dox_socketio 3.0.0-alpha.4

Socket.IO v4 server (Engine.IO v4, Socket.IO protocol v5) for the Dox framework and plain dart:io.

dox_socketio

A Socket.IO server for Dart. The official clients can connect to it without changes: socket.io-client (JavaScript v4) and the Dart socket_io_client package.

It speaks Engine.IO protocol v4 and Socket.IO protocol v5. These are the protocols of Socket.IO v4.

Quick start

import 'package:dox_socketio/dox_socketio.dart';

Future<void> main() async {
  SocketIoServer io = SocketIoServer();
  io.on('connection', onConnection);
  await io.listen(3000);
}

void onConnection(Socket socket) {
  socket.emit('welcome', 'hello');
  socket.on('chat', (SocketEvent event) {
    socket.to('lobby').emit('chat', event.data); // everyone in lobby but me
    event.ack('ok'); // answer the client callback
  });
}

Class-based style

Put a namespace in a class. Its dependencies come in through the constructor, so it works with any DI container.

class ChatNamespace extends NamespaceHandler {
  ChatNamespace(this.messages);

  final MessageService messages;

  @override
  String get path => '/chat';

  @override
  List<Middleware> get middleware => <Middleware>[checkToken];

  void checkToken(Socket socket) {
    if (socket.handshake.auth['token'] != 'secret') {
      throw SocketIoException('unauthorized', data: {'reason': 'bad token'});
    }
  }

  @override
  void onConnection(Socket socket) => socket.on('message', onMessage);

  void onMessage(SocketEvent event) => event.ack(messages.save(event.data));
}

io.register(ChatNamespace(MessageService()));

When a middleware throws, the client gets connect_error with the message and data.

API overview

Node.js	Dart
io.of('/chat')	io.of('/chat')
io.use(fn) / nsp.use(fn)	io.use(fn) / nsp.use(fn)
io.on('connection', fn)	io.on('connection', fn)
socket.on('e', (a, cb) => ...)	socket.on('e', (SocketEvent e) => ...), e.data, e.args, e.ack(x)
socket.emit('e', a, b)	socket.emit('e', a) or socket.emitArgs('e', [a, b])
await socket.timeout(5000).emitWithAck('e', a)	await socket.emitWithAck('e', a, timeout: Duration(seconds: 5))
socket.join(r) / socket.leave(r)	socket.join(r) / socket.leave(r)
socket.to(r).emit(...)	socket.to(r).emit(...)
socket.broadcast.emit(...)	socket.broadcast.emit(...)
io.to(r).except(x).emit(...)	io.to(r).except(x).emit(...)
io.local.emit(...)	io.local.emit(...)
socket.handshake	socket.handshake.headers, .query, .auth, .address
socket.data	socket.data (a Map)
socket.disconnect(true)	socket.disconnect(true)
io.in(r).fetchSockets()	io.to(r).fetchSockets() (this server only)

Events disconnecting and disconnect give the reason in event.data, like transport close, ping timeout or client namespace disconnect.

Binary data: send a Uint8List. It can be anywhere inside lists and maps.

Mounting

• Standalone: await io.listen(3000). Or io.attach(httpServer).
• Inside your own dart:io server: send the request to io.handle(request) when io.matches(request) is true. The path is /socket.io/ by default.

Options

SocketIoServer(
  options: ServerOptions(
    path: '/socket.io/',
    pingInterval: Duration(seconds: 25),
    pingTimeout: Duration(seconds: 20),
    maxHttpBufferSize: 1000000,
    transports: ['polling', 'websocket'],
    cors: CorsOptions(origins: ['https://my.app'], credentials: true),
  ),
);

Many servers: Redis adapter

Use the Redis adapter when you run more than one server process. A broadcast on one server then reaches the clients of all servers.

Redis sub = Redis(RedisOptions(host: '127.0.0.1', port: 6379));
SocketIoServer io = SocketIoServer(
  adapter: RedisAdapter(subscriber: sub, publisher: sub.duplicate()),
);

The messages use the format of @socket.io/redis-adapter. A Node.js server can share broadcasts with a Dart server when it uses a JSON parser:

createAdapter(pub, sub, { parser: { encode: JSON.stringify, decode: JSON.parse } })

The Dart adapter listens with PSUBSCRIBE, so it also gets the room channels that Node.js uses when it broadcasts to exactly one room.

Limits: fetchSockets, socketsJoin and broadcast acks only work on the local server.

HTTP long-polling needs sticky sessions when you run many servers behind one port. Use transports: ['websocket'] on the client if you can not have them.

Tests

dart test

• The interop tests run the real socket.io-client with Node.js. They run npm ci in test/interop the first time. They skip when Node.js is missing.
• The Redis tests read REDIS_HOST and REDIS_PORT (default 127.0.0.1:6379). They skip when Redis is not reachable.