The whole process from entering URL to displaying page (interview)

From input url The whole process from to the display page

• Enter... In the client URL url
• Will input url Send to DNS Get the corresponding WEB Server's ip Address
• Client browser and WEB Server setup TCP Connect
• The client browser sends to WEB Server send HTTP or HTTPS request
• WEB Server responds to requests , Returns the specified URL Data or error messages
• The client gets WEB Parse the source file after the data of the server , Page layout , Display the basic page
• Analyze the hyperlinks in the page , Render the page

1、 Input url Address

When you enter url After the address , The moment you press OK, the viewer will first look for the local cache , See if there is page data corresponding to the domain name , Load directly if you have , There is no next step

2、DNS lookup ip Address

• First on the local disk hosts Check whether there is a corresponding... In the file ip Address , Go straight back if you have
• Local hosts Not in file , Then you can further find local NDS The server , Find out if there is a corresponding... In its cache ip
• If local DNS The server doesn't have , Then go further and find DNS Root server . The root server does not store domain names and ip The mapping relation of , Instead, give the domain server address , Inform local DNS To find a domain server
• Local DNS And then send a request to the domain server , Such as www.baidu.com Your domain server is .com. The domain server returns the corresponding ip Address and will ip Address in cache , It is convenient to return next time

3、 establish TCP Connect , send out HTTP request

• The viewer will use a random port （1024< port <65535） server-oriented WEB programmatic 80 Port application establishment TCP Connect
• establish TCP After the connection , The viewer sends a message to the server HTTP request , A normal browser can only launch GET perhaps POST request

4、 The server permanently redirects the response

• The server responds with a 301 Redirect Respond to , So the viewer can access http://www.google.com/ Instead of http://google.com/
• Expand ：
• 1. Why respond 301 Permanent redirection ？
  • Because if a page has multiple access addresses , As above http://www.google.com/ and http://google.com/, Search engines will see these two addresses as different websites , This will cause multiple names of a page to appear in the cache , Waste of memory
• 2. Why redirect ？
  • Website adjustment , Such as changing the directory structure of the web page
  • The web page has changed its address
  • Page extension changed

5、 The viewer displays HTML page 、 Load page resources

• HTTP After the request is successfully established , The server will send the resources requested by the browser to the browser , The viewer will parse the resources 、 Typesetting
• After that, the browser sends a request to get embedded in HTML The resource （ Such as images 、 Audio 、 video 、CSS、JS wait ）
• thus , The whole process is finished , You will see a complete page