Understanding the HTTP Protocol

The HTTP protocol serves as the “common language” of the internet, supporting our daily web browsing, app usage, and API calls. Today, let’s discuss this seemingly simple yet profoundly rich protocol.

What is HTTP?

HTTP (Hypertext Transfer Protocol) acts like a courier in the internet world, responsible for delivering information between the client (such as your mobile browser) and the server (like the backend of a website). It was born in 1989, proposed by Tim Berners-Lee, and has since become the cornerstone of the World Wide Web.

How does HTTP work?

Imagine the process of ordering takeout:

1. You open the takeout app (client) and select dishes (request)
2. The merchant (server) receives the order and starts preparing
3. The delivery person brings the prepared meal to you (response)

The workflow of HTTP is similar:

• The client initiates a request: “I want the homepage content”
• The server processes the request: “Okay, here is the HTML you requested”
• The client receives and displays the content

The “Delivery Slip” of an HTTP Request

Each HTTP request contains three parts of information:

Request Line

Indicates what to do (GET to retrieve/POST to submit), what resource is needed (/index.html), and which version is used (HTTP/1.1)

Request Headers

Additional information, such as your device type and acceptable content formats

Request Body

Optional, such as data submitted when filling out a form

GET /article/123 HTTP/1.1
Host: tech.example.com
User-Agent: iPhone Safari
Accept: application/json

How the Server Responds

The server’s response contains three parts

Status Line

The response status code, such as 200 for success, 404 for resource not found

Response Headers

Information such as content type and length

Response Body

The actual data, such as HTML or images

HTTP/1.1 200 OK
Content-Type: application/json
Cache-Control: max-age=3600

{"title":"Detailed Explanation of HTTP","author":"Zhang San"}

Key Features of HTTP

1. Statelessness

HTTP is a stateless protocol, meaning each request is independent, and the server does not retain any information from previous requests. This simplifies server design, but if state needs to be maintained across multiple requests, mechanisms like Cookie and Session are required.

2. Flexibility

HTTP allows the transmission of any type of data object. The content type is specified by the Content-Type header field.

3. Extensibility

HTTP is extensible, allowing new features to be added through custom header fields and extended protocols.

4. Request-Response Model

HTTP uses a request-response model where the client sends a request, and the server returns a response.

5. Support for Multiple Transfer Methods

HTTP supports various request methods, such as GET, POST, PUT, and DELETE, each used for different types of operations.

6. Plaintext Transmission

By default, HTTP transmits data in plaintext, meaning the transmitted data can be intercepted by intermediaries. HTTPS (HTTP Secure) provides encrypted transmission by using the SSL/TLS protocol on top of HTTP.