add grpc-proxy (github.com/mwitkow/grpc-proxy)

Signed-off-by: Adphi <philippe.adrien.nousse@gmail.com>

proxy/director.go

@@ -0,0 +1,25 @@
+// Copyright 2017 Michal Witkowski. All Rights Reserved.
+// See LICENSE for licensing terms.
+
+package proxy
+
+import (
+	"context"
+
+	"google.golang.org/grpc"
+)
+
+// StreamDirector returns a gRPC ClientConn to be used to forward the call to.
+//
+// The presence of the `Context` allows for rich filtering, e.g. based on Metadata (headers).
+// If no handling is meant to be done, a `codes.NotImplemented` gRPC error should be returned.
+//
+// The context returned from this function should be the context for the *outgoing* (to backend) call. In case you want
+// to forward any Metadata between the inbound request and outbound requests, you should do it manually. However, you
+// *must* propagate the cancel function (`context.WithCancel`) of the inbound context to the one returned.
+//
+// It is worth noting that the StreamDirector will be fired *after* all server-side stream interceptors
+// are invoked. So decisions around authorization, monitoring etc. are better to be handled there.
+//
+// See the rather rich example.
+type StreamDirector func(ctx context.Context, fullMethodName string) (context.Context, grpc.ClientConnInterface, error)