rpc_dart_wasm

WASM runtime bridge transport for rpc_dart.

This package is intentionally runtime-agnostic. It does not load .wasm modules by itself. Instead, a runtime backend implements the byte-only RpcWasmBridge, and RpcWasmTransport.fromBridge turns it into a normal IRpcTransport.

final transport = RpcWasmTransport.fromBridge(
  bridge: myWasmBridge,
  isClient: true,
);

final endpoint = RpcPeerEndpoint(transport: transport);
endpoint.start();

WASM Bootstrap

Code compiled to WASM can bootstrap itself with RpcWasm.run(...):

import 'package:rpc_dart_wasm/rpc_wasm.dart';

void main() {
  RpcWasm.run(
    isClient: false,
    configure: (endpoint) {
      // Register RPC services here, then let the bootstrap start listening.
    },
  );
}

RpcWasm.run installs the runtime-side rpcWasmReceiveBytes callback, adapts the host byte pipe into RpcWasmTransport, creates a RpcPeerEndpoint, and starts it after configure returns.

Flutter Backend

RpcFlutterWasmBridge is the built-in Flutter plugin backend:

final support = await RpcFlutterWasmBridge.checkSupport();
if (!support.canRunDartWasm) {
  throw StateError('Dart WASM is not supported on this device');
}

final bridge = await RpcFlutterWasmBridge.load(
  wasmBytes: wasmBytes,
  mjsCode: mjsCode,
);

final transport = RpcWasmTransport.fromBridge(
  bridge: bridge,
  isClient: true,
);

Native backends:

Android: androidx.javascriptengine.JavaScriptSandbox
iOS: JavaScriptCore

The Flutter host keeps lifecycle calls on the rpc_dart_wasm method channel, but runtime byte traffic goes over raw binary messenger channels:

rpc_dart_wasm/<runtimeId>/outgoing for Dart to native
rpc_dart_wasm/<runtimeId>/incoming for native to Dart

The WASM JavaScript side should expose a byte receiver:

globalThis.rpcWasmReceiveBytes = function(bytes) {
  // bytes is a Uint8Array containing one RpcChannelFrame.
};

To send bytes back to the host, call:

_rpcWasmSendBytes(bytes); // bytes is Uint8Array

Bridge Protocol

RpcWasmBridge exchanges only Uint8List frames:

abstract interface class RpcWasmBridge {
  Stream<Uint8List> get incoming;
  Future<void> send(Uint8List data);
  bool get isClosed;
  Future<void> close();
}

No RPC-level JSON and no WASM-specific envelope is added by this package. RpcWasmTransport adapts the bridge to IRpcChannel and reuses RpcChannelTransport.fromChannel, so the wire format is the existing RpcChannelFrame.

Runtime Backends

Expected backends:

Flutter plugin backend: JavaScriptCore on iOS, JavaScriptSandbox on Android.
Browser backend: dart:js_interop / JS functions.
Native backend: wasmtime/wasmer embedding.
Test backend: paired in-memory bridge.

The transport itself does not guarantee zero-copy. Most WASM host boundaries copy bytes; backends may optimize byte transfer independently.

rpc_dart_wasm

WASM Bootstrap

Flutter Backend

Bridge Protocol

Runtime Backends

Libraries

rpc_dart_wasm package