1. What happens after you enter the URL

(1) the DNS

  • 1. Browser DNS cache: first, it reads the last access record from the browser cache
  • 2, computer DNS cache: find the cache stored in the system running memory.
  • 3, router DNS cache: Some routers also have DNS cache function, the visited domain name will be stored on the router.
  • 4. Network operator DNS cache: Internet service providers will also provide DNS services
  • 5, recursive query to find a.b.c.d.com

(2) a TCP connection

  • First handshake: The browser sends a SYN request to the server telling it that I’m ready
  • Second handshake: The server sends to the browser to tell the browser that I’m ready, too, and need to double-check. Syn + ACK
  • Third handshake: The browser sends an ACK request to the server

(3) the HTTP request

  • 1, the browser sends an HTTP request to the server to request the packet from the server.Copy the code
  • 2. Build tools can be used to optimize performance: reduce the number of requests and the time spent on a single request.Copy the code

(4) the HTTP response

  • Connection Uses the keep-alive feature
  • Content-encoding Compresses resources in gzip mode
  • Content-type The MIME type is HTML, and the character set is UTF-8
  • Date Indicates the Date of the response
  • Server Indicates the WEB Server used
  • Transfer-encoding is a data Transfer mechanism provided in HTTP (HTTP/1.1)

(5) Browser parsing and rendering

  • 1. Call the HTML parser to parse the HTML into a DOM tree
  • 2. Call the CSS parser to parse the CSS into a CSSOM tree
  • 3. Call the JS engine to parse the JS code.
  • 4. If a DOM node is modified, it is reparsed into a DOM tree
  • 5. If the CSS node is modified, it is re-parsed into the CSSOM tree
  • DOM + CSSOM = render tree
  • The layout has been rendered

(6)TCP four wave disconnection

  • First wave: The browser sends the request packet to the server to inform the server that the request packet is sent
  • Second wave: The server sends a message to the browser to inform the browser that the request packet is received and the browser waits to disconnect
  • Third wave: The server sends the response packet to the browser
  • Fourth wave: The browser sends a message to the server to inform the server that the response packet has been received and the connection is disconnected

2. The difference between HTTP and HTTPS

  1. In terms of security, HTTPS is a secure hypertext protocol, which is more secure than HTTP. Simply put, HTTPS is the HTTP protocol that uses TLS/SSL encryption
  2. When applying for a certificate, HTTPS requires ca to apply for a certificate
  3. In terms of transport protocol, HTTP is hypertext transfer protocol and plaintext transfer. HTTPS is a secure SSL encrypted transport protocol
  4. Connection mode and port, HTTP connection is simple, is stateless, port is 80; HTTPS uses THE SSL protocol for encrypted transmission based on HTTP and uses port 443

3. The difference between POST and GET and other request methods

  1. Request caching: GET is cached, but POST is not
  2. Bookmark: GET works, POST doesn’t
  3. Keep browser history: GET does, POST does not
  4. Uses: GET is often used to fetch data, post is used to submit data
  5. Security: POST is more secure than GET
  6. Request parameters: QueryString is part of the URL get,post can be added,post is placed in the body, unique!

The maximum length of a get request is 1024kb. The maximum length of a post request is not limited

  1. GET: to request a resource in its entirety.
  2. POST: Submit a form (common)
  3. HEAD: requests only the response HEAD
  4. PUT: (webdav) Upload files (but browsers do not support this method)
  5. DELETE :(webdav) DELETE
  6. OPTIONS: Methods that return methods supported by the requested resource