Take you to understand the HTTP module in depth

1. Web server

What is a web server?

When an application (client) needs a certain resource, it can request the resource through HTTP to a server; the server that provides the resource is a Web server;

1.1 First experience with the server

1.2 Two ways to create a server

• http.createServer will return the server object.
• In fact, the bottom layer uses the direct new Server object.

1.3 request object

The request object encapsulates all the information passed by the client to our server.

• The URL of this request, the server needs to perform different processing according to different URLs;

• the request method of this request, such as GET, POST request incoming The parameters and processing methods are different;

• the headers of this request will also carry some information, such as client information, format for receiving data, supported encoding formats, etc...

Regular request:

1.3.1 request-url

When sending a request, the client will request different data, and then different request addresses will be passed in. The server needs to make different responses based on different request addresses.

If the user's request address also carries some additional parameters, how should we parse them?

We can use the url module.

Among them, the url module provides utility tools for URL processing and parsing.

Import url const url = require('url')

Suppose our request data is:

The result of the console parsing the url is:

Among them, pathname is the last path we need to obtain. Our purpose is to obtain the username and password separately in the query.

Import querystring module const qs = require('querystring')；

const http = require("http")const url = require('url')const qs = require('querystring')// 1. Create a server const server = http .createServer((req, res) => {
  // Use built-in module const{ pathname,query } = url.parse(req.url)
  if(pathname === '/login'){
    console.log(query);
    console.log(qs.parse(query));
    const { username, password } = qs.parse(query)
    console.log(username,password);
    res.end('Request ends')
  }});// 2. Set the port number and start the server server.listen(8888,'0.0.0.0',()=>{
  console.log("Server started successfully~");})

• ✅Console output results:
  

1.3.2 request-method

In the Restful specification (design style), we should use different request methods to add, delete, modify and check data:

• GET: query data;
• POST: create new data;
• PATCH: update data;
• DELETE: delete data.

We can Perform different processing by judging different request methods.

Assume that the following is our JSON request data in the body -> How to make our server obtain the username and password?

• ✅Console output results
  

1.3.2 request-headers

content-type is the type of data carried in this request:

• application/json means a json type;
• text/plain means a text type;
• application/xml means an xml type;
• multipart/form-data means an uploaded file;

** content-length: **The size and length of the file

keep-alive:

• http is based on the TCP protocol, but it is usually interrupted immediately after a request and response;
• in http1.0, if you want to continue to maintain the connection: ① The browser needs to add connection: keep-alive in the request header; ② The server needs to add connection: keey-alive in the response header; ③ When the client makes a request again, the same connection will be used, and the direct party will interrupt the connection
• ; In http1.1, all connections default to connection: keep-alive: ① Different Web servers will have different keep-alive times; ② The default in Node is 5s

**accept-encoding: ** inform the server, the client The file compression format supported by the client, for example, js files can use gzip encoding, corresponding to .gz files

**accept:** Inform the server that the client can accept the file format type;

**user-agent:** Client-related information ;

1.4 response object

1.4.1 response-response object

If we want to respond to the client with result data, we can do so in two ways:

• Write method: This method writes the data directly, but does not close the stream;
• end method: This method The first way is to write the last data and close the stream after writing;

note: if we do not call end and close, the client will wait for the result.

1.4.2 response-response code

Http status code (Http Status Code) is a numeric code used to represent the Http response status:

• There are many Http status codes, and different status codes can be returned to the client according to different situations;
• common status The codes are as follows (the status codes will also be used in subsequent projects)
• http status code collection

Common response codes:

:

1.4.3 response-Response header

returns header information. There are two main ways:

• res.setHeader: write one header information at a time;
• res.writeHead: write header and status at the same time