Facebook PHP SDK getLoginUrl failed - strange - facebook

Question

I was developing facebook canvas application, and I found this simple code fails. I don't know what went wrong, because I took it straight from tutorial:
<?php
require 'facebook.php';
/*
Facebook::$CURL_OPTS[CURLOPT_SSL_VERIFYPEER] = false;
Facebook::$CURL_OPTS[CURLOPT_SSL_VERIFYHOST] = 2;
*/
$facebook = new Facebook(array(
'appId' => 'xxx',
'secret' => 'xxx',
'cookie' => true,
));
//Request params
if(!($facebook->getSession()))
{
header("Location:" . $facebook->getLoginUrl(array('req_perms' => 'publish_stream')));
exit;
}
?>
the problem is at header("Location:" . $facebook->getLoginUrl(array('req_perms' => 'publish_stream')));. When I remove it (including removing the exit), the application can run well. However, when I have it, the application doesn;t show anything. Just blank page. And there is "load resource error from channel.facebook.com" on chrome's developer tools.
Can anybody help me spot what when wrong? I don't understand what went wrong In this code. I have made sure that appId and secret are correct.

Answer 1

This might help you:
load resource error from channel.facebook.com is irrelevant to your problem, I've seen that error plenty of times on the facebook page, it is their problem.
Most likely you are getting a blank screen because there is a PHP error, and you have error_reporting set to 0. Try error_reporting(E_ALL) to see if this is the problem.
Where is this code located, is the header you are sending ahead of other text output? Try placing the code on top of the page.
These are just some basic stuff you can check, hope it helps. Good luck.

Answer 2

I had the same problem (blank page) when trying to redirect (in PHP from the server side) to the login URL generated with the function getLoginUrl of the Facebook PHP SDK.
The problem seems to be related to the fact that the redirection is in the iFrame.
The redirection needs to be for the parent frame and not the canvas frame.
In PHP there is no way to tell the browser to redirect the parent frame soo you have to do it in Javascript:
$loginUrl = $facebook->getLoginUrl(array('req_perms' => 'publish_stream'));
echo '<script type="text/javascript">top.window.location="'.$loginUrl.'";</script>';