated *after* the RPC completes.
+// This is an EXPERIMENTAL API.
+type PeerCallOption struct {
+	PeerAddr *peer.Peer
+}
+
+func (o PeerCallOption) before(c *callInfo) error { return nil }
+func (o PeerCallOption) after(c *callInfo) {
+	if c.stream != nil {
+		if x, ok := peer.FromContext(c.stream.Context()); ok {
+			*o.PeerAddr = *x
+		}
+	}
+}
+
+// WaitForReady configures the action to take when an RPC is attempted on broken
+// connections or unreachable servers. If waitForReady is false, the RPC will fail
+// immediately. Otherwise, the RPC client will block the call until a
+// connection is available (or the call is canceled or times out) and will
+// retry the call if it fails due to a transient error.  gRPC will not retry if
+// data was written to the wire unless the server indicates it did not process
+// the data.  Please refer to
+// https://github.com/grpc/grpc/blob/master/doc/wait-for-ready.md.
+//
+// By default, RPCs don't "wait for ready".
+func WaitForReady(waitForReady bool) CallOption {
+	return FailFastCallOption{FailFast: !waitForReady}
+}
+
+// FailFast is the opposite of WaitForReady.
+//
+// Deprecated: use WaitForReady.
+func FailFast(failFast bool) CallOption {
+	return FailFastCallOption{FailFast: failFast}
+}
+
+// FailFastCallOption is a CallOption for indicating whether an RPC should fail
+// fast or not.
+// This is an EXPERIMENTAL API.
+type FailFastCallOption struct {
+	FailFast bool
+}
+
+func (o FailFastCallOption) before(c *callInfo) error {
+	c.failFast = o.FailFast
+	return nil
+}
+func (o FailFastCallOption) after(c *callInfo) {}
+
+// MaxCallRecvMsgSize returns a CallOption which sets the maximum message size
+// in bytes the client can receive.
+func MaxCallRecvMsgSize(bytes int) CallOption {
+	return MaxRecvMsgSizeCallOption{MaxRecvMsgSize: bytes}
+}
+
+// MaxRecvMsgSizeCallOption is a CallOption that indicates the maximum message
+// size in bytes the client can receive.
+// This is an EXPERIMENTAL API.
+type MaxRecvMsgSizeCallOption struct {
+	MaxRecvMsgSize int
+}
+
+func (o MaxRecvMsgSizeCallOption) before(c *callInfo) error {
+	c.maxReceiveMessageSize = &o.MaxRecvMsgSize
+	return nil
+}
+func (o MaxRecvMsgSizeCallOption) after(c *callInfo) {}
+
+// MaxCallSendMsgSize returns a CallOption which sets the maximum message size
+// in bytes the client can send.
+func MaxCallSendMsgSize(bytes int) CallOption {
+	return MaxSendMsgSizeCallOption{MaxSendMsgSize: bytes}
+}
+
+// MaxSendMsgSizeCallOption is a CallOption that indicates the maximum message
+// size in bytes the client can send.
+// This is an EXPERIMENTAL API.
+type MaxSendMsgSizeCallOption struct {
+	MaxSendMsgSize int
+}
+
+func (o MaxSendMsgSizeCallOption) before(c *callInfo) error {
+	c.maxSendMessageSize = &o.MaxSendMsgSize
+	return nil
+}
+func (o MaxSendMsgSizeCallOption) after(c *callInfo) {}
+
+// PerRPCCredentials returns a CallOption that sets credentials.PerRPCCredentials
+// for a call.
+func PerRPCCredentials(creds credentials.PerRPCCredentials) CallOption {
+	return PerRPCCredsCallOption{Creds: creds}
+}
+
+// PerRPCCredsCallOption is a CallOption that indicates the per-RPC
+// credentials to use for the call.
+// This is an EXPERIMENTAL API.
+type PerRPCCredsCallOption struct {
+	Creds credentials.PerRPCCredentials
+}
+
+func (o PerRPCCredsCallOption) before(c *callInfo) error {
+	c.creds = o.Creds
+	return nil
+}
+func (o PerRPCCredsCallOption) after(c *callInfo) {}
+
+// UseCompressor returns a CallOption which sets the compressor used when
+// sending the request.  If WithCompressor is also set, UseCompressor has
+// higher priority.
+//
+// This API is EXPERIMENTAL.
+func UseCompressor(name string) CallOption {
+	return CompressorCallOption{CompressorType: name}
+}
+
+// CompressorCallOption is a CallOption that indicates the compressor to use.
+// This is an EXPERIMENTAL API.
+type CompressorCallOption struct {
+	CompressorType string
+}
+
+func (o CompressorCallOption) before(c *callInfo) error {
+	c.compressorType = o.CompressorType
+	return nil
+}
+func (o CompressorCallOption) after(c *callInfo) {}
+
+// CallContentSubtype returns a CallOption that will set the content-subtype
+// for a call. For example, if content-subtype is "json", the Content-Type over
+// the wire will be "application/grpc+json". The content-subtype is converted
+// to lowercase before being included in Content-Type. See Content-Type on
+// https://github.com/grpc/grpc/blob/master/doc/PROTOCOL-HTTP2.md#requests for
+// more details.
+//
+// If ForceCodec is not also used, the content-subtype will be used to look up
+// the Codec to use in the registry controlled by RegisterCodec. See the
+// documentation on RegisterCodec for details on registration. The lookup of
+// content-subtype is case-insensitive. If no such Codec is found, the call
+// will result in an error with code codes.Internal.
+//
+// If ForceCodec is also used, that Codec will be used for all request and
+// response messages, with the content-subtype set to the given contentSubtype
+// here for requests.
+func CallContentSubtype(contentSubtype string) CallOption {
+	return ContentSubtypeCallOption{ContentSubtype: strings.ToLower(contentSubtype)}
+}
+
+// ContentSubtypeCallOption is a CallOption that indicates the content-subtype
+// used for marshaling messages.
+// This is an EXPERIMENTAL API.
+type ContentSubtypeCallOption struct {
+	ContentSubtype string
+}
+
+func (o ContentSubtypeCallOption) before(c *callInfo) error {
+	c.contentSubtype = o.ContentSubtype
+	return nil
+}
+func (o ContentSubtypeCallOption) after(c *callInfo) {}
+
+// ForceCodec returns a CallOption that will set the given Codec to be
+// used for all request and response messages for a call. The result of calling
+// String() will be used as the content-subtype in a case-insensitive manner.
+//
+// See Content-Type on
+// https://github.com/grpc/grpc/blob/master/doc/PROTOCOL-HTTP2.md#requests for
+// more details. Also see the documentation on RegisterCodec and
+// CallContentSubtype for more details on the interaction between Codec and
+// content-subtype.
+//
+// This function is provided for advanced users; prefer to use only
+// CallContentSubtype to select a registered codec instead.
+//
+// This is an EXPERIMENTAL API.
+func ForceCodec(codec encoding.Codec) CallOption {
+	return ForceCodecCallOption{Codec: codec}
+}
+
+// ForceCodecCallOption is a CallOption that indicates the codec used for
+// marshaling messages.
+//
+// This is an EXPERIMENTAL API.
+type ForceCodecCallOption struct {
+	Codec encoding.Codec
+}
+
+func (o ForceCodecCallOption) before(c *callInfo) error {
+	c.codec = o.Codec
+	return nil
+}
+func (o ForceCodecCallOption) after(c *callInfo) {}
+
+// CallCustomCodec behaves like ForceCodec, but accepts a grpc.Codec instead of
+// an encoding.Codec.
+//
+// Deprecated: use ForceCodec instead.
+func CallCustomCodec(codec Codec) CallOption {
+	return CustomCodecCallOption{Codec: codec}
+}
+
+// CustomCodecCallOption is a CallOption that indicates the codec used for
+// marshaling messages.
+//
+// This is an EXPERIMENTAL API.
+type CustomCodecCallOption struct {
+	Codec Codec
+}
+
+func (o CustomCodecCallOption) before(c *callInfo) error {
+	c.codec = o.Codec
+	return nil
+}
+func (o CustomCodecCallOption) after(c *callInfo) {}
+
+// MaxRetryRPCBufferSize returns a CallOption that limits the amount of memory
+// used for buffering this RPC's requests for retry purposes.
+//
+// This API is EXPERIMENTAL.
+func MaxRetryRPCBufferSize(bytes int) CallOption {
+	return MaxRetryRPCBufferSizeCallOption{bytes}
+}
+
+// MaxRetryRPCBufferSizeCallOption is a CallOption indicating the amount of
+// memory to be used for caching this RPC for retry purposes.
+// This is an EXPERIMENTAL API.
+type MaxRetryRPCBufferSizeCallOption struct {
+	MaxRetryRPCBufferSize int
+}
+
+func (o MaxRetryRPCBufferSizeCallOption) before(c *callInfo) error {
+	c.maxRetryRPCBufferSize = o.MaxRetryRPCBufferSize
+	return nil
+}
+func (o MaxRetryRPCBufferSizeCallOption) after(c *callInfo) {}
+
+// The format of the payload: compressed or not?
+type payloadFormat uint8
+
+const (
+	compressionNone payloadFormat = 0 // no compression
+	compressionMade payloadFormat = 1 // compressed
+)
+
+// parser reads complete gRPC messages from the underlying reader.
+type parser struct {
+	// r is the underlying reader.
+	// See the comment on recvMsg for the permissible
+	// error types.
+	r io.Reader
+
+	// The header of a gRPC message. Find more detail at
+	// https://github.com/grpc/grpc/blob/master/doc/PROTOCOL-HTTP2.md
+	header [5]byte
+}
+
+// recvMsg reads a complete gRPC message from the stream.
+//
+// It returns the message and its payload (compression/encoding)
+// format. The caller owns the returned msg memory.
+//
+// If there is an error, possible values are:
+//   * io.EOF, when no messages remain
+//   * io.ErrUnexpectedEOF
+//   * of type transport.ConnectionError
+//   * an error from the status package
+// No other error values or types must be returned, which also means
+// that the underlying io.Reader must not return an incompatible
+// error.
+func (p *parser) recvMsg(maxReceiveMessageSize int) (pf payloadFormat, msg []byte, err error) {
+	if _, err := p.r.Read(p.header[:]); err != nil {
+		return 0, nil, err
+	}
+
+	pf = payloadFormat(p.header[0])
+	length := binary.BigEndian.Uint32(p.header[1:])
+
+	if length == 0 {
+		return pf, nil, nil
+	}
+	if int64(length) > int64(maxInt) {
+		return 0, nil, status.Errorf(codes.ResourceExhausted, "grpc: received message larger than max length allowed on current machine (%d vs. %d)", length, maxInt)
+	}
+	if int(length) > maxReceiveMessageSize {
+		return 0, nil, status.Errorf(codes.ResourceExhausted, "grpc: received message larger than max (%d vs. %d)", length, maxReceiveMessageSize)
+	}
+	// TODO(bradfitz,zhaoq): garbage. reuse buffer after proto decoding instead
+	// of making it for each message:
+	msg = make([]byte, int(length))
+	if _, err := p.r.Read(msg); err != nil {
+		if err == io.EOF {
+			err = io.ErrUnexpectedEOF
+		}
+		return 0, nil, err
+	}
+	return pf, msg, nil
+}
+
+// encode serializes msg and returns a buffer containing the message, or an
+// error if it is too large to be transmitted by grpc.  If msg is nil, it
+// generates an empty message.
+func encode(c baseCodec, msg interface{}) ([]byte, error) {
+	if msg == nil { // NOTE: typed nils will not be caught by this check
+		return nil, nil
+	}
+	b, err := c.Marshal(msg)
+	if err != nil {
+		return nil, status.Errorf(codes.Internal, "grpc: error while marshaling: %v", err.Error())
+	}
+	if uint(len(b)) > math.MaxUint32 {
+		return nil, status.Errorf(codes.ResourceExhausted, "grpc: message too large (%d bytes)", len(b))
+	}
+	return b, nil
+}
+
+// compress returns the input bytes compressed by compressor or cp.  If both
+// compressors are nil, returns nil.
+//
+// TODO(dfawley): eliminate cp parameter by wrapping Compressor in an encoding.Compressor.
+func compress(in []byte, cp Compressor, compressor encoding.Compressor) ([]byte, error) {
+	if compressor == nil && cp == nil {
+		return nil, nil
+	}
+	wrapErr := func(err error) error {
+		return status.Errorf(codes.Internal, "grpc: error while compressing: %v", err.Error())
+	}
+	cbuf := &bytes.Buffer{}
+	if compressor != nil {
+		z, err := compressor.Compress(cbuf)
+		if err != nil {
+			return nil, wrapErr(err)
+		}
+		if _, err := z.Write(in); err != nil {
+			return nil, wrapErr(err)
+		}
+		if err := z.Close(); err != nil {
+			return nil, wrapErr(err)
+		}
+	} else {
+		if err := cp.Do(cbuf, in); err != nil {
+			return nil, wrapErr(err)
+		}
+	}
+	return cbuf.Bytes(), nil
+}
+
+const (
+	payloadLen = 1
+	sizeLen    = 4
+	headerLen  = payloadLen + sizeLen
+)
+
+// msgHeader returns a 5-byte header for the message being transmitted and the
+// payload, which is compData if non-nil or data otherwise.
+func msgHeader(data, compData []byte) (hdr []byte, payload []byte) {
+	hdr = make([]byte, headerLen)
+	if compData != nil {
+		hdr[0] = byte(compressionMade)
+		data = compData
+	} else {
+		hdr[0] = byte(compressionNone)
+	}
+
+	// Write length of payload into buf
+	binary.BigEndian.PutUint32(hdr[payloadLen:], uint32(len(data)))
+	return hdr, data
+}
+
+func outPayload(client bool, msg interface{}, data, payload []byte, t time.Time) *stats.OutPayload {
+	return &stats.OutPayload{
+		Client:     client,
+		Payload:    msg,
+		Data:       data,
+		Length:     len(data),
+		WireLength: len(payload) + headerLen,
+		SentTime:   t,
+	}
+}
+
+func checkRecvPayload(pf payloadFormat, recvCompress string, haveCompressor bool) *status.Status {
+	switch pf {
+	case compressionNone:
+	case compressionMade:
+		if recvCompress == "" || recvCompress == encoding.Identity {
+			return status.New(codes.Internal, "grpc: compressed flag set with identity or empty encoding")
+		}
+		if !haveCompressor {
+			return status.Newf(codes.Unimplemented, "grpc: Decompressor is not installed for grpc-encoding %q", recvCompress)
+		}
+	default:
+		return status.Newf(codes.Internal, "grpc: received unexpected payload format %d", pf)
+	}
+	return nil
+}
+
+type payloadInfo struct {
+	wireLength        int // The compressed length got from wire.
+	uncompressedBytes []byte
+}
+
+func recvAndDecompress(p *parser, s *transport.Stream, dc Decompressor, maxReceiveMessageSize int, payInfo *payloadInfo, compressor encoding.Compressor) ([]byte, error) {
+	pf, d, err := p.recvMsg(maxReceiveMessageSize)
+	if err != nil {
+		return nil, err
+	}
+	if payInfo != nil {
+		payInfo.wireLength = len(d)
+	}
+
+	if st := checkRecvPayload(pf, s.RecvCompress(), compressor != nil || dc != nil); st != nil {
+		return nil, st.Err()
+	}
+
+	var size int
+	if pf == compressionMade {
+		// To match legacy behavior, if the decompressor is set by WithDecompressor or RPCDecompressor,
+		// use this decompressor as the default.
+		if dc != nil {
+			d, err = dc.Do(bytes.NewReader(d))
+			size = len(d)
+		} else {
+			d, size, err = decompress(compressor, d, maxReceiveMessageSize)
+		}
+		if err != nil {
+			return nil, status.Errorf(codes.Internal, "grpc: failed to decompress the received message %v", err)
+		}
+	} else {
+		size = len(d)
+	}
+	if size > maxReceiveMessageSize {
+		// TODO: Revisit the error code. Currently keep it consistent with java
+		// implementation.
+		return nil, status.Errorf(codes.ResourceExhausted, "grpc: received message larger than max (%d vs. %d)", size, maxReceiveMessageSize)
+	}
+	return d, nil
+}
+
+// Using compressor, decompress d, returning data and size.
+// Optionally, if data will be over maxReceiveMessageSize, just return the size.
+func decompress(compressor encoding.Compressor, d []byte, maxReceiveMessageSize int) ([]byte, int, error) {
+	dcReader, err := compressor.Decompress(bytes.NewReader(d))
+	if err != nil {
+		return nil, 0, err
+	}
+	if sizer, ok := compressor.(interface {
+		DecompressedSize(compressedBytes []byte) int
+	}); ok {
+		if size := sizer.DecompressedSize(d); size >= 0 {
+			if size > maxReceiveMessageSize {
+				return nil, size, nil
+			}
+			// size is used as an estimate to size the buffer, but we
+			// will read more data if available.
+			// +MinRead so ReadFrom will not reallocate if size is correct.
+			buf := bytes.NewBuffer(make([]byte, 0, size+bytes.MinRead))
+			bytesRead, err := buf.ReadFrom(io.LimitReader(dcReader, int64(maxReceiveMessageSize)+1))
+			return buf.Bytes(), int(bytesRead), err
+		}
+	}
+	// Read from LimitReader with limit max+1. So if the underlying
+	// reader is over limit, the result will be bigger than max.
+	d, err = ioutil.ReadAll(io.LimitReader(dcReader, int64(maxReceiveMessageSize)+1))
+	return d, len(d), err
+}
+
+// For the two compressor parameters, both should not be set, but if they are,
+// dc takes precedence over compressor.
+// TODO(dfawley): wrap the old compressor/decompressor using the new API?
+func recv(p *parser, c baseCodec, s *transport.Stream, dc Decompressor, m interface{}, maxReceiveMessageSize int, payInfo *payloadInfo, compressor encoding.Compressor) error {
+	d, err := recvAndDecompress(p, s, dc, maxReceiveMessageSize, payInfo, compressor)
+	if err != nil {
+		return err
+	}
+	if err := c.Unmarshal(d, m); err != nil {
+		return status.Errorf(codes.Internal, "grpc: failed to unmarshal the received message %v", err)
+	}
+	if payInfo != nil {
+		payInfo.uncompressedBytes = d
+	}
+	return nil
+}
+
+// Information about RPC
+type rpcInfo struct {
+	failfast      bool
+	preloaderInfo *compressorInfo
+}
+
+// Information about Preloader
+// Responsible for storing codec, and compressors
+// If stream (s) has  context s.Context which stores rpcInfo that has non nil
+// pointers to codec, and compressors, then we can use preparedMsg for Async message prep
+// and reuse marshalled bytes
+type compressorInfo struct {
+	codec baseCodec
+	cp    Compressor
+	comp  encoding.Compressor
+}
+
+type rpcInfoContextKey struct{}
+
+func newContextWithRPCInfo(ctx context.Context, failfast bool, codec baseCodec, cp Compressor, comp encoding.Compressor) context.Context {
+	return context.WithValue(ctx, rpcInfoContextKey{}, &rpcInfo{
+		failfast: failfast,
+		preloaderInfo: &compressorInfo{
+			codec: codec,
+			cp:    cp,
+			comp:  comp,
+		},
+	})
+}
+
+func rpcInfoFromContext(ctx context.Context) (s *rpcInfo, ok bool) {
+	s, ok = ctx.Value(rpcInfoContextKey{}).(*rpcInfo)
+	return
+}
+
+// Code returns the error code for err if it was produced by the rpc system.
+// Otherwise, it returns codes.Unknown.
+//
+// Deprecated: use status.Code instead.
+func Code(err error) codes.Code {
+	return status.Code(err)
+}
+
+// ErrorDesc returns the error description of err if it was produced by the rpc system.
+// Otherwise, it returns err.Error() or empty string when err is nil.
+//
+// Deprecated: use status.Convert and Message method instead.
+func ErrorDesc(err error) string {
+	return status.Convert(err).Message()
+}
+
+// Errorf returns an error containing an error code and a description;
+// Errorf returns nil if c is OK.
+//
+// Deprecated: use status.Errorf instead.
+func Errorf(c codes.Code, format string, a ...interface{}) error {
+	return status.Errorf(c, format, a...)
+}
+
+// toRPCErr converts an error into an error from the status package.
+func toRPCErr(err error) error {
+	if err == nil || err == io.EOF {
+		return err
+	}
+	if err == io.ErrUnexpectedEOF {
+		return status.Error(codes.Internal, err.Error())
+	}
+	if _, ok := status.FromError(err); ok {
+		return err
+	}
+	switch e := err.(type) {
+	case transport.ConnectionError:
+		return status.Error(codes.Unavailable, e.Desc)
+	default:
+		switch err {
+		case context.DeadlineExceeded:
+			return status.Error(codes.DeadlineExceeded, err.Error())
+		case context.Canceled:
+			return status.Error(codes.Canceled, err.Error())
+		}
+	}
+	return status.Error(codes.Unknown, err.Error())
+}
+
+// setCallInfoCodec should only be called after CallOptions have been applied.
+func setCallInfoCodec(c *callInfo) error {
+	if c.codec != nil {
+		// codec was already set by a CallOption; use it.
+		return nil
+	}
+
+	if c.contentSubtype == "" {
+		// No codec specified in CallOptions; use proto by default.
+		c.codec = encoding.GetCodec(proto.Name)
+		return nil
+	}
+
+	// c.contentSubtype is already lowercased in CallContentSubtype
+	c.codec = encoding.GetCodec(c.contentSubtype)
+	if c.codec == nil {
+		return status.Errorf(codes.Internal, "no codec registered for content-subtype %s", c.contentSubtype)
+	}
+	return nil
+}
+
+// parseDialTarget returns the network and address to pass to dialer
+func parseDialTarget(target string) (net string, addr string) {
+	net = "tcp"
+
+	m1 := strings.Index(target, ":")
+	m2 := strings.Index(target, ":/")
+
+	// handle unix:addr which will fail with url.Parse
+	if m1 >= 0 && m2 < 0 {
+		if n := target[0:m1]; n == "unix" {
+			net = n
+			addr = target[m1+1:]
+			return net, addr
+		}
+	}
+	if m2 >= 0 {
+		t, err := url.Parse(target)
+		if err != nil {
+			return net, target
+		}
+		scheme := t.Scheme
+		addr = t.Path
+		if scheme == "unix" {
+			net = scheme
+			if addr == "" {
+				addr = t.Host
+			}
+			return net, addr
+		}
+	}
+
+	return net, target
+}
+
+// channelzData is used to store channelz related data for ClientConn, addrConn and Server.
+// These fields cannot be embedded in the original structs (e.g. ClientConn), since to do atomic
+// operation on int64 variable on 32-bit machine, user is responsible to enforce memory alignment.
+// Here, by grouping those int64 fields inside a struct, we are enforcing the alignment.
+type channelzData struct {
+	callsStarted   int64
+	callsFailed    int64
+	callsSucceeded int64
+	// lastCallStartedTime stores the timestamp that last call starts. It is of int64 type instead of
+	// time.Time since it's more costly to atomically update time.Time variable than int64 variable.
+	lastCallStartedTime int64
+}
+
+// The SupportPackageIsVersion variables are referenced from generated protocol
+// buffer files to ensure compatibility with the gRPC version used.  The latest
+// support package version is 6.
+//
+// Older versions are kept for compatibility. They may be removed if
+// compatibility cannot be maintained.
+//
+// These constants should not be referenced from any other code.
+const (
+	SupportPackageIsVersion3 = true
+	SupportPackageIsVersion4 = true
+	SupportPackageIsVersion5 = true
+	SupportPackageIsVersion6 = true
+)
+
+const grpcUA = "grpc-go/" + Version
diff --git a/demo_test/vendor/google.golang.org/grpc/server.go b/demo_test/vendor/google.golang.org/grpc/server.go
new file mode 100644
index 0000000..edfcdca
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/server.go
@@ -0,0 +1,1640 @@
+/*
+ *
+ * Copyright 2014 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package grpc
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"io"
+	"math"
+	"net"
+	"net/http"
+	"reflect"
+	"runtime"
+	"strings"
+	"sync"
+	"sync/atomic"
+	"time"
+
+	"golang.org/x/net/trace"
+
+	"google.golang.org/grpc/codes"
+	"google.golang.org/grpc/credentials"
+	"google.golang.org/grpc/encoding"
+	"google.golang.org/grpc/encoding/proto"
+	"google.golang.org/grpc/grpclog"
+	"google.golang.org/grpc/internal/binarylog"
+	"google.golang.org/grpc/internal/channelz"
+	"google.golang.org/grpc/internal/grpcsync"
+	"google.golang.org/grpc/internal/transport"
+	"google.golang.org/grpc/keepalive"
+	"google.golang.org/grpc/metadata"
+	"google.golang.org/grpc/peer"
+	"google.golang.org/grpc/stats"
+	"google.golang.org/grpc/status"
+	"google.golang.org/grpc/tap"
+)
+
+const (
+	defaultServerMaxReceiveMessageSize = 1024 * 1024 * 4
+	defaultServerMaxSendMessageSize    = math.MaxInt32
+)
+
+var statusOK = status.New(codes.OK, "")
+
+type methodHandler func(srv interface{}, ctx context.Context, dec func(interface{}) error, interceptor UnaryServerInterceptor) (interface{}, error)
+
+// MethodDesc represents an RPC service's method specification.
+type MethodDesc struct {
+	MethodName string
+	Handler    methodHandler
+}
+
+// ServiceDesc represents an RPC service's specification.
+type ServiceDesc struct {
+	ServiceName string
+	// The pointer to the service interface. Used to check whether the user
+	// provided implementation satisfies the interface requirements.
+	HandlerType interface{}
+	Methods     []MethodDesc
+	Streams     []StreamDesc
+	Metadata    interface{}
+}
+
+// service consists of the information of the server serving this service and
+// the methods in this service.
+type service struct {
+	server interface{} // the server for service methods
+	md     map[string]*MethodDesc
+	sd     map[string]*StreamDesc
+	mdata  interface{}
+}
+
+// Server is a gRPC server to serve RPC requests.
+type Server struct {
+	opts serverOptions
+
+	mu     sync.Mutex // guards following
+	lis    map[net.Listener]bool
+	conns  map[transport.ServerTransport]bool
+	serve  bool
+	drain  bool
+	cv     *sync.Cond          // signaled when connections close for GracefulStop
+	m      map[string]*service // service name -> service info
+	events trace.EventLog
+
+	quit               *grpcsync.Event
+	done               *grpcsync.Event
+	channelzRemoveOnce sync.Once
+	serveWG            sync.WaitGroup // counts active Serve goroutines for GracefulStop
+
+	channelzID int64 // channelz unique identification number
+	czData     *channelzData
+}
+
+type serverOptions struct {
+	creds                 credentials.TransportCredentials
+	codec                 baseCodec
+	cp                    Compressor
+	dc                    Decompressor
+	unaryInt              UnaryServerInterceptor
+	streamInt             StreamServerInterceptor
+	chainUnaryInts        []UnaryServerInterceptor
+	chainStreamInts       []StreamServerInterceptor
+	inTapHandle           tap.ServerInHandle
+	statsHandler          stats.Handler
+	maxConcurrentStreams  uint32
+	maxReceiveMessageSize int
+	maxSendMessageSize    int
+	unknownStreamDesc     *StreamDesc
+	keepaliveParams       keepalive.ServerParameters
+	keepalivePolicy       keepalive.EnforcementPolicy
+	initialWindowSize     int32
+	initialConnWindowSize int32
+	writeBufferSize       int
+	readBufferSize        int
+	connectionTimeout     time.Duration
+	maxHeaderListSize     *uint32
+	headerTableSize       *uint32
+}
+
+var defaultServerOptions = serverOptions{
+	maxReceiveMessageSize: defaultServerMaxReceiveMessageSize,
+	maxSendMessageSize:    defaultServerMaxSendMessageSize,
+	connectionTimeout:     120 * time.Second,
+	writeBufferSize:       defaultWriteBufSize,
+	readBufferSize:        defaultReadBufSize,
+}
+
+// A ServerOption sets options such as credentials, codec and keepalive parameters, etc.
+type ServerOption interface {
+	apply(*serverOptions)
+}
+
+// EmptyServerOption does not alter the server configuration. It can be embedded
+// in another structure to build custom server options.
+//
+// This API is EXPERIMENTAL.
+type EmptyServerOption struct{}
+
+func (EmptyServerOption) apply(*serverOptions) {}
+
+// funcServerOption wraps a function that modifies serverOptions into an
+// implementation of the ServerOption interface.
+type funcServerOption struct {
+	f func(*serverOptions)
+}
+
+func (fdo *funcServerOption) apply(do *serverOptions) {
+	fdo.f(do)
+}
+
+func newFuncServerOption(f func(*serverOptions)) *funcServerOption {
+	return &funcServerOption{
+		f: f,
+	}
+}
+
+// WriteBufferSize determines how much data can be batched before doing a write on the wire.
+// The corresponding memory allocation for this buffer will be twice the size to keep syscalls low.
+// The default value for this buffer is 32KB.
+// Zero will disable the write buffer such that each write will be on underlying connection.
+// Note: A Send call may not directly translate to a write.
+func WriteBufferSize(s int) ServerOption {
+	return newFuncServerOption(func(o *serverOptions) {
+		o.writeBufferSize = s
+	})
+}
+
+// ReadBufferSize lets you set the size of read buffer, this determines how much data can be read at most
+// for one read syscall.
+// The default value for this buffer is 32KB.
+// Zero will disable read buffer for a connection so data framer can access the underlying
+// conn directly.
+func ReadBufferSize(s int) ServerOption {
+	return newFuncServerOption(func(o *serverOptions) {
+		o.readBufferSize = s
+	})
+}
+
+// InitialWindowSize returns a ServerOption that sets window size for stream.
+// The lower bound for window size is 64K and any value smaller than that will be ignored.
+func InitialWindowSize(s int32) ServerOption {
+	return newFuncServerOption(func(o *serverOptions) {
+		o.initialWindowSize = s
+	})
+}
+
+// InitialConnWindowSize returns a ServerOption that sets window size for a connection.
+// The lower bound for window size is 64K and any value smaller than that will be ignored.
+func InitialConnWindowSize(s int32) ServerOption {
+	return newFuncServerOption(func(o *serverOptions) {
+		o.initialConnWindowSize = s
+	})
+}
+
+// KeepaliveParams returns a ServerOption that sets keepalive and max-age parameters for the server.
+func KeepaliveParams(kp keepalive.ServerParameters) ServerOption {
+	if kp.Time > 0 && kp.Time < time.Second {
+		grpclog.Warning("Adjusting keepalive ping interval to minimum period of 1s")
+		kp.Time = time.Second
+	}
+
+	return newFuncServerOption(func(o *serverOptions) {
+		o.keepaliveParams = kp
+	})
+}
+
+// KeepaliveEnforcementPolicy returns a ServerOption that sets keepalive enforcement policy for the server.
+func KeepaliveEnforcementPolicy(kep keepalive.EnforcementPolicy) ServerOption {
+	return newFuncServerOption(func(o *serverOptions) {
+		o.keepalivePolicy = kep
+	})
+}
+
+// CustomCodec returns a ServerOption that sets a codec for message marshaling and unmarshaling.
+//
+// This will override any lookups by content-subtype for Codecs registered with RegisterCodec.
+func CustomCodec(codec Codec) ServerOption {
+	return newFuncServerOption(func(o *serverOptions) {
+		o.codec = codec
+	})
+}
+
+// RPCCompressor returns a ServerOption that sets a compressor for outbound
+// messages.  For backward compatibility, all outbound messages will be sent
+// using this compressor, regardless of incoming message compression.  By
+// default, server messages will be sent using the same compressor with which
+// request messages were sent.
+//
+// Deprecated: use encoding.RegisterCompressor instead.
+func RPCCompressor(cp Compressor) ServerOption {
+	return newFuncServerOption(func(o *serverOptions) {
+		o.cp = cp
+	})
+}
+
+// RPCDecompressor returns a ServerOption that sets a decompressor for inbound
+// messages.  It has higher priority than decompressors registered via
+// encoding.RegisterCompressor.
+//
+// Deprecated: use encoding.RegisterCompressor instead.
+func RPCDecompressor(dc Decompressor) ServerOption {
+	return newFuncServerOption(func(o *serverOptions) {
+		o.dc = dc
+	})
+}
+
+// MaxMsgSize returns a ServerOption to set the max message size in bytes the server can receive.
+// If this is not set, gRPC uses the default limit.
+//
+// Deprecated: use MaxRecvMsgSize instead.
+func MaxMsgSize(m int) ServerOption {
+	return MaxRecvMsgSize(m)
+}
+
+// MaxRecvMsgSize returns a ServerOption to set the max message size in bytes the server can receive.
+// If this is not set, gRPC uses the default 4MB.
+func MaxRecvMsgSize(m int) ServerOption {
+	return newFuncServerOption(func(o *serverOptions) {
+		o.maxReceiveMessageSize = m
+	})
+}
+
+// MaxSendMsgSize returns a ServerOption to set the max message size in bytes the server can send.
+// If this is not set, gRPC uses the default `math.MaxInt32`.
+func MaxSendMsgSize(m int) ServerOption {
+	return newFuncServerOption(func(o *serverOptions) {
+		o.maxSendMessageSize = m
+	})
+}
+
+// MaxConcurrentStreams returns a ServerOption that will apply a limit on the number
+// of concurrent streams to each ServerTransport.
+func MaxConcurrentStreams(n uint32) ServerOption {
+	return newFuncServerOption(func(o *serverOptions) {
+		o.maxConcurrentStreams = n
+	})
+}
+
+// Creds returns a ServerOption that sets credentials for server connections.
+func Creds(c credentials.TransportCredentials) ServerOption {
+	return newFuncServerOption(func(o *serverOptions) {
+		o.creds = c
+	})
+}
+
+// UnaryInterceptor returns a ServerOption that sets the UnaryServerInterceptor for the
+// server. Only one unary interceptor can be installed. The construction of multiple
+// interceptors (e.g., chaining) can be implemented at the caller.
+func UnaryInterceptor(i UnaryServerInterceptor) ServerOption {
+	return newFuncServerOption(func(o *serverOptions) {
+		if o.unaryInt != nil {
+			panic("The unary server interceptor was already set and may not be reset.")
+		}
+		o.unaryInt = i
+	})
+}
+
+// ChainUnaryInterceptor returns a ServerOption that specifies the chained interceptor
+// for unary RPCs. The first interceptor will be the outer most,
+// while the last interceptor will be the inner most wrapper around the real call.
+// All unary interceptors added by this method will be chained.
+func ChainUnaryInterceptor(interceptors ...UnaryServerInterceptor) ServerOption {
+	return newFuncServerOption(func(o *serverOptions) {
+		o.chainUnaryInts = append(o.chainUnaryInts, interceptors...)
+	})
+}
+
+// StreamInterceptor returns a ServerOption that sets the StreamServerInterceptor for the
+// server. Only one stream interceptor can be installed.
+func StreamInterceptor(i StreamServerInterceptor) ServerOption {
+	return newFuncServerOption(func(o *serverOptions) {
+		if o.streamInt != nil {
+			panic("The stream server interceptor was already set and may not be reset.")
+		}
+		o.streamInt = i
+	})
+}
+
+// ChainStreamInterceptor returns a ServerOption that specifies the chained interceptor
+// for stream RPCs. The first interceptor will be the outer most,
+// while the last interceptor will be the inner most wrapper around the real call.
+// All stream interceptors added by this method will be chained.
+func ChainStreamInterceptor(interceptors ...StreamServerInterceptor) ServerOption {
+	return newFuncServerOption(func(o *serverOptions) {
+		o.chainStreamInts = append(o.chainStreamInts, interceptors...)
+	})
+}
+
+// InTapHandle returns a ServerOption that sets the tap handle for all the server
+// transport to be created. Only one can be installed.
+func InTapHandle(h tap.ServerInHandle) ServerOption {
+	return newFuncServerOption(func(o *serverOptions) {
+		if o.inTapHandle != nil {
+			panic("The tap handle was already set and may not be reset.")
+		}
+		o.inTapHandle = h
+	})
+}
+
+// StatsHandler returns a ServerOption that sets the stats handler for the server.
+func StatsHandler(h stats.Handler) ServerOption {
+	return newFuncServerOption(func(o *serverOptions) {
+		o.statsHandler = h
+	})
+}
+
+// UnknownServiceHandler returns a ServerOption that allows for adding a custom
+// unknown service handler. The provided method is a bidi-streaming RPC service
+// handler that will be invoked instead of returning the "unimplemented" gRPC
+// error whenever a request is received for an unregistered service or method.
+// The handling function and stream interceptor (if set) have full access to
+// the ServerStream, including its Context.
+func UnknownServiceHandler(streamHandler StreamHandler) ServerOption {
+	return newFuncServerOption(func(o *serverOptions) {
+		o.unknownStreamDesc = &StreamDesc{
+			StreamName: "unknown_service_handler",
+			Handler:    streamHandler,
+			// We need to assume that the users of the streamHandler will want to use both.
+			ClientStreams: true,
+			ServerStreams: true,
+		}
+	})
+}
+
+// ConnectionTimeout returns a ServerOption that sets the timeout for
+// connection establishment (up to and including HTTP/2 handshaking) for all
+// new connections.  If this is not set, the default is 120 seconds.  A zero or
+// negative value will result in an immediate timeout.
+//
+// This API is EXPERIMENTAL.
+func ConnectionTimeout(d time.Duration) ServerOption {
+	return newFuncServerOption(func(o *serverOptions) {
+		o.connectionTimeout = d
+	})
+}
+
+// MaxHeaderListSize returns a ServerOption that sets the max (uncompressed) size
+// of header list that the server is prepared to accept.
+func MaxHeaderListSize(s uint32) ServerOption {
+	return newFuncServerOption(func(o *serverOptions) {
+		o.maxHeaderListSize = &s
+	})
+}
+
+// HeaderTableSize returns a ServerOption that sets the size of dynamic
+// header table for stream.
+//
+// This API is EXPERIMENTAL.
+func HeaderTableSize(s uint32) ServerOption {
+	return newFuncServerOption(func(o *serverOptions) {
+		o.headerTableSize = &s
+	})
+}
+
+// NewServer creates a gRPC server which has no service registered and has not
+// started to accept requests yet.
+func NewServer(opt ...ServerOption) *Server {
+	opts := defaultServerOptions
+	for _, o := range opt {
+		o.apply(&opts)
+	}
+	s := &Server{
+		lis:    make(map[net.Listener]bool),
+		opts:   opts,
+		conns:  make(map[transport.ServerTransport]bool),
+		m:      make(map[string]*service),
+		quit:   grpcsync.NewEvent(),
+		done:   grpcsync.NewEvent(),
+		czData: new(channelzData),
+	}
+	chainUnaryServerInterceptors(s)
+	chainStreamServerInterceptors(s)
+	s.cv = sync.NewCond(&s.mu)
+	if EnableTracing {
+		_, file, line, _ := runtime.Caller(1)
+		s.events = trace.NewEventLog("grpc.Server", fmt.Sprintf("%s:%d", file, line))
+	}
+
+	if channelz.IsOn() {
+		s.channelzID = channelz.RegisterServer(&channelzServer{s}, "")
+	}
+	return s
+}
+
+// printf records an event in s's event log, unless s has been stopped.
+// REQUIRES s.mu is held.
+func (s *Server) printf(format string, a ...interface{}) {
+	if s.events != nil {
+		s.events.Printf(format, a...)
+	}
+}
+
+// errorf records an error in s's event log, unless s has been stopped.
+// REQUIRES s.mu is held.
+func (s *Server) errorf(format string, a ...interface{}) {
+	if s.events != nil {
+		s.events.Errorf(format, a...)
+	}
+}
+
+// RegisterService registers a service and its implementation to the gRPC
+// server. It is called from the IDL generated code. This must be called before
+// invoking Serve.
+func (s *Server) RegisterService(sd *ServiceDesc, ss interface{}) {
+	ht := reflect.TypeOf(sd.HandlerType).Elem()
+	st := reflect.TypeOf(ss)
+	if !st.Implements(ht) {
+		grpclog.Fatalf("grpc: Server.RegisterService found the handler of type %v that does not satisfy %v", st, ht)
+	}
+	s.register(sd, ss)
+}
+
+func (s *Server) register(sd *ServiceDesc, ss interface{}) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	s.printf("RegisterService(%q)", sd.ServiceName)
+	if s.serve {
+		grpclog.Fatalf("grpc: Server.RegisterService after Server.Serve for %q", sd.ServiceName)
+	}
+	if _, ok := s.m[sd.ServiceName]; ok {
+		grpclog.Fatalf("grpc: Server.RegisterService found duplicate service registration for %q", sd.ServiceName)
+	}
+	srv := &service{
+		server: ss,
+		md:     make(map[string]*MethodDesc),
+		sd:     make(map[string]*StreamDesc),
+		mdata:  sd.Metadata,
+	}
+	for i := range sd.Methods {
+		d := &sd.Methods[i]
+		srv.md[d.MethodName] = d
+	}
+	for i := range sd.Streams {
+		d := &sd.Streams[i]
+		srv.sd[d.StreamName] = d
+	}
+	s.m[sd.ServiceName] = srv
+}
+
+// MethodInfo contains the information of an RPC including its method name and type.
+type MethodInfo struct {
+	// Name is the method name only, without the service name or package name.
+	Name string
+	// IsClientStream indicates whether the RPC is a client streaming RPC.
+	IsClientStream bool
+	// IsServerStream indicates whether the RPC is a server streaming RPC.
+	IsServerStream bool
+}
+
+// ServiceInfo contains unary RPC method info, streaming RPC method info and metadata for a service.
+type ServiceInfo struct {
+	Methods []MethodInfo
+	// Metadata is the metadata specified in ServiceDesc when registering service.
+	Metadata interface{}
+}
+
+// GetServiceInfo returns a map from service names to ServiceInfo.
+// Service names include the package names, in the form of <package>.<service>.
+func (s *Server) GetServiceInfo() map[string]ServiceInfo {
+	ret := make(map[string]ServiceInfo)
+	for n, srv := range s.m {
+		methods := make([]MethodInfo, 0, len(srv.md)+len(srv.sd))
+		for m := range srv.md {
+			methods = append(methods, MethodInfo{
+				Name:           m,
+				IsClientStream: false,
+				IsServerStream: false,
+			})
+		}
+		for m, d := range srv.sd {
+			methods = append(methods, MethodInfo{
+				Name:           m,
+				IsClientStream: d.ClientStreams,
+				IsServerStream: d.ServerStreams,
+			})
+		}
+
+		ret[n] = ServiceInfo{
+			Methods:  methods,
+			Metadata: srv.mdata,
+		}
+	}
+	return ret
+}
+
+// ErrServerStopped indicates that the operation is now illegal because of
+// the server being stopped.
+var ErrServerStopped = errors.New("grpc: the server has been stopped")
+
+func (s *Server) useTransportAuthenticator(rawConn net.Conn) (net.Conn, credentials.AuthInfo, error) {
+	if s.opts.creds == nil {
+		return rawConn, nil, nil
+	}
+	return s.opts.creds.ServerHandshake(rawConn)
+}
+
+type listenSocket struct {
+	net.Listener
+	channelzID int64
+}
+
+func (l *listenSocket) ChannelzMetric() *channelz.SocketInternalMetric {
+	return &channelz.SocketInternalMetric{
+		SocketOptions: channelz.GetSocketOption(l.Listener),
+		LocalAddr:     l.Listener.Addr(),
+	}
+}
+
+func (l *listenSocket) Close() error {
+	err := l.Listener.Close()
+	if channelz.IsOn() {
+		channelz.RemoveEntry(l.channelzID)
+	}
+	return err
+}
+
+// Serve accepts incoming connections on the listener lis, creating a new
+// ServerTransport and service goroutine for each. The service goroutines
+// read gRPC requests and then call the registered handlers to reply to them.
+// Serve returns when lis.Accept fails with fatal errors.  lis will be closed when
+// this method returns.
+// Serve will return a non-nil error unless Stop or GracefulStop is called.
+func (s *Server) Serve(lis net.Listener) error {
+	s.mu.Lock()
+	s.printf("serving")
+	s.serve = true
+	if s.lis == nil {
+		// Serve called after Stop or GracefulStop.
+		s.mu.Unlock()
+		lis.Close()
+		return ErrServerStopped
+	}
+
+	s.serveWG.Add(1)
+	defer func() {
+		s.serveWG.Done()
+		if s.quit.HasFired() {
+			// Stop or GracefulStop called; block until done and return nil.
+			<-s.done.Done()
+		}
+	}()
+
+	ls := &listenSocket{Listener: lis}
+	s.lis[ls] = true
+
+	if channelz.IsOn() {
+		ls.channelzID = channelz.RegisterListenSocket(ls, s.channelzID, lis.Addr().String())
+	}
+	s.mu.Unlock()
+
+	defer func() {
+		s.mu.Lock()
+		if s.lis != nil && s.lis[ls] {
+			ls.Close()
+			delete(s.lis, ls)
+		}
+		s.mu.Unlock()
+	}()
+
+	var tempDelay time.Duration // how long to sleep on accept failure
+
+	for {
+		rawConn, err := lis.Accept()
+		if err != nil {
+			if ne, ok := err.(interface {
+				Temporary() bool
+			}); ok && ne.Temporary() {
+				if tempDelay == 0 {
+					tempDelay = 5 * time.Millisecond
+				} else {
+					tempDelay *= 2
+				}
+				if max := 1 * time.Second; tempDelay > max {
+					tempDelay = max
+				}
+				s.mu.Lock()
+				s.printf("Accept error: %v; retrying in %v", err, tempDelay)
+				s.mu.Unlock()
+				timer := time.NewTimer(tempDelay)
+				select {
+				case <-timer.C:
+				case <-s.quit.Done():
+					timer.Stop()
+					return nil
+				}
+				continue
+			}
+			s.mu.Lock()
+			s.printf("done serving; Accept = %v", err)
+			s.mu.Unlock()
+
+			if s.quit.HasFired() {
+				return nil
+			}
+			return err
+		}
+		tempDelay = 0
+		// Start a new goroutine to deal with rawConn so we don't stall this Accept
+		// loop goroutine.
+		//
+		// Make sure we account for the goroutine so GracefulStop doesn't nil out
+		// s.conns before this conn can be added.
+		s.serveWG.Add(1)
+		go func() {
+			s.handleRawConn(rawConn)
+			s.serveWG.Done()
+		}()
+	}
+}
+
+// handleRawConn forks a goroutine to handle a just-accepted connection that
+// has not had any I/O performed on it yet.
+func (s *Server) handleRawConn(rawConn net.Conn) {
+	if s.quit.HasFired() {
+		rawConn.Close()
+		return
+	}
+	rawConn.SetDeadline(time.Now().Add(s.opts.connectionTimeout))
+	conn, authInfo, err := s.useTransportAuthenticator(rawConn)
+	if err != nil {
+		// ErrConnDispatched means that the connection was dispatched away from
+		// gRPC; those connections should be left open.
+		if err != credentials.ErrConnDispatched {
+			s.mu.Lock()
+			s.errorf("ServerHandshake(%q) failed: %v", rawConn.RemoteAddr(), err)
+			s.mu.Unlock()
+			channelz.Warningf(s.channelzID, "grpc: Server.Serve failed to complete security handshake from %q: %v", rawConn.RemoteAddr(), err)
+			rawConn.Close()
+		}
+		rawConn.SetDeadline(time.Time{})
+		return
+	}
+
+	// Finish handshaking (HTTP2)
+	st := s.newHTTP2Transport(conn, authInfo)
+	if st == nil {
+		return
+	}
+
+	rawConn.SetDeadline(time.Time{})
+	if !s.addConn(st) {
+		return
+	}
+	go func() {
+		s.serveStreams(st)
+		s.removeConn(st)
+	}()
+}
+
+// newHTTP2Transport sets up a http/2 transport (using the
+// gRPC http2 server transport in transport/http2_server.go).
+func (s *Server) newHTTP2Transport(c net.Conn, authInfo credentials.AuthInfo) transport.ServerTransport {
+	config := &transport.ServerConfig{
+		MaxStreams:            s.opts.maxConcurrentStreams,
+		AuthInfo:              authInfo,
+		InTapHandle:           s.opts.inTapHandle,
+		StatsHandler:          s.opts.statsHandler,
+		KeepaliveParams:       s.opts.keepaliveParams,
+		KeepalivePolicy:       s.opts.keepalivePolicy,
+		InitialWindowSize:     s.opts.initialWindowSize,
+		InitialConnWindowSize: s.opts.initialConnWindowSize,
+		WriteBufferSize:       s.opts.writeBufferSize,
+		ReadBufferSize:        s.opts.readBufferSize,
+		ChannelzParentID:      s.channelzID,
+		MaxHeaderListSize:     s.opts.maxHeaderListSize,
+		HeaderTableSize:       s.opts.headerTableSize,
+	}
+	st, err := transport.NewServerTransport("http2", c, config)
+	if err != nil {
+		s.mu.Lock()
+		s.errorf("NewServerTransport(%q) failed: %v", c.RemoteAddr(), err)
+		s.mu.Unlock()
+		c.Close()
+		channelz.Warning(s.channelzID, "grpc: Server.Serve failed to create ServerTransport: ", err)
+		return nil
+	}
+
+	return st
+}
+
+func (s *Server) serveStreams(st transport.ServerTransport) {
+	defer st.Close()
+	var wg sync.WaitGroup
+	st.HandleStreams(func(stream *transport.Stream) {
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			s.handleStream(st, stream, s.traceInfo(st, stream))
+		}()
+	}, func(ctx context.Context, method string) context.Context {
+		if !EnableTracing {
+			return ctx
+		}
+		tr := trace.New("grpc.Recv."+methodFamily(method), method)
+		return trace.NewContext(ctx, tr)
+	})
+	wg.Wait()
+}
+
+var _ http.Handler = (*Server)(nil)
+
+// ServeHTTP implements the Go standard library's http.Handler
+// interface by responding to the gRPC request r, by looking up
+// the requested gRPC method in the gRPC server s.
+//
+// The provided HTTP request must have arrived on an HTTP/2
+// connection. When using the Go standard library's server,
+// practically this means that the Request must also have arrived
+// over TLS.
+//
+// To share one port (such as 443 for https) between gRPC and an
+// existing http.Handler, use a root http.Handler such as:
+//
+//   if r.ProtoMajor == 2 && strings.HasPrefix(
+//   	r.Header.Get("Content-Type"), "application/grpc") {
+//   	grpcServer.ServeHTTP(w, r)
+//   } else {
+//   	yourMux.ServeHTTP(w, r)
+//   }
+//
+// Note that ServeHTTP uses Go's HTTP/2 server implementation which is totally
+// separate from grpc-go's HTTP/2 server. Performance and features may vary
+// between the two paths. ServeHTTP does not support some gRPC features
+// available through grpc-go's HTTP/2 server, and it is currently EXPERIMENTAL
+// and subject to change.
+func (s *Server) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	st, err := transport.NewServerHandlerTransport(w, r, s.opts.statsHandler)
+	if err != nil {
+		http.Error(w, err.Error(), http.StatusInternalServerError)
+		return
+	}
+	if !s.addConn(st) {
+		return
+	}
+	defer s.removeConn(st)
+	s.serveStreams(st)
+}
+
+// traceInfo returns a traceInfo and associates it with stream, if tracing is enabled.
+// If tracing is not enabled, it returns nil.
+func (s *Server) traceInfo(st transport.ServerTransport, stream *transport.Stream) (trInfo *traceInfo) {
+	if !EnableTracing {
+		return nil
+	}
+	tr, ok := trace.FromContext(stream.Context())
+	if !ok {
+		return nil
+	}
+
+	trInfo = &traceInfo{
+		tr: tr,
+		firstLine: firstLine{
+			client:     false,
+			remoteAddr: st.RemoteAddr(),
+		},
+	}
+	if dl, ok := stream.Context().Deadline(); ok {
+		trInfo.firstLine.deadline = time.Until(dl)
+	}
+	return trInfo
+}
+
+func (s *Server) addConn(st transport.ServerTransport) bool {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	if s.conns == nil {
+		st.Close()
+		return false
+	}
+	if s.drain {
+		// Transport added after we drained our existing conns: drain it
+		// immediately.
+		st.Drain()
+	}
+	s.conns[st] = true
+	return true
+}
+
+func (s *Server) removeConn(st transport.ServerTransport) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	if s.conns != nil {
+		delete(s.conns, st)
+		s.cv.Broadcast()
+	}
+}
+
+func (s *Server) channelzMetric() *channelz.ServerInternalMetric {
+	return &channelz.ServerInternalMetric{
+		CallsStarted:             atomic.LoadInt64(&s.czData.callsStarted),
+		CallsSucceeded:           atomic.LoadInt64(&s.czData.callsSucceeded),
+		CallsFailed:              atomic.LoadInt64(&s.czData.callsFailed),
+		LastCallStartedTimestamp: time.Unix(0, atomic.LoadInt64(&s.czData.lastCallStartedTime)),
+	}
+}
+
+func (s *Server) incrCallsStarted() {
+	atomic.AddInt64(&s.czData.callsStarted, 1)
+	atomic.StoreInt64(&s.czData.lastCallStartedTime, time.Now().UnixNano())
+}
+
+func (s *Server) incrCallsSucceeded() {
+	atomic.AddInt64(&s.czData.callsSucceeded, 1)
+}
+
+func (s *Server) incrCallsFailed() {
+	atomic.AddInt64(&s.czData.callsFailed, 1)
+}
+
+func (s *Server) sendResponse(t transport.ServerTransport, stream *transport.Stream, msg interface{}, cp Compressor, opts *transport.Options, comp encoding.Compressor) error {
+	data, err := encode(s.getCodec(stream.ContentSubtype()), msg)
+	if err != nil {
+		channelz.Error(s.channelzID, "grpc: server failed to encode response: ", err)
+		return err
+	}
+	compData, err := compress(data, cp, comp)
+	if err != nil {
+		channelz.Error(s.channelzID, "grpc: server failed to compress response: ", err)
+		return err
+	}
+	hdr, payload := msgHeader(data, compData)
+	// TODO(dfawley): should we be checking len(data) instead?
+	if len(payload) > s.opts.maxSendMessageSize {
+		return status.Errorf(codes.ResourceExhausted, "grpc: trying to send message larger than max (%d vs. %d)", len(payload), s.opts.maxSendMessageSize)
+	}
+	err = t.Write(stream, hdr, payload, opts)
+	if err == nil && s.opts.statsHandler != nil {
+		s.opts.statsHandler.HandleRPC(stream.Context(), outPayload(false, msg, data, payload, time.Now()))
+	}
+	return err
+}
+
+// chainUnaryServerInterceptors chains all unary server interceptors into one.
+func chainUnaryServerInterceptors(s *Server) {
+	// Prepend opts.unaryInt to the chaining interceptors if it exists, since unaryInt will
+	// be executed before any other chained interceptors.
+	interceptors := s.opts.chainUnaryInts
+	if s.opts.unaryInt != nil {
+		interceptors = append([]UnaryServerInterceptor{s.opts.unaryInt}, s.opts.chainUnaryInts...)
+	}
+
+	var chainedInt UnaryServerInterceptor
+	if len(interceptors) == 0 {
+		chainedInt = nil
+	} else if len(interceptors) == 1 {
+		chainedInt = interceptors[0]
+	} else {
+		chainedInt = func(ctx context.Context, req interface{}, info *UnaryServerInfo, handler UnaryHandler) (interface{}, error) {
+			return interceptors[0](ctx, req, info, getChainUnaryHandler(interceptors, 0, info, handler))
+		}
+	}
+
+	s.opts.unaryInt = chainedInt
+}
+
+// getChainUnaryHandler recursively generate the chained UnaryHandler
+func getChainUnaryHandler(interceptors []UnaryServerInterceptor, curr int, info *UnaryServerInfo, finalHandler UnaryHandler) UnaryHandler {
+	if curr == len(interceptors)-1 {
+		return finalHandler
+	}
+
+	return func(ctx context.Context, req interface{}) (interface{}, error) {
+		return interceptors[curr+1](ctx, req, info, getChainUnaryHandler(interceptors, curr+1, info, finalHandler))
+	}
+}
+
+func (s *Server) processUnaryRPC(t transport.ServerTransport, stream *transport.Stream, srv *service, md *MethodDesc, trInfo *traceInfo) (err error) {
+	sh := s.opts.statsHandler
+	if sh != nil || trInfo != nil || channelz.IsOn() {
+		if channelz.IsOn() {
+			s.incrCallsStarted()
+		}
+		var statsBegin *stats.Begin
+		if sh != nil {
+			beginTime := time.Now()
+			statsBegin = &stats.Begin{
+				BeginTime: beginTime,
+			}
+			sh.HandleRPC(stream.Context(), statsBegin)
+		}
+		if trInfo != nil {
+			trInfo.tr.LazyLog(&trInfo.firstLine, false)
+		}
+		// The deferred error handling for tracing, stats handler and channelz are
+		// combined into one function to reduce stack usage -- a defer takes ~56-64
+		// bytes on the stack, so overflowing the stack will require a stack
+		// re-allocation, which is expensive.
+		//
+		// To maintain behavior similar to separate deferred statements, statements
+		// should be executed in the reverse order. That is, tracing first, stats
+		// handler second, and channelz last. Note that panics *within* defers will
+		// lead to different behavior, but that's an acceptable compromise; that
+		// would be undefined behavior territory anyway.
+		defer func() {
+			if trInfo != nil {
+				if err != nil && err != io.EOF {
+					trInfo.tr.LazyLog(&fmtStringer{"%v", []interface{}{err}}, true)
+					trInfo.tr.SetError()
+				}
+				trInfo.tr.Finish()
+			}
+
+			if sh != nil {
+				end := &stats.End{
+					BeginTime: statsBegin.BeginTime,
+					EndTime:   time.Now(),
+				}
+				if err != nil && err != io.EOF {
+					end.Error = toRPCErr(err)
+				}
+				sh.HandleRPC(stream.Context(), end)
+			}
+
+			if channelz.IsOn() {
+				if err != nil && err != io.EOF {
+					s.incrCallsFailed()
+				} else {
+					s.incrCallsSucceeded()
+				}
+			}
+		}()
+	}
+
+	binlog := binarylog.GetMethodLogger(stream.Method())
+	if binlog != nil {
+		ctx := stream.Context()
+		md, _ := metadata.FromIncomingContext(ctx)
+		logEntry := &binarylog.ClientHeader{
+			Header:     md,
+			MethodName: stream.Method(),
+			PeerAddr:   nil,
+		}
+		if deadline, ok := ctx.Deadline(); ok {
+			logEntry.Timeout = time.Until(deadline)
+			if logEntry.Timeout < 0 {
+				logEntry.Timeout = 0
+			}
+		}
+		if a := md[":authority"]; len(a) > 0 {
+			logEntry.Authority = a[0]
+		}
+		if peer, ok := peer.FromContext(ctx); ok {
+			logEntry.PeerAddr = peer.Addr
+		}
+		binlog.Log(logEntry)
+	}
+
+	// comp and cp are used for compression.  decomp and dc are used for
+	// decompression.  If comp and decomp are both set, they are the same;
+	// however they are kept separate to ensure that at most one of the
+	// compressor/decompressor variable pairs are set for use later.
+	var comp, decomp encoding.Compressor
+	var cp Compressor
+	var dc Decompressor
+
+	// If dc is set and matches the stream's compression, use it.  Otherwise, try
+	// to find a matching registered compressor for decomp.
+	if rc := stream.RecvCompress(); s.opts.dc != nil && s.opts.dc.Type() == rc {
+		dc = s.opts.dc
+	} else if rc != "" && rc != encoding.Identity {
+		decomp = encoding.GetCompressor(rc)
+		if decomp == nil {
+			st := status.Newf(codes.Unimplemented, "grpc: Decompressor is not installed for grpc-encoding %q", rc)
+			t.WriteStatus(stream, st)
+			return st.Err()
+		}
+	}
+
+	// If cp is set, use it.  Otherwise, attempt to compress the response using
+	// the incoming message compression method.
+	//
+	// NOTE: this needs to be ahead of all handling, https://github.com/grpc/grpc-go/issues/686.
+	if s.opts.cp != nil {
+		cp = s.opts.cp
+		stream.SetSendCompress(cp.Type())
+	} else if rc := stream.RecvCompress(); rc != "" && rc != encoding.Identity {
+		// Legacy compressor not specified; attempt to respond with same encoding.
+		comp = encoding.GetCompressor(rc)
+		if comp != nil {
+			stream.SetSendCompress(rc)
+		}
+	}
+
+	var payInfo *payloadInfo
+	if sh != nil || binlog != nil {
+		payInfo = &payloadInfo{}
+	}
+	d, err := recvAndDecompress(&parser{r: stream}, stream, dc, s.opts.maxReceiveMessageSize, payInfo, decomp)
+	if err != nil {
+		if st, ok := status.FromError(err); ok {
+			if e := t.WriteStatus(stream, st); e != nil {
+				channelz.Warningf(s.channelzID, "grpc: Server.processUnaryRPC failed to write status %v", e)
+			}
+		}
+		return err
+	}
+	if channelz.IsOn() {
+		t.IncrMsgRecv()
+	}
+	df := func(v interface{}) error {
+		if err := s.getCodec(stream.ContentSubtype()).Unmarshal(d, v); err != nil {
+			return status.Errorf(codes.Internal, "grpc: error unmarshalling request: %v", err)
+		}
+		if sh != nil {
+			sh.HandleRPC(stream.Context(), &stats.InPayload{
+				RecvTime:   time.Now(),
+				Payload:    v,
+				WireLength: payInfo.wireLength,
+				Data:       d,
+				Length:     len(d),
+			})
+		}
+		if binlog != nil {
+			binlog.Log(&binarylog.ClientMessage{
+				Message: d,
+			})
+		}
+		if trInfo != nil {
+			trInfo.tr.LazyLog(&payload{sent: false, msg: v}, true)
+		}
+		return nil
+	}
+	ctx := NewContextWithServerTransportStream(stream.Context(), stream)
+	reply, appErr := md.Handler(srv.server, ctx, df, s.opts.unaryInt)
+	if appErr != nil {
+		appStatus, ok := status.FromError(appErr)
+		if !ok {
+			// Convert appErr if it is not a grpc status error.
+			appErr = status.Error(codes.Unknown, appErr.Error())
+			appStatus, _ = status.FromError(appErr)
+		}
+		if trInfo != nil {
+			trInfo.tr.LazyLog(stringer(appStatus.Message()), true)
+			trInfo.tr.SetError()
+		}
+		if e := t.WriteStatus(stream, appStatus); e != nil {
+			channelz.Warningf(s.channelzID, "grpc: Server.processUnaryRPC failed to write status: %v", e)
+		}
+		if binlog != nil {
+			if h, _ := stream.Header(); h.Len() > 0 {
+				// Only log serverHeader if there was header. Otherwise it can
+				// be trailer only.
+				binlog.Log(&binarylog.ServerHeader{
+					Header: h,
+				})
+			}
+			binlog.Log(&binarylog.ServerTrailer{
+				Trailer: stream.Trailer(),
+				Err:     appErr,
+			})
+		}
+		return appErr
+	}
+	if trInfo != nil {
+		trInfo.tr.LazyLog(stringer("OK"), false)
+	}
+	opts := &transport.Options{Last: true}
+
+	if err := s.sendResponse(t, stream, reply, cp, opts, comp); err != nil {
+		if err == io.EOF {
+			// The entire stream is done (for unary RPC only).
+			return err
+		}
+		if sts, ok := status.FromError(err); ok {
+			if e := t.WriteStatus(stream, sts); e != nil {
+				channelz.Warningf(s.channelzID, "grpc: Server.processUnaryRPC failed to write status: %v", e)
+			}
+		} else {
+			switch st := err.(type) {
+			case transport.ConnectionError:
+				// Nothing to do here.
+			default:
+				panic(fmt.Sprintf("grpc: Unexpected error (%T) from sendResponse: %v", st, st))
+			}
+		}
+		if binlog != nil {
+			h, _ := stream.Header()
+			binlog.Log(&binarylog.ServerHeader{
+				Header: h,
+			})
+			binlog.Log(&binarylog.ServerTrailer{
+				Trailer: stream.Trailer(),
+				Err:     appErr,
+			})
+		}
+		return err
+	}
+	if binlog != nil {
+		h, _ := stream.Header()
+		binlog.Log(&binarylog.ServerHeader{
+			Header: h,
+		})
+		binlog.Log(&binarylog.ServerMessage{
+			Message: reply,
+		})
+	}
+	if channelz.IsOn() {
+		t.IncrMsgSent()
+	}
+	if trInfo != nil {
+		trInfo.tr.LazyLog(&payload{sent: true, msg: reply}, true)
+	}
+	// TODO: Should we be logging if writing status failed here, like above?
+	// Should the logging be in WriteStatus?  Should we ignore the WriteStatus
+	// error or allow the stats handler to see it?
+	err = t.WriteStatus(stream, statusOK)
+	if binlog != nil {
+		binlog.Log(&binarylog.ServerTrailer{
+			Trailer: stream.Trailer(),
+			Err:     appErr,
+		})
+	}
+	return err
+}
+
+// chainStreamServerInterceptors chains all stream server interceptors into one.
+func chainStreamServerInterceptors(s *Server) {
+	// Prepend opts.streamInt to the chaining interceptors if it exists, since streamInt will
+	// be executed before any other chained interceptors.
+	interceptors := s.opts.chainStreamInts
+	if s.opts.streamInt != nil {
+		interceptors = append([]StreamServerInterceptor{s.opts.streamInt}, s.opts.chainStreamInts...)
+	}
+
+	var chainedInt StreamServerInterceptor
+	if len(interceptors) == 0 {
+		chainedInt = nil
+	} else if len(interceptors) == 1 {
+		chainedInt = interceptors[0]
+	} else {
+		chainedInt = func(srv interface{}, ss ServerStream, info *StreamServerInfo, handler StreamHandler) error {
+			return interceptors[0](srv, ss, info, getChainStreamHandler(interceptors, 0, info, handler))
+		}
+	}
+
+	s.opts.streamInt = chainedInt
+}
+
+// getChainStreamHandler recursively generate the chained StreamHandler
+func getChainStreamHandler(interceptors []StreamServerInterceptor, curr int, info *StreamServerInfo, finalHandler StreamHandler) StreamHandler {
+	if curr == len(interceptors)-1 {
+		return finalHandler
+	}
+
+	return func(srv interface{}, ss ServerStream) error {
+		return interceptors[curr+1](srv, ss, info, getChainStreamHandler(interceptors, curr+1, info, finalHandler))
+	}
+}
+
+func (s *Server) processStreamingRPC(t transport.ServerTransport, stream *transport.Stream, srv *service, sd *StreamDesc, trInfo *traceInfo) (err error) {
+	if channelz.IsOn() {
+		s.incrCallsStarted()
+	}
+	sh := s.opts.statsHandler
+	var statsBegin *stats.Begin
+	if sh != nil {
+		beginTime := time.Now()
+		statsBegin = &stats.Begin{
+			BeginTime: beginTime,
+		}
+		sh.HandleRPC(stream.Context(), statsBegin)
+	}
+	ctx := NewContextWithServerTransportStream(stream.Context(), stream)
+	ss := &serverStream{
+		ctx:                   ctx,
+		t:                     t,
+		s:                     stream,
+		p:                     &parser{r: stream},
+		codec:                 s.getCodec(stream.ContentSubtype()),
+		maxReceiveMessageSize: s.opts.maxReceiveMessageSize,
+		maxSendMessageSize:    s.opts.maxSendMessageSize,
+		trInfo:                trInfo,
+		statsHandler:          sh,
+	}
+
+	if sh != nil || trInfo != nil || channelz.IsOn() {
+		// See comment in processUnaryRPC on defers.
+		defer func() {
+			if trInfo != nil {
+				ss.mu.Lock()
+				if err != nil && err != io.EOF {
+					ss.trInfo.tr.LazyLog(&fmtStringer{"%v", []interface{}{err}}, true)
+					ss.trInfo.tr.SetError()
+				}
+				ss.trInfo.tr.Finish()
+				ss.trInfo.tr = nil
+				ss.mu.Unlock()
+			}
+
+			if sh != nil {
+				end := &stats.End{
+					BeginTime: statsBegin.BeginTime,
+					EndTime:   time.Now(),
+				}
+				if err != nil && err != io.EOF {
+					end.Error = toRPCErr(err)
+				}
+				sh.HandleRPC(stream.Context(), end)
+			}
+
+			if channelz.IsOn() {
+				if err != nil && err != io.EOF {
+					s.incrCallsFailed()
+				} else {
+					s.incrCallsSucceeded()
+				}
+			}
+		}()
+	}
+
+	ss.binlog = binarylog.GetMethodLogger(stream.Method())
+	if ss.binlog != nil {
+		md, _ := metadata.FromIncomingContext(ctx)
+		logEntry := &binarylog.ClientHeader{
+			Header:     md,
+			MethodName: stream.Method(),
+			PeerAddr:   nil,
+		}
+		if deadline, ok := ctx.Deadline(); ok {
+			logEntry.Timeout = time.Until(deadline)
+			if logEntry.Timeout < 0 {
+				logEntry.Timeout = 0
+			}
+		}
+		if a := md[":authority"]; len(a) > 0 {
+			logEntry.Authority = a[0]
+		}
+		if peer, ok := peer.FromContext(ss.Context()); ok {
+			logEntry.PeerAddr = peer.Addr
+		}
+		ss.binlog.Log(logEntry)
+	}
+
+	// If dc is set and matches the stream's compression, use it.  Otherwise, try
+	// to find a matching registered compressor for decomp.
+	if rc := stream.RecvCompress(); s.opts.dc != nil && s.opts.dc.Type() == rc {
+		ss.dc = s.opts.dc
+	} else if rc != "" && rc != encoding.Identity {
+		ss.decomp = encoding.GetCompressor(rc)
+		if ss.decomp == nil {
+			st := status.Newf(codes.Unimplemented, "grpc: Decompressor is not installed for grpc-encoding %q", rc)
+			t.WriteStatus(ss.s, st)
+			return st.Err()
+		}
+	}
+
+	// If cp is set, use it.  Otherwise, attempt to compress the response using
+	// the incoming message compression method.
+	//
+	// NOTE: this needs to be ahead of all handling, https://github.com/grpc/grpc-go/issues/686.
+	if s.opts.cp != nil {
+		ss.cp = s.opts.cp
+		stream.SetSendCompress(s.opts.cp.Type())
+	} else if rc := stream.RecvCompress(); rc != "" && rc != encoding.Identity {
+		// Legacy compressor not specified; attempt to respond with same encoding.
+		ss.comp = encoding.GetCompressor(rc)
+		if ss.comp != nil {
+			stream.SetSendCompress(rc)
+		}
+	}
+
+	if trInfo != nil {
+		trInfo.tr.LazyLog(&trInfo.firstLine, false)
+	}
+	var appErr error
+	var server interface{}
+	if srv != nil {
+		server = srv.server
+	}
+	if s.opts.streamInt == nil {
+		appErr = sd.Handler(server, ss)
+	} else {
+		info := &StreamServerInfo{
+			FullMethod:     stream.Method(),
+			IsClientStream: sd.ClientStreams,
+			IsServerStream: sd.ServerStreams,
+		}
+		appErr = s.opts.streamInt(server, ss, info, sd.Handler)
+	}
+	if appErr != nil {
+		appStatus, ok := status.FromError(appErr)
+		if !ok {
+			appStatus = status.New(codes.Unknown, appErr.Error())
+			appErr = appStatus.Err()
+		}
+		if trInfo != nil {
+			ss.mu.Lock()
+			ss.trInfo.tr.LazyLog(stringer(appStatus.Message()), true)
+			ss.trInfo.tr.SetError()
+			ss.mu.Unlock()
+		}
+		t.WriteStatus(ss.s, appStatus)
+		if ss.binlog != nil {
+			ss.binlog.Log(&binarylog.ServerTrailer{
+				Trailer: ss.s.Trailer(),
+				Err:     appErr,
+			})
+		}
+		// TODO: Should we log an error from WriteStatus here and below?
+		return appErr
+	}
+	if trInfo != nil {
+		ss.mu.Lock()
+		ss.trInfo.tr.LazyLog(stringer("OK"), false)
+		ss.mu.Unlock()
+	}
+	err = t.WriteStatus(ss.s, statusOK)
+	if ss.binlog != nil {
+		ss.binlog.Log(&binarylog.ServerTrailer{
+			Trailer: ss.s.Trailer(),
+			Err:     appErr,
+		})
+	}
+	return err
+}
+
+func (s *Server) handleStream(t transport.ServerTransport, stream *transport.Stream, trInfo *traceInfo) {
+	sm := stream.Method()
+	if sm != "" && sm[0] == '/' {
+		sm = sm[1:]
+	}
+	pos := strings.LastIndex(sm, "/")
+	if pos == -1 {
+		if trInfo != nil {
+			trInfo.tr.LazyLog(&fmtStringer{"Malformed method name %q", []interface{}{sm}}, true)
+			trInfo.tr.SetError()
+		}
+		errDesc := fmt.Sprintf("malformed method name: %q", stream.Method())
+		if err := t.WriteStatus(stream, status.New(codes.ResourceExhausted, errDesc)); err != nil {
+			if trInfo != nil {
+				trInfo.tr.LazyLog(&fmtStringer{"%v", []interface{}{err}}, true)
+				trInfo.tr.SetError()
+			}
+			channelz.Warningf(s.channelzID, "grpc: Server.handleStream failed to write status: %v", err)
+		}
+		if trInfo != nil {
+			trInfo.tr.Finish()
+		}
+		return
+	}
+	service := sm[:pos]
+	method := sm[pos+1:]
+
+	srv, knownService := s.m[service]
+	if knownService {
+		if md, ok := srv.md[method]; ok {
+			s.processUnaryRPC(t, stream, srv, md, trInfo)
+			return
+		}
+		if sd, ok := srv.sd[method]; ok {
+			s.processStreamingRPC(t, stream, srv, sd, trInfo)
+			return
+		}
+	}
+	// Unknown service, or known server unknown method.
+	if unknownDesc := s.opts.unknownStreamDesc; unknownDesc != nil {
+		s.processStreamingRPC(t, stream, nil, unknownDesc, trInfo)
+		return
+	}
+	var errDesc string
+	if !knownService {
+		errDesc = fmt.Sprintf("unknown service %v", service)
+	} else {
+		errDesc = fmt.Sprintf("unknown method %v for service %v", method, service)
+	}
+	if trInfo != nil {
+		trInfo.tr.LazyPrintf("%s", errDesc)
+		trInfo.tr.SetError()
+	}
+	if err := t.WriteStatus(stream, status.New(codes.Unimplemented, errDesc)); err != nil {
+		if trInfo != nil {
+			trInfo.tr.LazyLog(&fmtStringer{"%v", []interface{}{err}}, true)
+			trInfo.tr.SetError()
+		}
+		channelz.Warningf(s.channelzID, "grpc: Server.handleStream failed to write status: %v", err)
+	}
+	if trInfo != nil {
+		trInfo.tr.Finish()
+	}
+}
+
+// The key to save ServerTransportStream in the context.
+type streamKey struct{}
+
+// NewContextWithServerTransportStream creates a new context from ctx and
+// attaches stream to it.
+//
+// This API is EXPERIMENTAL.
+func NewContextWithServerTransportStream(ctx context.Context, stream ServerTransportStream) context.Context {
+	return context.WithValue(ctx, streamKey{}, stream)
+}
+
+// ServerTransportStream is a minimal interface that a transport stream must
+// implement. This can be used to mock an actual transport stream for tests of
+// handler code that use, for example, grpc.SetHeader (which requires some
+// stream to be in context).
+//
+// See also NewContextWithServerTransportStream.
+//
+// This API is EXPERIMENTAL.
+type ServerTransportStream interface {
+	Method() string
+	SetHeader(md metadata.MD) error
+	SendHeader(md metadata.MD) error
+	SetTrailer(md metadata.MD) error
+}
+
+// ServerTransportStreamFromContext returns the ServerTransportStream saved in
+// ctx. Returns nil if the given context has no stream associated with it
+// (which implies it is not an RPC invocation context).
+//
+// This API is EXPERIMENTAL.
+func ServerTransportStreamFromContext(ctx context.Context) ServerTransportStream {
+	s, _ := ctx.Value(streamKey{}).(ServerTransportStream)
+	return s
+}
+
+// Stop stops the gRPC server. It immediately closes all open
+// connections and listeners.
+// It cancels all active RPCs on the server side and the corresponding
+// pending RPCs on the client side will get notified by connection
+// errors.
+func (s *Server) Stop() {
+	s.quit.Fire()
+
+	defer func() {
+		s.serveWG.Wait()
+		s.done.Fire()
+	}()
+
+	s.channelzRemoveOnce.Do(func() {
+		if channelz.IsOn() {
+			channelz.RemoveEntry(s.channelzID)
+		}
+	})
+
+	s.mu.Lock()
+	listeners := s.lis
+	s.lis = nil
+	st := s.conns
+	s.conns = nil
+	// interrupt GracefulStop if Stop and GracefulStop are called concurrently.
+	s.cv.Broadcast()
+	s.mu.Unlock()
+
+	for lis := range listeners {
+		lis.Close()
+	}
+	for c := range st {
+		c.Close()
+	}
+
+	s.mu.Lock()
+	if s.events != nil {
+		s.events.Finish()
+		s.events = nil
+	}
+	s.mu.Unlock()
+}
+
+// GracefulStop stops the gRPC server gracefully. It stops the server from
+// accepting new connections and RPCs and blocks until all the pending RPCs are
+// finished.
+func (s *Server) GracefulStop() {
+	s.quit.Fire()
+	defer s.done.Fire()
+
+	s.channelzRemoveOnce.Do(func() {
+		if channelz.IsOn() {
+			channelz.RemoveEntry(s.channelzID)
+		}
+	})
+	s.mu.Lock()
+	if s.conns == nil {
+		s.mu.Unlock()
+		return
+	}
+
+	for lis := range s.lis {
+		lis.Close()
+	}
+	s.lis = nil
+	if !s.drain {
+		for st := range s.conns {
+			st.Drain()
+		}
+		s.drain = true
+	}
+
+	// Wait for serving threads to be ready to exit.  Only then can we be sure no
+	// new conns will be created.
+	s.mu.Unlock()
+	s.serveWG.Wait()
+	s.mu.Lock()
+
+	for len(s.conns) != 0 {
+		s.cv.Wait()
+	}
+	s.conns = nil
+	if s.events != nil {
+		s.events.Finish()
+		s.events = nil
+	}
+	s.mu.Unlock()
+}
+
+// contentSubtype must be lowercase
+// cannot return nil
+func (s *Server) getCodec(contentSubtype string) baseCodec {
+	if s.opts.codec != nil {
+		return s.opts.codec
+	}
+	if contentSubtype == "" {
+		return encoding.GetCodec(proto.Name)
+	}
+	codec := encoding.GetCodec(contentSubtype)
+	if codec == nil {
+		return encoding.GetCodec(proto.Name)
+	}
+	return codec
+}
+
+// SetHeader sets the header metadata.
+// When called multiple times, all the provided metadata will be merged.
+// All the metadata will be sent out when one of the following happens:
+//  - grpc.SendHeader() is called;
+//  - The first response is sent out;
+//  - An RPC status is sent out (error or success).
+func SetHeader(ctx context.Context, md metadata.MD) error {
+	if md.Len() == 0 {
+		return nil
+	}
+	stream := ServerTransportStreamFromContext(ctx)
+	if stream == nil {
+		return status.Errorf(codes.Internal, "grpc: failed to fetch the stream from the context %v", ctx)
+	}
+	return stream.SetHeader(md)
+}
+
+// SendHeader sends header metadata. It may be called at most once.
+// The provided md and headers set by SetHeader() will be sent.
+func SendHeader(ctx context.Context, md metadata.MD) error {
+	stream := ServerTransportStreamFromContext(ctx)
+	if stream == nil {
+		return status.Errorf(codes.Internal, "grpc: failed to fetch the stream from the context %v", ctx)
+	}
+	if err := stream.SendHeader(md); err != nil {
+		return toRPCErr(err)
+	}
+	return nil
+}
+
+// SetTrailer sets the trailer metadata that will be sent when an RPC returns.
+// When called more than once, all the provided metadata will be merged.
+func SetTrailer(ctx context.Context, md metadata.MD) error {
+	if md.Len() == 0 {
+		return nil
+	}
+	stream := ServerTransportStreamFromContext(ctx)
+	if stream == nil {
+		return status.Errorf(codes.Internal, "grpc: failed to fetch the stream from the context %v", ctx)
+	}
+	return stream.SetTrailer(md)
+}
+
+// Method returns the method string for the server context.  The returned
+// string is in the format of "/service/method".
+func Method(ctx context.Context) (string, bool) {
+	s := ServerTransportStreamFromContext(ctx)
+	if s == nil {
+		return "", false
+	}
+	return s.Method(), true
+}
+
+type channelzServer struct {
+	s *Server
+}
+
+func (c *channelzServer) ChannelzMetric() *channelz.ServerInternalMetric {
+	return c.s.channelzMetric()
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/service_config.go b/demo_test/vendor/google.golang.org/grpc/service_config.go
new file mode 100644
index 0000000..5a80a57
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/service_config.go
@@ -0,0 +1,434 @@
+/*
+ *
+ * Copyright 2017 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package grpc
+
+import (
+	"encoding/json"
+	"fmt"
+	"strconv"
+	"strings"
+	"time"
+
+	"google.golang.org/grpc/balancer"
+	"google.golang.org/grpc/codes"
+	"google.golang.org/grpc/grpclog"
+	"google.golang.org/grpc/internal"
+	"google.golang.org/grpc/serviceconfig"
+)
+
+const maxInt = int(^uint(0) >> 1)
+
+// MethodConfig defines the configuration recommended by the service providers for a
+// particular method.
+//
+// Deprecated: Users should not use this struct. Service config should be received
+// through name resolver, as specified here
+// https://github.com/grpc/grpc/blob/master/doc/service_config.md
+type MethodConfig struct {
+	// WaitForReady indicates whether RPCs sent to this method should wait until
+	// the connection is ready by default (!failfast). The value specified via the
+	// gRPC client API will override the value set here.
+	WaitForReady *bool
+	// Timeout is the default timeout for RPCs sent to this method. The actual
+	// deadline used will be the minimum of the value specified here and the value
+	// set by the application via the gRPC client API.  If either one is not set,
+	// then the other will be used.  If neither is set, then the RPC has no deadline.
+	Timeout *time.Duration
+	// MaxReqSize is the maximum allowed payload size for an individual request in a
+	// stream (client->server) in bytes. The size which is measured is the serialized
+	// payload after per-message compression (but before stream compression) in bytes.
+	// The actual value used is the minimum of the value specified here and the value set
+	// by the application via the gRPC client API. If either one is not set, then the other
+	// will be used.  If neither is set, then the built-in default is used.
+	MaxReqSize *int
+	// MaxRespSize is the maximum allowed payload size for an individual response in a
+	// stream (server->client) in bytes.
+	MaxRespSize *int
+	// RetryPolicy configures retry options for the method.
+	retryPolicy *retryPolicy
+}
+
+type lbConfig struct {
+	name string
+	cfg  serviceconfig.LoadBalancingConfig
+}
+
+// ServiceConfig is provided by the service provider and contains parameters for how
+// clients that connect to the service should behave.
+//
+// Deprecated: Users should not use this struct. Service config should be received
+// through name resolver, as specified here
+// https://github.com/grpc/grpc/blob/master/doc/service_config.md
+type ServiceConfig struct {
+	serviceconfig.Config
+
+	// LB is the load balancer the service providers recommends. The balancer
+	// specified via grpc.WithBalancer will override this.  This is deprecated;
+	// lbConfigs is preferred.  If lbConfig and LB are both present, lbConfig
+	// will be used.
+	LB *string
+
+	// lbConfig is the service config's load balancing configuration.  If
+	// lbConfig and LB are both present, lbConfig will be used.
+	lbConfig *lbConfig
+
+	// Methods contains a map for the methods in this service.  If there is an
+	// exact match for a method (i.e. /service/method) in the map, use the
+	// corresponding MethodConfig.  If there's no exact match, look for the
+	// default config for the service (/service/) and use the corresponding
+	// MethodConfig if it exists.  Otherwise, the method has no MethodConfig to
+	// use.
+	Methods map[string]MethodConfig
+
+	// If a retryThrottlingPolicy is provided, gRPC will automatically throttle
+	// retry attempts and hedged RPCs when the client’s ratio of failures to
+	// successes exceeds a threshold.
+	//
+	// For each server name, the gRPC client will maintain a token_count which is
+	// initially set to maxTokens, and can take values between 0 and maxTokens.
+	//
+	// Every outgoing RPC (regardless of service or method invoked) will change
+	// token_count as follows:
+	//
+	//   - Every failed RPC will decrement the token_count by 1.
+	//   - Every successful RPC will increment the token_count by tokenRatio.
+	//
+	// If token_count is less than or equal to maxTokens / 2, then RPCs will not
+	// be retried and hedged RPCs will not be sent.
+	retryThrottling *retryThrottlingPolicy
+	// healthCheckConfig must be set as one of the requirement to enable LB channel
+	// health check.
+	healthCheckConfig *healthCheckConfig
+	// rawJSONString stores service config json string that get parsed into
+	// this service config struct.
+	rawJSONString string
+}
+
+// healthCheckConfig defines the go-native version of the LB channel health check config.
+type healthCheckConfig struct {
+	// serviceName is the service name to use in the health-checking request.
+	ServiceName string
+}
+
+// retryPolicy defines the go-native version of the retry policy defined by the
+// service config here:
+// https://github.com/grpc/proposal/blob/master/A6-client-retries.md#integration-with-service-config
+type retryPolicy struct {
+	// MaxAttempts is the maximum number of attempts, including the original RPC.
+	//
+	// This field is required and must be two or greater.
+	maxAttempts int
+
+	// Exponential backoff parameters. The initial retry attempt will occur at
+	// random(0, initialBackoff). In general, the nth attempt will occur at
+	// random(0,
+	//   min(initialBackoff*backoffMultiplier**(n-1), maxBackoff)).
+	//
+	// These fields are required and must be greater than zero.
+	initialBackoff    time.Duration
+	maxBackoff        time.Duration
+	backoffMultiplier float64
+
+	// The set of status codes which may be retried.
+	//
+	// Status codes are specified as strings, e.g., "UNAVAILABLE".
+	//
+	// This field is required and must be non-empty.
+	// Note: a set is used to store this for easy lookup.
+	retryableStatusCodes map[codes.Code]bool
+}
+
+type jsonRetryPolicy struct {
+	MaxAttempts          int
+	InitialBackoff       string
+	MaxBackoff           string
+	BackoffMultiplier    float64
+	RetryableStatusCodes []codes.Code
+}
+
+// retryThrottlingPolicy defines the go-native version of the retry throttling
+// policy defined by the service config here:
+// https://github.com/grpc/proposal/blob/master/A6-client-retries.md#integration-with-service-config
+type retryThrottlingPolicy struct {
+	// The number of tokens starts at maxTokens. The token_count will always be
+	// between 0 and maxTokens.
+	//
+	// This field is required and must be greater than zero.
+	MaxTokens float64
+	// The amount of tokens to add on each successful RPC. Typically this will
+	// be some number between 0 and 1, e.g., 0.1.
+	//
+	// This field is required and must be greater than zero. Up to 3 decimal
+	// places are supported.
+	TokenRatio float64
+}
+
+func parseDuration(s *string) (*time.Duration, error) {
+	if s == nil {
+		return nil, nil
+	}
+	if !strings.HasSuffix(*s, "s") {
+		return nil, fmt.Errorf("malformed duration %q", *s)
+	}
+	ss := strings.SplitN((*s)[:len(*s)-1], ".", 3)
+	if len(ss) > 2 {
+		return nil, fmt.Errorf("malformed duration %q", *s)
+	}
+	// hasDigits is set if either the whole or fractional part of the number is
+	// present, since both are optional but one is required.
+	hasDigits := false
+	var d time.Duration
+	if len(ss[0]) > 0 {
+		i, err := strconv.ParseInt(ss[0], 10, 32)
+		if err != nil {
+			return nil, fmt.Errorf("malformed duration %q: %v", *s, err)
+		}
+		d = time.Duration(i) * time.Second
+		hasDigits = true
+	}
+	if len(ss) == 2 && len(ss[1]) > 0 {
+		if len(ss[1]) > 9 {
+			return nil, fmt.Errorf("malformed duration %q", *s)
+		}
+		f, err := strconv.ParseInt(ss[1], 10, 64)
+		if err != nil {
+			return nil, fmt.Errorf("malformed duration %q: %v", *s, err)
+		}
+		for i := 9; i > len(ss[1]); i-- {
+			f *= 10
+		}
+		d += time.Duration(f)
+		hasDigits = true
+	}
+	if !hasDigits {
+		return nil, fmt.Errorf("malformed duration %q", *s)
+	}
+
+	return &d, nil
+}
+
+type jsonName struct {
+	Service *string
+	Method  *string
+}
+
+func (j jsonName) generatePath() (string, bool) {
+	if j.Service == nil {
+		return "", false
+	}
+	res := "/" + *j.Service + "/"
+	if j.Method != nil {
+		res += *j.Method
+	}
+	return res, true
+}
+
+// TODO(lyuxuan): delete this struct after cleaning up old service config implementation.
+type jsonMC struct {
+	Name                    *[]jsonName
+	WaitForReady            *bool
+	Timeout                 *string
+	MaxRequestMessageBytes  *int64
+	MaxResponseMessageBytes *int64
+	RetryPolicy             *jsonRetryPolicy
+}
+
+type loadBalancingConfig map[string]json.RawMessage
+
+// TODO(lyuxuan): delete this struct after cleaning up old service config implementation.
+type jsonSC struct {
+	LoadBalancingPolicy *string
+	LoadBalancingConfig *[]loadBalancingConfig
+	MethodConfig        *[]jsonMC
+	RetryThrottling     *retryThrottlingPolicy
+	HealthCheckConfig   *healthCheckConfig
+}
+
+func init() {
+	internal.ParseServiceConfigForTesting = parseServiceConfig
+}
+func parseServiceConfig(js string) *serviceconfig.ParseResult {
+	if len(js) == 0 {
+		return &serviceconfig.ParseResult{Err: fmt.Errorf("no JSON service config provided")}
+	}
+	var rsc jsonSC
+	err := json.Unmarshal([]byte(js), &rsc)
+	if err != nil {
+		grpclog.Warningf("grpc: parseServiceConfig error unmarshaling %s due to %v", js, err)
+		return &serviceconfig.ParseResult{Err: err}
+	}
+	sc := ServiceConfig{
+		LB:                rsc.LoadBalancingPolicy,
+		Methods:           make(map[string]MethodConfig),
+		retryThrottling:   rsc.RetryThrottling,
+		healthCheckConfig: rsc.HealthCheckConfig,
+		rawJSONString:     js,
+	}
+	if rsc.LoadBalancingConfig != nil {
+		for i, lbcfg := range *rsc.LoadBalancingConfig {
+			if len(lbcfg) != 1 {
+				err := fmt.Errorf("invalid loadBalancingConfig: entry %v does not contain exactly 1 policy/config pair: %q", i, lbcfg)
+				grpclog.Warningf(err.Error())
+				return &serviceconfig.ParseResult{Err: err}
+			}
+			var name string
+			var jsonCfg json.RawMessage
+			for name, jsonCfg = range lbcfg {
+			}
+			builder := balancer.Get(name)
+			if builder == nil {
+				continue
+			}
+			sc.lbConfig = &lbConfig{name: name}
+			if parser, ok := builder.(balancer.ConfigParser); ok {
+				var err error
+				sc.lbConfig.cfg, err = parser.ParseConfig(jsonCfg)
+				if err != nil {
+					return &serviceconfig.ParseResult{Err: fmt.Errorf("error parsing loadBalancingConfig for policy %q: %v", name, err)}
+				}
+			} else if string(jsonCfg) != "{}" {
+				grpclog.Warningf("non-empty balancer configuration %q, but balancer does not implement ParseConfig", string(jsonCfg))
+			}
+			break
+		}
+		if sc.lbConfig == nil {
+			// We had a loadBalancingConfig field but did not encounter a
+			// supported policy.  The config is considered invalid in this
+			// case.
+			err := fmt.Errorf("invalid loadBalancingConfig: no supported policies found")
+			grpclog.Warningf(err.Error())
+			return &serviceconfig.ParseResult{Err: err}
+		}
+	}
+
+	if rsc.MethodConfig == nil {
+		return &serviceconfig.ParseResult{Config: &sc}
+	}
+	for _, m := range *rsc.MethodConfig {
+		if m.Name == nil {
+			continue
+		}
+		d, err := parseDuration(m.Timeout)
+		if err != nil {
+			grpclog.Warningf("grpc: parseServiceConfig error unmarshaling %s due to %v", js, err)
+			return &serviceconfig.ParseResult{Err: err}
+		}
+
+		mc := MethodConfig{
+			WaitForReady: m.WaitForReady,
+			Timeout:      d,
+		}
+		if mc.retryPolicy, err = convertRetryPolicy(m.RetryPolicy); err != nil {
+			grpclog.Warningf("grpc: parseServiceConfig error unmarshaling %s due to %v", js, err)
+			return &serviceconfig.ParseResult{Err: err}
+		}
+		if m.MaxRequestMessageBytes != nil {
+			if *m.MaxRequestMessageBytes > int64(maxInt) {
+				mc.MaxReqSize = newInt(maxInt)
+			} else {
+				mc.MaxReqSize = newInt(int(*m.MaxRequestMessageBytes))
+			}
+		}
+		if m.MaxResponseMessageBytes != nil {
+			if *m.MaxResponseMessageBytes > int64(maxInt) {
+				mc.MaxRespSize = newInt(maxInt)
+			} else {
+				mc.MaxRespSize = newInt(int(*m.MaxResponseMessageBytes))
+			}
+		}
+		for _, n := range *m.Name {
+			if path, valid := n.generatePath(); valid {
+				sc.Methods[path] = mc
+			}
+		}
+	}
+
+	if sc.retryThrottling != nil {
+		if mt := sc.retryThrottling.MaxTokens; mt <= 0 || mt > 1000 {
+			return &serviceconfig.ParseResult{Err: fmt.Errorf("invalid retry throttling config: maxTokens (%v) out of range (0, 1000]", mt)}
+		}
+		if tr := sc.retryThrottling.TokenRatio; tr <= 0 {
+			return &serviceconfig.ParseResult{Err: fmt.Errorf("invalid retry throttling config: tokenRatio (%v) may not be negative", tr)}
+		}
+	}
+	return &serviceconfig.ParseResult{Config: &sc}
+}
+
+func convertRetryPolicy(jrp *jsonRetryPolicy) (p *retryPolicy, err error) {
+	if jrp == nil {
+		return nil, nil
+	}
+	ib, err := parseDuration(&jrp.InitialBackoff)
+	if err != nil {
+		return nil, err
+	}
+	mb, err := parseDuration(&jrp.MaxBackoff)
+	if err != nil {
+		return nil, err
+	}
+
+	if jrp.MaxAttempts <= 1 ||
+		*ib <= 0 ||
+		*mb <= 0 ||
+		jrp.BackoffMultiplier <= 0 ||
+		len(jrp.RetryableStatusCodes) == 0 {
+		grpclog.Warningf("grpc: ignoring retry policy %v due to illegal configuration", jrp)
+		return nil, nil
+	}
+
+	rp := &retryPolicy{
+		maxAttempts:          jrp.MaxAttempts,
+		initialBackoff:       *ib,
+		maxBackoff:           *mb,
+		backoffMultiplier:    jrp.BackoffMultiplier,
+		retryableStatusCodes: make(map[codes.Code]bool),
+	}
+	if rp.maxAttempts > 5 {
+		// TODO(retry): Make the max maxAttempts configurable.
+		rp.maxAttempts = 5
+	}
+	for _, code := range jrp.RetryableStatusCodes {
+		rp.retryableStatusCodes[code] = true
+	}
+	return rp, nil
+}
+
+func min(a, b *int) *int {
+	if *a < *b {
+		return a
+	}
+	return b
+}
+
+func getMaxSize(mcMax, doptMax *int, defaultVal int) *int {
+	if mcMax == nil && doptMax == nil {
+		return &defaultVal
+	}
+	if mcMax != nil && doptMax != nil {
+		return min(mcMax, doptMax)
+	}
+	if mcMax != nil {
+		return mcMax
+	}
+	return doptMax
+}
+
+func newInt(b int) *int {
+	return &b
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/serviceconfig/serviceconfig.go b/demo_test/vendor/google.golang.org/grpc/serviceconfig/serviceconfig.go
new file mode 100644
index 0000000..187c304
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/serviceconfig/serviceconfig.go
@@ -0,0 +1,41 @@
+/*
+ *
+ * Copyright 2019 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+// Package serviceconfig defines types and methods for operating on gRPC
+// service configs.
+//
+// This package is EXPERIMENTAL.
+package serviceconfig
+
+// Config represents an opaque data structure holding a service config.
+type Config interface {
+	isServiceConfig()
+}
+
+// LoadBalancingConfig represents an opaque data structure holding a load
+// balancing config.
+type LoadBalancingConfig interface {
+	isLoadBalancingConfig()
+}
+
+// ParseResult contains a service config or an error.  Exactly one must be
+// non-nil.
+type ParseResult struct {
+	Config Config
+	Err    error
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/stats/handlers.go b/demo_test/vendor/google.golang.org/grpc/stats/handlers.go
new file mode 100644
index 0000000..dc03731
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/stats/handlers.go
@@ -0,0 +1,63 @@
+/*
+ *
+ * Copyright 2016 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package stats
+
+import (
+	"context"
+	"net"
+)
+
+// ConnTagInfo defines the relevant information needed by connection context tagger.
+type ConnTagInfo struct {
+	// RemoteAddr is the remote address of the corresponding connection.
+	RemoteAddr net.Addr
+	// LocalAddr is the local address of the corresponding connection.
+	LocalAddr net.Addr
+}
+
+// RPCTagInfo defines the relevant information needed by RPC context tagger.
+type RPCTagInfo struct {
+	// FullMethodName is the RPC method in the format of /package.service/method.
+	FullMethodName string
+	// FailFast indicates if this RPC is failfast.
+	// This field is only valid on client side, it's always false on server side.
+	FailFast bool
+}
+
+// Handler defines the interface for the related stats handling (e.g., RPCs, connections).
+type Handler interface {
+	// TagRPC can attach some information to the given context.
+	// The context used for the rest lifetime of the RPC will be derived from
+	// the returned context.
+	TagRPC(context.Context, *RPCTagInfo) context.Context
+	// HandleRPC processes the RPC stats.
+	HandleRPC(context.Context, RPCStats)
+
+	// TagConn can attach some information to the given context.
+	// The returned context will be used for stats handling.
+	// For conn stats handling, the context used in HandleConn for this
+	// connection will be derived from the context returned.
+	// For RPC stats handling,
+	//  - On server side, the context used in HandleRPC for all RPCs on this
+	// connection will be derived from the context returned.
+	//  - On client side, the context is not derived from the context returned.
+	TagConn(context.Context, *ConnTagInfo) context.Context
+	// HandleConn processes the Conn stats.
+	HandleConn(context.Context, ConnStats)
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/stats/stats.go b/demo_test/vendor/google.golang.org/grpc/stats/stats.go
new file mode 100644
index 0000000..a7970c7
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/stats/stats.go
@@ -0,0 +1,314 @@
+/*
+ *
+ * Copyright 2016 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+//go:generate protoc --go_out=plugins=grpc:. grpc_testing/test.proto
+
+// Package stats is for collecting and reporting various network and RPC stats.
+// This package is for monitoring purpose only. All fields are read-only.
+// All APIs are experimental.
+package stats // import "google.golang.org/grpc/stats"
+
+import (
+	"context"
+	"net"
+	"time"
+
+	"google.golang.org/grpc/metadata"
+)
+
+// RPCStats contains stats information about RPCs.
+type RPCStats interface {
+	isRPCStats()
+	// IsClient returns true if this RPCStats is from client side.
+	IsClient() bool
+}
+
+// Begin contains stats when an RPC begins.
+// FailFast is only valid if this Begin is from client side.
+type Begin struct {
+	// Client is true if this Begin is from client side.
+	Client bool
+	// BeginTime is the time when the RPC begins.
+	BeginTime time.Time
+	// FailFast indicates if this RPC is failfast.
+	FailFast bool
+}
+
+// IsClient indicates if the stats information is from client side.
+func (s *Begin) IsClient() bool { return s.Client }
+
+func (s *Begin) isRPCStats() {}
+
+// InPayload contains the information for an incoming payload.
+type InPayload struct {
+	// Client is true if this InPayload is from client side.
+	Client bool
+	// Payload is the payload with original type.
+	Payload interface{}
+	// Data is the serialized message payload.
+	Data []byte
+	// Length is the length of uncompressed data.
+	Length int
+	// WireLength is the length of data on wire (compressed, signed, encrypted).
+	WireLength int
+	// RecvTime is the time when the payload is received.
+	RecvTime time.Time
+}
+
+// IsClient indicates if the stats information is from client side.
+func (s *InPayload) IsClient() bool { return s.Client }
+
+func (s *InPayload) isRPCStats() {}
+
+// InHeader contains stats when a header is received.
+type InHeader struct {
+	// Client is true if this InHeader is from client side.
+	Client bool
+	// WireLength is the wire length of header.
+	WireLength int
+	// Compression is the compression algorithm used for the RPC.
+	Compression string
+	// Header contains the header metadata received.
+	Header metadata.MD
+
+	// The following fields are valid only if Client is false.
+	// FullMethod is the full RPC method string, i.e., /package.service/method.
+	FullMethod string
+	// RemoteAddr is the remote address of the corresponding connection.
+	RemoteAddr net.Addr
+	// LocalAddr is the local address of the corresponding connection.
+	LocalAddr net.Addr
+}
+
+// IsClient indicates if the stats information is from client side.
+func (s *InHeader) IsClient() bool { return s.Client }
+
+func (s *InHeader) isRPCStats() {}
+
+// InTrailer contains stats when a trailer is received.
+type InTrailer struct {
+	// Client is true if this InTrailer is from client side.
+	Client bool
+	// WireLength is the wire length of trailer.
+	WireLength int
+	// Trailer contains the trailer metadata received from the server. This
+	// field is only valid if this InTrailer is from the client side.
+	Trailer metadata.MD
+}
+
+// IsClient indicates if the stats information is from client side.
+func (s *InTrailer) IsClient() bool { return s.Client }
+
+func (s *InTrailer) isRPCStats() {}
+
+// OutPayload contains the information for an outgoing payload.
+type OutPayload struct {
+	// Client is true if this OutPayload is from client side.
+	Client bool
+	// Payload is the payload with original type.
+	Payload interface{}
+	// Data is the serialized message payload.
+	Data []byte
+	// Length is the length of uncompressed data.
+	Length int
+	// WireLength is the length of data on wire (compressed, signed, encrypted).
+	WireLength int
+	// SentTime is the time when the payload is sent.
+	SentTime time.Time
+}
+
+// IsClient indicates if this stats information is from client side.
+func (s *OutPayload) IsClient() bool { return s.Client }
+
+func (s *OutPayload) isRPCStats() {}
+
+// OutHeader contains stats when a header is sent.
+type OutHeader struct {
+	// Client is true if this OutHeader is from client side.
+	Client bool
+	// Compression is the compression algorithm used for the RPC.
+	Compression string
+	// Header contains the header metadata sent.
+	Header metadata.MD
+
+	// The following fields are valid only if Client is true.
+	// FullMethod is the full RPC method string, i.e., /package.service/method.
+	FullMethod string
+	// RemoteAddr is the remote address of the corresponding connection.
+	RemoteAddr net.Addr
+	// LocalAddr is the local address of the corresponding connection.
+	LocalAddr net.Addr
+}
+
+// IsClient indicates if this stats information is from client side.
+func (s *OutHeader) IsClient() bool { return s.Client }
+
+func (s *OutHeader) isRPCStats() {}
+
+// OutTrailer contains stats when a trailer is sent.
+type OutTrailer struct {
+	// Client is true if this OutTrailer is from client side.
+	Client bool
+	// WireLength is the wire length of trailer.
+	//
+	// Deprecated: This field is never set. The length is not known when this message is
+	// emitted because the trailer fields are compressed with hpack after that.
+	WireLength int
+	// Trailer contains the trailer metadata sent to the client. This
+	// field is only valid if this OutTrailer is from the server side.
+	Trailer metadata.MD
+}
+
+// IsClient indicates if this stats information is from client side.
+func (s *OutTrailer) IsClient() bool { return s.Client }
+
+func (s *OutTrailer) isRPCStats() {}
+
+// End contains stats when an RPC ends.
+type End struct {
+	// Client is true if this End is from client side.
+	Client bool
+	// BeginTime is the time when the RPC began.
+	BeginTime time.Time
+	// EndTime is the time when the RPC ends.
+	EndTime time.Time
+	// Trailer contains the trailer metadata received from the server. This
+	// field is only valid if this End is from the client side.
+	// Deprecated: use Trailer in InTrailer instead.
+	Trailer metadata.MD
+	// Error is the error the RPC ended with. It is an error generated from
+	// status.Status and can be converted back to status.Status using
+	// status.FromError if non-nil.
+	Error error
+}
+
+// IsClient indicates if this is from client side.
+func (s *End) IsClient() bool { return s.Client }
+
+func (s *End) isRPCStats() {}
+
+// ConnStats contains stats information about connections.
+type ConnStats interface {
+	isConnStats()
+	// IsClient returns true if this ConnStats is from client side.
+	IsClient() bool
+}
+
+// ConnBegin contains the stats of a connection when it is established.
+type ConnBegin struct {
+	// Client is true if this ConnBegin is from client side.
+	Client bool
+}
+
+// IsClient indicates if this is from client side.
+func (s *ConnBegin) IsClient() bool { return s.Client }
+
+func (s *ConnBegin) isConnStats() {}
+
+// ConnEnd contains the stats of a connection when it ends.
+type ConnEnd struct {
+	// Client is true if this ConnEnd is from client side.
+	Client bool
+}
+
+// IsClient indicates if this is from client side.
+func (s *ConnEnd) IsClient() bool { return s.Client }
+
+func (s *ConnEnd) isConnStats() {}
+
+type incomingTagsKey struct{}
+type outgoingTagsKey struct{}
+
+// SetTags attaches stats tagging data to the context, which will be sent in
+// the outgoing RPC with the header grpc-tags-bin.  Subsequent calls to
+// SetTags will overwrite the values from earlier calls.
+//
+// NOTE: this is provided only for backward compatibility with existing clients
+// and will likely be removed in an upcoming release.  New uses should transmit
+// this type of data using metadata with a different, non-reserved (i.e. does
+// not begin with "grpc-") header name.
+func SetTags(ctx context.Context, b []byte) context.Context {
+	return context.WithValue(ctx, outgoingTagsKey{}, b)
+}
+
+// Tags returns the tags from the context for the inbound RPC.
+//
+// NOTE: this is provided only for backward compatibility with existing clients
+// and will likely be removed in an upcoming release.  New uses should transmit
+// this type of data using metadata with a different, non-reserved (i.e. does
+// not begin with "grpc-") header name.
+func Tags(ctx context.Context) []byte {
+	b, _ := ctx.Value(incomingTagsKey{}).([]byte)
+	return b
+}
+
+// SetIncomingTags attaches stats tagging data to the context, to be read by
+// the application (not sent in outgoing RPCs).
+//
+// This is intended for gRPC-internal use ONLY.
+func SetIncomingTags(ctx context.Context, b []byte) context.Context {
+	return context.WithValue(ctx, incomingTagsKey{}, b)
+}
+
+// OutgoingTags returns the tags from the context for the outbound RPC.
+//
+// This is intended for gRPC-internal use ONLY.
+func OutgoingTags(ctx context.Context) []byte {
+	b, _ := ctx.Value(outgoingTagsKey{}).([]byte)
+	return b
+}
+
+type incomingTraceKey struct{}
+type outgoingTraceKey struct{}
+
+// SetTrace attaches stats tagging data to the context, which will be sent in
+// the outgoing RPC with the header grpc-trace-bin.  Subsequent calls to
+// SetTrace will overwrite the values from earlier calls.
+//
+// NOTE: this is provided only for backward compatibility with existing clients
+// and will likely be removed in an upcoming release.  New uses should transmit
+// this type of data using metadata with a different, non-reserved (i.e. does
+// not begin with "grpc-") header name.
+func SetTrace(ctx context.Context, b []byte) context.Context {
+	return context.WithValue(ctx, outgoingTraceKey{}, b)
+}
+
+// Trace returns the trace from the context for the inbound RPC.
+//
+// NOTE: this is provided only for backward compatibility with existing clients
+// and will likely be removed in an upcoming release.  New uses should transmit
+// this type of data using metadata with a different, non-reserved (i.e. does
+// not begin with "grpc-") header name.
+func Trace(ctx context.Context) []byte {
+	b, _ := ctx.Value(incomingTraceKey{}).([]byte)
+	return b
+}
+
+// SetIncomingTrace attaches stats tagging data to the context, to be read by
+// the application (not sent in outgoing RPCs).  It is intended for
+// gRPC-internal use.
+func SetIncomingTrace(ctx context.Context, b []byte) context.Context {
+	return context.WithValue(ctx, incomingTraceKey{}, b)
+}
+
+// OutgoingTrace returns the trace from the context for the outbound RPC.  It is
+// intended for gRPC-internal use.
+func OutgoingTrace(ctx context.Context) []byte {
+	b, _ := ctx.Value(outgoingTraceKey{}).([]byte)
+	return b
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/status/status.go b/demo_test/vendor/google.golang.org/grpc/status/status.go
new file mode 100644
index 0000000..01e182c
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/status/status.go
@@ -0,0 +1,127 @@
+/*
+ *
+ * Copyright 2017 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+// Package status implements errors returned by gRPC.  These errors are
+// serialized and transmitted on the wire between server and client, and allow
+// for additional data to be transmitted via the Details field in the status
+// proto.  gRPC service handlers should return an error created by this
+// package, and gRPC clients should expect a corresponding error to be
+// returned from the RPC call.
+//
+// This package upholds the invariants that a non-nil error may not
+// contain an OK code, and an OK code must result in a nil error.
+package status
+
+import (
+	"context"
+	"fmt"
+
+	spb "google.golang.org/genproto/googleapis/rpc/status"
+
+	"google.golang.org/grpc/codes"
+	"google.golang.org/grpc/internal/status"
+)
+
+// Status references google.golang.org/grpc/internal/status. It represents an
+// RPC status code, message, and details.  It is immutable and should be
+// created with New, Newf, or FromProto.
+// https://godoc.org/google.golang.org/grpc/internal/status
+type Status = status.Status
+
+// New returns a Status representing c and msg.
+func New(c codes.Code, msg string) *Status {
+	return status.New(c, msg)
+}
+
+// Newf returns New(c, fmt.Sprintf(format, a...)).
+func Newf(c codes.Code, format string, a ...interface{}) *Status {
+	return New(c, fmt.Sprintf(format, a...))
+}
+
+// Error returns an error representing c and msg.  If c is OK, returns nil.
+func Error(c codes.Code, msg string) error {
+	return New(c, msg).Err()
+}
+
+// Errorf returns Error(c, fmt.Sprintf(format, a...)).
+func Errorf(c codes.Code, format string, a ...interface{}) error {
+	return Error(c, fmt.Sprintf(format, a...))
+}
+
+// ErrorProto returns an error representing s.  If s.Code is OK, returns nil.
+func ErrorProto(s *spb.Status) error {
+	return FromProto(s).Err()
+}
+
+// FromProto returns a Status representing s.
+func FromProto(s *spb.Status) *Status {
+	return status.FromProto(s)
+}
+
+// FromError returns a Status representing err if it was produced from this
+// package or has a method `GRPCStatus() *Status`. Otherwise, ok is false and a
+// Status is returned with codes.Unknown and the original error message.
+func FromError(err error) (s *Status, ok bool) {
+	if err == nil {
+		return nil, true
+	}
+	if se, ok := err.(interface {
+		GRPCStatus() *Status
+	}); ok {
+		return se.GRPCStatus(), true
+	}
+	return New(codes.Unknown, err.Error()), false
+}
+
+// Convert is a convenience function which removes the need to handle the
+// boolean return value from FromError.
+func Convert(err error) *Status {
+	s, _ := FromError(err)
+	return s
+}
+
+// Code returns the Code of the error if it is a Status error, codes.OK if err
+// is nil, or codes.Unknown otherwise.
+func Code(err error) codes.Code {
+	// Don't use FromError to avoid allocation of OK status.
+	if err == nil {
+		return codes.OK
+	}
+	if se, ok := err.(interface {
+		GRPCStatus() *Status
+	}); ok {
+		return se.GRPCStatus().Code()
+	}
+	return codes.Unknown
+}
+
+// FromContextError converts a context error into a Status.  It returns a
+// Status with codes.OK if err is nil, or a Status with codes.Unknown if err is
+// non-nil and not a context error.
+func FromContextError(err error) *Status {
+	switch err {
+	case nil:
+		return nil
+	case context.DeadlineExceeded:
+		return New(codes.DeadlineExceeded, err.Error())
+	case context.Canceled:
+		return New(codes.Canceled, err.Error())
+	default:
+		return New(codes.Unknown, err.Error())
+	}
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/stream.go b/demo_test/vendor/google.golang.org/grpc/stream.go
new file mode 100644
index 0000000..934ef68
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/stream.go
@@ -0,0 +1,1528 @@
+/*
+ *
+ * Copyright 2014 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package grpc
+
+import (
+	"context"
+	"errors"
+	"io"
+	"math"
+	"strconv"
+	"sync"
+	"time"
+
+	"golang.org/x/net/trace"
+	"google.golang.org/grpc/balancer"
+	"google.golang.org/grpc/codes"
+	"google.golang.org/grpc/encoding"
+	"google.golang.org/grpc/internal/balancerload"
+	"google.golang.org/grpc/internal/binarylog"
+	"google.golang.org/grpc/internal/channelz"
+	"google.golang.org/grpc/internal/grpcrand"
+	"google.golang.org/grpc/internal/transport"
+	"google.golang.org/grpc/metadata"
+	"google.golang.org/grpc/peer"
+	"google.golang.org/grpc/stats"
+	"google.golang.org/grpc/status"
+)
+
+// StreamHandler defines the handler called by gRPC server to complete the
+// execution of a streaming RPC. If a StreamHandler returns an error, it
+// should be produced by the status package, or else gRPC will use
+// codes.Unknown as the status code and err.Error() as the status message
+// of the RPC.
+type StreamHandler func(srv interface{}, stream ServerStream) error
+
+// StreamDesc represents a streaming RPC service's method specification.
+type StreamDesc struct {
+	StreamName string
+	Handler    StreamHandler
+
+	// At least one of these is true.
+	ServerStreams bool
+	ClientStreams bool
+}
+
+// Stream defines the common interface a client or server stream has to satisfy.
+//
+// Deprecated: See ClientStream and ServerStream documentation instead.
+type Stream interface {
+	// Deprecated: See ClientStream and ServerStream documentation instead.
+	Context() context.Context
+	// Deprecated: See ClientStream and ServerStream documentation instead.
+	SendMsg(m interface{}) error
+	// Deprecated: See ClientStream and ServerStream documentation instead.
+	RecvMsg(m interface{}) error
+}
+
+// ClientStream defines the client-side behavior of a streaming RPC.
+//
+// All errors returned from ClientStream methods are compatible with the
+// status package.
+type ClientStream interface {
+	// Header returns the header metadata received from the server if there
+	// is any. It blocks if the metadata is not ready to read.
+	Header() (metadata.MD, error)
+	// Trailer returns the trailer metadata from the server, if there is any.
+	// It must only be called after stream.CloseAndRecv has returned, or
+	// stream.Recv has returned a non-nil error (including io.EOF).
+	Trailer() metadata.MD
+	// CloseSend closes the send direction of the stream. It closes the stream
+	// when non-nil error is met. It is also not safe to call CloseSend
+	// concurrently with SendMsg.
+	CloseSend() error
+	// Context returns the context for this stream.
+	//
+	// It should not be called until after Header or RecvMsg has returned. Once
+	// called, subsequent client-side retries are disabled.
+	Context() context.Context
+	// SendMsg is generally called by generated code. On error, SendMsg aborts
+	// the stream. If the error was generated by the client, the status is
+	// returned directly; otherwise, io.EOF is returned and the status of
+	// the stream may be discovered using RecvMsg.
+	//
+	// SendMsg blocks until:
+	//   - There is sufficient flow control to schedule m with the transport, or
+	//   - The stream is done, or
+	//   - The stream breaks.
+	//
+	// SendMsg does not wait until the message is received by the server. An
+	// untimely stream closure may result in lost messages. To ensure delivery,
+	// users should ensure the RPC completed successfully using RecvMsg.
+	//
+	// It is safe to have a goroutine calling SendMsg and another goroutine
+	// calling RecvMsg on the same stream at the same time, but it is not safe
+	// to call SendMsg on the same stream in different goroutines. It is also
+	// not safe to call CloseSend concurrently with SendMsg.
+	SendMsg(m interface{}) error
+	// RecvMsg blocks until it receives a message into m or the stream is
+	// done. It returns io.EOF when the stream completes successfully. On
+	// any other error, the stream is aborted and the error contains the RPC
+	// status.
+	//
+	// It is safe to have a goroutine calling SendMsg and another goroutine
+	// calling RecvMsg on the same stream at the same time, but it is not
+	// safe to call RecvMsg on the same stream in different goroutines.
+	RecvMsg(m interface{}) error
+}
+
+// NewStream creates a new Stream for the client side. This is typically
+// called by generated code. ctx is used for the lifetime of the stream.
+//
+// To ensure resources are not leaked due to the stream returned, one of the following
+// actions must be performed:
+//
+//      1. Call Close on the ClientConn.
+//      2. Cancel the context provided.
+//      3. Call RecvMsg until a non-nil error is returned. A protobuf-generated
+//         client-streaming RPC, for instance, might use the helper function
+//         CloseAndRecv (note that CloseSend does not Recv, therefore is not
+//         guaranteed to release all resources).
+//      4. Receive a non-nil, non-io.EOF error from Header or SendMsg.
+//
+// If none of the above happen, a goroutine and a context will be leaked, and grpc
+// will not call the optionally-configured stats handler with a stats.End message.
+func (cc *ClientConn) NewStream(ctx context.Context, desc *StreamDesc, method string, opts ...CallOption) (ClientStream, error) {
+	// allow interceptor to see all applicable call options, which means those
+	// configured as defaults from dial option as well as per-call options
+	opts = combine(cc.dopts.callOptions, opts)
+
+	if cc.dopts.streamInt != nil {
+		return cc.dopts.streamInt(ctx, desc, cc, method, newClientStream, opts...)
+	}
+	return newClientStream(ctx, desc, cc, method, opts...)
+}
+
+// NewClientStream is a wrapper for ClientConn.NewStream.
+func NewClientStream(ctx context.Context, desc *StreamDesc, cc *ClientConn, method string, opts ...CallOption) (ClientStream, error) {
+	return cc.NewStream(ctx, desc, method, opts...)
+}
+
+func newClientStream(ctx context.Context, desc *StreamDesc, cc *ClientConn, method string, opts ...CallOption) (_ ClientStream, err error) {
+	if channelz.IsOn() {
+		cc.incrCallsStarted()
+		defer func() {
+			if err != nil {
+				cc.incrCallsFailed()
+			}
+		}()
+	}
+	c := defaultCallInfo()
+	// Provide an opportunity for the first RPC to see the first service config
+	// provided by the resolver.
+	if err := cc.waitForResolvedAddrs(ctx); err != nil {
+		return nil, err
+	}
+	mc := cc.GetMethodConfig(method)
+	if mc.WaitForReady != nil {
+		c.failFast = !*mc.WaitForReady
+	}
+
+	// Possible context leak:
+	// The cancel function for the child context we create will only be called
+	// when RecvMsg returns a non-nil error, if the ClientConn is closed, or if
+	// an error is generated by SendMsg.
+	// https://github.com/grpc/grpc-go/issues/1818.
+	var cancel context.CancelFunc
+	if mc.Timeout != nil && *mc.Timeout >= 0 {
+		ctx, cancel = context.WithTimeout(ctx, *mc.Timeout)
+	} else {
+		ctx, cancel = context.WithCancel(ctx)
+	}
+	defer func() {
+		if err != nil {
+			cancel()
+		}
+	}()
+
+	for _, o := range opts {
+		if err := o.before(c); err != nil {
+			return nil, toRPCErr(err)
+		}
+	}
+	c.maxSendMessageSize = getMaxSize(mc.MaxReqSize, c.maxSendMessageSize, defaultClientMaxSendMessageSize)
+	c.maxReceiveMessageSize = getMaxSize(mc.MaxRespSize, c.maxReceiveMessageSize, defaultClientMaxReceiveMessageSize)
+	if err := setCallInfoCodec(c); err != nil {
+		return nil, err
+	}
+
+	callHdr := &transport.CallHdr{
+		Host:           cc.authority,
+		Method:         method,
+		ContentSubtype: c.contentSubtype,
+	}
+
+	// Set our outgoing compression according to the UseCompressor CallOption, if
+	// set.  In that case, also find the compressor from the encoding package.
+	// Otherwise, use the compressor configured by the WithCompressor DialOption,
+	// if set.
+	var cp Compressor
+	var comp encoding.Compressor
+	if ct := c.compressorType; ct != "" {
+		callHdr.SendCompress = ct
+		if ct != encoding.Identity {
+			comp = encoding.GetCompressor(ct)
+			if comp == nil {
+				return nil, status.Errorf(codes.Internal, "grpc: Compressor is not installed for requested grpc-encoding %q", ct)
+			}
+		}
+	} else if cc.dopts.cp != nil {
+		callHdr.SendCompress = cc.dopts.cp.Type()
+		cp = cc.dopts.cp
+	}
+	if c.creds != nil {
+		callHdr.Creds = c.creds
+	}
+	var trInfo *traceInfo
+	if EnableTracing {
+		trInfo = &traceInfo{
+			tr: trace.New("grpc.Sent."+methodFamily(method), method),
+			firstLine: firstLine{
+				client: true,
+			},
+		}
+		if deadline, ok := ctx.Deadline(); ok {
+			trInfo.firstLine.deadline = time.Until(deadline)
+		}
+		trInfo.tr.LazyLog(&trInfo.firstLine, false)
+		ctx = trace.NewContext(ctx, trInfo.tr)
+	}
+	ctx = newContextWithRPCInfo(ctx, c.failFast, c.codec, cp, comp)
+	sh := cc.dopts.copts.StatsHandler
+	var beginTime time.Time
+	if sh != nil {
+		ctx = sh.TagRPC(ctx, &stats.RPCTagInfo{FullMethodName: method, FailFast: c.failFast})
+		beginTime = time.Now()
+		begin := &stats.Begin{
+			Client:    true,
+			BeginTime: beginTime,
+			FailFast:  c.failFast,
+		}
+		sh.HandleRPC(ctx, begin)
+	}
+
+	cs := &clientStream{
+		callHdr:      callHdr,
+		ctx:          ctx,
+		methodConfig: &mc,
+		opts:         opts,
+		callInfo:     c,
+		cc:           cc,
+		desc:         desc,
+		codec:        c.codec,
+		cp:           cp,
+		comp:         comp,
+		cancel:       cancel,
+		beginTime:    beginTime,
+		firstAttempt: true,
+	}
+	if !cc.dopts.disableRetry {
+		cs.retryThrottler = cc.retryThrottler.Load().(*retryThrottler)
+	}
+	cs.binlog = binarylog.GetMethodLogger(method)
+
+	cs.callInfo.stream = cs
+	// Only this initial attempt has stats/tracing.
+	// TODO(dfawley): move to newAttempt when per-attempt stats are implemented.
+	if err := cs.newAttemptLocked(sh, trInfo); err != nil {
+		cs.finish(err)
+		return nil, err
+	}
+
+	op := func(a *csAttempt) error { return a.newStream() }
+	if err := cs.withRetry(op, func() { cs.bufferForRetryLocked(0, op) }); err != nil {
+		cs.finish(err)
+		return nil, err
+	}
+
+	if cs.binlog != nil {
+		md, _ := metadata.FromOutgoingContext(ctx)
+		logEntry := &binarylog.ClientHeader{
+			OnClientSide: true,
+			Header:       md,
+			MethodName:   method,
+			Authority:    cs.cc.authority,
+		}
+		if deadline, ok := ctx.Deadline(); ok {
+			logEntry.Timeout = time.Until(deadline)
+			if logEntry.Timeout < 0 {
+				logEntry.Timeout = 0
+			}
+		}
+		cs.binlog.Log(logEntry)
+	}
+
+	if desc != unaryStreamDesc {
+		// Listen on cc and stream contexts to cleanup when the user closes the
+		// ClientConn or cancels the stream context.  In all other cases, an error
+		// should already be injected into the recv buffer by the transport, which
+		// the client will eventually receive, and then we will cancel the stream's
+		// context in clientStream.finish.
+		go func() {
+			select {
+			case <-cc.ctx.Done():
+				cs.finish(ErrClientConnClosing)
+			case <-ctx.Done():
+				cs.finish(toRPCErr(ctx.Err()))
+			}
+		}()
+	}
+	return cs, nil
+}
+
+// newAttemptLocked creates a new attempt with a transport.
+// If it succeeds, then it replaces clientStream's attempt with this new attempt.
+func (cs *clientStream) newAttemptLocked(sh stats.Handler, trInfo *traceInfo) (retErr error) {
+	newAttempt := &csAttempt{
+		cs:           cs,
+		dc:           cs.cc.dopts.dc,
+		statsHandler: sh,
+		trInfo:       trInfo,
+	}
+	defer func() {
+		if retErr != nil {
+			// This attempt is not set in the clientStream, so it's finish won't
+			// be called. Call it here for stats and trace in case they are not
+			// nil.
+			newAttempt.finish(retErr)
+		}
+	}()
+
+	if err := cs.ctx.Err(); err != nil {
+		return toRPCErr(err)
+	}
+	t, done, err := cs.cc.getTransport(cs.ctx, cs.callInfo.failFast, cs.callHdr.Method)
+	if err != nil {
+		return err
+	}
+	if trInfo != nil {
+		trInfo.firstLine.SetRemoteAddr(t.RemoteAddr())
+	}
+	newAttempt.t = t
+	newAttempt.done = done
+	cs.attempt = newAttempt
+	return nil
+}
+
+func (a *csAttempt) newStream() error {
+	cs := a.cs
+	cs.callHdr.PreviousAttempts = cs.numRetries
+	s, err := a.t.NewStream(cs.ctx, cs.callHdr)
+	if err != nil {
+		return toRPCErr(err)
+	}
+	cs.attempt.s = s
+	cs.attempt.p = &parser{r: s}
+	return nil
+}
+
+// clientStream implements a client side Stream.
+type clientStream struct {
+	callHdr  *transport.CallHdr
+	opts     []CallOption
+	callInfo *callInfo
+	cc       *ClientConn
+	desc     *StreamDesc
+
+	codec baseCodec
+	cp    Compressor
+	comp  encoding.Compressor
+
+	cancel context.CancelFunc // cancels all attempts
+
+	sentLast  bool // sent an end stream
+	beginTime time.Time
+
+	methodConfig *MethodConfig
+
+	ctx context.Context // the application's context, wrapped by stats/tracing
+
+	retryThrottler *retryThrottler // The throttler active when the RPC began.
+
+	binlog *binarylog.MethodLogger // Binary logger, can be nil.
+	// serverHeaderBinlogged is a boolean for whether server header has been
+	// logged. Server header will be logged when the first time one of those
+	// happens: stream.Header(), stream.Recv().
+	//
+	// It's only read and used by Recv() and Header(), so it doesn't need to be
+	// synchronized.
+	serverHeaderBinlogged bool
+
+	mu                      sync.Mutex
+	firstAttempt            bool // if true, transparent retry is valid
+	numRetries              int  // exclusive of transparent retry attempt(s)
+	numRetriesSincePushback int  // retries since pushback; to reset backoff
+	finished                bool // TODO: replace with atomic cmpxchg or sync.Once?
+	// attempt is the active client stream attempt.
+	// The only place where it is written is the newAttemptLocked method and this method never writes nil.
+	// So, attempt can be nil only inside newClientStream function when clientStream is first created.
+	// One of the first things done after clientStream's creation, is to call newAttemptLocked which either
+	// assigns a non nil value to the attempt or returns an error. If an error is returned from newAttemptLocked,
+	// then newClientStream calls finish on the clientStream and returns. So, finish method is the only
+	// place where we need to check if the attempt is nil.
+	attempt *csAttempt
+	// TODO(hedging): hedging will have multiple attempts simultaneously.
+	committed  bool                       // active attempt committed for retry?
+	buffer     []func(a *csAttempt) error // operations to replay on retry
+	bufferSize int                        // current size of buffer
+}
+
+// csAttempt implements a single transport stream attempt within a
+// clientStream.
+type csAttempt struct {
+	cs   *clientStream
+	t    transport.ClientTransport
+	s    *transport.Stream
+	p    *parser
+	done func(balancer.DoneInfo)
+
+	finished  bool
+	dc        Decompressor
+	decomp    encoding.Compressor
+	decompSet bool
+
+	mu sync.Mutex // guards trInfo.tr
+	// trInfo may be nil (if EnableTracing is false).
+	// trInfo.tr is set when created (if EnableTracing is true),
+	// and cleared when the finish method is called.
+	trInfo *traceInfo
+
+	statsHandler stats.Handler
+}
+
+func (cs *clientStream) commitAttemptLocked() {
+	cs.committed = true
+	cs.buffer = nil
+}
+
+func (cs *clientStream) commitAttempt() {
+	cs.mu.Lock()
+	cs.commitAttemptLocked()
+	cs.mu.Unlock()
+}
+
+// shouldRetry returns nil if the RPC should be retried; otherwise it returns
+// the error that should be returned by the operation.
+func (cs *clientStream) shouldRetry(err error) error {
+	if cs.attempt.s == nil && !cs.callInfo.failFast {
+		// In the event of any error from NewStream (attempt.s == nil), we
+		// never attempted to write anything to the wire, so we can retry
+		// indefinitely for non-fail-fast RPCs.
+		return nil
+	}
+	if cs.finished || cs.committed {
+		// RPC is finished or committed; cannot retry.
+		return err
+	}
+	// Wait for the trailers.
+	if cs.attempt.s != nil {
+		<-cs.attempt.s.Done()
+	}
+	if cs.firstAttempt && (cs.attempt.s == nil || cs.attempt.s.Unprocessed()) {
+		// First attempt, stream unprocessed: transparently retry.
+		cs.firstAttempt = false
+		return nil
+	}
+	cs.firstAttempt = false
+	if cs.cc.dopts.disableRetry {
+		return err
+	}
+
+	pushback := 0
+	hasPushback := false
+	if cs.attempt.s != nil {
+		if !cs.attempt.s.TrailersOnly() {
+			return err
+		}
+
+		// TODO(retry): Move down if the spec changes to not check server pushback
+		// before considering this a failure for throttling.
+		sps := cs.attempt.s.Trailer()["grpc-retry-pushback-ms"]
+		if len(sps) == 1 {
+			var e error
+			if pushback, e = strconv.Atoi(sps[0]); e != nil || pushback < 0 {
+				channelz.Infof(cs.cc.channelzID, "Server retry pushback specified to abort (%q).", sps[0])
+				cs.retryThrottler.throttle() // This counts as a failure for throttling.
+				return err
+			}
+			hasPushback = true
+		} else if len(sps) > 1 {
+			channelz.Warningf(cs.cc.channelzID, "Server retry pushback specified multiple values (%q); not retrying.", sps)
+			cs.retryThrottler.throttle() // This counts as a failure for throttling.
+			return err
+		}
+	}
+
+	var code codes.Code
+	if cs.attempt.s != nil {
+		code = cs.attempt.s.Status().Code()
+	} else {
+		code = status.Convert(err).Code()
+	}
+
+	rp := cs.methodConfig.retryPolicy
+	if rp == nil || !rp.retryableStatusCodes[code] {
+		return err
+	}
+
+	// Note: the ordering here is important; we count this as a failure
+	// only if the code matched a retryable code.
+	if cs.retryThrottler.throttle() {
+		return err
+	}
+	if cs.numRetries+1 >= rp.maxAttempts {
+		return err
+	}
+
+	var dur time.Duration
+	if hasPushback {
+		dur = time.Millisecond * time.Duration(pushback)
+		cs.numRetriesSincePushback = 0
+	} else {
+		fact := math.Pow(rp.backoffMultiplier, float64(cs.numRetriesSincePushback))
+		cur := float64(rp.initialBackoff) * fact
+		if max := float64(rp.maxBackoff); cur > max {
+			cur = max
+		}
+		dur = time.Duration(grpcrand.Int63n(int64(cur)))
+		cs.numRetriesSincePushback++
+	}
+
+	// TODO(dfawley): we could eagerly fail here if dur puts us past the
+	// deadline, but unsure if it is worth doing.
+	t := time.NewTimer(dur)
+	select {
+	case <-t.C:
+		cs.numRetries++
+		return nil
+	case <-cs.ctx.Done():
+		t.Stop()
+		return status.FromContextError(cs.ctx.Err()).Err()
+	}
+}
+
+// Returns nil if a retry was performed and succeeded; error otherwise.
+func (cs *clientStream) retryLocked(lastErr error) error {
+	for {
+		cs.attempt.finish(lastErr)
+		if err := cs.shouldRetry(lastErr); err != nil {
+			cs.commitAttemptLocked()
+			return err
+		}
+		if err := cs.newAttemptLocked(nil, nil); err != nil {
+			return err
+		}
+		if lastErr = cs.replayBufferLocked(); lastErr == nil {
+			return nil
+		}
+	}
+}
+
+func (cs *clientStream) Context() context.Context {
+	cs.commitAttempt()
+	// No need to lock before using attempt, since we know it is committed and
+	// cannot change.
+	return cs.attempt.s.Context()
+}
+
+func (cs *clientStream) withRetry(op func(a *csAttempt) error, onSuccess func()) error {
+	cs.mu.Lock()
+	for {
+		if cs.committed {
+			cs.mu.Unlock()
+			return op(cs.attempt)
+		}
+		a := cs.attempt
+		cs.mu.Unlock()
+		err := op(a)
+		cs.mu.Lock()
+		if a != cs.attempt {
+			// We started another attempt already.
+			continue
+		}
+		if err == io.EOF {
+			<-a.s.Done()
+		}
+		if err == nil || (err == io.EOF && a.s.Status().Code() == codes.OK) {
+			onSuccess()
+			cs.mu.Unlock()
+			return err
+		}
+		if err := cs.retryLocked(err); err != nil {
+			cs.mu.Unlock()
+			return err
+		}
+	}
+}
+
+func (cs *clientStream) Header() (metadata.MD, error) {
+	var m metadata.MD
+	err := cs.withRetry(func(a *csAttempt) error {
+		var err error
+		m, err = a.s.Header()
+		return toRPCErr(err)
+	}, cs.commitAttemptLocked)
+	if err != nil {
+		cs.finish(err)
+		return nil, err
+	}
+	if cs.binlog != nil && !cs.serverHeaderBinlogged {
+		// Only log if binary log is on and header has not been logged.
+		logEntry := &binarylog.ServerHeader{
+			OnClientSide: true,
+			Header:       m,
+			PeerAddr:     nil,
+		}
+		if peer, ok := peer.FromContext(cs.Context()); ok {
+			logEntry.PeerAddr = peer.Addr
+		}
+		cs.binlog.Log(logEntry)
+		cs.serverHeaderBinlogged = true
+	}
+	return m, err
+}
+
+func (cs *clientStream) Trailer() metadata.MD {
+	// On RPC failure, we never need to retry, because usage requires that
+	// RecvMsg() returned a non-nil error before calling this function is valid.
+	// We would have retried earlier if necessary.
+	//
+	// Commit the attempt anyway, just in case users are not following those
+	// directions -- it will prevent races and should not meaningfully impact
+	// performance.
+	cs.commitAttempt()
+	if cs.attempt.s == nil {
+		return nil
+	}
+	return cs.attempt.s.Trailer()
+}
+
+func (cs *clientStream) replayBufferLocked() error {
+	a := cs.attempt
+	for _, f := range cs.buffer {
+		if err := f(a); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+func (cs *clientStream) bufferForRetryLocked(sz int, op func(a *csAttempt) error) {
+	// Note: we still will buffer if retry is disabled (for transparent retries).
+	if cs.committed {
+		return
+	}
+	cs.bufferSize += sz
+	if cs.bufferSize > cs.callInfo.maxRetryRPCBufferSize {
+		cs.commitAttemptLocked()
+		return
+	}
+	cs.buffer = append(cs.buffer, op)
+}
+
+func (cs *clientStream) SendMsg(m interface{}) (err error) {
+	defer func() {
+		if err != nil && err != io.EOF {
+			// Call finish on the client stream for errors generated by this SendMsg
+			// call, as these indicate problems created by this client.  (Transport
+			// errors are converted to an io.EOF error in csAttempt.sendMsg; the real
+			// error will be returned from RecvMsg eventually in that case, or be
+			// retried.)
+			cs.finish(err)
+		}
+	}()
+	if cs.sentLast {
+		return status.Errorf(codes.Internal, "SendMsg called after CloseSend")
+	}
+	if !cs.desc.ClientStreams {
+		cs.sentLast = true
+	}
+
+	// load hdr, payload, data
+	hdr, payload, data, err := prepareMsg(m, cs.codec, cs.cp, cs.comp)
+	if err != nil {
+		return err
+	}
+
+	// TODO(dfawley): should we be checking len(data) instead?
+	if len(payload) > *cs.callInfo.maxSendMessageSize {
+		return status.Errorf(codes.ResourceExhausted, "trying to send message larger than max (%d vs. %d)", len(payload), *cs.callInfo.maxSendMessageSize)
+	}
+	msgBytes := data // Store the pointer before setting to nil. For binary logging.
+	op := func(a *csAttempt) error {
+		err := a.sendMsg(m, hdr, payload, data)
+		// nil out the message and uncomp when replaying; they are only needed for
+		// stats which is disabled for subsequent attempts.
+		m, data = nil, nil
+		return err
+	}
+	err = cs.withRetry(op, func() { cs.bufferForRetryLocked(len(hdr)+len(payload), op) })
+	if cs.binlog != nil && err == nil {
+		cs.binlog.Log(&binarylog.ClientMessage{
+			OnClientSide: true,
+			Message:      msgBytes,
+		})
+	}
+	return
+}
+
+func (cs *clientStream) RecvMsg(m interface{}) error {
+	if cs.binlog != nil && !cs.serverHeaderBinlogged {
+		// Call Header() to binary log header if it's not already logged.
+		cs.Header()
+	}
+	var recvInfo *payloadInfo
+	if cs.binlog != nil {
+		recvInfo = &payloadInfo{}
+	}
+	err := cs.withRetry(func(a *csAttempt) error {
+		return a.recvMsg(m, recvInfo)
+	}, cs.commitAttemptLocked)
+	if cs.binlog != nil && err == nil {
+		cs.binlog.Log(&binarylog.ServerMessage{
+			OnClientSide: true,
+			Message:      recvInfo.uncompressedBytes,
+		})
+	}
+	if err != nil || !cs.desc.ServerStreams {
+		// err != nil or non-server-streaming indicates end of stream.
+		cs.finish(err)
+
+		if cs.binlog != nil {
+			// finish will not log Trailer. Log Trailer here.
+			logEntry := &binarylog.ServerTrailer{
+				OnClientSide: true,
+				Trailer:      cs.Trailer(),
+				Err:          err,
+			}
+			if logEntry.Err == io.EOF {
+				logEntry.Err = nil
+			}
+			if peer, ok := peer.FromContext(cs.Context()); ok {
+				logEntry.PeerAddr = peer.Addr
+			}
+			cs.binlog.Log(logEntry)
+		}
+	}
+	return err
+}
+
+func (cs *clientStream) CloseSend() error {
+	if cs.sentLast {
+		// TODO: return an error and finish the stream instead, due to API misuse?
+		return nil
+	}
+	cs.sentLast = true
+	op := func(a *csAttempt) error {
+		a.t.Write(a.s, nil, nil, &transport.Options{Last: true})
+		// Always return nil; io.EOF is the only error that might make sense
+		// instead, but there is no need to signal the client to call RecvMsg
+		// as the only use left for the stream after CloseSend is to call
+		// RecvMsg.  This also matches historical behavior.
+		return nil
+	}
+	cs.withRetry(op, func() { cs.bufferForRetryLocked(0, op) })
+	if cs.binlog != nil {
+		cs.binlog.Log(&binarylog.ClientHalfClose{
+			OnClientSide: true,
+		})
+	}
+	// We never returned an error here for reasons.
+	return nil
+}
+
+func (cs *clientStream) finish(err error) {
+	if err == io.EOF {
+		// Ending a stream with EOF indicates a success.
+		err = nil
+	}
+	cs.mu.Lock()
+	if cs.finished {
+		cs.mu.Unlock()
+		return
+	}
+	cs.finished = true
+	cs.commitAttemptLocked()
+	cs.mu.Unlock()
+	// For binary logging. only log cancel in finish (could be caused by RPC ctx
+	// canceled or ClientConn closed). Trailer will be logged in RecvMsg.
+	//
+	// Only one of cancel or trailer needs to be logged. In the cases where
+	// users don't call RecvMsg, users must have already canceled the RPC.
+	if cs.binlog != nil && status.Code(err) == codes.Canceled {
+		cs.binlog.Log(&binarylog.Cancel{
+			OnClientSide: true,
+		})
+	}
+	if err == nil {
+		cs.retryThrottler.successfulRPC()
+	}
+	if channelz.IsOn() {
+		if err != nil {
+			cs.cc.incrCallsFailed()
+		} else {
+			cs.cc.incrCallsSucceeded()
+		}
+	}
+	if cs.attempt != nil {
+		cs.attempt.finish(err)
+		// after functions all rely upon having a stream.
+		if cs.attempt.s != nil {
+			for _, o := range cs.opts {
+				o.after(cs.callInfo)
+			}
+		}
+	}
+	cs.cancel()
+}
+
+func (a *csAttempt) sendMsg(m interface{}, hdr, payld, data []byte) error {
+	cs := a.cs
+	if a.trInfo != nil {
+		a.mu.Lock()
+		if a.trInfo.tr != nil {
+			a.trInfo.tr.LazyLog(&payload{sent: true, msg: m}, true)
+		}
+		a.mu.Unlock()
+	}
+	if err := a.t.Write(a.s, hdr, payld, &transport.Options{Last: !cs.desc.ClientStreams}); err != nil {
+		if !cs.desc.ClientStreams {
+			// For non-client-streaming RPCs, we return nil instead of EOF on error
+			// because the generated code requires it.  finish is not called; RecvMsg()
+			// will call it with the stream's status independently.
+			return nil
+		}
+		return io.EOF
+	}
+	if a.statsHandler != nil {
+		a.statsHandler.HandleRPC(cs.ctx, outPayload(true, m, data, payld, time.Now()))
+	}
+	if channelz.IsOn() {
+		a.t.IncrMsgSent()
+	}
+	return nil
+}
+
+func (a *csAttempt) recvMsg(m interface{}, payInfo *payloadInfo) (err error) {
+	cs := a.cs
+	if a.statsHandler != nil && payInfo == nil {
+		payInfo = &payloadInfo{}
+	}
+
+	if !a.decompSet {
+		// Block until we receive headers containing received message encoding.
+		if ct := a.s.RecvCompress(); ct != "" && ct != encoding.Identity {
+			if a.dc == nil || a.dc.Type() != ct {
+				// No configured decompressor, or it does not match the incoming
+				// message encoding; attempt to find a registered compressor that does.
+				a.dc = nil
+				a.decomp = encoding.GetCompressor(ct)
+			}
+		} else {
+			// No compression is used; disable our decompressor.
+			a.dc = nil
+		}
+		// Only initialize this state once per stream.
+		a.decompSet = true
+	}
+	err = recv(a.p, cs.codec, a.s, a.dc, m, *cs.callInfo.maxReceiveMessageSize, payInfo, a.decomp)
+	if err != nil {
+		if err == io.EOF {
+			if statusErr := a.s.Status().Err(); statusErr != nil {
+				return statusErr
+			}
+			return io.EOF // indicates successful end of stream.
+		}
+		return toRPCErr(err)
+	}
+	if a.trInfo != nil {
+		a.mu.Lock()
+		if a.trInfo.tr != nil {
+			a.trInfo.tr.LazyLog(&payload{sent: false, msg: m}, true)
+		}
+		a.mu.Unlock()
+	}
+	if a.statsHandler != nil {
+		a.statsHandler.HandleRPC(cs.ctx, &stats.InPayload{
+			Client:   true,
+			RecvTime: time.Now(),
+			Payload:  m,
+			// TODO truncate large payload.
+			Data:       payInfo.uncompressedBytes,
+			WireLength: payInfo.wireLength,
+			Length:     len(payInfo.uncompressedBytes),
+		})
+	}
+	if channelz.IsOn() {
+		a.t.IncrMsgRecv()
+	}
+	if cs.desc.ServerStreams {
+		// Subsequent messages should be received by subsequent RecvMsg calls.
+		return nil
+	}
+	// Special handling for non-server-stream rpcs.
+	// This recv expects EOF or errors, so we don't collect inPayload.
+	err = recv(a.p, cs.codec, a.s, a.dc, m, *cs.callInfo.maxReceiveMessageSize, nil, a.decomp)
+	if err == nil {
+		return toRPCErr(errors.New("grpc: client streaming protocol violation: get <nil>, want <EOF>"))
+	}
+	if err == io.EOF {
+		return a.s.Status().Err() // non-server streaming Recv returns nil on success
+	}
+	return toRPCErr(err)
+}
+
+func (a *csAttempt) finish(err error) {
+	a.mu.Lock()
+	if a.finished {
+		a.mu.Unlock()
+		return
+	}
+	a.finished = true
+	if err == io.EOF {
+		// Ending a stream with EOF indicates a success.
+		err = nil
+	}
+	var tr metadata.MD
+	if a.s != nil {
+		a.t.CloseStream(a.s, err)
+		tr = a.s.Trailer()
+	}
+
+	if a.done != nil {
+		br := false
+		if a.s != nil {
+			br = a.s.BytesReceived()
+		}
+		a.done(balancer.DoneInfo{
+			Err:           err,
+			Trailer:       tr,
+			BytesSent:     a.s != nil,
+			BytesReceived: br,
+			ServerLoad:    balancerload.Parse(tr),
+		})
+	}
+	if a.statsHandler != nil {
+		end := &stats.End{
+			Client:    true,
+			BeginTime: a.cs.beginTime,
+			EndTime:   time.Now(),
+			Trailer:   tr,
+			Error:     err,
+		}
+		a.statsHandler.HandleRPC(a.cs.ctx, end)
+	}
+	if a.trInfo != nil && a.trInfo.tr != nil {
+		if err == nil {
+			a.trInfo.tr.LazyPrintf("RPC: [OK]")
+		} else {
+			a.trInfo.tr.LazyPrintf("RPC: [%v]", err)
+			a.trInfo.tr.SetError()
+		}
+		a.trInfo.tr.Finish()
+		a.trInfo.tr = nil
+	}
+	a.mu.Unlock()
+}
+
+// newClientStream creates a ClientStream with the specified transport, on the
+// given addrConn.
+//
+// It's expected that the given transport is either the same one in addrConn, or
+// is already closed. To avoid race, transport is specified separately, instead
+// of using ac.transpot.
+//
+// Main difference between this and ClientConn.NewStream:
+// - no retry
+// - no service config (or wait for service config)
+// - no tracing or stats
+func newNonRetryClientStream(ctx context.Context, desc *StreamDesc, method string, t transport.ClientTransport, ac *addrConn, opts ...CallOption) (_ ClientStream, err error) {
+	if t == nil {
+		// TODO: return RPC error here?
+		return nil, errors.New("transport provided is nil")
+	}
+	// defaultCallInfo contains unnecessary info(i.e. failfast, maxRetryRPCBufferSize), so we just initialize an empty struct.
+	c := &callInfo{}
+
+	// Possible context leak:
+	// The cancel function for the child context we create will only be called
+	// when RecvMsg returns a non-nil error, if the ClientConn is closed, or if
+	// an error is generated by SendMsg.
+	// https://github.com/grpc/grpc-go/issues/1818.
+	ctx, cancel := context.WithCancel(ctx)
+	defer func() {
+		if err != nil {
+			cancel()
+		}
+	}()
+
+	for _, o := range opts {
+		if err := o.before(c); err != nil {
+			return nil, toRPCErr(err)
+		}
+	}
+	c.maxReceiveMessageSize = getMaxSize(nil, c.maxReceiveMessageSize, defaultClientMaxReceiveMessageSize)
+	c.maxSendMessageSize = getMaxSize(nil, c.maxSendMessageSize, defaultServerMaxSendMessageSize)
+	if err := setCallInfoCodec(c); err != nil {
+		return nil, err
+	}
+
+	callHdr := &transport.CallHdr{
+		Host:           ac.cc.authority,
+		Method:         method,
+		ContentSubtype: c.contentSubtype,
+	}
+
+	// Set our outgoing compression according to the UseCompressor CallOption, if
+	// set.  In that case, also find the compressor from the encoding package.
+	// Otherwise, use the compressor configured by the WithCompressor DialOption,
+	// if set.
+	var cp Compressor
+	var comp encoding.Compressor
+	if ct := c.compressorType; ct != "" {
+		callHdr.SendCompress = ct
+		if ct != encoding.Identity {
+			comp = encoding.GetCompressor(ct)
+			if comp == nil {
+				return nil, status.Errorf(codes.Internal, "grpc: Compressor is not installed for requested grpc-encoding %q", ct)
+			}
+		}
+	} else if ac.cc.dopts.cp != nil {
+		callHdr.SendCompress = ac.cc.dopts.cp.Type()
+		cp = ac.cc.dopts.cp
+	}
+	if c.creds != nil {
+		callHdr.Creds = c.creds
+	}
+
+	// Use a special addrConnStream to avoid retry.
+	as := &addrConnStream{
+		callHdr:  callHdr,
+		ac:       ac,
+		ctx:      ctx,
+		cancel:   cancel,
+		opts:     opts,
+		callInfo: c,
+		desc:     desc,
+		codec:    c.codec,
+		cp:       cp,
+		comp:     comp,
+		t:        t,
+	}
+
+	as.callInfo.stream = as
+	s, err := as.t.NewStream(as.ctx, as.callHdr)
+	if err != nil {
+		err = toRPCErr(err)
+		return nil, err
+	}
+	as.s = s
+	as.p = &parser{r: s}
+	ac.incrCallsStarted()
+	if desc != unaryStreamDesc {
+		// Listen on cc and stream contexts to cleanup when the user closes the
+		// ClientConn or cancels the stream context.  In all other cases, an error
+		// should already be injected into the recv buffer by the transport, which
+		// the client will eventually receive, and then we will cancel the stream's
+		// context in clientStream.finish.
+		go func() {
+			select {
+			case <-ac.ctx.Done():
+				as.finish(status.Error(codes.Canceled, "grpc: the SubConn is closing"))
+			case <-ctx.Done():
+				as.finish(toRPCErr(ctx.Err()))
+			}
+		}()
+	}
+	return as, nil
+}
+
+type addrConnStream struct {
+	s         *transport.Stream
+	ac        *addrConn
+	callHdr   *transport.CallHdr
+	cancel    context.CancelFunc
+	opts      []CallOption
+	callInfo  *callInfo
+	t         transport.ClientTransport
+	ctx       context.Context
+	sentLast  bool
+	desc      *StreamDesc
+	codec     baseCodec
+	cp        Compressor
+	comp      encoding.Compressor
+	decompSet bool
+	dc        Decompressor
+	decomp    encoding.Compressor
+	p         *parser
+	mu        sync.Mutex
+	finished  bool
+}
+
+func (as *addrConnStream) Header() (metadata.MD, error) {
+	m, err := as.s.Header()
+	if err != nil {
+		as.finish(toRPCErr(err))
+	}
+	return m, err
+}
+
+func (as *addrConnStream) Trailer() metadata.MD {
+	return as.s.Trailer()
+}
+
+func (as *addrConnStream) CloseSend() error {
+	if as.sentLast {
+		// TODO: return an error and finish the stream instead, due to API misuse?
+		return nil
+	}
+	as.sentLast = true
+
+	as.t.Write(as.s, nil, nil, &transport.Options{Last: true})
+	// Always return nil; io.EOF is the only error that might make sense
+	// instead, but there is no need to signal the client to call RecvMsg
+	// as the only use left for the stream after CloseSend is to call
+	// RecvMsg.  This also matches historical behavior.
+	return nil
+}
+
+func (as *addrConnStream) Context() context.Context {
+	return as.s.Context()
+}
+
+func (as *addrConnStream) SendMsg(m interface{}) (err error) {
+	defer func() {
+		if err != nil && err != io.EOF {
+			// Call finish on the client stream for errors generated by this SendMsg
+			// call, as these indicate problems created by this client.  (Transport
+			// errors are converted to an io.EOF error in csAttempt.sendMsg; the real
+			// error will be returned from RecvMsg eventually in that case, or be
+			// retried.)
+			as.finish(err)
+		}
+	}()
+	if as.sentLast {
+		return status.Errorf(codes.Internal, "SendMsg called after CloseSend")
+	}
+	if !as.desc.ClientStreams {
+		as.sentLast = true
+	}
+
+	// load hdr, payload, data
+	hdr, payld, _, err := prepareMsg(m, as.codec, as.cp, as.comp)
+	if err != nil {
+		return err
+	}
+
+	// TODO(dfawley): should we be checking len(data) instead?
+	if len(payld) > *as.callInfo.maxSendMessageSize {
+		return status.Errorf(codes.ResourceExhausted, "trying to send message larger than max (%d vs. %d)", len(payld), *as.callInfo.maxSendMessageSize)
+	}
+
+	if err := as.t.Write(as.s, hdr, payld, &transport.Options{Last: !as.desc.ClientStreams}); err != nil {
+		if !as.desc.ClientStreams {
+			// For non-client-streaming RPCs, we return nil instead of EOF on error
+			// because the generated code requires it.  finish is not called; RecvMsg()
+			// will call it with the stream's status independently.
+			return nil
+		}
+		return io.EOF
+	}
+
+	if channelz.IsOn() {
+		as.t.IncrMsgSent()
+	}
+	return nil
+}
+
+func (as *addrConnStream) RecvMsg(m interface{}) (err error) {
+	defer func() {
+		if err != nil || !as.desc.ServerStreams {
+			// err != nil or non-server-streaming indicates end of stream.
+			as.finish(err)
+		}
+	}()
+
+	if !as.decompSet {
+		// Block until we receive headers containing received message encoding.
+		if ct := as.s.RecvCompress(); ct != "" && ct != encoding.Identity {
+			if as.dc == nil || as.dc.Type() != ct {
+				// No configured decompressor, or it does not match the incoming
+				// message encoding; attempt to find a registered compressor that does.
+				as.dc = nil
+				as.decomp = encoding.GetCompressor(ct)
+			}
+		} else {
+			// No compression is used; disable our decompressor.
+			as.dc = nil
+		}
+		// Only initialize this state once per stream.
+		as.decompSet = true
+	}
+	err = recv(as.p, as.codec, as.s, as.dc, m, *as.callInfo.maxReceiveMessageSize, nil, as.decomp)
+	if err != nil {
+		if err == io.EOF {
+			if statusErr := as.s.Status().Err(); statusErr != nil {
+				return statusErr
+			}
+			return io.EOF // indicates successful end of stream.
+		}
+		return toRPCErr(err)
+	}
+
+	if channelz.IsOn() {
+		as.t.IncrMsgRecv()
+	}
+	if as.desc.ServerStreams {
+		// Subsequent messages should be received by subsequent RecvMsg calls.
+		return nil
+	}
+
+	// Special handling for non-server-stream rpcs.
+	// This recv expects EOF or errors, so we don't collect inPayload.
+	err = recv(as.p, as.codec, as.s, as.dc, m, *as.callInfo.maxReceiveMessageSize, nil, as.decomp)
+	if err == nil {
+		return toRPCErr(errors.New("grpc: client streaming protocol violation: get <nil>, want <EOF>"))
+	}
+	if err == io.EOF {
+		return as.s.Status().Err() // non-server streaming Recv returns nil on success
+	}
+	return toRPCErr(err)
+}
+
+func (as *addrConnStream) finish(err error) {
+	as.mu.Lock()
+	if as.finished {
+		as.mu.Unlock()
+		return
+	}
+	as.finished = true
+	if err == io.EOF {
+		// Ending a stream with EOF indicates a success.
+		err = nil
+	}
+	if as.s != nil {
+		as.t.CloseStream(as.s, err)
+	}
+
+	if err != nil {
+		as.ac.incrCallsFailed()
+	} else {
+		as.ac.incrCallsSucceeded()
+	}
+	as.cancel()
+	as.mu.Unlock()
+}
+
+// ServerStream defines the server-side behavior of a streaming RPC.
+//
+// All errors returned from ServerStream methods are compatible with the
+// status package.
+type ServerStream interface {
+	// SetHeader sets the header metadata. It may be called multiple times.
+	// When call multiple times, all the provided metadata will be merged.
+	// All the metadata will be sent out when one of the following happens:
+	//  - ServerStream.SendHeader() is called;
+	//  - The first response is sent out;
+	//  - An RPC status is sent out (error or success).
+	SetHeader(metadata.MD) error
+	// SendHeader sends the header metadata.
+	// The provided md and headers set by SetHeader() will be sent.
+	// It fails if called multiple times.
+	SendHeader(metadata.MD) error
+	// SetTrailer sets the trailer metadata which will be sent with the RPC status.
+	// When called more than once, all the provided metadata will be merged.
+	SetTrailer(metadata.MD)
+	// Context returns the context for this stream.
+	Context() context.Context
+	// SendMsg sends a message. On error, SendMsg aborts the stream and the
+	// error is returned directly.
+	//
+	// SendMsg blocks until:
+	//   - There is sufficient flow control to schedule m with the transport, or
+	//   - The stream is done, or
+	//   - The stream breaks.
+	//
+	// SendMsg does not wait until the message is received by the client. An
+	// untimely stream closure may result in lost messages.
+	//
+	// It is safe to have a goroutine calling SendMsg and another goroutine
+	// calling RecvMsg on the same stream at the same time, but it is not safe
+	// to call SendMsg on the same stream in different goroutines.
+	SendMsg(m interface{}) error
+	// RecvMsg blocks until it receives a message into m or the stream is
+	// done. It returns io.EOF when the client has performed a CloseSend. On
+	// any non-EOF error, the stream is aborted and the error contains the
+	// RPC status.
+	//
+	// It is safe to have a goroutine calling SendMsg and another goroutine
+	// calling RecvMsg on the same stream at the same time, but it is not
+	// safe to call RecvMsg on the same stream in different goroutines.
+	RecvMsg(m interface{}) error
+}
+
+// serverStream implements a server side Stream.
+type serverStream struct {
+	ctx   context.Context
+	t     transport.ServerTransport
+	s     *transport.Stream
+	p     *parser
+	codec baseCodec
+
+	cp     Compressor
+	dc     Decompressor
+	comp   encoding.Compressor
+	decomp encoding.Compressor
+
+	maxReceiveMessageSize int
+	maxSendMessageSize    int
+	trInfo                *traceInfo
+
+	statsHandler stats.Handler
+
+	binlog *binarylog.MethodLogger
+	// serverHeaderBinlogged indicates whether server header has been logged. It
+	// will happen when one of the following two happens: stream.SendHeader(),
+	// stream.Send().
+	//
+	// It's only checked in send and sendHeader, doesn't need to be
+	// synchronized.
+	serverHeaderBinlogged bool
+
+	mu sync.Mutex // protects trInfo.tr after the service handler runs.
+}
+
+func (ss *serverStream) Context() context.Context {
+	return ss.ctx
+}
+
+func (ss *serverStream) SetHeader(md metadata.MD) error {
+	if md.Len() == 0 {
+		return nil
+	}
+	return ss.s.SetHeader(md)
+}
+
+func (ss *serverStream) SendHeader(md metadata.MD) error {
+	err := ss.t.WriteHeader(ss.s, md)
+	if ss.binlog != nil && !ss.serverHeaderBinlogged {
+		h, _ := ss.s.Header()
+		ss.binlog.Log(&binarylog.ServerHeader{
+			Header: h,
+		})
+		ss.serverHeaderBinlogged = true
+	}
+	return err
+}
+
+func (ss *serverStream) SetTrailer(md metadata.MD) {
+	if md.Len() == 0 {
+		return
+	}
+	ss.s.SetTrailer(md)
+}
+
+func (ss *serverStream) SendMsg(m interface{}) (err error) {
+	defer func() {
+		if ss.trInfo != nil {
+			ss.mu.Lock()
+			if ss.trInfo.tr != nil {
+				if err == nil {
+					ss.trInfo.tr.LazyLog(&payload{sent: true, msg: m}, true)
+				} else {
+					ss.trInfo.tr.LazyLog(&fmtStringer{"%v", []interface{}{err}}, true)
+					ss.trInfo.tr.SetError()
+				}
+			}
+			ss.mu.Unlock()
+		}
+		if err != nil && err != io.EOF {
+			st, _ := status.FromError(toRPCErr(err))
+			ss.t.WriteStatus(ss.s, st)
+			// Non-user specified status was sent out. This should be an error
+			// case (as a server side Cancel maybe).
+			//
+			// This is not handled specifically now. User will return a final
+			// status from the service handler, we will log that error instead.
+			// This behavior is similar to an interceptor.
+		}
+		if channelz.IsOn() && err == nil {
+			ss.t.IncrMsgSent()
+		}
+	}()
+
+	// load hdr, payload, data
+	hdr, payload, data, err := prepareMsg(m, ss.codec, ss.cp, ss.comp)
+	if err != nil {
+		return err
+	}
+
+	// TODO(dfawley): should we be checking len(data) instead?
+	if len(payload) > ss.maxSendMessageSize {
+		return status.Errorf(codes.ResourceExhausted, "trying to send message larger than max (%d vs. %d)", len(payload), ss.maxSendMessageSize)
+	}
+	if err := ss.t.Write(ss.s, hdr, payload, &transport.Options{Last: false}); err != nil {
+		return toRPCErr(err)
+	}
+	if ss.binlog != nil {
+		if !ss.serverHeaderBinlogged {
+			h, _ := ss.s.Header()
+			ss.binlog.Log(&binarylog.ServerHeader{
+				Header: h,
+			})
+			ss.serverHeaderBinlogged = true
+		}
+		ss.binlog.Log(&binarylog.ServerMessage{
+			Message: data,
+		})
+	}
+	if ss.statsHandler != nil {
+		ss.statsHandler.HandleRPC(ss.s.Context(), outPayload(false, m, data, payload, time.Now()))
+	}
+	return nil
+}
+
+func (ss *serverStream) RecvMsg(m interface{}) (err error) {
+	defer func() {
+		if ss.trInfo != nil {
+			ss.mu.Lock()
+			if ss.trInfo.tr != nil {
+				if err == nil {
+					ss.trInfo.tr.LazyLog(&payload{sent: false, msg: m}, true)
+				} else if err != io.EOF {
+					ss.trInfo.tr.LazyLog(&fmtStringer{"%v", []interface{}{err}}, true)
+					ss.trInfo.tr.SetError()
+				}
+			}
+			ss.mu.Unlock()
+		}
+		if err != nil && err != io.EOF {
+			st, _ := status.FromError(toRPCErr(err))
+			ss.t.WriteStatus(ss.s, st)
+			// Non-user specified status was sent out. This should be an error
+			// case (as a server side Cancel maybe).
+			//
+			// This is not handled specifically now. User will return a final
+			// status from the service handler, we will log that error instead.
+			// This behavior is similar to an interceptor.
+		}
+		if channelz.IsOn() && err == nil {
+			ss.t.IncrMsgRecv()
+		}
+	}()
+	var payInfo *payloadInfo
+	if ss.statsHandler != nil || ss.binlog != nil {
+		payInfo = &payloadInfo{}
+	}
+	if err := recv(ss.p, ss.codec, ss.s, ss.dc, m, ss.maxReceiveMessageSize, payInfo, ss.decomp); err != nil {
+		if err == io.EOF {
+			if ss.binlog != nil {
+				ss.binlog.Log(&binarylog.ClientHalfClose{})
+			}
+			return err
+		}
+		if err == io.ErrUnexpectedEOF {
+			err = status.Errorf(codes.Internal, io.ErrUnexpectedEOF.Error())
+		}
+		return toRPCErr(err)
+	}
+	if ss.statsHandler != nil {
+		ss.statsHandler.HandleRPC(ss.s.Context(), &stats.InPayload{
+			RecvTime: time.Now(),
+			Payload:  m,
+			// TODO truncate large payload.
+			Data:       payInfo.uncompressedBytes,
+			WireLength: payInfo.wireLength,
+			Length:     len(payInfo.uncompressedBytes),
+		})
+	}
+	if ss.binlog != nil {
+		ss.binlog.Log(&binarylog.ClientMessage{
+			Message: payInfo.uncompressedBytes,
+		})
+	}
+	return nil
+}
+
+// MethodFromServerStream returns the method string for the input stream.
+// The returned string is in the format of "/service/method".
+func MethodFromServerStream(stream ServerStream) (string, bool) {
+	return Method(stream.Context())
+}
+
+// prepareMsg returns the hdr, payload and data
+// using the compressors passed or using the
+// passed preparedmsg
+func prepareMsg(m interface{}, codec baseCodec, cp Compressor, comp encoding.Compressor) (hdr, payload, data []byte, err error) {
+	if preparedMsg, ok := m.(*PreparedMsg); ok {
+		return preparedMsg.hdr, preparedMsg.payload, preparedMsg.encodedData, nil
+	}
+	// The input interface is not a prepared msg.
+	// Marshal and Compress the data at this point
+	data, err = encode(codec, m)
+	if err != nil {
+		return nil, nil, nil, err
+	}
+	compData, err := compress(data, cp, comp)
+	if err != nil {
+		return nil, nil, nil, err
+	}
+	hdr, payload = msgHeader(data, compData)
+	return hdr, payload, data, nil
+}
diff --git a/demo_test/vendor/google.golang.org/grpc/tap/tap.go b/demo_test/vendor/google.golang.org/grpc/tap/tap.go
new file mode 100644
index 0000000..584360f
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/tap/tap.go
@@ -0,0 +1,51 @@
+/*
+ *
+ * Copyright 2016 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+// Package tap defines the function handles which are executed on the transport
+// layer of gRPC-Go and related information. Everything here is EXPERIMENTAL.
+package tap
+
+import (
+	"context"
+)
+
+// Info defines the relevant information needed by the handles.
+type Info struct {
+	// FullMethodName is the string of grpc method (in the format of
+	// /package.service/method).
+	FullMethodName string
+	// TODO: More to be added.
+}
+
+// ServerInHandle defines the function which runs before a new stream is created
+// on the server side. If it returns a non-nil error, the stream will not be
+// created and a RST_STREAM will be sent back to the client with REFUSED_STREAM.
+// The client will receive an RPC error "code = Unavailable, desc = stream
+// terminated by RST_STREAM with error code: REFUSED_STREAM".
+//
+// It's intended to be used in situations where you don't want to waste the
+// resources to accept the new stream (e.g. rate-limiting). And the content of
+// the error will be ignored and won't be sent back to the client. For other
+// general usages, please use interceptors.
+//
+// Note that it is executed in the per-connection I/O goroutine(s) instead of
+// per-RPC goroutine. Therefore, users should NOT have any
+// blocking/time-consuming work in this handle. Otherwise all the RPCs would
+// slow down. Also, for the same reason, this handle won't be called
+// concurrently by gRPC.
+type ServerInHandle func(ctx context.Context, info *Info) (context.Context, error)
diff --git a/demo_test/vendor/google.golang.org/grpc/trace.go b/demo_test/vendor/google.golang.org/grpc/trace.go
new file mode 100644
index 0000000..07a2d26
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/trace.go
@@ -0,0 +1,123 @@
+/*
+ *
+ * Copyright 2015 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package grpc
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"net"
+	"strings"
+	"sync"
+	"time"
+
+	"golang.org/x/net/trace"
+)
+
+// EnableTracing controls whether to trace RPCs using the golang.org/x/net/trace package.
+// This should only be set before any RPCs are sent or received by this program.
+var EnableTracing bool
+
+// methodFamily returns the trace family for the given method.
+// It turns "/pkg.Service/GetFoo" into "pkg.Service".
+func methodFamily(m string) string {
+	m = strings.TrimPrefix(m, "/") // remove leading slash
+	if i := strings.Index(m, "/"); i >= 0 {
+		m = m[:i] // remove everything from second slash
+	}
+	return m
+}
+
+// traceInfo contains tracing information for an RPC.
+type traceInfo struct {
+	tr        trace.Trace
+	firstLine firstLine
+}
+
+// firstLine is the first line of an RPC trace.
+// It may be mutated after construction; remoteAddr specifically may change
+// during client-side use.
+type firstLine struct {
+	mu         sync.Mutex
+	client     bool // whether this is a client (outgoing) RPC
+	remoteAddr net.Addr
+	deadline   time.Duration // may be zero
+}
+
+func (f *firstLine) SetRemoteAddr(addr net.Addr) {
+	f.mu.Lock()
+	f.remoteAddr = addr
+	f.mu.Unlock()
+}
+
+func (f *firstLine) String() string {
+	f.mu.Lock()
+	defer f.mu.Unlock()
+
+	var line bytes.Buffer
+	io.WriteString(&line, "RPC: ")
+	if f.client {
+		io.WriteString(&line, "to")
+	} else {
+		io.WriteString(&line, "from")
+	}
+	fmt.Fprintf(&line, " %v deadline:", f.remoteAddr)
+	if f.deadline != 0 {
+		fmt.Fprint(&line, f.deadline)
+	} else {
+		io.WriteString(&line, "none")
+	}
+	return line.String()
+}
+
+const truncateSize = 100
+
+func truncate(x string, l int) string {
+	if l > len(x) {
+		return x
+	}
+	return x[:l]
+}
+
+// payload represents an RPC request or response payload.
+type payload struct {
+	sent bool        // whether this is an outgoing payload
+	msg  interface{} // e.g. a proto.Message
+	// TODO(dsymonds): add stringifying info to codec, and limit how much we hold here?
+}
+
+func (p payload) String() string {
+	if p.sent {
+		return truncate(fmt.Sprintf("sent: %v", p.msg), truncateSize)
+	}
+	return truncate(fmt.Sprintf("recv: %v", p.msg), truncateSize)
+}
+
+type fmtStringer struct {
+	format string
+	a      []interface{}
+}
+
+func (f *fmtStringer) String() string {
+	return fmt.Sprintf(f.format, f.a...)
+}
+
+type stringer string
+
+func (s stringer) String() string { return string(s) }
diff --git a/demo_test/vendor/google.golang.org/grpc/version.go b/demo_test/vendor/google.golang.org/grpc/version.go
new file mode 100644
index 0000000..ca5d55f
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/version.go
@@ -0,0 +1,22 @@
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package grpc
+
+// Version is the current grpc version.
+const Version = "1.29.1"
diff --git a/demo_test/vendor/google.golang.org/grpc/vet.sh b/demo_test/vendor/google.golang.org/grpc/vet.sh
new file mode 100644
index 0000000..e12024f
--- /dev/null
+++ b/demo_test/vendor/google.golang.org/grpc/vet.sh
@@ -0,0 +1,163 @@
+#!/bin/bash
+
+set -ex  # Exit on error; debugging enabled.
+set -o pipefail  # Fail a pipe if any sub-command fails.
+
+# not makes sure the command passed to it does not exit with a return code of 0.
+not() {
+  # This is required instead of the earlier (! $COMMAND) because subshells and
+  # pipefail don't work the same on Darwin as in Linux.
+  ! "$@"
+}
+
+die() {
+  echo "$@" >&2
+  exit 1
+}
+
+fail_on_output() {
+  tee /dev/stderr | not read
+}
+
+# Check to make sure it's safe to modify the user's git repo.
+git status --porcelain | fail_on_output
+
+# Undo any edits made by this script.
+cleanup() {
+  git reset --hard HEAD
+}
+trap cleanup EXIT
+
+PATH="${GOPATH}/bin:${GOROOT}/bin:${PATH}"
+
+if [[ "$1" = "-install" ]]; then
+  # Check for module support
+  if go help mod >& /dev/null; then
+    # Install the pinned versions as defined in module tools.
+    pushd ./test/tools
+    go install \
+      golang.org/x/lint/golint \
+      golang.org/x/tools/cmd/goimports \
+      honnef.co/go/tools/cmd/staticcheck \
+      github.com/client9/misspell/cmd/misspell \
+      github.com/golang/protobuf/protoc-gen-go
+    popd
+  else
+    # Ye olde `go get` incantation.
+    # Note: this gets the latest version of all tools (vs. the pinned versions
+    # with Go modules).
+    go get -u \
+      golang.org/x/lint/golint \
+      golang.org/x/tools/cmd/goimports \
+      honnef.co/go/tools/cmd/staticcheck \
+      github.com/client9/misspell/cmd/misspell \
+      github.com/golang/protobuf/protoc-gen-go
+  fi
+  if [[ -z "${VET_SKIP_PROTO}" ]]; then
+    if [[ "${TRAVIS}" = "true" ]]; then
+      PROTOBUF_VERSION=3.3.0
+      PROTOC_FILENAME=protoc-${PROTOBUF_VERSION}-linux-x86_64.zip
+      pushd /home/travis
+      wget https://github.com/google/protobuf/releases/download/v${PROTOBUF_VERSION}/${PROTOC_FILENAME}
+      unzip ${PROTOC_FILENAME}
+      bin/protoc --version
+      popd
+    elif not which protoc > /dev/null; then
+      die "Please install protoc into your path"
+    fi
+  fi
+  exit 0
+elif [[ "$#" -ne 0 ]]; then
+  die "Unknown argument(s): $*"
+fi
+
+# - Ensure all source files contain a copyright message.
+not git grep -L "\(Copyright [0-9]\{4,\} gRPC authors\)\|DO NOT EDIT" -- '*.go'
+
+# - Make sure all tests in grpc and grpc/test use leakcheck via Teardown.
+not grep 'func Test[^(]' *_test.go
+not grep 'func Test[^(]' test/*.go
+
+# - Do not import x/net/context.
+not git grep -l 'x/net/context' -- "*.go"
+
+# - Do not import math/rand for real library code.  Use internal/grpcrand for
+#   thread safety.
+git grep -l '"math/rand"' -- "*.go" 2>&1 | not grep -v '^examples\|^stress\|grpcrand\|^benchmark\|wrr_test'
+
+# - Ensure all ptypes proto packages are renamed when importing.
+not git grep "\(import \|^\s*\)\"github.com/golang/protobuf/ptypes/" -- "*.go"
+
+# - Check imports that are illegal in appengine (until Go 1.11).
+# TODO: Remove when we drop Go 1.10 support
+go list -f {{.Dir}} ./... | xargs go run test/go_vet/vet.go
+
+# - gofmt, goimports, golint (with exceptions for generated code), go vet.
+gofmt -s -d -l . 2>&1 | fail_on_output
+goimports -l . 2>&1 | not grep -vE "(_mock|\.pb)\.go"
+golint ./... 2>&1 | not grep -vE "(_mock|\.pb)\.go:"
+go vet -all ./...
+
+misspell -error .
+
+# - Check that generated proto files are up to date.
+if [[ -z "${VET_SKIP_PROTO}" ]]; then
+  PATH="/home/travis/bin:${PATH}" make proto && \
+    git status --porcelain 2>&1 | fail_on_output || \
+    (git status; git --no-pager diff; exit 1)
+fi
+
+# - Check that our module is tidy.
+if go help mod >& /dev/null; then
+  go mod tidy && \
+    git status --porcelain 2>&1 | fail_on_output || \
+    (git status; git --no-pager diff; exit 1)
+fi
+
+# - Collection of static analysis checks
+#
+# TODO(dfawley): don't use deprecated functions in examples or first-party
+# plugins.
+SC_OUT="$(mktemp)"
+staticcheck -go 1.9 -checks 'inherit,-ST1015' ./... > "${SC_OUT}" || true
+# Error if anything other than deprecation warnings are printed.
+not grep -v "is deprecated:.*SA1019" "${SC_OUT}"
+# Only ignore the following deprecated types/fields/functions.
+not grep -Fv '.HandleResolvedAddrs
+.HandleSubConnStateChange
+.HeaderMap
+.NewAddress
+.NewServiceConfig
+.Metadata is deprecated: use Attributes
+.Type is deprecated: use Attributes
+.UpdateBalancerState
+balancer.Picker
+grpc.CallCustomCodec
+grpc.Code
+grpc.Compressor
+grpc.Decompressor
+grpc.MaxMsgSize
+grpc.MethodConfig
+grpc.NewGZIPCompressor
+grpc.NewGZIPDecompressor
+grpc.RPCCompressor
+grpc.RPCDecompressor
+grpc.RoundRobin
+grpc.ServiceConfig
+grpc.WithBalancer
+grpc.WithBalancerName
+grpc.WithCompressor
+grpc.WithDecompressor
+grpc.WithDialer
+grpc.WithMaxMsgSize
+grpc.WithServiceConfig
+grpc.WithTimeout
+http.CloseNotifier
+info.SecurityVersion
+naming.Resolver
+naming.Update
+naming.Watcher
+resolver.Backend
+resolver.GRPCLB' "${SC_OUT}"
+
+echo SUCCESS