Forward PayPal IPN data to multiple URLs.

paypal-ipn-forwarder.php

<?php
// Curl function to send POST data to a server.
function curl_request($url, $req, $ssl)
{
	$curl_result=$curl_err='';
	
	$ch = curl_init();
	curl_setopt($ch, CURLOPT_URL,$url);
	curl_setopt($ch, CURLOPT_RETURNTRANSFER,1);
	curl_setopt($ch, CURLOPT_POSTFIELDS, $req);
	curl_setopt($ch, CURLOPT_HTTPHEADER, array("Content-Type: application/x-www-form-urlencoded", "Content-Length: ".strlen($req)));
	curl_setopt($ch, CURLOPT_HEADER , 0);   
	curl_setopt($ch, CURLOPT_VERBOSE, 1);
	curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, $ssl);
	curl_setopt($ch, CURLOPT_TIMEOUT, 90);
	
	$curl_result = curl_exec($ch);
	$curl_err = curl_error($ch);
	curl_close($ch);
	
	return $curl_result;	
}
/////////////////////////////////////////////////////

// Set config fields
$sandbox = isset($_POST['test_ipn']) ? true : false;
$ppHost = $sandbox ? 'www.sandbox.paypal.com' : 'www.paypal.com';
$ssl = $_SERVER['SERVER_PORT'] == '443' ? true : false;

// Loop through POST data and generate NVP string to return back to PayPal (or forward on to secondary listeners)
$req = '';
foreach ($_POST as $key => $value)
{
    $req .= "&$key.=".urlencode(stripslashes($value));
}
	
// Forward IPN data to secondary IPN listener
curl_request('http://www.domain.com/paypal/ipn/ipn-listener.php', $req, $ssl);
curl_request('http://www.otherdomain.com/paypal/ipn/ipn-listener.php', $req, $ssl);
curl_request('http://www.yetanotherdomain.com/paypal/ipn/ipn-listener.php', $req, $ssl);

// Validate with PayPal using CURL is much the same way we forwarded data to our secondary listener.
$req = 'cmd=_notify-validate'.$req;
$curl_result = curl_request($ppHost.'/cgi-bin/webscr', $req, $ssl);
$valid = strpos($curl_result, "VERIFIED")!==false ? true : false;

// Process accordingly
if($valid)
{
	// Process valid IPN
}
else
{
	// Process invalid IPN
}