Facebook API works, but not with codeigniter?

Question

I'm working on a site which uses the Facebook API to log users in, but I'm having some baffling trouble with the Facebook API itself. I think it's a result of using CodeIgniter.

I added a PHP script that does not use Codeigniter, and it can connect. It looks like this:

require_once("application/libraries/Facebook/facebook.php");

$facebook = new Facebook(array(
        'appId'  => 'appid-removed-for-question',
        'secret' => 'secret-removed-for-question',
));

$user = $facebook->getUser();
echo $user;

This returns the appropriate UID from Facebook.

As soon as I try to do this using a CodeIgniter library, the UID consistently comes back as 0. Here's the library code:

include(APPPATH.'libraries/Facebook/facebook.php');

class Fb_connect extends Facebook{

    public $user;

    public function __construct()
    {
        $CI =& get_instance();
        $CI->config->load("facebook",TRUE);
        $config = $CI->config->item('facebook');
        parent::__construct($config);

        $this->user = $this->getUser();
        echo $this->user;
    }
}

I've double and triple-checked my appid and secret in the config file, and even echoed it here to make sure it's coming through as an array correctly, but still nothing. $this->user; constantly returns 0 for the UID. What am I missing?

I just saw this question which talks about the uri_protocol being the problem, but I had to set $config['uri_protocol'] = 'QUERY_STRING'; to get my mod_rewrite script working in the first place, which makes me wonder if it's the same issue or not. Any advice?

Answer 1

The answer to the question I linked to actually fixed the problem for me:

$config['uri_protocol'] = 
    (isset($_SERVER['HTTP_REFERER']) && 
     strpos($_SERVER['HTTP_REFERER'], 'apps.facebook.com') !== false) ? 
         "PATH_INFO" : "REQUEST_URI";

Answer 2

use this.. require_once($_SERVER['DOCUMENT_ROOT']."/".$this->config->item('app_folder_path')."application/libraries/Facebook/facebook.php");

Make sure you've set the app_folder_path config variable in your config.php file.