How to prevent ajax requests to follow redirects using jQuery

Question

I use the jQuery ajax functions to access a web service, but the server, instead of returning a response with a status code describing a problem, the request is redirected to a page with a 200 header, describing the problem. I can't make any changes to this, so I need to solve it on the client somehow.

Example: A request goes to some URL which is not found, so I receive a 302 Redirect to another location. A new request is sent, and I receive a 200 OK, thus preventing the error callback to fire.

Is there some way I can prevent the ajax request to follow redirects and instead invoke a callback, preferably the error method. Alternatively, is it possible to detect if a redirect has happened in the client?

Answer 1

I find your question interesting, but the problem in whole seems me more a misunderstanding. At least I'll try to explain my understanding of the problem.

The silent (transparent) redirection is the part of XMLHttpRequest specification (see here especially the words "... transparently follow the redirect ..."). The standard mention only that the user agent (the web browser) can prevent or notify of certain kinds of automatic redirections, but it's not a part of XMLHttpRequest. It's the part of HTTP client configuration (OS configuration) or the web browser configuration. So jQuery.ajax can't have any option where you can prevent redirection.

You can see that HTTP redirection is the part of HTTP protocol and not a part of XMLHttpRequest. So it's on the another level of abstraction or the network stack. For example the data from the XMLHttpRequest can be retrieved from the HTTP proxy or from the local browser cache, and it's the part of HTTP protocol. Mostly the server which provide the data and not the client can influence on caching.

You can compare the requirement from your question with the requirement to prevent changing of IP address of the web server or the changing of the IP route during the communication. All the things can be interesting in some scenarios, but there are parts of another level of the communication stack and can't be managed by jQuery.ajax or XMLHttpRequest.

The XMLHttpRequest standard say that the client configuration can have options which prevent redirection. In case of "Microsoft world", which I better know, you can look at WinHttpSetOption function which can be used to set WINHTTP_OPTION_DISABLE_FEATURE option with the WINHTTP_DISABLE_REDIRECTS value. Another way are the usage of WINHTTP_OPTION_REDIRECT_POLICY option with the WINHTTP_OPTION_REDIRECT_POLICY_NEVER value. One more feature which one can use in Windows is the WinHttpSetStatusCallback function which can set callback function received some notifications like WINHTTP_CALLBACK_FLAG_REDIRECT.

So it's do possible to implement your requirements in general, but the solution will be probably not independent from the operation system or the web browser and be not on the level of jQuery.ajax or XMLHttpRequest.

Answer 2

I don't believe it is possible. The underlying library (XHR) makes the new request transparently. That being said, what I have done in these situations (usually a session-timeout type of deal that takes me to a login page) is send back a custom response header. I also have setup a global ajax handler that checks for the presence of that header, and responds appropriately when present (for example, redirecting the whole page to the login screen).

In case you're interested, here's the jQuery code I have to watch for that custom header:

/* redirects main window when AJAX request indicates that the session has expired on the backend. */ function checkSession(event, xhr, ajaxOptions) {     if (xhr.readyState == 4)     {         if(xhr.getResponseHeader("Login-Screen") != null && xhr.getResponseHeader("Login-Screen").length)         {             window.location.href='sessionExpired.html'; //whatever         }     } }  $(document).ajaxComplete(checkSession)