How to bring a gRPC defined API to the web browser

We want to build a Javascript/HTML gui for our gRPC-microservices. Since gRPC is not supported on the browser side, we thought of using web-sockets to connect to a node.js server, which calls the target service via grpc. We struggle to find an elegant solution to do this. Especially, since we use gRPC streams to push events between our micro-services. It seems that we need a second RPC system, just to communicate between the front end and the node.js server. This seems to be a lot of overhead and additional code that must be maintained.

Does anyone have experience doing something like this or has an idea how this could be solved?

Solution 1:

Edit: Since Oct 23,2018 the gRPC-Web project is GA, which might be the most official/standardized way to solve your problem. (Even if it's already 2018 now... ;) )

From the GA-Blog: "gRPC-Web, just like gRPC, lets you define the service “contract” between client (web) and backend gRPC services using Protocol Buffers. The client can then be auto generated. [...]"

We recently built gRPC-Web (https://github.com/improbable-eng/grpc-web) - a browser client and server wrapper that follows the proposed gRPC-Web protocol. The example in that repo should provide a good starting point.

It requires either a standalone proxy or a wrapper for your gRPC server if you're using Golang. The proxy/wrapper modifies the response to package the trailers in the response body so that they can be read by the browser.

Disclosure: I'm a maintainer of the project.

Solution 2:

Unfortunately, there isn't any good answer for you yet.

Supporting streaming RPCs from the browser fully requires HTTP2 trailers to be supported by the browsers, and at the time of the writing of this answer, they aren't.

See this issue for the discussion on the topic.

Otherwise, yes, you'd require a full translation system between WebSockets and gRPC. Maybe getting inspiration from grpc-gateway could be the start of such a project, but that's still a very long shot.

Solution 3:

An official grpc-web (beta) implementation was released on 3/23/2018. You can find it at

https://github.com/grpc/grpc-web

The following instructions are taken from the README:

Define your gRPC service:

service EchoService {
  rpc Echo(EchoRequest) returns (EchoResponse);

  rpc ServerStreamingEcho(ServerStreamingEchoRequest)
      returns (stream ServerStreamingEchoResponse);
}

Build the server in whatever language you want.

Create your JS client to make calls from the browser:

var echoService = new proto.grpc.gateway.testing.EchoServiceClient(
  'http://localhost:8080');

Make a unary RPC call

var unaryRequest = new proto.grpc.gateway.testing.EchoRequest();
unaryRequest.setMessage(msg);
echoService.echo(unaryRequest, {},
  function(err, response) {
    console.log(response.getMessage());
  });

Streams from the server to the browser are supported:

var stream = echoService.serverStreamingEcho(streamRequest, {});
stream.on('data', function(response) {
  console.log(response.getMessage());
});

Bidirectional streams are NOT supported:

This is a work in progress and on the grpc-web roadmap. While there is an example protobuf showing bidi streaming, this comment make it clear that this example doesn't actually work yet.

Hopefully this will change soon. :)

Solution 4:

https://github.com/tmc/grpc-websocket-proxy sounds like it may meet your needs. This translates json over web sockets to grpc (layer on top of grpc-gateway).