Outputting `service` for @grpc/grpc-js

Hey, is there currently any way of outputting service definitions as code? Basically --ts_proto_opt=outputServices=grpc-js from https://github.com/stephenh/ts-proto but for this package.

Currently I’m using a mix of protobuf-es and ts-proto where ts-proto is used for our gRPC server. Would it be possible with some extensions or transpiler if it isn’t possible out of the box?

[timostamm]

Yes we do, Sebastian. I hope to share our roadmap and plans along with the first public commits for connect-node.

[jellydn]

There is no built-in feature to generate service definitions that are compatible with @grpc/grpc-js, but something quite similar. In protobuf-es, services are represented as a ServiceType - an object with a name and a set of methods, each with information about the streaming type, and the type of the input and output message.

For example, let’s take the following service definition in protobuf:

syntax="proto3";
package demo;

service ElizaService {
  // Say is a unary request demo. This method should allow for a one sentence
  // response given a one sentence request.
  rpc Say(SayRequest) returns (SayResponse) {}
}

// SayRequest describes the sentence said to the ELIZA program.
message SayRequest {
  string sentence = 1;
}

// SayResponse describes the sentence responded by the ELIZA program.
message SayResponse {
  string sentence = 1;
}

The corresponding ServiceType would be:

const ElizaService: ServiceType = {
  typeName: "demo.ElizaService",
  methods: {
    say: {
      name: "Say",
      I: SayRequest,
      O: SayResponse,
      kind: MethodKind.Unary,
    },
  }
};

@bufbuild/protoc-gen-es does not generate anything for services, but @bufbuild/protoc-gen-connect-web does. It happens to generate pretty much the example above, and @bufbuild/connect-web uses TypeScript’s mapped types to turn it into a client:

import {createPromiseClient} from "@bufbuild/connect-web";

const client = createPromiseClient(ElizaService, ...);
client.say({ sentence: "Hello" }); // this is type-safe

The fun part is that you can simply use @bufbuild/protoc-gen-connect-web to generate service types, and turn them to @grpc/grpc-js clients and servers. We’re making sure that this works in unit tests here and here. So connecting a few dots, you end up with a @grpc/grpc-js client:

import * as grpc from "@grpc/grpc-js";

const client = createGrpcClient(ElizaService, { 
   address: "localhost",
   channelCredentials: grpc.ChannelCredentials.createInsecure()
});

client.say({ sentence: "Hello" }, (err: grpc.ServiceError | null, value?: SayResponse) => {
  //       
});

This is just a proof of concept, but it should work pretty well. If you want to give it a try, let us know if you encounter any problems!

Just FYI - This approach is working. I’ve implemented a simple on my monorepo just in case if someone need this.