This is the fourth day of my participation in the August More text Challenge. For details, see: August More Text Challenge

The same-origin policy

  • The same origin policy is given by the browser

  • Browsers don’t allow us to send requests to others, only to our own servers

  • When we want to send a request to someone else’s server, we are blocked by the browser

  • What is “someone else’s server”?

    • If the request protocol/domain name/port number is any different, then it is someone else’s server
    • At this point, the same origin policy is triggered

  • Requests that trigger the same origin policy are called cross-domain requests

Implement a cross-domain request

  • Sometimes we need to implement cross-domain requests
  • We need multiple servers to feed data to a single page
  • So this is where we have to figure out how to solve cross-domain problems

JSONP

  • jsonpIt’s the way we implement cross-domain requests, it’s just the technical way we put together what we had before
  • Using the script tag to achieve

The nature of the script tag

  • The browser gives us a script tag

  • Its essence is to request an external resource, which is not affected by the same origin policy

  • The SRC attribute of the script tag, which is also a request, can also be received by the server

  • And:

    • scriptOf the labelsrcProperty is a string that the browser will treat asjsCode to execute

  • So we can use the SRC attribute of the script tag to make cross-domain requests

CORS implements cross-domain requests

<? php header("Access-Control-Allow-Origin:*"); header("Access-Control-Request-Methods:GET, POST, PUT, DELETE, OPTIONS"); header('Access-Control-Allow-Headers:x-requested-with,content-type,test-token,test-sessid'); ? >Copy the code

Configure the agent

  • There are two kinds of agents, forward agents and reverse agents

Forward agent

  • There is a client that needs to send a request to a non-identical server B
  • We set up A server A that is the same as the client
  • When the client sends A request, server A accepts it
  • Server A then sends the request to server B, because the same origin policy is sent by the browser, and the servers do not have the same origin policy
  • After server B receives the request, it processes the request and sends the response back to server A
  • Then the server A responds to the client
  • We can make cross-domain requests in this way

The reverse proxy

  • Reverse proxies are generally used for load balancing
  • When I ask for a server, I’m actually asking for a proxy server set up on the server side
  • The proxy server distributes a number of large requests to different servers for processing
  • The server sends the response to the proxy server
  • The proxy server returns to the client