WebSocket enables bidirectional real-time communication between client and server.
HTTP vs WebSocket¶
- HTTP — request/response, stateless, polling
- WebSocket — persistent connection, bidirectional, real-time
Handshake¶
GET /ws HTTP/1.1
Upgrade: websocket
Connection: Upgrade
HTTP/1.1 101 Switching Protocols
Upgrade: websocket
Connection: Upgrade
Server (Node.js)¶
import { WebSocketServer } from “ws”;
const wss = new WebSocketServer({ port: 8080 });
wss.on(“connection”, (ws) => {
ws.on(“message”, (data) => {
// broadcast to all
wss.clients.forEach((client) => client.send(data));
});
});
Client¶
const ws = new WebSocket(“ws://localhost:8080”);
ws.onmessage = (event) => console.log(event.data);
ws.send(“Hello”);
Use cases¶
- Chat applications
- Live notifications
- Real-time dashboards
- Collaborative editing
- Gaming
- Trading/finance feeds
Scaling¶
WebSocket holds a persistent connection. For scaling: Redis pub/sub for coordination between servers. Or Socket.io with Redis adapter.
Alternatives¶
- SSE (Server-Sent Events) — unidirectional (server → client), simpler
- Long polling — fallback for older clients
- gRPC streaming — for service-to-service
When to Use WebSocket¶
Real-time bidirectional data. For unidirectional streams (notifications, feeds) consider SSE — simpler.