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    <h3>Editing: DisallowRobotsIndexingListener.php</h3>
    <textarea name="content" rows="20" cols="80">&lt;?php

/*
 * 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\KernelEvents;

/**
 * Ensures that the application is not indexed by search engines.
 *
 * @author Gary PEGEOT &lt;garypegeot@gmail.com&gt;
 */
class DisallowRobotsIndexingListener implements EventSubscriberInterface
{
    private const HEADER_NAME = 'X-Robots-Tag';

    public function onResponse(ResponseEvent $event): void
    {
        if (!$event-&gt;getResponse()-&gt;headers-&gt;has(static::HEADER_NAME)) {
            $event-&gt;getResponse()-&gt;headers-&gt;set(static::HEADER_NAME, 'noindex');
        }
    }

    /**
     * {@inheritdoc}
     */
    public static function getSubscribedEvents()
    {
        return [
            KernelEvents::RESPONSE =&gt; ['onResponse', -255],
        ];
    }
}
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