PHP实现文件下载详解

<?php
$file_name="哈哈.jpg";//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";
    exit();
}
$file_size=filesize("a.jpg");//判断文件大小
//返回的文件
Header("Content-type: application/octet-stream");
//按照字节格式返回
Header("Accept-Ranges: bytes");
//返回文件大小
Header("Accept-Length: ".$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);
?>

     function download_by_path($path_name, $save_name){
         ob_end_clean();
         $hfile = fopen($path_name, "rb") or die("Can not find file: $path_name\n");
         Header("Content-type: application/octet-stream");
         Header("Content-Transfer-Encoding: binary");
         Header("Accept-Ranges: bytes");
         Header("Content-Length: ".filesize($path_name));
         Header("Content-Disposition: attachment; filename=\"$save_name\"");
         while (!feof($hfile)) {
            echo fread($hfile, 32768);
         }
         fclose($hfile);
    }