The basic principle websocket

• HTTP in a request can be only one response. And the response is passive, can not initiate
  • Therefore, past service side push information is kept by the client to achieve the polling
• websocket is a two-way communication protocol that provides server capacity to take the initiative to push information
• Websocket need to create a connection, which makes it become a stateful protocol, status information may be omitted after partial communication. The stateless HTTP requests may need to have to carry the state information (such as authentication, etc.) in each request
• The default port is 80 and 443
• Need client (browser) and server support both
• If after the agent, then the agent also need support, otherwise some agents will automatically disconnect when a long time without communication
  • Therefore in order to ensure WS connection is not cut off, it will send a heartbeat
• After WebSocket connection is established, the subsequent data are transmitted in the form of a sequence of frames
  • HTTP is only responsible for establishing the WebSocket connection
  • HTTP header does not need to send the subsequent data can be exchanged
    • Improve the efficiency of information exchange

• Websocket is based on the HTTP protocol, or borrow the HTTP protocol to complete part of the handshake
  • Sec-WebSocket-KeyIs a browser-generated Base64 value for the server to verify the validity of
  • Sec-WebSocket-AcceptAfter the server is identified and encryptedSec-WebSocket-Key
    • Will be Sec-WebSocket-Keywith 258EAFA5-E914-47DA-95CA-C5AB0DC85B11stitching
    • Calculated by SHA1 digest, and turn into a base64 string.
• After the completion status code in response to http requests 101, showing switching protocol
  • Description WebSocket protocol to establish TCP transport layer connection via http protocol, after they have nothing to do with the http protocol

// 客户端请求
GET ws://example.com/ 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

// 服务器应答
HTTP/1.1 101 Switching Protocols
Upgrade: websocket
Connection: Upgrade
Sec-WebSocket-Accept: HSmrc0sMlYUkAGmm5OPpG2HaGWk=
Sec-WebSocket-Protocol: chat