Request: The client sends data to the server
Response: The server sends data to the client
Sending data conforms to the HTTP transport protocol
Features:
Advanced Protocol Based on TCP/IP
Default port number: 80
Based on request/response model: one request, one response
Stateless: each request is independent of each other and cannot exchange data
historic version:
1.0: A new connection is established for each request correspondingly
1.1: Multiplexing connections
Request method:
get：
*Request parameters are in the request line, after the url
*The length of the requested url is limited
post：
*Request parameters are in the request body
* There is no limit to the length of the requested url
Data Format:
Request message data format:
Request line: request method request url request protocol/version
request header: request header name: request header value
Common request headers:
HOST: The requested host
User-Agent: Tell the server the version information of the browser used (you can get the information of this header on the server side to solve the compatibility problem of browsers, different browsers respond to different codes)
Accept: what kind of information can be parsed
Accept-Encoding: Acceptable compression format
Connection: keep-alive (reusable connection)
Referer: Notify where the server comes from (hot chain (prevent entry from other pages), statistical work (where statistics come from to enter the website))
Request blank line: blank line, separating request header and request body
Request body: the request parameters that encapsulate the POST request message
Right click, check, network, refresh, click login.html
