[VOL-3196] Enhanced gRPC interfaces to create and propagate Span for log correlation
Change-Id: I8bbf2263a7090b73555027cc54ff5c55a66ee4fb
diff --git a/vendor/github.com/grpc-ecosystem/go-grpc-middleware/doc.go b/vendor/github.com/grpc-ecosystem/go-grpc-middleware/doc.go
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+// Copyright 2016 Michal Witkowski. All Rights Reserved.
+// See LICENSE for licensing terms.
+
+/*
+`grpc_middleware` is a collection of gRPC middleware packages: interceptors, helpers and tools.
+
+Middleware
+
+gRPC is a fantastic RPC middleware, which sees a lot of adoption in the Golang world. However, the
+upstream gRPC codebase is relatively bare bones.
+
+This package, and most of its child packages provides commonly needed middleware for gRPC:
+client-side interceptors for retires, server-side interceptors for input validation and auth,
+functions for chaining said interceptors, metadata convenience methods and more.
+
+Chaining
+
+By default, gRPC doesn't allow one to have more than one interceptor either on the client nor on
+the server side. `grpc_middleware` provides convenient chaining methods
+
+Simple way of turning a multiple interceptors into a single interceptor. Here's an example for
+server chaining:
+
+ myServer := grpc.NewServer(
+ grpc.StreamInterceptor(grpc_middleware.ChainStreamServer(loggingStream, monitoringStream, authStream)),
+ grpc.UnaryInterceptor(grpc_middleware.ChainUnaryServer(loggingUnary, monitoringUnary, authUnary),
+ )
+
+These interceptors will be executed from left to right: logging, monitoring and auth.
+
+Here's an example for client side chaining:
+
+ clientConn, err = grpc.Dial(
+ address,
+ grpc.WithUnaryInterceptor(grpc_middleware.ChainUnaryClient(monitoringClientUnary, retryUnary)),
+ grpc.WithStreamInterceptor(grpc_middleware.ChainStreamClient(monitoringClientStream, retryStream)),
+ )
+ client = pb_testproto.NewTestServiceClient(clientConn)
+ resp, err := client.PingEmpty(s.ctx, &myservice.Request{Msg: "hello"})
+
+These interceptors will be executed from left to right: monitoring and then retry logic.
+
+The retry interceptor will call every interceptor that follows it whenever when a retry happens.
+
+Writing Your Own
+
+Implementing your own interceptor is pretty trivial: there are interfaces for that. But the interesting
+bit exposing common data to handlers (and other middleware), similarly to HTTP Middleware design.
+For example, you may want to pass the identity of the caller from the auth interceptor all the way
+to the handling function.
+
+For example, a client side interceptor example for auth looks like:
+
+ func FakeAuthUnaryInterceptor(ctx context.Context, req interface{}, info *grpc.UnaryServerInfo, handler grpc.UnaryHandler) (interface{}, error) {
+ newCtx := context.WithValue(ctx, "user_id", "john@example.com")
+ return handler(newCtx, req)
+ }
+
+Unfortunately, it's not as easy for streaming RPCs. These have the `context.Context` embedded within
+the `grpc.ServerStream` object. To pass values through context, a wrapper (`WrappedServerStream`) is
+needed. For example:
+
+ func FakeAuthStreamingInterceptor(srv interface{}, stream grpc.ServerStream, info *grpc.StreamServerInfo, handler grpc.StreamHandler) error {
+ newStream := grpc_middleware.WrapServerStream(stream)
+ newStream.WrappedContext = context.WithValue(ctx, "user_id", "john@example.com")
+ return handler(srv, stream)
+ }
+*/
+package grpc_middleware