class BigPipeStrategy in Drupal 8

Defines the BigPipe placeholder strategy, to send HTML in chunks.

First: the BigPipe placeholder strategy only activates if the current request is associated with a session. Without a session, it is assumed this response is not actually dynamic: if none of the placeholders show session-dependent information, then none of the placeholders are uncacheable or poorly cacheable, which means the Page Cache (for anonymous users) can deal with it. In other words: BigPipe works for all authenticated users and for anonymous users that have a session (typical example: a shopping cart).

(This is the default, and other modules can subclass this placeholder strategy to have different rules for enabling BigPipe.)

The BigPipe placeholder strategy actually consists of two substrategies, depending on whether the current session is in a browser with JavaScript enabled or not: 1. with JavaScript enabled: #attached[big_pipe_js_placeholders]. Their replacements are streamed at the end of the page: chunk 1 is the entire page until the closing </body> tag, chunks 2 to (N-1) are replacement values for the placeholders, chunk N is </body> and everything after it. 2. with JavaScript disabled: #attached[big_pipe_nojs_placeholders]. Their replacements are streamed in situ: chunk 1 is the entire page until the first no-JS BigPipe placeholder, chunk 2 is the replacement for that placeholder, chunk 3 is the chunk from after that placeholder until the next no-JS BigPipe placeholder, et cetera.

JS BigPipe placeholders are preferred because they result in better perceived performance: the entire page can be sent, minus the placeholders. But it requires JavaScript.

No-JS BigPipe placeholders result in more visible blocking: only the part of the page can be sent until the first placeholder, after it is rendered until the second, et cetera. (In essence: multiple flushes.)

Finally, both of those substrategies can also be combined: some placeholders live in places that cannot be efficiently replaced by JavaScript, for example CSRF tokens in URLs. Using no-JS BigPipe placeholders in those cases allows the first part of the page (until the first no-JS BigPipe placeholder) to be sent sooner than when they would be replaced using SingleFlushStrategy, which would prevent anything from being sent until all those non-HTML placeholders would have been replaced.

See \Drupal\big_pipe\Render\BigPipe for detailed documentation on how those different placeholders are actually replaced.

Hierarchy

• class \Drupal\big_pipe\Render\Placeholder\BigPipeStrategy implements PlaceholderStrategyInterface

See also

\Drupal\big_pipe\Render\BigPipe

4 files declare their use of BigPipeStrategy

BigPipeController.php in core/modules/big_pipe/src/Controller/BigPipeController.php

BigPipeStrategyTest.php in core/modules/big_pipe/tests/src/Unit/Render/Placeholder/BigPipeStrategyTest.php

BigPipeTest.php in core/modules/big_pipe/tests/src/Functional/BigPipeTest.php

big_pipe.module in core/modules/big_pipe/big_pipe.module

Adds BigPipe no-JS detection.

1 string reference to 'BigPipeStrategy'

big_pipe.services.yml in core/modules/big_pipe/big_pipe.services.yml

core/modules/big_pipe/big_pipe.services.yml

1 service uses BigPipeStrategy

placeholder_strategy.big_pipe in core/modules/big_pipe/big_pipe.services.yml

Drupal\big_pipe\Render\Placeholder\BigPipeStrategy

File

core/modules/big_pipe/src/Render/Placeholder/BigPipeStrategy.php, line 61

Namespace

Drupal\big_pipe\Render\Placeholder

class BigPipeStrategy implements PlaceholderStrategyInterface {

  /**
   * BigPipe no-JS cookie name.
   */
  const NOJS_COOKIE = 'big_pipe_nojs';

  /**
   * The session configuration.
   *
   * @var \Drupal\Core\Session\SessionConfigurationInterface
   */
  protected $sessionConfiguration;

  /**
   * The request stack.
   *
   * @var \Symfony\Component\HttpFoundation\RequestStack
   */
  protected $requestStack;

  /**
   * The current route match.
   *
   * @var \Drupal\Core\Routing\RouteMatchInterface
   */
  protected $routeMatch;

  /**
   * Constructs a new BigPipeStrategy class.
   *
   * @param \Drupal\Core\Session\SessionConfigurationInterface $session_configuration
   *   The session configuration.
   * @param \Symfony\Component\HttpFoundation\RequestStack $request_stack
   *   The request stack.
   * @param \Drupal\Core\Routing\RouteMatchInterface $route_match
   *   The current route match.
   */
  public function __construct(SessionConfigurationInterface $session_configuration, RequestStack $request_stack, RouteMatchInterface $route_match) {
    $this->sessionConfiguration = $session_configuration;
    $this->requestStack = $request_stack;
    $this->routeMatch = $route_match;
  }

  /**
   * {@inheritdoc}
   */
  public function processPlaceholders(array $placeholders) {
    $request = $this->requestStack
      ->getCurrentRequest();

    // @todo remove this check when https://www.drupal.org/node/2367555 lands.
    if (!$request
      ->isMethodCacheable()) {
      return [];
    }

    // Routes can opt out from using the BigPipe HTML delivery technique.
    if ($this->routeMatch
      ->getRouteObject()
      ->getOption('_no_big_pipe')) {
      return [];
    }
    if (!$this->sessionConfiguration
      ->hasSession($request)) {
      return [];
    }
    return $this
      ->doProcessPlaceholders($placeholders);
  }

  /**
   * Transforms placeholders to BigPipe placeholders, either no-JS or JS.
   *
   * @param array $placeholders
   *   The placeholders to process.
   *
   * @return array
   *   The BigPipe placeholders.
   */
  protected function doProcessPlaceholders(array $placeholders) {
    $overridden_placeholders = [];
    foreach ($placeholders as $placeholder => $placeholder_elements) {

      // BigPipe uses JavaScript and the DOM to find the placeholder to replace.
      // This means finding the placeholder to replace must be efficient. Most
      // placeholders are HTML, which we can find efficiently thanks to the
      // querySelector API. But some placeholders are HTML attribute values or
      // parts thereof, and potentially even plain text in DOM text nodes. For
      // BigPipe's JavaScript to find those placeholders, it would need to
      // iterate over all DOM text nodes. This is highly inefficient. Therefore,
      // the BigPipe placeholder strategy only converts HTML placeholders into
      // BigPipe placeholders. The other placeholders need to be replaced on the
      // server, not via BigPipe.
      // @see \Drupal\Core\Access\RouteProcessorCsrf::renderPlaceholderCsrfToken()
      // @see \Drupal\Core\Form\FormBuilder::renderFormTokenPlaceholder()
      // @see \Drupal\Core\Form\FormBuilder::renderPlaceholderFormAction()
      if (static::placeholderIsAttributeSafe($placeholder)) {
        $overridden_placeholders[$placeholder] = static::createBigPipeNoJsPlaceholder($placeholder, $placeholder_elements, TRUE);
      }
      else {

        // If the current request/session doesn't have JavaScript, fall back to
        // no-JS BigPipe.
        if ($this->requestStack
          ->getCurrentRequest()->cookies
          ->has(static::NOJS_COOKIE)) {
          $overridden_placeholders[$placeholder] = static::createBigPipeNoJsPlaceholder($placeholder, $placeholder_elements, FALSE);
        }
        else {
          $overridden_placeholders[$placeholder] = static::createBigPipeJsPlaceholder($placeholder, $placeholder_elements);
        }
        $overridden_placeholders[$placeholder]['#cache']['contexts'][] = 'cookies:' . static::NOJS_COOKIE;
      }
    }
    return $overridden_placeholders;
  }

  /**
   * Determines whether the given placeholder is attribute-safe or not.
   *
   * @param string $placeholder
   *   A placeholder.
   *
   * @return bool
   *   Whether the placeholder is safe for use in a HTML attribute (in case it's
   *   a placeholder for a HTML attribute value or a subset of it).
   */
  protected static function placeholderIsAttributeSafe($placeholder) {
    assert(is_string($placeholder));
    return $placeholder[0] !== '<' || $placeholder !== Html::normalize($placeholder);
  }

  /**
   * Creates a BigPipe JS placeholder.
   *
   * @param string $original_placeholder
   *   The original placeholder.
   * @param array $placeholder_render_array
   *   The render array for a placeholder.
   *
   * @return array
   *   The resulting BigPipe JS placeholder render array.
   */
  protected static function createBigPipeJsPlaceholder($original_placeholder, array $placeholder_render_array) {
    $big_pipe_placeholder_id = static::generateBigPipePlaceholderId($original_placeholder, $placeholder_render_array);
    return [
      '#markup' => '<span data-big-pipe-placeholder-id="' . Html::escape($big_pipe_placeholder_id) . '"></span>',
      '#cache' => [
        'max-age' => 0,
        'contexts' => [
          'session.exists',
        ],
      ],
      '#attached' => [
        'library' => [
          'big_pipe/big_pipe',
        ],
        // Inform BigPipe' JavaScript known BigPipe placeholder IDs.
        'drupalSettings' => [
          'bigPipePlaceholderIds' => [
            $big_pipe_placeholder_id => TRUE,
          ],
        ],
        'big_pipe_placeholders' => [
          Html::escape($big_pipe_placeholder_id) => $placeholder_render_array,
        ],
      ],
    ];
  }

  /**
   * Creates a BigPipe no-JS placeholder.
   *
   * @param string $original_placeholder
   *   The original placeholder.
   * @param array $placeholder_render_array
   *   The render array for a placeholder.
   * @param bool $placeholder_must_be_attribute_safe
   *   Whether the placeholder must be safe for use in a HTML attribute (in case
   *   it's a placeholder for a HTML attribute value or a subset of it).
   *
   * @return array
   *   The resulting BigPipe no-JS placeholder render array.
   */
  protected static function createBigPipeNoJsPlaceholder($original_placeholder, array $placeholder_render_array, $placeholder_must_be_attribute_safe = FALSE) {
    if (!$placeholder_must_be_attribute_safe) {
      $big_pipe_placeholder = '<span data-big-pipe-nojs-placeholder-id="' . Html::escape(static::generateBigPipePlaceholderId($original_placeholder, $placeholder_render_array)) . '"></span>';
    }
    else {
      $big_pipe_placeholder = 'big_pipe_nojs_placeholder_attribute_safe:' . Html::escape($original_placeholder);
    }
    return [
      '#markup' => $big_pipe_placeholder,
      '#cache' => [
        'max-age' => 0,
        'contexts' => [
          'session.exists',
        ],
      ],
      '#attached' => [
        'big_pipe_nojs_placeholders' => [
          $big_pipe_placeholder => $placeholder_render_array,
        ],
      ],
    ];
  }

  /**
   * Generates a BigPipe placeholder ID.
   *
   * @param string $original_placeholder
   *   The original placeholder.
   * @param array $placeholder_render_array
   *   The render array for a placeholder.
   *
   * @return string
   *   The generated BigPipe placeholder ID.
   */
  protected static function generateBigPipePlaceholderId($original_placeholder, array $placeholder_render_array) {

    // Generate a BigPipe placeholder ID (to be used by BigPipe's JavaScript).
    // @see \Drupal\Core\Render\PlaceholderGenerator::createPlaceholder()
    if (isset($placeholder_render_array['#lazy_builder'])) {
      $callback = $placeholder_render_array['#lazy_builder'][0];
      $arguments = $placeholder_render_array['#lazy_builder'][1];
      $token = Crypt::hashBase64(serialize($placeholder_render_array));
      return UrlHelper::buildQuery([
        'callback' => $callback,
        'args' => $arguments,
        'token' => $token,
      ]);
    }
    else {
      return Html::getId($original_placeholder);
    }
  }

}

Members

Name	Modifiers	Type	Description	Overrides
BigPipeStrategy::$requestStack	protected	property	The request stack.
BigPipeStrategy::$routeMatch	protected	property	The current route match.
BigPipeStrategy::$sessionConfiguration	protected	property	The session configuration.
BigPipeStrategy::createBigPipeJsPlaceholder	protected static	function	Creates a BigPipe JS placeholder.
BigPipeStrategy::createBigPipeNoJsPlaceholder	protected static	function	Creates a BigPipe no-JS placeholder.
BigPipeStrategy::doProcessPlaceholders	protected	function	Transforms placeholders to BigPipe placeholders, either no-JS or JS.
BigPipeStrategy::generateBigPipePlaceholderId	protected static	function	Generates a BigPipe placeholder ID.
BigPipeStrategy::NOJS_COOKIE		constant	BigPipe no-JS cookie name.
BigPipeStrategy::placeholderIsAttributeSafe	protected static	function	Determines whether the given placeholder is attribute-safe or not.
BigPipeStrategy::processPlaceholders	public	function	Processes placeholders to render them with different strategies. Overrides PlaceholderStrategyInterface::processPlaceholders
BigPipeStrategy::__construct	public	function	Constructs a new BigPipeStrategy class.