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<?php
namespace Drupal\big_pipe\Render\Placeholder;
use Drupal\Component\Utility\Html;
use Drupal\Component\Utility\UrlHelper;
use Drupal\Core\Render\Placeholder\PlaceholderStrategyInterface;
use Drupal\Core\Routing\RouteMatchInterface;
use Drupal\Core\Session\SessionConfigurationInterface;
use Symfony\Component\HttpFoundation\RequestStack;
/**
* 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.
*
* @see \Drupal\big_pipe\Render\BigPipeInterface
*/
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->isMethodSafe()) {
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)) {
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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 => $placeholder_elements) {
// BigPipe uses JavaScript and the DOM to find the placeholder to replace.
// This means finding the placeholder to replace must be efficient. Most
// placeholders are HTML, which we can find efficiently thanks to the
// querySelector API. But some placeholders are HTML attribute values or
// parts thereof, and potentially even plain text in DOM text nodes. For
// BigPipe's JavaScript to find those placeholders, it would need to
// iterate over all DOM text nodes. This is highly inefficient. Therefore,
// the BigPipe placeholder strategy only converts HTML placeholders into
// BigPipe placeholders. The other placeholders need to be replaced on the
// server, not via BigPipe.
// @see \Drupal\Core\Access\RouteProcessorCsrf::renderPlaceholderCsrfToken()
// @see \Drupal\Core\Form\FormBuilder::renderFormTokenPlaceholder()
// @see \Drupal\Core\Form\FormBuilder::renderPlaceholderFormAction()
if ($placeholder[0] !== '<' || $placeholder !== Html::normalize($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;
}
/**
* 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, $placeholder_render_array);
return [
'#markup' => '<div data-big-pipe-placeholder-id="' . Html::escape($big_pipe_placeholder_id) . '"></div>',
'#cache' => [
'max-age' => 0,
'contexts' => [
'session.exists',
],
],
'#attached' => [
'library' => [
'big_pipe/big_pipe',
],
// Inform BigPipe' JavaScript known BigPipe placeholder IDs (a whitelist).
'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) {
$big_pipe_placeholder = '<div data-big-pipe-nojs-placeholder-id="' . Html::escape(static::generateBigPipePlaceholderId($original_placeholder, $placeholder_render_array)) . '"></div>';
}
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];
$token = hash('crc32b', serialize($placeholder_render_array));
return UrlHelper::buildQuery(['callback' => $callback, 'args' => $arguments, 'token' => $token]);
}
// When the placeholder's render array is not using a #lazy_builder,
// anything could be in there: only #lazy_builder has a strict contract that
// allows us to create a more sane selector. Therefore, simply the original
// placeholder into a usable placeholder ID, at the cost of it being obtuse.
else {
return Html::getId($original_placeholder);
}
}
}