RevisionStore.php

Go to the documentation of this file.

<?php
namespace MediaWiki\Storage;
 
use ActorMigration;
use CommentStore;
use CommentStoreComment;
use Content;
use ContentHandler;
use DBAccessObjectUtils;
use Hooks;
use IDBAccessObject;
use InvalidArgumentException;
use IP;
use LogicException;
use MediaWiki\Linker\LinkTarget;
use MediaWiki\User\UserIdentity;
use MediaWiki\User\UserIdentityValue;
use Message;
use MWException;
use MWUnknownContentModelException;
use Psr\Log\LoggerAwareInterface;
use Psr\Log\LoggerInterface;
use Psr\Log\NullLogger;
use RecentChange;
use stdClass;
use Title;
use User;
use WANObjectCache;
use Wikimedia\Assert\Assert;
use Wikimedia\Rdbms\Database;
use Wikimedia\Rdbms\DBConnRef;
use Wikimedia\Rdbms\IDatabase;
use Wikimedia\Rdbms\LoadBalancer;
 
class RevisionStore
    implements IDBAccessObject, RevisionFactory, RevisionLookup, LoggerAwareInterface {
 
    private $blobStore;
 
    private $wikiId;
 
    private $contentHandlerUseDB = true;
 
    private $loadBalancer;
 
    private $cache;
 
    private $commentStore;
 
    private $actorMigration;
 
    private $logger;
 
    public function __construct(
        LoadBalancer $loadBalancer,
        SqlBlobStore $blobStore,
        WANObjectCache $cache,
        CommentStore $commentStore,
        ActorMigration $actorMigration,
        $wikiId = false
    ) {
        Assert::parameterType( 'string|boolean', $wikiId, '$wikiId' );
 
        $this->loadBalancer = $loadBalancer;
        $this->blobStore = $blobStore;
        $this->cache = $cache;
        $this->commentStore = $commentStore;
        $this->actorMigration = $actorMigration;
        $this->wikiId = $wikiId;
        $this->logger = new NullLogger();
    }
 
    public function setLogger( LoggerInterface $logger ) {
        $this->logger = $logger;
    }
 
    public function isReadOnly() {
        return $this->blobStore->isReadOnly();
    }
 
    public function getContentHandlerUseDB() {
        return $this->contentHandlerUseDB;
    }
 
    public function setContentHandlerUseDB( $contentHandlerUseDB ) {
        $this->contentHandlerUseDB = $contentHandlerUseDB;
    }
 
    private function getDBLoadBalancer() {
        return $this->loadBalancer;
    }
 
    private function getDBConnection( $mode ) {
        $lb = $this->getDBLoadBalancer();
        return $lb->getConnection( $mode, [], $this->wikiId );
    }
 
    private function releaseDBConnection( IDatabase $connection ) {
        $lb = $this->getDBLoadBalancer();
        $lb->reuseConnection( $connection );
    }
 
    private function getDBConnectionRef( $mode ) {
        $lb = $this->getDBLoadBalancer();
        return $lb->getConnectionRef( $mode, [], $this->wikiId );
    }
 
    public function getTitle( $pageId, $revId, $queryFlags = self::READ_NORMAL ) {
        if ( !$pageId && !$revId ) {
            throw new InvalidArgumentException( '$pageId and $revId cannot both be 0 or null' );
        }
 
        // This method recalls itself with READ_LATEST if READ_NORMAL doesn't get us a Title
        // So ignore READ_LATEST_IMMUTABLE flags and handle the fallback logic in this method
        if ( DBAccessObjectUtils::hasFlags( $queryFlags, self::READ_LATEST_IMMUTABLE ) ) {
            $queryFlags = self::READ_NORMAL;
        }
 
        $canUseTitleNewFromId = ( $pageId !== null && $pageId > 0 && $this->wikiId === false );
        list( $dbMode, $dbOptions ) = DBAccessObjectUtils::getDBOptions( $queryFlags );
        $titleFlags = ( $dbMode == DB_MASTER ? Title::GAID_FOR_UPDATE : 0 );
 
        // Loading by ID is best, but Title::newFromID does not support that for foreign IDs.
        if ( $canUseTitleNewFromId ) {
            // TODO: better foreign title handling (introduce TitleFactory)
            $title = Title::newFromID( $pageId, $titleFlags );
            if ( $title ) {
                return $title;
            }
        }
 
        // rev_id is defined as NOT NULL, but this revision may not yet have been inserted.
        $canUseRevId = ( $revId !== null && $revId > 0 );
 
        if ( $canUseRevId ) {
            $dbr = $this->getDBConnectionRef( $dbMode );
            // @todo: Title::getSelectFields(), or Title::getQueryInfo(), or something like that
            $row = $dbr->selectRow(
                [ 'revision', 'page' ],
                [
                    'page_namespace',
                    'page_title',
                    'page_id',
                    'page_latest',
                    'page_is_redirect',
                    'page_len',
                ],
                [ 'rev_id' => $revId ],
                __METHOD__,
                $dbOptions,
                [ 'page' => [ 'JOIN', 'page_id=rev_page' ] ]
            );
            if ( $row ) {
                // TODO: better foreign title handling (introduce TitleFactory)
                return Title::newFromRow( $row );
            }
        }
 
        // If we still don't have a title, fallback to master if that wasn't already happening.
        if ( $dbMode !== DB_MASTER ) {
            $title = $this->getTitle( $pageId, $revId, self::READ_LATEST );
            if ( $title ) {
                $this->logger->info(
                    __METHOD__ . ' fell back to READ_LATEST and got a Title.',
                    [ 'trace' => wfBacktrace() ]
                );
                return $title;
            }
        }
 
        throw new RevisionAccessException(
            "Could not determine title for page ID $pageId and revision ID $revId"
        );
    }
 
    private function failOnNull( $value, $name ) {
        if ( $value === null ) {
            throw new IncompleteRevisionException(
                "$name must not be " . var_export( $value, true ) . "!"
            );
        }
 
        return $value;
    }
 
    private function failOnEmpty( $value, $name ) {
        if ( $value === null || $value === 0 || $value === '' ) {
            throw new IncompleteRevisionException(
                "$name must not be " . var_export( $value, true ) . "!"
            );
        }
 
        return $value;
    }
 
    public function insertRevisionOn( RevisionRecord $rev, IDatabase $dbw ) {
        // TODO: pass in a DBTransactionContext instead of a database connection.
        $this->checkDatabaseWikiId( $dbw );
 
        if ( !$rev->getSlotRoles() ) {
            throw new InvalidArgumentException( 'At least one slot needs to be defined!' );
        }
 
        if ( $rev->getSlotRoles() !== [ 'main' ] ) {
            throw new InvalidArgumentException( 'Only the main slot is supported for now!' );
        }
 
        // TODO: we shouldn't need an actual Title here.
        $title = Title::newFromLinkTarget( $rev->getPageAsLinkTarget() );
        $pageId = $this->failOnEmpty( $rev->getPageId(), 'rev_page field' ); // check this early
 
        $parentId = $rev->getParentId() === null
            ? $this->getPreviousRevisionId( $dbw, $rev )
            : $rev->getParentId();
 
        // Record the text (or external storage URL) to the blob store
        $slot = $rev->getSlot( 'main', RevisionRecord::RAW );
 
        $size = $this->failOnNull( $rev->getSize(), 'size field' );
        $sha1 = $this->failOnEmpty( $rev->getSha1(), 'sha1 field' );
 
        if ( !$slot->hasAddress() ) {
            $content = $slot->getContent();
            $format = $content->getDefaultFormat();
            $model = $content->getModel();
 
            $this->checkContentModel( $content, $title );
 
            $data = $content->serialize( $format );
 
            // Hints allow the blob store to optimize by "leaking" application level information to it.
            // TODO: with the new MCR storage schema, we rev_id have this before storing the blobs.
            // When we have it, add rev_id as a hint. Can be used with rev_parent_id for
            // differential storage or compression of subsequent revisions.
            $blobHints = [
                BlobStore::DESIGNATION_HINT => 'page-content', // BlobStore may be used for other things too.
                BlobStore::PAGE_HINT => $pageId,
                BlobStore::ROLE_HINT => $slot->getRole(),
                BlobStore::PARENT_HINT => $parentId,
                BlobStore::SHA1_HINT => $slot->getSha1(),
                BlobStore::MODEL_HINT => $model,
                BlobStore::FORMAT_HINT => $format,
            ];
 
            $blobAddress = $this->blobStore->storeBlob( $data, $blobHints );
        } else {
            $blobAddress = $slot->getAddress();
            $model = $slot->getModel();
            $format = $slot->getFormat();
        }
 
        $textId = $this->blobStore->getTextIdFromAddress( $blobAddress );
 
        if ( !$textId ) {
            throw new LogicException(
                'Blob address not supported in 1.29 database schema: ' . $blobAddress
            );
        }
 
        // getTextIdFromAddress() is free to insert something into the text table, so $textId
        // may be a new value, not anything already contained in $blobAddress.
        $blobAddress = 'tt:' . $textId;
 
        $comment = $this->failOnNull( $rev->getComment( RevisionRecord::RAW ), 'comment' );
        $user = $this->failOnNull( $rev->getUser( RevisionRecord::RAW ), 'user' );
        $timestamp = $this->failOnEmpty( $rev->getTimestamp(), 'timestamp field' );
 
        // Checks.
        $this->failOnNull( $user->getId(), 'user field' );
        $this->failOnEmpty( $user->getName(), 'user_text field' );
 
        # Record the edit in revisions
        $row = [
            'rev_page'       => $pageId,
            'rev_parent_id'  => $parentId,
            'rev_text_id'    => $textId,
            'rev_minor_edit' => $rev->isMinor() ? 1 : 0,
            'rev_timestamp'  => $dbw->timestamp( $timestamp ),
            'rev_deleted'    => $rev->getVisibility(),
            'rev_len'        => $size,
            'rev_sha1'       => $sha1,
        ];
 
        if ( $rev->getId() !== null ) {
            // Needed to restore revisions with their original ID
            $row['rev_id'] = $rev->getId();
        }
 
        list( $commentFields, $commentCallback ) =
            $this->commentStore->insertWithTempTable( $dbw, 'rev_comment', $comment );
        $row += $commentFields;
 
        list( $actorFields, $actorCallback ) =
            $this->actorMigration->getInsertValuesWithTempTable( $dbw, 'rev_user', $user );
        $row += $actorFields;
 
        if ( $this->contentHandlerUseDB ) {
            // MCR migration note: rev_content_model and rev_content_format will go away
 
            $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 ( !isset( $row['rev_id'] ) ) {
            // only if auto-increment was used
            $row['rev_id'] = intval( $dbw->insertId() );
        }
        $commentCallback( $row['rev_id'] );
        $actorCallback( $row['rev_id'], $row );
 
        // Insert IP revision into ip_changes for use when querying for a range.
        if ( $user->getId() === 0 && IP::isValid( $user->getName() ) ) {
            $ipcRow = [
                'ipc_rev_id'        => $row['rev_id'],
                'ipc_rev_timestamp' => $row['rev_timestamp'],
                'ipc_hex'           => IP::toHex( $user->getName() ),
            ];
            $dbw->insert( 'ip_changes', $ipcRow, __METHOD__ );
        }
 
        $newSlot = SlotRecord::newSaved( $row['rev_id'], $textId, $blobAddress, $slot );
        $slots = new RevisionSlots( [ 'main' => $newSlot ] );
 
        $rev = new RevisionStoreRecord(
            $title,
            $user,
            $comment,
            (object)$row,
            $slots,
            $this->wikiId
        );
 
        $newSlot = $rev->getSlot( 'main', RevisionRecord::RAW );
 
        // sanity checks
        Assert::postcondition( $rev->getId() > 0, 'revision must have an ID' );
        Assert::postcondition( $rev->getPageId() > 0, 'revision must have a page ID' );
        Assert::postcondition(
            $rev->getComment( RevisionRecord::RAW ) !== null,
            'revision must have a comment'
        );
        Assert::postcondition(
            $rev->getUser( RevisionRecord::RAW ) !== null,
            'revision must have a user'
        );
 
        Assert::postcondition( $newSlot !== null, 'revision must have a main slot' );
        Assert::postcondition(
            $newSlot->getAddress() !== null,
            'main slot must have an addess'
        );
 
        Hooks::run( 'RevisionRecordInserted', [ $rev ] );
 
        return $rev;
    }
 
    private function checkContentModel( Content $content, Title $title ) {
        // Note: may return null for revisions that have not yet been inserted
 
        $model = $content->getModel();
        $format = $content->getDefaultFormat();
        $handler = $content->getContentHandler();
 
        $name = "$title";
 
        if ( !$handler->isSupportedFormat( $format ) ) {
            throw new MWException( "Can't use format $format with content model $model on $name" );
        }
 
        if ( !$this->contentHandlerUseDB ) {
            // 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 ( $model != $defaultModel ) {
                throw new MWException( "Can't save non-default content model with "
                    . "\$wgContentHandlerUseDB disabled: model is $model, "
                    . "default for $name is $defaultModel"
                );
            }
 
            if ( $format != $defaultFormat ) {
                throw new MWException( "Can't use non-default content format with "
                    . "\$wgContentHandlerUseDB disabled: format is $format, "
                    . "default for $name is $defaultFormat"
                );
            }
        }
 
        if ( !$content->isValid() ) {
            throw new MWException(
                "New content for $name is not valid! Content model is $model"
            );
        }
    }
 
    public function newNullRevision(
        IDatabase $dbw,
        Title $title,
        CommentStoreComment $comment,
        $minor,
        User $user
    ) {
        $this->checkDatabaseWikiId( $dbw );
 
        $fields = [ 'page_latest', 'page_namespace', 'page_title',
            'rev_id', 'rev_text_id', 'rev_len', 'rev_sha1' ];
 
        if ( $this->contentHandlerUseDB ) {
            $fields[] = 'rev_content_model';
            $fields[] = 'rev_content_format';
        }
 
        $current = $dbw->selectRow(
            [ 'page', 'revision' ],
            $fields,
            [
                'page_id' => $title->getArticleID(),
                'page_latest=rev_id',
            ],
            __METHOD__,
            [ 'FOR UPDATE' ] // T51581
        );
 
        if ( $current ) {
            $fields = [
                'page'        => $title->getArticleID(),
                'user_text'   => $user->getName(),
                'user'        => $user->getId(),
                'actor'       => $user->getActorId(),
                'comment'     => $comment,
                'minor_edit'  => $minor,
                'text_id'     => $current->rev_text_id,
                'parent_id'   => $current->page_latest,
                'slot_origin' => $current->page_latest,
                'len'         => $current->rev_len,
                'sha1'        => $current->rev_sha1
            ];
 
            if ( $this->contentHandlerUseDB ) {
                $fields['content_model'] = $current->rev_content_model;
                $fields['content_format'] = $current->rev_content_format;
            }
 
            $fields['title'] = Title::makeTitle( $current->page_namespace, $current->page_title );
 
            $mainSlot = $this->emulateMainSlot_1_29( $fields, self::READ_LATEST, $title );
            $revision = new MutableRevisionRecord( $title, $this->wikiId );
            $this->initializeMutableRevisionFromArray( $revision, $fields );
            $revision->setSlot( $mainSlot );
        } else {
            $revision = null;
        }
 
        return $revision;
    }
 
    public function getRcIdIfUnpatrolled( RevisionRecord $rev ) {
        $rc = $this->getRecentChange( $rev );
        if ( $rc && $rc->getAttribute( 'rc_patrolled' ) == RecentChange::PRC_UNPATROLLED ) {
            return $rc->getAttribute( 'rc_id' );
        } else {
            return 0;
        }
    }
 
    public function getRecentChange( RevisionRecord $rev, $flags = 0 ) {
        $dbr = $this->getDBConnection( DB_REPLICA );
 
        list( $dbType, ) = DBAccessObjectUtils::getDBOptions( $flags );
 
        $userIdentity = $rev->getUser( RevisionRecord::RAW );
 
        if ( !$userIdentity ) {
            // If the revision has no user identity, chances are it never went
            // into the database, and doesn't have an RC entry.
            return null;
        }
 
        // TODO: Select by rc_this_oldid alone - but as of Nov 2017, there is no index on that!
        $actorWhere = $this->actorMigration->getWhere( $dbr, 'rc_user', $rev->getUser(), false );
        $rc = RecentChange::newFromConds(
            [
                $actorWhere['conds'],
                'rc_timestamp' => $dbr->timestamp( $rev->getTimestamp() ),
                'rc_this_oldid' => $rev->getId()
            ],
            __METHOD__,
            $dbType
        );
 
        $this->releaseDBConnection( $dbr );
 
        // XXX: cache this locally? Glue it to the RevisionRecord?
        return $rc;
    }
 
    private static function mapArchiveFields( $archiveRow ) {
        $fieldMap = [
            // keep with ar prefix:
            'ar_id'        => 'ar_id',
 
            // not the same suffix:
            'ar_page_id'        => 'rev_page',
            'ar_rev_id'         => 'rev_id',
 
            // same suffix:
            'ar_text_id'        => 'rev_text_id',
            'ar_timestamp'      => 'rev_timestamp',
            'ar_user_text'      => 'rev_user_text',
            'ar_user'           => 'rev_user',
            'ar_actor'          => 'rev_actor',
            'ar_minor_edit'     => 'rev_minor_edit',
            'ar_deleted'        => 'rev_deleted',
            'ar_len'            => 'rev_len',
            'ar_parent_id'      => 'rev_parent_id',
            'ar_sha1'           => 'rev_sha1',
            'ar_comment'        => 'rev_comment',
            'ar_comment_cid'    => 'rev_comment_cid',
            'ar_comment_id'     => 'rev_comment_id',
            'ar_comment_text'   => 'rev_comment_text',
            'ar_comment_data'   => 'rev_comment_data',
            'ar_comment_old'    => 'rev_comment_old',
            'ar_content_format' => 'rev_content_format',
            'ar_content_model'  => 'rev_content_model',
        ];
 
        $revRow = new stdClass();
        foreach ( $fieldMap as $arKey => $revKey ) {
            if ( property_exists( $archiveRow, $arKey ) ) {
                $revRow->$revKey = $archiveRow->$arKey;
            }
        }
 
        return $revRow;
    }
 
    private function emulateMainSlot_1_29( $row, $queryFlags, Title $title ) {
        $mainSlotRow = new stdClass();
        $mainSlotRow->role_name = 'main';
        $mainSlotRow->model_name = null;
        $mainSlotRow->slot_revision_id = null;
        $mainSlotRow->content_address = null;
        $mainSlotRow->slot_content_id = null;
 
        $content = null;
        $blobData = null;
        $blobFlags = null;
 
        if ( is_object( $row ) ) {
            // archive row
            if ( !isset( $row->rev_id ) && ( isset( $row->ar_user ) || isset( $row->ar_actor ) ) ) {
                $row = $this->mapArchiveFields( $row );
            }
 
            if ( isset( $row->rev_text_id ) && $row->rev_text_id > 0 ) {
                $mainSlotRow->slot_content_id = $row->rev_text_id;
                $mainSlotRow->content_address = 'tt:' . $row->rev_text_id;
            }
 
            // This is used by null-revisions
            $mainSlotRow->slot_origin = isset( $row->slot_origin )
                ? intval( $row->slot_origin )
                : null;
 
            if ( isset( $row->old_text ) ) {
                // this happens when the text-table gets joined directly, in the pre-1.30 schema
                $blobData = isset( $row->old_text ) ? strval( $row->old_text ) : null;
                // Check against selects that might have not included old_flags
                if ( !property_exists( $row, 'old_flags' ) ) {
                    throw new InvalidArgumentException( 'old_flags was not set in $row' );
                }
                $blobFlags = ( $row->old_flags === null ) ? '' : $row->old_flags;
            }
 
            $mainSlotRow->slot_revision_id = intval( $row->rev_id );
 
            $mainSlotRow->content_size = isset( $row->rev_len ) ? intval( $row->rev_len ) : null;
            $mainSlotRow->content_sha1 = isset( $row->rev_sha1 ) ? strval( $row->rev_sha1 ) : null;
            $mainSlotRow->model_name = isset( $row->rev_content_model )
                ? strval( $row->rev_content_model )
                : null;
            // XXX: in the future, we'll probably always use the default format, and drop content_format
            $mainSlotRow->format_name = isset( $row->rev_content_format )
                ? strval( $row->rev_content_format )
                : null;
        } elseif ( is_array( $row ) ) {
            $mainSlotRow->slot_revision_id = isset( $row['id'] ) ? intval( $row['id'] ) : null;
 
            $mainSlotRow->slot_content_id = isset( $row['text_id'] )
                ? intval( $row['text_id'] )
                : null;
            $mainSlotRow->slot_origin = isset( $row['slot_origin'] )
                ? intval( $row['slot_origin'] )
                : null;
            $mainSlotRow->content_address = isset( $row['text_id'] )
                ? 'tt:' . intval( $row['text_id'] )
                : null;
            $mainSlotRow->content_size = isset( $row['len'] ) ? intval( $row['len'] ) : null;
            $mainSlotRow->content_sha1 = isset( $row['sha1'] ) ? strval( $row['sha1'] ) : null;
 
            $mainSlotRow->model_name = isset( $row['content_model'] )
                ? strval( $row['content_model'] ) : null;  // XXX: must be a string!
            // XXX: in the future, we'll probably always use the default format, and drop content_format
            $mainSlotRow->format_name = isset( $row['content_format'] )
                ? strval( $row['content_format'] ) : null;
            $blobData = isset( $row['text'] ) ? rtrim( strval( $row['text'] ) ) : null;
            // XXX: If the flags field is not set then $blobFlags should be null so that no
            // decoding will happen. An empty string will result in default decodings.
            $blobFlags = isset( $row['flags'] ) ? trim( strval( $row['flags'] ) ) : 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.' );
                }
 
                $content = $row['content'];
                $handler = $content->getContentHandler();
 
                $mainSlotRow->model_name = $content->getModel();
 
                // XXX: in the future, we'll probably always use the default format.
                if ( $mainSlotRow->format_name === null ) {
                    $mainSlotRow->format_name = $handler->getDefaultFormat();
                }
            }
        } else {
            throw new MWException( 'Revision constructor passed invalid row format.' );
        }
 
        // With the old schema, the content changes with every revision,
        // except for null-revisions.
        if ( !isset( $mainSlotRow->slot_origin ) ) {
            $mainSlotRow->slot_origin = $mainSlotRow->slot_revision_id;
        }
 
        if ( $mainSlotRow->model_name === null ) {
            $mainSlotRow->model_name = function ( SlotRecord $slot ) use ( $title ) {
                // TODO: MCR: consider slot role in getDefaultModelFor()! Use LinkTarget!
                // TODO: MCR: deprecate $title->getModel().
                return ContentHandler::getDefaultModelFor( $title );
            };
        }
 
        if ( !$content ) {
            $content = function ( SlotRecord $slot )
                use ( $blobData, $blobFlags, $queryFlags, $mainSlotRow )
            {
                return $this->loadSlotContent(
                    $slot,
                    $blobData,
                    $blobFlags,
                    $mainSlotRow->format_name,
                    $queryFlags
                );
            };
        }
 
        $mainSlotRow->slot_id = $mainSlotRow->slot_revision_id;
        return new SlotRecord( $mainSlotRow, $content );
    }
 
    private function loadSlotContent(
        SlotRecord $slot,
        $blobData = null,
        $blobFlags = null,
        $blobFormat = null,
        $queryFlags = 0
    ) {
        if ( $blobData !== null ) {
            Assert::parameterType( 'string', $blobData, '$blobData' );
            Assert::parameterType( 'string|null', $blobFlags, '$blobFlags' );
 
            $cacheKey = $slot->hasAddress() ? $slot->getAddress() : null;
 
            if ( $blobFlags === null ) {
                // No blob flags, so use the blob verbatim.
                $data = $blobData;
            } else {
                $data = $this->blobStore->expandBlob( $blobData, $blobFlags, $cacheKey );
                if ( $data === false ) {
                    throw new RevisionAccessException(
                        "Failed to expand blob data using flags $blobFlags (key: $cacheKey)"
                    );
                }
            }
 
        } else {
            $address = $slot->getAddress();
            try {
                $data = $this->blobStore->getBlob( $address, $queryFlags );
            } catch ( BlobAccessException $e ) {
                throw new RevisionAccessException(
                    "Failed to load data blob from $address: " . $e->getMessage(), 0, $e
                );
            }
        }
 
        // Unserialize content
        $handler = ContentHandler::getForModelID( $slot->getModel() );
 
        $content = $handler->unserializeContent( $data, $blobFormat );
        return $content;
    }
 
    public function getRevisionById( $id, $flags = 0 ) {
        return $this->newRevisionFromConds( [ 'rev_id' => intval( $id ) ], $flags );
    }
 
    public function getRevisionByTitle( LinkTarget $linkTarget, $revId = 0, $flags = 0 ) {
        $conds = [
            'page_namespace' => $linkTarget->getNamespace(),
            'page_title' => $linkTarget->getDBkey()
        ];
        if ( $revId ) {
            // Use the specified revision ID.
            // Note that we use newRevisionFromConds here because we want to retry
            // and fall back to master if the page is not found on a replica.
            // Since the caller supplied a revision ID, we are pretty sure the revision is
            // supposed to exist, so we should try hard to find it.
            $conds['rev_id'] = $revId;
            return $this->newRevisionFromConds( $conds, $flags );
        } else {
            // Use a join to get the latest revision.
            // Note that we don't use newRevisionFromConds here because we don't want to retry
            // and fall back to master. The assumption is that we only want to force the fallback
            // if we are quite sure the revision exists because the caller supplied a revision ID.
            // If the page isn't found at all on a replica, it probably simply does not exist.
            $db = $this->getDBConnection( ( $flags & self::READ_LATEST ) ? DB_MASTER : DB_REPLICA );
 
            $conds[] = 'rev_id=page_latest';
            $rev = $this->loadRevisionFromConds( $db, $conds, $flags );
 
            $this->releaseDBConnection( $db );
            return $rev;
        }
    }
 
    public function getRevisionByPageId( $pageId, $revId = 0, $flags = 0 ) {
        $conds = [ 'page_id' => $pageId ];
        if ( $revId ) {
            // Use the specified revision ID.
            // Note that we use newRevisionFromConds here because we want to retry
            // and fall back to master if the page is not found on a replica.
            // Since the caller supplied a revision ID, we are pretty sure the revision is
            // supposed to exist, so we should try hard to find it.
            $conds['rev_id'] = $revId;
            return $this->newRevisionFromConds( $conds, $flags );
        } else {
            // Use a join to get the latest revision.
            // Note that we don't use newRevisionFromConds here because we don't want to retry
            // and fall back to master. The assumption is that we only want to force the fallback
            // if we are quite sure the revision exists because the caller supplied a revision ID.
            // If the page isn't found at all on a replica, it probably simply does not exist.
            $db = $this->getDBConnection( ( $flags & self::READ_LATEST ) ? DB_MASTER : DB_REPLICA );
 
            $conds[] = 'rev_id=page_latest';
            $rev = $this->loadRevisionFromConds( $db, $conds, $flags );
 
            $this->releaseDBConnection( $db );
            return $rev;
        }
    }
 
    public function getRevisionByTimestamp( $title, $timestamp ) {
        $db = $this->getDBConnection( DB_REPLICA );
        return $this->newRevisionFromConds(
            [
                'rev_timestamp' => $db->timestamp( $timestamp ),
                'page_namespace' => $title->getNamespace(),
                'page_title' => $title->getDBkey()
            ],
            0,
            $title
        );
    }
 
    public function newRevisionFromArchiveRow(
        $row,
        $queryFlags = 0,
        Title $title = null,
        array $overrides = []
    ) {
        Assert::parameterType( 'object', $row, '$row' );
 
        // check second argument, since Revision::newFromArchiveRow had $overrides in that spot.
        Assert::parameterType( 'integer', $queryFlags, '$queryFlags' );
 
        if ( !$title && isset( $overrides['title'] ) ) {
            if ( !( $overrides['title'] instanceof Title ) ) {
                throw new MWException( 'title field override must contain a Title object.' );
            }
 
            $title = $overrides['title'];
        }
 
        if ( !isset( $title ) ) {
            if ( isset( $row->ar_namespace ) && isset( $row->ar_title ) ) {
                $title = Title::makeTitle( $row->ar_namespace, $row->ar_title );
            } else {
                throw new InvalidArgumentException(
                    'A Title or ar_namespace and ar_title must be given'
                );
            }
        }
 
        foreach ( $overrides as $key => $value ) {
            $field = "ar_$key";
            $row->$field = $value;
        }
 
        try {
            $user = User::newFromAnyId(
                isset( $row->ar_user ) ? $row->ar_user : null,
                isset( $row->ar_user_text ) ? $row->ar_user_text : null,
                isset( $row->ar_actor ) ? $row->ar_actor : null
            );
        } catch ( InvalidArgumentException $ex ) {
            wfWarn( __METHOD__ . ': ' . $ex->getMessage() );
            $user = new UserIdentityValue( 0, '', 0 );
        }
 
        $comment = $this->commentStore
            // Legacy because $row may have come from self::selectFields()
            ->getCommentLegacy( $this->getDBConnection( DB_REPLICA ), 'ar_comment', $row, true );
 
        $mainSlot = $this->emulateMainSlot_1_29( $row, $queryFlags, $title );
        $slots = new RevisionSlots( [ 'main' => $mainSlot ] );
 
        return new RevisionArchiveRecord( $title, $user, $comment, $row, $slots, $this->wikiId );
    }
 
    private function newRevisionFromRow_1_29( $row, $queryFlags = 0, Title $title = null ) {
        Assert::parameterType( 'object', $row, '$row' );
 
        if ( !$title ) {
            $pageId = isset( $row->rev_page ) ? $row->rev_page : 0; // XXX: also check page_id?
            $revId = isset( $row->rev_id ) ? $row->rev_id : 0;
 
            $title = $this->getTitle( $pageId, $revId, $queryFlags );
        }
 
        if ( !isset( $row->page_latest ) ) {
            $row->page_latest = $title->getLatestRevID();
            if ( $row->page_latest === 0 && $title->exists() ) {
                wfWarn( 'Encountered title object in limbo: ID ' . $title->getArticleID() );
            }
        }
 
        try {
            $user = User::newFromAnyId(
                isset( $row->rev_user ) ? $row->rev_user : null,
                isset( $row->rev_user_text ) ? $row->rev_user_text : null,
                isset( $row->rev_actor ) ? $row->rev_actor : null
            );
        } catch ( InvalidArgumentException $ex ) {
            wfWarn( __METHOD__ . ': ' . $ex->getMessage() );
            $user = new UserIdentityValue( 0, '', 0 );
        }
 
        $comment = $this->commentStore
            // Legacy because $row may have come from self::selectFields()
            ->getCommentLegacy( $this->getDBConnection( DB_REPLICA ), 'rev_comment', $row, true );
 
        $mainSlot = $this->emulateMainSlot_1_29( $row, $queryFlags, $title );
        $slots = new RevisionSlots( [ 'main' => $mainSlot ] );
 
        return new RevisionStoreRecord( $title, $user, $comment, $row, $slots, $this->wikiId );
    }
 
    public function newRevisionFromRow( $row, $queryFlags = 0, Title $title = null ) {
        return $this->newRevisionFromRow_1_29( $row, $queryFlags, $title );
    }
 
    public function newMutableRevisionFromArray(
        array $fields,
        $queryFlags = 0,
        Title $title = null
    ) {
        if ( !$title && isset( $fields['title'] ) ) {
            if ( !( $fields['title'] instanceof Title ) ) {
                throw new MWException( 'title field must contain a Title object.' );
            }
 
            $title = $fields['title'];
        }
 
        if ( !$title ) {
            $pageId = isset( $fields['page'] ) ? $fields['page'] : 0;
            $revId = isset( $fields['id'] ) ? $fields['id'] : 0;
 
            $title = $this->getTitle( $pageId, $revId, $queryFlags );
        }
 
        if ( !isset( $fields['page'] ) ) {
            $fields['page'] = $title->getArticleID( $queryFlags );
        }
 
        // if we have a content object, use it to set the model and type
        if ( !empty( $fields['content'] ) ) {
            if ( !( $fields['content'] instanceof Content ) ) {
                throw new MWException( 'content field must contain a Content object.' );
            }
 
            if ( !empty( $fields['text_id'] ) ) {
                throw new MWException(
                    "Text already stored in external store (id {$fields['text_id']}), " .
                    "can't serialize content object"
                );
            }
        }
 
        if (
            isset( $fields['comment'] )
            && !( $fields['comment'] instanceof CommentStoreComment )
        ) {
            $commentData = isset( $fields['comment_data'] ) ? $fields['comment_data'] : null;
 
            if ( $fields['comment'] instanceof Message ) {
                $fields['comment'] = CommentStoreComment::newUnsavedComment(
                    $fields['comment'],
                    $commentData
                );
            } else {
                $commentText = trim( strval( $fields['comment'] ) );
                $fields['comment'] = CommentStoreComment::newUnsavedComment(
                    $commentText,
                    $commentData
                );
            }
        }
 
        $mainSlot = $this->emulateMainSlot_1_29( $fields, $queryFlags, $title );
 
        $revision = new MutableRevisionRecord( $title, $this->wikiId );
        $this->initializeMutableRevisionFromArray( $revision, $fields );
        $revision->setSlot( $mainSlot );
 
        return $revision;
    }
 
    private function initializeMutableRevisionFromArray(
        MutableRevisionRecord $record,
        array $fields
    ) {
        $user = null;
 
        if ( isset( $fields['user'] ) && ( $fields['user'] instanceof UserIdentity ) ) {
            $user = $fields['user'];
        } else {
            try {
                $user = User::newFromAnyId(
                    isset( $fields['user'] ) ? $fields['user'] : null,
                    isset( $fields['user_text'] ) ? $fields['user_text'] : null,
                    isset( $fields['actor'] ) ? $fields['actor'] : null
                );
            } catch ( InvalidArgumentException $ex ) {
                $user = null;
            }
        }
 
        if ( $user ) {
            $record->setUser( $user );
        }
 
        $timestamp = isset( $fields['timestamp'] )
            ? strval( $fields['timestamp'] )
            : wfTimestampNow(); // TODO: use a callback, so we can override it for testing.
 
        $record->setTimestamp( $timestamp );
 
        if ( isset( $fields['page'] ) ) {
            $record->setPageId( intval( $fields['page'] ) );
        }
 
        if ( isset( $fields['id'] ) ) {
            $record->setId( intval( $fields['id'] ) );
        }
        if ( isset( $fields['parent_id'] ) ) {
            $record->setParentId( intval( $fields['parent_id'] ) );
        }
 
        if ( isset( $fields['sha1'] ) ) {
            $record->setSha1( $fields['sha1'] );
        }
        if ( isset( $fields['size'] ) ) {
            $record->setSize( intval( $fields['size'] ) );
        }
 
        if ( isset( $fields['minor_edit'] ) ) {
            $record->setMinorEdit( intval( $fields['minor_edit'] ) !== 0 );
        }
        if ( isset( $fields['deleted'] ) ) {
            $record->setVisibility( intval( $fields['deleted'] ) );
        }
 
        if ( isset( $fields['comment'] ) ) {
            Assert::parameterType(
                CommentStoreComment::class,
                $fields['comment'],
                '$row[\'comment\']'
            );
            $record->setComment( $fields['comment'] );
        }
    }
 
    public function loadRevisionFromId( IDatabase $db, $id ) {
        return $this->loadRevisionFromConds( $db, [ 'rev_id' => intval( $id ) ] );
    }
 
    public function loadRevisionFromPageId( IDatabase $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 $this->loadRevisionFromConds( $db, $conds );
    }
 
    public function loadRevisionFromTitle( IDatabase $db, $title, $id = 0 ) {
        if ( $id ) {
            $matchId = intval( $id );
        } else {
            $matchId = 'page_latest';
        }
 
        return $this->loadRevisionFromConds(
            $db,
            [
                "rev_id=$matchId",
                'page_namespace' => $title->getNamespace(),
                'page_title' => $title->getDBkey()
            ],
            0,
            $title
        );
    }
 
    public function loadRevisionFromTimestamp( IDatabase $db, $title, $timestamp ) {
        return $this->loadRevisionFromConds( $db,
            [
                'rev_timestamp' => $db->timestamp( $timestamp ),
                'page_namespace' => $title->getNamespace(),
                'page_title' => $title->getDBkey()
            ],
            0,
            $title
        );
    }
 
    private function newRevisionFromConds( $conditions, $flags = 0, Title $title = null ) {
        $db = $this->getDBConnection( ( $flags & self::READ_LATEST ) ? DB_MASTER : DB_REPLICA );
        $rev = $this->loadRevisionFromConds( $db, $conditions, $flags, $title );
        $this->releaseDBConnection( $db );
 
        $lb = $this->getDBLoadBalancer();
 
        // 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 )
            && $lb->getServerCount() > 1
            && $lb->hasOrMadeRecentMasterChanges()
        ) {
            $flags = self::READ_LATEST;
            $db = $this->getDBConnection( DB_MASTER );
            $rev = $this->loadRevisionFromConds( $db, $conditions, $flags, $title );
            $this->releaseDBConnection( $db );
        }
 
        return $rev;
    }
 
    private function loadRevisionFromConds(
        IDatabase $db,
        $conditions,
        $flags = 0,
        Title $title = null
    ) {
        $row = $this->fetchRevisionRowFromConds( $db, $conditions, $flags );
        if ( $row ) {
            $rev = $this->newRevisionFromRow( $row, $flags, $title );
 
            return $rev;
        }
 
        return null;
    }
 
    private function checkDatabaseWikiId( IDatabase $db ) {
        $storeWiki = $this->wikiId;
        $dbWiki = $db->getDomainID();
 
        if ( $dbWiki === $storeWiki ) {
            return;
        }
 
        // XXX: we really want the default database ID...
        $storeWiki = $storeWiki ?: wfWikiID();
        $dbWiki = $dbWiki ?: wfWikiID();
 
        if ( $dbWiki === $storeWiki ) {
            return;
        }
 
        // HACK: counteract encoding imposed by DatabaseDomain
        $storeWiki = str_replace( '?h', '-', $storeWiki );
        $dbWiki = str_replace( '?h', '-', $dbWiki );
 
        if ( $dbWiki === $storeWiki ) {
            return;
        }
 
        throw new MWException( "RevisionStore for $storeWiki "
            . "cannot be used with a DB connection for $dbWiki" );
    }
 
    private function fetchRevisionRowFromConds( IDatabase $db, $conditions, $flags = 0 ) {
        $this->checkDatabaseWikiId( $db );
 
        $revQuery = self::getQueryInfo( [ 'page', 'user' ] );
        $options = [];
        if ( ( $flags & self::READ_LOCKING ) == self::READ_LOCKING ) {
            $options[] = 'FOR UPDATE';
        }
        return $db->selectRow(
            $revQuery['tables'],
            $revQuery['fields'],
            $conditions,
            __METHOD__,
            $options,
            $revQuery['joins']
        );
    }
 
    public function getQueryInfo( $options = [] ) {
        $ret = [
            'tables' => [],
            'fields' => [],
            'joins'  => [],
        ];
 
        $ret['tables'][] = 'revision';
        $ret['fields'] = array_merge( $ret['fields'], [
            'rev_id',
            'rev_page',
            'rev_text_id',
            'rev_timestamp',
            'rev_minor_edit',
            'rev_deleted',
            'rev_len',
            'rev_parent_id',
            'rev_sha1',
        ] );
 
        $commentQuery = $this->commentStore->getJoin( 'rev_comment' );
        $ret['tables'] = array_merge( $ret['tables'], $commentQuery['tables'] );
        $ret['fields'] = array_merge( $ret['fields'], $commentQuery['fields'] );
        $ret['joins'] = array_merge( $ret['joins'], $commentQuery['joins'] );
 
        $actorQuery = $this->actorMigration->getJoin( 'rev_user' );
        $ret['tables'] = array_merge( $ret['tables'], $actorQuery['tables'] );
        $ret['fields'] = array_merge( $ret['fields'], $actorQuery['fields'] );
        $ret['joins'] = array_merge( $ret['joins'], $actorQuery['joins'] );
 
        if ( $this->contentHandlerUseDB ) {
            $ret['fields'][] = 'rev_content_format';
            $ret['fields'][] = 'rev_content_model';
        }
 
        if ( in_array( 'page', $options, true ) ) {
            $ret['tables'][] = 'page';
            $ret['fields'] = array_merge( $ret['fields'], [
                'page_namespace',
                'page_title',
                'page_id',
                'page_latest',
                'page_is_redirect',
                'page_len',
            ] );
            $ret['joins']['page'] = [ 'INNER JOIN', [ 'page_id = rev_page' ] ];
        }
 
        if ( in_array( 'user', $options, true ) ) {
            $ret['tables'][] = 'user';
            $ret['fields'] = array_merge( $ret['fields'], [
                'user_name',
            ] );
            $u = $actorQuery['fields']['rev_user'];
            $ret['joins']['user'] = [ 'LEFT JOIN', [ "$u != 0", "user_id = $u" ] ];
        }
 
        if ( in_array( 'text', $options, true ) ) {
            $ret['tables'][] = 'text';
            $ret['fields'] = array_merge( $ret['fields'], [
                'old_text',
                'old_flags'
            ] );
            $ret['joins']['text'] = [ 'INNER JOIN', [ 'rev_text_id=old_id' ] ];
        }
 
        return $ret;
    }
 
    public function getArchiveQueryInfo() {
        $commentQuery = $this->commentStore->getJoin( 'ar_comment' );
        $actorQuery = $this->actorMigration->getJoin( 'ar_user' );
        $ret = [
            'tables' => [ 'archive' ] + $commentQuery['tables'] + $actorQuery['tables'],
            'fields' => [
                    'ar_id',
                    'ar_page_id',
                    'ar_namespace',
                    'ar_title',
                    'ar_rev_id',
                    'ar_text_id',
                    'ar_timestamp',
                    'ar_minor_edit',
                    'ar_deleted',
                    'ar_len',
                    'ar_parent_id',
                    'ar_sha1',
                ] + $commentQuery['fields'] + $actorQuery['fields'],
            'joins' => $commentQuery['joins'] + $actorQuery['joins'],
        ];
 
        if ( $this->contentHandlerUseDB ) {
            $ret['fields'][] = 'ar_content_format';
            $ret['fields'][] = 'ar_content_model';
        }
 
        return $ret;
    }
 
    public function getRevisionSizes( array $revIds ) {
        return $this->listRevisionSizes( $this->getDBConnection( DB_REPLICA ), $revIds );
    }
 
    public function listRevisionSizes( IDatabase $db, array $revIds ) {
        $this->checkDatabaseWikiId( $db );
 
        $revLens = [];
        if ( !$revIds ) {
            return $revLens; // empty
        }
 
        $res = $db->select(
            'revision',
            [ 'rev_id', 'rev_len' ],
            [ 'rev_id' => $revIds ],
            __METHOD__
        );
 
        foreach ( $res as $row ) {
            $revLens[$row->rev_id] = intval( $row->rev_len );
        }
 
        return $revLens;
    }
 
    public function getPreviousRevision( RevisionRecord $rev, Title $title = null ) {
        if ( $title === null ) {
            $title = $this->getTitle( $rev->getPageId(), $rev->getId() );
        }
        $prev = $title->getPreviousRevisionID( $rev->getId() );
        if ( $prev ) {
            return $this->getRevisionByTitle( $title, $prev );
        }
        return null;
    }
 
    public function getNextRevision( RevisionRecord $rev, Title $title = null ) {
        if ( $title === null ) {
            $title = $this->getTitle( $rev->getPageId(), $rev->getId() );
        }
        $next = $title->getNextRevisionID( $rev->getId() );
        if ( $next ) {
            return $this->getRevisionByTitle( $title, $next );
        }
        return null;
    }
 
    private function getPreviousRevisionId( IDatabase $db, RevisionRecord $rev ) {
        $this->checkDatabaseWikiId( $db );
 
        if ( $rev->getPageId() === null ) {
            return 0;
        }
        # Use page_latest if ID is not given
        if ( !$rev->getId() ) {
            $prevId = $db->selectField(
                'page', 'page_latest',
                [ 'page_id' => $rev->getPageId() ],
                __METHOD__
            );
        } else {
            $prevId = $db->selectField(
                'revision', 'rev_id',
                [ 'rev_page' => $rev->getPageId(), 'rev_id < ' . $rev->getId() ],
                __METHOD__,
                [ 'ORDER BY' => 'rev_id DESC' ]
            );
        }
        return intval( $prevId );
    }
 
    public function getTimestampFromId( $title, $id, $flags = 0 ) {
        $db = $this->getDBConnection(
            ( $flags & IDBAccessObject::READ_LATEST ) ? DB_MASTER : DB_REPLICA
        );
 
        $conds = [ 'rev_id' => $id ];
        $conds['rev_page'] = $title->getArticleID();
        $timestamp = $db->selectField( 'revision', 'rev_timestamp', $conds, __METHOD__ );
 
        $this->releaseDBConnection( $db );
        return ( $timestamp !== false ) ? wfTimestamp( TS_MW, $timestamp ) : false;
    }
 
    public function countRevisionsByPageId( IDatabase $db, $id ) {
        $this->checkDatabaseWikiId( $db );
 
        $row = $db->selectRow( 'revision',
            [ 'revCount' => 'COUNT(*)' ],
            [ 'rev_page' => $id ],
            __METHOD__
        );
        if ( $row ) {
            return intval( $row->revCount );
        }
        return 0;
    }
 
    public function countRevisionsByTitle( IDatabase $db, $title ) {
        $id = $title->getArticleID();
        if ( $id ) {
            return $this->countRevisionsByPageId( $db, $id );
        }
        return 0;
    }
 
    public function userWasLastToEdit( IDatabase $db, $pageId, $userId, $since ) {
        $this->checkDatabaseWikiId( $db );
 
        if ( !$userId ) {
            return false;
        }
 
        $revQuery = self::getQueryInfo();
        $res = $db->select(
            $revQuery['tables'],
            [
                'rev_user' => $revQuery['fields']['rev_user'],
            ],
            [
                'rev_page' => $pageId,
                'rev_timestamp > ' . $db->addQuotes( $db->timestamp( $since ) )
            ],
            __METHOD__,
            [ 'ORDER BY' => 'rev_timestamp ASC', 'LIMIT' => 50 ],
            $revQuery['joins']
        );
        foreach ( $res as $row ) {
            if ( $row->rev_user != $userId ) {
                return false;
            }
        }
        return true;
    }
 
    public function getKnownCurrentRevision( Title $title, $revId ) {
        $db = $this->getDBConnectionRef( DB_REPLICA );
 
        $pageId = $title->getArticleID();
 
        if ( !$pageId ) {
            return false;
        }
 
        if ( !$revId ) {
            $revId = $title->getLatestRevID();
        }
 
        if ( !$revId ) {
            wfWarn(
                'No latest revision known for page ' . $title->getPrefixedDBkey()
                . ' even though it exists with page ID ' . $pageId
            );
            return false;
        }
 
        $row = $this->cache->getWithSetCallback(
            // Page/rev IDs passed in from DB to reflect history merges
            $this->cache->makeGlobalKey( 'revision-row-1.29', $db->getDomainID(), $pageId, $revId ),
            WANObjectCache::TTL_WEEK,
            function ( $curValue, &$ttl, array &$setOpts ) use ( $db, $pageId, $revId ) {
                $setOpts += Database::getCacheSetOptions( $db );
 
                $conds = [
                    'rev_page' => intval( $pageId ),
                    'page_id' => intval( $pageId ),
                    'rev_id' => intval( $revId ),
                ];
 
                $row = $this->fetchRevisionRowFromConds( $db, $conds );
                return $row ?: false; // don't cache negatives
            }
        );
 
        // Reflect revision deletion and user renames
        if ( $row ) {
            return $this->newRevisionFromRow( $row, 0, $title );
        } else {
            return false;
        }
    }
 
    // TODO: move relevant methods from Title here, e.g. getFirstRevision, isBigDeletion, etc.
 
}