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
$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'];