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, and we expect to announce General-Available by Oct. 2018.

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 Envoy, in which gRPC-Web support is built-in. Envoy will become the default gateway for gRPC-Web by GA.

In the 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-compose up echo-server envoy commonjs-client

Open a browser tab, and inspect

https://localhost:8081/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 Envoy proxy. 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());
});

Multiple proxies supports the gRPC-Web protocol. Currently, the default proxy is Envoy, which supports gRPC-Web out of the box.

$ docker-compose up echo-server envoy commonjs-client

An alternative is to build Nginx that comes with this repository.

$ docker-compose up echo-server nginx commonjs-client

Finally, you can also try this gRPC-Web Go Proxy.

$ docker-compose up echo-server grpcwebproxy binary-client

Typically, you will run the following command to generate the client stub from your proto definitions:

$ protoc -I=$DIR echo.proto \
--plugin=protoc-gen-grpc-web=/path-to/protoc-gen-grpc-web \
--js_out=import_style=commonjs:$OUT_DIR \
--grpc-web_out=import_style=commonjs,mode=grpcwebtext,out=echo_grpc_pb.js:$OUT_DIR

The default generated code has Closure goog.require() import style. Pass in import_style=closure.

The CommonJS style require() is also supported. Pass in import_style=commonjs.

Note: ES6 style import is not supported yet.

For more information about the gRPC-Web wire format, please see the spec here.

The default generated code sends the payload in the grpc-web-text format. Pass in mode=grpcwebtext.

• Content-type: application/grpc-web-text
• Payload are base64-encoded.
• Both unary and server streaming calls are supported.

A binary protobuf format is also supported. Pass in mode=grpcweb.

• Content-type: application/grpc-web+proto
• Payload are in the binary protobuf format.
• Only unary calls are supported for now.