web server

When an application (client) needs a resource, it can obtain the resource from a server through Http request; The server that provides resources is a Web server;

First experience

// Introduce http module
const http = require('http')

// Create a web server
const server = http.createServer((req, res) => {
  res.end('Hello Http')
})

// Turn on the server and listen on the port
server.listen(8000, 'localhost' ,() => {
  console.log('The server started successfully');
})

request

• req.url: the URL of this request. The server needs to process it differently according to different URLs;
• req.method: the request method of this request, such as the parameters passed in and processing methods of GET and POST requests are different;
• req.headers: the headers of this request will also carry some information, such as client information, format of received data, supported coding format, etc;

req.url

Sending requests using postman

url transfer data: localhost: 8000 / users? username=htf&password=123456

Basic usage

Return different contents according to different request paths

const http = require('http')

// Create a web server
const server = http.createServer((req, res) => {

  if(req.url == '/login') {
    res.end('welcome back');
  } else if(req.url == '/user') {
    res.end('Welcome to the user list');
  } else {
    res.end('The page does not exist');
  }
  
})

// Turn on the server and listen on the port
server.listen(8000, () => {
  console.log('The server started successfully');
})

url module

When sending a request, it can be parsed with the help of the url module

const http = require('http')
const url = require('url')

// Create a web server
const server = http.createServer((req, res) => {

  const parseInfo = url.parse(req.url)
  console.log(parseInfo);

  res.end('Sent successfully')
})

// Turn on the server and listen on the port
server.listen(8000, () => {
  console.log('The server started successfully');
})

At this time, the console outputs the object after successful parsing

Url {
  protocol: null,
  slashes: null,
  auth: null,
  host: null,
  port: null,
  hostname: null,
  hash: null,
  search: '?username=htf&password=123456',
  query: 'username=htf&password=123456',
  pathname: '/users',
  path: '/users?username=htf&password=123456',
  href: '/users?username=htf&password=123456'
}

We can get query and pathname

const http = require('http')
const url = require('url')

// Create a web server
const server = http.createServer((req, res) => {

  const { pathname, query } = url.parse(req.url)
  console.log(pathname, query);

  res.end('Sent successfully')
})

// Turn on the server and listen on the port
server.listen(8000, () => {
  console.log('The server started successfully');
})

Output result: / users username = HTF & password = 123456

The first mock exam can be done by borrowing another module to analyze query.

querystring

At this point, the console output (htf 123456) successfully parses the query

const http = require('http')
const url = require('url')
const qs = require('querystring')

// Create a web server
const server = http.createServer((req, res) => {

  const { pathname, query } = url.parse(req.url)
  const queryObj = qs.parse(query)
  console.log(queryObj.username);
  console.log(queryObj.password);

  res.end('Sent successfully')
})

// Turn on the server and listen on the port
server.listen(8000, () => {
  console.log('The server started successfully');
})

methods

{

"name": "htf",

"password": "123456"

}

The json data in the above body sends the request through post

const http = require("http");
const url = require("url");
const qs = require("querystring");

// Create a web server
const server = http.createServer((req, res) => {
  const { pathname } = url.parse(req.url);

  // Can judge the request mode
  if (req.method === "POST") {

    if (pathname == "/login") {
      // Get the data in the body
      // Specifies the encoding method, otherwise binary is returned
      req.setEncoding("utf-8");
      req.on("data", (data) => {
      
        // Because the json data sent is parsed in this way
        const { name, password } = JSON.parse(data);
        console.log(name, password);                  // htf 123456
      });
    } else {
      res.end("The page does not exist");
      console.log("Acceptance failed");
    }
  }

});

// Turn on the server and listen on the port
server.listen(8000, () => {
  console.log("The server started successfully");
});

In Restful specification (design style), we should add, delete, modify and query data through different request methods

• GET: query data;
• POST: new data;
• PATCH: update data;
• DELETE: DELETE data;

headers

The header of the request object also contains a lot of information. The client will pass some information by default:

{
  'content-type': 'application/json',
  'user-agent': 'PostmanRuntime/7.28.1',
  accept: '*/*',
  'postman-token': 'bf377318-75ca-4a27-b524-6ffcfa9dddad',
  host: 'localhost:8000',
  'accept-encoding': 'gzip, deflate, br',
  connection: 'keep-alive',
  'content-length': '50'
}

Content type is the type of data carried in this request

• application/json represents a json type;
• text/plain indicates text type;
• The application/xml representation is of xml type;
• Multipart / form data means upload file;

User agent: client related information;

Accept: tells the server that the client can accept the format type of the file;

Accept encoding: tell the server that the file compression format supported by the client, such as js files, can be gzip encoded, corresponding to gz documents;

Content length: the size and length of the file

connection: 'keep-alive'

• http is based on TCP protocol, but it is usually interrupted immediately after a request and response;
• In http1 0, if you want to stay connected:
  • The browser needs to add connection: keep alive in the request header;
  • The server needs to add connection: keey alive in the response header;
  • When the client puts the request again, it will use the same connection and directly interrupt the connection on one side;
• In http1 1, all connections are connection: keep alive by default;
  • Different Web servers have different keep alive times;
  • Node defaults to 5s

response

Status code

Http Status Code is a digital code used to indicate the status of Http response

Status code	State description	explain
200	OK	Client request succeeded
400	Bad Request	Because the client request has syntax error, it cannot be understood by the server
401	Unauthorized	The request is unauthorized. This status code must be used with the WWW authenticate header field
403	Forbidden	The server received the request but refused service. The server usually gives the reason why the service is not provided in the response body
404	Not Found	The requested resource does not exist. For example, enter the wrong URL
500	internal Serve Error	An unexpected error occurred on the server that prevented the client from completing the request
503	Service Unavailable	The server is currently unable to process the client's request. After a period of time, the server may return to normal

Set status code

const http = require("http");
const url = require("url");
const qs = require("querystring");

// Create a web server
const server = http.createServer((req, res) => {

  // Set status code
  // Method 1: directly assign values to attributes
  // res.statusCode = 404
  
  // Method 2: set with head
  res.writeHead(404)

  // Response results
 res.end('Hello Http')

});

// Turn on the server and listen on the port
server.listen(8000, () => {
  console.log("The server started successfully");
});