为什么成功的jQuery跨域发布请求无法触发成功处理程序？

Question

I am making the following JQuery cross domain ajax post request from a phonegap (appgyver steroids) app.

function do_something(callback_method, some_vars)
{
    var stringified_some_vars = JSON.stringify(some_vars);
    $.ajax({ 
    type: "POST",
    url:"http://www.somedomain.com/endpoint",
    data: {'some_vars' : stringified_some_vars},
    async: true,
    dataType: 'json', 
    crossDomain: true,
    xhrFields: {
      withCredentials: true
    },
    success: function(result) 
        {
            var myObject = $.parseJSON(result);
            callback_method(myObject);
        },
    error: function(fail)
    {
        supersonic.logger.debug(fail);
    }
    });
}

The post request is successfully sent to the server (Google Appengine - Python) - ie the server fires the relevant method. However, when the server response is received the jQuery Ajax method doesn't fire the success handler - it instead fires the error handler. The error text prints to console as

{"readyState":0,"responseText":"","status":0,"statusText":"error"}

The headers in the json response from the server are as follows:

Content-Length: 0 
Cache-Control: no-cache 
Access-Control-Allow-Origin: * 
Content-Type: application/json

the content of the response is as expected. and is written using

text_to_send = json.dumps(python_dict)
self.response.headers.add_header('Access-Control-Allow-Origin', '*')
self.response.headers['Content-Type'] = 'application/json'
self.response.write(text_to_send)

It's not clear to me where this error is coming from. Allowing cross domain requests doesn't seem to have fixed the issue. jsonp GET requests work fine - but obviously these aren't allowed for POST requests. Could anyone tell me where I'm going wrong?

Edit 1

Following the suggestion of @Faisal I adjusted the server code as follows

    from urlparse import urlparse
    uri = urlparse(self.request.referer)
    origin = '{}://{}'.format(uri.scheme, uri.netloc)
    self.response.headers.add_header('Access-Control-Allow-Origin', origin)
    self.response.headers['Content-Type'] = 'application/json'

The headers are now

Content-Length: 0 
Cache-Control: no-cache 
Access-Control-Allow-Origin: http://localhost 
Content-Type: application/json 

However the same error is encountered

Answer 1

I think if it's withCredentials: true you need your origin to be exact match instead of wildcard (*). Here is a quick code to get it from referer. But you should probably also check if its one of the allowed origins:

from urlparse import urlparse

uri = urlparse(self.request.referer)
origin = '{}://{}'.format(uri.scheme, uri.netloc)

Edit

Try adding:

self.response.headers.add_header('Access-Control-Allow-Credentials', 'true')