PageCache.php

<?php

namespace Drupal\page_cache\StackMiddleware;

use Drupal\Core\Cache\Cache;
use Drupal\Core\Cache\CacheableResponseInterface;
use Drupal\Core\Cache\CacheBackendInterface;
use Drupal\Core\PageCache\RequestPolicyInterface;
use Drupal\Core\PageCache\ResponsePolicyInterface;
use Drupal\Core\Site\Settings;
use Symfony\Component\HttpFoundation\BinaryFileResponse;
use Symfony\Component\HttpFoundation\Request;
use Symfony\Component\HttpFoundation\Response;
use Symfony\Component\HttpFoundation\StreamedResponse;
use Symfony\Component\HttpKernel\HttpKernelInterface;

/**
 * Executes the page caching before the main kernel takes over the request.
 */
class PageCache implements HttpKernelInterface {

  /**
   * The wrapped HTTP kernel.
   *
   * @var \Symfony\Component\HttpKernel\HttpKernelInterface
   */
  protected $httpKernel;

  /**
   * The cache bin.
   *
   * @var \Drupal\Core\Cache\CacheBackendInterface
   */
  protected $cache;

  /**
   * A policy rule determining the cacheability of a request.
   *
   * @var \Drupal\Core\PageCache\RequestPolicyInterface
   */
  protected $requestPolicy;

  /**
   * A policy rule determining the cacheability of the response.
   *
   * @var \Drupal\Core\PageCache\ResponsePolicyInterface
   */
  protected $responsePolicy;

  /**
   * The cache ID for the (master) request.
   *
   * @var string
   */
  protected $cid;

  /**
   * Constructs a PageCache object.
   *
   * @param \Symfony\Component\HttpKernel\HttpKernelInterface $http_kernel
   *   The decorated kernel.
   * @param \Drupal\Core\Cache\CacheBackendInterface $cache
   *   The cache bin.
   * @param \Drupal\Core\PageCache\RequestPolicyInterface $request_policy
   *   A policy rule determining the cacheability of a request.
   * @param \Drupal\Core\PageCache\ResponsePolicyInterface $response_policy
   *   A policy rule determining the cacheability of the response.
   */
  public function __construct(HttpKernelInterface $http_kernel, CacheBackendInterface $cache, RequestPolicyInterface $request_policy, ResponsePolicyInterface $response_policy) {
    $this->httpKernel = $http_kernel;