Node http module learning: talk about basic usage

This article will introduce you to the Node.js http module and introduce the createServer and listen methods. I hope it will be helpful to you!

http module

Use Node.js to create Web services, mainly relying on the built-in http module. The classic express.js and koa.js frameworks are all encapsulated to varying degrees with the http module as the core.

Creating the simplest web service only requires a few lines of code. Create a new index.js file and enter the following content:

// 1.导入 http 模块
const http = require('http');

// 2. 调用 createServer 方法创建服务
const server = http.createServer((request, response) => {
    // 3.响应给浏览器的内容
	response.end('Hello, World'); 
});

// 4.执行 listen 方法，启动服务
server.listen(3000, () => {
    console.log('服务器启动成功：http://localhost:3000')
})

Then open the command line tool and use the node command to execute the file:

node index.js

The command line tool will print:

服务器启动成功：http://localhost:3000

Then open the browser and visit http://localhost:3000, you will see the following content:

At this point, a web service is created with just 6 lines of code. [Related tutorial recommendations: nodejs video tutorial, Programming teaching]

createServer method

As you can see, the core method of creating a Web service iscreateServer method.

It receives a callback function, and the callback parameter receives two parameters, which are:

• request object: represents the HTTP request object, which contains the client’s request The information carried
• response object: represents the HTTP response object, used toset the response information to the client

This callback function is the processing http request, the main place to set the http response. Therefore, writing a web service actually means constantly processing the request and response content in this function. This is also determined by the request-response model based on the HTTP protocol itself. Of course, in actual development, we definitely cannot write in such a mixed manner. We all use frameworks, which will have very reasonable middleware mechanisms and layering.

listen method

We all know that the TCP protocol is the underlying protocol of the HTTP protocol, and all HTTP request data is transmitted using TCP. To send an HTTP request, a TCP connection must be established first.

The same is true for creating HTTP services in Node. After the createServer method is executed, an instance of the Server class will be created. The Server class inherits from # in another built-in module net ##Server class, it has a listen method. Below are the relevant type declarations to understand the relationship.

// net 模块

class Server extends EventEmitter {
 
        /**
         * 启动服务器监听连接。此 Server 可以是 TCP 或 IPC 服务器，具体取决于它所监听的内容。
         */
        // 有若干重载，这是最常使用的一种方法
        listen(port?: number, hostname?: string, listeningListener?: () => void): this;
        listen(port?: number, listeningListener?: () => void): this;
}


// http 模块
import { Server as NetServer } from 'node:net';

function createServer<
        Request extends typeof IncomingMessage = typeof IncomingMessage,
        Response extends typeof ServerResponse = typeof ServerResponse,
    >(requestListener?: RequestListener<Request, Response>): Server<Request, Response>;
      
class Server<
        Request extends typeof IncomingMessage = typeof IncomingMessage,
        Response extends typeof ServerResponse = typeof ServerResponse,
    > extends NetServer {}

So after creating the service through the

createServer method, call the listen method to start the service and listen for the connection.

It has multiple overloads. The most commonly used one is to listen to a port. After the startup is successful, execute the callback function:

server.listen(3000, () => {
    console.log('服务器启动成功：http://localhost:3000')
})

If the service fails to start, such as when the port is occupied, An error will be reported directly in the console, and the subsequent callback function will no longer be executed.

Introducing two other overloads, which are not used much.

One is

without specifying the port number. At this time, the operating system will randomly assign an available port number. After the service is started successfully, you can obtain the assigned port number through the server.address().port property:

server.listen(() => {
    const port = server.address().port
    console.log(port)
    console.log('服务器启动成功：http://localhost:', port)
})

Try it:

One is to

specify the host name to be monitored.

When

host is not specified, the default is 0.0.0.0 (IPv4) or :: (IPv6), supports network Access all hosts in .

If set to

locolhost or 127.0.0.1, you can only access it from your own host.

server.listen(3000, 'localhost', () => {
    console.log('服务器启动成功：http://localhost:', port)
})

Summary

We have introduced the basic usage of the

http module, mainly using createServer to create services, and then calling listen Method to start the service and listen for connections. createServer The callback function is received to process a specific request. Writing web services mainly uses the two parameters of the callback function, request and response, which will be introduced in detail later. .

For more node-related knowledge, please visit:

nodejs tutorial!

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