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The most complete ajax cross-domain solution

小云云Original: 2017-12-18 15:32:475325browse

This article will share with you the most complete ajax cross-domain solution. Ever since I first came into contact with front-end development, the word cross-domain has always been It reappears around me with a very high frequency. Until now, I have debugged N cross-domain related issues. I also compiled a related article in 2016, but I still feel that something is missing, so I have reorganized it now. one time.

Question outline

Regarding cross-domain, there are N types. This article only focuses on ajax requests Cross-domain (, Ajax cross-domain is only part of the browser's "same-origin policy", others include Cookie cross-domain, iframe cross-domain, LocalStorage cross-domain, etc., which will not be introduced here), The content is roughly as follows:

What is ajax cross-domain

Principle
Performance (organized some problems encountered and solutions)

How to solve ajax cross-domain

JSONP way
CORS way
Proxy request method

How to analyze ajax cross-domain

http packet capture analysis
Some examples

What is ajax cross-domain

The principle of ajax cross-domain

ajax request appears The main reason for the cross-domain error problem is the browser's "same origin policy". You can refer to

Browser Same Origin Policy and How to Avoid It (Ruan Yifeng)

CORS request principle

CORS is a W3C standard, the full name is "Cross-origin resource sharing" (Cross-origin resource sharing). It allows the browser to issue XMLHttpRequest requests to cross-origin servers, thus overcoming the limitation that AJAX can only be used from the same origin.

Basically all current browsers have implemented the CORS standard. In fact, almost all browser ajax requests are based on the CORS mechanism. However, front-end developers may not usually Just concerned (so in fact, the current CORS solution mainly considers how to implement the background).

Regarding CORS, it is highly recommended to read
Detailed explanation of CORS for cross-domain resource sharing (Ruan Yifeng)

In addition, here is also a summary Implementation schematic diagram (simplified version):

The most complete ajax cross-domain solution

##How to judge whether it is a simple request?

Browsers divide CORS requests into two categories: simple requests and not-so-simple requests. As long as the following two conditions are met at the same time, it is a simple request.

The request method is one of the following three methods: HEAD, GET, POST
HTTP header information does not exceed the following fields:

Accept
Accept-Language
##Content-Language

Ajax cross-domain performance

To be honest, I compiled an article at first and then used it as a solution, but later I found that it was still Many people still don't know how. We have no choice but to debug it which is time-consuming and labor-intensive. However, even if I analyze it, I will only judge whether it is cross-domain based on the corresponding performance, so this is very important.

When making an ajax request, if there is a cross-domain phenomenon and it is not resolved, the following behavior will occur: (Note, it is an ajax request. Please do not say why http requests are OK but ajax is not, because ajax is accompanied by Cross-domain, so just http request ok is not enough)

Note: Please see the title position for specific back-end cross-domain configuration.

The first phenomenon:`No 'Access-Control-Allow-Origin' header is present on the requested resource`, and`The response had HTTP status code 404`

The most complete ajax cross-domain solution

## The reasons for this situation are as follows:

This ajax request is a "non-simple request", so a preflight request (OPTIONS) will be sent before the request
The server-side background interface does not allow OPTIONS requests, resulting in the inability to find the corresponding interface address

## Solution: The backend allows options requests

Second phenomenon:

No 'Access-Control-Allow-Origin' header is present on the requested resource`, and`The response had HTTP status code 405``

The most complete ajax cross-domain solution

This phenomenon is different from the first one. In this case, the background method allows OPTIONS requests, but some configuration files (such as

Security Configuration ), blocking the OPTIONS request will cause this phenomenon

Solution: Close the corresponding security configuration on the backend

The third phenomenon:

No 'Access-Control-Allow-Origin' header is present on the requested resource`, and` status 200``

The most complete ajax cross-domain solution ##This phenomenon is different from the first and second ones. In this case, the server-side background allows OPTIONS requests, and the interface also allows OPTIONS requests, but there is a mismatch when the header matches.

For example, the origin header check does not match, for example, it is missing Support for some headers (such as the common X-Requested-With header), then the server will return the response to the front-end. After the front-end detects this, it will trigger XHR.onerror, causing the front-end console to report an error

Solution: Add corresponding header support to the backend

Fourth phenomenon:

heade contains multiple values '* ,*'``

The most complete ajax cross-domain solution

The most complete ajax cross-domain solution ##phenomenon Yes, the background response http header information has two

Access-Control-Allow-Origin:*To be honest, this kind of The main reason for the problem is that people who perform cross-domain configuration do not understand the principles, resulting in repeated configurations, such as:

is common in the .net background (generally in the web The origin is configured once in .config, and then the origin is manually added to the code (for example, the code manually sets the return *))

commonly found in the .net backend (Set Origin:* in both IIS and the project's webconfig)
Solution (one-to-one correspondence):

It is recommended to delete the manually added * in the code and only use the ones in the project configuration

It is recommended to delete the configuration* under IIS , just use the ones in the project configuration

How to solve ajax cross-domain

Generally, ajax cross-domain solution is solved through JSONP or CORS, as follows: (Note, now it has been solved I almost never use JSONP anymore, so just understand JSONP)

JSONP way to solve cross-domain problems

jsonp solves cross-domain problems It is a relatively old solution (not recommended in practice). Here is a brief introduction (if you want to use JSONP in actual projects, you will generally use JQ and other class libraries that encapsulate JSONP to make ajax requests)

Implementation Principle

The reason why JSONP can be used to solve cross-domain solutions is mainly because

The most complete ajax cross-domain solution

Question outline