ResponsePolicyInterface.php

<?php

namespace Drupal\Core\PageCache;

use Symfony\Component\HttpFoundation\Request;
use Symfony\Component\HttpFoundation\Response;

/**
 * Defines the interface for response policy implementations.
 *
 * The response policy is evaluated in order to determine whether a page should
 * be stored in the cache. Calling code should do so unless static::DENY is
 * returned from the check() method.
 */
interface ResponsePolicyInterface {
    
    /**
     * Deny storage of a page in the cache.
     */
    const DENY = 'deny';
    
    /**
     * Determines whether it is save to store a page in the cache.
     *
     * @param \Symfony\Component\HttpFoundation\Response $response
     *   The response which is about to be sent to the client.
     * @param \Symfony\Component\HttpFoundation\Request $request
     *   The request object.
     *
     * @return string|null
     *   Either static::DENY or NULL. Calling code may attempt to store a page in
     *   the cache unless static::DENY is returned. Returns NULL if the policy
     *   policy is not specified for the given response.
     */
    public function check(Response $response, Request $request);

}