Is $request->isXmlHttpRequest() reliable in symfony2? - ajax

Question

Let's consider a scenario like below:
User selects filter button which create a AJAX call to a symfony2 controller and return the result in JSON format.
User select some other links and system will redirect him to the page
User select browser Back button.
User will see JSON response, but he should see the original page.
My controller look like below :
/**
*
*
* #Route("/ajax", name="ajax_route" , options={"expose"=true})
* #Template()
*/
public function someAction()
{
$request = $this->getRequest();
$json = array( );
if($request->isXmlHttpRequest())
{
$res = json_encode($json);
return new Response($res , 200 , array( 'Content-Type' => 'application/json' ));
}
return array( );
}
In other words, if user press back button the if($request->isXmlHttpRequest()) returns true which is not the result I am looking for. Is it a normal behavior or what ?

Answer 1

Symfony\Component\HttpFoundation\Request::isXmlHttpRequest() is a simply utility-method that checks whether HTTP request came up with X-Requested-With header with value XMLHttpRequest. So it's as reliable as X-Requested-With header is.
However, this is not really important. The important thing to notice is the fact that when the user clicks on the back button the browser does not send a new HTTP request to the server. It just restores the page from its internal memory/cache.

Answer 2

I understand that this is an old question, but the same issue just caught me so I figured I'd write up an answer anyway.
In most scenarios, you can invalidate the back button cache by attaching an onUnload handler to the window, like so:
window.addEventListener('unload',function(){});
or, if you prefer jQuery:
$(window).unload(function(){});
but, since your AJAX response is in JSON, that's obviously not possible since you can't include script fragments. In this case, I think the best idea is to set the cache-control: no-store header so the browser wont attempt to cache the result.
You can do that in the OP's case with Symfony2 using:
return new Response($res , 200 , array(
'Content-Type' => 'application/json',
'Cache-Control' => 'no-store',
));
or for more general PHP:
header('Cache-Control: no-store');
There's a caveat here in that it may degrade your performance quite a bit, depending on your app's structure, in which case your best bet would probably be to just use a different URL for your AJAX call. Sucks, I know.
You can find some documentation on the bfcache here, which may be more helpful in different cases.

Answer 3

The browser caches the response using just the url and the request method (GET, POST, etc) as the key.
If you want the browser to recognize additional variations, you can tell it to do so by setting the Vary header in your response. So in your case, you want to tell the browser that the response from the server will vary depending on whether or not the 'X-Requested-With' header was set in the request.
Here's how to do it:
$response = new Response();
$response->setVary("X-Requested-With"); // <=========== Set the Vary header
if($request->isXmlHttpRequest()) {
//...
}
return $response;
Note: that you want to set the Vary header on both versions of the response (this is why I've set it outside of the if statement).