怎么样通过php curl模拟post请求内容后并下载文件？

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&id=26881&uhash=eecf3d3071a7b672c314bc39';
$ret = curl_post($header, $data,$url);
//需将内容显示修改为文件下载
echo $ret;

$ret = curl_post($header, $data,$url);
//需将内容显示修改为文件下载
$filename = 'x.torrent';
header("Content-Type: application/force-download");
header("Content-Disposition: attachment; filename=$filename"); 
echo $ret;