grpc client HTTP/2 to HTTP/1.1 proxy

Go grpc "proxy" that transcodes grpc to JSON+HTTP/1.1

Why?

This probably doesn't have any practical use, but it was a fun thing to write.

I've been frustrated with all the steps needed to get a grpc service hosted in GKE and exposed to the public internet. It's doable, but one day while reading docs, my mind wandered and I thought "hmm, could I do this over HTTP/1.1" and wound up hacking this together. It's not exactly grpc over HTTP/1.1.

I wanted to test this with unmodified Go grpc clients.

TL;DR - I like doing silly things with gRPC, so why not.

What is it?

This provides a "proxy" that transcodes grpc to JSON+HTTP/1.1. The proxy runs in process.

The proxy was written to interact with grpc services fronted by the grpc gateway. Google Cloud Endpoints also supports similar server side transcoding.

Why transcode grpc to JSON+HTTP/1.1 just to transcode it back? As stated above, this probably has no practical usage, but if one needed to contact a grpc service but was unable to do end-to-end HTTP/2, this this may inspire some workarounds.

General Flow

• A new proxy is created and started.
• A client connection is created by the proxy. The proxy sets ForceCodec on the connection to JSONPb which is the same codec used by grpc-gateway to transcode JSON<->protobuf.
• A grpc client is created using the client connection. This example uses the hello world client.
• The client connection uses a net.Pipe to copy requests to the grpc server in the proxy.
• The proxy grpc server uses a CutomCodec that passes that passes the data from the client through. See grpc proxy for more information on how this works.
• The proxy grpc server uses an UnknownServiceHandler that uses HTTP/1.1 POST requests. It receieves the responses and passes them pack to the client.
• The client, uses the JSONPb to Unmarshal the response to the Go struct.

This should work with streaming responses. It expects newline separated JSON lines like grpc gateway produces.

What's included?

The proxy package does the heavy lifting. It creates an in-process grpc sever that handles the transcoding and can create connections to this server that can be used by normal Go grpc clients.

The top level directory includes a sample client that uses the proxy in main.go.

A sample server is included in server

Inspired by

• https://github.com/glerchundi/grpc-boomerang - grpc over HTTP websockets
• https://github.com/mwitkow/grpc-proxy - grpc passthrough proxy
• https://github.com/grpc-ecosystem/grpc-gateway

LICENSE

See LICENSE