rdbms: Avoid selectDB() call in LoadMonitor new connections

[mediawiki.git] / includes / Revision.php

<?php
/**
 * Representation of a page version.
 *
 * 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
 */

use Wikimedia\Rdbms\Database;
use Wikimedia\Rdbms\IDatabase;
use MediaWiki\Linker\LinkTarget;
use MediaWiki\MediaWikiServices;
use Wikimedia\Rdbms\ResultWrapper;
use Wikimedia\Rdbms\FakeResultWrapper;

/**
 * @todo document
 */
class Revision implements IDBAccessObject {
        /** @var int|null */
        protected $mId;
        /** @var int|null */
        protected $mPage;
        /** @var string */
        protected $mUserText;
        /** @var string */
        protected $mOrigUserText;
        /** @var int */
        protected $mUser;
        /** @var bool */
        protected $mMinorEdit;
        /** @var string */
        protected $mTimestamp;
        /** @var int */
        protected $mDeleted;
        /** @var int */
        protected $mSize;
        /** @var string */
        protected $mSha1;
        /** @var int */
        protected $mParentId;
        /** @var string */
        protected $mComment;
        /** @var string */
        protected $mText;
        /** @var int */
        protected $mTextId;
        /** @var int */
        protected $mUnpatrolled;

        /** @var stdClass|null */
        protected $mTextRow;

        /**  @var null|Title */
        protected $mTitle;
        /** @var bool */
        protected $mCurrent;
        /** @var string */
        protected $mContentModel;
        /** @var string */
        protected $mContentFormat;

        /** @var Content|null|bool */
        protected $mContent;
        /** @var null|ContentHandler */
        protected $mContentHandler;

        /** @var int */
        protected $mQueryFlags = 0;
        /** @var bool Used for cached values to reload user text and rev_deleted */
        protected $mRefreshMutableFields = false;
        /** @var string Wiki ID; false means the current wiki */
        protected $mWiki = false;

        // Revision deletion constants
        const DELETED_TEXT = 1;
        const DELETED_COMMENT = 2;
        const DELETED_USER = 4;
        const DELETED_RESTRICTED = 8;
        const SUPPRESSED_USER = 12; // convenience
        const SUPPRESSED_ALL = 15; // convenience

        // Audience options for accessors
        const FOR_PUBLIC = 1;
        const FOR_THIS_USER = 2;
        const RAW = 3;

        const TEXT_CACHE_GROUP = 'revisiontext:10'; // process cache name and max key count

        /**
         * Load a page revision from a given revision ID number.
         * Returns null if no such revision can be found.
         *
         * $flags include:
         *      Revision::READ_LATEST  : Select the data from the master
         *      Revision::READ_LOCKING : Select & lock the data from the master
         *
         * @param int $id
         * @param int $flags (optional)
         * @return Revision|null
         */
        public static function newFromId( $id, $flags = 0 ) {
                return self::newFromConds( [ 'rev_id' => intval( $id ) ], $flags );
        }

        /**
         * Load either the current, or a specified, revision
         * that's attached to a given link target. If not attached
         * to that link target, will return null.
         *
         * $flags include:
         *      Revision::READ_LATEST  : Select the data from the master
         *      Revision::READ_LOCKING : Select & lock the data from the master
         *
         * @param LinkTarget $linkTarget
         * @param int $id (optional)
         * @param int $flags Bitfield (optional)
         * @return Revision|null
         */
        public static function newFromTitle( LinkTarget $linkTarget, $id = 0, $flags = 0 ) {
                $conds = [
                        'page_namespace' => $linkTarget->getNamespace(),
                        'page_title' => $linkTarget->getDBkey()
                ];
                if ( $id ) {
                        // Use the specified ID
                        $conds['rev_id'] = $id;
                        return self::newFromConds( $conds, $flags );
                } else {
                        // Use a join to get the latest revision
                        $conds[] = 'rev_id=page_latest';
                        $db = wfGetDB( ( $flags & self::READ_LATEST ) ? DB_MASTER : DB_REPLICA );
                        return self::loadFromConds( $db, $conds, $flags );
                }
        }

        /**
         * Load either the current, or a specified, revision
         * that's attached to a given page ID.
         * Returns null if no such revision can be found.
         *
         * $flags include:
         *      Revision::READ_LATEST  : Select the data from the master (since 1.20)
         *      Revision::READ_LOCKING : Select & lock the data from the master
         *
         * @param int $pageId
         * @param int $revId (optional)
         * @param int $flags Bitfield (optional)
         * @return Revision|null
         */
        public static function newFromPageId( $pageId, $revId = 0, $flags = 0 ) {
                $conds = [ 'page_id' => $pageId ];
                if ( $revId ) {
                        $conds['rev_id'] = $revId;
                        return self::newFromConds( $conds, $flags );
                } else {
                        // Use a join to get the latest revision
                        $conds[] = 'rev_id = page_latest';
                        $db = wfGetDB( ( $flags & self::READ_LATEST ) ? DB_MASTER : DB_REPLICA );
                        return self::loadFromConds( $db, $conds, $flags );
                }
        }

        /**
         * Make a fake revision object from an archive table row. This is queried
         * for permissions or even inserted (as in Special:Undelete)
         * @todo FIXME: Should be a subclass for RevisionDelete. [TS]
         *
         * @param object $row
         * @param array $overrides
         *
         * @throws MWException
         * @return Revision
         */
        public static function newFromArchiveRow( $row, $overrides = [] ) {
                global $wgContentHandlerUseDB;

                $attribs = $overrides + [
                        'page'       => isset( $row->ar_page_id ) ? $row->ar_page_id : null,
                        'id'         => isset( $row->ar_rev_id ) ? $row->ar_rev_id : null,
                        'comment'    => $row->ar_comment,
                        'user'       => $row->ar_user,
                        'user_text'  => $row->ar_user_text,
                        'timestamp'  => $row->ar_timestamp,
                        'minor_edit' => $row->ar_minor_edit,
                        'text_id'    => isset( $row->ar_text_id ) ? $row->ar_text_id : null,
                        'deleted'    => $row->ar_deleted,
                        'len'        => $row->ar_len,
                        'sha1'       => isset( $row->ar_sha1 ) ? $row->ar_sha1 : null,
                        'content_model'   => isset( $row->ar_content_model ) ? $row->ar_content_model : null,
                        'content_format'  => isset( $row->ar_content_format ) ? $row->ar_content_format : null,
                ];

                if ( !$wgContentHandlerUseDB ) {
                        unset( $attribs['content_model'] );
                        unset( $attribs['content_format'] );
                }

                if ( !isset( $attribs['title'] )
                        && isset( $row->ar_namespace )
                        && isset( $row->ar_title )
                ) {
                        $attribs['title'] = Title::makeTitle( $row->ar_namespace, $row->ar_title );
                }

                if ( isset( $row->ar_text ) && !$row->ar_text_id ) {
                        // Pre-1.5 ar_text row
                        $attribs['text'] = self::getRevisionText( $row, 'ar_' );
                        if ( $attribs['text'] === false ) {
                                throw new MWException( 'Unable to load text from archive row (possibly T24624)' );
                        }
                }
                return new self( $attribs );
        }

        /**
         * @since 1.19
         *
         * @param object $row
         * @return Revision
         */
        public static function newFromRow( $row ) {
                return new self( $row );
        }

        /**
         * Load a page revision from a given revision ID number.
         * Returns null if no such revision can be found.
         *
         * @param IDatabase $db
         * @param int $id
         * @return Revision|null
         */
        public static function loadFromId( $db, $id ) {
                return self::loadFromConds( $db, [ 'rev_id' => intval( $id ) ] );
        }

        /**
         * Load either the current, or a specified, revision
         * that's attached to a given page. If not attached
         * to that page, will return null.
         *
         * @param IDatabase $db
         * @param int $pageid
         * @param int $id
         * @return Revision|null
         */
        public static function loadFromPageId( $db, $pageid, $id = 0 ) {
                $conds = [ 'rev_page' => intval( $pageid ), 'page_id' => intval( $pageid ) ];
                if ( $id ) {
                        $conds['rev_id'] = intval( $id );
                } else {
                        $conds[] = 'rev_id=page_latest';
                }
                return self::loadFromConds( $db, $conds );
        }

        /**
         * Load either the current, or a specified, revision
         * that's attached to a given page. If not attached
         * to that page, will return null.
         *
         * @param IDatabase $db
         * @param Title $title
         * @param int $id
         * @return Revision|null
         */
        public static function loadFromTitle( $db, $title, $id = 0 ) {
                if ( $id ) {
                        $matchId = intval( $id );
                } else {
                        $matchId = 'page_latest';
                }
                return self::loadFromConds( $db,
                        [
                                "rev_id=$matchId",
                                'page_namespace' => $title->getNamespace(),
                                'page_title' => $title->getDBkey()
                        ]
                );
        }

        /**
         * Load the revision for the given title with the given timestamp.
         * WARNING: Timestamps may in some circumstances not be unique,
         * so this isn't the best key to use.
         *
         * @param IDatabase $db
         * @param Title $title
         * @param string $timestamp
         * @return Revision|null
         */
        public static function loadFromTimestamp( $db, $title, $timestamp ) {
                return self::loadFromConds( $db,
                        [
                                'rev_timestamp' => $db->timestamp( $timestamp ),
                                'page_namespace' => $title->getNamespace(),
                                'page_title' => $title->getDBkey()
                        ]
                );
        }

        /**
         * Given a set of conditions, fetch a revision
         *
         * This method is used then a revision ID is qualified and
         * will incorporate some basic replica DB/master fallback logic
         *
         * @param array $conditions
         * @param int $flags (optional)
         * @return Revision|null
         */
        private static function newFromConds( $conditions, $flags = 0 ) {
                $db = wfGetDB( ( $flags & self::READ_LATEST ) ? DB_MASTER : DB_REPLICA );

                $rev = self::loadFromConds( $db, $conditions, $flags );
                // Make sure new pending/committed revision are visibile later on
                // within web requests to certain avoid bugs like T93866 and T94407.
                if ( !$rev
                        && !( $flags & self::READ_LATEST )
                        && wfGetLB()->getServerCount() > 1
                        && wfGetLB()->hasOrMadeRecentMasterChanges()
                ) {
                        $flags = self::READ_LATEST;
                        $db = wfGetDB( DB_MASTER );
                        $rev = self::loadFromConds( $db, $conditions, $flags );
                }

                if ( $rev ) {
                        $rev->mQueryFlags = $flags;
                }

                return $rev;
        }

        /**
         * Given a set of conditions, fetch a revision from
         * the given database connection.
         *
         * @param IDatabase $db
         * @param array $conditions
         * @param int $flags (optional)
         * @return Revision|null
         */
        private static function loadFromConds( $db, $conditions, $flags = 0 ) {
                $row = self::fetchFromConds( $db, $conditions, $flags );
                if ( $row ) {
                        $rev = new Revision( $row );
                        $rev->mWiki = $db->getWikiID();

                        return $rev;
                }

                return null;
        }

        /**
         * Return a wrapper for a series of database rows to
         * fetch all of a given page's revisions in turn.
         * Each row can be fed to the constructor to get objects.
         *
         * @param LinkTarget $title
         * @return ResultWrapper
         * @deprecated Since 1.28
         */
        public static function fetchRevision( LinkTarget $title ) {
                $row = self::fetchFromConds(
                        wfGetDB( DB_REPLICA ),
                        [
                                'rev_id=page_latest',
                                'page_namespace' => $title->getNamespace(),
                                'page_title' => $title->getDBkey()
                        ]
                );

                return new FakeResultWrapper( $row ? [ $row ] : [] );
        }

        /**
         * Given a set of conditions, return a ResultWrapper
         * which will return matching database rows with the
         * fields necessary to build Revision objects.
         *
         * @param IDatabase $db
         * @param array $conditions
         * @param int $flags (optional)
         * @return stdClass
         */
        private static function fetchFromConds( $db, $conditions, $flags = 0 ) {
                $fields = array_merge(
                        self::selectFields(),
                        self::selectPageFields(),
                        self::selectUserFields()
                );
                $options = [];
                if ( ( $flags & self::READ_LOCKING ) == self::READ_LOCKING ) {
                        $options[] = 'FOR UPDATE';
                }
                return $db->selectRow(
                        [ 'revision', 'page', 'user' ],
                        $fields,
                        $conditions,
                        __METHOD__,
                        $options,
                        [ 'page' => self::pageJoinCond(), 'user' => self::userJoinCond() ]
                );
        }

        /**
         * Return the value of a select() JOIN conds array for the user table.
         * This will get user table rows for logged-in users.
         * @since 1.19
         * @return array
         */
        public static function userJoinCond() {
                return [ 'LEFT JOIN', [ 'rev_user != 0', 'user_id = rev_user' ] ];
        }

        /**
         * Return the value of a select() page conds array for the page table.
         * This will assure that the revision(s) are not orphaned from live pages.
         * @since 1.19
         * @return array
         */
        public static function pageJoinCond() {
                return [ 'INNER JOIN', [ 'page_id = rev_page' ] ];
        }

        /**
         * Return the list of revision fields that should be selected to create
         * a new revision.
         * @return array
         */
        public static function selectFields() {
                global $wgContentHandlerUseDB;

                $fields = [
                        'rev_id',
                        'rev_page',
                        'rev_text_id',
                        'rev_timestamp',
                        'rev_comment',
                        'rev_user_text',
                        'rev_user',
                        'rev_minor_edit',
                        'rev_deleted',
                        'rev_len',
                        'rev_parent_id',
                        'rev_sha1',
                ];

                if ( $wgContentHandlerUseDB ) {
                        $fields[] = 'rev_content_format';
                        $fields[] = 'rev_content_model';
                }

                return $fields;
        }

        /**
         * Return the list of revision fields that should be selected to create
         * a new revision from an archive row.
         * @return array
         */
        public static function selectArchiveFields() {
                global $wgContentHandlerUseDB;
                $fields = [
                        'ar_id',
                        'ar_page_id',
                        'ar_rev_id',
                        'ar_text',
                        'ar_text_id',
                        'ar_timestamp',
                        'ar_comment',
                        'ar_user_text',
                        'ar_user',
                        'ar_minor_edit',
                        'ar_deleted',
                        'ar_len',
                        'ar_parent_id',
                        'ar_sha1',
                ];

                if ( $wgContentHandlerUseDB ) {
                        $fields[] = 'ar_content_format';
                        $fields[] = 'ar_content_model';
                }
                return $fields;
        }

        /**
         * Return the list of text fields that should be selected to read the
         * revision text
         * @return array
         */
        public static function selectTextFields() {
                return [
                        'old_text',
                        'old_flags'
                ];
        }

        /**
         * Return the list of page fields that should be selected from page table
         * @return array
         */
        public static function selectPageFields() {
                return [
                        'page_namespace',
                        'page_title',
                        'page_id',
                        'page_latest',
                        'page_is_redirect',
                        'page_len',
                ];
        }

        /**
         * Return the list of user fields that should be selected from user table
         * @return array
         */
        public static function selectUserFields() {
                return [ 'user_name' ];
        }

        /**
         * Do a batched query to get the parent revision lengths
         * @param IDatabase $db
         * @param array $revIds
         * @return array
         */
        public static function getParentLengths( $db, array $revIds ) {
                $revLens = [];
                if ( !$revIds ) {
                        return $revLens; // empty
                }
                $res = $db->select( 'revision',
                        [ 'rev_id', 'rev_len' ],
                        [ 'rev_id' => $revIds ],
                        __METHOD__ );
                foreach ( $res as $row ) {
                        $revLens[$row->rev_id] = $row->rev_len;
                }
                return $revLens;
        }

        /**
         * @param object|array $row Either a database row or an array
         * @throws MWException
         * @access private
         */
        function __construct( $row ) {
                if ( is_object( $row ) ) {
                        $this->mId = intval( $row->rev_id );
                        $this->mPage = intval( $row->rev_page );
                        $this->mTextId = intval( $row->rev_text_id );
                        $this->mComment = $row->rev_comment;
                        $this->mUser = intval( $row->rev_user );
                        $this->mMinorEdit = intval( $row->rev_minor_edit );
                        $this->mTimestamp = $row->rev_timestamp;
                        $this->mDeleted = intval( $row->rev_deleted );

                        if ( !isset( $row->rev_parent_id ) ) {
                                $this->mParentId = null;
                        } else {
                                $this->mParentId = intval( $row->rev_parent_id );
                        }

                        if ( !isset( $row->rev_len ) ) {
                                $this->mSize = null;
                        } else {
                                $this->mSize = intval( $row->rev_len );
                        }

                        if ( !isset( $row->rev_sha1 ) ) {
                                $this->mSha1 = null;
                        } else {
                                $this->mSha1 = $row->rev_sha1;
                        }

                        if ( isset( $row->page_latest ) ) {
                                $this->mCurrent = ( $row->rev_id == $row->page_latest );
                                $this->mTitle = Title::newFromRow( $row );
                        } else {
                                $this->mCurrent = false;
                                $this->mTitle = null;
                        }

                        if ( !isset( $row->rev_content_model ) ) {
                                $this->mContentModel = null; # determine on demand if needed
                        } else {
                                $this->mContentModel = strval( $row->rev_content_model );
                        }

                        if ( !isset( $row->rev_content_format ) ) {
                                $this->mContentFormat = null; # determine on demand if needed
                        } else {
                                $this->mContentFormat = strval( $row->rev_content_format );
                        }

                        // Lazy extraction...
                        $this->mText = null;
                        if ( isset( $row->old_text ) ) {
                                $this->mTextRow = $row;
                        } else {
                                // 'text' table row entry will be lazy-loaded
                                $this->mTextRow = null;
                        }

                        // Use user_name for users and rev_user_text for IPs...
                        $this->mUserText = null; // lazy load if left null
                        if ( $this->mUser == 0 ) {
                                $this->mUserText = $row->rev_user_text; // IP user
                        } elseif ( isset( $row->user_name ) ) {
                                $this->mUserText = $row->user_name; // logged-in user
                        }
                        $this->mOrigUserText = $row->rev_user_text;
                } elseif ( is_array( $row ) ) {
                        // Build a new revision to be saved...
                        global $wgUser; // ugh

                        # if we have a content object, use it to set the model and type
                        if ( !empty( $row['content'] ) ) {
                                // @todo when is that set? test with external store setup! check out insertOn() [dk]
                                if ( !empty( $row['text_id'] ) ) {
                                        throw new MWException( "Text already stored in external store (id {$row['text_id']}), " .
                                                "can't serialize content object" );
                                }

                                $row['content_model'] = $row['content']->getModel();
                                # note: mContentFormat is initializes later accordingly
                                # note: content is serialized later in this method!
                                # also set text to null?
                        }

                        $this->mId = isset( $row['id'] ) ? intval( $row['id'] ) : null;
                        $this->mPage = isset( $row['page'] ) ? intval( $row['page'] ) : null;
                        $this->mTextId = isset( $row['text_id'] ) ? intval( $row['text_id'] ) : null;
                        $this->mUserText = isset( $row['user_text'] )
                                ? strval( $row['user_text'] ) : $wgUser->getName();
                        $this->mUser = isset( $row['user'] ) ? intval( $row['user'] ) : $wgUser->getId();
                        $this->mMinorEdit = isset( $row['minor_edit'] ) ? intval( $row['minor_edit'] ) : 0;
                        $this->mTimestamp = isset( $row['timestamp'] )
                                ? strval( $row['timestamp'] ) : wfTimestampNow();
                        $this->mDeleted = isset( $row['deleted'] ) ? intval( $row['deleted'] ) : 0;
                        $this->mSize = isset( $row['len'] ) ? intval( $row['len'] ) : null;
                        $this->mParentId = isset( $row['parent_id'] ) ? intval( $row['parent_id'] ) : null;
                        $this->mSha1 = isset( $row['sha1'] ) ? strval( $row['sha1'] ) : null;

                        $this->mContentModel = isset( $row['content_model'] )
                                ? strval( $row['content_model'] ) : null;
                        $this->mContentFormat = isset( $row['content_format'] )
                                ? strval( $row['content_format'] ) : null;

                        // Enforce spacing trimming on supplied text
                        $this->mComment = isset( $row['comment'] ) ? trim( strval( $row['comment'] ) ) : null;
                        $this->mText = isset( $row['text'] ) ? rtrim( strval( $row['text'] ) ) : null;
                        $this->mTextRow = null;

                        $this->mTitle = isset( $row['title'] ) ? $row['title'] : null;

                        // if we have a Content object, override mText and mContentModel
                        if ( !empty( $row['content'] ) ) {
                                if ( !( $row['content'] instanceof Content ) ) {
                                        throw new MWException( '`content` field must contain a Content object.' );
                                }

                                $handler = $this->getContentHandler();
                                $this->mContent = $row['content'];

                                $this->mContentModel = $this->mContent->getModel();
                                $this->mContentHandler = null;

                                $this->mText = $handler->serializeContent( $row['content'], $this->getContentFormat() );
                        } elseif ( $this->mText !== null ) {
                                $handler = $this->getContentHandler();
                                $this->mContent = $handler->unserializeContent( $this->mText );
                        }

                        // If we have a Title object, make sure it is consistent with mPage.
                        if ( $this->mTitle && $this->mTitle->exists() ) {
                                if ( $this->mPage === null ) {
                                        // if the page ID wasn't known, set it now
                                        $this->mPage = $this->mTitle->getArticleID();
                                } elseif ( $this->mTitle->getArticleID() !== $this->mPage ) {
                                        // Got different page IDs. This may be legit (e.g. during undeletion),
                                        // but it seems worth mentioning it in the log.
                                        wfDebug( "Page ID " . $this->mPage . " mismatches the ID " .
                                                $this->mTitle->getArticleID() . " provided by the Title object." );
                                }
                        }

                        $this->mCurrent = false;

                        // If we still have no length, see it we have the text to figure it out
                        if ( !$this->mSize && $this->mContent !== null ) {
                                $this->mSize = $this->mContent->getSize();
                        }

                        // Same for sha1
                        if ( $this->mSha1 === null ) {
                                $this->mSha1 = $this->mText === null ? null : self::base36Sha1( $this->mText );
                        }

                        // force lazy init
                        $this->getContentModel();
                        $this->getContentFormat();
                } else {
                        throw new MWException( 'Revision constructor passed invalid row format.' );
                }
                $this->mUnpatrolled = null;
        }

        /**
         * Get revision ID
         *
         * @return int|null
         */
        public function getId() {
                return $this->mId;
        }

        /**
         * Set the revision ID
         *
         * This should only be used for proposed revisions that turn out to be null edits
         *
         * @since 1.19
         * @param int $id
         */
        public function setId( $id ) {
                $this->mId = (int)$id;
        }

        /**
         * Set the user ID/name
         *
         * This should only be used for proposed revisions that turn out to be null edits
         *
         * @since 1.28
         * @param integer $id User ID
         * @param string $name User name
         */
        public function setUserIdAndName( $id, $name ) {
                $this->mUser = (int)$id;
                $this->mUserText = $name;
                $this->mOrigUserText = $name;
        }

        /**
         * Get text row ID
         *
         * @return int|null
         */
        public function getTextId() {
                return $this->mTextId;
        }

        /**
         * Get parent revision ID (the original previous page revision)
         *
         * @return int|null
         */
        public function getParentId() {
                return $this->mParentId;
        }

        /**
         * Returns the length of the text in this revision, or null if unknown.
         *
         * @return int|null
         */
        public function getSize() {
                return $this->mSize;
        }

        /**
         * Returns the base36 sha1 of the text in this revision, or null if unknown.
         *
         * @return string|null
         */
        public function getSha1() {
                return $this->mSha1;
        }

        /**
         * Returns the title of the page associated with this entry or null.
         *
         * Will do a query, when title is not set and id is given.
         *
         * @return Title|null
         */
        public function getTitle() {
                if ( $this->mTitle !== null ) {
                        return $this->mTitle;
                }
                // rev_id is defined as NOT NULL, but this revision may not yet have been inserted.
                if ( $this->mId !== null ) {
                        $dbr = wfGetLB( $this->mWiki )->getConnectionRef( DB_REPLICA, [], $this->mWiki );
                        $row = $dbr->selectRow(
                                [ 'page', 'revision' ],
                                self::selectPageFields(),
                                [ 'page_id=rev_page', 'rev_id' => $this->mId ],
                                __METHOD__
                        );
                        if ( $row ) {
                                // @TODO: better foreign title handling
                                $this->mTitle = Title::newFromRow( $row );
                        }
                }

                if ( $this->mWiki === false || $this->mWiki === wfWikiID() ) {
                        // Loading by ID is best, though not possible for foreign titles
                        if ( !$this->mTitle && $this->mPage !== null && $this->mPage > 0 ) {
                                $this->mTitle = Title::newFromID( $this->mPage );
                        }
                }

                return $this->mTitle;
        }

        /**
         * Set the title of the revision
         *
         * @param Title $title
         */
        public function setTitle( $title ) {
                $this->mTitle = $title;
        }

        /**
         * Get the page ID
         *
         * @return int|null
         */
        public function getPage() {
                return $this->mPage;
        }

        /**
         * Fetch revision's user id if it's available to the specified audience.
         * If the specified audience does not have access to it, zero will be
         * returned.
         *
         * @param int $audience One of:
         *   Revision::FOR_PUBLIC       to be displayed to all users
         *   Revision::FOR_THIS_USER    to be displayed to the given user
         *   Revision::RAW              get the ID regardless of permissions
         * @param User|null $user User object to check for, only if FOR_THIS_USER is passed
         *   to the $audience parameter
         * @return int
         */
        public function getUser( $audience = self::FOR_PUBLIC, User $user = null ) {
                if ( $audience == self::FOR_PUBLIC && $this->isDeleted( self::DELETED_USER ) ) {
                        return 0;
                } elseif ( $audience == self::FOR_THIS_USER && !$this->userCan( self::DELETED_USER, $user ) ) {
                        return 0;
                } else {
                        return $this->mUser;
                }
        }

        /**
         * Fetch revision's user id without regard for the current user's permissions
         *
         * @return int
         * @deprecated since 1.25, use getUser( Revision::RAW )
         */
        public function getRawUser() {
                wfDeprecated( __METHOD__, '1.25' );
                return $this->getUser( self::RAW );
        }

        /**
         * Fetch revision's username if it's available to the specified audience.
         * If the specified audience does not have access to the username, an
         * empty string will be returned.
         *
         * @param int $audience One of:
         *   Revision::FOR_PUBLIC       to be displayed to all users
         *   Revision::FOR_THIS_USER    to be displayed to the given user
         *   Revision::RAW              get the text regardless of permissions
         * @param User|null $user User object to check for, only if FOR_THIS_USER is passed
         *   to the $audience parameter
         * @return string
         */
        public function getUserText( $audience = self::FOR_PUBLIC, User $user = null ) {
                $this->loadMutableFields();

                if ( $audience == self::FOR_PUBLIC && $this->isDeleted( self::DELETED_USER ) ) {
                        return '';
                } elseif ( $audience == self::FOR_THIS_USER && !$this->userCan( self::DELETED_USER, $user ) ) {
                        return '';
                } else {
                        if ( $this->mUserText === null ) {
                                $this->mUserText = User::whoIs( $this->mUser ); // load on demand
                                if ( $this->mUserText === false ) {
                                        # This shouldn't happen, but it can if the wiki was recovered
                                        # via importing revs and there is no user table entry yet.
                                        $this->mUserText = $this->mOrigUserText;
                                }
                        }
                        return $this->mUserText;
                }
        }

        /**
         * Fetch revision's username without regard for view restrictions
         *
         * @return string
         * @deprecated since 1.25, use getUserText( Revision::RAW )
         */
        public function getRawUserText() {
                wfDeprecated( __METHOD__, '1.25' );
                return $this->getUserText( self::RAW );
        }

        /**
         * Fetch revision comment if it's available to the specified audience.
         * If the specified audience does not have access to the comment, an
         * empty string will be returned.
         *
         * @param int $audience One of:
         *   Revision::FOR_PUBLIC       to be displayed to all users
         *   Revision::FOR_THIS_USER    to be displayed to the given user
         *   Revision::RAW              get the text regardless of permissions
         * @param User|null $user User object to check for, only if FOR_THIS_USER is passed
         *   to the $audience parameter
         * @return string
         */
        function getComment( $audience = self::FOR_PUBLIC, User $user = null ) {
                if ( $audience == self::FOR_PUBLIC && $this->isDeleted( self::DELETED_COMMENT ) ) {
                        return '';
                } elseif ( $audience == self::FOR_THIS_USER && !$this->userCan( self::DELETED_COMMENT, $user ) ) {
                        return '';
                } else {
                        return $this->mComment;
                }
        }

        /**
         * Fetch revision comment without regard for the current user's permissions
         *
         * @return string
         * @deprecated since 1.25, use getComment( Revision::RAW )
         */
        public function getRawComment() {
                wfDeprecated( __METHOD__, '1.25' );
                return $this->getComment( self::RAW );
        }

        /**
         * @return bool
         */
        public function isMinor() {
                return (bool)$this->mMinorEdit;
        }

        /**
         * @return int Rcid of the unpatrolled row, zero if there isn't one
         */
        public function isUnpatrolled() {
                if ( $this->mUnpatrolled !== null ) {
                        return $this->mUnpatrolled;
                }
                $rc = $this->getRecentChange();
                if ( $rc && $rc->getAttribute( 'rc_patrolled' ) == 0 ) {
                        $this->mUnpatrolled = $rc->getAttribute( 'rc_id' );
                } else {
                        $this->mUnpatrolled = 0;
                }
                return $this->mUnpatrolled;
        }

        /**
         * Get the RC object belonging to the current revision, if there's one
         *
         * @param int $flags (optional) $flags include:
         *      Revision::READ_LATEST  : Select the data from the master
         *
         * @since 1.22
         * @return RecentChange|null
         */
        public function getRecentChange( $flags = 0 ) {
                $dbr = wfGetDB( DB_REPLICA );

                list( $dbType, ) = DBAccessObjectUtils::getDBOptions( $flags );

                return RecentChange::newFromConds(
                        [
                                'rc_user_text' => $this->getUserText( self::RAW ),
                                'rc_timestamp' => $dbr->timestamp( $this->getTimestamp() ),
                                'rc_this_oldid' => $this->getId()
                        ],
                        __METHOD__,
                        $dbType
                );
        }

        /**
         * @param int $field One of DELETED_* bitfield constants
         *
         * @return bool
         */
        public function isDeleted( $field ) {
                if ( $this->isCurrent() && $field === self::DELETED_TEXT ) {
                        // Current revisions of pages cannot have the content hidden. Skipping this
                        // check is very useful for Parser as it fetches templates using newKnownCurrent().
                        // Calling getVisibility() in that case triggers a verification database query.
                        return false; // no need to check
                }

                return ( $this->getVisibility() & $field ) == $field;
        }

        /**
         * Get the deletion bitfield of the revision
         *
         * @return int
         */
        public function getVisibility() {
                $this->loadMutableFields();

                return (int)$this->mDeleted;
        }

        /**
         * Fetch revision content if it's available to the specified audience.
         * If the specified audience does not have the ability to view this
         * revision, null will be returned.
         *
         * @param int $audience One of:
         *   Revision::FOR_PUBLIC       to be displayed to all users
         *   Revision::FOR_THIS_USER    to be displayed to $wgUser
         *   Revision::RAW              get the text regardless of permissions
         * @param User $user User object to check for, only if FOR_THIS_USER is passed
         *   to the $audience parameter
         * @since 1.21
         * @return Content|null
         */
        public function getContent( $audience = self::FOR_PUBLIC, User $user = null ) {
                if ( $audience == self::FOR_PUBLIC && $this->isDeleted( self::DELETED_TEXT ) ) {
                        return null;
                } elseif ( $audience == self::FOR_THIS_USER && !$this->userCan( self::DELETED_TEXT, $user ) ) {
                        return null;
                } else {
                        return $this->getContentInternal();
                }
        }

        /**
         * Get original serialized data (without checking view restrictions)
         *
         * @since 1.21
         * @return string
         */
        public function getSerializedData() {
                if ( $this->mText === null ) {
                        // Revision is immutable. Load on demand.
                        $this->mText = $this->loadText();
                }

                return $this->mText;
        }

        /**
         * Gets the content object for the revision (or null on failure).
         *
         * Note that for mutable Content objects, each call to this method will return a
         * fresh clone.
         *
         * @since 1.21
         * @return Content|null The Revision's content, or null on failure.
         */
        protected function getContentInternal() {
                if ( $this->mContent === null ) {
                        $text = $this->getSerializedData();

                        if ( $text !== null && $text !== false ) {
                                // Unserialize content
                                $handler = $this->getContentHandler();
                                $format = $this->getContentFormat();

                                $this->mContent = $handler->unserializeContent( $text, $format );
                        }
                }

                // NOTE: copy() will return $this for immutable content objects
                return $this->mContent ? $this->mContent->copy() : null;
        }

        /**
         * Returns the content model for this revision.
         *
         * If no content model was stored in the database, the default content model for the title is
         * used to determine the content model to use. If no title is know, CONTENT_MODEL_WIKITEXT
         * is used as a last resort.
         *
         * @return string The content model id associated with this revision,
         *     see the CONTENT_MODEL_XXX constants.
         */
        public function getContentModel() {
                if ( !$this->mContentModel ) {
                        $title = $this->getTitle();
                        if ( $title ) {
                                $this->mContentModel = ContentHandler::getDefaultModelFor( $title );
                        } else {
                                $this->mContentModel = CONTENT_MODEL_WIKITEXT;
                        }

                        assert( !empty( $this->mContentModel ) );
                }

                return $this->mContentModel;
        }

        /**
         * Returns the content format for this revision.
         *
         * If no content format was stored in the database, the default format for this
         * revision's content model is returned.
         *
         * @return string The content format id associated with this revision,
         *     see the CONTENT_FORMAT_XXX constants.
         */
        public function getContentFormat() {
                if ( !$this->mContentFormat ) {
                        $handler = $this->getContentHandler();
                        $this->mContentFormat = $handler->getDefaultFormat();

                        assert( !empty( $this->mContentFormat ) );
                }

                return $this->mContentFormat;
        }

        /**
         * Returns the content handler appropriate for this revision's content model.
         *
         * @throws MWException
         * @return ContentHandler
         */
        public function getContentHandler() {
                if ( !$this->mContentHandler ) {
                        $model = $this->getContentModel();
                        $this->mContentHandler = ContentHandler::getForModelID( $model );

                        $format = $this->getContentFormat();

                        if ( !$this->mContentHandler->isSupportedFormat( $format ) ) {
                                throw new MWException( "Oops, the content format $format is not supported for "
                                        . "this content model, $model" );
                        }
                }

                return $this->mContentHandler;
        }

        /**
         * @return string
         */
        public function getTimestamp() {
                return wfTimestamp( TS_MW, $this->mTimestamp );
        }

        /**
         * @return bool
         */
        public function isCurrent() {
                return $this->mCurrent;
        }

        /**
         * Get previous revision for this title
         *
         * @return Revision|null
         */
        public function getPrevious() {
                if ( $this->getTitle() ) {
                        $prev = $this->getTitle()->getPreviousRevisionID( $this->getId() );
                        if ( $prev ) {
                                return self::newFromTitle( $this->getTitle(), $prev );
                        }
                }
                return null;
        }

        /**
         * Get next revision for this title
         *
         * @return Revision|null
         */
        public function getNext() {
                if ( $this->getTitle() ) {
                        $next = $this->getTitle()->getNextRevisionID( $this->getId() );
                        if ( $next ) {
                                return self::newFromTitle( $this->getTitle(), $next );
                        }
                }
                return null;
        }

        /**
         * Get previous revision Id for this page_id
         * This is used to populate rev_parent_id on save
         *
         * @param IDatabase $db
         * @return int
         */
        private function getPreviousRevisionId( $db ) {
                if ( $this->mPage === null ) {
                        return 0;
                }
                # Use page_latest if ID is not given
                if ( !$this->mId ) {
                        $prevId = $db->selectField( 'page', 'page_latest',
                                [ 'page_id' => $this->mPage ],
                                __METHOD__ );
                } else {
                        $prevId = $db->selectField( 'revision', 'rev_id',
                                [ 'rev_page' => $this->mPage, 'rev_id < ' . $this->mId ],
                                __METHOD__,
                                [ 'ORDER BY' => 'rev_id DESC' ] );
                }
                return intval( $prevId );
        }

        /**
         * Get revision text associated with an old or archive row
         *
         * Both the flags and the text field must be included. Including the old_id
         * field will activate cache usage as long as the $wiki parameter is not set.
         *
         * @param stdClass $row The text data
         * @param string $prefix Table prefix (default 'old_')
         * @param string|bool $wiki The name of the wiki to load the revision text from
         *   (same as the the wiki $row was loaded from) or false to indicate the local
         *   wiki (this is the default). Otherwise, it must be a symbolic wiki database
         *   identifier as understood by the LoadBalancer class.
         * @return string|false Text the text requested or false on failure
         */
        public static function getRevisionText( $row, $prefix = 'old_', $wiki = false ) {
                $textField = $prefix . 'text';
                $flagsField = $prefix . 'flags';

                if ( isset( $row->$flagsField ) ) {
                        $flags = explode( ',', $row->$flagsField );
                } else {
                        $flags = [];
                }

                if ( isset( $row->$textField ) ) {
                        $text = $row->$textField;
                } else {
                        return false;
                }

                // Use external methods for external objects, text in table is URL-only then
                if ( in_array( 'external', $flags ) ) {
                        $url = $text;
                        $parts = explode( '://', $url, 2 );
                        if ( count( $parts ) == 1 || $parts[1] == '' ) {
                                return false;
                        }

                        if ( isset( $row->old_id ) && $wiki === false ) {
                                // Make use of the wiki-local revision text cache
                                $cache = MediaWikiServices::getInstance()->getMainWANObjectCache();
                                // The cached value should be decompressed, so handle that and return here
                                return $cache->getWithSetCallback(
                                        $cache->makeKey( 'revisiontext', 'textid', $row->old_id ),
                                        self::getCacheTTL( $cache ),
                                        function () use ( $url, $wiki, $flags ) {
                                                // No negative caching per Revision::loadText()
                                                $text = ExternalStore::fetchFromURL( $url, [ 'wiki' => $wiki ] );

                                                return self::decompressRevisionText( $text, $flags );
                                        },
                                        [ 'pcGroup' => self::TEXT_CACHE_GROUP, 'pcTTL' => $cache::TTL_PROC_LONG ]
                                );
                        } else {
                                $text = ExternalStore::fetchFromURL( $url, [ 'wiki' => $wiki ] );
                        }
                }

                return self::decompressRevisionText( $text, $flags );
        }

        /**
         * If $wgCompressRevisions is enabled, we will compress data.
         * The input string is modified in place.
         * Return value is the flags field: contains 'gzip' if the
         * data is compressed, and 'utf-8' if we're saving in UTF-8
         * mode.
         *
         * @param mixed &$text Reference to a text
         * @return string
         */
        public static function compressRevisionText( &$text ) {
                global $wgCompressRevisions;
                $flags = [];

                # Revisions not marked this way will be converted
                # on load if $wgLegacyCharset is set in the future.
                $flags[] = 'utf-8';

                if ( $wgCompressRevisions ) {
                        if ( function_exists( 'gzdeflate' ) ) {
                                $deflated = gzdeflate( $text );

                                if ( $deflated === false ) {
                                        wfLogWarning( __METHOD__ . ': gzdeflate() failed' );
                                } else {
                                        $text = $deflated;
                                        $flags[] = 'gzip';
                                }
                        } else {
                                wfDebug( __METHOD__ . " -- no zlib support, not compressing\n" );
                        }
                }
                return implode( ',', $flags );
        }

        /**
         * Re-converts revision text according to it's flags.
         *
         * @param mixed $text Reference to a text
         * @param array $flags Compression flags
         * @return string|bool Decompressed text, or false on failure
         */
        public static function decompressRevisionText( $text, $flags ) {
                global $wgLegacyEncoding, $wgContLang;

                if ( $text === false ) {
                        // Text failed to be fetched; nothing to do
                        return false;
                }

                if ( in_array( 'gzip', $flags ) ) {
                        # Deal with optional compression of archived pages.
                        # This can be done periodically via maintenance/compressOld.php, and
                        # as pages are saved if $wgCompressRevisions is set.
                        $text = gzinflate( $text );

                        if ( $text === false ) {
                                wfLogWarning( __METHOD__ . ': gzinflate() failed' );
                                return false;
                        }
                }

                if ( in_array( 'object', $flags ) ) {
                        # Generic compressed storage
                        $obj = unserialize( $text );
                        if ( !is_object( $obj ) ) {
                                // Invalid object
                                return false;
                        }
                        $text = $obj->getText();
                }

                if ( $text !== false && $wgLegacyEncoding
                        && !in_array( 'utf-8', $flags ) && !in_array( 'utf8', $flags )
                ) {
                        # Old revisions kept around in a legacy encoding?
                        # Upconvert on demand.
                        # ("utf8" checked for compatibility with some broken
                        #  conversion scripts 2008-12-30)
                        $text = $wgContLang->iconv( $wgLegacyEncoding, 'UTF-8', $text );
                }

                return $text;
        }

        /**
         * Insert a new revision into the database, returning the new revision ID
         * number on success and dies horribly on failure.
         *
         * @param IDatabase $dbw (master connection)
         * @throws MWException
         * @return int
         */
        public function insertOn( $dbw ) {
                global $wgDefaultExternalStore, $wgContentHandlerUseDB;

                // We're inserting a new revision, so we have to use master anyway.
                // If it's a null revision, it may have references to rows that
                // are not in the replica yet (the text row).
                $this->mQueryFlags |= self::READ_LATEST;

                // Not allowed to have rev_page equal to 0, false, etc.
                if ( !$this->mPage ) {
                        $title = $this->getTitle();
                        if ( $title instanceof Title ) {
                                $titleText = ' for page ' . $title->getPrefixedText();
                        } else {
                                $titleText = '';
                        }
                        throw new MWException( "Cannot insert revision$titleText: page ID must be nonzero" );
                }

                $this->checkContentModel();

                $data = $this->mText;
                $flags = self::compressRevisionText( $data );

                # Write to external storage if required
                if ( $wgDefaultExternalStore ) {
                        // Store and get the URL
                        $data = ExternalStore::insertToDefault( $data );
                        if ( !$data ) {
                                throw new MWException( "Unable to store text to external storage" );
                        }
                        if ( $flags ) {
                                $flags .= ',';
                        }
                        $flags .= 'external';
                }

                # Record the text (or external storage URL) to the text table
                if ( $this->mTextId === null ) {
                        $old_id = $dbw->nextSequenceValue( 'text_old_id_seq' );
                        $dbw->insert( 'text',
                                [
                                        'old_id' => $old_id,
                                        'old_text' => $data,
                                        'old_flags' => $flags,
                                ], __METHOD__
                        );
                        $this->mTextId = $dbw->insertId();
                }

                if ( $this->mComment === null ) {
                        $this->mComment = "";
                }

                # Record the edit in revisions
                $rev_id = $this->mId !== null
                        ? $this->mId
                        : $dbw->nextSequenceValue( 'revision_rev_id_seq' );
                $row = [
                        'rev_id'         => $rev_id,
                        'rev_page'       => $this->mPage,
                        'rev_text_id'    => $this->mTextId,
                        'rev_comment'    => $this->mComment,
                        'rev_minor_edit' => $this->mMinorEdit ? 1 : 0,
                        'rev_user'       => $this->mUser,
                        'rev_user_text'  => $this->mUserText,
                        'rev_timestamp'  => $dbw->timestamp( $this->mTimestamp ),
                        'rev_deleted'    => $this->mDeleted,
                        'rev_len'        => $this->mSize,
                        'rev_parent_id'  => $this->mParentId === null
                                ? $this->getPreviousRevisionId( $dbw )
                                : $this->mParentId,
                        'rev_sha1'       => $this->mSha1 === null
                                ? self::base36Sha1( $this->mText )
                                : $this->mSha1,
                ];

                if ( $wgContentHandlerUseDB ) {
                        // NOTE: Store null for the default model and format, to save space.
                        // XXX: Makes the DB sensitive to changed defaults.
                        // Make this behavior optional? Only in miser mode?

                        $model = $this->getContentModel();
                        $format = $this->getContentFormat();

                        $title = $this->getTitle();

                        if ( $title === null ) {
                                throw new MWException( "Insufficient information to determine the title of the "
                                        . "revision's page!" );
                        }

                        $defaultModel = ContentHandler::getDefaultModelFor( $title );
                        $defaultFormat = ContentHandler::getForModelID( $defaultModel )->getDefaultFormat();

                        $row['rev_content_model'] = ( $model === $defaultModel ) ? null : $model;
                        $row['rev_content_format'] = ( $format === $defaultFormat ) ? null : $format;
                }

                $dbw->insert( 'revision', $row, __METHOD__ );

                if ( $this->mId === null ) {
                        // Only if nextSequenceValue() was called
                        $this->mId = $dbw->insertId();
                }

                // Assertion to try to catch T92046
                if ( (int)$this->mId === 0 ) {
                        throw new UnexpectedValueException(
                                'After insert, Revision mId is ' . var_export( $this->mId, 1 ) . ': ' .
                                        var_export( $row, 1 )
                        );
                }

                // Avoid PHP 7.1 warning of passing $this by reference
                $revision = $this;
                Hooks::run( 'RevisionInsertComplete', [ &$revision, $data, $flags ] );

                return $this->mId;
        }

        protected function checkContentModel() {
                global $wgContentHandlerUseDB;

                // Note: may return null for revisions that have not yet been inserted
                $title = $this->getTitle();

                $model = $this->getContentModel();
                $format = $this->getContentFormat();
                $handler = $this->getContentHandler();

                if ( !$handler->isSupportedFormat( $format ) ) {
                        $t = $title->getPrefixedDBkey();

                        throw new MWException( "Can't use format $format with content model $model on $t" );
                }

                if ( !$wgContentHandlerUseDB && $title ) {
                        // if $wgContentHandlerUseDB is not set,
                        // all revisions must use the default content model and format.

                        $defaultModel = ContentHandler::getDefaultModelFor( $title );
                        $defaultHandler = ContentHandler::getForModelID( $defaultModel );
                        $defaultFormat = $defaultHandler->getDefaultFormat();

                        if ( $this->getContentModel() != $defaultModel ) {
                                $t = $title->getPrefixedDBkey();

                                throw new MWException( "Can't save non-default content model with "
                                        . "\$wgContentHandlerUseDB disabled: model is $model, "
                                        . "default for $t is $defaultModel" );
                        }

                        if ( $this->getContentFormat() != $defaultFormat ) {
                                $t = $title->getPrefixedDBkey();

                                throw new MWException( "Can't use non-default content format with "
                                        . "\$wgContentHandlerUseDB disabled: format is $format, "
                                        . "default for $t is $defaultFormat" );
                        }
                }

                $content = $this->getContent( self::RAW );
                $prefixedDBkey = $title->getPrefixedDBkey();
                $revId = $this->mId;

                if ( !$content ) {
                        throw new MWException(
                                "Content of revision $revId ($prefixedDBkey) could not be loaded for validation!"
                        );
                }
                if ( !$content->isValid() ) {
                        throw new MWException(
                                "Content of revision $revId ($prefixedDBkey) is not valid! Content model is $model"
                        );
                }
        }

        /**
         * Get the base 36 SHA-1 value for a string of text
         * @param string $text
         * @return string
         */
        public static function base36Sha1( $text ) {
                return Wikimedia\base_convert( sha1( $text ), 16, 36, 31 );
        }

        /**
         * Get the text cache TTL
         *
         * @param WANObjectCache $cache
         * @return integer
         */
        private static function getCacheTTL( WANObjectCache $cache ) {
                global $wgRevisionCacheExpiry;

                if ( $cache->getQoS( $cache::ATTR_EMULATION ) <= $cache::QOS_EMULATION_SQL ) {
                        // Do not cache RDBMs blobs in...the RDBMs store
                        $ttl = $cache::TTL_UNCACHEABLE;
                } else {
                        $ttl = $wgRevisionCacheExpiry ?: $cache::TTL_UNCACHEABLE;
                }

                return $ttl;
        }

        /**
         * Lazy-load the revision's text.
         * Currently hardcoded to the 'text' table storage engine.
         *
         * @return string|bool The revision's text, or false on failure
         */
        private function loadText() {
                $cache = ObjectCache::getMainWANInstance();

                // No negative caching; negative hits on text rows may be due to corrupted replica DBs
                return $cache->getWithSetCallback(
                        $cache->makeKey( 'revisiontext', 'textid', $this->getTextId() ),
                        self::getCacheTTL( $cache ),
                        function () {
                                return $this->fetchText();
                        },
                        [ 'pcGroup' => self::TEXT_CACHE_GROUP, 'pcTTL' => $cache::TTL_PROC_LONG ]
                );
        }

        private function fetchText() {
                $textId = $this->getTextId();

                // If we kept data for lazy extraction, use it now...
                if ( $this->mTextRow !== null ) {
                        $row = $this->mTextRow;
                        $this->mTextRow = null;
                } else {
                        $row = null;
                }

                // Callers doing updates will pass in READ_LATEST as usual. Since the text/blob tables
                // do not normally get rows changed around, set READ_LATEST_IMMUTABLE in those cases.
                $flags = $this->mQueryFlags;
                $flags |= DBAccessObjectUtils::hasFlags( $flags, self::READ_LATEST )
                        ? self::READ_LATEST_IMMUTABLE
                        : 0;

                list( $index, $options, $fallbackIndex, $fallbackOptions ) =
                        DBAccessObjectUtils::getDBOptions( $flags );

                if ( !$row ) {
                        // Text data is immutable; check replica DBs first.
                        $row = wfGetDB( $index )->selectRow(
                                'text',
                                [ 'old_text', 'old_flags' ],
                                [ 'old_id' => $textId ],
                                __METHOD__,
                                $options
                        );
                }

                // Fallback to DB_MASTER in some cases if the row was not found
                if ( !$row && $fallbackIndex !== null ) {
                        // Use FOR UPDATE if it was used to fetch this revision. This avoids missing the row
                        // due to REPEATABLE-READ. Also fallback to the master if READ_LATEST is provided.
                        $row = wfGetDB( $fallbackIndex )->selectRow(
                                'text',
                                [ 'old_text', 'old_flags' ],
                                [ 'old_id' => $textId ],
                                __METHOD__,
                                $fallbackOptions
                        );
                }

                if ( !$row ) {
                        wfDebugLog( 'Revision', "No text row with ID '$textId' (revision {$this->getId()})." );
                }

                $text = self::getRevisionText( $row );
                if ( $row && $text === false ) {
                        wfDebugLog( 'Revision', "No blob for text row '$textId' (revision {$this->getId()})." );
                }

                return is_string( $text ) ? $text : false;
        }

        /**
         * Create a new null-revision for insertion into a page's
         * history. This will not re-save the text, but simply refer
         * to the text from the previous version.
         *
         * Such revisions can for instance identify page rename
         * operations and other such meta-modifications.
         *
         * @param IDatabase $dbw
         * @param int $pageId ID number of the page to read from
         * @param string $summary Revision's summary
         * @param bool $minor Whether the revision should be considered as minor
         * @param User|null $user User object to use or null for $wgUser
         * @return Revision|null Revision or null on error
         */
        public static function newNullRevision( $dbw, $pageId, $summary, $minor, $user = null ) {
                global $wgContentHandlerUseDB, $wgContLang;

                $fields = [ 'page_latest', 'page_namespace', 'page_title',
                                                'rev_text_id', 'rev_len', 'rev_sha1' ];

                if ( $wgContentHandlerUseDB ) {
                        $fields[] = 'rev_content_model';
                        $fields[] = 'rev_content_format';
                }

                $current = $dbw->selectRow(
                        [ 'page', 'revision' ],
                        $fields,
                        [
                                'page_id' => $pageId,
                                'page_latest=rev_id',
                        ],
                        __METHOD__,
                        [ 'FOR UPDATE' ] // T51581
                );

                if ( $current ) {
                        if ( !$user ) {
                                global $wgUser;
                                $user = $wgUser;
                        }

                        // Truncate for whole multibyte characters
                        $summary = $wgContLang->truncate( $summary, 255 );

                        $row = [
                                'page'       => $pageId,
                                'user_text'  => $user->getName(),
                                'user'       => $user->getId(),
                                'comment'    => $summary,
                                'minor_edit' => $minor,
                                'text_id'    => $current->rev_text_id,
                                'parent_id'  => $current->page_latest,
                                'len'        => $current->rev_len,
                                'sha1'       => $current->rev_sha1
                        ];

                        if ( $wgContentHandlerUseDB ) {
                                $row['content_model'] = $current->rev_content_model;
                                $row['content_format'] = $current->rev_content_format;
                        }

                        $row['title'] = Title::makeTitle( $current->page_namespace, $current->page_title );

                        $revision = new Revision( $row );
                } else {
                        $revision = null;
                }

                return $revision;
        }

        /**
         * Determine if the current user is allowed to view a particular
         * field of this revision, if it's marked as deleted.
         *
         * @param int $field One of self::DELETED_TEXT,
         *                              self::DELETED_COMMENT,
         *                              self::DELETED_USER
         * @param User|null $user User object to check, or null to use $wgUser
         * @return bool
         */
        public function userCan( $field, User $user = null ) {
                return self::userCanBitfield( $this->getVisibility(), $field, $user );
        }

        /**
         * Determine if the current user is allowed to view a particular
         * field of this revision, if it's marked as deleted. This is used
         * by various classes to avoid duplication.
         *
         * @param int $bitfield Current field
         * @param int $field One of self::DELETED_TEXT = File::DELETED_FILE,
         *                               self::DELETED_COMMENT = File::DELETED_COMMENT,
         *                               self::DELETED_USER = File::DELETED_USER
         * @param User|null $user User object to check, or null to use $wgUser
         * @param Title|null $title A Title object to check for per-page restrictions on,
         *                          instead of just plain userrights
         * @return bool
         */
        public static function userCanBitfield( $bitfield, $field, User $user = null,
                Title $title = null
        ) {
                if ( $bitfield & $field ) { // aspect is deleted
                        if ( $user === null ) {
                                global $wgUser;
                                $user = $wgUser;
                        }
                        if ( $bitfield & self::DELETED_RESTRICTED ) {
                                $permissions = [ 'suppressrevision', 'viewsuppressed' ];
                        } elseif ( $field & self::DELETED_TEXT ) {
                                $permissions = [ 'deletedtext' ];
                        } else {
                                $permissions = [ 'deletedhistory' ];
                        }
                        $permissionlist = implode( ', ', $permissions );
                        if ( $title === null ) {
                                wfDebug( "Checking for $permissionlist due to $field match on $bitfield\n" );
                                return call_user_func_array( [ $user, 'isAllowedAny' ], $permissions );
                        } else {
                                $text = $title->getPrefixedText();
                                wfDebug( "Checking for $permissionlist on $text due to $field match on $bitfield\n" );
                                foreach ( $permissions as $perm ) {
                                        if ( $title->userCan( $perm, $user ) ) {
                                                return true;
                                        }
                                }
                                return false;
                        }
                } else {
                        return true;
                }
        }

        /**
         * Get rev_timestamp from rev_id, without loading the rest of the row
         *
         * @param Title $title
         * @param int $id
         * @param int $flags
         * @return string|bool False if not found
         */
        static function getTimestampFromId( $title, $id, $flags = 0 ) {
                $db = ( $flags & self::READ_LATEST )
                        ? wfGetDB( DB_MASTER )
                        : wfGetDB( DB_REPLICA );
                // Casting fix for databases that can't take '' for rev_id
                if ( $id == '' ) {
                        $id = 0;
                }
                $conds = [ 'rev_id' => $id ];
                $conds['rev_page'] = $title->getArticleID();
                $timestamp = $db->selectField( 'revision', 'rev_timestamp', $conds, __METHOD__ );

                return ( $timestamp !== false ) ? wfTimestamp( TS_MW, $timestamp ) : false;
        }

        /**
         * Get count of revisions per page...not very efficient
         *
         * @param IDatabase $db
         * @param int $id Page id
         * @return int
         */
        static function countByPageId( $db, $id ) {
                $row = $db->selectRow( 'revision', [ 'revCount' => 'COUNT(*)' ],
                        [ 'rev_page' => $id ], __METHOD__ );
                if ( $row ) {
                        return $row->revCount;
                }
                return 0;
        }

        /**
         * Get count of revisions per page...not very efficient
         *
         * @param IDatabase $db
         * @param Title $title
         * @return int
         */
        static function countByTitle( $db, $title ) {
                $id = $title->getArticleID();
                if ( $id ) {
                        return self::countByPageId( $db, $id );
                }
                return 0;
        }

        /**
         * Check if no edits were made by other users since
         * the time a user started editing the page. Limit to
         * 50 revisions for the sake of performance.
         *
         * @since 1.20
         * @deprecated since 1.24
         *
         * @param IDatabase|int $db The Database to perform the check on. May be given as a
         *        Database object or a database identifier usable with wfGetDB.
         * @param int $pageId The ID of the page in question
         * @param int $userId The ID of the user in question
         * @param string $since Look at edits since this time
         *
         * @return bool True if the given user was the only one to edit since the given timestamp
         */
        public static function userWasLastToEdit( $db, $pageId, $userId, $since ) {
                if ( !$userId ) {
                        return false;
                }

                if ( is_int( $db ) ) {
                        $db = wfGetDB( $db );
                }

                $res = $db->select( 'revision',
                        'rev_user',
                        [
                                'rev_page' => $pageId,
                                'rev_timestamp > ' . $db->addQuotes( $db->timestamp( $since ) )
                        ],
                        __METHOD__,
                        [ 'ORDER BY' => 'rev_timestamp ASC', 'LIMIT' => 50 ] );
                foreach ( $res as $row ) {
                        if ( $row->rev_user != $userId ) {
                                return false;
                        }
                }
                return true;
        }

        /**
         * Load a revision based on a known page ID and current revision ID from the DB
         *
         * This method allows for the use of caching, though accessing anything that normally
         * requires permission checks (aside from the text) will trigger a small DB lookup.
         * The title will also be lazy loaded, though setTitle() can be used to preload it.
         *
         * @param IDatabase $db
         * @param int $pageId Page ID
         * @param int $revId Known current revision of this page
         * @return Revision|bool Returns false if missing
         * @since 1.28
         */
        public static function newKnownCurrent( IDatabase $db, $pageId, $revId ) {
                $cache = MediaWikiServices::getInstance()->getMainWANObjectCache();
                return $cache->getWithSetCallback(
                        // Page/rev IDs passed in from DB to reflect history merges
                        $cache->makeGlobalKey( 'revision', $db->getWikiID(), $pageId, $revId ),
                        $cache::TTL_WEEK,
                        function ( $curValue, &$ttl, array &$setOpts ) use ( $db, $pageId, $revId ) {
                                $setOpts += Database::getCacheSetOptions( $db );

                                $rev = Revision::loadFromPageId( $db, $pageId, $revId );
                                // Reflect revision deletion and user renames
                                if ( $rev ) {
                                        $rev->mTitle = null; // mutable; lazy-load
                                        $rev->mRefreshMutableFields = true;
                                }

                                return $rev ?: false; // don't cache negatives
                        }
                );
        }

        /**
         * For cached revisions, make sure the user name and rev_deleted is up-to-date
         */
        private function loadMutableFields() {
                if ( !$this->mRefreshMutableFields ) {
                        return; // not needed
                }

                $this->mRefreshMutableFields = false;
                $dbr = wfGetLB( $this->mWiki )->getConnectionRef( DB_REPLICA, [], $this->mWiki );
                $row = $dbr->selectRow(
                        [ 'revision', 'user' ],
                        [ 'rev_deleted', 'user_name' ],
                        [ 'rev_id' => $this->mId, 'user_id = rev_user' ],
                        __METHOD__
                );
                if ( $row ) { // update values
                        $this->mDeleted = (int)$row->rev_deleted;
                        $this->mUserText = $row->user_name;
                }
        }
}