CORS "No 'Access-Control-Allow-Origin' header is present" yet there is

Question

These three headers are added using PHP

    header('Content-Type: application/json; charset=UTF-8;');
    header('Access-Control-Allow-Methods: GET, POST');
    header('Access-Control-Allow-Origin: *');

All the headers sent are:

    HTTP/1.1 200 OK
    Date: Mon, 30 Jun 2014 06:39:29 GMT
    Server: Apache
    X-Powered-By: PHP/5.3.28
    Expires: Thu, 19 Nov 1981 08:52:00 GMT
    Cache-Control: no-store, no-cache, must-revalidate, post-check=0, pre-check=0
    Pragma: no-cache
    Access-Control-Allow-Methods: GET, POST
    Access-Control-Allow-Origin: *
    Vary: Accept-Encoding,User-Agent
    Content-Encoding: gzip
    Cache-Control: max-age=1, private, must-revalidate
    Content-Length: 20
    Keep-Alive: timeout=3, max=100
    Connection: Keep-Alive
    Content-Type: application/json; charset=UTF-8;

Yet when trying to use $.json or $.post to target this server, I get this error in the Chrome Console:

    XMLHttpRequest cannot load http://cms.webdevguru.co.uk/gurucms.php?mode=addto&apikey=606717496665bcba. No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'http://remote.webdevguru.co.uk' is therefore not allowed access.

I know this is a possible duplicate of a few other questions, but since I have gone through many of them and tried a few things out of them to try and fix this: I would appreciate some specific replies to deal with my issue at hand.

As Joachim Isaksson figured out, its because the initial headers consist of a 301 Redirect, is there any way to force the request to follow the Redirect before checking for the Access-Control-Allow-Origin headers?

Answer 1

The reason CORS isn't working is that your link gives a "301 Moved Permanently" without a CORS header, redirecting to another link.

The link it redirects to sends the header, however it seems CORS has already given up the preflight on the first response.

Passing back a "Access-Control-Allow-Origin" header with the 301 may solve your problem, that should allow the preflight to continue.