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

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

proxy/proxy.go

@@ -0,0 +1,33 @@
+// Copyright 2021 Michal Witkowski. All Rights Reserved.
+// See LICENSE for licensing terms.
+
+package proxy
+
+import (
+	"context"
+
+	"google.golang.org/grpc"
+	"google.golang.org/grpc/metadata"
+)
+
+// NewProxy sets up a simple proxy that forwards all requests to dst.
+func NewProxy(dst *grpc.ClientConn, opts ...grpc.ServerOption) *grpc.Server {
+	opts = append(opts, DefaultProxyOpt(dst))
+	// Set up the proxy server and then serve from it like in step one.
+	return grpc.NewServer(opts...)
+}
+
+// DefaultProxyOpt returns an grpc.UnknownServiceHandler with a DefaultDirector.
+func DefaultProxyOpt(cc *grpc.ClientConn) grpc.ServerOption {
+	return grpc.UnknownServiceHandler(TransparentHandler(DefaultDirector(cc)))
+}
+
+// DefaultDirector returns a very simple forwarding StreamDirector that forwards all
+// calls.
+func DefaultDirector(cc *grpc.ClientConn) StreamDirector {
+	return func(ctx context.Context, fullMethodName string) (context.Context, grpc.ClientConnInterface, error) {
+		md, _ := metadata.FromIncomingContext(ctx)
+		ctx = metadata.NewOutgoingContext(ctx, md.Copy())
+		return ctx, cc, nil
+	}
+}