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a7d7463 | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 | # WebSocket Protocol
## What is WebSocket?
WebSocket provides full-duplex communication channels over a single TCP connection. Unlike HTTP, WebSocket allows real-time bidirectional communication.
## Connection Flow
```
Client Server
│ │
│──── HTTP Upgrade Request ────▶│
│ Upgrade: websocket │
│ │
│◀─── HTTP 101 Switching -------│
│ Protocol: ws │
│ │
│◀═════ WebSocket Open ═════════▶│
│ │
│◀═════ Messages ══════════════▶│
│ │
│◀═════ Connection Close ═══════▶│
```
## WebSocket Headers
### Upgrade Request
```
GET /ws HTTP/1.1
Host: api.example.com
Upgrade: websocket
Connection: Upgrade
Sec-WebSocket-Key: dGhlIHNhbXBsZSBub25jZQ==
Sec-WebSocket-Version: 13
```
### Server Response
```
HTTP/1.1 101 Switching Protocols
Upgrade: websocket
Connection: Upgrade
Sec-WebSocket-Accept: s3pPLMBiTxaQ9kYGzzhZRbK+xOo=
```
## Implementation Examples
### Server (Node.js + ws)
```javascript
const WebSocket = require('ws');
const wss = new WebSocket.Server({ port: 8080 });
wss.on('connection', (ws) => {
console.log('Client connected');
ws.on('message', (message) => {
console.log('Received:', message.toString());
ws.send('Echo: ' + message);
});
ws.on('close', () => {
console.log('Client disconnected');
});
// Send periodic message
const interval = setInterval(() => {
ws.send('Ping: ' + Date.now());
}, 30000);
ws.on('close', () => clearInterval(interval));
});
```
### Client (Browser)
```javascript
const ws = new WebSocket('ws://localhost:8080');
ws.onopen = () => {
console.log('Connected to WebSocket');
ws.send('Hello Server!');
};
ws.onmessage = (event) => {
console.log('Received:', event.data);
};
ws.onerror = (error) => {
console.error('WebSocket error:', error);
};
ws.onclose = () => {
console.log('Disconnected');
};
```
### Client (Python)
```python
import asyncio
import websockets
async def main():
async with websockets.connect('ws://localhost:8080') as ws:
await ws.send('Hello Server!')
response = await ws.recv()
print(f"Received: {response}")
asyncio.run(main())
```
## Socket.IO (Higher Level)
### Server
```javascript
const { Server } = require('socket.io');
const io = new Server(3000, {
cors: { origin: '*' }
});
io.on('connection', (socket) => {
console.log('User connected:', socket.id);
socket.on('message', (data) => {
console.log('Message:', data);
io.emit('message', data);
});
socket.on('disconnect', () => {
console.log('User disconnected');
});
socket.on('join-room', (room) => {
socket.join(room);
socket.to(room).emit('user-joined', socket.id);
});
});
```
### Client
```javascript
import { io } from 'socket.io-client';
const socket = io('http://localhost:3000');
socket.on('connect', () => {
console.log('Connected:', socket.id);
socket.emit('message', 'Hello everyone!');
});
socket.on('message', (data) => {
console.log('Received:', data);
});
```
## WebSocket vs HTTP
| Aspect | WebSocket | HTTP |
|--------|----------|------|
| Connection | Persistent | Request-Response |
| Direction | Bidirectional | Client → Server |
| Overhead | Low (after handshake) | High (headers each request) |
| Use Case | Real-time apps | REST APIs, simple requests |
| Browser Support | Modern browsers | All browsers |
## Best Practices
1. **Heartbeat/Ping-Pong** - Keep connections alive
2. **Reconnection Logic** - Handle connection drops
3. **Message Queueing** - Queue messages during disconnect
4. **Authentication** - Validate on connection
5. **Rate Limiting** - Prevent abuse
6. **Compression** - Consider permessage-deflate
|