Added output processor for Google AMP

diff --git a/wcfsetup/install/files/lib/system/html/output/AmpHtmlOutputProcessor.class.php b/wcfsetup/install/files/lib/system/html/output/AmpHtmlOutputProcessor.class.php
new file mode 100644 (file)
index 0000000..215b0d4
--- /dev/null
+++ b/wcfsetup/install/files/lib/system/html/output/AmpHtmlOutputProcessor.class.php
@@ -0,0 +1,107 @@
+<?php
+namespace wcf\system\html\output;
+use wcf\util\DOMUtil;
+
+/**
+ * Processes stored HTML for final display and modifies/removes elements to
+ * match the Google AMP specifications.
+ * 
+ * See https://github.com/ampproject/amphtml/blob/master/spec/amp-html-format.md#html-tags
+ * 
+ * @author      Alexander Ebert
+ * @copyright   2001-2016 WoltLab GmbH
+ * @license     GNU Lesser General Public License <http://opensource.org/licenses/lgpl-license.php>
+ * @package     WoltLabSuite\Core\System\Html\Output
+ * @since       3.0
+ */
+class AmpHtmlOutputProcessor extends HtmlOutputProcessor {
+       /**
+        * @inheritDoc
+        */
+       public function process($html, $objectType, $objectID) {
+               parent::process($html, $objectType, $objectID);
+               
+               $document = $this->getHtmlOutputNodeProcessor()->getDocument();
+                       
+               // remove tags and discarding content
+               $tags = [
+                       // general
+                       'base', 'frame', 'frameset', 'object', 'param', 'applet', 'embed',
+                       
+                       // forms
+                       'input', 'textarea', 'select', 'option',
+                       
+                       // special
+                       'style'
+               ];
+               foreach ($tags as $tag) {
+                       $elements = $document->getElementsByTagName($tag);
+                       while ($elements->length) DOMUtil::removeNode($elements->item(0), true);
+               }
+               
+               // remove tags but keep child nodes
+               $tags = ['form'];
+               foreach ($tags as $tag) {
+                       $elements = $document->getElementsByTagName($tag);
+                       while ($elements->length) DOMUtil::removeNode($elements->item(0), false);
+               }
+               
+               // remove script tags unless the type is application/ld+json
+               $elements = $this->filterElements(
+                       $document->getElementsByTagName('script'),
+                       function ($element) {
+                               /** @var \DOMElement $element */
+                               return ($element->getAttribute('type') === 'application/ld+json');
+                       }
+               );
+               foreach ($elements as $element) DOMUtil::removeNode($element);
+               
+               // replace tags
+               $tags = ['img', 'video', 'audio', 'iframe'];
+               foreach ($tags as $tag) {
+                       $elements = $document->getElementsByTagName($tag);
+                       while ($elements->length) {
+                               /** @var \DOMElement $element */
+                               $element = $elements->item(0);
+                               if ($tag === 'img') {
+                                       $styles = $element->getAttribute('style');
+                                       if (preg_match('~\bheight:\s*(\d+)px\b~', $styles, $matches)) $element->setAttribute('height', $matches[1]);
+                                       if (preg_match('~\bwidth:\s*(\d+)px\b~', $styles, $matches)) $element->setAttribute('width', $matches[1]);
+                                       
+                                       if (!$element->getAttribute('height') || !$element->getAttribute('width')) {
+                                               DOMUtil::removeNode($element);
+                                               continue;
+                                       }
+                                       
+                                       $element->removeAttribute('style');
+                               }
+                               
+                               $newElement = $element->ownerDocument->createElement('amp-' . $tag);
+                               
+                               // copy attributes
+                               for ($i = 0, $length = $element->attributes->length; $i < $length; $i++) {
+                                       $attr = $element->attributes->item($i);
+                                       
+                                       $newElement->setAttribute($attr->localName, $attr->nodeValue);
+                               }
+                               
+                               $element->parentNode->insertBefore($newElement, $element);
+                               DOMUtil::removeNode($element);
+                       }
+               }
+               
+               
+       }
+       
+       protected function filterElements(\DOMNodeList $elements, callable $callback) {
+               $badElements = [];
+               
+               foreach ($elements as $element) {
+                       if ($callback($element) === false) {
+                               $badElements[] = $element;
+                       }
+               }
+               
+               return $badElements;
+       }
+}