PHP: Force Download Function

<?php
 function force_download ($data, $name, $mimetype='', $filesize=false) {
     // File size not set?
     if ($filesize == false OR !is_numeric($filesize)) {
         $filesize = strlen($data);
     }
 
     // Mimetype not set?
     if (empty($mimetype)) {
         $mimetype = 'application/octet-stream';
     }
 
     // Make sure there's not anything else left
     ob_clean_all();
 
     // Start sending headers
     header("Pragma: public"); // required
     header("Expires: 0");
     header("Cache-Control: must-revalidate, post-check=0, pre-check=0");
     header("Cache-Control: private",false); // required for certain browsers
     header("Content-Transfer-Encoding: binary");
     header("Content-Type: " . $mimetype);
     header("Content-Length: " . $filesize);
     header("Content-Disposition: attachment; filename=\"" . $name . "\";" );
 
     // Send data
     echo $data;
     die();
 }
 
 function ob_clean_all () {
     $ob_active = ob_get_length () !== false;
     while($ob_active) {
         ob_end_clean();
         $ob_active = ob_get_length () !== false;
     }
 
     return true;
 }
 ?>