public function getETags()
    {
        if ($this->getHeaders()->has('If-None-Match')) {
            /** @var string $ifNoneHeader */
            $ifNoneHeader = $this->getHeaders()->get('If-None-Match');
            $eTags = preg_split('/[\s,]+/', str_replace('-gzip', '', $ifNoneHeader), -1, PREG_SPLIT_NO_EMPTY);
            return is_array($eTags) ? $eTags : [];
        }

        return [];
    }