跨浏览器PHP下载文件名中的中文乱码问题解决方法

<?php
$ua = $_server["http_user_agent"];
$filename = "中文 文件名.txt";
$encoded_filename = urlencode($filename);
$encoded_filename = str_replace("+", "%20", $encoded_filename);
header('content-type: application/octet-stream');
if (preg_match("/msie/", $ua)) {
    header('content-disposition: attachment; filename="' . $encoded_filename . '"');
} else if (preg_match("/firefox/", $ua)) {
    header('content-disposition: attachment; filename*="utf8\'\'' . $filename . '"');
} else {
    header('content-disposition: attachment; filename="' . $filename . '"');
}
print 'abc';
?>