Wordpress function to force Facebook to refresh it's cache as a scheduled post

functions.php

<?
 
// Ping Facebook with (via a POST request) to refresh the cache (scrape) for a scheduled post as it is published
// Relevant docs: https://developers.facebook.com/docs/opengraph/using-objects#selfhosted-update
// Place this in your Wordpress functions.php file
 
add_action('transition_post_status', 'purge_future_post', 10, 3);
 
function purge_future_post($new_status, $old_status, $post) {
	if($new_status == 'publish') {
		purge_facebook_cache($post);
	}
}
 
function purge_facebook_cache($post_id) {
	$fbUrl = 'https://graph.facebook.com';
	$pageUrl = get_permalink($post_id);
	$fields = array(
		'id' => urlencode($pageUrl), 
		'scrape' => true
	);
	foreach($fields as $key=>$value) { $fields_string .= $key.'='.$value.'&'; }
	rtrim($fields_string,'&');
	$ch = curl_init();
	curl_setopt($ch,CURLOPT_URL,$fbUrl);
	curl_setopt($ch,CURLOPT_POST,count($fields));
	curl_setopt($ch,CURLOPT_POSTFIELDS,$fields_string);
	$result = curl_exec($ch);
	curl_close($ch);
}
 
?>

Not sure how this code would run as expected.
Line 19: $url is not set before it is used.
Line 25: $postUrl is not set before it is used.
Also its good practice to curl_close($ch) when you're done.
Since it's an https address we should probably toss in a curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, 0); too.

Edit: Added CURLOPT_SSL_VERIFYPEER suggestion.

@coltjones Oops, yes, I had a tangle of vars there, $url and $postUrl were supposed to be $pageUrl and $fbUrl respectively. I've updated the code now.