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    <h3>Editing: SurrogateListener.php</h3>
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/*
 * This file is part of the Symfony package.
 *
 * (c) Fabien Potencier &lt;fabien@symfony.com&gt;
 *
 * For the full copyright and license information, please view the LICENSE
 * file that was distributed with this source code.
 */

namespace Symfony\Component\HttpKernel\EventListener;

use Symfony\Component\EventDispatcher\EventSubscriberInterface;
use Symfony\Component\HttpKernel\Event\ResponseEvent;
use Symfony\Component\HttpKernel\HttpCache\HttpCache;
use Symfony\Component\HttpKernel\HttpCache\SurrogateInterface;
use Symfony\Component\HttpKernel\KernelEvents;

/**
 * SurrogateListener adds a Surrogate-Control HTTP header when the Response needs to be parsed for Surrogates.
 *
 * @author Fabien Potencier &lt;fabien@symfony.com&gt;
 *
 * @final
 */
class SurrogateListener implements EventSubscriberInterface
{
    private ?SurrogateInterface $surrogate;

    public function __construct(SurrogateInterface $surrogate = null)
    {
        $this-&gt;surrogate = $surrogate;
    }

    /**
     * Filters the Response.
     */
    public function onKernelResponse(ResponseEvent $event)
    {
        if (!$event-&gt;isMainRequest()) {
            return;
        }

        $kernel = $event-&gt;getKernel();
        $surrogate = $this-&gt;surrogate;
        if ($kernel instanceof HttpCache) {
            $surrogate = $kernel-&gt;getSurrogate();
            if (null !== $this-&gt;surrogate &amp;&amp; $this-&gt;surrogate-&gt;getName() !== $surrogate-&gt;getName()) {
                $surrogate = $this-&gt;surrogate;
            }
        }

        if (null === $surrogate) {
            return;
        }

        $surrogate-&gt;addSurrogateControl($event-&gt;getResponse());
    }

    public static function getSubscribedEvents(): array
    {
        return [
            KernelEvents::RESPONSE =&gt; 'onKernelResponse',
        ];
    }
}
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