MessageCache.php

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<?php
use MediaWiki\Config\ServiceOptions;
use MediaWiki\HookContainer\HookContainer;
use MediaWiki\HookContainer\HookRunner;
use MediaWiki\Languages\LanguageConverterFactory;
use MediaWiki\Languages\LanguageFactory;
use MediaWiki\Languages\LanguageFallback;
use MediaWiki\Languages\LanguageNameUtils;
use MediaWiki\Linker\LinkTarget;
use MediaWiki\Logger\LoggerFactory;
use MediaWiki\MainConfigNames;
use MediaWiki\MediaWikiServices;
use MediaWiki\Page\PageReference;
use MediaWiki\Page\PageReferenceValue;
use MediaWiki\Revision\SlotRecord;
use MediaWiki\StubObject\StubObject;
use Psr\Log\LoggerAwareInterface;
use Psr\Log\LoggerInterface;
use Wikimedia\Rdbms\Database;
use Wikimedia\Rdbms\IResultWrapper;
use Wikimedia\RequestTimeout\TimeoutException;
use Wikimedia\ScopedCallback;
 
define( 'MSG_CACHE_VERSION', 2 );
 
class MessageCache implements LoggerAwareInterface {
    public const CONSTRUCTOR_OPTIONS = [
        MainConfigNames::UseDatabaseMessages,
        MainConfigNames::MaxMsgCacheEntrySize,
        MainConfigNames::AdaptiveMessageCache,
    ];
 
    public const MAX_REQUEST_LANGUAGES = 10;
 
    private const FOR_UPDATE = 1; // force message reload
 
    private const WAIT_SEC = 15;
    private const LOCK_TTL = 30;
 
    private const WAN_TTL = IExpiringStore::TTL_DAY;
 
    private $logger;
 
    private $cache;
 
    private $systemMessageNames;
 
    private $cacheVolatile = [];
 
    private $disable;
 
    private $maxEntrySize;
 
    private $adaptive;
 
    private $parserOptions;
    private $parser;
 
    private $inParser = false;
 
    private $wanCache;
    private $clusterCache;
    private $srvCache;
    private $contLang;
    private $contLangCode;
    private $contLangConverter;
    private $langFactory;
    private $localisationCache;
    private $languageNameUtils;
    private $languageFallback;
    private $hookRunner;
 
    public static function normalizeKey( $key ) {
        $lckey = strtr( $key, ' ', '_' );
        if ( $lckey === '' ) {
            // T300792
            return $lckey;
        }
 
        if ( ord( $lckey ) < 128 ) {
            $lckey[0] = strtolower( $lckey[0] );
        } else {
            $lckey = MediaWikiServices::getInstance()->getContentLanguage()->lcfirst( $lckey );
        }
 
        return $lckey;
    }
 
    public function __construct(
        WANObjectCache $wanCache,
        BagOStuff $clusterCache,
        BagOStuff $serverCache,
        Language $contLang,
        LanguageConverterFactory $langConverterFactory,
        LoggerInterface $logger,
        ServiceOptions $options,
        LanguageFactory $langFactory,
        LocalisationCache $localisationCache,
        LanguageNameUtils $languageNameUtils,
        LanguageFallback $languageFallback,
        HookContainer $hookContainer
    ) {
        $this->wanCache = $wanCache;
        $this->clusterCache = $clusterCache;
        $this->srvCache = $serverCache;
        $this->contLang = $contLang;
        $this->contLangConverter = $langConverterFactory->getLanguageConverter( $contLang );
        $this->contLangCode = $contLang->getCode();
        $this->logger = $logger;
        $this->langFactory = $langFactory;
        $this->localisationCache = $localisationCache;
        $this->languageNameUtils = $languageNameUtils;
        $this->languageFallback = $languageFallback;
        $this->hookRunner = new HookRunner( $hookContainer );
 
        // limit size
        $this->cache = new MapCacheLRU( self::MAX_REQUEST_LANGUAGES );
 
        $options->assertRequiredOptions( self::CONSTRUCTOR_OPTIONS );
        $this->disable = !$options->get( MainConfigNames::UseDatabaseMessages );
        $this->maxEntrySize = $options->get( MainConfigNames::MaxMsgCacheEntrySize );
        $this->adaptive = $options->get( MainConfigNames::AdaptiveMessageCache );
    }
 
    public function setLogger( LoggerInterface $logger ) {
        $this->logger = $logger;
    }
 
    private function getParserOptions() {
        if ( !$this->parserOptions ) {
            $context = RequestContext::getMain();
            $user = $context->getUser();
            if ( !$user->isSafeToLoad() ) {
                // It isn't safe to use the context user yet, so don't try to get a
                // ParserOptions for it. And don't cache this ParserOptions
                // either.
                $po = ParserOptions::newFromAnon();
                $po->setAllowUnsafeRawHtml( false );
                return $po;
            }
 
            $this->parserOptions = ParserOptions::newFromContext( $context );
            // Messages may take parameters that could come
            // from malicious sources. As a precaution, disable
            // the <html> parser tag when parsing messages.
            $this->parserOptions->setAllowUnsafeRawHtml( false );
        }
 
        return $this->parserOptions;
    }
 
    private function getLocalCache( $code ) {
        $cacheKey = $this->srvCache->makeKey( __CLASS__, $code );
 
        return $this->srvCache->get( $cacheKey );
    }
 
    private function saveToLocalCache( $code, $cache ) {
        $cacheKey = $this->srvCache->makeKey( __CLASS__, $code );
        $this->srvCache->set( $cacheKey, $cache );
    }
 
    private function load( string $code, $mode = null ) {
        // Don't do double loading...
        if ( $this->isLanguageLoaded( $code ) && $mode !== self::FOR_UPDATE ) {
            return true;
        }
 
        // Show a log message (once) if loading is disabled
        if ( $this->disable ) {
            static $shownDisabled = false;
            if ( !$shownDisabled ) {
                $this->logger->debug( __METHOD__ . ': disabled' );
                $shownDisabled = true;
            }
 
            return true;
        }
 
        try {
            return $this->loadUnguarded( $code, $mode );
        } catch ( Throwable $e ) {
            // Don't try to load again during the exception handler
            $this->disable = true;
            throw $e;
        }
    }
 
    private function loadUnguarded( $code, $mode ) {
        $success = false; // Keep track of success
        $staleCache = false; // a cache array with expired data, or false if none has been loaded
        $where = []; // Debug info, delayed to avoid spamming debug log too much
 
        // Hash of the contents is stored in memcache, to detect if data-center cache
        // or local cache goes out of date (e.g. due to replace() on some other server)
        [ $hash, $hashVolatile ] = $this->getValidationHash( $code );
        $this->cacheVolatile[$code] = $hashVolatile;
 
        // Try the local cache and check against the cluster hash key...
        $cache = $this->getLocalCache( $code );
        if ( !$cache ) {
            $where[] = 'local cache is empty';
        } elseif ( !isset( $cache['HASH'] ) || $cache['HASH'] !== $hash ) {
            $where[] = 'local cache has the wrong hash';
            $staleCache = $cache;
        } elseif ( $this->isCacheExpired( $cache ) ) {
            $where[] = 'local cache is expired';
            $staleCache = $cache;
        } elseif ( $hashVolatile ) {
            $where[] = 'local cache validation key is expired/volatile';
            $staleCache = $cache;
        } else {
            $where[] = 'got from local cache';
            $this->cache->set( $code, $cache );
            $success = true;
        }
 
        if ( !$success ) {
            $cacheKey = $this->clusterCache->makeKey( 'messages', $code );
            // 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 <= 1; $failedAttempts++ ) {
                if ( $hashVolatile && $staleCache ) {
                    // Do not bother fetching the whole cache blob to avoid I/O.
                    // Instead, just try to get the non-blocking $statusKey lock
                    // below, and use the local stale value if it was not acquired.
                    $where[] = 'global cache is presumed expired';
                } else {
                    $cache = $this->clusterCache->get( $cacheKey );
                    if ( !$cache ) {
                        $where[] = 'global cache is empty';
                    } elseif ( $this->isCacheExpired( $cache ) ) {
                        $where[] = 'global cache is expired';
                        $staleCache = $cache;
                    } elseif ( $hashVolatile ) {
                        // DB results are replica DB lag prone until the holdoff TTL passes.
                        // By then, updates should be reflected in loadFromDBWithLock().
                        // One thread regenerates the cache while others use old values.
                        $where[] = 'global cache is expired/volatile';
                        $staleCache = $cache;
                    } else {
                        $where[] = 'got from global cache';
                        $this->cache->set( $code, $cache );
                        $this->saveToCaches( $cache, 'local-only', $code );
                        $success = true;
                    }
                }
 
                if ( $success ) {
                    // Done, no need to retry
                    break;
                }
 
                // We need to call loadFromDB. Limit the concurrency to one process.
                // This prevents the site from going down when the cache expires.
                // Note that the DB slam protection lock here is non-blocking.
                $loadStatus = $this->loadFromDBWithLock( $code, $where, $mode );
                if ( $loadStatus === true ) {
                    $success = true;
                    break;
                } elseif ( $staleCache ) {
                    // Use the stale cache while some other thread constructs the new one
                    $where[] = 'using stale cache';
                    $this->cache->set( $code, $staleCache );
                    $success = true;
                    break;
                } elseif ( $failedAttempts > 0 ) {
                    // Already blocked once, so avoid another lock/unlock cycle.
                    // This case will typically be hit if memcached is down, or if
                    // loadFromDB() takes longer than LOCK_WAIT.
                    $where[] = "could not acquire status key.";
                    break;
                } elseif ( $loadStatus === 'cantacquire' ) {
                    // Wait for the other thread to finish, then retry. Normally,
                    // the memcached get() will then yield the other thread's result.
                    $where[] = 'waited for other thread to complete';
                    $this->getReentrantScopedLock( $cacheKey );
                } else {
                    // Disable cache; $loadStatus is 'disabled'
                    break;
                }
            }
        }
 
        if ( !$success ) {
            $where[] = 'loading FAILED - cache is disabled';
            $this->disable = true;
            $this->cache->set( $code, [] );
            $this->logger->error( __METHOD__ . ": Failed to load $code" );
            // 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
        }
 
        if ( !$this->isLanguageLoaded( $code ) ) {
            throw new LogicException( "Process cache for '$code' should be set by now." );
        }
 
        $info = implode( ', ', $where );
        $this->logger->debug( __METHOD__ . ": Loading $code... $info" );
 
        return $success;
    }
 
    private function loadFromDBWithLock( $code, array &$where, $mode = null ) {
        // If cache updates on all levels fail, give up on message overrides.
        // This is to avoid easy site outages; see $saveSuccess comments below.
        $statusKey = $this->clusterCache->makeKey( 'messages', $code, 'status' );
        $status = $this->clusterCache->get( $statusKey );
        if ( $status === 'error' ) {
            $where[] = "could not load; method is still globally disabled";
            return 'disabled';
        }
 
        // Now let's regenerate
        $where[] = 'loading from database';
 
        // Lock the cache to prevent conflicting writes.
        // This lock is non-blocking so stale cache can quickly be used.
        // Note that load() will call a blocking getReentrantScopedLock()
        // after this if it really need to wait for any current thread.
        $cacheKey = $this->clusterCache->makeKey( 'messages', $code );
        $scopedLock = $this->getReentrantScopedLock( $cacheKey, 0 );
        if ( !$scopedLock ) {
            $where[] = 'could not acquire main lock';
            return 'cantacquire';
        }
 
        $cache = $this->loadFromDB( $code, $mode );
        $this->cache->set( $code, $cache );
        $saveSuccess = $this->saveToCaches( $cache, 'all', $code );
 
        if ( !$saveSuccess ) {
            if ( $this->srvCache instanceof EmptyBagOStuff ) {
                $this->clusterCache->set( $statusKey, 'error', 60 * 5 );
                $where[] = 'could not save cache, disabled globally for 5 minutes';
            } else {
                $where[] = "could not save global cache";
            }
        }
 
        return true;
    }
 
    private function loadFromDB( $code, $mode = null ) {
        $dbr = wfGetDB( ( $mode === self::FOR_UPDATE ) ? DB_PRIMARY : DB_REPLICA );
 
        $cache = [];
 
        $mostused = []; // list of "<cased message key>/<code>"
        if ( $this->adaptive && $code !== $this->contLangCode ) {
            if ( !$this->cache->has( $this->contLangCode ) ) {
                $this->load( $this->contLangCode );
            }
            $mostused = array_keys( $this->cache->get( $this->contLangCode ) );
            foreach ( $mostused as $key => $value ) {
                $mostused[$key] = "$value/$code";
            }
        }
 
        // Common conditions
        $conds = [
            'page_is_redirect' => 0,
            'page_namespace' => NS_MEDIAWIKI,
        ];
        if ( count( $mostused ) ) {
            $conds['page_title'] = $mostused;
        } elseif ( $code !== $this->contLangCode ) {
            $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() );
        }
 
        // Set the stubs for oversized software-defined messages in the main cache map
        $res = $dbr->select(
            'page',
            [ 'page_title', 'page_latest' ],
            array_merge( $conds, [ 'page_len > ' . intval( $this->maxEntrySize ) ] ),
            __METHOD__ . "($code)-big"
        );
        foreach ( $res as $row ) {
            // Include entries/stubs for all keys in $mostused in adaptive mode
            if ( $this->adaptive || $this->isMainCacheable( $row->page_title ) ) {
                $cache[$row->page_title] = '!TOO BIG';
            }
            // At least include revision ID so page changes are reflected in the hash
            $cache['EXCESSIVE'][$row->page_title] = $row->page_latest;
        }
 
        // Can not inject the RevisionStore as it would break the installer since
        // it instantiates MessageCache before the DB.
        $revisionStore = MediaWikiServices::getInstance()->getRevisionStore();
        // Set the text for small software-defined messages in the main cache map
        $revQuery = $revisionStore->getQueryInfo( [ 'page' ] );
 
        // T231196: MySQL/MariaDB (10.1.37) can sometimes irrationally decide that querying `actor` then
        // `revision` then `page` is somehow better than starting with `page`. Tell it not to reorder the
        // query (and also reorder it ourselves because as generated by RevisionStore it'll have
        // `revision` first rather than `page`).
        $revQuery['joins']['revision'] = $revQuery['joins']['page'];
        unset( $revQuery['joins']['page'] );
        // It isn't actually necessary to reorder $revQuery['tables'] as Database does the right thing
        // when join conditions are given for all joins, but Gergő is wary of relying on that so pull
        // `page` to the start.
        $revQuery['tables'] = array_merge(
            [ 'page' ],
            array_diff( $revQuery['tables'], [ 'page' ] )
        );
 
        $res = $dbr->select(
            $revQuery['tables'],
            $revQuery['fields'],
            array_merge( $conds, [
                'page_len <= ' . intval( $this->maxEntrySize ),
                'page_latest = rev_id' // get the latest revision only
            ] ),
            __METHOD__ . "($code)-small",
            [ 'STRAIGHT_JOIN' ],
            $revQuery['joins']
        );
 
        // Don't load content from uncacheable rows (T313004)
        [ $cacheableRows, $uncacheableRows ] = $this->separateCacheableRows( $res );
        $result = $revisionStore->newRevisionsFromBatch( $cacheableRows, [
            'slots' => [ SlotRecord::MAIN ],
            'content' => true
        ] );
        $revisions = $result->isOK() ? $result->getValue() : [];
 
        foreach ( $cacheableRows as $row ) {
            try {
                $rev = $revisions[$row->rev_id] ?? null;
                $content = $rev ? $rev->getContent( SlotRecord::MAIN ) : null;
                $text = $this->getMessageTextFromContent( $content );
            } catch ( TimeoutException $e ) {
                throw $e;
            } catch ( Exception $ex ) {
                $text = false;
            }
 
            if ( !is_string( $text ) ) {
                $entry = '!ERROR';
                $this->logger->error(
                    __METHOD__
                    . ": failed to load message page text for {$row->page_title} ($code)"
                );
            } else {
                $entry = ' ' . $text;
            }
            $cache[$row->page_title] = $entry;
        }
 
        foreach ( $uncacheableRows as $row ) {
            // T193271: cache object gets too big and slow to generate.
            // At least include revision ID so page changes are reflected in the hash.
            $cache['EXCESSIVE'][$row->page_title] = $row->page_latest;
        }
 
        $cache['VERSION'] = MSG_CACHE_VERSION;
        ksort( $cache );
 
        // Hash for validating local cache (APC). No need to take into account
        // messages larger than $wgMaxMsgCacheEntrySize, since those are only
        // stored and fetched from memcache.
        $cache['HASH'] = md5( serialize( $cache ) );
        $cache['EXPIRY'] = wfTimestamp( TS_MW, time() + self::WAN_TTL );
        unset( $cache['EXCESSIVE'] ); // only needed for hash
 
        return $cache;
    }
 
    private function isLanguageLoaded( $lang ) {
        // It is important that this only returns true if the cache was fully
        // populated by load(), so that callers can assume all cache keys exist.
        // It is possible for $this->cache to be only partially populated through
        // methods like MessageCache::replace(), which must not make this method
        // return true (T208897). And this method must cease to return true
        // if the language was evicted by MapCacheLRU (T230690).
        return $this->cache->hasField( $lang, 'VERSION' );
    }
 
    private function isMainCacheable( $name, $code = null ) {
        // Convert first letter to lowercase, and strip /code suffix
        $name = $this->contLang->lcfirst( $name );
        // Include common conversion table pages. This also avoids problems with
        // Installer::parse() bailing out due to disallowed DB queries (T207979).
        if ( strpos( $name, 'conversiontable/' ) === 0 ) {
            return true;
        }
        $msg = preg_replace( '/\/[a-z0-9-]{2,}$/', '', $name );
 
        if ( $code === null ) {
            // Bulk load
            if ( $this->systemMessageNames === null ) {
                $this->systemMessageNames = array_fill_keys(
                    $this->localisationCache->getSubitemList( $this->contLangCode, 'messages' ),
                    true );
            }
            return isset( $this->systemMessageNames[$msg] );
        } else {
            // Use individual subitem
            return $this->localisationCache->getSubitem( $code, 'messages', $msg ) !== null;
        }
    }
 
    private function separateCacheableRows( $res ) {
        if ( $this->adaptive ) {
            // Include entries/stubs for all keys in $mostused in adaptive mode
            return [ $res, [] ];
        }
        $cacheableRows = [];
        $uncacheableRows = [];
        foreach ( $res as $row ) {
            if ( $this->isMainCacheable( $row->page_title ) ) {
                $cacheableRows[] = $row;
            } else {
                $uncacheableRows[] = $row;
            }
        }
        return [ $cacheableRows, $uncacheableRows ];
    }
 
    public function replace( $title, $text ) {
        if ( $this->disable ) {
            return;
        }
 
        [ $msg, $code ] = $this->figureMessage( $title );
        if ( strpos( $title, '/' ) !== false && $code === $this->contLangCode ) {
            // Content language overrides do not use the /<code> suffix
            return;
        }
 
        // (a) Update the process cache with the new message text
        if ( $text === false ) {
            // Page deleted
            $this->cache->setField( $code, $title, '!NONEXISTENT' );
        } else {
            // Ignore $wgMaxMsgCacheEntrySize so the process cache is up to date
            $this->cache->setField( $code, $title, ' ' . $text );
        }
 
        // (b) Update the shared caches in a deferred update with a fresh DB snapshot
        DeferredUpdates::addUpdate(
            new MessageCacheUpdate( $code, $title, $msg ),
            DeferredUpdates::PRESEND
        );
    }
 
    public function refreshAndReplaceInternal( string $code, array $replacements ) {
        // Allow one caller at a time to avoid race conditions
        $scopedLock = $this->getReentrantScopedLock(
            $this->clusterCache->makeKey( 'messages', $code )
        );
        if ( !$scopedLock ) {
            foreach ( $replacements as [ $title ] ) {
                $this->logger->error(
                    __METHOD__ . ': could not acquire lock to update {title} ({code})',
                    [ 'title' => $title, 'code' => $code ] );
            }
 
            return;
        }
 
        // Load the existing cache to update it in the local DC cache.
        // The other DCs will see a hash mismatch.
        if ( $this->load( $code, self::FOR_UPDATE ) ) {
            $cache = $this->cache->get( $code );
        } else {
            // Err? Fall back to loading from the database.
            $cache = $this->loadFromDB( $code, self::FOR_UPDATE );
        }
        // Check if individual cache keys should exist and update cache accordingly
        $newTextByTitle = []; // map of (title => content)
        $newBigTitles = []; // map of (title => latest revision ID), like EXCESSIVE in loadFromDB()
        // Can not inject the WikiPageFactory as it would break the installer since
        // it instantiates MessageCache before the DB.
        $wikiPageFactory = MediaWikiServices::getInstance()->getWikiPageFactory();
        foreach ( $replacements as [ $title ] ) {
            $page = $wikiPageFactory->newFromTitle( Title::makeTitle( NS_MEDIAWIKI, $title ) );
            $page->loadPageData( $page::READ_LATEST );
            $text = $this->getMessageTextFromContent( $page->getContent() );
            // Remember the text for the blob store update later on
            $newTextByTitle[$title] = $text ?? '';
            // Note that if $text is false, then $cache should have a !NONEXISTANT entry
            if ( !is_string( $text ) ) {
                $cache[$title] = '!NONEXISTENT';
            } elseif ( strlen( $text ) > $this->maxEntrySize ) {
                $cache[$title] = '!TOO BIG';
                $newBigTitles[$title] = $page->getLatest();
            } else {
                $cache[$title] = ' ' . $text;
            }
        }
        // Update HASH for the new key. Incorporates various administrative keys,
        // including the old HASH (and thereby the EXCESSIVE value from loadFromDB()
        // and previous replace() calls), but that doesn't really matter since we
        // only ever compare it for equality with a copy saved by saveToCaches().
        $cache['HASH'] = md5( serialize( $cache + [ 'EXCESSIVE' => $newBigTitles ] ) );
        // Update the too-big WAN cache entries now that we have the new HASH
        foreach ( $newBigTitles as $title => $id ) {
            // Match logic of loadCachedMessagePageEntry()
            $this->wanCache->set(
                $this->bigMessageCacheKey( $cache['HASH'], $title ),
                ' ' . $newTextByTitle[$title],
                self::WAN_TTL
            );
        }
        // Mark this cache as definitely being "latest" (non-volatile) so
        // load() calls do not try to refresh the cache with replica DB data
        $cache['LATEST'] = time();
        // Update the process cache
        $this->cache->set( $code, $cache );
        // Pre-emptively update the local datacenter cache so things like edit filter and
        // prevented changes are reflected immediately; these often use MediaWiki: pages.
        // The datacenter handling replace() calls should be the same one handling edits
        // as they require HTTP POST.
        $this->saveToCaches( $cache, 'all', $code );
        // Release the lock now that the cache is saved
        ScopedCallback::consume( $scopedLock );
 
        // Relay the purge. Touching this check key expires cache contents
        // and local cache (APC) validation hash across all datacenters.
        $this->wanCache->touchCheckKey( $this->getCheckKey( $code ) );
 
        // Purge the messages in the message blob store and fire any hook handlers
        $blobStore = MediaWikiServices::getInstance()->getResourceLoader()->getMessageBlobStore();
        foreach ( $replacements as [ $title, $msg ] ) {
            $blobStore->updateMessage( $this->contLang->lcfirst( $msg ) );
            $this->hookRunner->onMessageCacheReplace( $title, $newTextByTitle[$title] );
        }
    }
 
    private 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;
    }
 
    private function saveToCaches( array $cache, $dest, $code = false ) {
        if ( $dest === 'all' ) {
            $cacheKey = $this->clusterCache->makeKey( 'messages', $code );
            $success = $this->clusterCache->set( $cacheKey, $cache );
            $this->setValidationHash( $code, $cache );
        } else {
            $success = true;
        }
 
        $this->saveToLocalCache( $code, $cache );
 
        return $success;
    }
 
    private function getValidationHash( $code ) {
        $curTTL = null;
        $value = $this->wanCache->get(
            $this->wanCache->makeKey( 'messages', $code, 'hash', 'v1' ),
            $curTTL,
            [ $this->getCheckKey( $code ) ]
        );
 
        if ( $value ) {
            $hash = $value['hash'];
            if ( ( time() - $value['latest'] ) < WANObjectCache::TTL_MINUTE ) {
                // Cache was recently updated via replace() and should be up-to-date.
                // That method is only called in the primary datacenter and uses FOR_UPDATE.
                // Also, it is unlikely that the current datacenter is *now* secondary one.
                $expired = false;
            } else {
                // See if the "check" key was bumped after the hash was generated
                $expired = ( $curTTL < 0 );
            }
        } else {
            // No hash found at all; cache must regenerate to be safe
            $hash = false;
            $expired = true;
        }
 
        return [ $hash, $expired ];
    }
 
    private function setValidationHash( $code, array $cache ) {
        $this->wanCache->set(
            $this->wanCache->makeKey( 'messages', $code, 'hash', 'v1' ),
            [
                'hash' => $cache['HASH'],
                'latest' => $cache['LATEST'] ?? 0
            ],
            WANObjectCache::TTL_INDEFINITE
        );
    }
 
    private function getReentrantScopedLock( $key, $timeout = self::WAIT_SEC ) {
        return $this->clusterCache->getScopedLock( $key, $timeout, self::LOCK_TTL, __METHOD__ );
    }
 
    public function get( $key, $useDB = true, $langcode = true ) {
        if ( is_int( $key ) ) {
            // Fix numerical strings that somehow become ints on their way here
            $key = (string)$key;
        } elseif ( !is_string( $key ) ) {
            throw new TypeError( 'Message key must be a string' );
        } elseif ( $key === '' ) {
            // Shortcut: the empty key is always missing
            return false;
        }
 
        // Normalise title-case input (with some inlining)
        $lckey = self::normalizeKey( $key );
 
        $this->hookRunner->onMessageCache__get( $lckey );
 
        // Loop through each language in the fallback list until we find something useful
        $message = $this->getMessageFromFallbackChain(
            wfGetLangObj( $langcode ),
            $lckey,
            !$this->disable && $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 = $this->localisationCache->getSubitem( $parts[1], 'messages', $parts[0] );
                if ( $message === null ) {
                    $message = false;
                }
            }
        }
 
        // Post-processing if the message exists
        if ( $message !== false ) {
            // Fix whitespace
            $message = str_replace(
                [
                    // Fix for trailing whitespace, removed by textarea
                    '&#32;',
                    // Fix for NBSP, converted to space by firefox
                    '&nbsp;',
                    '&#160;',
                    '&shy;'
                ],
                [
                    ' ',
                    "\u{00A0}",
                    "\u{00A0}",
                    "\u{00AD}"
                ],
                $message
            );
        }
 
        return $message;
    }
 
    private function getMessageFromFallbackChain( $lang, $lckey, $useDB ) {
        $alreadyTried = [];
 
        // First try the requested language.
        $message = $this->getMessageForLang( $lang, $lckey, $useDB, $alreadyTried );
        if ( $message !== false ) {
            return $message;
        }
 
        // Now try checking the site language.
        $message = $this->getMessageForLang( $this->contLang, $lckey, $useDB, $alreadyTried );
        return $message;
    }
 
    private function getMessageForLang( $lang, $lckey, $useDB, &$alreadyTried ) {
        $langcode = $lang->getCode();
 
        // Try checking the database for the requested language
        if ( $useDB ) {
            $uckey = $this->contLang->ucfirst( $lckey );
 
            if ( !isset( $alreadyTried[$langcode] ) ) {
                $message = $this->getMsgFromNamespace(
                    $this->getMessagePageName( $langcode, $uckey ),
                    $langcode
                );
                if ( $message !== false ) {
                    return $message;
                }
                $alreadyTried[$langcode] = true;
            }
        } else {
            $uckey = null;
        }
 
        // Check the CDB cache
        $message = $lang->getMessage( $lckey );
        if ( $message !== null ) {
            return $message;
        }
 
        // Try checking the database for all of the fallback languages
        if ( $useDB ) {
            $fallbackChain = $this->languageFallback->getAll( $langcode );
 
            foreach ( $fallbackChain as $code ) {
                if ( isset( $alreadyTried[$code] ) ) {
                    continue;
                }
 
                $message = $this->getMsgFromNamespace(
                    // @phan-suppress-next-line PhanTypeMismatchArgumentNullable uckey is set when used
                    $this->getMessagePageName( $code, $uckey ), $code );
 
                if ( $message !== false ) {
                    return $message;
                }
                $alreadyTried[$code] = true;
            }
        }
 
        return false;
    }
 
    private function getMessagePageName( $langcode, $uckey ) {
        if ( $langcode === $this->contLangCode ) {
            // Messages created in the content language will not have the /lang extension
            return $uckey;
        } else {
            return "$uckey/$langcode";
        }
    }
 
    public function getMsgFromNamespace( $title, $code ) {
        // Load all MediaWiki page definitions into cache. Note that individual keys
        // already loaded into cache during this request remain in the cache, which
        // includes the value of hook-defined messages.
        $this->load( $code );
 
        $entry = $this->cache->getField( $code, $title );
 
        if ( $entry !== null ) {
            // Message page exists as an override of a software messages
            if ( substr( $entry, 0, 1 ) === ' ' ) {
                // The message exists and is not '!TOO BIG' or '!ERROR'
                return (string)substr( $entry, 1 );
            } elseif ( $entry === '!NONEXISTENT' ) {
                // The text might be '-' or missing due to some data loss
                return false;
            }
            // Load the message page, utilizing the individual message cache.
            // If the page does not exist, there will be no hook handler fallbacks.
            $entry = $this->loadCachedMessagePageEntry(
                $title,
                $code,
                $this->cache->getField( $code, 'HASH' )
            );
        } else {
            // Message page either does not exist or does not override a software message
            if ( !$this->isMainCacheable( $title, $code ) ) {
                // Message page does not override any software-defined message. A custom
                // message might be defined to have content or settings specific to the wiki.
                // Load the message page, utilizing the individual message cache as needed.
                $entry = $this->loadCachedMessagePageEntry(
                    $title,
                    $code,
                    $this->cache->getField( $code, 'HASH' )
                );
            }
            if ( $entry === null || substr( $entry, 0, 1 ) !== ' ' ) {
                // Message does not have a MediaWiki page definition; try hook handlers
                $message = false;
                // @phan-suppress-next-line PhanTypeMismatchArgument Type mismatch on pass-by-ref args
                $this->hookRunner->onMessagesPreLoad( $title, $message, $code );
                if ( $message !== false ) {
                    $this->cache->setField( $code, $title, ' ' . $message );
                } else {
                    $this->cache->setField( $code, $title, '!NONEXISTENT' );
                }
 
                return $message;
            }
        }
 
        if ( $entry !== false && substr( $entry, 0, 1 ) === ' ' ) {
            if ( $this->cacheVolatile[$code] ) {
                // Make sure that individual keys respect the WAN cache holdoff period too
                $this->logger->debug(
                    __METHOD__ . ': loading volatile key \'{titleKey}\'',
                    [ 'titleKey' => $title, 'code' => $code ] );
            } else {
                $this->cache->setField( $code, $title, $entry );
            }
            // The message exists, so make sure a string is returned
            return (string)substr( $entry, 1 );
        }
 
        $this->cache->setField( $code, $title, '!NONEXISTENT' );
 
        return false;
    }
 
    private function loadCachedMessagePageEntry( $dbKey, $code, $hash ) {
        $fname = __METHOD__;
        return $this->srvCache->getWithSetCallback(
            $this->srvCache->makeKey( 'messages-big', $hash, $dbKey ),
            BagOStuff::TTL_HOUR,
            function () use ( $code, $dbKey, $hash, $fname ) {
                return $this->wanCache->getWithSetCallback(
                    $this->bigMessageCacheKey( $hash, $dbKey ),
                    self::WAN_TTL,
                    function ( $oldValue, &$ttl, &$setOpts ) use ( $dbKey, $code, $fname ) {
                        // Try loading the message from the database
                        $setOpts += Database::getCacheSetOptions( wfGetDB( DB_REPLICA ) );
                        // Use newKnownCurrent() to avoid querying revision/user tables
                        $title = Title::makeTitle( NS_MEDIAWIKI, $dbKey );
                        // Injecting RevisionStore breaks installer since it
                        // instantiates MessageCache before DB.
                        $revision = MediaWikiServices::getInstance()
                            ->getRevisionLookup()
                            ->getKnownCurrentRevision( $title );
                        if ( !$revision ) {
                            // The wiki doesn't have a local override page. Cache absence with normal TTL.
                            // When overrides are created, self::replace() takes care of the cache.
                            return '!NONEXISTENT';
                        }
                        $content = $revision->getContent( SlotRecord::MAIN );
                        if ( $content ) {
                            $message = $this->getMessageTextFromContent( $content );
                        } else {
                            $this->logger->warning(
                                $fname . ': failed to load page text for \'{titleKey}\'',
                                [ 'titleKey' => $dbKey, 'code' => $code ]
                            );
                            $message = null;
                        }
 
                        if ( !is_string( $message ) ) {
                            // Revision failed to load Content, or Content is incompatible with wikitext.
                            // Possibly a temporary loading failure.
                            $ttl = 5;
 
                            return '!NONEXISTENT';
                        }
 
                        return ' ' . $message;
                    }
                );
            }
        );
    }
 
    public function transform( $message, $interface = false, $language = null, PageReference $page = null ) {
        // Avoid creating parser if nothing to transform
        if ( strpos( $message, '{{' ) === false ) {
            return $message;
        }
 
        if ( $this->inParser ) {
            return $message;
        }
 
        $parser = $this->getParser();
        if ( $parser ) {
            $popts = $this->getParserOptions();
            $popts->setInterfaceMessage( $interface );
            $popts->setTargetLanguage( $language );
 
            $userlang = $popts->setUserLang( $language );
            $this->inParser = true;
            $message = $parser->transformMsg( $message, $popts, $page );
            $this->inParser = false;
            $popts->setUserLang( $userlang );
        }
 
        return $message;
    }
 
    public function getParser() {
        if ( !$this->parser ) {
            $parser = MediaWikiServices::getInstance()->getParser();
            // Clone it and store it
            $this->parser = clone $parser;
        }
 
        return $this->parser;
    }
 
    public function parse( $text, PageReference $page = null, $linestart = true,
        $interface = false, $language = null
    ) {
        global $wgTitle;
 
        if ( $this->inParser ) {
            return htmlspecialchars( $text );
        }
 
        $parser = $this->getParser();
        $popts = $this->getParserOptions();
        $popts->setInterfaceMessage( $interface );
 
        if ( is_string( $language ) ) {
            $language = $this->langFactory->getLanguage( $language );
        }
        $popts->setTargetLanguage( $language );
 
        if ( !$page ) {
            $logger = LoggerFactory::getInstance( 'GlobalTitleFail' );
            $logger->info(
                __METHOD__ . ' called with no title set.',
                [ 'exception' => new Exception ]
            );
            $page = $wgTitle;
        }
        // Sometimes $wgTitle isn't set either...
        if ( !$page ) {
            // It's not uncommon having a null $wgTitle in scripts. See r80898
            // Create a ghost title in such case
            $page = PageReferenceValue::localReference(
                NS_SPECIAL,
                'Badtitle/title not set in ' . __METHOD__
            );
        }
 
        $this->inParser = true;
        $res = $parser->parse( $text, $page, $popts, $linestart );
        $this->inParser = false;
 
        return $res;
    }
 
    public function disable() {
        $this->disable = true;
    }
 
    public function enable() {
        $this->disable = false;
    }
 
    public function isDisabled() {
        return $this->disable;
    }
 
    public function clear() {
        $langs = $this->languageNameUtils->getLanguageNames();
        foreach ( array_keys( $langs ) as $code ) {
            $this->wanCache->touchCheckKey( $this->getCheckKey( $code ) );
        }
        $this->cache->clear();
    }
 
    public function figureMessage( $key ) {
        $pieces = explode( '/', $key );
        if ( count( $pieces ) < 2 ) {
            return [ $key, $this->contLangCode ];
        }
 
        $lang = array_pop( $pieces );
        if ( !$this->languageNameUtils->getLanguageName(
            $lang,
            LanguageNameUtils::AUTONYMS,
            LanguageNameUtils::DEFINED
        ) ) {
            return [ $key, $this->contLangCode ];
        }
 
        $message = implode( '/', $pieces );
 
        return [ $message, $lang ];
    }
 
    public function getAllMessageKeys( $code ) {
        $this->load( $code );
        if ( !$this->cache->has( $code ) ) {
            // Apparently load() failed
            return null;
        }
        // Remove administrative keys
        $cache = $this->cache->get( $code );
        unset( $cache['VERSION'] );
        unset( $cache['EXPIRY'] );
        unset( $cache['EXCESSIVE'] );
        // Remove any !NONEXISTENT keys
        $cache = array_diff( $cache, [ '!NONEXISTENT' ] );
 
        // Keys may appear with a capital first letter. lcfirst them.
        return array_map( [ $this->contLang, 'lcfirst' ], array_keys( $cache ) );
    }
 
    public function updateMessageOverride( LinkTarget $linkTarget, Content $content = null ) {
        $msgText = $this->getMessageTextFromContent( $content );
        if ( $msgText === null ) {
            $msgText = false; // treat as not existing
        }
 
        $this->replace( $linkTarget->getDBkey(), $msgText );
 
        if ( $this->contLangConverter->hasVariants() ) {
            $this->contLangConverter->updateConversionTable( $linkTarget );
        }
    }
 
    public function getCheckKey( $code ) {
        return $this->wanCache->makeKey( 'messages', $code );
    }
 
    private function getMessageTextFromContent( Content $content = null ) {
        // @TODO: could skip pseudo-messages like js/css here, based on content model
        if ( $content ) {
            // Message page exists...
            // 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.
            $msgText = $content->getWikitextForTransclusion();
            if ( $msgText === false || $msgText === null ) {
                // This might be due to some kind of misconfiguration...
                $msgText = null;
                $this->logger->warning(
                    __METHOD__ . ": message content doesn't provide wikitext "
                    . "(content model: " . $content->getModel() . ")" );
            }
        } else {
            // Message page does not exist...
            $msgText = false;
        }
 
        return $msgText;
    }
 
    private function bigMessageCacheKey( $hash, $title ) {
        return $this->wanCache->makeKey( 'messages-big', $hash, $title );
    }
}