websocket-implementation

# WebSocket Implementation

Build scalable real-time communication systems with proper connection management.

## Server Implementation (Socket.IO)

```javascript
const { Server } = require('socket.io');
const { createAdapter } = require('@socket.io/redis-adapter');
const { createClient } = require('redis');

const io = new Server(server, {
  cors: { origin: process.env.CLIENT_URL, credentials: true }
});

// Redis adapter for horizontal scaling
const pubClient = createClient({ url: process.env.REDIS_URL });
const subClient = pubClient.duplicate();
Promise.all([pubClient.connect(), subClient.connect()]).then(() => {
  io.adapter(createAdapter(pubClient, subClient));
});

// Connection management
const users = new Map();

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

io.on('connection', (socket) => {
  users.set(socket.user.id, socket.id);
  console.log(`User ${socket.user.id} connected`);

  socket.on('join-room', (roomId) => {
    socket.join(roomId);
    socket.to(roomId).emit('user-joined', socket.user);
  });

  socket.on('message', ({ roomId, content }) => {
    io.to(roomId).emit('message', {
      userId: socket.user.id,
      content,
      timestamp: Date.now()
    });
  });

  socket.on('disconnect', () => {
    users.delete(socket.user.id);
  });
});

// Utility methods for message distribution
function broadcastUserUpdate(userId, data) {
  io.to(`user:${userId}`).emit('user-update', data);
}

function notifyRoom(roomId, event, data) {
  io.to(`room:${roomId}`).emit(event, data);
}

function sendDirectMessage(userId, message) {
  const socketId = users.get(userId);
  if (socketId) {
    io.to(socketId).emit('direct-message', message);
  }
}
```

## Client Implementation

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

class WebSocketClient {
  constructor(url, token) {
    this.socket = io(url,