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Asked: 2026-05-10T20:07:01+00:00

I have written a web app in PHP which makes use of Ajax requests

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I have written a web app in PHP which makes use of Ajax requests (made using YUI.util.Connect.asyncRequest).

Most of the time, this works fine. The request is sent with an X-Requested-With value of XMLHttpRequest. My PHP controller code uses apache_request_headers() to check whether an incoming request is Ajax or not and all works well.

But not always. Intermittently, I’m getting a situation where the Ajax request is sent (and Firebug confirms for me that the headers on the request include an X-Requested-With of XMLHttpRequest) but apache_request_headers() is not returning that header in its list.

The output from when I var_dump the apache_request_headers() is as follows (note the lack of X-

'Host' => string 'peterh.labs.example.com' (length=26) 'User-Agent' => string 'Mozilla/5.0 (X11; U; Linux i686; en-GB; rv:1.9.0.3) Gecko/2008101315 Ubuntu/8.10 (intrepid) Firefox/3.0.3' (length=105) 'Accept' => string 'text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8' (length=63) 'Accept-Language' => string 'en-gb,en;q=0.5' (length=14) 'Accept-Encoding' => string 'gzip,deflate' (length=12) 'Accept-Charset' => string 'ISO-8859-1,utf-8;q=0.7,*;q=0.7' (length=30) 'Keep-Alive' => string '300' (length=3) 'Connection' => string 'keep-alive' (length=10) 'Referer' => string 'http://peterh.labs.example.com/qmail/' (length=40) 'Cookie' => string 'WORKFLOW_SESSION=55f9aff2051746851de453c1f776ad10745354f6' (length=57) 'Pragma' => string 'no-cache' (length=8) 'Cache-Control' => string 'no-cache' (length=8)

But Firebug tells me:

Request Headers: Host             peterh.labs.example.com User-Agent       Mozilla/5.0 (X11; U; Linux i686; en-GB; rv:1.9.0.3) Gecko/2008101315 Ubuntu/8.10 (intrepid) Firefox/3.0.3 Accept           text/html,application/xhtml+xml,application/xml;q=0.9,**;q=0.8 Accept-Language  en-gb,en;q=0.5 Accept-Encoding  gzip,deflate Accept-Charset   ISO-8859-1,utf-8;q=0.7,*;q=0.7 Keep-Alive       300 Connection       keep-alive X-Requested-With XMLHttpRequest Referer          http://peterh.labs.example.com/qmail/ Cookie           WORKFLOW_SESSION=55f9aff2051746851de453c1f776ad10745354f6

This mismatch is (apparently) intermittent when executing the same code. But I don’t believe in ‘intermittent’ when it comes to software! Help!

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1 Answer

  1. I’m not sure why the apache_request_headers() and firebug mismatching, but in order to read request headers you can use the $_SERVER super global

    each header that is being sent by a client (and it doesn’t matter how is the client) will arrive to the $SERVER array. The key of that header will be with HTTP prefix, all letters capital and dash is converted to underscore (_)

    in your case you can find your necessary value in:

    $_SERVER[‘HTTP_X_REQUESTED_WITH’] = ‘XMLHttpRequest’

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