What is HTTP? A detailed explanation of the core concepts and working principles of HTTP

in the daily operation of the Internet, there is a set of invisible rules supporting the information exchange between the browser and the server, from opening a web page to completing an online payment, it is inseparable from its scheduling. This is what we often call the network communication protocol, and HTTP is one of the most core members. This article will disassemble the running logic of HTTP in an all-round way from the basic concept, core structure, workflow to security upgrade and other angles to help you understand the "common language" of the Internet world.

What is the core concept of HTTP?

to understand the role of HTTP, we must first clarify its essence and its central role in network architecture.

1, basic definition of HTTP

HTTP full name Hypertext Transfer Protocol, is an application layer protocol based on TCP/IP protocol suite, mainly used to transmit hypertext data on the World Wide Web, such as HTML pages, pictures, audio and other content. It was born in the 1990s, after decades of iterative updates, has now become the core protocol supporting Internet content transmission, almost all web page access, data interaction rely on HTTP to complete.

2, the core features of HTTP

HTTP most notable feature is statelessness, meaning that the server does not keep any request records from the client, and each request is an independent interaction. This design makes HTTP easier to implement and consumes less server resources, but it also brings the problem of requiring additional mechanisms to store session information, such as common cookie technology. In addition, HTTP also has clear text transmission and request-responsive interaction mode, which together form the basis of its operation.

What is the core structure of HTTP?

HTTP communication process relies on a fixed packet structure, and only by following this structure can the client side and the server accurately resolve each other's information.

1 Composition of the request message

when the client side makes a request to the server, it will send an HTTP request message, which is mainly composed of four parts: the request line, the request header, the blank line and the request body. The request line contains the request method, the request URL and the HTTP version, such as GET /index.html HTTP/1.1; the request header carries the client's browser information, the accepted data type and other additional information; the request body is used to transmit the form data, file content and other entity information in the POST request.

2, the composition of the response message

the server receives the request, it will return an HTTP response message with a similar structure to the request message, including a status line, a response header, a blank line, and a response body. The status code in the status line is the core information, such as 200 to indicate that the request was successful, 404 to indicate that the resource was not found, and 500 to indicate an internal error of the server; the response header will inform the client side of the type and length of the response content; the response body is the actual content returned by the server, such as the HTML code of the webpage.

What is the complete workflow of HTTP?

from the user entering the URL in the browser to the completion of the page display, HTTP will complete a series of coherent communication steps, each step has a clear division of labor.

1, establishing a TCP connection

HTTP based on the TCP protocol to achieve reliable transmission, so before sending a request, the client side needs to establish a TCP connection with the server. Usually, the reliability of the connection is confirmed by a three-way handshake to ensure that both parties can receive and send data normally, which is the pre-foundation of HTTP communication.

2, send HTTP request message

connection is established, the client side will assemble the HTTP request message in line with the format and send it to the server. The message clearly contains the resource address of the request, the request method and the relevant information of the client. The server will judge the operation to be performed according to these contents.

3, the server processes and returns a response

server receives the HTTP request, it will parse the information in the message, find the corresponding resource or execute the specified business logic, and then assemble the response message and return it to the client side. The status code in the response message will directly feed back the processing result of the request, and the client side will carry out subsequent processing according to the status code and the content of the response body.

4, close the TCP connection

in earlier versions of HTTP/1.0, the TCP connection was closed after each request response was completed, while HTTP/1.1 and later versions supported persistent connections, allowing multiple HTTP request responses to be completed in one connection, effectively reducing the overhead of connection establishment and improving transmission efficiency.

What are the types of HTTP security extensions?

because early HTTP uses plaintext transmission, there is a risk of data theft and tampering, so there are a variety of security extensions to make up for this defect.

1, HTTPS encryption mechanism

HTTPS is a secure version of HTTP, which adds an SSL/TLS encryption layer between HTTP and TCP to encrypt the transmitted data. Exchanging session keys through asymmetric encryption and then using symmetric encryption to transmit actual data not only ensures the security of the key, but also takes into account the transmission efficiency. Today HTTPS has become the mainstream network transmission method, and most websites have completed the upgrade of HTTP to HTTPS.

2, other security enhancements

in addition to HTTPS, there are some other security mechanisms that can enhance the security of HTTP, such as HTTP Strict Transport Security Protocol, which can force the client side to use HTTPS to communicate with the server to avoid being hijacked to HTTP plaintext connection; in addition, by setting the security fields in the request header, such as X-Frame-Options, Content-Security-Policy, etc., can also effectively prevent click jacking, Cross Site Scripting and other security issues.

To sum up, HTTP, as the core protocol that supports the operation of the Internet, has a set of rigorous operation logic from basic definition, message structure to communication flow. Its stateless nature simplifies the implementation but also brings the need for session management, while HTTPS and other security extensions make up for the shortcomings of its plaintext transmission. Clarifying these core points of HTTP can help you understand the underlying logic of Internet information interaction more clearly, and lay a solid foundation for in-depth study of network technology.