[web] the process that the browser enters the URL to the page display

technological process

Generally speaking, it is divided into the following processes

• NDS analysis ： Resolve the domain name to IP Address
• TCP Connect ：TCP Three handshakes
• send out HTTP request
• The server processes the request and returns HTTP message
• The browser parses the rendered image
• break link ：TCP Four waves

What is? URL

URL It is the web address commonly known as my life , Follow the following syntax rules

scheme://host.domain:port/path/filename

The parts are explained as follows

• scheme - Define the service types of the Internet . Common protocols are http、https、ftp、file
• host - Define domain host （ Default www）
• domain - domain name , such as baidu.com.cn
• port - Port number （ The default is 80 port ）
• path - Routing on server
• filename - Define documents / The name of the resource

One 、 Domain name resolution （DNS）

DNS The protocol runs in UDP The agreement above , Use port number 53, After entering the web address in the browser , First, domain name resolution , Will be similar to baidu.com Converting to the corresponding domain name is similar to

104.193.88.123

As for why not give a IP Address , It also saves the trouble of parsing , It is because we are more used to memorizing websites through words or letters than numbers , Computers are better at handling numbers , therefore DNS emerge as the times require

How to search by domain name in browser URL Medium IP Well

• Browser cache ： The browser will cache at a certain frequency DNS Record
• Operating system cache ： If the browser cannot find , Go to the operating system ==（ Personal understanding is to find the operating system hosts file ）==
• The routing cache ： Routers also have DNS cache
• ISP Of DNS The server ：ISP It is the establishment of Internet service providers ,ISP Specialized DNS The server corresponds to DNS request
• If you can't find , He will want to send a request to the server , Make recursive queries （ First visit the root domain name server .com Domain name server IP Address , And then visit again .baidu Domain name server , And so on ）
  

Two 、TCP Three handshakes

This article

3、 ... and 、 send out HTTP request

After three handshakes , Start sending HTTP Message request
The request message is sent by Request line 、 Request header 、 Request body Three parts

• Request line ： Including the requestor, Ah Fu 、URL、 Protocol version
  • There are eight request methods ：GET,POST,PUT,DELETE,HEAD,OPTIONS,TRACE
  • URL
  • Protocol version , Both HTTP Version number
• Request header ： Contains additional information requested , By key word / value Pairs make up one pair per line , By English ： separate
• Request body ： It can carry data of multiple request parameters , But not all requests have request data

Four 、 The server processes the request and returns HTTP message

1. The server

For requests sent by different users , Will be combined with the configuration file , Delegate different requests to a program on the server that processes the corresponding requests , Then return the effect produced by the daemon processing as a response

2.MVC Background processing stage

MVC Divide the program into three core components ： Model （MODEL）– View （view）– controller （controller）

View

Provide the user with the operation interface , It's the shell of the program

Model

Mainly responsible for data interaction

controller

Responsible for the commands that the user passes in from the view layer , Select the data in the model layer , Then carry out the corresponding operation , Present the final result

3.HTTP response message

The response message is sent by Response line 、 Response head 、 Response subject Three parts

• The response line contains ： Protocol version , Status code , Status code description
  The status code rules can be viewed as This article
• The response header contains additional information of the response message , from name / value To claim to be
• The response body contains a carriage return 、 Line breaks and response return data , Not all response messages have corresponding data

5、 ... and 、 The browser parses the rendered image

There are five steps

• according to HTML It is concluded that DOM Trees
• according to CSS Parse generation CSS The rule tree
• combination DOM Trees and CSS The rule tree , Generate render tree
• Calculate the information of each node according to the rendering tree
• Draw the page according to the calculated information

6、 ... and 、 break link

Four waves

Reference article
Browser input a url The whole page shows what process it has gone through ？