MessageCache.php

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<?php
define( 'MSG_CACHE_VERSION', 1 );

define( 'MSG_LOAD_TIMEOUT', 60 );

define( 'MSG_LOCK_TIMEOUT', 30 );
define( 'MSG_WAIT_TIMEOUT', 30 );

class MessageCache {
    protected $mCache;

    protected $mDisable;

    protected $mExpiry;

    protected $mParserOptions, $mParser;

    protected $mLoadedLanguages = array();

    private static $instance;

    protected $mInParser = false;

    public static function singleton() {
        if ( is_null( self::$instance ) ) {
            global $wgUseDatabaseMessages, $wgMsgCacheExpiry;
            self::$instance = new self(
                wfGetMessageCacheStorage(),
                $wgUseDatabaseMessages,
                $wgMsgCacheExpiry
            );
        }

        return self::$instance;
    }

    public static function destroyInstance() {
        self::$instance = null;
    }

    function __construct( $memCached, $useDB, $expiry ) {
        if ( !$memCached ) {
            $memCached = wfGetCache( CACHE_NONE );
        }

        $this->mMemc = $memCached;
        $this->mDisable = !$useDB;
        $this->mExpiry = $expiry;
    }

    function getParserOptions() {
        if ( !$this->mParserOptions ) {
            $this->mParserOptions = new ParserOptions;
            $this->mParserOptions->setEditSection( false );
        }

        return $this->mParserOptions;
    }

    function getLocalCache( $hash, $code ) {
        global $wgCacheDirectory;

        $filename = "$wgCacheDirectory/messages-" . wfWikiID() . "-$code";

        # Check file existence
        wfSuppressWarnings();
        $file = fopen( $filename, 'r' );
        wfRestoreWarnings();
        if ( !$file ) {
            return false; // No cache file
        }

        // Check to see if the file has the hash specified
        $localHash = fread( $file, 32 );
        if ( $hash === $localHash ) {
            // All good, get the rest of it
            $serialized = '';
            while ( !feof( $file ) ) {
                $serialized .= fread( $file, 100000 );
            }
            fclose( $file );

            return unserialize( $serialized );
        } else {
            fclose( $file );

            return false; // Wrong hash
        }
    }

    function saveToLocal( $serialized, $hash, $code ) {
        global $wgCacheDirectory;

        $filename = "$wgCacheDirectory/messages-" . wfWikiID() . "-$code";
        wfMkdirParents( $wgCacheDirectory, null, __METHOD__ ); // might fail

        wfSuppressWarnings();
        $file = fopen( $filename, 'w' );
        wfRestoreWarnings();

        if ( !$file ) {
            wfDebug( "Unable to open local cache file for writing\n" );

            return;
        }

        fwrite( $file, $hash . $serialized );
        fclose( $file );
        wfSuppressWarnings();
        chmod( $filename, 0666 );
        wfRestoreWarnings();
    }

    function load( $code = false ) {
        global $wgUseLocalMessageCache;

        if ( !is_string( $code ) ) {
            # This isn't really nice, so at least make a note about it and try to
            # fall back
            wfDebug( __METHOD__ . " called without providing a language code\n" );
            $code = 'en';
        }

        # Don't do double loading...
        if ( isset( $this->mLoadedLanguages[$code] ) ) {
            return true;
        }

        # 8 lines of code just to say (once) that message cache is disabled
        if ( $this->mDisable ) {
            static $shownDisabled = false;
            if ( !$shownDisabled ) {
                wfDebug( __METHOD__ . ": disabled\n" );
                $shownDisabled = true;
            }

            return true;
        }

        # Loading code starts
        wfProfileIn( __METHOD__ );
        $success = false; # Keep track of success
        $staleCache = false; # a cache array with expired data, or false if none has been loaded
        $where = array(); # Debug info, delayed to avoid spamming debug log too much
        $cacheKey = wfMemcKey( 'messages', $code ); # Key in memc for messages

        # Local cache
        # Hash of the contents is stored in memcache, to detect if local cache goes
        # out of date (e.g. due to replace() on some other server)
        if ( $wgUseLocalMessageCache ) {
            wfProfileIn( __METHOD__ . '-fromlocal' );

            $hash = $this->mMemc->get( wfMemcKey( 'messages', $code, 'hash' ) );
            if ( $hash ) {
                $cache = $this->getLocalCache( $hash, $code );
                if ( !$cache ) {
                    $where[] = 'local cache is empty or has the wrong hash';
                } elseif ( $this->isCacheExpired( $cache ) ) {
                    $where[] = 'local cache is expired';
                    $staleCache = $cache;
                } else {
                    $where[] = 'got from local cache';
                    $success = true;
                    $this->mCache[$code] = $cache;
                }
            }
            wfProfileOut( __METHOD__ . '-fromlocal' );
        }

        if ( !$success ) {
            # Try the global cache. If it is empty, try to acquire a lock. If
            # the lock can't be acquired, wait for the other thread to finish
            # and then try the global cache a second time.
            for ( $failedAttempts = 0; $failedAttempts < 2; $failedAttempts++ ) {
                wfProfileIn( __METHOD__ . '-fromcache' );
                $cache = $this->mMemc->get( $cacheKey );
                if ( !$cache ) {
                    $where[] = 'global cache is empty';
                } elseif ( $this->isCacheExpired( $cache ) ) {
                    $where[] = 'global cache is expired';
                    $staleCache = $cache;
                } else {
                    $where[] = 'got from global cache';
                    $this->mCache[$code] = $cache;
                    $this->saveToCaches( $cache, 'local-only', $code );
                    $success = true;
                }

                wfProfileOut( __METHOD__ . '-fromcache' );

                if ( $success ) {
                    # Done, no need to retry
                    break;
                }

                # We need to call loadFromDB. Limit the concurrency to a single
                # process. This prevents the site from going down when the cache
                # expires.
                $statusKey = wfMemcKey( 'messages', $code, 'status' );
                $acquired = $this->mMemc->add( $statusKey, 'loading', MSG_LOAD_TIMEOUT );
                if ( $acquired ) {
                    # Unlock the status key if there is an exception
                    $that = $this;
                    $statusUnlocker = new ScopedCallback( function () use ( $that, $statusKey ) {
                        $that->mMemc->delete( $statusKey );
                    } );

                    # Now let's regenerate
                    $where[] = 'loading from database';

                    # Lock the cache to prevent conflicting writes
                    # If this lock fails, it doesn't really matter, it just means the
                    # write is potentially non-atomic, e.g. the results of a replace()
                    # may be discarded.
                    if ( $this->lock( $cacheKey ) ) {
                        $mainUnlocker = new ScopedCallback( function () use ( $that, $cacheKey ) {
                            $that->unlock( $cacheKey );
                        } );
                    } else {
                        $mainUnlocker = null;
                        $where[] = 'could not acquire main lock';
                    }

                    $cache = $this->loadFromDB( $code );
                    $this->mCache[$code] = $cache;
                    $success = true;
                    $saveSuccess = $this->saveToCaches( $cache, 'all', $code );

                    # Unlock
                    ScopedCallback::consume( $mainUnlocker );
                    ScopedCallback::consume( $statusUnlocker );

                    if ( !$saveSuccess ) {
                        # Cache save has failed.
                        # There are two main scenarios where this could be a problem:
                        #
                        #   - The cache is more than the maximum size (typically
                        #     1MB compressed).
                        #
                        #   - Memcached has no space remaining in the relevant slab
                        #     class. This is unlikely with recent versions of
                        #     memcached.
                        #
                        # Either way, if there is a local cache, nothing bad will
                        # happen. If there is no local cache, disabling the message
                        # cache for all requests avoids incurring a loadFromDB()
                        # overhead on every request, and thus saves the wiki from
                        # complete downtime under moderate traffic conditions.
                        if ( !$wgUseLocalMessageCache ) {
                            $this->mMemc->set( $statusKey, 'error', 60 * 5 );
                            $where[] = 'could not save cache, disabled globally for 5 minutes';
                        } else {
                            $where[] = "could not save global cache";
                        }
                    }

                    # Load from DB complete, no need to retry
                    break;
                } elseif ( $staleCache ) {
                    # Use the stale cache while some other thread constructs the new one
                    $where[] = 'using stale cache';
                    $this->mCache[$code] = $staleCache;
                    $success = true;
                    break;
                } elseif ( $failedAttempts > 0 ) {
                    # Already retried once, still failed, so don't do another lock/unlock cycle
                    # This case will typically be hit if memcached is down, or if
                    # loadFromDB() takes longer than MSG_WAIT_TIMEOUT
                    $where[] = "could not acquire status key.";
                    break;
                } else {
                    $status = $this->mMemc->get( $statusKey );
                    if ( $status === 'error' ) {
                        # Disable cache
                        break;
                    } else {
                        # Wait for the other thread to finish, then retry
                        $where[] = 'waited for other thread to complete';
                        $this->lock( $cacheKey );
                        $this->unlock( $cacheKey );
                    }
                }
            }
        }

        if ( !$success ) {
            $where[] = 'loading FAILED - cache is disabled';
            $this->mDisable = true;
            $this->mCache = false;
            # This used to throw an exception, but that led to nasty side effects like
            # the whole wiki being instantly down if the memcached server died
        } else {
            # All good, just record the success
            $this->mLoadedLanguages[$code] = true;
        }
        $info = implode( ', ', $where );
        wfDebug( __METHOD__ . ": Loading $code... $info\n" );
        wfProfileOut( __METHOD__ );

        return $success;
    }

    function loadFromDB( $code ) {
        wfProfileIn( __METHOD__ );
        global $wgMaxMsgCacheEntrySize, $wgLanguageCode, $wgAdaptiveMessageCache;
        $dbr = wfGetDB( DB_SLAVE );
        $cache = array();

        # Common conditions
        $conds = array(
            'page_is_redirect' => 0,
            'page_namespace' => NS_MEDIAWIKI,
        );

        $mostused = array();
        if ( $wgAdaptiveMessageCache && $code !== $wgLanguageCode ) {
            if ( !isset( $this->mCache[$wgLanguageCode] ) ) {
                $this->load( $wgLanguageCode );
            }
            $mostused = array_keys( $this->mCache[$wgLanguageCode] );
            foreach ( $mostused as $key => $value ) {
                $mostused[$key] = "$value/$code";
            }
        }

        if ( count( $mostused ) ) {
            $conds['page_title'] = $mostused;
        } elseif ( $code !== $wgLanguageCode ) {
            $conds[] = 'page_title' . $dbr->buildLike( $dbr->anyString(), '/', $code );
        } else {
            # Effectively disallows use of '/' character in NS_MEDIAWIKI for uses
            # other than language code.
            $conds[] = 'page_title NOT' . $dbr->buildLike( $dbr->anyString(), '/', $dbr->anyString() );
        }

        # Conditions to fetch oversized pages to ignore them
        $bigConds = $conds;
        $bigConds[] = 'page_len > ' . intval( $wgMaxMsgCacheEntrySize );

        # Load titles for all oversized pages in the MediaWiki namespace
        $res = $dbr->select( 'page', 'page_title', $bigConds, __METHOD__ . "($code)-big" );
        foreach ( $res as $row ) {
            $cache[$row->page_title] = '!TOO BIG';
        }

        # Conditions to load the remaining pages with their contents
        $smallConds = $conds;
        $smallConds[] = 'page_latest=rev_id';
        $smallConds[] = 'rev_text_id=old_id';
        $smallConds[] = 'page_len <= ' . intval( $wgMaxMsgCacheEntrySize );

        $res = $dbr->select(
            array( 'page', 'revision', 'text' ),
            array( 'page_title', 'old_text', 'old_flags' ),
            $smallConds,
            __METHOD__ . "($code)-small"
        );

        foreach ( $res as $row ) {
            $text = Revision::getRevisionText( $row );
            if ( $text === false ) {
                // Failed to fetch data; possible ES errors?
                // Store a marker to fetch on-demand as a workaround...
                $entry = '!TOO BIG';
                wfDebugLog(
                    'MessageCache',
                    __METHOD__
                        . ": failed to load message page text for {$row->page_title} ($code)"
                );
            } else {
                $entry = ' ' . $text;
            }
            $cache[$row->page_title] = $entry;
        }

        $cache['VERSION'] = MSG_CACHE_VERSION;
        $cache['EXPIRY'] = wfTimestamp( TS_MW, time() + $this->mExpiry );
        wfProfileOut( __METHOD__ );

        return $cache;
    }

    public function replace( $title, $text ) {
        global $wgMaxMsgCacheEntrySize;
        wfProfileIn( __METHOD__ );

        if ( $this->mDisable ) {
            wfProfileOut( __METHOD__ );

            return;
        }

        list( $msg, $code ) = $this->figureMessage( $title );

        $cacheKey = wfMemcKey( 'messages', $code );
        $this->load( $code );
        $this->lock( $cacheKey );

        $titleKey = wfMemcKey( 'messages', 'individual', $title );

        if ( $text === false ) {
            # Article was deleted
            $this->mCache[$code][$title] = '!NONEXISTENT';
            $this->mMemc->delete( $titleKey );
        } elseif ( strlen( $text ) > $wgMaxMsgCacheEntrySize ) {
            # Check for size
            $this->mCache[$code][$title] = '!TOO BIG';
            $this->mMemc->set( $titleKey, ' ' . $text, $this->mExpiry );
        } else {
            $this->mCache[$code][$title] = ' ' . $text;
            $this->mMemc->delete( $titleKey );
        }

        # Update caches
        $this->saveToCaches( $this->mCache[$code], 'all', $code );
        $this->unlock( $cacheKey );

        // Also delete cached sidebar... just in case it is affected
        $codes = array( $code );
        if ( $code === 'en' ) {
            // Delete all sidebars, like for example on action=purge on the
            // sidebar messages
            $codes = array_keys( Language::fetchLanguageNames() );
        }

        global $wgMemc;
        foreach ( $codes as $code ) {
            $sidebarKey = wfMemcKey( 'sidebar', $code );
            $wgMemc->delete( $sidebarKey );
        }

        // Update the message in the message blob store
        global $wgContLang;
        MessageBlobStore::updateMessage( $wgContLang->lcfirst( $msg ) );

        wfRunHooks( 'MessageCacheReplace', array( $title, $text ) );

        wfProfileOut( __METHOD__ );
    }

    protected function isCacheExpired( $cache ) {
        if ( !isset( $cache['VERSION'] ) || !isset( $cache['EXPIRY'] ) ) {
            return true;
        }
        if ( $cache['VERSION'] != MSG_CACHE_VERSION ) {
            return true;
        }
        if ( wfTimestampNow() >= $cache['EXPIRY'] ) {
            return true;
        }

        return false;
    }

    protected function saveToCaches( $cache, $dest, $code = false ) {
        wfProfileIn( __METHOD__ );
        global $wgUseLocalMessageCache;

        $cacheKey = wfMemcKey( 'messages', $code );

        if ( $dest === 'all' ) {
            $success = $this->mMemc->set( $cacheKey, $cache );
        } else {
            $success = true;
        }

        # Save to local cache
        if ( $wgUseLocalMessageCache ) {
            $serialized = serialize( $cache );
            $hash = md5( $serialized );
            $this->mMemc->set( wfMemcKey( 'messages', $code, 'hash' ), $hash );
            $this->saveToLocal( $serialized, $hash, $code );
        }

        wfProfileOut( __METHOD__ );

        return $success;
    }

    function lock( $key ) {
        $lockKey = $key . ':lock';
        $acquired = false;
        $testDone = false;
        for ( $i = 0; $i < MSG_WAIT_TIMEOUT && !$acquired; $i++ ) {
            $acquired = $this->mMemc->add( $lockKey, 1, MSG_LOCK_TIMEOUT );
            if ( $acquired ) {
                break;
            }

            # Fail fast if memcached is totally down
            if ( !$testDone ) {
                $testDone = true;
                if ( !$this->mMemc->set( wfMemcKey( 'test' ), 'test', 1 ) ) {
                    break;
                }
            }
            sleep( 1 );
        }

        return $acquired;
    }

    function unlock( $key ) {
        $lockKey = $key . ':lock';
        $this->mMemc->delete( $lockKey );
    }

    function get( $key, $useDB = true, $langcode = true, $isFullKey = false ) {
        global $wgContLang;

        $section = new ProfileSection( __METHOD__ );

        if ( is_int( $key ) ) {
            // Fix numerical strings that somehow become ints
            // on their way here
            $key = (string)$key;
        } elseif ( !is_string( $key ) ) {
            throw new MWException( 'Non-string key given' );
        } elseif ( $key === '' ) {
            // Shortcut: the empty key is always missing
            return false;
        }

        // For full keys, get the language code from the key
        $pos = strrpos( $key, '/' );
        if ( $isFullKey && $pos !== false ) {
            $langcode = substr( $key, $pos + 1 );
            $key = substr( $key, 0, $pos );
        }

        // Normalise title-case input (with some inlining)
        $lckey = strtr( $key, ' ', '_' );
        if ( ord( $lckey ) < 128 ) {
            $lckey[0] = strtolower( $lckey[0] );
        } else {
            $lckey = $wgContLang->lcfirst( $lckey );
        }

        wfRunHooks( 'MessageCache::get', array( &$lckey ) );

        if ( ord( $lckey ) < 128 ) {
            $uckey = ucfirst( $lckey );
        } else {
            $uckey = $wgContLang->ucfirst( $lckey );
        }

        // Loop through each language in the fallback list until we find something useful
        $lang = wfGetLangObj( $langcode );
        $message = $this->getMessageFromFallbackChain(
            $lang,
            $lckey,
            $uckey,
            !$this->mDisable && $useDB
        );

        // If we still have no message, maybe the key was in fact a full key so try that
        if ( $message === false ) {
            $parts = explode( '/', $lckey );
            // We may get calls for things that are http-urls from sidebar
            // Let's not load nonexistent languages for those
            // They usually have more than one slash.
            if ( count( $parts ) == 2 && $parts[1] !== '' ) {
                $message = Language::getMessageFor( $parts[0], $parts[1] );
                if ( $message === null ) {
                    $message = false;
                }
            }
        }

        // Post-processing if the message exists
        if ( $message !== false ) {
            // Fix whitespace
            $message = str_replace(
                array(
                    # Fix for trailing whitespace, removed by textarea
                    '&#32;',
                    # Fix for NBSP, converted to space by firefox
                    '&nbsp;',
                    '&#160;',
                ),
                array(
                    ' ',
                    "\xc2\xa0",
                    "\xc2\xa0"
                ),
                $message
            );
        }

        return $message;
    }

    protected function getMessageFromFallbackChain( $lang, $lckey, $uckey, $useDB ) {
        global $wgLanguageCode, $wgContLang;

        $langcode = $lang->getCode();
        $message = false;

        // First try the requested language.
        if ( $useDB ) {
            if ( $langcode === $wgLanguageCode ) {
                // Messages created in the content language will not have the /lang extension
                $message = $this->getMsgFromNamespace( $uckey, $langcode );
            } else {
                $message = $this->getMsgFromNamespace( "$uckey/$langcode", $langcode );
            }
        }

        if ( $message !== false ) {
            return $message;
        }

        // Check the CDB cache
        $message = $lang->getMessage( $lckey );
        if ( $message !== null ) {
            return $message;
        }

        list( $fallbackChain, $siteFallbackChain ) =
            Language::getFallbacksIncludingSiteLanguage( $langcode );

        // Next try checking the database for all of the fallback languages of the requested language.
        if ( $useDB ) {
            foreach ( $fallbackChain as $code ) {
                if ( $code === $wgLanguageCode ) {
                    // Messages created in the content language will not have the /lang extension
                    $message = $this->getMsgFromNamespace( $uckey, $code );
                } else {
                    $message = $this->getMsgFromNamespace( "$uckey/$code", $code );
                }

                if ( $message !== false ) {
                    // Found the message.
                    return $message;
                }
            }
        }

        // Now try checking the site language.
        if ( $useDB ) {
            $message = $this->getMsgFromNamespace( $uckey, $wgLanguageCode );
            if ( $message !== false ) {
                return $message;
            }
        }

        $message = $wgContLang->getMessage( $lckey );
        if ( $message !== null ) {
            return $message;
        }

        // Finally try the DB for the site language's fallbacks.
        if ( $useDB ) {
            foreach ( $siteFallbackChain as $code ) {
                $message = $this->getMsgFromNamespace( "$uckey/$code", $code );
                if ( $message === false && $code === $wgLanguageCode ) {
                    // Messages created in the content language will not have the /lang extension
                    $message = $this->getMsgFromNamespace( $uckey, $code );
                }

                if ( $message !== false ) {
                    // Found the message.
                    return $message;
                }
            }
        }

        return false;
    }

    function getMsgFromNamespace( $title, $code ) {
        $this->load( $code );
        if ( isset( $this->mCache[$code][$title] ) ) {
            $entry = $this->mCache[$code][$title];
            if ( substr( $entry, 0, 1 ) === ' ' ) {
                // The message exists, so make sure a string
                // is returned.
                return (string)substr( $entry, 1 );
            } elseif ( $entry === '!NONEXISTENT' ) {
                return false;
            } elseif ( $entry === '!TOO BIG' ) {
                // Fall through and try invididual message cache below
            }
        } else {
            // XXX: This is not cached in process cache, should it?
            $message = false;
            wfRunHooks( 'MessagesPreLoad', array( $title, &$message ) );
            if ( $message !== false ) {
                return $message;
            }

            return false;
        }

        # Try the individual message cache
        $titleKey = wfMemcKey( 'messages', 'individual', $title );
        $entry = $this->mMemc->get( $titleKey );
        if ( $entry ) {
            if ( substr( $entry, 0, 1 ) === ' ' ) {
                $this->mCache[$code][$title] = $entry;

                // The message exists, so make sure a string
                // is returned.
                return (string)substr( $entry, 1 );
            } elseif ( $entry === '!NONEXISTENT' ) {
                $this->mCache[$code][$title] = '!NONEXISTENT';

                return false;
            } else {
                # Corrupt/obsolete entry, delete it
                $this->mMemc->delete( $titleKey );
            }
        }

        # Try loading it from the database
        $revision = Revision::newFromTitle(
            Title::makeTitle( NS_MEDIAWIKI, $title ), false, Revision::READ_LATEST
        );
        if ( $revision ) {
            $content = $revision->getContent();
            if ( !$content ) {
                // A possibly temporary loading failure.
                wfDebugLog(
                    'MessageCache',
                    __METHOD__ . ": failed to load message page text for {$title} ($code)"
                );
                $message = null; // no negative caching
            } else {
                // XXX: Is this the right way to turn a Content object into a message?
                // NOTE: $content is typically either WikitextContent, JavaScriptContent or
                //       CssContent. MessageContent is *not* used for storing messages, it's
                //       only used for wrapping them when needed.
                $message = $content->getWikitextForTransclusion();

                if ( $message === false || $message === null ) {
                    wfDebugLog(
                        'MessageCache',
                        __METHOD__ . ": message content doesn't provide wikitext "
                            . "(content model: " . $content->getContentHandler() . ")"
                    );

                    $message = false; // negative caching
                } else {
                    $this->mCache[$code][$title] = ' ' . $message;
                    $this->mMemc->set( $titleKey, ' ' . $message, $this->mExpiry );
                }
            }
        } else {
            $message = false; // negative caching
        }

        if ( $message === false ) { // negative caching
            $this->mCache[$code][$title] = '!NONEXISTENT';
            $this->mMemc->set( $titleKey, '!NONEXISTENT', $this->mExpiry );
        }

        return $message;
    }

    function transform( $message, $interface = false, $language = null, $title = null ) {
        // Avoid creating parser if nothing to transform
        if ( strpos( $message, '{{' ) === false ) {
            return $message;
        }

        if ( $this->mInParser ) {
            return $message;
        }

        $parser = $this->getParser();
        if ( $parser ) {
            $popts = $this->getParserOptions();
            $popts->setInterfaceMessage( $interface );
            $popts->setTargetLanguage( $language );

            $userlang = $popts->setUserLang( $language );
            $this->mInParser = true;
            $message = $parser->transformMsg( $message, $popts, $title );
            $this->mInParser = false;
            $popts->setUserLang( $userlang );
        }

        return $message;
    }

    function getParser() {
        global $wgParser, $wgParserConf;
        if ( !$this->mParser && isset( $wgParser ) ) {
            # Do some initialisation so that we don't have to do it twice
            $wgParser->firstCallInit();
            # Clone it and store it
            $class = $wgParserConf['class'];
            if ( $class == 'Parser_DiffTest' ) {
                # Uncloneable
                $this->mParser = new $class( $wgParserConf );
            } else {
                $this->mParser = clone $wgParser;
            }
        }

        return $this->mParser;
    }

    public function parse( $text, $title = null, $linestart = true,
        $interface = false, $language = null
    ) {
        if ( $this->mInParser ) {
            return htmlspecialchars( $text );
        }

        $parser = $this->getParser();
        $popts = $this->getParserOptions();
        $popts->setInterfaceMessage( $interface );
        $popts->setTargetLanguage( $language );

        wfProfileIn( __METHOD__ );
        if ( !$title || !$title instanceof Title ) {
            global $wgTitle;
            $title = $wgTitle;
        }
        // Sometimes $wgTitle isn't set either...
        if ( !$title ) {
            # It's not uncommon having a null $wgTitle in scripts. See r80898
            # Create a ghost title in such case
            $title = Title::newFromText( 'Dwimmerlaik' );
        }

        $this->mInParser = true;
        $res = $parser->parse( $text, $title, $popts, $linestart );
        $this->mInParser = false;

        wfProfileOut( __METHOD__ );

        return $res;
    }

    function disable() {
        $this->mDisable = true;
    }

    function enable() {
        $this->mDisable = false;
    }

    function clear() {
        $langs = Language::fetchLanguageNames( null, 'mw' );
        foreach ( array_keys( $langs ) as $code ) {
            # Global cache
            $this->mMemc->delete( wfMemcKey( 'messages', $code ) );
            # Invalidate all local caches
            $this->mMemc->delete( wfMemcKey( 'messages', $code, 'hash' ) );
        }
        $this->mLoadedLanguages = array();
    }

    public function figureMessage( $key ) {
        global $wgLanguageCode;
        $pieces = explode( '/', $key );
        if ( count( $pieces ) < 2 ) {
            return array( $key, $wgLanguageCode );
        }

        $lang = array_pop( $pieces );
        if ( !Language::fetchLanguageName( $lang, null, 'mw' ) ) {
            return array( $key, $wgLanguageCode );
        }

        $message = implode( '/', $pieces );

        return array( $message, $lang );
    }

    public function getAllMessageKeys( $code ) {
        global $wgContLang;
        $this->load( $code );
        if ( !isset( $this->mCache[$code] ) ) {
            // Apparently load() failed
            return null;
        }
        // Remove administrative keys
        $cache = $this->mCache[$code];
        unset( $cache['VERSION'] );
        unset( $cache['EXPIRY'] );
        // Remove any !NONEXISTENT keys
        $cache = array_diff( $cache, array( '!NONEXISTENT' ) );

        // Keys may appear with a capital first letter. lcfirst them.
        return array_map( array( $wgContLang, 'lcfirst' ), array_keys( $cache ) );
    }
}