ChainRequestPolicy.php

<?php

namespace Drupal\Core\PageCache;

use Symfony\Component\HttpFoundation\Request;

/**
 * Implements a compound request policy.
 *
 * When evaluating the compound policy, all of the contained rules are applied
 * to the request. The overall result is computed according to the following
 * rules:
 *
 * <ol>
 *   <li>Returns static::DENY if any of the rules evaluated to static::DENY</li>
 *   <li>Returns static::ALLOW if at least one of the rules evaluated to
 *       static::ALLOW and none to static::DENY</li>
 *   <li>Otherwise returns NULL</li>
 * </ol>
 */
class ChainRequestPolicy implements ChainRequestPolicyInterface {
    
    /**
     * A list of policy rules to apply when this policy is evaluated.
     *
     * @var \Drupal\Core\PageCache\RequestPolicyInterface[]
     */
    protected $rules = [];
    
    /**
     * {@inheritdoc}
     */
    public function check(Request $request) {
        $final_result = NULL;
        foreach ($this->rules as $rule) {
            $result = $rule->check($request);
            if ($result === static::DENY) {
                return $result;
            }
            elseif ($result === static::ALLOW) {
                $final_result = $result;
            }
            elseif (isset($result)) {
                throw new \UnexpectedValueException('Return value of RequestPolicyInterface::check() must be one of RequestPolicyInterface::ALLOW, RequestPolicyInterface::DENY or NULL');
            }
        }
        return $final_result;
    }
    
    /**
     * {@inheritdoc}
     */
    public function addPolicy(RequestPolicyInterface $policy) {
        $this->rules[] = $policy;
        return $this;
    }

}