How to download and modify file name in php

/download.php?controller=down_file&file=1.zip

$file = './路径/1.zip';
filename = '2.zip';
header('Content-Description: File Transfer');
header('Content-Type: application/octet-stream');
header("Content-type:text/html;charset=utf-8");
header('Content-Disposition: attachment; filename='. $filename);
header('Content-Transfer-Encoding: binary');
header('Expires: 0'); header('Cache-Control: must-revalidate, post-check=0, pre-check=0');
header('Pragma: public');
readfile($file);
exit;

<?php
$file_name="aa.rar";//需要下载的文件
$file_name=iconv("utf-8","gb2312","$file_name");
$fp=fopen($file_name,"r+");//下载文件必须先要将文件打开，写入内存
if(!file_exists($file_name)){//判断文件是否存在
    echo "文件不存在";         //如果不存在
    exit();                              //直接退出
}                                         //如果存在，继续执行下载
$file_size=filesize("aa.rar");//判断文件大小
//返回的文件
Header("Content-type: application/octet-stream");
//按照字节格式返回
Header("Accept-Ranges: bytes");
//返回文件大小
Header("Accept-Length: ".$file_size);
//弹出客户端对话框，对应的文件名
Header("Content-Disposition: attachment; filename=".$file_name);
//防止服务器瞬时压力增大，分段读取
$buffer=1024;
while(!feof($fp)){
    $file_data=fread($fp,$buffer);
    echo $file_data;
}
//关闭文件
fclose($fp);
?>

<?
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();
}
?>