如何使用PHP总结下载？

Question

我想知道如何使用从外部服务器获取文件的PHP代码来总结下载。有人能帮助我吗？我是新手。

代码：

<?php
function get_size($url) {
    $my_ch = curl_init();
    curl_setopt($my_ch, CURLOPT_URL,$url);
    curl_setopt($my_ch, CURLOPT_HEADER, true);
    curl_setopt($my_ch, CURLOPT_NOBODY, true);
    curl_setopt($my_ch, CURLOPT_RETURNTRANSFER, true);
    curl_setopt($my_ch, CURLOPT_TIMEOUT, 10);
    $r = curl_exec($my_ch);
    foreach(explode("\n", $r) as $header) {
    if(strpos($header, 'Content-Length:') === 0) {
        return trim(substr($header,16));
    }
    }
    return '';
}
// Set operation params

$mime = "video/mp4";
$ext = str_replace(array('/', 'x-'), '', strstr($mime, '/'));
$url = "https://www.googleapis.com/drive/v3/files/".$_GET['url']."?alt=media&key=";
$name = urldecode($_GET['title']). '.' .$ext;

// Fetch and serve
if ($url)
{
$size=get_size($url);
// Generate the server headers
if (strpos($_SERVER['HTTP_USER_AGENT'], 'MSIE') !== FALSE)
{
header('Content-Type: "' . $mime . '"');
header('Content-Disposition: attachment; filename="' . $name . '"');
header('Expires: 0');
header('Content-Length: '.$size);
header('Cache-Control: must-revalidate, post-check=0, pre-check=0');
header("Content-Transfer-Encoding: binary");
header('Pragma: public');
}
else
{
header('Content-Type: "' . $mime . '"');
header('Content-Disposition: attachment; filename="' . $name . '"');
header("Content-Transfer-Encoding: binary");
header('Expires: 0');
header('Content-Length: '.$size);
header('Pragma: no-cache');
}

readfile($url);
exit;
}

// Not found
exit('File not found');
?>