public function img_url()
{
    $id = request()->param('id', 1122);
    $info = Db::name('attachment')->where(array('id' => $id))->find(); if ($info['drawing']) {
        $filename = substr($info['drawing'],1);
    } else {
        $filename = substr($info['url'],1);
    } 
 Header("Content-type: application/octet-stream");
     Header("Accept-Ranges: bytes");
   Header("Accept-Length: " . filesize($filename));
   Header("Content-Disposition: attachment; filename=" . basename($filename));
   header('Cache-Control: must-revalidate, post-check=0, pre-check=0'); 
 header('Pragma: public'); 
 echo file_get_contents($filename); 
 exit();
}