实现php文件安全下载！

public function downloads($name){          $name_tmp = explode("_",$name);          $type = $name_tmp[0];          $file_time = explode(".",$name_tmp[3]);          $file_time = $file_time[0];          $file_date = date("Y/md",$file_time);          $file_dir = SITE_PATH."/data/uploads/$type/$file_date/";                if (!file_exists($file_dir.$name)){              header("Content-type: text/html; charset=utf-8");              echo "File not found!";              exit;           } else {              $file = fopen($file_dir.$name,"r");               Header("Content-type: application/octet-stream");              Header("Accept-Ranges: bytes");              Header("Accept-Length: ".filesize($file_dir . $name));              Header("Content-Disposition: attachment; filename=".$name);              echo fread($file, filesize($file_dir.$name));              fclose($file);          }      }