Take you to understand the HTTP module in depth

This article will help you learn about the http module and lay the foundation for writing interfaces. I hope it will be helpful to you!

1. Web server

What is a web server?

When the application (client) needs a certain resource, it can obtain the resource through an HTTP request 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
• The bottom layer actually 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 process it differently according to different URLs;

• The request method of this request, such as the parameters passed in GET and POST requests The processing method is different;

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

General request:

##1.3.1 request-url

When the client sends a request, it 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 it?

We can use the url module.

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

Import url const url = require('url')

Assume that our request data is:

The result of the console parsing the url is:

The pathname is the final path we need to obtain. Our purpose is to obtain username and password separately in the query.

Import querystring module

const qs = require('querystring');

<pre class="brush:php;toolbar:false">const http = require(&quot;http&quot;)const url = require('url')const qs = require('querystring')// 1. 创建服务器const server = http.createServer((req, res) =&gt; {   // 使用内置模块   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('请求结束')   }});// 2. 设置端口号并启动服务器server.listen(8888,'0.0.0.0',()=&gt;{   console.log(&quot;服务器启动成功~&quot;);})</pre>

✅Console output result:

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1.3.2 request-method

In the Restful specification (design style), we should use different request methods for adding, deleting, modifying and checking 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 the following is our JSON request data in the body ->How to make our server obtain the username and password?

---

##✅Console output

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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 Indicates uploading a 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: ①The browser requires 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 that the file compression format supported by the client. For example, js files can be encoded using gzip, corresponding to .gz files

**accept: **Inform the server that the client is acceptable 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 writes the last data, and the stream will be closed 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:

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

1xxInformational (Informational Status Code)Accepted Request Processing2xxSuccess (success status code)The request has been processed normally3xx RedirectionAdditional action required to complete the request4xxClient error Client request error, the server cannot process the request5xxServer ErrorThe server has an error processing the request

	##Category	Reason Phrase

Common response codes:

##Status codeDescription statusDescription##200OKThe request was successful. Generally used for GET and POST requests400Bad RequestThe client request has a syntax error and the server cannot understand401UnauthorizedThe request requires user authentication403ForbiddenThe server understands the request from the client, but refuses to execute the request 404Not FoundThe server cannot find the resource based on the client's request ( Web page). Through this code, website designers can set up a personalized page for "The resource you requested cannot be found"500Internal Server ErrorServer Internal error, unable to complete the request503Service UnavailableThe server is temporarily unable to process the client's request due to overload or system maintenance. The length of the delay can be included in the server's Retry-After header informationSet status code:

1.4.3 response-response header

There are two main ways to return header information:

res.setHeader: Write one header information at a time;

res.writeHead: Write header and status at the same time
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