ถึงผู้รู้ผมไปต่อไม่ถูกช่วยเขียนต่อหน่อยครับ(เกี่ยวกับการdownload)

<?php
$path	=	'download';
$filename = $path .'/'.$_GET['filename'];
$filename = realpath($filename);
$file_extension = strtolower(substr(strrchr($filename,"."),1));
switch ($file_extension) {
     case "pdf":  $ctype="application/pdf"; break;
     case "exe":  $ctype="application/octet-stream"; break;
     case "zip":   $ctype="application/zip"; break;
     case "doc": $ctype="application/msword"; break;
     case "xls":   $ctype="application/vnd.ms-excel"; break;
     case "ppt":  $ctype="application/vnd.ms-powerpoint"; break;
     case "gif":   $ctype="image/gif"; break;
     case "png": $ctype="image/png"; break;
     case "jpe": case "jpeg":
     case "jpg":  $ctype="image/jpg"; break;
     case "txt":   $ctype="text/plain"; break;
     case "php": $ctype="text/html"; break;
     case "docx": $ctype="application/vnd.openxmlformats-officedocument.wordprocessingml.document"; break;
     case "doc": $ctype="application/msword"; break;
     default: $ctype="application/force-download";
}
if (!file_exists($filename)) {
     die("NO FILE HERE");
}
header("Pragma: public");
header("Expires: 0");
header("Cache-Control: must-revalidate, post-check=0, pre-check=0");
header("Cache-Control: private",false);
header("Content-Type: $ctype");
header("Content-Disposition: attachment; filename="".basename($filename)."";");
header("Content-Transfer-Encoding: binary");
header("Content-Length: ".@filesize($filename));
set_time_limit(0);
@readfile("$filename") or die("File not found.");

?>