Why does iframe nested Baidu have no cross-domain problem?

The reason why iframe nesting in Baidu does not exist across domains is that the Baidu homepage sets the Access-Control-Allow-Origin field to allow cross-domain access. When we embed the Baidu homepage in a web page, the browser will send a request to the Baidu server, and the Baidu server will return a response header with the Access-Control-Allow-Origin field. The browser will check this field and find that it is allowed. The visited domain name list contains the domain name of the current web page, so cross-domain access is allowed.

# Operating system for this tutorial: Windows 10 system, Dell G3 computer.

In web development, we often encounter situations where we need to nest a web page within another web page. To achieve this functionality, we can use the HTML iframe element. The iframe element allows us to embed a web page within another web page, and the address of the web page to be embedded can be specified by setting the src attribute.

However, due to security considerations, browsers implement the Same Origin Policy, which restricts scripts in a web page to only access files from the same origin (same protocol, domain name and port). resource. This means that if a web page attempts to access resources from different origins through scripts, the browser will block this operation, thus protecting the user's security and privacy.

Cross-domain problem is a common problem in web development, because in practical applications, we often need to embed content from different domains in a web page. However, the wonderful thing is that when we try to embed the Baidu homepage in a web page, no cross-domain problems occur.

Why is this so? The reason is that Baidu homepage sets the Access-Control-Allow-Origin field in the HTTP response header. This field specifies the domain name that is allowed to access the resource. When the browser receives this response header, it will check whether the requested domain name is in the list of allowed access, and if so, cross-domain access will be allowed.

So, when we embed the Baidu homepage in a web page, the browser will send a request to the Baidu server, and the Baidu server will return a response header with the Access-Control-Allow-Origin field. Browse The server will check this field and find that the domain name of the current web page is included in the list of allowed domain names, so cross-domain access is allowed.

It should be noted that this cross-domain access method is only applicable to web pages such as Baidu homepage where the Access-Control-Allow-Origin field is set. For other web pages that do not have this field set, the browser will process them according to the same-origin policy and prevent cross-domain access.

Summary

The reason why iframe nesting in Baidu does not exist across domains is that the Baidu homepage sets the Access-Control-Allow-Origin field to allow cross-domain access. This example tells us that by setting response headers on the server side, we can solve some cross-domain access problems and provide a better user experience. At the same time, we are also reminded to pay attention to the security and legality of cross-domain access during development and abide by the regulations of the same-origin policy.

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