class RssResponseCdata

class RssResponseCdata implements EventSubscriberInterface {
    
    /**
     * Wraps RSS descriptions in CDATA.
     *
     * @param \Symfony\Component\HttpKernel\Event\ResponseEvent $event
     *   The response event.
     */
    public function onResponse(ResponseEvent $event) : void {
        // Skip responses that are not RSS.
        if (stripos($event->getResponse()->headers
            ->get('Content-Type', ''), 'application/rss+xml') === FALSE) {
            return;
        }
        $response = $event->getResponse();
        $response->setContent($this->wrapDescriptionCdata($response->getContent()));
    }
    
    /**
     * Converts description node to CDATA RSS markup.
     *
     * @param string $rss_markup
     *   The RSS markup to update.
     *
     * @return string|false
     *   The updated RSS XML or FALSE if there is an error saving the xml.
     */
    protected function wrapDescriptionCdata(string $rss_markup) : string|false {
        $rss_dom = new \DOMDocument();
        // Load the RSS, if there are parsing errors, abort and return the unchanged
        // markup.
        $previous_value = libxml_use_internal_errors(TRUE);
        $rss_dom->loadXML($rss_markup);
        $errors = libxml_get_errors();
        libxml_use_internal_errors($previous_value);
        if ($errors) {
            return $rss_markup;
        }
        foreach ($rss_dom->getElementsByTagName('item') as $item) {
            foreach ($item->getElementsByTagName('description') as $node) {
                $html_markup = $node->nodeValue;
                if (!empty($html_markup)) {
                    $html_markup = Xss::filter($html_markup, [
                        'a',
                        'abbr',
                        'acronym',
                        'address',
                        'b',
                        'bdo',
                        'big',
                        'blockquote',
                        'br',
                        'caption',
                        'cite',
                        'code',
                        'col',
                        'colgroup',
                        'dd',
                        'del',
                        'dfn',
                        'dl',
                        'dt',
                        'em',
                        'h1',
                        'h2',
                        'h3',
                        'h4',
                        'h5',
                        'h6',
                        'hr',
                        'i',
                        'ins',
                        'kbd',
                        'li',
                        'ol',
                        'p',
                        'pre',
                        'q',
                        'samp',
                        'small',
                        'span',
                        'strong',
                        'sub',
                        'sup',
                        'table',
                        'tbody',
                        'td',
                        'tfoot',
                        'th',
                        'thead',
                        'tr',
                        'tt',
                        'ul',
                        'var',
                    ]);
                    $new_node = $rss_dom->createCDATASection($html_markup);
                    $node->replaceChild($new_node, $node->firstChild);
                }
            }
        }
        return $rss_dom->saveXML();
    }
    
    /**
     * {@inheritdoc}
     */
    public static function getSubscribedEvents() : array {
        // This should run after any other response subscriber that modifies the
        // markup.
        // @see \Drupal\Core\EventSubscriber\RssResponseRelativeUrlFilter
        $events[KernelEvents::RESPONSE][] = [
            'onResponse',
            -513,
        ];
        return $events;
    }

}