检测url是否有效

  public function validateActiveUrl($value)
    {
        if (! is_string($value)) {
            return false;
        }

        if ($url = parse_url($value, PHP_URL_HOST)) {
            try {
                return count(dns_get_record($url, DNS_A | DNS_AAAA)) > 0;
            } catch (Exception $e) {
                return false;
            }
        }

        return false;
    }