Network communication protocol-HTTP protocol explained in detail!

HTTP (Hypertext Transfer Protocol) is an application layer protocol mainly used to transmit hypertext and other resources over the network. It follows the request-response model, is stateless, and each request is independent. HTTP uses a simple text format for communication, including request headers and response headers. The main methods of HTTP include GET, POST, PUT, DELETE, etc., which are used for different operations and purposes. Through HTTP, the client can request resources from the server, and the server processes the request and returns a corresponding response. The development of the HTTP protocol has promoted the development of the Internet, allowing information to be transmitted and shared globally quickly and reliably.

1. Request-response model:

   • Client sends request: The client (usually a web browser) sends an HTTP request message to the server to request a specific resource (such as web pages, images, videos, etc.).
   • The server sends a response: After the server receives the request, it processes the request and returns an HTTP response message, which contains the requested resource or error information.

2. HTTP method:

   • GET: Used to request specified resources.
   • POST: Used to submit data to the server, usually used to submit form data or create resources.
   • PUT: Used to update resources to the server.
   • DELETE: Used to request deletion of specified resources.
   • HEAD: Similar to the GET method, but only returns the response header information, not the actual content.
   • OPTIONS: Used to obtain communication options supported by the server.
   • PATCH: used for partial updates of resources.

3. HTTP message format:
   
   HTTP message consists of request message and response message, and has the following basic format:

   请求报文： METHOD URL HTTP/版本头部字段1: 值1头部字段2: 值2... 响应报文： HTTP/版本 状态码 状态消息头部字段1: 值1头部字段2: 值2... 实体数据（请求报文和响应报文中可选的实体数据）

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4. HTTP status code:

   • 1xx: Informational status code, indicating that the request has been received and processing continues.
   • 2xx: Success status code, indicating that the request has been successfully processed.
   • 3xx: Redirect status code, indicating that further operations are required to complete the request.
   • 4xx: Client error status code, indicating that the request contains errors or cannot be completed.
   • 5xx: Server error status code, indicating that an error occurred when the server processed the request.

5. Characteristics of HTTP:

   • No connection: Each request-response cycle is independent of each other, and the server does not retain the connection status with the client.
   • Stateless: The server does not save the session state with the client. Each request is independent, which results in the need to use Cookie, Session and other mechanisms to maintain state.
   • Extensible: The HTTP protocol can be extended by adding new header fields or methods to meet changing needs.

6. HTTP application:

   • Web browsers use the HTTP protocol to communicate with the web server and obtain web pages and resources.
   • Web API provides access to applications through the HTTP protocol, such as RESTful API.

• Web services use the HTTP protocol for communication and data exchange across networks.

HTTP is a request-response model application layer protocol used to transmit hypertext and other resources between Web browsers and Web servers. It communicates in a simple text format, supports multiple methods and status codes, and is connectionless and stateless. HTTP plays a key role in the Internet and is the basic protocol for Web communication and data exchange.

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