/library/PaymentGateway/Paypal.php

<?php

/**
 * Paypal Class
 *
 * Integrate the Paypal payment gateway in your site using this easy
 * to use library. Just see the example code to know how you should
 * proceed. Btw, this library does not support the recurring payment
 * system. If you need that, drop me a note and I will send to you.
 *
 * @package		Payment Gateway
 * @category	Library
 * @author      Md Emran Hasan <phpfour@gmail.com>
 * @link        http://www.phpfour.com
 */

include_once ('PaymentGateway.php');

class Paypal extends PaymentGateway
{

    /**
	 * Initialize the Paypal gateway
	 *
	 * @param none
	 * @return void
	 */
	public function __construct()
	{
        parent::__construct();

        // Some default values of the class
	    $this->gatewayUrl = 'https://www.paypal.com/cgi-bin/webscr';
	    $this->ipnLogFile = 'paypal.ipn_results.log';

	    // Populate $fields array with a few default
	    $this->addField('rm', '2');      
	    // Return method = POST
	
	    $this->addField('cmd', '_cart');
	    $this->addField('upload', 1);		
	}

    /**
     * Enables the test mode
     *
     * @param none
     * @return none
     */
    public function enableTestMode()
    {
        $this->testMode = TRUE;
        $this->gatewayUrl = 'https://www.sandbox.paypal.com/cgi-bin/webscr';
    }

    /**
	 * Validate the IPN notification
	 *
	 * @param none
	 * @return boolean
	 */
	public function validateIpn()
	{
		// parse the paypal URL
		$urlParsed = parse_url($this->gatewayUrl);

		// generate the post string from the _POST vars
		$postString = '';

		foreach ($_POST as $field=>$value)
		{
			$this->ipnData["$field"] = $value;
			$postString .= $field .'=' . urlencode(stripslashes($value)) . '&';
		}

		$postString .="cmd=_notify-validate"; // append ipn command

		// open the connection to paypal
		$fp = fsockopen($urlParsed['host'], "80", $errNum, $errStr, 30);

		if(!$fp)
		{
			// Could not open the connection, log error if enabled
			$this->lastError = "fsockopen error no. $errNum: $errStr";
			$this->logResults(false);

			return false;
		}
		else
		{
			// Post the data back to paypal

			fputs($fp, "POST ".$urlParsed['path']." HTTP/1.1\r\n");
			fputs($fp, "Host: ".$urlParsed['host']."\r\n");
			fputs($fp, "Content-type: application/x-www-form-urlencoded\r\n");
			fputs($fp, "Content-length: " . strlen($postString) . "\r\n");
			fputs($fp, "Connection: close\r\n\r\n");
			fputs($fp, $postString . "\r\n\r\n");

			// loop through the response from the server and append to variable
			while(!feof($fp))
			{
				$this->ipnResponse .= fgets($fp, 1024);
			}

		 	fclose($fp); // close connection
		}

		if (eregi("VERIFIED", $this->ipnResponse))
		{
		 	// Valid IPN transaction.
		 	$this->logResults(true);
		 	return true;
		}
		else
		{
		 	// Invalid IPN transaction.  Check the log for details.
			$this->lastError = "IPN Validation Failed . $urlParsed[path] : $urlParsed[host]";
			$this->logResults(false);
			return false;
		}
	}
}