chrishuffman5/websocket

WebSocket (RFC 6455)

This skill covers the WebSocket protocol, standardized as RFC 6455. WebSocket provides full-duplex, bidirectional communication over a single persistent TCP connection. It has deep knowledge of:

• RFC 6455 protocol: opening handshake, frame format, opcodes, masking, fragmentation
• Close handshake and status codes (1000-1015, 4000-4999)
• Extensions: permessage-deflate (RFC 7692)
• Subprotocols: graphql-ws, mqtt, stomp
• Browser WebSocket API: constructor, events, readyState, bufferedAmount
• Server implementations: ws (Node.js), websockets (Python), gorilla/websocket (Go)
• Authentication patterns (query string, first-message, cookies)
• Reconnection strategies with exponential backoff
• Proxy/firewall traversal and load balancing

How to Approach Tasks

1. Classify the request:

   • Protocol / architecture -- Load references/architecture.md for RFC 6455, frames, handshake, close codes, extensions
   • Best practices -- Load references/best-practices.md for authentication, reconnection, backpressure, compression, security
   • Troubleshooting -- Load references/diagnostics.md for connection failures, close codes, proxy issues, performance
   • Cross-technology comparison -- Read the overview skill

2. Gather context -- Client type (browser, server), server language, proxy/CDN in use, subprotocol, authentication method

3. Analyze -- Apply WebSocket-specific reasoning: stateful connections, no built-in reconnection, proxy traversal, authentication constraints.

4. Recommend -- Provide browser API code, server implementation code, proxy configuration.

Core Protocol

Opening Handshake

HTTP/1.1 upgrade request. Server accepts with 101 Switching Protocols and computed Sec-WebSocket-Accept header.

Frame Format

Lightweight binary framing: FIN bit, opcode (text=1, binary=2, close=8, ping=9, pong=10), mask bit, payload length, optional masking key, payload.

Client-to-server frames are ALWAYS masked. Server-to-client NEVER masked.

Close Codes

| Code | Meaning | |---|---| | 1000 | Normal closure | | 1001 | Going away (server shutdown, page navigation) | | 1002 | Protocol error | | 1006 | Abnormal closure (no close frame -- TCP dropped) | | 1008 | Policy violation | | 1009 | Message too big | | 1011 | Server internal error | | 4000-4999 | Application-defined |

Browser API

const ws = new WebSocket("wss://example.com/ws");
ws.onopen = () => ws.send("hello");
ws.onmessage = (e) => console.log(e.data);
ws.onclose = (e) => console.log(e.code, e.reason, e.wasClean);
ws.onerror = () => {};

Cannot set custom headers from browser. Auth via query string or cookies.

Anti-Patterns

1. No reconnection logic -- WebSocket has no built-in reconnection. Always implement with exponential backoff.
2. WebSocket for one-way server push -- Use SSE instead. Simpler, auto-reconnects, works through all proxies.
3. Ignoring bufferedAmount -- Sending faster than network can deliver causes memory growth. Check ws.bufferedAmount.
4. Auth token in URL without short-lived exchange -- Query string tokens appear in logs. Use a REST-issued short-lived connection token.
5. No ping/pong keepalive -- Without keepalive, silent connection drops go undetected for minutes.
6. Open WebSocket preventing bfcache -- Always close connections on page navigation.
7. L4 load balancing -- WebSocket needs sticky sessions or L7-aware proxies.
8. No message size limits -- Set maximum message size on server to prevent memory exhaustion.

Reference Files

• references/architecture.md -- RFC 6455 handshake, frame format, opcodes, masking, fragmentation, close codes, extensions, subprotocols, browser API
• references/best-practices.md -- Authentication, reconnection, backpressure, compression, ping/pong, security, proxy configuration, server implementations
• references/diagnostics.md -- Connection failures, close code debugging, proxy issues, performance, memory leaks, cross-origin errors

Cross-References

• overview skill -- WebSocket vs SSE, SignalR, Socket.IO comparisons
• socketio skill -- Socket.IO (builds on WebSocket via Engine.IO)
• signalr skill -- SignalR (uses WebSocket as primary transport)