php 下载封装方法

<?php     //下载接口    function downloadf(){           $name=$_GET['name'];               if(session('ID')!=null){                                            $file_path=iconv("UTF-8","GBK","./Uploads/download/".$name);        if(!file_exists($file_path)){    header("Content-Type: text/html;charset=utf-8");         echo "<script type='text/javascript'> alert('文件不存在！'); history.back(); </script>";     //   return ;    }    $fp=fopen($file_path,"r");    $file_size=filesize($file_path);    //下载文件需要用到的头       Header("Content-type:application/octet-stream");     Header("Accept-Ranges: bytes");     Header("Accept-Length:".$file_size);       if ( preg_match('/MSIE/i', $_SERVER['HTTP_USER_AGENT'])) {    Header("Content-Disposition: attachment; filename=".urlencode($name));     } else {         if ( preg_match('/Trident/i', $_SERVER['HTTP_USER_AGENT'])) {        Header("Content-Disposition: attachment; filename=".urlencode($name));     } else {             Header("Content-Disposition: attachment; filename=".$name);     }    }           $buffer=1024;    $file_count=0;    //向浏览器返回数据    while(!feof($fp) && $file_count<$file_size){        $file_con=fread($fp,$buffer);        $file_count+=$buffer;        echo $file_con;    }                            fclose($fp);                                             }else{                                echo "<script>alert('请登录！');history.back();</script>";               }         }?>