Chris@0: <?php
Chris@0: 
Chris@0: namespace Drupal\Core\Render;
Chris@0: 
Chris@0: use Drupal\Core\Cache\CacheFactoryInterface;
Chris@0: use Drupal\Core\Cache\Context\CacheContextsManager;
Chris@0: use Symfony\Component\HttpFoundation\RequestStack;
Chris@0: 
Chris@0: /**
Chris@0:  * Adds automatic placeholdering to the RenderCache.
Chris@0:  *
Chris@0:  * This automatic placeholdering is performed to ensure the containing elements
Chris@0:  * and overarching response are as cacheable as possible. Elements whose subtree
Chris@0:  * bubble either max-age=0 or high-cardinality cache contexts (such as 'user'
Chris@0:  * and 'session') are considered poorly cacheable.
Chris@0:  *
Chris@0:  * @see sites/default/default.services.yml
Chris@0:  *
Chris@0:  * Automatic placeholdering is performed only on elements whose subtree was
Chris@0:  * generated using a #lazy_builder callback and whose bubbled cacheability meets
Chris@0:  * the auto-placeholdering conditions as configured in the renderer.config
Chris@0:  * container parameter.
Chris@0:  *
Chris@0:  * This RenderCache implementation automatically replaces an element with a
Chris@0:  * placeholder:
Chris@0:  * - on render cache hit, i.e. ::get()
Chris@0:  * - on render cache miss, i.e. ::set() (in subsequent requests, it will be a
Chris@0:  *   cache hit)
Chris@0:  *
Chris@0:  * In either case, the render cache is guaranteed to contain the to-be-rendered
Chris@0:  * placeholder, so replacing (rendering) the placeholder will be very fast.
Chris@0:  *
Chris@0:  * Finally, in case the render cache item disappears between the time it is
Chris@0:  * decided to automatically placeholder the element and the time where the
Chris@0:  * placeholder is replaced (rendered), that is guaranteed to not be problematic.
Chris@0:  * Because this only automatically placeholders elements that have a
Chris@0:  * #lazy_builder callback set, which means that in the worst case, it will need
Chris@0:  * to be re-rendered.
Chris@0:  */
Chris@0: class PlaceholderingRenderCache extends RenderCache {
Chris@0: 
Chris@0:   /**
Chris@0:    * The placeholder generator.
Chris@0:    *
Chris@0:    * @var \Drupal\Core\Render\PlaceholderGeneratorInterface
Chris@0:    */
Chris@0:   protected $placeholderGenerator;
Chris@0: 
Chris@0:   /**
Chris@0:    * Stores rendered results for automatically placeholdered elements.
Chris@0:    *
Chris@0:    * This allows us to avoid talking to the cache twice per auto-placeholdered
Chris@0:    * element, or in case of an uncacheable element, to render it twice.
Chris@0:    *
Chris@0:    * Scenario A. The double cache read would happen because:
Chris@0:    * 1. when rendering, cache read, but auto-placeholdered
Chris@0:    * 2. when rendering placeholders, again cache read
Chris@0:    *
Chris@0:    * Scenario B. The cache write plus read would happen because:
Chris@0:    * 1. when rendering, cache write, but auto-placeholdered
Chris@0:    * 2. when rendering placeholders, cache read
Chris@0:    *
Chris@0:    * Scenario C. The double rendering for an uncacheable element would happen because:
Chris@0:    * 1. when rendering, not cacheable, but auto-placeholdered
Chris@0:    * 2. when rendering placeholders, rendered again
Chris@0:    *
Chris@0:    * In all three scenarios, this static cache avoids the second step, thus
Chris@0:    * avoiding expensive work.
Chris@0:    *
Chris@0:    * @var array
Chris@0:    */
Chris@0:   protected $placeholderResultsCache = [];
Chris@0: 
Chris@0:   /**
Chris@0:    * Constructs a new PlaceholderingRenderCache object.
Chris@0:    *
Chris@0:    * @param \Symfony\Component\HttpFoundation\RequestStack $request_stack
Chris@0:    *   The request stack.
Chris@0:    * @param \Drupal\Core\Cache\CacheFactoryInterface $cache_factory
Chris@0:    *   The cache factory.
Chris@0:    * @param \Drupal\Core\Cache\Context\CacheContextsManager $cache_contexts_manager
Chris@0:    *   The cache contexts manager.
Chris@0:    * @param \Drupal\Core\Render\PlaceholderGeneratorInterface $placeholder_generator
Chris@0:    *   The placeholder generator.
Chris@0:    */
Chris@0:   public function __construct(RequestStack $request_stack, CacheFactoryInterface $cache_factory, CacheContextsManager $cache_contexts_manager, PlaceholderGeneratorInterface $placeholder_generator) {
Chris@0:     parent::__construct($request_stack, $cache_factory, $cache_contexts_manager);
Chris@0:     $this->placeholderGenerator = $placeholder_generator;
Chris@0:   }
Chris@0: 
Chris@0:   /**
Chris@0:    * {@inheritdoc}
Chris@0:    */
Chris@0:   public function get(array $elements) {
Chris@0:     // @todo remove this check when https://www.drupal.org/node/2367555 lands.
Chris@0:     if (!$this->requestStack->getCurrentRequest()->isMethodCacheable()) {
Chris@0:       return FALSE;
Chris@0:     }
Chris@0: 
Chris@0:     // When rendering placeholders, special case auto-placeholdered elements:
Chris@0:     // avoid retrieving them from cache again, or rendering them again.
Chris@0:     if (isset($elements['#create_placeholder']) && $elements['#create_placeholder'] === FALSE) {
Chris@0:       $cached_placeholder_result = $this->getFromPlaceholderResultsCache($elements);
Chris@0:       if ($cached_placeholder_result !== FALSE) {
Chris@0:         return $cached_placeholder_result;
Chris@0:       }
Chris@0:     }
Chris@0: 
Chris@0:     $cached_element = parent::get($elements);
Chris@0: 
Chris@0:     if ($cached_element === FALSE) {
Chris@0:       return FALSE;
Chris@0:     }
Chris@0:     else {
Chris@0:       if ($this->placeholderGenerator->canCreatePlaceholder($elements) && $this->placeholderGenerator->shouldAutomaticallyPlaceholder($cached_element)) {
Chris@0:         return $this->createPlaceholderAndRemember($cached_element, $elements);
Chris@0:       }
Chris@0: 
Chris@0:       return $cached_element;
Chris@0:     }
Chris@0:   }
Chris@0: 
Chris@0:   /**
Chris@0:    * {@inheritdoc}
Chris@0:    */
Chris@0:   public function set(array &$elements, array $pre_bubbling_elements) {
Chris@0:     $result = parent::set($elements, $pre_bubbling_elements);
Chris@0: 
Chris@0:     // @todo remove this check when https://www.drupal.org/node/2367555 lands.
Chris@0:     if (!$this->requestStack->getCurrentRequest()->isMethodCacheable()) {
Chris@0:       return FALSE;
Chris@0:     }
Chris@0: 
Chris@0:     if ($this->placeholderGenerator->canCreatePlaceholder($pre_bubbling_elements) && $this->placeholderGenerator->shouldAutomaticallyPlaceholder($elements)) {
Chris@0:       // Overwrite $elements with a placeholder. The Renderer (which called this
Chris@0:       // method) will update the context with the bubbleable metadata of the
Chris@0:       // overwritten $elements.
Chris@0:       $elements = $this->createPlaceholderAndRemember($this->getCacheableRenderArray($elements), $pre_bubbling_elements);
Chris@0:     }
Chris@0: 
Chris@0:     return $result;
Chris@0:   }
Chris@0: 
Chris@0:   /**
Chris@0:    * Create a placeholder for a renderable array and remember in a static cache.
Chris@0:    *
Chris@0:    * @param array $rendered_elements
Chris@0:    *   A fully rendered renderable array.
Chris@0:    * @param array $pre_bubbling_elements
Chris@0:    *   A renderable array corresponding to the state (in particular, the
Chris@0:    *   cacheability metadata) of $rendered_elements prior to the beginning of
Chris@0:    *   its rendering process, and therefore before any bubbling of child
Chris@0:    *   information has taken place. Only the #cache property is used by this
Chris@0:    *   function, so the caller may omit all other properties and children from
Chris@0:    *   this array.
Chris@0:    *
Chris@0:    * @return array
Chris@0:    *   Renderable array with placeholder markup and the attached placeholder
Chris@0:    *   replacement metadata.
Chris@0:    */
Chris@0:   protected function createPlaceholderAndRemember(array $rendered_elements, array $pre_bubbling_elements) {
Chris@0:     $placeholder_element = $this->placeholderGenerator->createPlaceholder($pre_bubbling_elements);
Chris@0:     // Remember the result for this placeholder to avoid double work.
Chris@0:     $placeholder = (string) $placeholder_element['#markup'];
Chris@0:     $this->placeholderResultsCache[$placeholder] = $rendered_elements;
Chris@0:     return $placeholder_element;
Chris@0:   }
Chris@0: 
Chris@0:   /**
Chris@0:    * Retrieves an auto-placeholdered renderable array from the static cache.
Chris@0:    *
Chris@0:    * @param array $elements
Chris@0:    *   A renderable array.
Chris@0:    *
Chris@0:    * @return array|false
Chris@0:    *   A renderable array, with the original element and all its children pre-
Chris@0:    *   rendered, or FALSE if no cached copy of the element is available.
Chris@0:    */
Chris@0:   protected function getFromPlaceholderResultsCache(array $elements) {
Chris@0:     $placeholder_element = $this->placeholderGenerator->createPlaceholder($elements);
Chris@0:     $placeholder = (string) $placeholder_element['#markup'];
Chris@0:     if (isset($this->placeholderResultsCache[$placeholder])) {
Chris@0:       return $this->placeholderResultsCache[$placeholder];
Chris@0:     }
Chris@0:     return FALSE;
Chris@0:   }
Chris@0: 
Chris@0: }