capnproto_dart_rpc

RPC runtime for Cap'n Proto in Dart.

How the pieces fit together

• capnpc_dart
  generates typed client and server classes from your .capnp schema.
• capnproto_dart_rpc (this package)
  the runtime generated classes use to connect, call, and dispatch. It already includes capnproto_dart (message serialization)

Install and generate stubs

Add this package and the code-generation builder to pubspec.yaml:

dependencies:
  capnproto_dart_rpc: ^0.1.0

dev_dependencies:
  build_runner: ^2.4.13
  capnpc_dart_builder: ^0.1.0

dart pub get

build_runner only looks under lib/, so put your schema there, e.g. lib/schema/greeter.capnp, then generate stubs:

dart run build_runner build

This writes lib/schema/greeter.capnp.dart. The official capnp compiler must also be installed and on PATH.

Connect and call

import 'package:capnproto_dart_rpc/capnproto_dart_rpc.dart';
import 'schema/greeter.capnp.dart';

Future<void> main() async {
  final connection =
      await RpcSystem.connect(Uri.parse('tcp://127.0.0.1:12345'));
  final greeter = connection.bootstrap(GreeterClientFactory());

  try {
    final result = await greeter.greet((params) => params.name = 'World');
    print(result.reply);
  } finally {
    await greeter.dispose();
    await connection.close();
  }
}

That's the core client workflow: connect, get the remote object(bootstrap), call its methods like normal Dart methods, and clean up when done.
Swap tcp:// for ws:// or wss:// to connect over WebSocket instead.

Always call dispose() on capabilities you're finished with, and close() on the connection — each remote reference stays alive on the server until you release it.

Serving requests

If your app also needs to accept incoming calls — acting as a server, or answering a callback passed to you by one — implement the generated <Name>Server base class:

class MyGreeter extends GreeterServer {
  @override
  Future<DispatchResult> greet(
    GreeterGreetParamsReader params,
    List<Capability> paramsCapabilities,
  ) async {
    return buildGreetResults((out) => out.reply = 'Hello, ${params.name}!');
  }
}

Future<void> main() async {
  final server = await RpcSystem.serve(
    Uri.parse('tcp://0.0.0.0:12345'),
    MyGreeter(),
  );
  // Later: await server.close();
}

RpcSystem.serve also accepts ws:// and wss:// addresses.

Learn more

See the RPC guide and API documentation for promise pipelining, streaming calls, error handling, and the full protocol support matrix.