PHP 下载文件

<?php$file = "a.js";$filename = basename($file);header("Content-type: application/octet-stream");$agent = $_SERVER["HTTP_USER_AGENT"];$encoded_filename = rawurlencode($filename);if (preg_match("/MSIE/", $agent)) {    header('Content-Disposition: attachment; filename="' . $encoded_filename . '"');} else if (preg_match("/Firefox/", $agent)) {    header("Content-Disposition: attachment; filename*=\"utf8''" . $filename . '"');} else {    header('Content-Disposition: attachment; filename="' . $filename . '"');}header("Content-Length: " . filesize($file));readfile($file);?>