loopback4-example-websocket

This example is created to explore how to expose Websocket (socket.io) endpoints in conjunction with LoopBack controllers.

Similarly as @loopback/rest, each websocket server is attached to an http/https server. WebSocket controllers are mapped to different routes (namespaces), for example:

/admins -> AdminController /chats -> ChatController

When a client connects to the endpoint, a controller is instantiated upon the connection event of the namespace with the socket object. Controller methods can subscribe to one or more message types and send messages to one or more clients.

Each socket can join/leave rooms. Rooms are used to group/tag clients for messaging purposes.

Middleware can be registered at global and namespace level.

Basic use

npm start
Open your browser to http://localhost:3000

Websocket controllers

import {Socket} from 'socket.io';
import {ws} from '../decorators/websocket.decorator';

/**
 * A demo controller for websocket
 */
@ws('/chats')
export class WebSocketController {
  constructor(
    @ws.socket() // Equivalent to `@inject('ws.socket')`
    private socket: Socket,
  ) {}

  /**
   * The method is invoked when a client connects to the server
   * @param socket
   */
  @ws.connect()
  connect(socket: Socket) {
    console.log('Client connected: %s', this.socket.id);
    socket.join('room 1');
  }

  /**
   * Register a handler for 'chat message' events
   * @param msg
   */
  @ws.subscribe('chat message')
  // @ws.emit('namespace' | 'requestor' | 'broadcast')
  handleChatMessage(msg: unknown) {
    console.log('Message: %s', msg);
    this.socket.nsp.emit('chat message', `[${this.socket.id}] ${msg}`);
  }

  /**
   * The method is invoked when a client disconnects from the server
   * @param socket
   */
  @ws.disconnect()
  disconnect() {
    console.log('Client disconnected: %s', this.socket.id);
  }
}