php下载程序

<?php 

$path = '1.rar'; 

$extension = getFileExt($f); 

switch ($extension){ 
case "jpg": 
case "jpeg": $ctype="image/jpeg"; break; 
case "pdf": $ctype="application/pdf"; break; 
case "gif": $ctype="image/gif"; break; 
case "png": $ctype="image/png"; break; 
case "doc": $ctype="application/msword"; break; 
case "zip": $ctype="application/zip";break; 
case "rar": $ctype="application/rar"; break;   
default: $ctype="application/force-download"; 
} 

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: ". $ctype); 
header("Content-Transfer-Encoding: binary"); 
header("Content-Length: ". filesize($path)); 
header('Content-Disposition: attachment; filename="100.jpg" ;'); 

readfile(   $path  ); 
function getFileExt($file_name){   
$extend = explode("." , $file_name);   
$type = $extend[count($extend)-1]; 
return strtolower($type);   
}   
?>