Implement extension registration from an extension.json file

[mediawiki.git] / includes / changes / RecentChange.php

<?php
/**
 * Utility class for creating and accessing recent change entries.
 *
 * 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
 */

/**
 * Utility class for creating new RC entries
 *
 * mAttribs:
 *  rc_id           id of the row in the recentchanges table
 *  rc_timestamp    time the entry was made
 *  rc_namespace    namespace #
 *  rc_title        non-prefixed db key
 *  rc_type         is new entry, used to determine whether updating is necessary
 *  rc_source       string representation of change source
 *  rc_minor        is minor
 *  rc_cur_id       page_id of associated page entry
 *  rc_user         user id who made the entry
 *  rc_user_text    user name who made the entry
 *  rc_comment      edit summary
 *  rc_this_oldid   rev_id associated with this entry (or zero)
 *  rc_last_oldid   rev_id associated with the entry before this one (or zero)
 *  rc_bot          is bot, hidden
 *  rc_ip           IP address of the user in dotted quad notation
 *  rc_new          obsolete, use rc_type==RC_NEW
 *  rc_patrolled    boolean whether or not someone has marked this edit as patrolled
 *  rc_old_len      integer byte length of the text before the edit
 *  rc_new_len      the same after the edit
 *  rc_deleted      partial deletion
 *  rc_logid        the log_id value for this log entry (or zero)
 *  rc_log_type     the log type (or null)
 *  rc_log_action   the log action (or null)
 *  rc_params       log params
 *
 * mExtra:
 *  prefixedDBkey   prefixed db key, used by external app via msg queue
 *  lastTimestamp   timestamp of previous entry, used in WHERE clause during update
 *  oldSize         text size before the change
 *  newSize         text size after the change
 *  pageStatus      status of the page: created, deleted, moved, restored, changed
 *
 * temporary:       not stored in the database
 *      notificationtimestamp
 *      numberofWatchingusers
 */
class RecentChange {
        // Constants for the rc_source field.  Extensions may also have
        // their own source constants.
        const SRC_EDIT = 'mw.edit';
        const SRC_NEW = 'mw.new';
        const SRC_LOG = 'mw.log';
        const SRC_EXTERNAL = 'mw.external'; // obsolete

        public $mAttribs = array();
        public $mExtra = array();

        /**
         * @var Title
         */
        public $mTitle = false;

        /**
         * @var User
         */
        private $mPerformer = false;

        public $numberofWatchingusers = 0; # Dummy to prevent error message in SpecialRecentChangesLinked
        public $notificationtimestamp;

        /**
         * @var int Line number of recent change. Default -1.
         */
        public $counter = -1;

        # Factory methods

        /**
         * @param mixed $row
         * @return RecentChange
         */
        public static function newFromRow( $row ) {
                $rc = new RecentChange;
                $rc->loadFromRow( $row );

                return $rc;
        }

        /**
         * Parsing text to RC_* constants
         * @since 1.24
         * @param string|array $type
         * @throws MWException
         * @return int|array RC_TYPE
         */
        public static function parseToRCType( $type ) {
                if ( is_array( $type ) ) {
                        $retval = array();
                        foreach ( $type as $t ) {
                                $retval[] = RecentChange::parseToRCType( $t );
                        }

                        return $retval;
                }

                switch ( $type ) {
                        case 'edit':
                                return RC_EDIT;
                        case 'new':
                                return RC_NEW;
                        case 'log':
                                return RC_LOG;
                        case 'external':
                                return RC_EXTERNAL;
                        default:
                                throw new MWException( "Unknown type '$type'" );
                }
        }

        /**
         * Parsing RC_* constants to human-readable test
         * @since 1.24
         * @param int $rcType
         * @return string $type
         */
        public static function parseFromRCType( $rcType ) {
                switch ( $rcType ) {
                        case RC_EDIT:
                                $type = 'edit';
                                break;
                        case RC_NEW:
                                $type = 'new';
                                break;
                        case RC_LOG:
                                $type = 'log';
                                break;
                        case RC_EXTERNAL:
                                $type = 'external';
                                break;
                        default:
                                $type = "$rcType";
                }

                return $type;
        }

        /**
         * Obtain the recent change with a given rc_id value
         *
         * @param int $rcid The rc_id value to retrieve
         * @return RecentChange
         */
        public static function newFromId( $rcid ) {
                return self::newFromConds( array( 'rc_id' => $rcid ), __METHOD__ );
        }

        /**
         * Find the first recent change matching some specific conditions
         *
         * @param array $conds Array of conditions
         * @param mixed $fname Override the method name in profiling/logs
         * @param array $options Query options
         * @return RecentChange
         */
        public static function newFromConds( $conds, $fname = __METHOD__, $options = array() ) {
                $dbr = wfGetDB( DB_SLAVE );
                $row = $dbr->selectRow( 'recentchanges', self::selectFields(), $conds, $fname, $options );
                if ( $row !== false ) {
                        return self::newFromRow( $row );
                } else {
                        return null;
                }
        }

        /**
         * Return the list of recentchanges fields that should be selected to create
         * a new recentchanges object.
         * @return array
         */
        public static function selectFields() {
                return array(
                        'rc_id',
                        'rc_timestamp',
                        'rc_user',
                        'rc_user_text',
                        'rc_namespace',
                        'rc_title',
                        'rc_comment',
                        'rc_minor',
                        'rc_bot',
                        'rc_new',
                        'rc_cur_id',
                        'rc_this_oldid',
                        'rc_last_oldid',
                        'rc_type',
                        'rc_source',
                        'rc_patrolled',
                        'rc_ip',
                        'rc_old_len',
                        'rc_new_len',
                        'rc_deleted',
                        'rc_logid',
                        'rc_log_type',
                        'rc_log_action',
                        'rc_params',
                );
        }

        # Accessors

        /**
         * @param array $attribs
         */
        public function setAttribs( $attribs ) {
                $this->mAttribs = $attribs;
        }

        /**
         * @param array $extra
         */
        public function setExtra( $extra ) {
                $this->mExtra = $extra;
        }

        /**
         * @return Title
         */
        public function &getTitle() {
                if ( $this->mTitle === false ) {
                        $this->mTitle = Title::makeTitle( $this->mAttribs['rc_namespace'], $this->mAttribs['rc_title'] );
                }

                return $this->mTitle;
        }

        /**
         * Get the User object of the person who performed this change.
         *
         * @return User
         */
        public function getPerformer() {
                if ( $this->mPerformer === false ) {
                        if ( $this->mAttribs['rc_user'] ) {
                                $this->mPerformer = User::newFromId( $this->mAttribs['rc_user'] );
                        } else {
                                $this->mPerformer = User::newFromName( $this->mAttribs['rc_user_text'], false );
                        }
                }

                return $this->mPerformer;
        }

        /**
         * Writes the data in this object to the database
         * @param bool $noudp
         */
        public function save( $noudp = false ) {
                global $wgPutIPinRC, $wgUseEnotif, $wgShowUpdatedMarker, $wgContLang;

                $dbw = wfGetDB( DB_MASTER );
                if ( !is_array( $this->mExtra ) ) {
                        $this->mExtra = array();
                }

                if ( !$wgPutIPinRC ) {
                        $this->mAttribs['rc_ip'] = '';
                }

                # If our database is strict about IP addresses, use NULL instead of an empty string
                if ( $dbw->strictIPs() && $this->mAttribs['rc_ip'] == '' ) {
                        unset( $this->mAttribs['rc_ip'] );
                }

                # Trim spaces on user supplied text
                $this->mAttribs['rc_comment'] = trim( $this->mAttribs['rc_comment'] );

                # Make sure summary is truncated (whole multibyte characters)
                $this->mAttribs['rc_comment'] = $wgContLang->truncate( $this->mAttribs['rc_comment'], 255 );

                # Fixup database timestamps
                $this->mAttribs['rc_timestamp'] = $dbw->timestamp( $this->mAttribs['rc_timestamp'] );
                $this->mAttribs['rc_id'] = $dbw->nextSequenceValue( 'recentchanges_rc_id_seq' );

                ## If we are using foreign keys, an entry of 0 for the page_id will fail, so use NULL
                if ( $dbw->cascadingDeletes() && $this->mAttribs['rc_cur_id'] == 0 ) {
                        unset( $this->mAttribs['rc_cur_id'] );
                }

                # Insert new row
                $dbw->insert( 'recentchanges', $this->mAttribs, __METHOD__ );

                # Set the ID
                $this->mAttribs['rc_id'] = $dbw->insertId();

                # Notify extensions
                Hooks::run( 'RecentChange_save', array( &$this ) );

                # Notify external application via UDP
                if ( !$noudp ) {
                        $this->notifyRCFeeds();
                }

                # E-mail notifications
                if ( $wgUseEnotif || $wgShowUpdatedMarker ) {
                        $editor = $this->getPerformer();
                        $title = $this->getTitle();

                        if ( Hooks::run( 'AbortEmailNotification', array( $editor, $title, $this ) ) ) {
                                # @todo FIXME: This would be better as an extension hook
                                $enotif = new EmailNotification();
                                $enotif->notifyOnPageChange( $editor, $title,
                                        $this->mAttribs['rc_timestamp'],
                                        $this->mAttribs['rc_comment'],
                                        $this->mAttribs['rc_minor'],
                                        $this->mAttribs['rc_last_oldid'],
                                        $this->mExtra['pageStatus'] );
                        }
                }
        }

        /**
         * Notify all the feeds about the change.
         * @param array $feeds Optional feeds to send to, defaults to $wgRCFeeds
         */
        public function notifyRCFeeds( array $feeds = null ) {
                global $wgRCFeeds;
                if ( $feeds === null ) {
                        $feeds = $wgRCFeeds;
                }

                $performer = $this->getPerformer();

                foreach ( $feeds as $feed ) {
                        $feed += array(
                                'omit_bots' => false,
                                'omit_anon' => false,
                                'omit_user' => false,
                                'omit_minor' => false,
                                'omit_patrolled' => false,
                        );

                        if (
                                ( $feed['omit_bots'] && $this->mAttribs['rc_bot'] ) ||
                                ( $feed['omit_anon'] && $performer->isAnon() ) ||
                                ( $feed['omit_user'] && !$performer->isAnon() ) ||
                                ( $feed['omit_minor'] && $this->mAttribs['rc_minor'] ) ||
                                ( $feed['omit_patrolled'] && $this->mAttribs['rc_patrolled'] ) ||
                                $this->mAttribs['rc_type'] == RC_EXTERNAL
                        ) {
                                continue;
                        }

                        $engine = self::getEngine( $feed['uri'] );

                        if ( isset( $this->mExtra['actionCommentIRC'] ) ) {
                                $actionComment = $this->mExtra['actionCommentIRC'];
                        } else {
                                $actionComment = null;
                        }

                        /** @var $formatter RCFeedFormatter */
                        $formatter = is_object( $feed['formatter'] ) ? $feed['formatter'] : new $feed['formatter']();
                        $line = $formatter->getLine( $feed, $this, $actionComment );

                        $engine->send( $feed, $line );
                }
        }

        /**
         * Gets the stream engine object for a given URI from $wgRCEngines
         *
         * @param string $uri URI to get the engine object for
         * @throws MWException
         * @return RCFeedEngine The engine object
         */
        public static function getEngine( $uri ) {
                global $wgRCEngines;

                $scheme = parse_url( $uri, PHP_URL_SCHEME );
                if ( !$scheme ) {
                        throw new MWException( __FUNCTION__ . ": Invalid stream logger URI: '$uri'" );
                }

                if ( !isset( $wgRCEngines[$scheme] ) ) {
                        throw new MWException( __FUNCTION__ . ": Unknown stream logger URI scheme: $scheme" );
                }

                return new $wgRCEngines[$scheme];
        }

        /**
         * Mark a given change as patrolled
         *
         * @param RecentChange|int $change RecentChange or corresponding rc_id
         * @param bool $auto For automatic patrol
         * @return array See doMarkPatrolled(), or null if $change is not an existing rc_id
         */
        public static function markPatrolled( $change, $auto = false ) {
                global $wgUser;

                $change = $change instanceof RecentChange
                        ? $change
                        : RecentChange::newFromId( $change );

                if ( !$change instanceof RecentChange ) {
                        return null;
                }

                return $change->doMarkPatrolled( $wgUser, $auto );
        }

        /**
         * Mark this RecentChange as patrolled
         *
         * NOTE: Can also return 'rcpatroldisabled', 'hookaborted' and
         * 'markedaspatrollederror-noautopatrol' as errors
         * @param User $user User object doing the action
         * @param bool $auto For automatic patrol
         * @return array Array of permissions errors, see Title::getUserPermissionsErrors()
         */
        public function doMarkPatrolled( User $user, $auto = false ) {
                global $wgUseRCPatrol, $wgUseNPPatrol;
                $errors = array();
                // If recentchanges patrol is disabled, only new pages
                // can be patrolled
                if ( !$wgUseRCPatrol && ( !$wgUseNPPatrol || $this->getAttribute( 'rc_type' ) != RC_NEW ) ) {
                        $errors[] = array( 'rcpatroldisabled' );
                }
                // Automatic patrol needs "autopatrol", ordinary patrol needs "patrol"
                $right = $auto ? 'autopatrol' : 'patrol';
                $errors = array_merge( $errors, $this->getTitle()->getUserPermissionsErrors( $right, $user ) );
                if ( !Hooks::run( 'MarkPatrolled', array( $this->getAttribute( 'rc_id' ), &$user, false ) ) ) {
                        $errors[] = array( 'hookaborted' );
                }
                // Users without the 'autopatrol' right can't patrol their
                // own revisions
                if ( $user->getName() == $this->getAttribute( 'rc_user_text' )
                        && !$user->isAllowed( 'autopatrol' )
                ) {
                        $errors[] = array( 'markedaspatrollederror-noautopatrol' );
                }
                if ( $errors ) {
                        return $errors;
                }
                // If the change was patrolled already, do nothing
                if ( $this->getAttribute( 'rc_patrolled' ) ) {
                        return array();
                }
                // Actually set the 'patrolled' flag in RC
                $this->reallyMarkPatrolled();
                // Log this patrol event
                PatrolLog::record( $this, $auto, $user );
                Hooks::run( 'MarkPatrolledComplete', array( $this->getAttribute( 'rc_id' ), &$user, false ) );

                return array();
        }

        /**
         * Mark this RecentChange patrolled, without error checking
         * @return int Number of affected rows
         */
        public function reallyMarkPatrolled() {
                $dbw = wfGetDB( DB_MASTER );
                $dbw->update(
                        'recentchanges',
                        array(
                                'rc_patrolled' => 1
                        ),
                        array(
                                'rc_id' => $this->getAttribute( 'rc_id' )
                        ),
                        __METHOD__
                );
                // Invalidate the page cache after the page has been patrolled
                // to make sure that the Patrol link isn't visible any longer!
                $this->getTitle()->invalidateCache();

                return $dbw->affectedRows();
        }

        /**
         * Makes an entry in the database corresponding to an edit
         *
         * @param string $timestamp
         * @param Title $title
         * @param bool $minor
         * @param User $user
         * @param string $comment
         * @param int $oldId
         * @param string $lastTimestamp
         * @param bool $bot
         * @param string $ip
         * @param int $oldSize
         * @param int $newSize
         * @param int $newId
         * @param int $patrol
         * @return RecentChange
         */
        public static function notifyEdit( $timestamp, &$title, $minor, &$user, $comment, $oldId,
                $lastTimestamp, $bot, $ip = '', $oldSize = 0, $newSize = 0, $newId = 0, $patrol = 0 ) {
                $rc = new RecentChange;
                $rc->mTitle = $title;
                $rc->mPerformer = $user;
                $rc->mAttribs = array(
                        'rc_timestamp' => $timestamp,
                        'rc_namespace' => $title->getNamespace(),
                        'rc_title' => $title->getDBkey(),
                        'rc_type' => RC_EDIT,
                        'rc_source' => self::SRC_EDIT,
                        'rc_minor' => $minor ? 1 : 0,
                        'rc_cur_id' => $title->getArticleID(),
                        'rc_user' => $user->getId(),
                        'rc_user_text' => $user->getName(),
                        'rc_comment' => $comment,
                        'rc_this_oldid' => $newId,
                        'rc_last_oldid' => $oldId,
                        'rc_bot' => $bot ? 1 : 0,
                        'rc_ip' => self::checkIPAddress( $ip ),
                        'rc_patrolled' => intval( $patrol ),
                        'rc_new' => 0, # obsolete
                        'rc_old_len' => $oldSize,
                        'rc_new_len' => $newSize,
                        'rc_deleted' => 0,
                        'rc_logid' => 0,
                        'rc_log_type' => null,
                        'rc_log_action' => '',
                        'rc_params' => ''
                );

                $rc->mExtra = array(
                        'prefixedDBkey' => $title->getPrefixedDBkey(),
                        'lastTimestamp' => $lastTimestamp,
                        'oldSize' => $oldSize,
                        'newSize' => $newSize,
                        'pageStatus' => 'changed'
                );
                $rc->save();

                return $rc;
        }

        /**
         * Makes an entry in the database corresponding to page creation
         * Note: the title object must be loaded with the new id using resetArticleID()
         *
         * @param string $timestamp
         * @param Title $title
         * @param bool $minor
         * @param User $user
         * @param string $comment
         * @param bool $bot
         * @param string $ip
         * @param int $size
         * @param int $newId
         * @param int $patrol
         * @return RecentChange
         */
        public static function notifyNew( $timestamp, &$title, $minor, &$user, $comment, $bot,
                $ip = '', $size = 0, $newId = 0, $patrol = 0 ) {
                $rc = new RecentChange;
                $rc->mTitle = $title;
                $rc->mPerformer = $user;
                $rc->mAttribs = array(
                        'rc_timestamp' => $timestamp,
                        'rc_namespace' => $title->getNamespace(),
                        'rc_title' => $title->getDBkey(),
                        'rc_type' => RC_NEW,
                        'rc_source' => self::SRC_NEW,
                        'rc_minor' => $minor ? 1 : 0,
                        'rc_cur_id' => $title->getArticleID(),
                        'rc_user' => $user->getId(),
                        'rc_user_text' => $user->getName(),
                        'rc_comment' => $comment,
                        'rc_this_oldid' => $newId,
                        'rc_last_oldid' => 0,
                        'rc_bot' => $bot ? 1 : 0,
                        'rc_ip' => self::checkIPAddress( $ip ),
                        'rc_patrolled' => intval( $patrol ),
                        'rc_new' => 1, # obsolete
                        'rc_old_len' => 0,
                        'rc_new_len' => $size,
                        'rc_deleted' => 0,
                        'rc_logid' => 0,
                        'rc_log_type' => null,
                        'rc_log_action' => '',
                        'rc_params' => ''
                );

                $rc->mExtra = array(
                        'prefixedDBkey' => $title->getPrefixedDBkey(),
                        'lastTimestamp' => 0,
                        'oldSize' => 0,
                        'newSize' => $size,
                        'pageStatus' => 'created'
                );
                $rc->save();

                return $rc;
        }

        /**
         * @param string $timestamp
         * @param Title $title
         * @param User $user
         * @param string $actionComment
         * @param string $ip
         * @param string $type
         * @param string $action
         * @param Title $target
         * @param string $logComment
         * @param string $params
         * @param int $newId
         * @param string $actionCommentIRC
         * @return bool
         */
        public static function notifyLog( $timestamp, &$title, &$user, $actionComment, $ip, $type,
                $action, $target, $logComment, $params, $newId = 0, $actionCommentIRC = ''
        ) {
                global $wgLogRestrictions;

                # Don't add private logs to RC!
                if ( isset( $wgLogRestrictions[$type] ) && $wgLogRestrictions[$type] != '*' ) {
                        return false;
                }
                $rc = self::newLogEntry( $timestamp, $title, $user, $actionComment, $ip, $type, $action,
                        $target, $logComment, $params, $newId, $actionCommentIRC );
                $rc->save();

                return true;
        }

        /**
         * @param string $timestamp
         * @param Title $title
         * @param User $user
         * @param string $actionComment
         * @param string $ip
         * @param string $type
         * @param string $action
         * @param Title $target
         * @param string $logComment
         * @param string $params
         * @param int $newId
         * @param string $actionCommentIRC
         * @return RecentChange
         */
        public static function newLogEntry( $timestamp, &$title, &$user, $actionComment, $ip,
                $type, $action, $target, $logComment, $params, $newId = 0, $actionCommentIRC = '' ) {
                global $wgRequest;

                ## Get pageStatus for email notification
                switch ( $type . '-' . $action ) {
                        case 'delete-delete':
                                $pageStatus = 'deleted';
                                break;
                        case 'move-move':
                        case 'move-move_redir':
                                $pageStatus = 'moved';
                                break;
                        case 'delete-restore':
                                $pageStatus = 'restored';
                                break;
                        case 'upload-upload':
                                $pageStatus = 'created';
                                break;
                        case 'upload-overwrite':
                        default:
                                $pageStatus = 'changed';
                                break;
                }

                $rc = new RecentChange;
                $rc->mTitle = $target;
                $rc->mPerformer = $user;
                $rc->mAttribs = array(
                        'rc_timestamp' => $timestamp,
                        'rc_namespace' => $target->getNamespace(),
                        'rc_title' => $target->getDBkey(),
                        'rc_type' => RC_LOG,
                        'rc_source' => self::SRC_LOG,
                        'rc_minor' => 0,
                        'rc_cur_id' => $target->getArticleID(),
                        'rc_user' => $user->getId(),
                        'rc_user_text' => $user->getName(),
                        'rc_comment' => $logComment,
                        'rc_this_oldid' => 0,
                        'rc_last_oldid' => 0,
                        'rc_bot' => $user->isAllowed( 'bot' ) ? $wgRequest->getBool( 'bot', true ) : 0,
                        'rc_ip' => self::checkIPAddress( $ip ),
                        'rc_patrolled' => 1,
                        'rc_new' => 0, # obsolete
                        'rc_old_len' => null,
                        'rc_new_len' => null,
                        'rc_deleted' => 0,
                        'rc_logid' => $newId,
                        'rc_log_type' => $type,
                        'rc_log_action' => $action,
                        'rc_params' => $params
                );

                $rc->mExtra = array(
                        'prefixedDBkey' => $title->getPrefixedDBkey(),
                        'lastTimestamp' => 0,
                        'actionComment' => $actionComment, // the comment appended to the action, passed from LogPage
                        'pageStatus' => $pageStatus,
                        'actionCommentIRC' => $actionCommentIRC
                );

                return $rc;
        }

        /**
         * Initialises the members of this object from a mysql row object
         *
         * @param mixed $row
         */
        public function loadFromRow( $row ) {
                $this->mAttribs = get_object_vars( $row );
                $this->mAttribs['rc_timestamp'] = wfTimestamp( TS_MW, $this->mAttribs['rc_timestamp'] );
                $this->mAttribs['rc_deleted'] = $row->rc_deleted; // MUST be set
        }

        /**
         * Get an attribute value
         *
         * @param string $name Attribute name
         * @return mixed
         */
        public function getAttribute( $name ) {
                return isset( $this->mAttribs[$name] ) ? $this->mAttribs[$name] : null;
        }

        /**
         * @return array
         */
        public function getAttributes() {
                return $this->mAttribs;
        }

        /**
         * Gets the end part of the diff URL associated with this object
         * Blank if no diff link should be displayed
         * @param bool $forceCur
         * @return string
         */
        public function diffLinkTrail( $forceCur ) {
                if ( $this->mAttribs['rc_type'] == RC_EDIT ) {
                        $trail = "curid=" . (int)( $this->mAttribs['rc_cur_id'] ) .
                                "&oldid=" . (int)( $this->mAttribs['rc_last_oldid'] );
                        if ( $forceCur ) {
                                $trail .= '&diff=0';
                        } else {
                                $trail .= '&diff=' . (int)( $this->mAttribs['rc_this_oldid'] );
                        }
                } else {
                        $trail = '';
                }

                return $trail;
        }

        /**
         * Returns the change size (HTML).
         * The lengths can be given optionally.
         * @param int $old
         * @param int $new
         * @return string
         */
        public function getCharacterDifference( $old = 0, $new = 0 ) {
                if ( $old === 0 ) {
                        $old = $this->mAttribs['rc_old_len'];
                }
                if ( $new === 0 ) {
                        $new = $this->mAttribs['rc_new_len'];
                }
                if ( $old === null || $new === null ) {
                        return '';
                }

                return ChangesList::showCharacterDifference( $old, $new );
        }

        /**
         * Purge expired changes from the recentchanges table
         * @since 1.22
         */
        public static function purgeExpiredChanges() {
                if ( wfReadOnly() ) {
                        return;
                }

                $method = __METHOD__;
                $dbw = wfGetDB( DB_MASTER );
                $dbw->onTransactionIdle( function () use ( $dbw, $method ) {
                        global $wgRCMaxAge;

                        $cutoff = $dbw->timestamp( time() - $wgRCMaxAge );
                        $dbw->delete(
                                'recentchanges',
                                array( 'rc_timestamp < ' . $dbw->addQuotes( $cutoff ) ),
                                $method
                        );
                } );
        }

        private static function checkIPAddress( $ip ) {
                global $wgRequest;
                if ( $ip ) {
                        if ( !IP::isIPAddress( $ip ) ) {
                                throw new MWException( "Attempt to write \"" . $ip .
                                        "\" as an IP address into recent changes" );
                        }
                } else {
                        $ip = $wgRequest->getIP();
                        if ( !$ip ) {
                                $ip = '';
                        }
                }

                return $ip;
        }

        /**
         * Check whether the given timestamp is new enough to have a RC row with a given tolerance
         * as the recentchanges table might not be cleared out regularly (so older entries might exist)
         * or rows which will be deleted soon shouldn't be included.
         *
         * @param mixed $timestamp MWTimestamp compatible timestamp
         * @param int $tolerance Tolerance in seconds
         * @return bool
         */
        public static function isInRCLifespan( $timestamp, $tolerance = 0 ) {
                global $wgRCMaxAge;

                return wfTimestamp( TS_UNIX, $timestamp ) > time() - $tolerance - $wgRCMaxAge;
        }
}