Debugging mysterious PHP requests

Whenever I get a 404 our logout script is being called mysteriously. What should be happening is our custom ErrorDocument defined in the root .htaccess file should be redirecting to a static HTML page, without any external logout actions being initiated.

I'm using Zend Studio's debugger and at first everything goes as expected -- it serves up the 404. But immediately afterward a separate request is picked up by the debugger which calls the logout page.

I can't find out what is initiating this second request. I stepped through the entire request that serves up the 404 and there were no headers or redirects that would开发者_开发百科 cause this to happen. It seems like something external may be going on here, but I can't locate it.

I've examined the php.ini and httpd.conf files for anything suspicious being initiated in the event of a 404 but with no luck. Any idea how I might debug the source of this second request for the logout page?

try to build some kind of tracking in the logout script. Try to track who calls is - if the request comes from the same client IP as 404 page request, or maybe there is a code somewhere in your app (e.g. file_get_contents()), where request is being generated from server itself (then 404 page request would have different IP compared to logout request, which comes after it)