gRPC-Web provides a Javascript client library that lets browser clients access a gRPC server. You can find out much more about gRPC in its own website.

The current release is a Beta release, mainly for early adopters to provide feedback on the JS API (both gRPC and Protobuf). The JS client library has been used for some time by Google and Alphabet projects with the Closure compiler and its TypeScript generator (which has not yet been open-sourced).

gRPC-Web clients connect to gRPC servers via a special gateway proxy: our provided version uses Nginx. The current gateway uses an older version of Nginx, which doesn't support gRPC as back-end servers and therefore can't be deployed as a reverse proxy to talk to multiple gRPC servers. Nginx has added support for gRPC backends on March 18, 2018. We plan to update the grpc-web gateway to the newer Nginx version in the next few months, which will allow the gateway to be used as a traditional Nginx-based reverse proxy.

We have also added gRPC-Web support to Envoy, if you wish to use this instead of an Nginx gateway. In future, we expect gRPC-Web to be supported in language-specific Web frameworks, such as Python, Java, and Node. See the roadmap doc.

Try gRPC-Web and run a quick Echo example from the browser!

From the repo root directory:

$ docker build -t grpc-web --build-arg with_examples=true \
  -f net/grpc/gateway/docker/ubuntu_16_04/Dockerfile .
$ docker run -t -p 8080:8080 grpc-web

Open a browser tab, and inspect

https://localhost:8080/net/grpc/gateway/examples/echo/echotest.html

Let's take a look at how gRPC-Web works with a simple example. You can find out how to build, run and explore the example yourself in Build and Run the Echo Example.

The first step when creating any gRPC service is to define it. Like all gRPC services, gRPC-Web uses protocol buffers to define its RPC service methods and their message request and response types.

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

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

Next you need to have a gRPC server that implements the service interface and a gateway that allows the client to connect to the server. Our example builds a simple C++ gRPC backend server and the Nginx gateway. You can find out more in the Echo Example.

Once the server and gateway are up and running, you can start making gRPC calls from the browser!

Create your client

var echoService = new proto.grpc.gateway.testing.EchoServiceClient(
  'https://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());
  });

Server-side streaming is supported!

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