protected function getConfigResolver()
    {
        if (is_null($this->configResolver) === false) {
            return $this->configResolver;
        }

        $resolver = new AttributesResolver();
        $resolver->setDefault('host', '0.0.0.0', 'string', true)
            ->setDefault('port', 4000, 'integer', true)
            ->setValidator('port', function ($value) {
                return $value >= 0;
            })
            ->setDefault('server_watch_ext', ['html'], 'array', true)
            ->setDefault('parsedown_activated', false, 'bool', true);

        $this->configResolver = $resolver;

        return $this->configResolver;
    }