BigPipe.php in Drupal 8
Same filename and directory in other branches
Namespace
Drupal\big_pipe\RenderFile
core/modules/big_pipe/src/Render/BigPipe.phpView source
<?php
namespace Drupal\big_pipe\Render;
use Drupal\Component\Utility\Crypt;
use Drupal\Component\Utility\Html;
use Drupal\Core\Ajax\AjaxResponse;
use Drupal\Core\Ajax\ReplaceCommand;
use Drupal\Core\Asset\AttachedAssets;
use Drupal\Core\Asset\AttachedAssetsInterface;
use Drupal\Core\Config\ConfigFactoryInterface;
use Drupal\Core\Render\HtmlResponse;
use Drupal\Core\Render\RendererInterface;
use Symfony\Component\EventDispatcher\EventDispatcherInterface;
use Symfony\Component\HttpFoundation\Request;
use Symfony\Component\HttpFoundation\RequestStack;
use Symfony\Component\HttpFoundation\Response;
use Symfony\Component\HttpFoundation\Session\SessionInterface;
use Symfony\Component\HttpKernel\Event\FilterResponseEvent;
use Symfony\Component\HttpKernel\HttpKernelInterface;
use Symfony\Component\HttpKernel\KernelEvents;
/**
* Service for sending an HTML response in chunks (to get faster page loads).
*
* At a high level, BigPipe sends a HTML response in chunks:
* 1. one chunk: everything until just before </body> — this contains BigPipe
* placeholders for the personalized parts of the page. Hence this sends the
* non-personalized parts of the page. Let's call it The Skeleton.
* 2. N chunks: a <script> tag per BigPipe placeholder in The Skeleton.
* 3. one chunk: </body> and everything after it.
*
* This is conceptually identical to Facebook's BigPipe (hence the name).
*
* @see https://www.facebook.com/notes/facebook-engineering/bigpipe-pipelining-web-pages-for-high-performance/389414033919
*
* The major way in which Drupal differs from Facebook's implementation (and
* others) is in its ability to automatically figure out which parts of the page
* can benefit from BigPipe-style delivery. Drupal's render system has the
* concept of "auto-placeholdering": content that is too dynamic is replaced
* with a placeholder that can then be rendered at a later time. On top of that,
* it also has the concept of "placeholder strategies": by default, placeholders
* are replaced on the server side and the response is blocked on all of them
* being replaced. But it's possible to add additional placeholder strategies.
* BigPipe is just another placeholder strategy. Others could be ESI, AJAX …
*
* @see https://www.drupal.org/developing/api/8/render/arrays/cacheability/auto-placeholdering
* @see \Drupal\Core\Render\PlaceholderGeneratorInterface::shouldAutomaticallyPlaceholder()
* @see \Drupal\Core\Render\Placeholder\PlaceholderStrategyInterface
* @see \Drupal\Core\Render\Placeholder\SingleFlushStrategy
* @see \Drupal\big_pipe\Render\Placeholder\BigPipeStrategy
*
* There is also one noteworthy technical addition that Drupal makes. BigPipe as
* described above, and as implemented by Facebook, can only work if JavaScript
* is enabled. The BigPipe module also makes it possible to replace placeholders
* using BigPipe in-situ, without JavaScript. This is not technically BigPipe at
* all; it's just the use of multiple flushes. Since it is able to reuse much of
* the logic though, we choose to call this "no-JS BigPipe".
*
* However, there is also a tangible benefit: some dynamic/expensive content is
* not HTML, but for example a HTML attribute value (or part thereof). It's not
* possible to efficiently replace such content using JavaScript, so "classic"
* BigPipe is out of the question. For example: CSRF tokens in URLs.
*
* This allows us to use both no-JS BigPipe and "classic" BigPipe in the same
* response to maximize the amount of content we can send as early as possible.
*
* Finally, a closer look at the implementation, and how it supports and reuses
* existing Drupal concepts:
* 1. BigPipe placeholders: 1 HtmlResponse + N embedded AjaxResponses.
* - Before a BigPipe response is sent, it is just a HTML response that
* contains BigPipe placeholders. Those placeholders look like
* <span data-big-pipe-placeholder-id="…"></span>. JavaScript is used to
* replace those placeholders.
* Therefore these placeholders are actually sent to the client.
* - The Skeleton of course has attachments, including most notably asset
* libraries. And those we track in drupalSettings.ajaxPageState.libraries —
* so that when we load new content through AJAX, we don't load the same
* asset libraries again. A HTML page can have multiple AJAX responses, each
* of which should take into account the combined AJAX page state of the
* HTML document and all preceding AJAX responses.
* - BigPipe does not make use of multiple AJAX requests/responses. It uses a
* single HTML response. But it is a more long-lived one: The Skeleton is
* sent first, the closing </body> tag is not yet sent, and the connection
* is kept open. Whenever another BigPipe Placeholder is rendered, Drupal
* sends (and so actually appends to the already-sent HTML) something like
* <script type="application/vnd.drupal-ajax">[{"command":"settings","settings":{…}}, {"command":…}.
* - So, for every BigPipe placeholder, we send such a <script
* type="application/vnd.drupal-ajax"> tag. And the contents of that tag is
* exactly like an AJAX response. The BigPipe module has JavaScript that
* listens for these and applies them. Let's call it an Embedded AJAX
* Response (since it is embedded in the HTML response). Now for the
* interesting bit: each of those Embedded AJAX Responses must also take
* into account the cumulative AJAX page state of the HTML document and all
* preceding Embedded AJAX responses.
* 2. No-JS BigPipe placeholders: 1 HtmlResponse + N embedded HtmlResponses.
* - Before a BigPipe response is sent, it is just a HTML response that
* contains no-JS BigPipe placeholders. Those placeholders can take two
* different forms:
* 1. <span data-big-pipe-nojs-placeholder-id="…"></span> if it's a
* placeholder that will be replaced by HTML
* 2. big_pipe_nojs_placeholder_attribute_safe:… if it's a placeholder
* inside a HTML attribute, in which 1. would be invalid (angle brackets
* are not allowed inside HTML attributes)
* No-JS BigPipe placeholders are not replaced using JavaScript, they must
* be replaced upon sending the BigPipe response. So, while the response is
* being sent, upon encountering these placeholders, their corresponding
* placeholder replacements are sent instead.
* Therefore these placeholders are never actually sent to the client.
* - See second bullet of point 1.
* - No-JS BigPipe does not use multiple AJAX requests/responses. It uses a
* single HTML response. But it is a more long-lived one: The Skeleton is
* split into multiple parts, the separators are where the no-JS BigPipe
* placeholders used to be. Whenever another no-JS BigPipe placeholder is
* rendered, Drupal sends (and so actually appends to the already-sent HTML)
* something like
* <link rel="stylesheet" …><script …><content>.
* - So, for every no-JS BigPipe placeholder, we send its associated CSS and
* header JS that has not already been sent (the bottom JS is not yet sent,
* so we can accumulate all of it and send it together at the end). This
* ensures that the markup is rendered as it was originally intended: its
* CSS and JS used to be blocking, and it still is. Let's call it an
* Embedded HTML response. Each of those Embedded HTML Responses must also
* take into account the cumulative AJAX page state of the HTML document and
* all preceding Embedded HTML responses.
* - Finally: any non-critical JavaScript associated with all Embedded HTML
* Responses, i.e. any footer/bottom/non-header JavaScript, is loaded after
* The Skeleton.
*
* Combining all of the above, when using both BigPipe placeholders and no-JS
* BigPipe placeholders, we therefore send: 1 HtmlResponse + M Embedded HTML
* Responses + N Embedded AJAX Responses. Schematically, we send these chunks:
* 1. Byte zero until 1st no-JS placeholder: headers + <html><head /><span>…</span>
* 2. 1st no-JS placeholder replacement: <link rel="stylesheet" …><script …><content>
* 3. Content until 2nd no-JS placeholder: <span>…</span>
* 4. 2nd no-JS placeholder replacement: <link rel="stylesheet" …><script …><content>
* 5. Content until 3rd no-JS placeholder: <span>…</span>
* 6. [… repeat until all no-JS placeholder replacements are sent …]
* 7. Send content after last no-JS placeholder.
* 8. Send script_bottom (markup to load bottom i.e. non-critical JS).
* 9. 1st placeholder replacement: <script type="application/vnd.drupal-ajax">[{"command":"settings","settings":{…}}, {"command":…}
* 10. 2nd placeholder replacement: <script type="application/vnd.drupal-ajax">[{"command":"settings","settings":{…}}, {"command":…}
* 11. [… repeat until all placeholder replacements are sent …]
* 12. Send </body> and everything after it.
* 13. Terminate request/response cycle.
*
* @see \Drupal\big_pipe\EventSubscriber\HtmlResponseBigPipeSubscriber
* @see \Drupal\big_pipe\Render\Placeholder\BigPipeStrategy
*/
class BigPipe {
/**
* The BigPipe placeholder replacements start signal.
*
* @var string
*/
const START_SIGNAL = '<script type="application/vnd.drupal-ajax" data-big-pipe-event="start"></script>';
/**
* The BigPipe placeholder replacements stop signal.
*
* @var string
*/
const STOP_SIGNAL = '<script type="application/vnd.drupal-ajax" data-big-pipe-event="stop"></script>';
/**
* The renderer.
*
* @var \Drupal\Core\Render\RendererInterface
*/
protected $renderer;
/**
* The session.
*
* @var \Symfony\Component\HttpFoundation\Session\SessionInterface
*/
protected $session;
/**
* The request stack.
*
* @var \Symfony\Component\HttpFoundation\RequestStack
*/
protected $requestStack;
/**
* The HTTP kernel.
*
* @var \Symfony\Component\HttpKernel\HttpKernelInterface
*/
protected $httpKernel;
/**
* The event dispatcher.
*
* @var \Symfony\Component\EventDispatcher\EventDispatcherInterface
*/
protected $eventDispatcher;
/**
* The config factory.
*
* @var \Drupal\Core\Config\ConfigFactoryInterface
*/
protected $configFactory;
/**
* Constructs a new BigPipe class.
*
* @param \Drupal\Core\Render\RendererInterface $renderer
* The renderer.
* @param \Symfony\Component\HttpFoundation\Session\SessionInterface $session
* The session.
* @param \Symfony\Component\HttpFoundation\RequestStack $request_stack
* The request stack.
* @param \Symfony\Component\HttpKernel\HttpKernelInterface $http_kernel
* The HTTP kernel.
* @param \Symfony\Component\EventDispatcher\EventDispatcherInterface $event_dispatcher
* The event dispatcher.
* @param \Drupal\Core\Config\ConfigFactoryInterface $config_factory
* The config factory.
*/
public function __construct(RendererInterface $renderer, SessionInterface $session, RequestStack $request_stack, HttpKernelInterface $http_kernel, EventDispatcherInterface $event_dispatcher, ConfigFactoryInterface $config_factory) {
$this->renderer = $renderer;
$this->session = $session;
$this->requestStack = $request_stack;
$this->httpKernel = $http_kernel;
$this->eventDispatcher = $event_dispatcher;
$this->configFactory = $config_factory;
}
/**
* Performs tasks before sending content (and rendering placeholders).
*/
protected function performPreSendTasks() {
// The content in the placeholders may depend on the session, and by the
// time the response is sent (see index.php), the session is already
// closed. Reopen it for the duration that we are rendering placeholders.
$this->session
->start();
}
/**
* Performs tasks after sending content (and rendering placeholders).
*/
protected function performPostSendTasks() {
// Close the session again.
$this->session
->save();
}
/**
* Sends a chunk.
*
* @param string|\Drupal\Core\Render\HtmlResponse $chunk
* The string or response to append. String if there's no cacheability
* metadata or attachments to merge.
*/
protected function sendChunk($chunk) {
assert(is_string($chunk) || $chunk instanceof HtmlResponse);
if ($chunk instanceof HtmlResponse) {
print $chunk
->getContent();
}
else {
print $chunk;
}
flush();
}
/**
* Sends an HTML response in chunks using the BigPipe technique.
*
* @param \Drupal\big_pipe\Render\BigPipeResponse $response
* The BigPipe response to send.
*
* @internal
* This method should only be invoked by
* \Drupal\big_pipe\Render\BigPipeResponse, which is itself an internal
* class.
*/
public function sendContent(BigPipeResponse $response) {
$content = $response
->getContent();
$attachments = $response
->getAttachments();
// First, gather the BigPipe placeholders that must be replaced.
$placeholders = isset($attachments['big_pipe_placeholders']) ? $attachments['big_pipe_placeholders'] : [];
$nojs_placeholders = isset($attachments['big_pipe_nojs_placeholders']) ? $attachments['big_pipe_nojs_placeholders'] : [];
// BigPipe sends responses using "Transfer-Encoding: chunked". To avoid
// sending already-sent assets, it is necessary to track cumulative assets
// from all previously rendered/sent chunks.
// @see http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.41
$cumulative_assets = AttachedAssets::createFromRenderArray([
'#attached' => $attachments,
]);
$cumulative_assets
->setAlreadyLoadedLibraries($attachments['library']);
$this
->performPreSendTasks();
// Find the closing </body> tag and get the strings before and after. But be
// careful to use the latest occurrence of the string "</body>", to ensure
// that strings in inline JavaScript or CDATA sections aren't used instead.
$parts = explode('</body>', $content);
$post_body = array_pop($parts);
$pre_body = implode('', $parts);
$this
->sendPreBody($pre_body, $nojs_placeholders, $cumulative_assets);
$this
->sendPlaceholders($placeholders, $this
->getPlaceholderOrder($pre_body, $placeholders), $cumulative_assets);
$this
->sendPostBody($post_body);
$this
->performPostSendTasks();
}
/**
* Sends everything until just before </body>.
*
* @param string $pre_body
* The HTML response's content until the closing </body> tag.
* @param array $no_js_placeholders
* The no-JS BigPipe placeholders.
* @param \Drupal\Core\Asset\AttachedAssetsInterface $cumulative_assets
* The cumulative assets sent so far; to be updated while rendering no-JS
* BigPipe placeholders.
*/
protected function sendPreBody($pre_body, array $no_js_placeholders, AttachedAssetsInterface $cumulative_assets) {
// If there are no no-JS BigPipe placeholders, we can send the pre-</body>
// part of the page immediately.
if (empty($no_js_placeholders)) {
$this
->sendChunk($pre_body);
return;
}
// Extract the scripts_bottom markup: the no-JS BigPipe placeholders that we
// will render may attach additional asset libraries, and if so, it will be
// necessary to re-render scripts_bottom.
list($pre_scripts_bottom, $scripts_bottom, $post_scripts_bottom) = explode('<drupal-big-pipe-scripts-bottom-marker>', $pre_body, 3);
$cumulative_assets_initial = clone $cumulative_assets;
$this
->sendNoJsPlaceholders($pre_scripts_bottom . $post_scripts_bottom, $no_js_placeholders, $cumulative_assets);
// If additional asset libraries or drupalSettings were attached by any of
// the placeholders, then we need to re-render scripts_bottom.
if ($cumulative_assets_initial != $cumulative_assets) {
// Create a new HtmlResponse. Ensure the CSS and (non-bottom) JS is sent
// before the HTML they're associated with.
// @see \Drupal\Core\Render\HtmlResponseSubscriber
// @see template_preprocess_html()
$js_bottom_placeholder = '<nojs-bigpipe-placeholder-scripts-bottom-placeholder token="' . Crypt::randomBytesBase64(55) . '">';
$html_response = new HtmlResponse();
$html_response
->setContent([
'#markup' => BigPipeMarkup::create($js_bottom_placeholder),
'#attached' => [
'drupalSettings' => $cumulative_assets
->getSettings(),
'library' => $cumulative_assets
->getAlreadyLoadedLibraries(),
'html_response_attachment_placeholders' => [
'scripts_bottom' => $js_bottom_placeholder,
],
],
]);
$html_response
->getCacheableMetadata()
->setCacheMaxAge(0);
// Push a fake request with the asset libraries loaded so far and dispatch
// KernelEvents::RESPONSE event. This results in the attachments for the
// HTML response being processed by HtmlResponseAttachmentsProcessor and
// hence the HTML to load the bottom JavaScript can be rendered.
$fake_request = $this->requestStack
->getMasterRequest()
->duplicate();
$html_response = $this
->filterEmbeddedResponse($fake_request, $html_response);
$scripts_bottom = $html_response
->getContent();
}
$this
->sendChunk($scripts_bottom);
}
/**
* Sends no-JS BigPipe placeholders' replacements as embedded HTML responses.
*
* @param string $html
* HTML markup.
* @param array $no_js_placeholders
* Associative array; the no-JS BigPipe placeholders. Keys are the BigPipe
* selectors.
* @param \Drupal\Core\Asset\AttachedAssetsInterface $cumulative_assets
* The cumulative assets sent so far; to be updated while rendering no-JS
* BigPipe placeholders.
*
* @throws \Exception
* If an exception is thrown during the rendering of a placeholder, it is
* caught to allow the other placeholders to still be replaced. But when
* error logging is configured to be verbose, the exception is rethrown to
* simplify debugging.
*/
protected function sendNoJsPlaceholders($html, $no_js_placeholders, AttachedAssetsInterface $cumulative_assets) {
// Split the HTML on every no-JS placeholder string.
$placeholder_strings = array_keys($no_js_placeholders);
$fragments = static::splitHtmlOnPlaceholders($html, $placeholder_strings);
// Determine how many occurrences there are of each no-JS placeholder.
$placeholder_occurrences = array_count_values(array_intersect($fragments, $placeholder_strings));
// Set up a variable to store the content of placeholders that have multiple
// occurrences.
$multi_occurrence_placeholders_content = [];
foreach ($fragments as $fragment) {
// If the fragment isn't one of the no-JS placeholders, it is the HTML in
// between placeholders and it must be printed & flushed immediately. The
// rest of the logic in the loop handles the placeholders.
if (!isset($no_js_placeholders[$fragment])) {
$this
->sendChunk($fragment);
continue;
}
// If there are multiple occurrences of this particular placeholder, and
// this is the second occurrence, we can skip all calculations and just
// send the same content.
if ($placeholder_occurrences[$fragment] > 1 && isset($multi_occurrence_placeholders_content[$fragment])) {
$this
->sendChunk($multi_occurrence_placeholders_content[$fragment]);
continue;
}
$placeholder = $fragment;
assert(isset($no_js_placeholders[$placeholder]));
$token = Crypt::randomBytesBase64(55);
// Render the placeholder, but include the cumulative settings assets, so
// we can calculate the overall settings for the entire page.
$placeholder_plus_cumulative_settings = [
'placeholder' => $no_js_placeholders[$placeholder],
'cumulative_settings_' . $token => [
'#attached' => [
'drupalSettings' => $cumulative_assets
->getSettings(),
],
],
];
try {
$elements = $this
->renderPlaceholder($placeholder, $placeholder_plus_cumulative_settings);
} catch (\Exception $e) {
if ($this->configFactory
->get('system.logging')
->get('error_level') === ERROR_REPORTING_DISPLAY_VERBOSE) {
throw $e;
}
else {
trigger_error($e, E_USER_ERROR);
continue;
}
}
// Create a new HtmlResponse. Ensure the CSS and (non-bottom) JS is sent
// before the HTML they're associated with. In other words: ensure the
// critical assets for this placeholder's markup are loaded first.
// @see \Drupal\Core\Render\HtmlResponseSubscriber
// @see template_preprocess_html()
$css_placeholder = '<nojs-bigpipe-placeholder-styles-placeholder token="' . $token . '">';
$js_placeholder = '<nojs-bigpipe-placeholder-scripts-placeholder token="' . $token . '">';
$elements['#markup'] = BigPipeMarkup::create($css_placeholder . $js_placeholder . (string) $elements['#markup']);
$elements['#attached']['html_response_attachment_placeholders']['styles'] = $css_placeholder;
$elements['#attached']['html_response_attachment_placeholders']['scripts'] = $js_placeholder;
$html_response = new HtmlResponse();
$html_response
->setContent($elements);
$html_response
->getCacheableMetadata()
->setCacheMaxAge(0);
// Push a fake request with the asset libraries loaded so far and dispatch
// KernelEvents::RESPONSE event. This results in the attachments for the
// HTML response being processed by HtmlResponseAttachmentsProcessor and
// hence:
// - the HTML to load the CSS can be rendered.
// - the HTML to load the JS (at the top) can be rendered.
$fake_request = $this->requestStack
->getMasterRequest()
->duplicate();
$fake_request->request
->set('ajax_page_state', [
'libraries' => implode(',', $cumulative_assets
->getAlreadyLoadedLibraries()),
]);
try {
$html_response = $this
->filterEmbeddedResponse($fake_request, $html_response);
} catch (\Exception $e) {
if ($this->configFactory
->get('system.logging')
->get('error_level') === ERROR_REPORTING_DISPLAY_VERBOSE) {
throw $e;
}
else {
trigger_error($e, E_USER_ERROR);
continue;
}
}
// Send this embedded HTML response.
$this
->sendChunk($html_response);
// Another placeholder was rendered and sent, track the set of asset
// libraries sent so far. Any new settings also need to be tracked, so
// they can be sent in ::sendPreBody().
$cumulative_assets
->setAlreadyLoadedLibraries(array_merge($cumulative_assets
->getAlreadyLoadedLibraries(), $html_response
->getAttachments()['library']));
$cumulative_assets
->setSettings($html_response
->getAttachments()['drupalSettings']);
// If there are multiple occurrences of this particular placeholder, track
// the content that was sent, so we can skip all calculations for the next
// occurrence.
if ($placeholder_occurrences[$fragment] > 1) {
$multi_occurrence_placeholders_content[$fragment] = $html_response
->getContent();
}
}
}
/**
* Sends BigPipe placeholders' replacements as embedded AJAX responses.
*
* @param array $placeholders
* Associative array; the BigPipe placeholders. Keys are the BigPipe
* placeholder IDs.
* @param array $placeholder_order
* Indexed array; the order in which the BigPipe placeholders must be sent.
* Values are the BigPipe placeholder IDs. (These values correspond to keys
* in $placeholders.)
* @param \Drupal\Core\Asset\AttachedAssetsInterface $cumulative_assets
* The cumulative assets sent so far; to be updated while rendering BigPipe
* placeholders.
*
* @throws \Exception
* If an exception is thrown during the rendering of a placeholder, it is
* caught to allow the other placeholders to still be replaced. But when
* error logging is configured to be verbose, the exception is rethrown to
* simplify debugging.
*/
protected function sendPlaceholders(array $placeholders, array $placeholder_order, AttachedAssetsInterface $cumulative_assets) {
// Return early if there are no BigPipe placeholders to send.
if (empty($placeholders)) {
return;
}
// Send the start signal.
$this
->sendChunk("\n" . static::START_SIGNAL . "\n");
// A BigPipe response consists of a HTML response plus multiple embedded
// AJAX responses. To process the attachments of those AJAX responses, we
// need a fake request that is identical to the master request, but with
// one change: it must have the right Accept header, otherwise the work-
// around for a bug in IE9 will cause not JSON, but <textarea>-wrapped JSON
// to be returned.
// @see \Drupal\Core\EventSubscriber\AjaxResponseSubscriber::onResponse()
$fake_request = $this->requestStack
->getMasterRequest()
->duplicate();
$fake_request->headers
->set('Accept', 'application/vnd.drupal-ajax');
foreach ($placeholder_order as $placeholder_id) {
if (!isset($placeholders[$placeholder_id])) {
continue;
}
// Render the placeholder.
$placeholder_render_array = $placeholders[$placeholder_id];
try {
$elements = $this
->renderPlaceholder($placeholder_id, $placeholder_render_array);
} catch (\Exception $e) {
if ($this->configFactory
->get('system.logging')
->get('error_level') === ERROR_REPORTING_DISPLAY_VERBOSE) {
throw $e;
}
else {
trigger_error($e, E_USER_ERROR);
continue;
}
}
// Create a new AjaxResponse.
$ajax_response = new AjaxResponse();
// JavaScript's querySelector automatically decodes HTML entities in
// attributes, so we must decode the entities of the current BigPipe
// placeholder ID (which has HTML entities encoded since we use it to find
// the placeholders).
$big_pipe_js_placeholder_id = Html::decodeEntities($placeholder_id);
$ajax_response
->addCommand(new ReplaceCommand(sprintf('[data-big-pipe-placeholder-id="%s"]', $big_pipe_js_placeholder_id), $elements['#markup']));
$ajax_response
->setAttachments($elements['#attached']);
// Push a fake request with the asset libraries loaded so far and dispatch
// KernelEvents::RESPONSE event. This results in the attachments for the
// AJAX response being processed by AjaxResponseAttachmentsProcessor and
// hence:
// - the necessary AJAX commands to load the necessary missing asset
// libraries and updated AJAX page state are added to the AJAX response
// - the attachments associated with the response are finalized, which
// allows us to track the total set of asset libraries sent in the
// initial HTML response plus all embedded AJAX responses sent so far.
$fake_request->request
->set('ajax_page_state', [
'libraries' => implode(',', $cumulative_assets
->getAlreadyLoadedLibraries()),
] + $cumulative_assets
->getSettings()['ajaxPageState']);
try {
$ajax_response = $this
->filterEmbeddedResponse($fake_request, $ajax_response);
} catch (\Exception $e) {
if ($this->configFactory
->get('system.logging')
->get('error_level') === ERROR_REPORTING_DISPLAY_VERBOSE) {
throw $e;
}
else {
trigger_error($e, E_USER_ERROR);
continue;
}
}
// Send this embedded AJAX response.
$json = $ajax_response
->getContent();
$output = <<<EOF
<script type="application/vnd.drupal-ajax" data-big-pipe-replacement-for-placeholder-with-id="{<span class="php-variable">$placeholder_id</span>}">
{<span class="php-variable">$json</span>}
</script>
EOF;
$this
->sendChunk($output);
// Another placeholder was rendered and sent, track the set of asset
// libraries sent so far. Any new settings are already sent; we don't need
// to track those.
if (isset($ajax_response
->getAttachments()['drupalSettings']['ajaxPageState']['libraries'])) {
$cumulative_assets
->setAlreadyLoadedLibraries(explode(',', $ajax_response
->getAttachments()['drupalSettings']['ajaxPageState']['libraries']));
}
}
// Send the stop signal.
$this
->sendChunk("\n" . static::STOP_SIGNAL . "\n");
}
/**
* Filters the given embedded response, using the cumulative AJAX page state.
*
* @param \Symfony\Component\HttpFoundation\Request $fake_request
* A fake subrequest that contains the cumulative AJAX page state of the
* HTML document and all preceding Embedded HTML or AJAX responses.
* @param \Symfony\Component\HttpFoundation\Response|\Drupal\Core\Render\HtmlResponse|\Drupal\Core\Ajax\AjaxResponse $embedded_response
* Either a HTML response or an AJAX response that will be embedded in the
* overall HTML response.
*
* @return \Symfony\Component\HttpFoundation\Response
* The filtered response, which will load only the assets that $fake_request
* did not indicate to already have been loaded, plus the updated cumulative
* AJAX page state.
*/
protected function filterEmbeddedResponse(Request $fake_request, Response $embedded_response) {
assert($embedded_response instanceof HtmlResponse || $embedded_response instanceof AjaxResponse);
return $this
->filterResponse($fake_request, HttpKernelInterface::SUB_REQUEST, $embedded_response);
}
/**
* Filters the given response.
*
* @param \Symfony\Component\HttpFoundation\Request $request
* The request for which a response is being sent.
* @param int $request_type
* The request type. Can either be
* \Symfony\Component\HttpKernel\HttpKernelInterface::MASTER_REQUEST or
* \Symfony\Component\HttpKernel\HttpKernelInterface::SUB_REQUEST.
* @param \Symfony\Component\HttpFoundation\Response $response
* The response to filter.
*
* @return \Symfony\Component\HttpFoundation\Response
* The filtered response.
*/
protected function filterResponse(Request $request, $request_type, Response $response) {
assert($request_type === HttpKernelInterface::MASTER_REQUEST || $request_type === HttpKernelInterface::SUB_REQUEST);
$this->requestStack
->push($request);
$event = new FilterResponseEvent($this->httpKernel, $request, $request_type, $response);
$this->eventDispatcher
->dispatch(KernelEvents::RESPONSE, $event);
$filtered_response = $event
->getResponse();
$this->requestStack
->pop();
return $filtered_response;
}
/**
* Sends </body> and everything after it.
*
* @param string $post_body
* The HTML response's content after the closing </body> tag.
*/
protected function sendPostBody($post_body) {
$this
->sendChunk('</body>' . $post_body);
}
/**
* Renders a placeholder, and just that placeholder.
*
* BigPipe renders placeholders independently of the rest of the content, so
* it needs to be able to render placeholders by themselves.
*
* @param string $placeholder
* The placeholder to render.
* @param array $placeholder_render_array
* The render array associated with that placeholder.
*
* @return array
* The render array representing the rendered placeholder.
*
* @see \Drupal\Core\Render\RendererInterface::renderPlaceholder()
*/
protected function renderPlaceholder($placeholder, array $placeholder_render_array) {
$elements = [
'#markup' => $placeholder,
'#attached' => [
'placeholders' => [
$placeholder => $placeholder_render_array,
],
],
];
return $this->renderer
->renderPlaceholder($placeholder, $elements);
}
/**
* Gets the BigPipe placeholder order.
*
* Determines the order in which BigPipe placeholders must be replaced.
*
* @param string $html
* HTML markup.
* @param array $placeholders
* Associative array; the BigPipe placeholders. Keys are the BigPipe
* placeholder IDs.
*
* @return array
* Indexed array; the order in which the BigPipe placeholders must be sent.
* Values are the BigPipe placeholder IDs. Note that only unique
* placeholders are kept: if the same placeholder occurs multiple times, we
* only keep the first occurrence.
*/
protected function getPlaceholderOrder($html, $placeholders) {
$fragments = explode('<span data-big-pipe-placeholder-id="', $html);
array_shift($fragments);
$placeholder_ids = [];
foreach ($fragments as $fragment) {
$t = explode('"></span>', $fragment, 2);
$placeholder_id = $t[0];
$placeholder_ids[] = $placeholder_id;
}
$placeholder_ids = array_unique($placeholder_ids);
// The 'status messages' placeholder needs to be special cased, because it
// depends on global state that can be modified when other placeholders are
// being rendered: any code can add messages to render.
// This violates the principle that each lazy builder must be able to render
// itself in isolation, and therefore in any order. However, we cannot
// change the way \Drupal\Core\Messenger\MessengerInterface::addMessage()
// works in the Drupal 8 cycle. So we have to accommodate its special needs.
// Allowing placeholders to be rendered in a particular order (in this case:
// last) would violate this isolation principle. Thus a monopoly is granted
// to this one special case, with this hard-coded solution.
// @see \Drupal\Core\Render\Element\StatusMessages
// @see \Drupal\Core\Render\Renderer::replacePlaceholders()
// @see https://www.drupal.org/node/2712935#comment-11368923
$message_placeholder_ids = [];
foreach ($placeholders as $placeholder_id => $placeholder_element) {
if (isset($placeholder_element['#lazy_builder']) && $placeholder_element['#lazy_builder'][0] === 'Drupal\\Core\\Render\\Element\\StatusMessages::renderMessages') {
$message_placeholder_ids[] = $placeholder_id;
}
}
// Return placeholder IDs in DOM order, but with the 'status messages'
// placeholders at the end, if they are present.
$ordered_placeholder_ids = array_merge(array_diff($placeholder_ids, $message_placeholder_ids), array_intersect($placeholder_ids, $message_placeholder_ids));
return $ordered_placeholder_ids;
}
/**
* Splits a HTML string into fragments.
*
* Creates an array of HTML fragments, separated by placeholders. The result
* includes the placeholders themselves. The original order is respected.
*
* @param string $html_string
* The HTML to split.
* @param string[] $html_placeholders
* The HTML placeholders to split on.
*
* @return string[]
* The resulting HTML fragments.
*/
private static function splitHtmlOnPlaceholders($html_string, array $html_placeholders) {
$prepare_for_preg_split = function ($placeholder_string) {
return '(' . preg_quote($placeholder_string, '/') . ')';
};
$preg_placeholder_strings = array_map($prepare_for_preg_split, $html_placeholders);
$pattern = '/' . implode('|', $preg_placeholder_strings) . '/';
if (strlen($pattern) < 31000) {
// Only small (<31K characters) patterns can be handled by preg_split().
$flags = PREG_SPLIT_NO_EMPTY | PREG_SPLIT_DELIM_CAPTURE;
$result = preg_split($pattern, $html_string, NULL, $flags);
}
else {
// For large amounts of placeholders we use a simpler but slower approach.
foreach ($html_placeholders as $placeholder) {
$html_string = str_replace($placeholder, "\37" . $placeholder . "\37", $html_string);
}
$result = array_filter(explode("\37", $html_string));
}
return $result;
}
}