RFC 6455 - The WebSocket Protocol
Full-duplex communication over a single TCP connection
What is WebSocket?
The WebSocket Protocol enables two-way communication between a client running untrusted code in a controlled environment and a remote host. It provides a full-duplex communication channel over a single TCP connection and is designed to work over HTTP ports 80 and 443.
Key Features
Full-Duplex
Simultaneous bidirectional communication between client and server.
Low Overhead
Minimal framing overhead compared to HTTP polling.
Real-Time
Instant message delivery without polling delays.
Firewall Friendly
Works through HTTP ports and proxy servers.
WebSocket Handshake
1. Client Request
GET /chat HTTP/1.1
Host: server.example.com
Upgrade: websocket
Connection: Upgrade
Sec-WebSocket-Key: dGhlIHNhbXBsZSBub25jZQ==
Sec-WebSocket-Version: 132. Server Response
HTTP/1.1 101 Switching Protocols
Upgrade: websocket
Connection: Upgrade
Sec-WebSocket-Accept: s3pPLMBiTxaQ9kYGzzhZRbK+xOo=WebSocket Frame Format
Frame Header
FIN: Final fragment flag
Opcode: Frame type (text, binary, close, etc.)
MASK: Masking flag
Payload Length: Data length
Frame Types
0x1: Text frame
0x2: Binary frame
0x8: Close frame
0x9: Ping frame
0xA: Pong frame
Security Features
- Origin Validation: Server can validate the origin of WebSocket requests
- Masking: Client-to-server frames are masked to prevent cache poisoning
- TLS Support: WebSocket Secure (WSS) provides encryption
- Same-Origin Policy: Browser enforces origin restrictions
- Subprotocol Negotiation: Application-level protocol selection
Connection Management
Opening
HTTP upgrade handshake establishes WebSocket connection.
Data Transfer
Bidirectional message exchange using WebSocket frames.
Ping/Pong
Keepalive mechanism to detect connection failures.
Closing
Graceful connection termination with close frames.
Common Applications
- Real-Time Chat: Instant messaging applications
- Live Updates: Social media feeds and notifications
- Gaming: Multiplayer online games
- Trading Platforms: Real-time financial data
- Collaborative Editing: Google Docs-style applications
- IoT Dashboards: Real-time sensor data visualization
- Video Streaming: Live video chat and streaming
- Remote Desktop: Screen sharing applications
Advantages over HTTP Polling
Lower Latency
No need to establish new connections for each message.
Reduced Overhead
Minimal frame headers vs. full HTTP headers.
Server Push
Server can initiate communication without client request.
Resource Efficiency
Single persistent connection vs. multiple HTTP requests.