在集成paypal时不能收到IPN,该如何解决

在集成paypal时不能收到IPN
1. 采用标准集成的方式，按钮进行支付（已经成功）
2. return 能收到。
3. IPN不能收到。。。但是在卖家账号设置里可以看到ipn已经发出去了。
4. sandbox环境

//从 PayPal 出读取 POST 信息同时添加变量?cmd?
$req = 'cmd=_notify-validate';
foreach ($_POST as $key => $value) {
$value = urlencode(stripslashes($value));
$req .= "&$key=$value";
}
//建议在此将接受到的信息记录到日志文件中以确认是否收到 IPN 信息
//将信息 POST 回给 PayPal 进行验证
$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";
//在 Sandbox 情况下，设置：
$fp = fsockopen('www.sandbox.paypal.com',80,$errno,$errstr,30);
//$fp = fsockopen ('www.paypal.com', 80, $errno, $errstr, 30);
//将 POST 变量记录在本地变量中
//该付款明细所有变量可参考：
//https://www.paypal.com/IntegrationCenter/ic_ipn-pdt-variable-reference.htm
$item_name = $_POST['item_name'];
$item_number = $_POST['item_number'];
$payment_status = $_POST['payment_status'];
$payment_amount = $_POST['mc_gross'];
$payment_currency = $_POST['mc_currency'];
$txn_id = $_POST['txn_id'];
$receiver_email = $_POST['receiver_email'];
$payer_email = $_POST['payer_email'];
//…
//判断回复 POST 是否创建成功
if (!$fp) {
//HTTP 错误
}else {
//将回复 POST 信息写入 SOCKET 端口
fputs ($fp, $header .$req);
//开始接受 PayPal 对回复 POST 信息的认证信息
while (!feof($fp)) {
$res = fgets ($fp, 1024);
//已经通过认证
if (strcmp ($res, "VERIFIED") == 0) {

@$fp = fopen("aaa.txt","w");
if(!$fp){
echo "system error";
exit();
}else {
fwrite($fp,"完成");
fclose($fp);
}

//检查付款状态
//检查 txn_id 是否已经处理过
//检查 receiver_email 是否是您的 PayPal 账户中的 EMAIL 地址
//检查付款金额和货币单位是否正确
//处理这次付款，包括写数据库
}else if (strcmp ($res, "INVALID") == 0) {
//未通过认证，有可能是编码错误或非法的 POST
@$fp = fopen("bbb.txt","w");
if(!$fp){
echo "system error";
exit();
}else {
fwrite($fp,"有错");
fclose($fp);
}


}
}
fclose ($fp);
}
?>

------解决方案--------------------

PHP code

//session_start();

$req = 'cmd=_notify-validate';

foreach ($_POST as $key => $value) {
$value = urlencode(stripslashes($value));
$req .= "&$key=$value";
}
$url='https://www.paypal.com/cgi-bin/webscr';
    $curl_result=$curl_err='';
    $ch = curl_init();
    curl_setopt($ch, CURLOPT_URL,$url);
    curl_setopt($ch, CURLOPT_RETURNTRANSFER,1);
    curl_setopt($ch, CURLOPT_POST, 1);
    curl_setopt($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, FALSE);
    curl_setopt($ch, CURLOPT_TIMEOUT, 3000);

    $curl_result = @curl_exec($ch);
    $curl_err = curl_error($ch);
    curl_close($ch);


$mc_gross = $_POST['mc_gross'];