private static function getFullIpHost($clientIpHost = null, $proxyIpHost = null): ?string
    {
        $fullIpHost = [];
        if ($clientIpHost !== null) {
            $fullIpHost[] = \sprintf('client: %s', $clientIpHost);
        }
        if ($proxyIpHost !== null) {
            $fullIpHost[] = \sprintf('proxy: %s', $proxyIpHost);
        }

        return (\count($fullIpHost) > 0) ? \implode(', ', $fullIpHost) : null;
    }