求帮忙修改个php curl模拟post请求内容后并下载文件的解决思路

下面代码使用curl模拟post请求链接后直接显示出了文件内容，如何修改成不显示内容而直接下载请求到的.torrent格式文件呢

function curl_post($header,$data,$url)
{
$ch = curl_init();
$res= curl_setopt ($ch, CURLOPT_URL,$url);
curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, FALSE);
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, FALSE);
curl_setopt ($ch, CURLOPT_HEADER, 0);
curl_setopt($ch, CURLOPT_POST, 1);
curl_setopt($ch, CURLOPT_POSTFIELDS, $data);
curl_setopt ($ch, CURLOPT_RETURNTRANSFER, 1);
curl_setopt($ch,CURLOPT_HTTPHEADER,$header);
$result = curl_exec ($ch);
curl_close($ch);
if ($result == NULL) {
return 0;
}
return $result;
}
$url = http://www.bttiantang.com/download4.php ;
$header = array(“Host:www.bttiantang.com”,
“Content-Type:application/x-www-form-urlencoded”,
User-Agent: Mozilla/4.0 (compatible; MSIE .0; Windows NT 6.1; Trident/4.0; SLCC2;));
$data = action=download