5. Introduction to http protocol, http request and response

http protocol overview

1. What is HTTP protocol

HTTP is short for hypertext transfer protocol, which transfers HTML files.

HTTP is the most widely used protocol on the Internet. All the protocols beginning with www follow this protocol (possibly https)

2. Role of HTTP protocol

HTTP function: used to define the process of data exchange between WEB browser and WEB server and the content of the data itself

Interaction process between browser and server: browser request, service request response

Request (request line, request header, request body)

Response (response line, response header, response body)

3. Summary

1. HTTP protocol: Hypertext Transfer Protocol, which defines the rules when the client and server interact
2. The role of HTTP protocol: define the interaction process between client and server and the transmitted data

http request

img

• get mode request

[[request line]
GET /myApp/success.html?username=zs&password=123456 HTTP/1.1

[[request header]
Accept: text/html, application/xhtml+xml, */*
X-HttpWatch-RID: 41723-10011
Referer: http://localhost:8080/myApp/login.html
Accept-Language: zh-Hans-CN,zh-Hans;q=0.5
User-Agent: Mozilla/5.0 (MSIE 9.0; qdesk 2.4.1266.203; Windows NT 6.3; WOW64; Trident/7.0; rv:11.0) like Gecko
Accept-Encoding: gzip, deflate
Host: localhost:8080
Connection: Keep-Alive
Cookie: Idea-b77ddca6=4bc282fe-febf-4fd1-b6c9-72e9e0f381e8

• post request

[[request line]
POST /myApp/success.html HTTP/1.1

[[request header]
Accept: text/html, application/xhtml+xml, */*
X-HttpWatch-RID: 37569-10012
Referer: http://localhost:8080/myApp/login.html
Accept-Language: zh-Hans-CN,zh-Hans;q=0.5
User-Agent: Mozilla/5.0 (MSIE 9.0; qdesk 2.4.1266.203; Windows NT 6.3; WOW64; Trident/7.0; rv:11.0) like Gecko
Content-Type: application/x-www-form-urlencoded
Accept-Encoding: gzip, deflate
Host: localhost:8080
Content-Length: 27
Connection: Keep-Alive
Cache-Control: no-cache

[[request body]
username=zs&password=123456

1. Request line

• Request line

GET  /myApp/success.html?username=zs&password=123456 HTTP/1.1 
POST /myApp/success.html HTTP/1.1

• Request mode (8, put,delete, etc.) GET: clear text transmission is unsafe. The parameters follow the request path. There are restrictions on the size of the request parameters, POST: dark text transmission is safer. The request parameters are in the request body. There is no limit on the size of the request parameters,
• URI: uniform resource identifier (i.e. remove the protocol and IP address)
• Protocol version: HTTP/1.1

2. Request header

From line 2 to blank line, it is called request header, which exists in the form of key value pair, but there is a request header with a key corresponding to multiple values

Function: the browser tells the server its own relevant settings

• Accept: the MIME type acceptable to the browser, which tells the server what type of files the client can receive.
• User agent: browser information. (browser type, browser version...)
• Accept charset: the browser uses this header to tell the server which character set it supports
• Content length: indicates the length of the request parameter
• Host: the host and port in the initial URL
• Referrer: where did it come from (which resource was it before), anti-theft chain
• Content type: content type, which tells the server the MIME type of data transmitted by the browser and the type of file transmission, application/x-www-form-urlencoded
• Accept encoding: the data encoding method that the browser can decode, such as gzip
• Connection: indicates whether a persistent connection is required. If the server sees that the value here is "Keep -Alive", or that the request uses HTTP 1.1 (HTTP 1.1 makes a persistent connection by default)
• Cookie: This is one of the most important request header information (session technology, which will be discussed later)
• Date: Date: Mon, 22Aug 2011 01:55:39 GMT request time GMT

3. Requestor

Only when the request method is post can there be a request body, that is, the location of the request parameters (submitted data) in the post request

4. Summary

1. Request line
  	   	1. Request mode
  	   	2. Request path
2. Request header: It consists of key value pairs
3. Request body: only post A request has a request body, post The request body of the request is used to carry the request parameters

http response

img

Response part

[[response line]
HTTP/1.1 200

[[response header]
Accept-Ranges: bytes
ETag: W/"143-1557909081579"
Last-Modified: Wed, 15 May 2019 08:31:21 GMT
Content-Type: text/html
Content-Length: 143
Date: Sun, 08 Dec 2019 02:20:04 GMT

[[responder]
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
    Success
</body>
</html>

1. Response line

HTTP/1.1 200

• Protocol / version
• Response status code

img

200: normal, the connection with the server is successful, and the sending request is successful

302: redirect (jump)

304: read cache indicates that the client cache version is the latest, and the client can continue to use it without requesting from the server

403: insufficient permission for forbidden. The server received the request from the client, but refused to process it

404: the server received the request from the client, but there is no resource you are looking for in my server

500: the server received the request from the client and found the specific resource processing request, but the server made an exception during the processing

2. Response head

The response header exists as key:vaue, and there may be multiple value s. The server instructs the browser to do and configure

• Location: usually used with status code 302 to complete request redirection
• Content type: text / HTML; charset = UTF-8; set the MIME type of the content sent by the server when downloading the file

a.mp3 b.mp4

• Refresh: 5;url=http://www.baidu.com Indicates the refresh frequency of the client. The unit is seconds. eg: tell the browser to jump to Baidu after 5s
• Content disposition: attachment; filename = a.jpg instructs the client (browser) to download files
• Content length: 80 tells the browser the length of the body
• Server: type of Apache Tomcat server
• Content encoding: the encoding type of data sent by gzip server
• Set Cookie: SS = Q0 = 5lb_nq; path = / search cookies sent by the server
• Cache-Control: no-cache (1.1)
• Pragma: no cache (1.0) means to tell the client not to use cache
• Connection:close/Keep-Alive
• Date:Tue, 11 Jul 2000 18:23:51 GMT

3. Responder

The page displays the content, which is the same as the source code of the right-click view of the web page

4. Summary

1. Response line: contains the response status code
       1. Common response status codes:
              1. 200 OK
              2. 302 Redirect redirect
              3. 304 Cache Read cache
              4. 400 BAD REQUEST There is a problem with the request(It may be that the request parameters do not meet the regulations)
              5. 403 Forbidden Reject processing
              6. 404 NOT FOUND Resource not found
              7. 500 SERVER ERROR Server exception
2. Response header: It consists of multiple key value pairs
3. Responder:
      1. It can be used for the display of client pages
      2. Available for download