protected static function getRequestHeaders(array $server)
    {
        static $headers;

        if ($headers !== null) {
            return $headers;
        }

        $headers = [];

        foreach ($server as $name => $value) {
            if (substr($name, 0, 5) == 'HTTP_') {
                $headers[str_replace(' ', '-', ucwords(strtolower(str_replace('_', ' ', substr($name, 5)))))] = $value;
            }
        }

        return $headers;
    }