我在我的网站上使用 PayPal 的“立即购买”按钮来销售产品。因为我在 MySQL 数据库中跟踪每种产品的库存数量，并且我希望系统中的库存跟踪自动化，所以我使用 PayPal 的即时付款通知功能来让我知道购买的时间完全的。当 Paypal 通知我的处理程序已经进行了有效购买时，脚本通过从所购买产品的库存中减去“1”来更新我的 MySQL 数据库。
我在下面附上了我的 IPN PHP 代码，该代码可与 Paypal 立即购买按钮一起成功运行（一次购买一次）。
我的问题是：我想用 PayPal 的“添加到购物车”按钮替换“立即购买”按钮，以便客户一次可以购买多个产品。我不确定我必须如何更改下面的代码以让它遍历所有购买的物品并相应地更新我的数据库。任何帮助将不胜感激！
编码：
// Paypal POSTs HTML FORM variables to this page
// we must post all the variables back to paypal exactly unchanged and add an extra parameter cmd with value _notify-validate
// initialise a variable with the requried cmd parameter
$req = 'cmd=_notify-validate';
// go through each of the POSTed vars and add them to the variable
foreach ($_POST as $key => $value) {
$value = urlencode(stripslashes($value));
$req .= "&$key=$value";
}
// post back to PayPal system to validate
$header .= "POST /cgi-bin/webscr HTTP/1.0\r\n";
$header .= "Content-Type: application/x-www-form-urlencoded\r\n";
$header .= "Content-Length: " . strlen($req) . "\r\n\r\n";
// In a live application send it back to www.paypal.com
// but during development you will want to uswe the paypal sandbox
// comment out one of the following lines
$fp = fsockopen ('www.sandbox.paypal.com', 80, $errno, $errstr, 30);
//$fp = fsockopen ('www.paypal.com', 80, $errno, $errstr, 30);
// or use port 443 for an SSL connection
//$fp = fsockopen ('ssl://www.paypal.com', 443, $errno, $errstr, 30);
if (!$fp) {
// HTTP ERROR
}
else
{
fputs ($fp, $header . $req);
while (!feof($fp)) {
$res = fgets ($fp, 1024);
if (strcmp ($res, "VERIFIED") == 0) {
$item_name = stripslashes($_POST['item_name']);
$item_number = $_POST['item_number'];
$item_id = $_POST['custom'];
$payment_status = $_POST['payment_status'];
$payment_amount = $_POST['mc_gross']; //full amount of payment. payment_gross in US
$payment_currency = $_POST['mc_currency'];
$txn_id = $_POST['txn_id']; //unique transaction id
$receiver_email = $_POST['receiver_email'];
$payer_email = $_POST['payer_email'];
$size = $_POST['option_selection1'];
$item_id = $_POST['item_id'];
$business = $_POST['business'];
if ($payment_status == 'Completed') {
// UPDATE THE DATABASE
}