php强制下载文件函数

{
$id = $this->_get('id');
$M = M("downloads");
$data=$M->where("id=$id and status=1")->find();
!$data && exit;
$filename = iconv('UTF-8','GBK',$data['filename']);
$savename = $data['savename'];
$myfile = $data[url] ? $data[url] : 'Uploads/file/'.$savename;
if(file_exists($myfile)){
　　$M->where("id=$id")->setInc('downloads');
　　$file = @ fopen($myfile,"r");
　　header("Content-type: application/octet-stream");
　　header("Content-Disposition: attachment; filename=" .$filename );
　　while (!feof($file)) {
echo fread($file,50000);
　　}
　　fclose($file);
　　exit;
}else{
　　echo '文件不存在！';

}
}