A CORS POST request works from plain JavaScript, but why not with jQuery?

UPDATE: As TimK pointed out, this isn't needed with jquery 1.5.2 any more. But if you want to add custom headers or allow the use of credentials (username, password, or cookies, etc), read on.

I think I found the answer! (4 hours and a lot of cursing later)

//This does not work!!Access-Control-Allow-Headers: *

You need to manually specify all the headers you will accept (at least that was the case for me in FF 4.0 & Chrome 10.0.648.204).

jQuery's $.ajax method sends the "x-requested-with" header for all cross domain requests (i think its only cross domain).

So the missing header needed to respond to the OPTIONS request is:

//no longer needed as of jquery 1.5.2Access-Control-Allow-Headers: x-requested-with

If you are passing any non "simple" headers, you will need to include them in your list (i send one more):

//only need part of this for my custom headerAccess-Control-Allow-Headers: x-requested-with, x-requested-by

So to put it all together, here is my PHP:

// * wont work in FF w/ Allow-Credentials//if you dont need Allow-Credentials, * seems to workheader('Access-Control-Allow-Origin: http://www.example.com');//if you need cookies or login etcheader('Access-Control-Allow-Credentials: true');if ($this->getRequestMethod() == 'OPTIONS'){  header('Access-Control-Allow-Methods: GET, POST, PUT, DELETE, OPTIONS');  header('Access-Control-Max-Age: 604800');  //if you need special headers  header('Access-Control-Allow-Headers: x-requested-with');  exit(0);}

Another possibility is that setting dataType: json causes JQuery to send the Content-Type: application/json header. This is considered a non-standard header by CORS, and requires a CORS preflight request. So a few things to try:

1) Try configuring your server to send the proper preflight responses. This will be in the form of additional headers like Access-Control-Allow-Methods and Access-Control-Allow-Headers.

2) Drop the dataType: json setting. JQuery should request Content-Type: application/x-www-form-urlencoded by default, but just to be sure, you can replace dataType: json with contentType: 'application/x-www-form-urlencoded'

You are sending "params" in js:request.send(params);

but "data" in jquery". Is data defined?: data:data,

Also, you have an error in the URL:

$.ajax( {url:url,         type:"POST",         dataType:"json",         data:data,          success:function(data, textStatus, jqXHR) {alert("success");},         error: function(jqXHR, textStatus, errorThrown) {alert("failure");}});

You are mixing the syntax with the one for $.post

Update: I was googling around based on monsur answer, and I found that you need to add Access-Control-Allow-Headers: Content-Type (below is the full paragraph)

http://metajack.im/2010/01/19/crossdomain-ajax-for-xmpp-http-binding-made-easy/

How CORS Works

CORS works very similarly to Flash's crossdomain.xml file. Basically, the browser will send a cross-domain request to a service, setting the HTTP header Origin to the requesting server. The service includes a few headers like Access-Control-Allow-Origin to indicate whether such a request is allowed.

For the BOSH connection managers, it is enough to specify that all origins are allowed, by setting the value of Access-Control-Allow-Origin to *. The Content-Type header must also be white-listed in the Access-Control-Allow-Headers header.

Finally, for certain types of requests, including BOSH connection manager requests, the permissions check will be pre-flighted. The browser will do an OPTIONS request and expect to get back some HTTP headers that indicate which origins are allowed, which methods are allowed, and how long this authorization will last. For example, here is what the Punjab and ejabberd patches I did return for OPTIONS:

Access-Control-Allow-Origin: *Access-Control-Allow-Methods: GET, POST, OPTIONSAccess-Control-Allow-Headers: Content-Type Access-Control-Max-Age: 86400