Analysis of the implementation principle of WebSocket Protocol in HTML5
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The purpose of the WebSocket protocol is to work on the existing network infrastructure. As part of this design principle, the protocol specification for WebSocket connections defines a HTTP connection as its initial life cycle, thus ensuring its full backward compatibility with the pre-WebSocket world. Generally speaking, switching WebSocket from HTTP protocol is called WebSocket handshake.
The browser sends a request to the server, which indicates that it wants to switch from the HTTP WebSocket protocol. The wish expressed by the client by upgrading the title, the code is as follows:
The code is as follows:
GET ws://echo.websocket.org/?encoding=text HTTP/1.1
Origin: http://websocket.org
Cookie: _ _ utma=99as
Connection: Upgrade
Host: echo.websocket.org
Sec-WebSocket-Key: uRovscZjNol/umbTt5uKmw==
Upgrade: websocket
Sec-WebSocket-Version: 13
If the server understands the WebSocket protocol, it agrees to the protocol switch through the upgrade header.
The code is as follows:
HTTP/1.1 101 WebSocket Protocol Handshake
Date: Fri, 10 Feb 2012 17:38:18 GMT
Connection: Upgrade Server: Kaazing Gateway
Upgrade: WebSocket
Access-Control-Allow-Origin: http://websocket.org
Access-Control-Allow-Credentials: true
Sec-WebSocket-Accept: rLHCkw/SKsO9GAH/ZSFhBATDKrU=
Access-Control-Allow-Headers: content-type
At this point, the HTTP connection breaks down and replaces the WebSocket connection in the same underlying TCP / IP connection. The WebSocket connection uses the same HTTP (80) as the HTTPS port (443), by default.
After the connection is established, WebSocket data frames can be sent back and forth between the client and the server in full-duplex mode. Both text and binary frames can be sent in both directions. There are only two bytes of data minimum framing. For text frames, each frame starts at 0 x00 bytes, ends with 0 xff bytes, and contains utf-8 data. WebSocket text frames use a Terminator, while binary frames use a prefix length.
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