Revision.php

Go to the documentation of this file.

<?php
class Revision implements IDBAccessObject {
    protected $mId;

    protected $mPage;
    protected $mUserText;
    protected $mOrigUserText;
    protected $mUser;
    protected $mMinorEdit;
    protected $mTimestamp;
    protected $mDeleted;
    protected $mSize;
    protected $mSha1;
    protected $mParentId;
    protected $mComment;
    protected $mText;
    protected $mTextRow;

    protected $mTitle;
    protected $mCurrent;
    protected $mContentModel;
    protected $mContentFormat;

    protected $mContent;

    protected $mContentHandler;

    protected $mQueryFlags = 0;

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

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

    public static function newFromId( $id, $flags = 0 ) {
        return self::newFromConds( array( 'rev_id' => intval( $id ) ), $flags );
    }

    public static function newFromTitle( $title, $id = 0, $flags = 0 ) {
        $conds = array(
            'page_namespace' => $title->getNamespace(),
            'page_title' => $title->getDBkey()
        );
        if ( $id ) {
            // Use the specified ID
            $conds['rev_id'] = $id;
            return self::newFromConds( $conds, (int)$flags );
        } else {
            // Use a join to get the latest revision
            $conds[] = 'rev_id=page_latest';
            $db = wfGetDB( ( $flags & self::READ_LATEST ) ? DB_MASTER : DB_SLAVE );
            return self::loadFromConds( $db, $conds, $flags );
        }
    }

    public static function newFromPageId( $pageId, $revId = 0, $flags = 0 ) {
        $conds = array( 'page_id' => $pageId );
        if ( $revId ) {
            $conds['rev_id'] = $revId;
        } else {
            // Use a join to get the latest revision
            $conds[] = 'rev_id = page_latest';
        }
        return self::newFromConds( $conds, (int)$flags );
    }

    public static function newFromArchiveRow( $row, $overrides = array() ) {
        global $wgContentHandlerUseDB;

        $attribs = $overrides + array(
            '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 bug 22624)' );
            }
        }
        return new self( $attribs );
    }

    public static function newFromRow( $row ) {
        return new self( $row );
    }

    public static function loadFromId( $db, $id ) {
        return self::loadFromConds( $db, array( 'rev_id' => intval( $id ) ) );
    }

    public static function loadFromPageId( $db, $pageid, $id = 0 ) {
        $conds = array( '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 );
    }

    public static function loadFromTitle( $db, $title, $id = 0 ) {
        if ( $id ) {
            $matchId = intval( $id );
        } else {
            $matchId = 'page_latest';
        }
        return self::loadFromConds( $db,
            array(
                "rev_id=$matchId",
                'page_namespace' => $title->getNamespace(),
                'page_title' => $title->getDBkey()
            )
        );
    }

    public static function loadFromTimestamp( $db, $title, $timestamp ) {
        return self::loadFromConds( $db,
            array(
                'rev_timestamp' => $db->timestamp( $timestamp ),
                'page_namespace' => $title->getNamespace(),
                'page_title' => $title->getDBkey()
            )
        );
    }

    private static function newFromConds( $conditions, $flags = 0 ) {
        $db = wfGetDB( ( $flags & self::READ_LATEST ) ? DB_MASTER : DB_SLAVE );
        $rev = self::loadFromConds( $db, $conditions, $flags );
        if ( is_null( $rev ) && wfGetLB()->getServerCount() > 1 ) {
            if ( !( $flags & self::READ_LATEST ) ) {
                $dbw = wfGetDB( DB_MASTER );
                $rev = self::loadFromConds( $dbw, $conditions, $flags );
            }
        }
        if ( $rev ) {
            $rev->mQueryFlags = $flags;
        }
        return $rev;
    }

    private static function loadFromConds( $db, $conditions, $flags = 0 ) {
        $res = self::fetchFromConds( $db, $conditions, $flags );
        if ( $res ) {
            $row = $res->fetchObject();
            if ( $row ) {
                $ret = new Revision( $row );
                return $ret;
            }
        }
        $ret = null;
        return $ret;
    }

    public static function fetchRevision( $title ) {
        return self::fetchFromConds(
            wfGetDB( DB_SLAVE ),
            array(
                'rev_id=page_latest',
                'page_namespace' => $title->getNamespace(),
                'page_title' => $title->getDBkey()
            )
        );
    }

    private static function fetchFromConds( $db, $conditions, $flags = 0 ) {
        $fields = array_merge(
            self::selectFields(),
            self::selectPageFields(),
            self::selectUserFields()
        );
        $options = array( 'LIMIT' => 1 );
        if ( ( $flags & self::READ_LOCKING ) == self::READ_LOCKING ) {
            $options[] = 'FOR UPDATE';
        }
        return $db->select(
            array( 'revision', 'page', 'user' ),
            $fields,
            $conditions,
            __METHOD__,
            $options,
            array( 'page' => self::pageJoinCond(), 'user' => self::userJoinCond() )
        );
    }

    public static function userJoinCond() {
        return array( 'LEFT JOIN', array( 'rev_user != 0', 'user_id = rev_user' ) );
    }

    public static function pageJoinCond() {
        return array( 'INNER JOIN', array( 'page_id = rev_page' ) );
    }

    public static function selectFields() {
        global $wgContentHandlerUseDB;

        $fields = array(
            '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;
    }

    public static function selectTextFields() {
        return array(
            'old_text',
            'old_flags'
        );
    }

    public static function selectPageFields() {
        return array(
            'page_namespace',
            'page_title',
            'page_id',
            'page_latest',
            'page_is_redirect',
            'page_len',
        );
    }

    public static function selectUserFields() {
        return array( 'user_name' );
    }

    public static function getParentLengths( $db, array $revIds ) {
        $revLens = array();
        if ( !$revIds ) {
            return $revLens; // empty
        }
        wfProfileIn( __METHOD__ );
        $res = $db->select( 'revision',
            array( 'rev_id', 'rev_len' ),
            array( 'rev_id' => $revIds ),
            __METHOD__ );
        foreach ( $res as $row ) {
            $revLens[$row->rev_id] = $row->rev_len;
        }
        wfProfileOut( __METHOD__ );
        return $revLens;
    }

    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 ) || is_null( $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 ) || is_null( $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 ( !is_null( $this->mText ) ) {
                $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 ) {
                if ( !is_null( $this->mContent ) ) {
                    $this->mSize = $this->mContent->getSize();
                } else {
                    #NOTE: this should never happen if we have either text or content object!
                    $this->mSize = null;
                }
            }

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

    public function getId() {
        return $this->mId;
    }

    public function setId( $id ) {
        $this->mId = $id;
    }

    public function getTextId() {
        return $this->mTextId;
    }

    public function getParentId() {
        return $this->mParentId;
    }

    public function getSize() {
        return $this->mSize;
    }

    public function getSha1() {
        return $this->mSha1;
    }

    public function getTitle() {
        if ( isset( $this->mTitle ) ) {
            return $this->mTitle;
        }
        if ( !is_null( $this->mId ) ) { //rev_id is defined as NOT NULL, but this revision may not yet have been inserted.
            $dbr = wfGetDB( DB_SLAVE );
            $row = $dbr->selectRow(
                array( 'page', 'revision' ),
                self::selectPageFields(),
                array( 'page_id=rev_page',
                    'rev_id' => $this->mId ),
                __METHOD__ );
            if ( $row ) {
                $this->mTitle = Title::newFromRow( $row );
            }
        }

        if ( !$this->mTitle && !is_null( $this->mPage ) && $this->mPage > 0 ) {
            $this->mTitle = Title::newFromID( $this->mPage );
        }

        return $this->mTitle;
    }

    public function setTitle( $title ) {
        $this->mTitle = $title;
    }

    public function getPage() {
        return $this->mPage;
    }

    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;
        }
    }

    public function getRawUser() {
        return $this->mUser;
    }

    public function getUserText( $audience = self::FOR_PUBLIC, User $user = null ) {
        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 {
            return $this->getRawUserText();
        }
    }

    public function getRawUserText() {
        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;
    }

    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;
        }
    }

    public function getRawComment() {
        return $this->mComment;
    }

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

    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;
    }

    public function getRecentChange() {
        $dbr = wfGetDB( DB_SLAVE );
        return RecentChange::newFromConds(
            array(
                'rc_user_text' => $this->getRawUserText(),
                'rc_timestamp' => $dbr->timestamp( $this->getTimestamp() ),
                'rc_this_oldid' => $this->getId()
            ),
            __METHOD__
        );
    }

    public function isDeleted( $field ) {
        return ( $this->mDeleted & $field ) == $field;
    }

    public function getVisibility() {
        return (int)$this->mDeleted;
    }

    public function getText( $audience = self::FOR_PUBLIC, User $user = null ) {
        ContentHandler::deprecated( __METHOD__, '1.21' );

        $content = $this->getContent( $audience, $user );
        return ContentHandler::getContentText( $content ); # returns the raw content text, if applicable
    }

    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();
        }
    }

    public function revText() {
        wfDeprecated( __METHOD__, '1.17' );
        return $this->getText( self::FOR_THIS_USER );
    }

    public function getRawText() {
        ContentHandler::deprecated( __METHOD__, "1.21" );
        return $this->getText( self::RAW );
    }

    public function getSerializedData() {
        if ( is_null( $this->mText ) ) {
            $this->mText = $this->loadText();
        }

        return $this->mText;
    }

    protected function getContentInternal() {
        if ( is_null( $this->mContent ) ) {
            // Revision is immutable. Load on demand:
            if ( is_null( $this->mText ) ) {
                $this->mText = $this->loadText();
            }

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

                $this->mContent = $handler->unserializeContent( $this->mText, $format );
            } else {
                $this->mContent = false; // negative caching!
            }
        }

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

    public function getContentModel() {
        if ( !$this->mContentModel ) {
            $title = $this->getTitle();
            $this->mContentModel = ( $title ? $title->getContentModel() : CONTENT_MODEL_WIKITEXT );

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

        return $this->mContentModel;
    }

    public function getContentFormat() {
        if ( !$this->mContentFormat ) {
            $handler = $this->getContentHandler();
            $this->mContentFormat = $handler->getDefaultFormat();

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

        return $this->mContentFormat;
    }

    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;
    }

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

    public function isCurrent() {
        return $this->mCurrent;
    }

    public function getPrevious() {
        if ( $this->getTitle() ) {
            $prev = $this->getTitle()->getPreviousRevisionID( $this->getId() );
            if ( $prev ) {
                return self::newFromTitle( $this->getTitle(), $prev );
            }
        }
        return null;
    }

    public function getNext() {
        if ( $this->getTitle() ) {
            $next = $this->getTitle()->getNextRevisionID( $this->getId() );
            if ( $next ) {
                return self::newFromTitle( $this->getTitle(), $next );
            }
        }
        return null;
    }

    private function getPreviousRevisionId( $db ) {
        if ( is_null( $this->mPage ) ) {
            return 0;
        }
        # Use page_latest if ID is not given
        if ( !$this->mId ) {
            $prevId = $db->selectField( 'page', 'page_latest',
                array( 'page_id' => $this->mPage ),
                __METHOD__ );
        } else {
            $prevId = $db->selectField( 'revision', 'rev_id',
                array( 'rev_page' => $this->mPage, 'rev_id < ' . $this->mId ),
                __METHOD__,
                array( 'ORDER BY' => 'rev_id DESC' ) );
        }
        return intval( $prevId );
    }

    public static function getRevisionText( $row, $prefix = 'old_', $wiki = false ) {
        wfProfileIn( __METHOD__ );

        # Get data
        $textField = $prefix . 'text';
        $flagsField = $prefix . 'flags';

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

        if ( isset( $row->$textField ) ) {
            $text = $row->$textField;
        } else {
            wfProfileOut( __METHOD__ );
            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] == '' ) {
                wfProfileOut( __METHOD__ );
                return false;
            }
            $text = ExternalStore::fetchFromURL( $url, array( 'wiki' => $wiki ) );
        }

        // If the text was fetched without an error, convert it
        if ( $text !== false ) {
            $text = self::decompressRevisionText( $text, $flags );
        }
        wfProfileOut( __METHOD__ );
        return $text;
    }

    public static function compressRevisionText( &$text ) {
        global $wgCompressRevisions;
        $flags = array();

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

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

        global $wgLegacyEncoding;
        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)
            global $wgContLang;
            $text = $wgContLang->iconv( $wgLegacyEncoding, 'UTF-8', $text );
        }

        return $text;
    }

    public function insertOn( $dbw ) {
        global $wgDefaultExternalStore, $wgContentHandlerUseDB;

        wfProfileIn( __METHOD__ );

        $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 ) {
                wfProfileOut( __METHOD__ );
                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 ( !isset( $this->mTextId ) ) {
            $old_id = $dbw->nextSequenceValue( 'text_old_id_seq' );
            $dbw->insert( 'text',
                array(
                    '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 = isset( $this->mId )
            ? $this->mId
            : $dbw->nextSequenceValue( 'revision_rev_id_seq' );
        $row = array(
            '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'  => is_null( $this->mParentId )
                ? $this->getPreviousRevisionId( $dbw )
                : $this->mParentId,
            'rev_sha1'       => is_null( $this->mSha1 )
                ? Revision::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 ) {
                wfProfileOut( __METHOD__ );
                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__ );

        $this->mId = !is_null( $rev_id ) ? $rev_id : $dbw->insertId();

        wfRunHooks( 'RevisionInsertComplete', array( &$this, $data, $flags ) );

        wfProfileOut( __METHOD__ );
        return $this->mId;
    }

    protected function checkContentModel() {
        global $wgContentHandlerUseDB;

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

        $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( Revision::RAW );

        if ( !$content || !$content->isValid() ) {
            $t = $title->getPrefixedDBkey();

            throw new MWException( "Content of $t is not valid! Content model is $model" );
        }
    }

    public static function base36Sha1( $text ) {
        return wfBaseConvert( sha1( $text ), 16, 36, 31 );
    }

    protected function loadText() {
        wfProfileIn( __METHOD__ );

        // Caching may be beneficial for massive use of external storage
        global $wgRevisionCacheExpiry, $wgMemc;
        $textId = $this->getTextId();
        $key = wfMemcKey( 'revisiontext', 'textid', $textId );
        if ( $wgRevisionCacheExpiry ) {
            $text = $wgMemc->get( $key );
            if ( is_string( $text ) ) {
                wfDebug( __METHOD__ . ": got id $textId from cache\n" );
                wfProfileOut( __METHOD__ );
                return $text;
            }
        }

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

        if ( !$row ) {
            // Text data is immutable; check slaves first.
            $dbr = wfGetDB( DB_SLAVE );
            $row = $dbr->selectRow( 'text',
                array( 'old_text', 'old_flags' ),
                array( 'old_id' => $textId ),
                __METHOD__ );
        }

        // Fallback to the master in case of slave lag. Also use FOR UPDATE if it was
        // used to fetch this revision to avoid missing the row due to REPEATABLE-READ.
        $forUpdate = ( $this->mQueryFlags & self::READ_LOCKING == self::READ_LOCKING );
        if ( !$row && ( $forUpdate || wfGetLB()->getServerCount() > 1 ) ) {
            $dbw = wfGetDB( DB_MASTER );
            $row = $dbw->selectRow( 'text',
                array( 'old_text', 'old_flags' ),
                array( 'old_id' => $textId ),
                __METHOD__,
                $forUpdate ? array( 'FOR UPDATE' ) : array() );
        }

        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()})." );
        }

        # No negative caching -- negative hits on text rows may be due to corrupted slave servers
        if ( $wgRevisionCacheExpiry && $text !== false ) {
            $wgMemc->set( $key, $text, $wgRevisionCacheExpiry );
        }

        wfProfileOut( __METHOD__ );

        return $text;
    }

    public static function newNullRevision( $dbw, $pageId, $summary, $minor ) {
        global $wgContentHandlerUseDB;

        wfProfileIn( __METHOD__ );

        $fields = array( '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(
            array( 'page', 'revision' ),
            $fields,
            array(
                'page_id' => $pageId,
                'page_latest=rev_id',
                ),
            __METHOD__ );

        if ( $current ) {
            $row = array(
                'page'       => $pageId,
                '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;
            }

            $revision = new Revision( $row );
            $revision->setTitle( Title::makeTitle( $current->page_namespace, $current->page_title ) );
        } else {
            $revision = null;
        }

        wfProfileOut( __METHOD__ );
        return $revision;
    }

    public function userCan( $field, User $user = null ) {
        return self::userCanBitfield( $this->mDeleted, $field, $user );
    }

    public static function userCanBitfield( $bitfield, $field, User $user = null ) {
        if ( $bitfield & $field ) { // aspect is deleted
            if ( $bitfield & self::DELETED_RESTRICTED ) {
                $permission = 'suppressrevision';
            } elseif ( $field & self::DELETED_TEXT ) {
                $permission = 'deletedtext';
            } else {
                $permission = 'deletedhistory';
            }
            wfDebug( "Checking for $permission due to $field match on $bitfield\n" );
            if ( $user === null ) {
                global $wgUser;
                $user = $wgUser;
            }
            return $user->isAllowed( $permission );
        } else {
            return true;
        }
    }

    static function getTimestampFromId( $title, $id ) {
        $dbr = wfGetDB( DB_SLAVE );
        // Casting fix for databases that can't take '' for rev_id
        if ( $id == '' ) {
            $id = 0;
        }
        $conds = array( 'rev_id' => $id );
        $conds['rev_page'] = $title->getArticleID();
        $timestamp = $dbr->selectField( 'revision', 'rev_timestamp', $conds, __METHOD__ );
        if ( $timestamp === false && wfGetLB()->getServerCount() > 1 ) {
            # Not in slave, try master
            $dbw = wfGetDB( DB_MASTER );
            $timestamp = $dbw->selectField( 'revision', 'rev_timestamp', $conds, __METHOD__ );
        }
        return wfTimestamp( TS_MW, $timestamp );
    }

    static function countByPageId( $db, $id ) {
        $row = $db->selectRow( 'revision', array( 'revCount' => 'COUNT(*)' ),
            array( 'rev_page' => $id ), __METHOD__ );
        if ( $row ) {
            return $row->revCount;
        }
        return 0;
    }

    static function countByTitle( $db, $title ) {
        $id = $title->getArticleID();
        if ( $id ) {
            return self::countByPageId( $db, $id );
        }
        return 0;
    }

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