WebSockets & Real-time

Socket.IO Server

import { Server } from 'socket.io';

const io = new Server(server, {
  cors: {
    origin: process.env.CLIENT_URL,
    methods: ['GET', 'POST']
  }
});

// Authentication middleware
io.use((socket, next) => {
  const token = socket.handshake.auth.token;
  try {
    const user = verifyToken(token);
    socket.data.user = user;
    next();
  } catch {
    next(new Error('Authentication failed'));
  }
});

// Connection handling
io.on('connection', (socket) => {
  console.log(`User connected: ${socket.data.user.id}`);

  // Join user's room
  socket.join(`user:${socket.data.user.id}`);

  // Handle events
  socket.on('message', async (data) => {
    const message = await saveMessage(data);
    io.to(data.roomId).emit('message', message);
  });

  socket.on('disconnect', () => {
    console.log(`User disconnected: ${socket.data.user.id}`);
  });
});

Socket.IO Client

import { io } from 'socket.io-client';

const socket = io(SERVER_URL, {
  auth: { token: getAuthToken() },
  reconnection: true,
  reconnectionAttempts: 5
});

socket.on('connect', () => {
  console.log('Connected');
});

socket.on('message', (message) => {
  addMessageToUI(message);
});

// Send message
socket.emit('message', {
  roomId: 'room-123',
  content: 'Hello!'
});

Room Patterns

// Join room
socket.join('room:123');

// Leave room
socket.leave('room:123');

// Broadcast to room
io.to('room:123').emit('event', data);

// Broadcast to all except sender
socket.to('room:123').emit('event', data);

// Private message
io.to(`user:${userId}`).emit('private', message);

Scaling with Redis

import { createAdapter } from '@socket.io/redis-adapter';
import { createClient } from 'redis';

const pubClient = createClient({ url: REDIS_URL });
const subClient = pubClient.duplicate();

io.adapter(createAdapter(pubClient, subClient));

Use Cases