PHP uses code to download files

<?
if( empty($_GET[&#39;FileName&#39;])|| empty($_GET[&#39;FileDir&#39;])|| empty($_GET[&#39;FileId&#39;])){ 
  echo&#39;<script> alert("非法连接 !"); location.replace ("index.php") </script>&#39;;
  exit();
}
$file_name=$_GET[&#39;FileName&#39;];
$file_dir=$_GET[&#39;FileDir&#39;];
$FileId=$_GET[&#39;FileId&#39;];
$file_dir = $file_dir."/";
if   (!file_exists($file_dir.$file_name))
   {  
    //检查文件是否存在  
  echo   "文件找不到";  
  exit;    
  }   else   {  
$file = fopen($file_dir . $file_name,"r"); // 打开文件// 输入文件标签Header("Content-type: application/octet-stream");
Header("Accept-Ranges: bytes");
Header("Accept-Length: ".filesize($file_dir . $file_name));
Header("Content-Disposition: attachment; filename=" . $file_name);// 输出文件内容echo fread($file,filesize($file_dir . $file_name));
fclose($file);exit();
}