php下載遠程大文件（獲取遠程文件大小）

<?php
    // 暫不支持斷點續傳
    // $url = 'http://www.mytest.com/debian.iso'; 不知道為何獲取本地文件大小為0
    $url = 'http://192.168.8.93/download/vm-672/18/0.vmdk';
    $file = basename($url);
    $header = get_headers($url, 1);
    $size = $header['Content-Length'];

    $fp = fopen($url, 'rb');
    if ($fp === false) exit('文件不存在或打開失敗');

    header('Content-Description: File Transfer');
    header('Content-Type: application/octet-stream');
    header('Content-Disposition: attachment; filename="'.$file.'"');
    header('Content-Transfer-Encoding: binary');
    header('Expires: 0');
    header('Cache-Control: must-revalidate, post-check=0, pre-check=0');
    header('Pragma: public');
    header('Content-Length: ' . $size);

    ob_clean();
    ob_end_flush();
    set_time_limit(0);
    
    $chunkSize = 1024 * 1024;
    while (!feof($fp)) {
        $buffer = fread($fp, $chunkSize);
        echo $buffer;
        ob_flush();
        flush();
    }
    fclose($fp);
    exit;