diff --git a/vendor/google.golang.org/grpc/internal/transport/http_util.go b/vendor/google.golang.org/grpc/internal/transport/http_util.go
new file mode 100644
index 0000000..8f5f334
--- /dev/null
+++ b/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
+}