Feed: Move feed-related classes to Feed/ and namespace them

Bug: T166010
Change-Id: Icdbe003e74d2f31b68b575acfa94c09c24d7aed5

5 files changed, 922 insertions, 0 deletions

diff --git a/includes/Feed/AtomFeed.php b/includes/Feed/AtomFeed.php
new file mode 100644
index 000000000000..4574a6230c66
--- /dev/null
+++ b/includes/Feed/AtomFeed.php
@@ -0,0 +1,120 @@
+<?php
+
+/**
+ * Copyright © 2004 Brion Vibber <brion@pobox.com>
+ * https://www.mediawiki.org/
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ * http://www.gnu.org/copyleft/gpl.html
+ *
+ * @file
+ */
+
+namespace MediaWiki\Feed;
+
+use MediaWiki\MainConfigNames;
+use MediaWiki\MediaWikiServices;
+
+/**
+ * Generate an Atom feed.
+ *
+ * @ingroup Feed
+ */
+class AtomFeed extends ChannelFeed {
+	/**
+	 * Format a date given timestamp, if one is given.
+	 *
+	 * @param string|int|null $timestamp
+	 * @return string|null
+	 */
+	private function formatTime( $timestamp ) {
+		if ( $timestamp ) {
+			// need to use RFC 822 time format at least for rss2.0
+			return gmdate( 'Y-m-d\TH:i:s', (int)wfTimestamp( TS_UNIX, $timestamp ) );
+		}
+		return null;
+	}
+
+	/**
+	 * Outputs a basic header for Atom 1.0 feeds.
+	 */
+	public function outHeader() {
+		$this->outXmlHeader();
+		// Manually escaping rather than letting Mustache do it because Mustache
+		// uses htmlentities, which does not work with XML
+		$templateParams = [
+			'language' => $this->xmlEncode( $this->getLanguage() ),
+			'feedID' => $this->getFeedId(),
+			'title' => $this->getTitle(),
+			'url' => $this->xmlEncode( wfExpandUrl( $this->getUrlUnescaped(), PROTO_CURRENT ) ),
+			'selfUrl' => $this->getSelfUrl(),
+			'timestamp' => $this->xmlEncode( $this->formatTime( wfTimestampNow() ) ),
+			'description' => $this->getDescription(),
+			'version' => $this->xmlEncode( MW_VERSION ),
+		];
+		print $this->templateParser->processTemplate( 'AtomHeader', $templateParams );
+	}
+
+	/**
+	 * Atom 1.0 requires a unique, opaque IRI as a unique identifier
+	 * for every feed we create. For now just use the URL, but who
+	 * can tell if that's right? If we put options on the feed, do we
+	 * have to change the id? Maybe? Maybe not.
+	 *
+	 * @return string
+	 */
+	private function getFeedId() {
+		return $this->getSelfUrl();
+	}
+
+	/**
+	 * Atom 1.0 requests a self-reference to the feed.
+	 * @return string
+	 */
+	private function getSelfUrl() {
+		global $wgRequest;
+		return htmlspecialchars( $wgRequest->getFullRequestURL() );
+	}
+
+	/**
+	 * Output a given item.
+	 * @param FeedItem $item
+	 */
+	public function outItem( $item ) {
+		$mimeType = MediaWikiServices::getInstance()->getMainConfig()
+			->get( MainConfigNames::MimeType );
+		// Manually escaping rather than letting Mustache do it because Mustache
+		// uses htmlentities, which does not work with XML
+		$templateParams = [
+			"uniqueID" => $item->getUniqueID(),
+			"title" => $item->getTitle(),
+			"mimeType" => $this->xmlEncode( $mimeType ),
+			"url" => $this->xmlEncode( wfExpandUrl( $item->getUrlUnescaped(), PROTO_CURRENT ) ),
+			"date" => $this->xmlEncode( $this->formatTime( $item->getDate() ) ),
+			"description" => $item->getDescription(),
+			"author" => $item->getAuthor()
+		];
+		print $this->templateParser->processTemplate( 'AtomItem', $templateParams );
+	}
+
+	/**
+	 * Outputs the footer for Atom 1.0 feed (basically '\</feed\>').
+	 */
+	public function outFooter() {
+		print "</feed>";
+	}
+}
+
+class_alias( AtomFeed::class, 'AtomFeed' );
diff --git a/includes/Feed/ChannelFeed.php b/includes/Feed/ChannelFeed.php
new file mode 100644
index 000000000000..2a58ba90784a
--- /dev/null
+++ b/includes/Feed/ChannelFeed.php
@@ -0,0 +1,147 @@
+<?php
+
+/**
+ * Copyright © 2004 Brion Vibber <brion@pobox.com>
+ * https://www.mediawiki.org/
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ * http://www.gnu.org/copyleft/gpl.html
+ *
+ * @file
+ */
+
+namespace MediaWiki\Feed;
+
+use MediaWiki\MainConfigNames;
+use MediaWiki\MediaWikiServices;
+use TemplateParser;
+use Title;
+
+/**
+ * Class to support the outputting of syndication feeds in Atom and RSS format.
+ *
+ * @stable to extend
+ * @ingroup Feed
+ */
+abstract class ChannelFeed extends FeedItem {
+
+	/** @var TemplateParser */
+	protected $templateParser;
+
+	/**
+	 * @stable to call
+	 *
+	 * @param string|Title $title Feed's title
+	 * @param string $description
+	 * @param string $url URL uniquely designating the feed.
+	 * @param string $date Feed's date
+	 * @param string $author Author's user name
+	 * @param string $comments
+	 *
+	 */
+	public function __construct(
+		$title, $description, $url, $date = '', $author = '', $comments = ''
+	) {
+		parent::__construct( $title, $description, $url, $date, $author, $comments );
+		$this->templateParser = new TemplateParser();
+	}
+
+	/**
+	 * Generate Header of the feed
+	 * @par Example:
+	 * @code
+	 * print "<feed>";
+	 * @endcode
+	 */
+	abstract public function outHeader();
+
+	/**
+	 * Generate an item
+	 * @par Example:
+	 * @code
+	 * print "<item>...</item>";
+	 * @endcode
+	 * @param FeedItem $item
+	 */
+	abstract public function outItem( $item );
+
+	/**
+	 * Generate Footer of the feed
+	 * @par Example:
+	 * @code
+	 * print "</feed>";
+	 * @endcode
+	 */
+	abstract public function outFooter();
+
+	/**
+	 * Setup and send HTTP headers. Don't send any content;
+	 * content might end up being cached and re-sent with
+	 * these same headers later.
+	 *
+	 * This should be called from the outHeader() method,
+	 * but can also be called separately.
+	 */
+	public function httpHeaders() {
+		global $wgOut;
+		$varyOnXFP = MediaWikiServices::getInstance()->getMainConfig()
+			->get( MainConfigNames::VaryOnXFP );
+		# We take over from $wgOut, excepting its cache header info
+		$wgOut->disable();
+		$mimetype = $this->contentType();
+		header( "Content-type: $mimetype; charset=UTF-8" );
+
+		// Set a sensible filename
+		$mimeAnalyzer = MediaWikiServices::getInstance()->getMimeAnalyzer();
+		$ext = $mimeAnalyzer->getExtensionFromMimeTypeOrNull( $mimetype ) ?? 'xml';
+		header( "Content-Disposition: inline; filename=\"feed.{$ext}\"" );
+
+		if ( $varyOnXFP ) {
+			$wgOut->addVaryHeader( 'X-Forwarded-Proto' );
+		}
+		$wgOut->sendCacheControl();
+	}
+
+	/**
+	 * Return an internet media type to be sent in the headers.
+	 *
+	 * @stable to override
+	 *
+	 * @return string
+	 */
+	private function contentType() {
+		global $wgRequest;
+
+		$ctype = $wgRequest->getVal( 'ctype', 'application/xml' );
+		$allowedctypes = [
+			'application/xml',
+			'text/xml',
+			'application/rss+xml',
+			'application/atom+xml'
+		];
+
+		return ( in_array( $ctype, $allowedctypes ) ? $ctype : 'application/xml' );
+	}
+
+	/**
+	 * Output the initial XML headers.
+	 */
+	protected function outXmlHeader() {
+		$this->httpHeaders();
+		echo '<?xml version="1.0"?>' . "\n";
+	}
+}
+
+class_alias( ChannelFeed::class, 'ChannelFeed' );
diff --git a/includes/Feed/FeedItem.php b/includes/Feed/FeedItem.php
new file mode 100644
index 000000000000..2968b964e228
--- /dev/null
+++ b/includes/Feed/FeedItem.php
@@ -0,0 +1,235 @@
+<?php
+/**
+ * Copyright © 2004 Brion Vibber <brion@pobox.com>
+ * https://www.mediawiki.org/
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ * http://www.gnu.org/copyleft/gpl.html
+ *
+ * @file
+ */
+
+namespace MediaWiki\Feed;
+
+use LanguageCode;
+use MediaWiki\MainConfigNames;
+use MediaWiki\MediaWikiServices;
+use Title;
+
+/**
+ * @defgroup Feed Feed
+ */
+
+/**
+ * A base class for outputting syndication feeds (e.g. RSS and other formats).
+ *
+ * @ingroup Feed
+ */
+class FeedItem {
+	/** @var Title */
+	public $title;
+
+	public $description;
+
+	public $url;
+
+	public $date;
+
+	public $author;
+
+	public $uniqueId;
+
+	public $comments;
+
+	public $rssIsPermalink = false;
+
+	/**
+	 * @param string|Title $title Item's title
+	 * @param string $description
+	 * @param string $url URL uniquely designating the item.
+	 * @param string $date Item's date
+	 * @param string $author Author's user name
+	 * @param string $comments
+	 */
+	public function __construct(
+		$title, $description, $url, $date = '', $author = '', $comments = ''
+	) {
+		$this->title = $title;
+		$this->description = $description;
+		$this->url = $url;
+		$this->uniqueId = $url;
+		$this->date = $date;
+		$this->author = $author;
+		$this->comments = $comments;
+	}
+
+	/**
+	 * Encode $string so that it can be safely embedded in a XML document
+	 *
+	 * @param string $string String to encode
+	 * @return string
+	 */
+	public function xmlEncode( $string ) {
+		$string = str_replace( "\r\n", "\n", $string );
+		$string = preg_replace( '/[\x00-\x08\x0b\x0c\x0e-\x1f]/', '', $string );
+		return htmlspecialchars( $string );
+	}
+
+	/**
+	 * Get the unique id of this item; already xml-encoded
+	 * @return string
+	 */
+	public function getUniqueID() {
+		$id = $this->getUniqueIdUnescaped();
+		if ( $id ) {
+			return $this->xmlEncode( $id );
+		}
+	}
+
+	/**
+	 * Get the unique id of this item, without any escaping
+	 * @return string
+	 */
+	public function getUniqueIdUnescaped() {
+		if ( $this->uniqueId ) {
+			return wfExpandUrl( $this->uniqueId, PROTO_CURRENT );
+		}
+	}
+
+	/**
+	 * Set the unique id of an item
+	 *
+	 * @param string $uniqueId Unique id for the item
+	 * @param bool $rssIsPermalink Set to true if the guid (unique id) is a permalink (RSS feeds only)
+	 */
+	public function setUniqueId( $uniqueId, $rssIsPermalink = false ) {
+		$this->uniqueId = $uniqueId;
+		$this->rssIsPermalink = $rssIsPermalink;
+	}
+
+	/**
+	 * Get the title of this item; already xml-encoded
+	 *
+	 * @return string
+	 */
+	public function getTitle() {
+		return $this->xmlEncode( $this->title );
+	}
+
+	/**
+	 * Get the URL of this item; already xml-encoded
+	 *
+	 * @return string
+	 */
+	public function getUrl() {
+		return $this->xmlEncode( $this->url );
+	}
+
+	/** Get the URL of this item without any escaping
+	 *
+	 * @return string
+	 */
+	public function getUrlUnescaped() {
+		return $this->url;
+	}
+
+	/**
+	 * Get the description of this item; already xml-encoded
+	 *
+	 * @return string
+	 */
+	public function getDescription() {
+		return $this->xmlEncode( $this->description );
+	}
+
+	/**
+	 * Get the description of this item without any escaping
+	 *
+	 * @return string
+	 */
+	public function getDescriptionUnescaped() {
+		return $this->description;
+	}
+
+	/**
+	 * Get the language of this item
+	 *
+	 * @return string
+	 */
+	public function getLanguage() {
+		$languageCode = MediaWikiServices::getInstance()->getMainConfig()
+			->get( MainConfigNames::LanguageCode );
+		return LanguageCode::bcp47( $languageCode );
+	}
+
+	/**
+	 * Get the date of this item
+	 *
+	 * @return string
+	 */
+	public function getDate() {
+		return $this->date;
+	}
+
+	/**
+	 * Get the author of this item; already xml-encoded
+	 *
+	 * @return string
+	 */
+	public function getAuthor() {
+		return $this->xmlEncode( $this->author );
+	}
+
+	/**
+	 * Get the author of this item without any escaping
+	 *
+	 * @return string
+	 */
+	public function getAuthorUnescaped() {
+		return $this->author;
+	}
+
+	/**
+	 * Get the comment of this item; already xml-encoded
+	 *
+	 * @return string
+	 */
+	public function getComments() {
+		return $this->xmlEncode( $this->comments );
+	}
+
+	/**
+	 * Get the comment of this item without any escaping
+	 *
+	 * @return string
+	 */
+	public function getCommentsUnescaped() {
+		return $this->comments;
+	}
+
+	/**
+	 * Quickie hack... strip out wikilinks to more legible form from the comment.
+	 *
+	 * @param string $text Wikitext
+	 * @return string
+	 */
+	public static function stripComment( $text ) {
+		return preg_replace( '/\[\[([^]]*\|)?([^]]+)\]\]/', '\2', $text );
+	}
+
+	/** #@- */
+}
+
+class_alias( FeedItem::class, 'FeedItem' );
diff --git a/includes/Feed/FeedUtils.php b/includes/Feed/FeedUtils.php
new file mode 100644
index 000000000000..2e818f680673
--- /dev/null
+++ b/includes/Feed/FeedUtils.php
@@ -0,0 +1,324 @@
+<?php
+/**
+ * Helper functions for feeds.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ * http://www.gnu.org/copyleft/gpl.html
+ *
+ * @file
+ * @ingroup Feed
+ */
+
+namespace MediaWiki\Feed;
+
+use CommentStore;
+use Html;
+use Linker;
+use LogFormatter;
+use MediaWiki\MainConfigNames;
+use MediaWiki\MediaWikiServices;
+use MediaWiki\Revision\RevisionRecord;
+use MediaWiki\Revision\SlotRecord;
+use OutputPage;
+use RequestContext;
+use TextContent;
+use Title;
+use User;
+use UtfNormal;
+
+/**
+ * Helper functions for feeds
+ *
+ * @ingroup Feed
+ */
+class FeedUtils {
+
+	/**
+	 * Check whether feeds can be used and that $type is a valid feed type
+	 *
+	 * @param string $type Feed type, as requested by the user
+	 * @param OutputPage|null $output Null falls back to $wgOut
+	 * @return bool
+	 * @since 1.36 $output parameter added
+	 *
+	 */
+	public static function checkFeedOutput( $type, $output = null ) {
+		$feed = MediaWikiServices::getInstance()->getMainConfig()->get( MainConfigNames::Feed );
+		$feedClasses = MediaWikiServices::getInstance()->getMainConfig()->get( MainConfigNames::FeedClasses );
+		if ( $output === null ) {
+			// Todo update GoogleNewsSitemap and deprecate
+			global $wgOut;
+			$output = $wgOut;
+		}
+
+		if ( !$feed ) {
+			$output->addWikiMsg( 'feed-unavailable' );
+			return false;
+		}
+
+		if ( !isset( $feedClasses[$type] ) ) {
+			$output->addWikiMsg( 'feed-invalid' );
+			return false;
+		}
+
+		return true;
+	}
+
+	/**
+	 * Format a diff for the newsfeed
+	 *
+	 * @param \stdClass $row Row from the recentchanges table, including fields as
+	 *  appropriate for CommentStore
+	 * @param string|null $formattedComment rc_comment in HTML format, or null
+	 *   to format it on demand.
+	 * @return string
+	 */
+	public static function formatDiff( $row, $formattedComment = null ) {
+		$titleObj = Title::makeTitle( $row->rc_namespace, $row->rc_title );
+		$timestamp = wfTimestamp( TS_MW, $row->rc_timestamp );
+		$actiontext = '';
+		if ( $row->rc_type == RC_LOG ) {
+			$rcRow = (array)$row; // newFromRow() only accepts arrays for RC rows
+			$actiontext = LogFormatter::newFromRow( $rcRow )->getActionText();
+		}
+		if ( $row->rc_deleted & RevisionRecord::DELETED_COMMENT ) {
+			$formattedComment = wfMessage( 'rev-deleted-comment' )->escaped();
+		} elseif ( $formattedComment === null ) {
+			$formattedComment = Linker::formatComment(
+				CommentStore::getStore()->getComment( 'rc_comment', $row )->text );
+		}
+		return self::formatDiffRow2( $titleObj,
+			$row->rc_last_oldid, $row->rc_this_oldid,
+			$timestamp,
+			$formattedComment,
+			$actiontext
+		);
+	}
+
+	/**
+	 * Really format a diff for the newsfeed
+	 *
+	 * @param Title $title
+	 * @param int $oldid Old revision's id
+	 * @param int $newid New revision's id
+	 * @param string $timestamp New revision's timestamp
+	 * @param string $comment New revision's comment
+	 * @param string $actiontext Text of the action; in case of log event
+	 * @return string
+	 * @deprecated since 1.38 use formatDiffRow2
+	 *
+	 */
+	public static function formatDiffRow( $title, $oldid, $newid, $timestamp,
+										 $comment, $actiontext = ''
+	) {
+		$formattedComment = MediaWikiServices::getInstance()->getCommentFormatter()
+			->format( $comment );
+		return self::formatDiffRow2( $title, $oldid, $newid, $timestamp,
+			$formattedComment, $actiontext );
+	}
+
+	/**
+	 * Really really format a diff for the newsfeed. Same as formatDiffRow()
+	 * except with preformatted comments.
+	 *
+	 * @param Title $title
+	 * @param int $oldid Old revision's id
+	 * @param int $newid New revision's id
+	 * @param string $timestamp New revision's timestamp
+	 * @param string $formattedComment New revision's comment in HTML format
+	 * @param string $actiontext Text of the action; in case of log event
+	 * @return string
+	 */
+	public static function formatDiffRow2( $title, $oldid, $newid, $timestamp,
+										  $formattedComment, $actiontext = ''
+	) {
+		$feedDiffCutoff = MediaWikiServices::getInstance()->getMainConfig()->get( MainConfigNames::FeedDiffCutoff );
+
+		// log entries
+		$unwrappedText = implode(
+			' ',
+			array_filter( [ $actiontext, $formattedComment ] )
+		);
+		$completeText = Html::rawElement( 'p', [], $unwrappedText ) . "\n";
+
+		// NOTE: Check permissions for anonymous users, not current user.
+		//       No "privileged" version should end up in the cache.
+		//       Most feed readers will not log in anyway.
+		$anon = new User();
+		$services = MediaWikiServices::getInstance();
+		$permManager = $services->getPermissionManager();
+		$accErrors = $permManager->getPermissionErrors(
+			'read',
+			$anon,
+			$title
+		);
+
+		// Can't diff special pages, unreadable pages or pages with no new revision
+		// to compare against: just return the text.
+		if ( $title->getNamespace() < 0 || $accErrors || !$newid ) {
+			return $completeText;
+		}
+
+		$revLookup = $services->getRevisionLookup();
+		$contentHandlerFactory = $services->getContentHandlerFactory();
+		if ( $oldid ) {
+			$diffText = '';
+			// Don't bother generating the diff if we won't be able to show it
+			if ( $feedDiffCutoff > 0 ) {
+				$revRecord = $revLookup->getRevisionById( $oldid );
+
+				if ( !$revRecord ) {
+					$diffText = false;
+				} else {
+					$mainContext = RequestContext::getMain();
+					$context = clone RequestContext::getMain();
+					$context->setTitle( $title );
+
+					$model = $revRecord->getSlot(
+						SlotRecord::MAIN,
+						RevisionRecord::RAW
+					)->getModel();
+					$contentHandler = $contentHandlerFactory->getContentHandler( $model );
+					$de = $contentHandler->createDifferenceEngine( $context, $oldid, $newid );
+					$lang = $mainContext->getLanguage();
+					$user = $mainContext->getUser();
+					$diffText = $de->getDiff(
+						$mainContext->msg( 'previousrevision' )->text(), // hack
+						$mainContext->msg( 'revisionasof',
+							$lang->userTimeAndDate( $timestamp, $user ),
+							$lang->userDate( $timestamp, $user ),
+							$lang->userTime( $timestamp, $user ) )->text() );
+				}
+			}
+
+			if ( $feedDiffCutoff <= 0 || ( strlen( $diffText ) > $feedDiffCutoff ) ) {
+				// Omit large diffs
+				$diffText = self::getDiffLink( $title, $newid, $oldid );
+			} elseif ( $diffText === false ) {
+				// Error in diff engine, probably a missing revision
+				$diffText = Html::rawElement(
+					'p',
+					[],
+					"Can't load revision $newid"
+				);
+			} else {
+				// Diff output fine, clean up any illegal UTF-8
+				$diffText = UtfNormal\Validator::cleanUp( $diffText );
+				$diffText = self::applyDiffStyle( $diffText );
+			}
+		} else {
+			$revRecord = $revLookup->getRevisionById( $newid );
+			if ( $feedDiffCutoff <= 0 || $revRecord === null ) {
+				$newContent = $contentHandlerFactory
+					->getContentHandler( $title->getContentModel() )
+					->makeEmptyContent();
+			} else {
+				$newContent = $revRecord->getContent( SlotRecord::MAIN );
+			}
+
+			if ( $newContent instanceof TextContent ) {
+				// only textual content has a "source view".
+				$text = $newContent->getText();
+
+				if ( $feedDiffCutoff <= 0 || strlen( $text ) > $feedDiffCutoff ) {
+					$html = null;
+				} else {
+					$html = nl2br( htmlspecialchars( $text ) );
+				}
+			} else {
+				// XXX: we could get an HTML representation of the content via getParserOutput, but that may
+				//     contain JS magic and generally may not be suitable for inclusion in a feed.
+				//     Perhaps Content should have a getDescriptiveHtml method and/or a getSourceText method.
+				// Compare also ApiFeedContributions::feedItemDesc
+				$html = null;
+			}
+
+			if ( $html === null ) {
+				// Omit large new page diffs, T31110
+				// Also use diff link for non-textual content
+				$diffText = self::getDiffLink( $title, $newid );
+			} else {
+				$diffText = Html::rawElement(
+					'p',
+					[],
+					Html::rawElement( 'b', [], wfMessage( 'newpage' )->text() )
+				);
+				$diffText .= Html::rawElement( 'div', [], $html );
+			}
+		}
+		$completeText .= $diffText;
+
+		return $completeText;
+	}
+
+	/**
+	 * Generates a diff link. Used when the full diff is not wanted for example
+	 * when $wgFeedDiffCutoff is 0.
+	 *
+	 * @param Title $title Title object: used to generate the diff URL
+	 * @param int $newid Newid for this diff
+	 * @param int|null $oldid Oldid for the diff. Null means it is a new article
+	 * @return string
+	 */
+	protected static function getDiffLink( Title $title, $newid, $oldid = null ) {
+		$queryParameters = [ 'diff' => $newid ];
+		if ( $oldid != null ) {
+			$queryParameters['oldid'] = $oldid;
+		}
+		$diffUrl = $title->getFullURL( $queryParameters );
+
+		$diffLink = Html::element( 'a', [ 'href' => $diffUrl ],
+			wfMessage( 'showdiff' )->inContentLanguage()->text() );
+
+		return $diffLink;
+	}
+
+	/**
+	 * Hacky application of diff styles for the feeds.
+	 * Might be 'cleaner' to use DOM or XSLT or something,
+	 * but *gack* it's a pain in the ass.
+	 *
+	 * @param string $text Diff's HTML output
+	 * @return string Modified HTML
+	 */
+	public static function applyDiffStyle( $text ) {
+		$styles = [
+			'diff' => 'background-color: #fff; color: #202122;',
+			'diff-otitle' => 'background-color: #fff; color: #202122; text-align: center;',
+			'diff-ntitle' => 'background-color: #fff; color: #202122; text-align: center;',
+			'diff-addedline' => 'color: #202122; font-size: 88%; border-style: solid; '
+				. 'border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; '
+				. 'vertical-align: top; white-space: pre-wrap;',
+			'diff-deletedline' => 'color: #202122; font-size: 88%; border-style: solid; '
+				. 'border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; '
+				. 'vertical-align: top; white-space: pre-wrap;',
+			'diff-context' => 'background-color: #f8f9fa; color: #202122; font-size: 88%; '
+				. 'border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; '
+				. 'border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;',
+			'diffchange' => 'font-weight: bold; text-decoration: none;',
+		];
+
+		foreach ( $styles as $class => $style ) {
+			$text = preg_replace( '/(<\w+\b[^<>]*)\bclass=([\'"])(?:[^\'"]*\s)?' .
+				preg_quote( $class ) . '(?:\s[^\'"]*)?\2(?=[^<>]*>)/',
+				'$1style="' . $style . '"', $text );
+		}
+
+		return $text;
+	}
+
+}
+
+class_alias( FeedUtils::class, 'FeedUtils' );
diff --git a/includes/Feed/RSSFeed.php b/includes/Feed/RSSFeed.php
new file mode 100644
index 000000000000..1e3efa727c83
--- /dev/null
+++ b/includes/Feed/RSSFeed.php
@@ -0,0 +1,96 @@
+<?php
+/**
+ * Copyright © 2004 Brion Vibber <brion@pobox.com>
+ * https://www.mediawiki.org/
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ * http://www.gnu.org/copyleft/gpl.html
+ *
+ * @file
+ */
+
+namespace MediaWiki\Feed;
+
+/**
+ * Generate an RSS feed.
+ *
+ * @ingroup Feed
+ */
+class RSSFeed extends ChannelFeed {
+
+	/**
+	 * Format a date given a timestamp. If a timestamp is not given, nothing is returned
+	 *
+	 * @param string|int|null $ts Timestamp
+	 * @return string|null Date string
+	 */
+	private function formatTime( $ts ) {
+		if ( $ts ) {
+			return gmdate( 'D, d M Y H:i:s \G\M\T', (int)wfTimestamp( TS_UNIX, $ts ) );
+		}
+		return null;
+	}
+
+	/**
+	 * Output an RSS 2.0 header
+	 */
+	public function outHeader() {
+		$this->outXmlHeader();
+		// Manually escaping rather than letting Mustache do it because Mustache
+		// uses htmlentities, which does not work with XML
+		$templateParams = [
+			'title' => $this->getTitle(),
+			'url' => $this->xmlEncode( wfExpandUrl( $this->getUrlUnescaped(), PROTO_CURRENT ) ),
+			'description' => $this->getDescription(),
+			'language' => $this->xmlEncode( $this->getLanguage() ),
+			'version' => $this->xmlEncode( MW_VERSION ),
+			'timestamp' => $this->xmlEncode( $this->formatTime( wfTimestampNow() ) )
+		];
+		print $this->templateParser->processTemplate( 'RSSHeader', $templateParams );
+	}
+
+	/**
+	 * Output an RSS 2.0 item
+	 * @param FeedItem $item Item to be output
+	 */
+	public function outItem( $item ) {
+		// Manually escaping rather than letting Mustache do it because Mustache
+		// uses htmlentities, which does not work with XML
+		$templateParams = [
+			"title" => $item->getTitle(),
+			"url" => $this->xmlEncode( wfExpandUrl( $item->getUrlUnescaped(), PROTO_CURRENT ) ),
+			"permalink" => $item->rssIsPermalink,
+			"uniqueID" => $item->getUniqueID(),
+			"description" => $item->getDescription(),
+			"date" => $this->xmlEncode( $this->formatTime( $item->getDate() ) ),
+			"author" => $item->getAuthor()
+		];
+		$comments = $item->getCommentsUnescaped();
+		if ( $comments ) {
+			$commentsEscaped = $this->xmlEncode( wfExpandUrl( $comments, PROTO_CURRENT ) );
+			$templateParams["comments"] = $commentsEscaped;
+		}
+		print $this->templateParser->processTemplate( 'RSSItem', $templateParams );
+	}
+
+	/**
+	 * Output an RSS 2.0 footer
+	 */
+	public function outFooter() {
+		print "</channel></rss>";
+	}
+}
+
+class_alias( RSSFeed::class, 'RSSFeed' );