function download_headers($filename)
{
    // disable caching
    $now = gmdate("D, d M Y H:i:s");
    header("Expires: Tue, 03 Jul 2001 06:00:00 GMT");
    header("Cache-Control: max-age=0, no-cache, must-revalidate, proxy-revalidate");
    header("Last-Modified: {$now} GMT");
 
    // force download
    header("Content-Type: application/force-download");
    header("Content-Type: application/octet-stream");
    header("Content-Type: application/download");
 
    // disposition / encoding on response body
    header("Content-Disposition: attachment;filename={$filename}");
    header("Content-Transfer-Encoding: binary");
}