Mine

      while( ob_get_level() ) {
        ob_end_clean();
      }

      header("Content-Type: application/octet-stream");
      header("Content-Disposition: filename=\"".strtr($FileName,',','_')."\"" );
      header("Content-Length: ".filesize('/tmp/c.php') );
      header("Accept-Ranges: bytes" );
      header("Cache-Control: no-store, no-cache, must-revalidate");    //HTTP/1.1
      header("Pragma: no-cache");                            //HTTP/1.0
      header("Expires: 0");
      print( "XXXXXXXX");
      ob_end_clean();
      readfile( '/tmp/c.php' );