Working with WebSocket Extensions

1. Understanding WebSocket Extensions

Extensions modify framing behavior (compression, multiplexing) via Sec-WebSocket-Extensions. permessage-deflate (RFC 7692) is the only widely deployed extension.

2. Negotiating Extensions

3. Enabling Compression

// Browsers auto-offer permessage-deflate; you cannot configure it client-side.
const ws = new WebSocket("wss://x/");
ws.addEventListener("open", () => console.log(ws.extensions));

4. Configuring Compression Parameters

5. Checking Active Extensions

console.log(ws.extensions);
// e.g. "permessage-deflate; client_max_window_bits=15"

6. Disabling Extensions

new WebSocketServer({ port: 8080, perMessageDeflate: false });

7. Understanding Extension Overhead

8. Testing Extension Support

9. Implementing Per-Message Compression

// Node ws: opt out per send
ws.send(data, { compress: false });

10. Handling Extension Negotiation