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

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

proxy/README.md

@@ -0,0 +1,83 @@
+# gRPC Proxy
+
+[![Travis Build](https://travis-ci.org/mwitkow/grpc-proxy.svg?branch=master)](https://travis-ci.org/mwitkow/grpc-proxy)
+[![Go Report Card](https://goreportcard.com/badge/github.com/mwitkow/grpc-proxy)](https://goreportcard.com/report/github.com/mwitkow/grpc-proxy)
+[![Go Reference](https://pkg.go.dev/badge/github.com/mwitkow/grpc-proxy.svg)](https://pkg.go.dev/github.com/mwitkow/grpc-proxy)
+[![Apache 2.0 License](https://img.shields.io/badge/License-Apache%202.0-blue.svg)](LICENSE)
+
+[gRPC Go](https://github.com/grpc/grpc-go) Proxy server
+
+## Project Goal
+
+Build a transparent reverse proxy for gRPC targets that will make it easy to expose gRPC services
+over the internet. This includes:
+ * no needed knowledge of the semantics of requests exchanged in the call (independent rollouts)
+ * easy, declarative definition of backends and their mappings to frontends
+ * simple round-robin load balancing of inbound requests from a single connection to multiple backends
+
+The project now exists as a **proof of concept**, with the key piece being the `proxy` package that
+is a generic gRPC reverse proxy handler.
+
+## Proxy Handler
+
+The package [`proxy`](proxy/) contains a generic gRPC reverse proxy handler that allows a gRPC server to
+not know about registered handlers or their data types. Please consult the docs, here's an exaple usage.
+
+You can call `proxy.NewProxy` to create a `*grpc.Server` that proxies requests.
+```go
+proxy := proxy.NewProxy(clientConn)
+``` 
+
+More advanced users will want to define a `StreamDirector` that can make more complex decisions on what
+to do with the request.
+```go
+director = func(ctx context.Context, fullMethodName string) (context.Context, *grpc.ClientConn, error) {
+    md, _ := metadata.FromIncomingContext(ctx)
+    outCtx = metadata.NewOutgoingContext(ctx, md.Copy())
+    return outCtx, cc, nil
+	
+    // Make sure we never forward internal services.
+    if strings.HasPrefix(fullMethodName, "/com.example.internal.") {
+        return outCtx, nil, status.Errorf(codes.Unimplemented, "Unknown method")
+    }
+    
+    if ok {
+        // Decide on which backend to dial
+        if val, exists := md[":authority"]; exists && val[0] == "staging.api.example.com" {
+            // Make sure we use DialContext so the dialing can be cancelled/time out together with the context.
+            return outCtx, grpc.DialContext(ctx, "api-service.staging.svc.local", grpc.WithCodec(proxy.Codec())), nil
+        } else if val, exists := md[":authority"]; exists && val[0] == "api.example.com" {
+            return outCtx, grpc.DialContext(ctx, "api-service.prod.svc.local", grpc.WithCodec(proxy.Codec())), nil
+        }
+    }
+    return outCtx, nil, status.Errorf(codes.Unimplemented, "Unknown method")
+}
+```
+
+Then you need to register it with a `grpc.Server`. The server may have other handlers that will be served
+locally.
+
+```go
+server := grpc.NewServer(
+    grpc.CustomCodec(proxy.Codec()),
+    grpc.UnknownServiceHandler(proxy.TransparentHandler(director)))
+pb_test.RegisterTestServiceServer(server, &testImpl{})
+```
+
+## Testing
+To make debugging a bit simpler, there are some helpers.
+
+`testservice` contains a method `TestTestServiceServerImpl` which performs a complete test against
+the reference implementation of the `TestServiceServer`.
+
+In `proxy_test.go`, the test framework spins up a `TestServiceServer` that it tests the proxy 
+against. To make debugging a bit simpler (eg. if the developer needs to step into 
+`google.golang.org/grpc` methods), this `TestServiceServer` can be provided by a server by 
+passing `-test-backend=addr` to `go test`. A simple, local-only implementation of 
+`TestServiceServer` exists in [`testservice/server`](./testservice/server).
+
+
+## License
+
+`grpc-proxy` is released under the Apache 2.0 license. See [LICENSE.txt](LICENSE.txt).
+