WebSocket Quick Start

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Demo

Git repo, create basic and secure websocket server and client via Python websockets module: https://github.com/chengdol/websocket-demo

Introduction

Difference between socket and websocket?

如果你已经理解了HTTP, HTTP CONNECT method 以及Proxy的知识，那么维基百科的描述已经比较清楚了. WebSocket Wiki WebSocket is a computer communications protocol, providing full-duplex communication channels over a single TCP connection.

WebSocket is distinct from HTTP (half-duplex, clients issue request). Both protocols are located at layer 5 in the OSI model and depend on TCP at layer 4. Although they are different, RFC 6455 states that WebSocket “is designed to work over HTTP ports 443 and 80 as well as to support HTTP proxies and intermediaries,” thus making it compatible with the HTTP protocol. To achieve compatibility, the WebSocket handshake uses the HTTP(1.1 version) Upgrade header to change from the HTTP protocol to the WebSocket protocol.

Some proxies also support WebSocket, for example, Envoy, some may not.

WebSocket handshake ws:// or wss:// (WebSocket Secure):

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// client request
GET /chat HTTP/1.1
Host: server.example.com
Upgrade: websocket
Connection: Upgrade
Sec-WebSocket-Key: x3JJHMbDL1EzLkh9GBhXDw==
Sec-WebSocket-Protocol: chat, superchat
Sec-WebSocket-Version: 13
Origin: http://example.com

// server response
HTTP/1.1 101 Switching Protocols
Upgrade: websocket
Connection: Upgrade
Sec-WebSocket-Accept: HSmrc0sMlYUkAGmm5OPpG2HaGWk=
Sec-WebSocket-Protocol: chat

WebSockets use cases:

  • chatting
  • live feed
  • multiplayer gaming
  • showing client progress/logging

Pros:

  • full-duplex (no polling)
  • HTTP compatible
  • firewall friendly

Cons:

  • lots of proxies and transparent proxies don’t support it yet
  • L7, LB challenging (timeouts)
  • stateful, difficult to horizontal scale

Do you have to use Web Sockets ? (alternatives) It is important to note that WebSockets is not the only HTTP realtime based solution, there are other ways to achieve real time such as eventsource, and long polling.

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