Please look over Paypal IPN Script

<?php
/*
	Project: www.ad-hit.com
	Purpose: Paypal IPN Script - Button (BUY NOW), Process (INCREASE CUSTOMERS AD-HIT POINTS)
	Author: Ryan Bayne
	Site: wwww.webtechglobal.co.uk
	Date: 19th January 2009
*/
 
 
################# PART ONE - Write to log, format time, connect to database
	$log = fopen("ipn.log", "a");
	fwrite($log, "\n\nipn - " . gmstrftime ("%b %d %Y %H:%M:%S", time()) . "\n"); //gmstrftime formats system time to something readable
	//$db = mysql_connect("localhost", "yourname", "yourpassword");
	//mysql_select_db("yourdb",$db);
 
 
############## PART TWO - Create reply to return Paypals POST data, back to Paypal using PayPals standard code(this creates authorisation)
	$postvars = array(); //create array to contain all values of POST from Paypal
	while (list ($key, $value) = each ($HTTP_POST_VARS)) //read the posted vars from Paypal
	{ 
		$postvars[] = $key;
	}
	$req = 'cmd=_notify-validate'; //start reply with Paypals own command
	for ($var = 0; $var < count ($postvars); $var++) 
	{   //for loop lists all POST variables in format: variable=value
		$postvar_key = $postvars[$var];
		$postvar_value = $$postvars[$var];
		$req .= "&" . $postvar_key . "=" . urlencode ($postvar_value); //urlencode is the data format for POST transmission from a web page
	}
	/* Extra Reading
	The function 'urlencode':
	 "Returns a string in which all non-alphanumeric characters except -_. have been replaced with a percent (%) 
	 sign followed by two hex digits and spaces encoded as plus (+) signs" (from the PHP manual).
	This is basically a method of transmitting an 8-bit character set in just 7-bits.
	*/
 
 
##############  PART THREE -  Create an HTTP header for the reply message, create the message, open a connection socket...
	//$header .= "POST /cgi-bin/webscr HTTP/1.0\r\n";// Create message to post back to PayPal...
	$header .= "https://www.sandbox.paypal.com/cgi-bin/webscr";// Create message to post back to PayPal...
	
	$header .= "Content-Type: application/x-www-form-urlencoded\r\n";//cont...
	$header .= "Content-Length: " . strlen ($req) . "\r\n\r\n";//cont...
	$fp = fsockopen ("www.paypal.com", 80, $errno, $errstr, 30);// Open a socket to the PayPal server...
	
	//Write the transaction details to the log file - useful for debugging especially if database is down or has issues
	//---------------------------------------------
	fwrite($log, "Vals: ". $invoice." ". $receiver_email." ". $item_name." ". $item_ number." ". $quantity." 
	". $payment_status." ". $pending_reason." ".$payment_dat e." ". $payment_gross." ". $payment_fee." 
	". $txn_id." ". $txn_type." ". $first_ name." ". $last_name." ". $address_street." ". $address_city." 
	". $address_state . " ".$address_zip." ". $address_country." ". $address_status." ". $payer_email. " 
	". $payer_status." ". $payment_type." ". $notify_version." ". $verify_sign. "\ n");
 
 
############# PART FOUR - Check Connection socket to paypal is OK and perform Final Verification on string of POST vars ($req) by sending to Paypal
	if (!$fp) 
	{	//connection has failed
		echo "$errstr ($errno)"; //errstr and errno are system variables which report last error
		fwrite($log, "Failed to open HTTP connection!");
		$res = "FAILED";
	}
	else 
	{	//connection is OK
		fputs ($fp, $header . $req);
		while (!feof($fp)) //read the results of the verification...
		{
			$res = fgets ($fp, 1024);
			if (strcmp ($res, "VERIFIED") == 0) // If VERIFIED = continue to process the TX...
			{
				//PERFORM ACTIONS UNIQUE TO YOUR APPLICATION - issue product basically (Excluding Main Database INSERT thats at end)
				if (strcmp ($payment_status, "Completed") == 0) //if payment status = Completed then payment is not an eCheck
				{
					//for Ad-Hit.Com customer is buying POINTS and so this is when we increase their points total depending on payment amount
 
 
					//email customer with
					$message .= "Dear Customer,\n Thankyou for your order.\n\nIf you have any problems, 
					please contact us: \n\nsales\@webtechglobal.com";
					
					mail($payer_email, "Your Book Password...", $message, "From: admin@ad-hit.com\nReply-To: admin@yourdomain.com");
				}
				else // If the payment_status is NOT Completed... You'll have to perform unique functions later (Dont issue product basically)
				{
					$message .= "Dear Customer,\n Thankyou for your order.\n\nSOME MESSAGE HERE FOR THE CUSTOMER ABOUT AWAITING PAYMENT COMPLETE.
					\n\nThankyou \n\nsales\@yourdomain.com";
					
					mail($payer_email, "Your Book Password...", $message, "From: admin@ad-hit.com\nReply-To: admin@ad-hit.com");
					mail($receiver_email, "Incomplete PayPal TX...", "An incomplete transaction requires your attention.");
				}
			}
			else //payment UNVERIFIED possibly attempted hack and should be checked by a human
			{
				mail($payer_email, "An Error Occurred...", "Dear Customer,\n an error occurred while PayPal was processing 
				your order. It will be investigated by a human at the earliest opportunity.\n\nWe apologise for any 
				inconvenience.", "From: admin@ad-hit.com\nReply-To: admin@ad-hit.com");
			
				mail($receiver_email, "Invalid PayPal TX", "An invalid transaction on Ad-Hit.Com requires your attention. It should be checked for possible hacking
				and other illegal activity.");
			}
		}
	}
 
 
############### PART FIVE - Insert all data into database (you don't have to do this if you do not want to collect this data)
	//The '\"' is placed around variable to ensure that they appear in double quotes in the query string.
	//This ensures that whatever they contain, they'll get inserted.
/*	$qry = "INSERT into paypal (
	invoice, receiver_email, item_name, item_number, quantity, payment_status, pendi ng_reason, payment_date, payment_gross, payment_fee, 
	txn_id, txn_type, first_nam e, last_name, address_street, address_city, address_state, address_zip, address_ country, address_status, payer_email, payer_status, payment_type, notify_version , verify_sign )
	VALUES
	( \"$invoice\", \"$receiver_email\", \"$item_name\", \"$item_number\", \"$quanti ty\", \"$payment_status\", \"$pending_reason\", 
	\"$payment_date\", \"$payment_gr oss\", \"$payment_fee\", \"$txn_id\", \"$txn_type\", \"$first_name\", \"$last_na me\", 
	\"$address_street\", \"$address_city\", \"$address_state\", \"$address_zip \", \"$address_country\", \"$address_status\", 
	\"$payer_email\", \"$payer_status \", \"$payment_type\", \"$notify_version\", \"$verify_sign\" ) ";
	
	$result = mysql_query($qry,$db);
	
	// Close PayPal Connection, Log File and DB.
	fclose ($fp);
	fclose ($log);
	mysql_close($db);
	*/
?>