Force Download Snippet Questions

<?php
$eventName = $modx->event->name;
switch($eventName) {
    case 'OnWebPageInit':
if(!empty($_GET['f'])){
$file = $modx->getOption('base_path').$_GET['f'];
if(!file_exists($file)){
    $modx->sendErrorPage();
}
if(ini_get('zlib.output_compression')){
    ini_set('zlib.output_compression', 'Off');
}
$file_extension = strtolower(substr(strrchr($file,"."),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 "jpeg":
  	case "jpg": $ctype="image/jpg"; break;
	case "scr": $ctype="application/octet-stream"; break;
	case 'kml': $ctype='application/vnd.google-earth.kml+xml';break;
  	default: $ctype="application/force-download";
}
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-Type: $ctype");
header("Content-Disposition: attachment; filename=\"".basename($file)."\";" );
header("Content-Transfer-Encoding: binary");
header("Content-Length: ".filesize($file));
readfile("$file");
exit();
};
break;
}