The HTTP knowledge you need to know is here!

Objective

HTTP network communication protocol plays a very important role in any development work, today, we will explain the relevant knowledge about HTTP.

Directory
5 minutes full understanding of HTTP knowledge. PNG computer network related knowledge

The computer network architecture is divided into five layers, with top-down applications, transports, networks, data links, and physical layers, such as:

Five-tier Protocol architecture

HTTP is present at the application layer at the top level, with a brief introduction to the application layer:

• Role
  Define communication rules for application-to-process (running programs) through application-layer Protocols

  The application layer protocol mainly includes HTTP, SMTP, FTP protocol and so on.

• The interacting data unit is called the message

• Basically based on the C/S method

HTTP INTRODUCTION 1. Defined

That is hypertext Transfer Protocol, Hypertext Transfer Protocol, which belongs to the application layer protocol.

2. Role

Provides guidelines for applying interprocess communication (Request & Response)

3. Features

• No connection: HTTP itself is not connected, that is, there is no need to establish an HTTP connection before exchanging HTTP messages
• Stateless: The HTTP protocol is stateless: During the data transfer process, no historical information and status information is saved. Stateless features simplify the design of servers, making it easier for servers to support a large number of concurrent HTTP requests.
• High Transmission reliability: TCP is used as Transport layer protocol (connection-oriented, reliable transmission), which requires a pre-established TCP connection when exchanging messages
• Good compatibility: Support B/s mode and C/s mode;
• Simple and fast: When a customer requests a service from the server, it simply transmits the request method and path. The request method commonly has, POST
• Flexible: HTTP allows the transfer of any type of data object

4. How to Work

The HTTP protocol takes the form of request/response work, workflow

Index.png5. HTTP message Explanation

HTTP messages are divided into request messages and response messages

5.1 Composition of HTTP request messages for HTTP request messages
HTTP request message composition. png

• Request line: Used to declare "request message", host domain name, resource path, and protocol version
• Request Header: A description of a client, server, or part of a message
• Request body: Used to store data information that needs to be sent to the server

1. Request Line

• Composition

The composition of the request line

Spaces cannot be saved

• Composition Introduction

1.1 Request method
That is, the request object operation, the request method has 8 kinds:

Method Category	meaning
OPTION	Request information for "options"
HEAD	Request to read "header of URL flag information" information
GET	Request to read information about "URL flags"
POST	Adding information to a server
PUT	Adds (stores) a document under the specified URL
DELETE	Deletes the information flagged by the specified URL
TRACE	Request message for loopback testing
CONNECT	For proxy Server

The most common is the Get and post methods .

1.2 Request Path
To understand the request address, first understand the following URL concepts:

• Definition: Uniform resoure Locator, Uniform Resource Locator, is a voluntary location of the abstract unique recognition method.
• Role: Methods used to represent resource locations and access to these resources
• Composition
  < protocol >://< host >:< port >/< path >

  1. Protocol: The application-layer communication protocol used, such as the URL address under the HTTP protocol:
     http://< host >:< ports >/< paths >
  2. Host: The domain name of the host on which the resource is requested
  3. Ports and paths can sometimes be omitted (HTTP default port number is 80)

As you can see from the above, the path is the part of the symbol "/" after the port number, for example

Path

URL (Uniform Resource Locator)	(Paths)
http://www.baidu.com/	/
Http://www.weibo.com/2874748/home	/2874748/home

1.3 Protocol version
The HTTP protocol version is mostly 1.0, 1.1, 2.0

The specific difference here is not much to explain, we are interested to understand the next

Request Line Example

First assume:

• The URL address is: http://www.tsinghua.edu.cn/chn/yxsz/index.htm
• Request message with Get method
• Request message with HTTP1.1 version
  The request line is: get/chn/yxsz/index.htm http/1.1

2. Request Header

• Role: A description of a client, server, or message part of the information
• How to use: Using header (field name): Value (value)
• Common Request Headers
  1. Generic header for request and response messages

Generic header for request and response messages

2. Common Request Header

Common Request Header

• Example:
  (URL address: http://www.tsinghua.edu.cn/chn/yxsz/index.htm)
  Host:www.tsinghua.edu.cn (indicates host domain name)
  user-agent:mozilla/5.0 (indicates that the user agent is using the Netscape browser)

3. The request body

• Function: Used to store data information that needs to be sent to the server
• How to use: At present, there are three kinds of

1. Data Interchange Format
The request body can be of any type, but the server needs additional parsing, such as JSON

｛"skill":{          "web":[                 {                  "name":"html",                  "year":"5"                 },                 {                  "name":"ht",                  "year":"4"                 }],           "database":[                  {                  "name":"h",                  "year":"2"                 }]`}}

To learn more about JSON parsing in Android development you can see another article I wrote:
Android Development: JSON introduction and the most comprehensive analytic Method!

2. Key-value pair form
A "=" connection between keys and values, with & connections between each key-value pair, and only ASCII characters, such as query String

key1=value1&key2&value2

3. Partial form
The request body is divided into several parts, the application scenario is file upload, such as mail upload and so on

• Each paragraph begins with--{boundary}
• And then the description header for that segment.
• Empty line after description header
• End of each paragraph with--{boundary}--

As follows:

Instances of request messages in partial format

In combination with the above mentioned request line, request header and request body, now assume that

• The URL address is: http://www.tsinghua.edu.cn/chn/yxsz/index.htm
• Request message with Get method
• Request message with HTTP1.1 version
• The request message wants to indicate that the host domain and user agent are using the Netscape browser
• The request body adopts the key-value pair form

The request message is as follows:

Composition of HTTP response message for request message 5.2HTTP Response message
HTTP response messages consist of. png

As can be seen from the above, in addition to the first line (Request line vs state line), the other structure of the response message is very similar to the request message. Where the response body is used to store data information that needs to be returned to the client.

1. Status line

• Composition

Status line composition

Where the space cannot be saved

1.1 Protocol version
The HTTP protocol version is mostly 1.0, 1.1, 2.0

The specific difference here is not much to explain, we are interested to understand the next

1.2 Status Code
The status code is divided into 5 major categories:

category	meaning
1xx	Represents an informational notification, such as a request received or being processed
2xx	To express success, as accepted or known.
3xx	Indicates redirection, and further action must be taken to complete the request
4xx	Customer errors, such as errors in the request syntax or inability to complete: 404
5xx	Indicates a server error, such as a server failure cannot complete the request

1.3 Status information
A simple explanation of the status code

Detailed status code information can be seen in detail

Example of status line

• http/1.1 202 Accepted (accepted)
• http/1.1 301 Bad Request (permanent transfer)
• http/1.1 404 Not Found (cannot be found)

2. Response header

• Role: A description of a client, server, or message part of the information
• How to use: Using header (field name): Value (value)
• Common Request Headers
  1. Generic header for request and response messages

Generic header for request and response messages

2. Common response Header

Common response Header3. Response body

• Function: Used to store data information that needs to be returned to the client
• Use: And the request body is consistent, also divided into: any type of data interchange format, key-value pair form and partial form, here does not make too much description.

The HTTP knowledge you need to know is here!