rdbms: Avoid selectDB() call in LoadMonitor new connections

[mediawiki.git] / includes / specialpage / QueryPage.php

<?php
/**
 * Base code for "query" special pages.
 *
 * 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 SpecialPage
 */

use Wikimedia\Rdbms\ResultWrapper;
use Wikimedia\Rdbms\IDatabase;
use Wikimedia\Rdbms\DBError;

/**
 * This is a class for doing query pages; since they're almost all the same,
 * we factor out some of the functionality into a superclass, and let
 * subclasses derive from it.
 * @ingroup SpecialPage
 */
abstract class QueryPage extends SpecialPage {
        /** @var bool Whether or not we want plain listoutput rather than an ordered list */
        protected $listoutput = false;

        /** @var int The offset and limit in use, as passed to the query() function */
        protected $offset = 0;

        /** @var int */
        protected $limit = 0;

        /**
         * The number of rows returned by the query. Reading this variable
         * only makes sense in functions that are run after the query has been
         * done, such as preprocessResults() and formatRow().
         */
        protected $numRows;

        protected $cachedTimestamp = null;

        /**
         * Whether to show prev/next links
         */
        protected $shownavigation = true;

        /**
         * Get a list of query page classes and their associated special pages,
         * for periodic updates.
         *
         * DO NOT CHANGE THIS LIST without testing that
         * maintenance/updateSpecialPages.php still works.
         * @return array
         */
        public static function getPages() {
                static $qp = null;

                if ( $qp === null ) {
                        // QueryPage subclass, Special page name
                        $qp = [
                                [ 'AncientPagesPage', 'Ancientpages' ],
                                [ 'BrokenRedirectsPage', 'BrokenRedirects' ],
                                [ 'DeadendPagesPage', 'Deadendpages' ],
                                [ 'DoubleRedirectsPage', 'DoubleRedirects' ],
                                [ 'FileDuplicateSearchPage', 'FileDuplicateSearch' ],
                                [ 'ListDuplicatedFilesPage', 'ListDuplicatedFiles' ],
                                [ 'LinkSearchPage', 'LinkSearch' ],
                                [ 'ListredirectsPage', 'Listredirects' ],
                                [ 'LonelyPagesPage', 'Lonelypages' ],
                                [ 'LongPagesPage', 'Longpages' ],
                                [ 'MediaStatisticsPage', 'MediaStatistics' ],
                                [ 'MIMEsearchPage', 'MIMEsearch' ],
                                [ 'MostcategoriesPage', 'Mostcategories' ],
                                [ 'MostimagesPage', 'Mostimages' ],
                                [ 'MostinterwikisPage', 'Mostinterwikis' ],
                                [ 'MostlinkedCategoriesPage', 'Mostlinkedcategories' ],
                                [ 'MostlinkedTemplatesPage', 'Mostlinkedtemplates' ],
                                [ 'MostlinkedPage', 'Mostlinked' ],
                                [ 'MostrevisionsPage', 'Mostrevisions' ],
                                [ 'FewestrevisionsPage', 'Fewestrevisions' ],
                                [ 'ShortPagesPage', 'Shortpages' ],
                                [ 'UncategorizedCategoriesPage', 'Uncategorizedcategories' ],
                                [ 'UncategorizedPagesPage', 'Uncategorizedpages' ],
                                [ 'UncategorizedImagesPage', 'Uncategorizedimages' ],
                                [ 'UncategorizedTemplatesPage', 'Uncategorizedtemplates' ],
                                [ 'UnusedCategoriesPage', 'Unusedcategories' ],
                                [ 'UnusedimagesPage', 'Unusedimages' ],
                                [ 'WantedCategoriesPage', 'Wantedcategories' ],
                                [ 'WantedFilesPage', 'Wantedfiles' ],
                                [ 'WantedPagesPage', 'Wantedpages' ],
                                [ 'WantedTemplatesPage', 'Wantedtemplates' ],
                                [ 'UnwatchedpagesPage', 'Unwatchedpages' ],
                                [ 'UnusedtemplatesPage', 'Unusedtemplates' ],
                                [ 'WithoutInterwikiPage', 'Withoutinterwiki' ],
                        ];
                        Hooks::run( 'wgQueryPages', [ &$qp ] );
                }

                return $qp;
        }

        /**
         * A mutator for $this->listoutput;
         *
         * @param bool $bool
         */
        function setListoutput( $bool ) {
                $this->listoutput = $bool;
        }

        /**
         * Subclasses return an SQL query here, formatted as an array with the
         * following keys:
         *    tables => Table(s) for passing to Database::select()
         *    fields => Field(s) for passing to Database::select(), may be *
         *    conds => WHERE conditions
         *    options => options
         *    join_conds => JOIN conditions
         *
         * Note that the query itself should return the following three columns:
         * 'namespace', 'title', and 'value'. 'value' is used for sorting.
         *
         * These may be stored in the querycache table for expensive queries,
         * and that cached data will be returned sometimes, so the presence of
         * extra fields can't be relied upon. The cached 'value' column will be
         * an integer; non-numeric values are useful only for sorting the
         * initial query (except if they're timestamps, see usesTimestamps()).
         *
         * Don't include an ORDER or LIMIT clause, they will be added.
         *
         * If this function is not overridden or returns something other than
         * an array, getSQL() will be used instead. This is for backwards
         * compatibility only and is strongly deprecated.
         * @return array
         * @since 1.18
         */
        public function getQueryInfo() {
                return null;
        }

        /**
         * For back-compat, subclasses may return a raw SQL query here, as a string.
         * This is strongly deprecated; getQueryInfo() should be overridden instead.
         * @throws MWException
         * @return string
         */
        function getSQL() {
                /* Implement getQueryInfo() instead */
                throw new MWException( "Bug in a QueryPage: doesn't implement getQueryInfo() nor "
                        . "getQuery() properly" );
        }

        /**
         * Subclasses return an array of fields to order by here. Don't append
         * DESC to the field names, that'll be done automatically if
         * sortDescending() returns true.
         * @return array
         * @since 1.18
         */
        function getOrderFields() {
                return [ 'value' ];
        }

        /**
         * Does this query return timestamps rather than integers in its
         * 'value' field? If true, this class will convert 'value' to a
         * UNIX timestamp for caching.
         * NOTE: formatRow() may get timestamps in TS_MW (mysql), TS_DB (pgsql)
         *       or TS_UNIX (querycache) format, so be sure to always run them
         *       through wfTimestamp()
         * @return bool
         * @since 1.18
         */
        public function usesTimestamps() {
                return false;
        }

        /**
         * Override to sort by increasing values
         *
         * @return bool
         */
        function sortDescending() {
                return true;
        }

        /**
         * Is this query expensive (for some definition of expensive)? Then we
         * don't let it run in miser mode. $wgDisableQueryPages causes all query
         * pages to be declared expensive. Some query pages are always expensive.
         *
         * @return bool
         */
        public function isExpensive() {
                return $this->getConfig()->get( 'DisableQueryPages' );
        }

        /**
         * Is the output of this query cacheable? Non-cacheable expensive pages
         * will be disabled in miser mode and will not have their results written
         * to the querycache table.
         * @return bool
         * @since 1.18
         */
        public function isCacheable() {
                return true;
        }

        /**
         * Whether or not the output of the page in question is retrieved from
         * the database cache.
         *
         * @return bool
         */
        public function isCached() {
                return $this->isExpensive() && $this->getConfig()->get( 'MiserMode' );
        }

        /**
         * Sometime we don't want to build rss / atom feeds.
         *
         * @return bool
         */
        function isSyndicated() {
                return true;
        }

        /**
         * Formats the results of the query for display. The skin is the current
         * skin; you can use it for making links. The result is a single row of
         * result data. You should be able to grab SQL results off of it.
         * If the function returns false, the line output will be skipped.
         * @param Skin $skin
         * @param object $result Result row
         * @return string|bool String or false to skip
         */
        abstract function formatResult( $skin, $result );

        /**
         * The content returned by this function will be output before any result
         *
         * @return string
         */
        function getPageHeader() {
                return '';
        }

        /**
         * Outputs some kind of an informative message (via OutputPage) to let the
         * user know that the query returned nothing and thus there's nothing to
         * show.
         *
         * @since 1.26
         */
        protected function showEmptyText() {
                $this->getOutput()->addWikiMsg( 'specialpage-empty' );
        }

        /**
         * If using extra form wheely-dealies, return a set of parameters here
         * as an associative array. They will be encoded and added to the paging
         * links (prev/next/lengths).
         *
         * @return array
         */
        function linkParameters() {
                return [];
        }

        /**
         * Some special pages (for example SpecialListusers used to) might not return the
         * current object formatted, but return the previous one instead.
         * Setting this to return true will ensure formatResult() is called
         * one more time to make sure that the very last result is formatted
         * as well.
         *
         * @deprecated since 1.27
         *
         * @return bool
         */
        function tryLastResult() {
                return false;
        }

        /**
         * Clear the cache and save new results
         *
         * @param int|bool $limit Limit for SQL statement
         * @param bool $ignoreErrors Whether to ignore database errors
         * @throws DBError|Exception
         * @return bool|int
         */
        public function recache( $limit, $ignoreErrors = true ) {
                if ( !$this->isCacheable() ) {
                        return 0;
                }

                $fname = static::class . '::recache';
                $dbw = wfGetDB( DB_MASTER );
                if ( !$dbw ) {
                        return false;
                }

                try {
                        # Do query
                        $res = $this->reallyDoQuery( $limit, false );
                        $num = false;
                        if ( $res ) {
                                $num = $res->numRows();
                                # Fetch results
                                $vals = [];
                                foreach ( $res as $row ) {
                                        if ( isset( $row->value ) ) {
                                                if ( $this->usesTimestamps() ) {
                                                        $value = wfTimestamp( TS_UNIX,
                                                                $row->value );
                                                } else {
                                                        $value = intval( $row->value ); // T16414
                                                }
                                        } else {
                                                $value = 0;
                                        }

                                        $vals[] = [
                                                'qc_type' => $this->getName(),
                                                'qc_namespace' => $row->namespace,
                                                'qc_title' => $row->title,
                                                'qc_value' => $value
                                        ];
                                }

                                $dbw->doAtomicSection(
                                        __METHOD__,
                                        function ( IDatabase $dbw, $fname ) use ( $vals ) {
                                                # Clear out any old cached data
                                                $dbw->delete( 'querycache',
                                                        [ 'qc_type' => $this->getName() ],
                                                        $fname
                                                );
                                                # Save results into the querycache table on the master
                                                if ( count( $vals ) ) {
                                                        $dbw->insert( 'querycache', $vals, $fname );
                                                }
                                                # Update the querycache_info record for the page
                                                $dbw->delete( 'querycache_info',
                                                        [ 'qci_type' => $this->getName() ],
                                                        $fname
                                                );
                                                $dbw->insert( 'querycache_info',
                                                        [ 'qci_type' => $this->getName(),
                                                                'qci_timestamp' => $dbw->timestamp() ],
                                                        $fname
                                                );
                                        }
                                );
                        }
                } catch ( DBError $e ) {
                        if ( !$ignoreErrors ) {
                                throw $e; // report query error
                        }
                        $num = false; // set result to false to indicate error
                }

                return $num;
        }

        /**
         * Get a DB connection to be used for slow recache queries
         * @return IDatabase
         */
        function getRecacheDB() {
                return wfGetDB( DB_REPLICA, [ $this->getName(), 'QueryPage::recache', 'vslow' ] );
        }

        /**
         * Run the query and return the result
         * @param int|bool $limit Numerical limit or false for no limit
         * @param int|bool $offset Numerical offset or false for no offset
         * @return ResultWrapper
         * @since 1.18
         */
        public function reallyDoQuery( $limit, $offset = false ) {
                $fname = static::class . '::reallyDoQuery';
                $dbr = $this->getRecacheDB();
                $query = $this->getQueryInfo();
                $order = $this->getOrderFields();

                if ( $this->sortDescending() ) {
                        foreach ( $order as &$field ) {
                                $field .= ' DESC';
                        }
                }

                if ( is_array( $query ) ) {
                        $tables = isset( $query['tables'] ) ? (array)$query['tables'] : [];
                        $fields = isset( $query['fields'] ) ? (array)$query['fields'] : [];
                        $conds = isset( $query['conds'] ) ? (array)$query['conds'] : [];
                        $options = isset( $query['options'] ) ? (array)$query['options'] : [];
                        $join_conds = isset( $query['join_conds'] ) ? (array)$query['join_conds'] : [];

                        if ( $order ) {
                                $options['ORDER BY'] = $order;
                        }

                        if ( $limit !== false ) {
                                $options['LIMIT'] = intval( $limit );
                        }

                        if ( $offset !== false ) {
                                $options['OFFSET'] = intval( $offset );
                        }

                        $res = $dbr->select( $tables, $fields, $conds, $fname,
                                        $options, $join_conds
                        );
                } else {
                        // Old-fashioned raw SQL style, deprecated
                        $sql = $this->getSQL();
                        $sql .= ' ORDER BY ' . implode( ', ', $order );
                        $sql = $dbr->limitResult( $sql, $limit, $offset );
                        $res = $dbr->query( $sql, $fname );
                }

                return $res;
        }

        /**
         * Somewhat deprecated, you probably want to be using execute()
         * @param int|bool $offset
         * @param int|bool $limit
         * @return ResultWrapper
         */
        public function doQuery( $offset = false, $limit = false ) {
                if ( $this->isCached() && $this->isCacheable() ) {
                        return $this->fetchFromCache( $limit, $offset );
                } else {
                        return $this->reallyDoQuery( $limit, $offset );
                }
        }

        /**
         * Fetch the query results from the query cache
         * @param int|bool $limit Numerical limit or false for no limit
         * @param int|bool $offset Numerical offset or false for no offset
         * @return ResultWrapper
         * @since 1.18
         */
        public function fetchFromCache( $limit, $offset = false ) {
                $dbr = wfGetDB( DB_REPLICA );
                $options = [];

                if ( $limit !== false ) {
                        $options['LIMIT'] = intval( $limit );
                }

                if ( $offset !== false ) {
                        $options['OFFSET'] = intval( $offset );
                }

                $order = $this->getCacheOrderFields();
                if ( $this->sortDescending() ) {
                        foreach ( $order as &$field ) {
                                $field .= " DESC";
                        }
                }
                if ( $order ) {
                        $options['ORDER BY'] = $order;
                }

                return $dbr->select( 'querycache',
                                [ 'qc_type',
                                'namespace' => 'qc_namespace',
                                'title' => 'qc_title',
                                'value' => 'qc_value' ],
                                [ 'qc_type' => $this->getName() ],
                                __METHOD__,
                                $options
                );
        }

        /**
         * Return the order fields for fetchFromCache. Default is to always use
         * "ORDER BY value" which was the default prior to this function.
         * @return array
         * @since 1.29
         */
        function getCacheOrderFields() {
                return [ 'value' ];
        }

        public function getCachedTimestamp() {
                if ( is_null( $this->cachedTimestamp ) ) {
                        $dbr = wfGetDB( DB_REPLICA );
                        $fname = static::class . '::getCachedTimestamp';
                        $this->cachedTimestamp = $dbr->selectField( 'querycache_info', 'qci_timestamp',
                                [ 'qci_type' => $this->getName() ], $fname );
                }
                return $this->cachedTimestamp;
        }

        /**
         * Returns limit and offset, as returned by $this->getRequest()->getLimitOffset().
         * Subclasses may override this to further restrict or modify limit and offset.
         *
         * @note Restricts the offset parameter, as most query pages have inefficient paging
         *
         * Its generally expected that the returned limit will not be 0, and the returned
         * offset will be less than the max results.
         *
         * @since 1.26
         * @return int[] list( $limit, $offset )
         */
        protected function getLimitOffset() {
                list( $limit, $offset ) = $this->getRequest()->getLimitOffset();
                if ( $this->getConfig()->get( 'MiserMode' ) ) {
                        $maxResults = $this->getMaxResults();
                        // Can't display more than max results on a page
                        $limit = min( $limit, $maxResults );
                        // Can't skip over more than the end of $maxResults
                        $offset = min( $offset, $maxResults + 1 );
                }
                return [ $limit, $offset ];
        }

        /**
         * What is limit to fetch from DB
         *
         * Used to make it appear the DB stores less results then it actually does
         * @param int $uiLimit Limit from UI
         * @param int $uiOffset Offset from UI
         * @return int Limit to use for DB (not including extra row to see if at end)
         */
        protected function getDBLimit( $uiLimit, $uiOffset ) {
                $maxResults = $this->getMaxResults();
                if ( $this->getConfig()->get( 'MiserMode' ) ) {
                        $limit = min( $uiLimit + 1, $maxResults - $uiOffset );
                        return max( $limit, 0 );
                } else {
                        return $uiLimit + 1;
                }
        }

        /**
         * Get max number of results we can return in miser mode.
         *
         * Most QueryPage subclasses use inefficient paging, so limit the max amount we return
         * This matters for uncached query pages that might otherwise accept an offset of 3 million
         *
         * @since 1.27
         * @return int
         */
        protected function getMaxResults() {
                // Max of 10000, unless we store more than 10000 in query cache.
                return max( $this->getConfig()->get( 'QueryCacheLimit' ), 10000 );
        }

        /**
         * This is the actual workhorse. It does everything needed to make a
         * real, honest-to-gosh query page.
         * @param string $par
         */
        public function execute( $par ) {
                $user = $this->getUser();
                if ( !$this->userCanExecute( $user ) ) {
                        $this->displayRestrictionError();
                        return;
                }

                $this->setHeaders();
                $this->outputHeader();

                $out = $this->getOutput();

                if ( $this->isCached() && !$this->isCacheable() ) {
                        $out->addWikiMsg( 'querypage-disabled' );
                        return;
                }

                $out->setSyndicated( $this->isSyndicated() );

                if ( $this->limit == 0 && $this->offset == 0 ) {
                        list( $this->limit, $this->offset ) = $this->getLimitOffset();
                }
                $dbLimit = $this->getDBLimit( $this->limit, $this->offset );
                // @todo Use doQuery()
                if ( !$this->isCached() ) {
                        # select one extra row for navigation
                        $res = $this->reallyDoQuery( $dbLimit, $this->offset );
                } else {
                        # Get the cached result, select one extra row for navigation
                        $res = $this->fetchFromCache( $dbLimit, $this->offset );
                        if ( !$this->listoutput ) {
                                # Fetch the timestamp of this update
                                $ts = $this->getCachedTimestamp();
                                $lang = $this->getLanguage();
                                $maxResults = $lang->formatNum( $this->getConfig()->get( 'QueryCacheLimit' ) );

                                if ( $ts ) {
                                        $updated = $lang->userTimeAndDate( $ts, $user );
                                        $updateddate = $lang->userDate( $ts, $user );
                                        $updatedtime = $lang->userTime( $ts, $user );
                                        $out->addMeta( 'Data-Cache-Time', $ts );
                                        $out->addJsConfigVars( 'dataCacheTime', $ts );
                                        $out->addWikiMsg( 'perfcachedts', $updated, $updateddate, $updatedtime, $maxResults );
                                } else {
                                        $out->addWikiMsg( 'perfcached', $maxResults );
                                }

                                # If updates on this page have been disabled, let the user know
                                # that the data set won't be refreshed for now
                                if ( is_array( $this->getConfig()->get( 'DisableQueryPageUpdate' ) )
                                        && in_array( $this->getName(), $this->getConfig()->get( 'DisableQueryPageUpdate' ) )
                                ) {
                                        $out->wrapWikiMsg(
                                                "<div class=\"mw-querypage-no-updates\">\n$1\n</div>",
                                                'querypage-no-updates'
                                        );
                                }
                        }
                }

                $this->numRows = $res->numRows();

                $dbr = $this->getRecacheDB();
                $this->preprocessResults( $dbr, $res );

                $out->addHTML( Xml::openElement( 'div', [ 'class' => 'mw-spcontent' ] ) );

                # Top header and navigation
                if ( $this->shownavigation ) {
                        $out->addHTML( $this->getPageHeader() );
                        if ( $this->numRows > 0 ) {
                                $out->addHTML( $this->msg( 'showingresultsinrange' )->numParams(
                                        min( $this->numRows, $this->limit ), # do not show the one extra row, if exist
                                        $this->offset + 1, ( min( $this->numRows, $this->limit ) + $this->offset ) )->parseAsBlock() );
                                # Disable the "next" link when we reach the end
                                $miserMaxResults = $this->getConfig()->get( 'MiserMode' )
                                        && ( $this->offset + $this->limit >= $this->getMaxResults() );
                                $atEnd = ( $this->numRows <= $this->limit ) || $miserMaxResults;
                                $paging = $this->getLanguage()->viewPrevNext( $this->getPageTitle( $par ), $this->offset,
                                        $this->limit, $this->linkParameters(), $atEnd );
                                $out->addHTML( '<p>' . $paging . '</p>' );
                        } else {
                                # No results to show, so don't bother with "showing X of Y" etc.
                                # -- just let the user know and give up now
                                $this->showEmptyText();
                                $out->addHTML( Xml::closeElement( 'div' ) );
                                return;
                        }
                }

                # The actual results; specialist subclasses will want to handle this
                # with more than a straight list, so we hand them the info, plus
                # an OutputPage, and let them get on with it
                $this->outputResults( $out,
                        $this->getSkin(),
                        $dbr, # Should use a ResultWrapper for this
                        $res,
                        min( $this->numRows, $this->limit ), # do not format the one extra row, if exist
                        $this->offset );

                # Repeat the paging links at the bottom
                if ( $this->shownavigation ) {
                        $out->addHTML( '<p>' . $paging . '</p>' );
                }

                $out->addHTML( Xml::closeElement( 'div' ) );
        }

        /**
         * Format and output report results using the given information plus
         * OutputPage
         *
         * @param OutputPage $out OutputPage to print to
         * @param Skin $skin User skin to use
         * @param IDatabase $dbr Database (read) connection to use
         * @param ResultWrapper $res Result pointer
         * @param int $num Number of available result rows
         * @param int $offset Paging offset
         */
        protected function outputResults( $out, $skin, $dbr, $res, $num, $offset ) {
                global $wgContLang;

                if ( $num > 0 ) {
                        $html = [];
                        if ( !$this->listoutput ) {
                                $html[] = $this->openList( $offset );
                        }

                        # $res might contain the whole 1,000 rows, so we read up to
                        # $num [should update this to use a Pager]
                        // @codingStandardsIgnoreStart Generic.CodeAnalysis.ForLoopWithTestFunctionCall.NotAllowed
                        for ( $i = 0; $i < $num && $row = $res->fetchObject(); $i++ ) {
                                // @codingStandardsIgnoreEnd
                                $line = $this->formatResult( $skin, $row );
                                if ( $line ) {
                                        $html[] = $this->listoutput
                                                ? $line
                                                : "<li>{$line}</li>\n";
                                }
                        }

                        # Flush the final result
                        if ( $this->tryLastResult() ) {
                                $row = null;
                                $line = $this->formatResult( $skin, $row );
                                if ( $line ) {
                                        $html[] = $this->listoutput
                                                ? $line
                                                : "<li>{$line}</li>\n";
                                }
                        }

                        if ( !$this->listoutput ) {
                                $html[] = $this->closeList();
                        }

                        $html = $this->listoutput
                                ? $wgContLang->listToText( $html )
                                : implode( '', $html );

                        $out->addHTML( $html );
                }
        }

        /**
         * @param int $offset
         * @return string
         */
        function openList( $offset ) {
                return "\n<ol start='" . ( $offset + 1 ) . "' class='special'>\n";
        }

        /**
         * @return string
         */
        function closeList() {
                return "</ol>\n";
        }

        /**
         * Do any necessary preprocessing of the result object.
         * @param IDatabase $db
         * @param ResultWrapper $res
         */
        function preprocessResults( $db, $res ) {
        }

        /**
         * Similar to above, but packaging in a syndicated feed instead of a web page
         * @param string $class
         * @param int $limit
         * @return bool
         */
        function doFeed( $class = '', $limit = 50 ) {
                if ( !$this->getConfig()->get( 'Feed' ) ) {
                        $this->getOutput()->addWikiMsg( 'feed-unavailable' );
                        return false;
                }

                $limit = min( $limit, $this->getConfig()->get( 'FeedLimit' ) );

                $feedClasses = $this->getConfig()->get( 'FeedClasses' );
                if ( isset( $feedClasses[$class] ) ) {
                        /** @var RSSFeed|AtomFeed $feed */
                        $feed = new $feedClasses[$class](
                                $this->feedTitle(),
                                $this->feedDesc(),
                                $this->feedUrl() );
                        $feed->outHeader();

                        $res = $this->reallyDoQuery( $limit, 0 );
                        foreach ( $res as $obj ) {
                                $item = $this->feedResult( $obj );
                                if ( $item ) {
                                        $feed->outItem( $item );
                                }
                        }

                        $feed->outFooter();
                        return true;
                } else {
                        return false;
                }
        }

        /**
         * Override for custom handling. If the titles/links are ok, just do
         * feedItemDesc()
         * @param object $row
         * @return FeedItem|null
         */
        function feedResult( $row ) {
                if ( !isset( $row->title ) ) {
                        return null;
                }
                $title = Title::makeTitle( intval( $row->namespace ), $row->title );
                if ( $title ) {
                        $date = isset( $row->timestamp ) ? $row->timestamp : '';
                        $comments = '';
                        if ( $title ) {
                                $talkpage = $title->getTalkPage();
                                $comments = $talkpage->getFullURL();
                        }

                        return new FeedItem(
                                $title->getPrefixedText(),
                                $this->feedItemDesc( $row ),
                                $title->getFullURL(),
                                $date,
                                $this->feedItemAuthor( $row ),
                                $comments );
                } else {
                        return null;
                }
        }

        function feedItemDesc( $row ) {
                return isset( $row->comment ) ? htmlspecialchars( $row->comment ) : '';
        }

        function feedItemAuthor( $row ) {
                return isset( $row->user_text ) ? $row->user_text : '';
        }

        function feedTitle() {
                $desc = $this->getDescription();
                $code = $this->getConfig()->get( 'LanguageCode' );
                $sitename = $this->getConfig()->get( 'Sitename' );
                return "$sitename - $desc [$code]";
        }

        function feedDesc() {
                return $this->msg( 'tagline' )->text();
        }

        function feedUrl() {
                return $this->getPageTitle()->getFullURL();
        }

        /**
         * Creates a new LinkBatch object, adds all pages from the passed ResultWrapper (MUST include
         * title and optional the namespace field) and executes the batch. This operation will pre-cache
         * LinkCache information like page existence and information for stub color and redirect hints.
         *
         * @param ResultWrapper $res The ResultWrapper object to process. Needs to include the title
         *  field and namespace field, if the $ns parameter isn't set.
         * @param null $ns Use this namespace for the given titles in the ResultWrapper object,
         *  instead of the namespace value of $res.
         */
        protected function executeLBFromResultWrapper( ResultWrapper $res, $ns = null ) {
                if ( !$res->numRows() ) {
                        return;
                }

                $batch = new LinkBatch;
                foreach ( $res as $row ) {
                        $batch->add( $ns !== null ? $ns : $row->namespace, $row->title );
                }
                $batch->execute();

                $res->seek( 0 );
        }
}