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WebSockets

#web-sockets #protocol #webdevelopement

TCP based network-protocol that enables bidirectional communication between client (web-browser) and server (WebSocket-Server).

(from 223_Multi-User App)

A WebSocket URI starts with ws: or wss: for a secured connection.

Handshake

Clients request

 GET /chat HTTP/1.1
 Host: server.example.com
 Upgrade: websocket
 Connection: Upgrade
 Sec-WebSocket-Key: dGhlIHNhbXBsZSBub25jZQ==
 Origin: http://example.com
 Sec-WebSocket-Protocol: chat, superchat
 Sec-WebSocket-Version: 13

Servers response

 HTTP/1.1 101 Switching Protocols
 Upgrade: websocket
 Connection: Upgrade
 Sec-WebSocket-Accept: s3pPLMBiTxaQ9kYGzzhZRbK+xOo=
 Sec-WebSocket-Protocol: chat

Sec-WebSocket-Key and Sec-WebSocket-Accept

Sec-WebSocket-Accept adds the Sec-WebSocket-Key to a GUID which is then hashed using SHA1.

Sec-WebSocket-Protocol

This header defines sub-protocols. Common ones are MQTT, WAMP or STOMP. It is also possible to define custom ones (like the ones above).

Implementations