How do you implement a custom WebSocket protocol handler?

Question

Accepted Answer

**WebSocket protocol** — handle WebSocket frames manually.

```javascript
const { createHash } = require("crypto");
const net = require("net");

const MAGIC_KEY = "258EAFA5-E914-47DA-95CA-5AB9FC1C1B5A";

const server = net.createServer((socket) => {
    socket.once("data", (data) => {
        const request = data.toString();

// Extract WebSocket key
        const keyMatch = request.match(/Sec-WebSocket-Key: (.+)
/);
        if (!keyMatch) return socket.end();

const key = keyMatch[1].trim();
        const acceptKey = createHash("sha1")
            .update(key + MAGIC_KEY)
            .digest("base64");

// Send handshake
        socket.write(
            "HTTP/1.1 101 Switching Protocols
" +
            "Upgrade: websocket
" +
            "Connection: Upgrade
" +
            `Sec-WebSocket-Accept: ${acceptKey}

`
        );

// Handle frames
        socket.on("data", (frame) => {
            const payload = decodeFrame(frame);
            console.log("Received:", payload);
            socket.write(encodeFrame("Echo: " + payload));
        });
    });
});

function decodeFrame(buffer) {
    const length = buffer[1] & 0x7f;
    const mask = buffer.slice(2, 6);
    const data = buffer.slice(6, 6 + length);
    return data.map((byte, i) => byte ^ mask[i % 4]).toString();
}

function encodeFrame(message) {
    const data = Buffer.from(message);
    const frame = Buffer.alloc(2 + data.length);
    frame[0] = 0x81; // FIN + text
    frame[1] = data.length;
    data.copy(frame, 2);
    return frame;
}
```

Node.js: How do you implement a custom WebSocket protocol handler?