class StackedKernelPass in Drupal 8

Provides a compiler pass for stacked HTTP kernels.

Builds the HTTP kernel by collecting all services tagged 'http_middleware' and assembling them into a StackedKernel. The middleware with the highest priority ends up as the outermost while the lowest priority middleware wraps the actual HTTP kernel defined by the http_kernel.basic service.

The 'http_middleware' service tag additionally accepts a 'responder' parameter. It should be set to TRUE if many or most requests will be handled directly by the middleware. Any underlying middleware and the HTTP kernel are then flagged as 'lazy'. As a result those low priority services and their dependencies are only initialized if the 'responder' middleware fails to generate a response and the request is delegated to the underlying kernel.

In general middlewares should not have heavy dependencies. This is especially important for high-priority services which need to run before the internal page cache.

An example of a high priority middleware.

http_middleware.reverse_proxy:
  class: Drupal\Core\StackMiddleware\ReverseProxyMiddleware
  arguments: ['@settings']
  tags:
    - { name: http_middleware, priority: 300 }

An example of a responder middleware:

http_middleware.page_cache:
  class: Drupal\page_cache\StackMiddleware\PageCache
  arguments: ['@cache.render', '@page_cache_request_policy', '@page_cache_response_policy']
  tags:
    - { name: http_middleware, priority: 200, responder: true }

Hierarchy

• class \Drupal\Core\DependencyInjection\Compiler\StackedKernelPass implements \Symfony\Component\DependencyInjection\Compiler\CompilerPassInterface

See also

\Stack\Builder

2 files declare their use of StackedKernelPass

CoreServiceProvider.php in core/lib/Drupal/Core/CoreServiceProvider.php

StackedKernelPassTest.php in core/tests/Drupal/Tests/Core/DependencyInjection/Compiler/StackedKernelPassTest.php

File

core/lib/Drupal/Core/DependencyInjection/Compiler/StackedKernelPass.php, line 48

Namespace

Drupal\Core\DependencyInjection\Compiler

class StackedKernelPass implements CompilerPassInterface {

  /**
   * {@inheritdoc}
   */
  public function process(ContainerBuilder $container) {
    if (!$container
      ->hasDefinition('http_kernel')) {
      return;
    }
    $stacked_kernel = $container
      ->getDefinition('http_kernel');

    // Return now if this is not a stacked kernel.
    if ($stacked_kernel
      ->getClass() !== 'Stack\\StackedHttpKernel') {
      return;
    }
    $middlewares = [];
    $priorities = [];
    $responders = [];
    foreach ($container
      ->findTaggedServiceIds('http_middleware') as $id => $attributes) {
      $priorities[$id] = isset($attributes[0]['priority']) ? $attributes[0]['priority'] : 0;
      $middlewares[$id] = $container
        ->getDefinition($id);
      $responders[$id] = !empty($attributes[0]['responder']);
    }
    array_multisort($priorities, SORT_ASC, $middlewares, $responders);
    $decorated_id = 'http_kernel.basic';
    $middlewares_param = [
      new Reference($decorated_id),
    ];
    $first_responder = array_search(TRUE, array_reverse($responders, TRUE), TRUE);
    if ($first_responder) {
      $container
        ->getDefinition($decorated_id)
        ->setLazy(TRUE);
    }
    foreach ($middlewares as $id => $decorator) {

      // Prepend a reference to the middlewares container parameter.
      array_unshift($middlewares_param, new Reference($id));

      // Prepend the inner kernel as first constructor argument.
      $arguments = $decorator
        ->getArguments();
      array_unshift($arguments, new Reference($decorated_id));
      $decorator
        ->setArguments($arguments);
      if ($first_responder === $id) {
        $first_responder = FALSE;
      }
      elseif ($first_responder) {
        $decorator
          ->setLazy(TRUE);
      }
      $decorated_id = $id;
    }
    $arguments = [
      $middlewares_param[0],
      $middlewares_param,
    ];
    $stacked_kernel
      ->setArguments($arguments);
  }

}

Members

Name	Modifiers	Type	Description	Overrides
StackedKernelPass::process	public	function	You can modify the container here before it is dumped to PHP code.