Question

I’m writing a very basic Facebook app, but I’m encountering an issue with cross-domain AJAX requests (using jQuery).

I’ve written a proxy page to make requests to the graph via cURL that I’m calling via AJAX. I can visit the page in the browser and see it has the correct output, but requesting the page via always causes jQuery to fire the error handler callback.

So I have two files:

Proxy, which does the cURL request

<?php
//Do some cURL requests, manipulate some data
//return it as JSON
print json_encode($data);
?>

The facebook canvas, which contains this AJAX call

$.getJSON("http://myDomain.com/proxy.php?get=stuff", 
          function(JSON)
          {
              alert("success");
          })
          .error(function(err)
          {
              alert("err");
          });

Inspecting the call with Firebug shows it returns with HTTP code 200 OK, but the error handler is always fired, and no content is returned. This happens whether I set Content-Type: application/json or not.

I have written JSON-returning APIs in PHP before using AJAX and never had this trouble.

What could be causing the request to always trigger the error handler?

Answer 1

Recently I experienced the same issue and my problem was the fact that there was a domain difference between the webpage and the API, due to the SSL.

The web page got a HTTP address (http://myDomain.com) and the content I was requesting with JQuery was on the same domain but HTTPS protocol (https://myDomain.com). The browser (Chrome in this case) considered that the domains were differents (the first one with HTTP, the second one with HTTPS), just because of the protocol, and because the request response type was “application/json”, the browser did not allowed it.

Basically, the request worked fine, but your browser did not allowed the response content.

I had to add a “Access-Control-Allow-Origin” header to make it work. If you’re in the same case, have a look there: https://developer.mozilla.org/en/http_access_control.

I hope that’ll help you, I got a headache myself.