Building Real-time APIs with WebSockets

Introduction to WebSockets

WebSockets provide full-duplex communication channels over a single TCP connection, enabling real-time data exchange between client and server.

Setting Up WebSocket Server

// server.js
const express = require('express');
const http = require('http');
const { WebSocketServer } = require('ws');

const app = express();
const server = http.createServer(app);
const wss = new WebSocketServer({ server });

wss.on('connection', (ws) => {
  console.log('Client connected');

  // Send welcome message
  ws.send(JSON.stringify({
    type: 'welcome',
    message: 'Connected to WebSocket server'
  }));

  // Handle incoming messages
  ws.on('message', (message) => {
    const data = JSON.parse(message);
    console.log('Received:', data);

    // Broadcast to all clients
    wss.clients.forEach((client) => {
      if (client !== ws && client.readyState === WebSocket.OPEN) {
        client.send(JSON.stringify({
          type: 'broadcast',
          data: data
        }));
      }
    });
  });

  ws.on('close', () => {
    console.log('Client disconnected');
  });
});

server.listen(3000, () => {
  console.log('WebSocket server running on port 3000');
});

Client Implementation

// client.js (Browser)
const ws = new WebSocket('ws://localhost:3000');

ws.onopen = () => {
  console.log('Connected to server');
  ws.send(JSON.stringify({
    type: 'message',
    content: 'Hello from client'
  }));
};

ws.onmessage = (event) => {
  const data = JSON.parse(event.data);
  console.log('Received:', data);
  
  if (data.type === 'broadcast') {
    // Update UI with new data
    updateUI(data.data);
  }
};

ws.onerror = (error) => {
  console.error('WebSocket error:', error);
};

ws.onclose = () => {
  console.log('Disconnected from server');
};

Use Cases

• Chat Applications: Real-time messaging
• Live Updates: Stock prices, sports scores
• Collaboration: Real-time document editing
• Gaming: Multiplayer game state sync
• Notifications: Push notifications

Scaling WebSockets

For production, consider:

• Using Redis for pub/sub across multiple servers
• Load balancing with sticky sessions
• Implementing reconnection logic
• Using Socket.io for easier WebSocket management