includes/cache/MessageCache.php

   1 <?php
   2 /**
   3  * Localisation messages cache.
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License as published by
   7  * the Free Software Foundation; either version 2 of the License, or
   8  * (at your option) any later version.
   9  *
  10  * This program is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  13  * GNU General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU General Public License along
  16  * with this program; if not, write to the Free Software Foundation, Inc.,
  17  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  18  * http://www.gnu.org/copyleft/gpl.html
  19  *
  20  * @file
  21  * @ingroup Cache
  22  */
  23 use MediaWiki\MediaWikiServices;
  24 use Wikimedia\ScopedCallback;
  25 use MediaWiki\Logger\LoggerFactory;
  26
  27 /**
  28  * MediaWiki message cache structure version.
  29  * Bump this whenever the message cache format has changed.
  30  */
  31 define( 'MSG_CACHE_VERSION', 2 );
  32
  33 /**
  34  * Message cache
  35  * Performs various MediaWiki namespace-related functions
  36  * @ingroup Cache
  37  */
  38 class MessageCache {
  39         const FOR_UPDATE = 1; // force message reload
  40
  41         /** How long to wait for memcached locks */
  42         const WAIT_SEC = 15;
  43         /** How long memcached locks last */
  44         const LOCK_TTL = 30;
  45
  46         /**
  47          * Process local cache of loaded messages that are defined in
  48          * MediaWiki namespace. First array level is a language code,
  49          * second level is message key and the values are either message
  50          * content prefixed with space, or !NONEXISTENT for negative
  51          * caching.
  52          * @var array $mCache
  53          */
  54         protected $mCache;
  55
  56         /**
  57          * @var bool[] Map of (language code => boolean)
  58          */
  59         protected $mCacheVolatile = [];
  60
  61         /**
  62          * Should mean that database cannot be used, but check
  63          * @var bool $mDisable
  64          */
  65         protected $mDisable;
  66
  67         /**
  68          * Lifetime for cache, used by object caching.
  69          * Set on construction, see __construct().
  70          */
  71         protected $mExpiry;
  72
  73         /**
  74          * Message cache has its own parser which it uses to transform messages
  75          * @var ParserOptions
  76          */
  77         protected $mParserOptions;
  78         /** @var Parser */
  79         protected $mParser;
  80
  81         /**
  82          * Variable for tracking which variables are already loaded
  83          * @var array $mLoadedLanguages
  84          */
  85         protected $mLoadedLanguages = [];
  86
  87         /**
  88          * @var bool $mInParser
  89          */
  90         protected $mInParser = false;
  91
  92         /** @var WANObjectCache */
  93         protected $wanCache;
  94         /** @var BagOStuff */
  95         protected $clusterCache;
  96         /** @var BagOStuff */
  97         protected $srvCache;
  98
  99         /**
 100          * Singleton instance
 101          *
 102          * @var MessageCache $instance
 103          */
 104         private static $instance;
 105
 106         /**
 107          * Get the signleton instance of this class
 108          *
 109          * @since 1.18
 110          * @return MessageCache
 111          */
 112         public static function singleton() {
 113                 if ( self::$instance === null ) {
 114                         global $wgUseDatabaseMessages, $wgMsgCacheExpiry, $wgUseLocalMessageCache;
 115                         self::$instance = new self(
 116                                 MediaWikiServices::getInstance()->getMainWANObjectCache(),
 117                                 wfGetMessageCacheStorage(),
 118                                 $wgUseLocalMessageCache
 119                                         ? MediaWikiServices::getInstance()->getLocalServerObjectCache()
 120                                         : new EmptyBagOStuff(),
 121                                 $wgUseDatabaseMessages,
 122                                 $wgMsgCacheExpiry
 123                         );
 124                 }
 125
 126                 return self::$instance;
 127         }
 128
 129         /**
 130          * Destroy the singleton instance
 131          *
 132          * @since 1.18
 133          */
 134         public static function destroyInstance() {
 135                 self::$instance = null;
 136         }
 137
 138         /**
 139          * Normalize message key input
 140          *
 141          * @param string $key Input message key to be normalized
 142          * @return string Normalized message key
 143          */
 144         public static function normalizeKey( $key ) {
 145                 global $wgContLang;
 146
 147                 $lckey = strtr( $key, ' ', '_' );
 148                 if ( ord( $lckey ) < 128 ) {
 149                         $lckey[0] = strtolower( $lckey[0] );
 150                 } else {
 151                         $lckey = $wgContLang->lcfirst( $lckey );
 152                 }
 153
 154                 return $lckey;
 155         }
 156
 157         /**
 158          * @param WANObjectCache $wanCache WAN cache instance
 159          * @param BagOStuff $clusterCache Cluster cache instance
 160          * @param BagOStuff $srvCache Server cache instance
 161          * @param bool $useDB Whether to look for message overrides (e.g. MediaWiki: pages)
 162          * @param int $expiry Lifetime for cache. @see $mExpiry.
 163          */
 164         public function __construct(
 165                 WANObjectCache $wanCache,
 166                 BagOStuff $clusterCache,
 167                 BagOStuff $srvCache,
 168                 $useDB,
 169                 $expiry
 170         ) {
 171                 $this->wanCache = $wanCache;
 172                 $this->clusterCache = $clusterCache;
 173                 $this->srvCache = $srvCache;
 174
 175                 $this->mDisable = !$useDB;
 176                 $this->mExpiry = $expiry;
 177         }
 178
 179         /**
 180          * ParserOptions is lazy initialised.
 181          *
 182          * @return ParserOptions
 183          */
 184         function getParserOptions() {
 185                 global $wgUser;
 186
 187                 if ( !$this->mParserOptions ) {
 188                         if ( !$wgUser->isSafeToLoad() ) {
 189                                 // $wgUser isn't unstubbable yet, so don't try to get a
 190                                 // ParserOptions for it. And don't cache this ParserOptions
 191                                 // either.
 192                                 $po = ParserOptions::newFromAnon();
 193                                 $po->setEditSection( false );
 194                                 $po->setAllowUnsafeRawHtml( false );
 195                                 return $po;
 196                         }
 197
 198                         $this->mParserOptions = new ParserOptions;
 199                         $this->mParserOptions->setEditSection( false );
 200                         // Messages may take parameters that could come
 201                         // from malicious sources. As a precaution, disable
 202                         // the <html> parser tag when parsing messages.
 203                         $this->mParserOptions->setAllowUnsafeRawHtml( false );
 204                 }
 205
 206                 return $this->mParserOptions;
 207         }
 208
 209         /**
 210          * Try to load the cache from APC.
 211          *
 212          * @param string $code Optional language code, see documenation of load().
 213          * @return array|bool The cache array, or false if not in cache.
 214          */
 215         protected function getLocalCache( $code ) {
 216                 $cacheKey = wfMemcKey( __CLASS__, $code );
 217
 218                 return $this->srvCache->get( $cacheKey );
 219         }
 220
 221         /**
 222          * Save the cache to APC.
 223          *
 224          * @param string $code
 225          * @param array $cache The cache array
 226          */
 227         protected function saveToLocalCache( $code, $cache ) {
 228                 $cacheKey = wfMemcKey( __CLASS__, $code );
 229                 $this->srvCache->set( $cacheKey, $cache );
 230         }
 231
 232         /**
 233          * Loads messages from caches or from database in this order:
 234          * (1) local message cache (if $wgUseLocalMessageCache is enabled)
 235          * (2) memcached
 236          * (3) from the database.
 237          *
 238          * When succesfully loading from (2) or (3), all higher level caches are
 239          * updated for the newest version.
 240          *
 241          * Nothing is loaded if member variable mDisable is true, either manually
 242          * set by calling code or if message loading fails (is this possible?).
 243          *
 244          * Returns true if cache is already populated or it was succesfully populated,
 245          * or false if populating empty cache fails. Also returns true if MessageCache
 246          * is disabled.
 247          *
 248          * @param string $code Language to which load messages
 249          * @param integer $mode Use MessageCache::FOR_UPDATE to skip process cache [optional]
 250          * @throws MWException
 251          * @return bool
 252          */
 253         protected function load( $code, $mode = null ) {
 254                 if ( !is_string( $code ) ) {
 255                         throw new InvalidArgumentException( "Missing language code" );
 256                 }
 257
 258                 # Don't do double loading...
 259                 if ( isset( $this->mLoadedLanguages[$code] ) && $mode != self::FOR_UPDATE ) {
 260                         return true;
 261                 }
 262
 263                 # 8 lines of code just to say (once) that message cache is disabled
 264                 if ( $this->mDisable ) {
 265                         static $shownDisabled = false;
 266                         if ( !$shownDisabled ) {
 267                                 wfDebug( __METHOD__ . ": disabled\n" );
 268                                 $shownDisabled = true;
 269                         }
 270
 271                         return true;
 272                 }
 273
 274                 # Loading code starts
 275                 $success = false; # Keep track of success
 276                 $staleCache = false; # a cache array with expired data, or false if none has been loaded
 277                 $where = []; # Debug info, delayed to avoid spamming debug log too much
 278
 279                 # Hash of the contents is stored in memcache, to detect if data-center cache
 280                 # or local cache goes out of date (e.g. due to replace() on some other server)
 281                 list( $hash, $hashVolatile ) = $this->getValidationHash( $code );
 282                 $this->mCacheVolatile[$code] = $hashVolatile;
 283
 284                 # Try the local cache and check against the cluster hash key...
 285                 $cache = $this->getLocalCache( $code );
 286                 if ( !$cache ) {
 287                         $where[] = 'local cache is empty';
 288                 } elseif ( !isset( $cache['HASH'] ) || $cache['HASH'] !== $hash ) {
 289                         $where[] = 'local cache has the wrong hash';
 290                         $staleCache = $cache;
 291                 } elseif ( $this->isCacheExpired( $cache ) ) {
 292                         $where[] = 'local cache is expired';
 293                         $staleCache = $cache;
 294                 } elseif ( $hashVolatile ) {
 295                         $where[] = 'local cache validation key is expired/volatile';
 296                         $staleCache = $cache;
 297                 } else {
 298                         $where[] = 'got from local cache';
 299                         $success = true;
 300                         $this->mCache[$code] = $cache;
 301                 }
 302
 303                 if ( !$success ) {
 304                         $cacheKey = wfMemcKey( 'messages', $code ); # Key in memc for messages
 305                         # Try the global cache. If it is empty, try to acquire a lock. If
 306                         # the lock can't be acquired, wait for the other thread to finish
 307                         # and then try the global cache a second time.
 308                         for ( $failedAttempts = 0; $failedAttempts <= 1; $failedAttempts++ ) {
 309                                 if ( $hashVolatile && $staleCache ) {
 310                                         # Do not bother fetching the whole cache blob to avoid I/O.
 311                                         # Instead, just try to get the non-blocking $statusKey lock
 312                                         # below, and use the local stale value if it was not acquired.
 313                                         $where[] = 'global cache is presumed expired';
 314                                 } else {
 315                                         $cache = $this->clusterCache->get( $cacheKey );
 316                                         if ( !$cache ) {
 317                                                 $where[] = 'global cache is empty';
 318                                         } elseif ( $this->isCacheExpired( $cache ) ) {
 319                                                 $where[] = 'global cache is expired';
 320                                                 $staleCache = $cache;
 321                                         } elseif ( $hashVolatile ) {
 322                                                 # DB results are replica DB lag prone until the holdoff TTL passes.
 323                                                 # By then, updates should be reflected in loadFromDBWithLock().
 324                                                 # One thread renerates the cache while others use old values.
 325                                                 $where[] = 'global cache is expired/volatile';
 326                                                 $staleCache = $cache;
 327                                         } else {
 328                                                 $where[] = 'got from global cache';
 329                                                 $this->mCache[$code] = $cache;
 330                                                 $this->saveToCaches( $cache, 'local-only', $code );
 331                                                 $success = true;
 332                                         }
 333                                 }
 334
 335                                 if ( $success ) {
 336                                         # Done, no need to retry
 337                                         break;
 338                                 }
 339
 340                                 # We need to call loadFromDB. Limit the concurrency to one process.
 341                                 # This prevents the site from going down when the cache expires.
 342                                 # Note that the DB slam protection lock here is non-blocking.
 343                                 $loadStatus = $this->loadFromDBWithLock( $code, $where, $mode );
 344                                 if ( $loadStatus === true ) {
 345                                         $success = true;
 346                                         break;
 347                                 } elseif ( $staleCache ) {
 348                                         # Use the stale cache while some other thread constructs the new one
 349                                         $where[] = 'using stale cache';
 350                                         $this->mCache[$code] = $staleCache;
 351                                         $success = true;
 352                                         break;
 353                                 } elseif ( $failedAttempts > 0 ) {
 354                                         # Already blocked once, so avoid another lock/unlock cycle.
 355                                         # This case will typically be hit if memcached is down, or if
 356                                         # loadFromDB() takes longer than LOCK_WAIT.
 357                                         $where[] = "could not acquire status key.";
 358                                         break;
 359                                 } elseif ( $loadStatus === 'cantacquire' ) {
 360                                         # Wait for the other thread to finish, then retry. Normally,
 361                                         # the memcached get() will then yeild the other thread's result.
 362                                         $where[] = 'waited for other thread to complete';
 363                                         $this->getReentrantScopedLock( $cacheKey );
 364                                 } else {
 365                                         # Disable cache; $loadStatus is 'disabled'
 366                                         break;
 367                                 }
 368                         }
 369                 }
 370
 371                 if ( !$success ) {
 372                         $where[] = 'loading FAILED - cache is disabled';
 373                         $this->mDisable = true;
 374                         $this->mCache = false;
 375                         wfDebugLog( 'MessageCacheError', __METHOD__ . ": Failed to load $code\n" );
 376                         # This used to throw an exception, but that led to nasty side effects like
 377                         # the whole wiki being instantly down if the memcached server died
 378                 } else {
 379                         # All good, just record the success
 380                         $this->mLoadedLanguages[$code] = true;
 381                 }
 382
 383                 $info = implode( ', ', $where );
 384                 wfDebugLog( 'MessageCache', __METHOD__ . ": Loading $code... $info\n" );
 385
 386                 return $success;
 387         }
 388
 389         /**
 390          * @param string $code
 391          * @param array $where List of wfDebug() comments
 392          * @param integer $mode Use MessageCache::FOR_UPDATE to use DB_MASTER
 393          * @return bool|string True on success or one of ("cantacquire", "disabled")
 394          */
 395         protected function loadFromDBWithLock( $code, array &$where, $mode = null ) {
 396                 # If cache updates on all levels fail, give up on message overrides.
 397                 # This is to avoid easy site outages; see $saveSuccess comments below.
 398                 $statusKey = wfMemcKey( 'messages', $code, 'status' );
 399                 $status = $this->clusterCache->get( $statusKey );
 400                 if ( $status === 'error' ) {
 401                         $where[] = "could not load; method is still globally disabled";
 402                         return 'disabled';
 403                 }
 404
 405                 # Now let's regenerate
 406                 $where[] = 'loading from database';
 407
 408                 # Lock the cache to prevent conflicting writes.
 409                 # This lock is non-blocking so stale cache can quickly be used.
 410                 # Note that load() will call a blocking getReentrantScopedLock()
 411                 # after this if it really need to wait for any current thread.
 412                 $cacheKey = wfMemcKey( 'messages', $code );
 413                 $scopedLock = $this->getReentrantScopedLock( $cacheKey, 0 );
 414                 if ( !$scopedLock ) {
 415                         $where[] = 'could not acquire main lock';
 416                         return 'cantacquire';
 417                 }
 418
 419                 $cache = $this->loadFromDB( $code, $mode );
 420                 $this->mCache[$code] = $cache;
 421                 $saveSuccess = $this->saveToCaches( $cache, 'all', $code );
 422
 423                 if ( !$saveSuccess ) {
 424                         /**
 425                          * Cache save has failed.
 426                          *
 427                          * There are two main scenarios where this could be a problem:
 428                          * - The cache is more than the maximum size (typically 1MB compressed).
 429                          * - Memcached has no space remaining in the relevant slab class. This is
 430                          *   unlikely with recent versions of memcached.
 431                          *
 432                          * Either way, if there is a local cache, nothing bad will happen. If there
 433                          * is no local cache, disabling the message cache for all requests avoids
 434                          * incurring a loadFromDB() overhead on every request, and thus saves the
 435                          * wiki from complete downtime under moderate traffic conditions.
 436                          */
 437                         if ( $this->srvCache instanceof EmptyBagOStuff ) {
 438                                 $this->clusterCache->set( $statusKey, 'error', 60 * 5 );
 439                                 $where[] = 'could not save cache, disabled globally for 5 minutes';
 440                         } else {
 441                                 $where[] = "could not save global cache";
 442                         }
 443                 }
 444
 445                 return true;
 446         }
 447
 448         /**
 449          * Loads cacheable messages from the database. Messages bigger than
 450          * $wgMaxMsgCacheEntrySize are assigned a special value, and are loaded
 451          * on-demand from the database later.
 452          *
 453          * @param string $code Language code
 454          * @param integer $mode Use MessageCache::FOR_UPDATE to skip process cache
 455          * @return array Loaded messages for storing in caches
 456          */
 457         protected function loadFromDB( $code, $mode = null ) {
 458                 global $wgMaxMsgCacheEntrySize, $wgLanguageCode, $wgAdaptiveMessageCache;
 459
 460                 $dbr = wfGetDB( ( $mode == self::FOR_UPDATE ) ? DB_MASTER : DB_REPLICA );
 461
 462                 $cache = [];
 463
 464                 # Common conditions
 465                 $conds = [
 466                         'page_is_redirect' => 0,
 467                         'page_namespace' => NS_MEDIAWIKI,
 468                 ];
 469
 470                 $mostused = [];
 471                 if ( $wgAdaptiveMessageCache && $code !== $wgLanguageCode ) {
 472                         if ( !isset( $this->mCache[$wgLanguageCode] ) ) {
 473                                 $this->load( $wgLanguageCode );
 474                         }
 475                         $mostused = array_keys( $this->mCache[$wgLanguageCode] );
 476                         foreach ( $mostused as $key => $value ) {
 477                                 $mostused[$key] = "$value/$code";
 478                         }
 479                 }
 480
 481                 if ( count( $mostused ) ) {
 482                         $conds['page_title'] = $mostused;
 483                 } elseif ( $code !== $wgLanguageCode ) {
 484                         $conds[] = 'page_title' . $dbr->buildLike( $dbr->anyString(), '/', $code );
 485                 } else {
 486                         # Effectively disallows use of '/' character in NS_MEDIAWIKI for uses
 487                         # other than language code.
 488                         $conds[] = 'page_title NOT' . $dbr->buildLike( $dbr->anyString(), '/', $dbr->anyString() );
 489                 }
 490
 491                 # Conditions to fetch oversized pages to ignore them
 492                 $bigConds = $conds;
 493                 $bigConds[] = 'page_len > ' . intval( $wgMaxMsgCacheEntrySize );
 494
 495                 # Load titles for all oversized pages in the MediaWiki namespace
 496                 $res = $dbr->select(
 497                         'page',
 498                         [ 'page_title', 'page_latest' ],
 499                         $bigConds,
 500                         __METHOD__ . "($code)-big"
 501                 );
 502                 foreach ( $res as $row ) {
 503                         $cache[$row->page_title] = '!TOO BIG';
 504                         // At least include revision ID so page changes are reflected in the hash
 505                         $cache['EXCESSIVE'][$row->page_title] = $row->page_latest;
 506                 }
 507
 508                 # Conditions to load the remaining pages with their contents
 509                 $smallConds = $conds;
 510                 $smallConds[] = 'page_latest=rev_id';
 511                 $smallConds[] = 'rev_text_id=old_id';
 512                 $smallConds[] = 'page_len <= ' . intval( $wgMaxMsgCacheEntrySize );
 513
 514                 $res = $dbr->select(
 515                         [ 'page', 'revision', 'text' ],
 516                         [ 'page_title', 'old_id', 'old_text', 'old_flags' ],
 517                         $smallConds,
 518                         __METHOD__ . "($code)-small"
 519                 );
 520
 521                 foreach ( $res as $row ) {
 522                         $text = Revision::getRevisionText( $row );
 523                         if ( $text === false ) {
 524                                 // Failed to fetch data; possible ES errors?
 525                                 // Store a marker to fetch on-demand as a workaround...
 526                                 // TODO Use a differnt marker
 527                                 $entry = '!TOO BIG';
 528                                 wfDebugLog(
 529                                         'MessageCache',
 530                                         __METHOD__
 531                                         . ": failed to load message page text for {$row->page_title} ($code)"
 532                                 );
 533                         } else {
 534                                 $entry = ' ' . $text;
 535                         }
 536                         $cache[$row->page_title] = $entry;
 537                 }
 538
 539                 $cache['VERSION'] = MSG_CACHE_VERSION;
 540                 ksort( $cache );
 541
 542                 # Hash for validating local cache (APC). No need to take into account
 543                 # messages larger than $wgMaxMsgCacheEntrySize, since those are only
 544                 # stored and fetched from memcache.
 545                 $cache['HASH'] = md5( serialize( $cache ) );
 546                 $cache['EXPIRY'] = wfTimestamp( TS_MW, time() + $this->mExpiry );
 547
 548                 return $cache;
 549         }
 550
 551         /**
 552          * Updates cache as necessary when message page is changed
 553          *
 554          * @param string $title Message cache key with initial uppercase letter.
 555          * @param string|bool $text New contents of the page (false if deleted)
 556          */
 557         public function replace( $title, $text ) {
 558                 global $wgLanguageCode;
 559
 560                 if ( $this->mDisable ) {
 561                         return;
 562                 }
 563
 564                 list( $msg, $code ) = $this->figureMessage( $title );
 565                 if ( strpos( $title, '/' ) !== false && $code === $wgLanguageCode ) {
 566                         // Content language overrides do not use the /<code> suffix
 567                         return;
 568                 }
 569
 570                 // (a) Update the process cache with the new message text
 571                 if ( $text === false ) {
 572                         // Page deleted
 573                         $this->mCache[$code][$title] = '!NONEXISTENT';
 574                 } else {
 575                         // Ignore $wgMaxMsgCacheEntrySize so the process cache is up to date
 576                         $this->mCache[$code][$title] = ' ' . $text;
 577                 }
 578
 579                 // (b) Update the shared caches in a deferred update with a fresh DB snapshot
 580                 DeferredUpdates::addCallableUpdate(
 581                         function () use ( $title, $msg, $code ) {
 582                                 global $wgContLang, $wgMaxMsgCacheEntrySize;
 583                                 // Allow one caller at a time to avoid race conditions
 584                                 $scopedLock = $this->getReentrantScopedLock( wfMemcKey( 'messages', $code ) );
 585                                 if ( !$scopedLock ) {
 586                                         LoggerFactory::getInstance( 'MessageCache' )->error(
 587                                                 __METHOD__ . ': could not acquire lock to update {title} ({code})',
 588                                                 [ 'title' => $title, 'code' => $code ] );
 589                                         return;
 590                                 }
 591                                 // Load the messages from the master DB to avoid race conditions
 592                                 $cache = $this->loadFromDB( $code, self::FOR_UPDATE );
 593                                 $this->mCache[$code] = $cache;
 594                                 // Load the process cache values and set the per-title cache keys
 595                                 $page = WikiPage::factory( Title::makeTitle( NS_MEDIAWIKI, $title ) );
 596                                 $page->loadPageData( $page::READ_LATEST );
 597                                 $text = $this->getMessageTextFromContent( $page->getContent() );
 598                                 // Check if an individual cache key should exist and update cache accordingly
 599                                 $titleKey = $this->wanCache->makeKey(
 600                                         'messages-big', $this->mCache[$code]['HASH'], $title );
 601                                 if ( is_string( $text ) && strlen( $text ) > $wgMaxMsgCacheEntrySize ) {
 602                                         $this->wanCache->set( $titleKey, ' ' . $text, $this->mExpiry );
 603                                 }
 604                                 // Mark this cache as definitely being "latest" (non-volatile) so
 605                                 // load() calls do try to refresh the cache with replica DB data
 606                                 $this->mCache[$code]['LATEST'] = time();
 607                                 // Pre-emptively update the local datacenter cache so things like edit filter and
 608                                 // blacklist changes are reflect immediately, as these often use MediaWiki: pages.
 609                                 // The datacenter handling replace() calls should be the same one handling edits
 610                                 // as they require HTTP POST.
 611                                 $this->saveToCaches( $this->mCache[$code], 'all', $code );
 612                                 // Release the lock now that the cache is saved
 613                                 ScopedCallback::consume( $scopedLock );
 614
 615                                 // Relay the purge. Touching this check key expires cache contents
 616                                 // and local cache (APC) validation hash across all datacenters.
 617                                 $this->wanCache->touchCheckKey( wfMemcKey( 'messages', $code ) );
 618                                 // Also delete cached sidebar... just in case it is affected
 619                                 // @TODO: shouldn't this be $code === $wgLanguageCode?
 620                                 if ( $code === 'en' ) {
 621                                         // Purge all language sidebars, e.g. on ?action=purge to the sidebar messages
 622                                         $codes = array_keys( Language::fetchLanguageNames() );
 623                                 } else {
 624                                         // Purge only the sidebar for this language
 625                                         $codes = [ $code ];
 626                                 }
 627                                 foreach ( $codes as $code ) {
 628                                         $this->wanCache->delete( wfMemcKey( 'sidebar', $code ) );
 629                                 }
 630
 631                                 // Purge the message in the message blob store
 632                                 $resourceloader = RequestContext::getMain()->getOutput()->getResourceLoader();
 633                                 $blobStore = $resourceloader->getMessageBlobStore();
 634                                 $blobStore->updateMessage( $wgContLang->lcfirst( $msg ) );
 635
 636                                 Hooks::run( 'MessageCacheReplace', [ $title, $text ] );
 637                         },
 638                         DeferredUpdates::PRESEND
 639                 );
 640         }
 641
 642         /**
 643          * Is the given cache array expired due to time passing or a version change?
 644          *
 645          * @param array $cache
 646          * @return bool
 647          */
 648         protected function isCacheExpired( $cache ) {
 649                 if ( !isset( $cache['VERSION'] ) || !isset( $cache['EXPIRY'] ) ) {
 650                         return true;
 651                 }
 652                 if ( $cache['VERSION'] != MSG_CACHE_VERSION ) {
 653                         return true;
 654                 }
 655                 if ( wfTimestampNow() >= $cache['EXPIRY'] ) {
 656                         return true;
 657                 }
 658
 659                 return false;
 660         }
 661
 662         /**
 663          * Shortcut to update caches.
 664          *
 665          * @param array $cache Cached messages with a version.
 666          * @param string $dest Either "local-only" to save to local caches only
 667          *   or "all" to save to all caches.
 668          * @param string|bool $code Language code (default: false)
 669          * @return bool
 670          */
 671         protected function saveToCaches( array $cache, $dest, $code = false ) {
 672                 if ( $dest === 'all' ) {
 673                         $cacheKey = wfMemcKey( 'messages', $code );
 674                         $success = $this->clusterCache->set( $cacheKey, $cache );
 675                         $this->setValidationHash( $code, $cache );
 676                 } else {
 677                         $success = true;
 678                 }
 679
 680                 $this->saveToLocalCache( $code, $cache );
 681
 682                 return $success;
 683         }
 684
 685         /**
 686          * Get the md5 used to validate the local APC cache
 687          *
 688          * @param string $code
 689          * @return array (hash or false, bool expiry/volatility status)
 690          */
 691         protected function getValidationHash( $code ) {
 692                 $curTTL = null;
 693                 $value = $this->wanCache->get(
 694                         $this->wanCache->makeKey( 'messages', $code, 'hash', 'v1' ),
 695                         $curTTL,
 696                         [ wfMemcKey( 'messages', $code ) ]
 697                 );
 698
 699                 if ( $value ) {
 700                         $hash = $value['hash'];
 701                         if ( ( time() - $value['latest'] ) < WANObjectCache::TTL_MINUTE ) {
 702                                 // Cache was recently updated via replace() and should be up-to-date.
 703                                 // That method is only called in the primary datacenter and uses FOR_UPDATE.
 704                                 // Also, it is unlikely that the current datacenter is *now* secondary one.
 705                                 $expired = false;
 706                         } else {
 707                                 // See if the "check" key was bumped after the hash was generated
 708                                 $expired = ( $curTTL < 0 );
 709                         }
 710                 } else {
 711                         // No hash found at all; cache must regenerate to be safe
 712                         $hash = false;
 713                         $expired = true;
 714                 }
 715
 716                 return [ $hash, $expired ];
 717         }
 718
 719         /**
 720          * Set the md5 used to validate the local disk cache
 721          *
 722          * If $cache has a 'LATEST' UNIX timestamp key, then the hash will not
 723          * be treated as "volatile" by getValidationHash() for the next few seconds.
 724          * This is triggered when $cache is generated using FOR_UPDATE mode.
 725          *
 726          * @param string $code
 727          * @param array $cache Cached messages with a version
 728          */
 729         protected function setValidationHash( $code, array $cache ) {
 730                 $this->wanCache->set(
 731                         $this->wanCache->makeKey( 'messages', $code, 'hash', 'v1' ),
 732                         [
 733                                 'hash' => $cache['HASH'],
 734                                 'latest' => isset( $cache['LATEST'] ) ? $cache['LATEST'] : 0
 735                         ],
 736                         WANObjectCache::TTL_INDEFINITE
 737                 );
 738         }
 739
 740         /**
 741          * @param string $key A language message cache key that stores blobs
 742          * @param integer $timeout Wait timeout in seconds
 743          * @return null|ScopedCallback
 744          */
 745         protected function getReentrantScopedLock( $key, $timeout = self::WAIT_SEC ) {
 746                 return $this->clusterCache->getScopedLock( $key, $timeout, self::LOCK_TTL, __METHOD__ );
 747         }
 748
 749         /**
 750          * Get a message from either the content language or the user language.
 751          *
 752          * First, assemble a list of languages to attempt getting the message from. This
 753          * chain begins with the requested language and its fallbacks and then continues with
 754          * the content language and its fallbacks. For each language in the chain, the following
 755          * process will occur (in this order):
 756          *  1. If a language-specific override, i.e., [[MW:msg/lang]], is available, use that.
 757          *     Note: for the content language, there is no /lang subpage.
 758          *  2. Fetch from the static CDB cache.
 759          *  3. If available, check the database for fallback language overrides.
 760          *
 761          * This process provides a number of guarantees. When changing this code, make sure all
 762          * of these guarantees are preserved.
 763          *  * If the requested language is *not* the content language, then the CDB cache for that
 764          *    specific language will take precedence over the root database page ([[MW:msg]]).
 765          *  * Fallbacks will be just that: fallbacks. A fallback language will never be reached if
 766          *    the message is available *anywhere* in the language for which it is a fallback.
 767          *
 768          * @param string $key The message key
 769          * @param bool $useDB If true, look for the message in the DB, false
 770          *   to use only the compiled l10n cache.
 771          * @param bool|string|object $langcode Code of the language to get the message for.
 772          *   - If string and a valid code, will create a standard language object
 773          *   - If string but not a valid code, will create a basic language object
 774          *   - If boolean and false, create object from the current users language
 775          *   - If boolean and true, create object from the wikis content language
 776          *   - If language object, use it as given
 777          * @param bool $isFullKey Specifies whether $key is a two part key "msg/lang".
 778          *
 779          * @throws MWException When given an invalid key
 780          * @return string|bool False if the message doesn't exist, otherwise the
 781          *   message (which can be empty)
 782          */
 783         function get( $key, $useDB = true, $langcode = true, $isFullKey = false ) {
 784                 if ( is_int( $key ) ) {
 785                         // Fix numerical strings that somehow become ints
 786                         // on their way here
 787                         $key = (string)$key;
 788                 } elseif ( !is_string( $key ) ) {
 789                         throw new MWException( 'Non-string key given' );
 790                 } elseif ( $key === '' ) {
 791                         // Shortcut: the empty key is always missing
 792                         return false;
 793                 }
 794
 795                 // For full keys, get the language code from the key
 796                 $pos = strrpos( $key, '/' );
 797                 if ( $isFullKey && $pos !== false ) {
 798                         $langcode = substr( $key, $pos + 1 );
 799                         $key = substr( $key, 0, $pos );
 800                 }
 801
 802                 // Normalise title-case input (with some inlining)
 803                 $lckey = MessageCache::normalizeKey( $key );
 804
 805                 Hooks::run( 'MessageCache::get', [ &$lckey ] );
 806
 807                 // Loop through each language in the fallback list until we find something useful
 808                 $lang = wfGetLangObj( $langcode );
 809                 $message = $this->getMessageFromFallbackChain(
 810                         $lang,
 811                         $lckey,
 812                         !$this->mDisable && $useDB
 813                 );
 814
 815                 // If we still have no message, maybe the key was in fact a full key so try that
 816                 if ( $message === false ) {
 817                         $parts = explode( '/', $lckey );
 818                         // We may get calls for things that are http-urls from sidebar
 819                         // Let's not load nonexistent languages for those
 820                         // They usually have more than one slash.
 821                         if ( count( $parts ) == 2 && $parts[1] !== '' ) {
 822                                 $message = Language::getMessageFor( $parts[0], $parts[1] );
 823                                 if ( $message === null ) {
 824                                         $message = false;
 825                                 }
 826                         }
 827                 }
 828
 829                 // Post-processing if the message exists
 830                 if ( $message !== false ) {
 831                         // Fix whitespace
 832                         $message = str_replace(
 833                                 [
 834                                         # Fix for trailing whitespace, removed by textarea
 835                                         '&#32;',
 836                                         # Fix for NBSP, converted to space by firefox
 837                                         '&nbsp;',
 838                                         '&#160;',
 839                                         '&shy;'
 840                                 ],
 841                                 [
 842                                         ' ',
 843                                         "\xc2\xa0",
 844                                         "\xc2\xa0",
 845                                         "\xc2\xad"
 846                                 ],
 847                                 $message
 848                         );
 849                 }
 850
 851                 return $message;
 852         }
 853
 854         /**
 855          * Given a language, try and fetch messages from that language.
 856          *
 857          * Will also consider fallbacks of that language, the site language, and fallbacks for
 858          * the site language.
 859          *
 860          * @see MessageCache::get
 861          * @param Language|StubObject $lang Preferred language
 862          * @param string $lckey Lowercase key for the message (as for localisation cache)
 863          * @param bool $useDB Whether to include messages from the wiki database
 864          * @return string|bool The message, or false if not found
 865          */
 866         protected function getMessageFromFallbackChain( $lang, $lckey, $useDB ) {
 867                 global $wgContLang;
 868
 869                 $alreadyTried = [];
 870
 871                 // First try the requested language.
 872                 $message = $this->getMessageForLang( $lang, $lckey, $useDB, $alreadyTried );
 873                 if ( $message !== false ) {
 874                         return $message;
 875                 }
 876
 877                 // Now try checking the site language.
 878                 $message = $this->getMessageForLang( $wgContLang, $lckey, $useDB, $alreadyTried );
 879                 return $message;
 880         }
 881
 882         /**
 883          * Given a language, try and fetch messages from that language and its fallbacks.
 884          *
 885          * @see MessageCache::get
 886          * @param Language|StubObject $lang Preferred language
 887          * @param string $lckey Lowercase key for the message (as for localisation cache)
 888          * @param bool $useDB Whether to include messages from the wiki database
 889          * @param bool[] $alreadyTried Contains true for each language that has been tried already
 890          * @return string|bool The message, or false if not found
 891          */
 892         private function getMessageForLang( $lang, $lckey, $useDB, &$alreadyTried ) {
 893                 global $wgContLang;
 894
 895                 $langcode = $lang->getCode();
 896
 897                 // Try checking the database for the requested language
 898                 if ( $useDB ) {
 899                         $uckey = $wgContLang->ucfirst( $lckey );
 900
 901                         if ( !isset( $alreadyTried[ $langcode ] ) ) {
 902                                 $message = $this->getMsgFromNamespace(
 903                                         $this->getMessagePageName( $langcode, $uckey ),
 904                                         $langcode
 905                                 );
 906
 907                                 if ( $message !== false ) {
 908                                         return $message;
 909                                 }
 910                                 $alreadyTried[ $langcode ] = true;
 911                         }
 912                 } else {
 913                         $uckey = null;
 914                 }
 915
 916                 // Check the CDB cache
 917                 $message = $lang->getMessage( $lckey );
 918                 if ( $message !== null ) {
 919                         return $message;
 920                 }
 921
 922                 // Try checking the database for all of the fallback languages
 923                 if ( $useDB ) {
 924                         $fallbackChain = Language::getFallbacksFor( $langcode );
 925
 926                         foreach ( $fallbackChain as $code ) {
 927                                 if ( isset( $alreadyTried[ $code ] ) ) {
 928                                         continue;
 929                                 }
 930
 931                                 $message = $this->getMsgFromNamespace(
 932                                         $this->getMessagePageName( $code, $uckey ), $code );
 933
 934                                 if ( $message !== false ) {
 935                                         return $message;
 936                                 }
 937                                 $alreadyTried[ $code ] = true;
 938                         }
 939                 }
 940
 941                 return false;
 942         }
 943
 944         /**
 945          * Get the message page name for a given language
 946          *
 947          * @param string $langcode
 948          * @param string $uckey Uppercase key for the message
 949          * @return string The page name
 950          */
 951         private function getMessagePageName( $langcode, $uckey ) {
 952                 global $wgLanguageCode;
 953
 954                 if ( $langcode === $wgLanguageCode ) {
 955                         // Messages created in the content language will not have the /lang extension
 956                         return $uckey;
 957                 } else {
 958                         return "$uckey/$langcode";
 959                 }
 960         }
 961
 962         /**
 963          * Get a message from the MediaWiki namespace, with caching. The key must
 964          * first be converted to two-part lang/msg form if necessary.
 965          *
 966          * Unlike self::get(), this function doesn't resolve fallback chains, and
 967          * some callers require this behavior. LanguageConverter::parseCachedTable()
 968          * and self::get() are some examples in core.
 969          *
 970          * @param string $title Message cache key with initial uppercase letter.
 971          * @param string $code Code denoting the language to try.
 972          * @return string|bool The message, or false if it does not exist or on error
 973          */
 974         public function getMsgFromNamespace( $title, $code ) {
 975                 $this->load( $code );
 976
 977                 if ( isset( $this->mCache[$code][$title] ) ) {
 978                         $entry = $this->mCache[$code][$title];
 979                         if ( substr( $entry, 0, 1 ) === ' ' ) {
 980                                 // The message exists, so make sure a string is returned.
 981                                 return (string)substr( $entry, 1 );
 982                         } elseif ( $entry === '!NONEXISTENT' ) {
 983                                 return false;
 984                         } elseif ( $entry === '!TOO BIG' ) {
 985                                 // Fall through and try invididual message cache below
 986                         }
 987                 } else {
 988                         // XXX: This is not cached in process cache, should it?
 989                         $message = false;
 990                         Hooks::run( 'MessagesPreLoad', [ $title, &$message, $code ] );
 991                         if ( $message !== false ) {
 992                                 return $message;
 993                         }
 994
 995                         return false;
 996                 }
 997
 998                 // Try the individual message cache
 999                 $titleKey = $this->wanCache->makeKey( 'messages-big', $this->mCache[$code]['HASH'], $title );
1000
1001                 if ( $this->mCacheVolatile[$code] ) {
1002                         $entry = false;
1003                         // Make sure that individual keys respect the WAN cache holdoff period too
1004                         LoggerFactory::getInstance( 'MessageCache' )->debug(
1005                                 __METHOD__ . ': loading volatile key \'{titleKey}\'',
1006                                 [ 'titleKey' => $titleKey, 'code' => $code ] );
1007                 } else {
1008                         $entry = $this->wanCache->get( $titleKey );
1009                 }
1010
1011                 if ( $entry !== false ) {
1012                         if ( substr( $entry, 0, 1 ) === ' ' ) {
1013                                 $this->mCache[$code][$title] = $entry;
1014                                 // The message exists, so make sure a string is returned
1015                                 return (string)substr( $entry, 1 );
1016                         } elseif ( $entry === '!NONEXISTENT' ) {
1017                                 $this->mCache[$code][$title] = '!NONEXISTENT';
1018
1019                                 return false;
1020                         } else {
1021                                 // Corrupt/obsolete entry, delete it
1022                                 $this->wanCache->delete( $titleKey );
1023                         }
1024                 }
1025
1026                 // Try loading the message from the database
1027                 $dbr = wfGetDB( DB_REPLICA );
1028                 $cacheOpts = Database::getCacheSetOptions( $dbr );
1029                 // Use newKnownCurrent() to avoid querying revision/user tables
1030                 $titleObj = Title::makeTitle( NS_MEDIAWIKI, $title );
1031                 if ( $titleObj->getLatestRevID() ) {
1032                         $revision = Revision::newKnownCurrent(
1033                                 $dbr,
1034                                 $titleObj->getArticleID(),
1035                                 $titleObj->getLatestRevID()
1036                         );
1037                 } else {
1038                         $revision = false;
1039                 }
1040
1041                 if ( $revision ) {
1042                         $content = $revision->getContent();
1043                         if ( $content ) {
1044                                 $message = $this->getMessageTextFromContent( $content );
1045                                 if ( is_string( $message ) ) {
1046                                         $this->mCache[$code][$title] = ' ' . $message;
1047                                         $this->wanCache->set( $titleKey, ' ' . $message, $this->mExpiry, $cacheOpts );
1048                                 }
1049                         } else {
1050                                 // A possibly temporary loading failure
1051                                 LoggerFactory::getInstance( 'MessageCache' )->warning(
1052                                         __METHOD__ . ': failed to load message page text for \'{titleKey}\'',
1053                                         [ 'titleKey' => $titleKey, 'code' => $code ] );
1054                                 $message = null; // no negative caching
1055                         }
1056                 } else {
1057                         $message = false; // negative caching
1058                 }
1059
1060                 if ( $message === false ) { // negative caching
1061                         $this->mCache[$code][$title] = '!NONEXISTENT';
1062                         $this->wanCache->set( $titleKey, '!NONEXISTENT', $this->mExpiry, $cacheOpts );
1063                 }
1064
1065                 return $message;
1066         }
1067
1068         /**
1069          * @param string $message
1070          * @param bool $interface
1071          * @param string $language Language code
1072          * @param Title $title
1073          * @return string
1074          */
1075         function transform( $message, $interface = false, $language = null, $title = null ) {
1076                 // Avoid creating parser if nothing to transform
1077                 if ( strpos( $message, '{{' ) === false ) {
1078                         return $message;
1079                 }
1080
1081                 if ( $this->mInParser ) {
1082                         return $message;
1083                 }
1084
1085                 $parser = $this->getParser();
1086                 if ( $parser ) {
1087                         $popts = $this->getParserOptions();
1088                         $popts->setInterfaceMessage( $interface );
1089                         $popts->setTargetLanguage( $language );
1090
1091                         $userlang = $popts->setUserLang( $language );
1092                         $this->mInParser = true;
1093                         $message = $parser->transformMsg( $message, $popts, $title );
1094                         $this->mInParser = false;
1095                         $popts->setUserLang( $userlang );
1096                 }
1097
1098                 return $message;
1099         }
1100
1101         /**
1102          * @return Parser
1103          */
1104         function getParser() {
1105                 global $wgParser, $wgParserConf;
1106
1107                 if ( !$this->mParser && isset( $wgParser ) ) {
1108                         # Do some initialisation so that we don't have to do it twice
1109                         $wgParser->firstCallInit();
1110                         # Clone it and store it
1111                         $class = $wgParserConf['class'];
1112                         if ( $class == 'ParserDiffTest' ) {
1113                                 # Uncloneable
1114                                 $this->mParser = new $class( $wgParserConf );
1115                         } else {
1116                                 $this->mParser = clone $wgParser;
1117                         }
1118                 }
1119
1120                 return $this->mParser;
1121         }
1122
1123         /**
1124          * @param string $text
1125          * @param Title $title
1126          * @param bool $linestart Whether or not this is at the start of a line
1127          * @param bool $interface Whether this is an interface message
1128          * @param Language|string $language Language code
1129          * @return ParserOutput|string
1130          */
1131         public function parse( $text, $title = null, $linestart = true,
1132                 $interface = false, $language = null
1133         ) {
1134                 global $wgTitle;
1135
1136                 if ( $this->mInParser ) {
1137                         return htmlspecialchars( $text );
1138                 }
1139
1140                 $parser = $this->getParser();
1141                 $popts = $this->getParserOptions();
1142                 $popts->setInterfaceMessage( $interface );
1143
1144                 if ( is_string( $language ) ) {
1145                         $language = Language::factory( $language );
1146                 }
1147                 $popts->setTargetLanguage( $language );
1148
1149                 if ( !$title || !$title instanceof Title ) {
1150                         wfDebugLog( 'GlobalTitleFail', __METHOD__ . ' called by ' .
1151                                 wfGetAllCallers( 6 ) . ' with no title set.' );
1152                         $title = $wgTitle;
1153                 }
1154                 // Sometimes $wgTitle isn't set either...
1155                 if ( !$title ) {
1156                         # It's not uncommon having a null $wgTitle in scripts. See r80898
1157                         # Create a ghost title in such case
1158                         $title = Title::makeTitle( NS_SPECIAL, 'Badtitle/title not set in ' . __METHOD__ );
1159                 }
1160
1161                 $this->mInParser = true;
1162                 $res = $parser->parse( $text, $title, $popts, $linestart );
1163                 $this->mInParser = false;
1164
1165                 return $res;
1166         }
1167
1168         function disable() {
1169                 $this->mDisable = true;
1170         }
1171
1172         function enable() {
1173                 $this->mDisable = false;
1174         }
1175
1176         /**
1177          * Whether DB/cache usage is disabled for determining messages
1178          *
1179          * If so, this typically indicates either:
1180          *   - a) load() failed to find a cached copy nor query the DB
1181          *   - b) we are in a special context or error mode that cannot use the DB
1182          * If the DB is ignored, any derived HTML output or cached objects may be wrong.
1183          * To avoid long-term cache pollution, TTLs can be adjusted accordingly.
1184          *
1185          * @return bool
1186          * @since 1.27
1187          */
1188         public function isDisabled() {
1189                 return $this->mDisable;
1190         }
1191
1192         /**
1193          * Clear all stored messages. Mainly used after a mass rebuild.
1194          */
1195         function clear() {
1196                 $langs = Language::fetchLanguageNames( null, 'mw' );
1197                 foreach ( array_keys( $langs ) as $code ) {
1198                         # Global and local caches
1199                         $this->wanCache->touchCheckKey( wfMemcKey( 'messages', $code ) );
1200                 }
1201
1202                 $this->mLoadedLanguages = [];
1203         }
1204
1205         /**
1206          * @param string $key
1207          * @return array
1208          */
1209         public function figureMessage( $key ) {
1210                 global $wgLanguageCode;
1211
1212                 $pieces = explode( '/', $key );
1213                 if ( count( $pieces ) < 2 ) {
1214                         return [ $key, $wgLanguageCode ];
1215                 }
1216
1217                 $lang = array_pop( $pieces );
1218                 if ( !Language::fetchLanguageName( $lang, null, 'mw' ) ) {
1219                         return [ $key, $wgLanguageCode ];
1220                 }
1221
1222                 $message = implode( '/', $pieces );
1223
1224                 return [ $message, $lang ];
1225         }
1226
1227         /**
1228          * Get all message keys stored in the message cache for a given language.
1229          * If $code is the content language code, this will return all message keys
1230          * for which MediaWiki:msgkey exists. If $code is another language code, this
1231          * will ONLY return message keys for which MediaWiki:msgkey/$code exists.
1232          * @param string $code Language code
1233          * @return array Array of message keys (strings)
1234          */
1235         public function getAllMessageKeys( $code ) {
1236                 global $wgContLang;
1237
1238                 $this->load( $code );
1239                 if ( !isset( $this->mCache[$code] ) ) {
1240                         // Apparently load() failed
1241                         return null;
1242                 }
1243                 // Remove administrative keys
1244                 $cache = $this->mCache[$code];
1245                 unset( $cache['VERSION'] );
1246                 unset( $cache['EXPIRY'] );
1247                 unset( $cache['EXCESSIVE'] );
1248                 // Remove any !NONEXISTENT keys
1249                 $cache = array_diff( $cache, [ '!NONEXISTENT' ] );
1250
1251                 // Keys may appear with a capital first letter. lcfirst them.
1252                 return array_map( [ $wgContLang, 'lcfirst' ], array_keys( $cache ) );
1253         }
1254
1255         /**
1256          * Purge message caches when a MediaWiki: page is created, updated, or deleted
1257          *
1258          * @param Title $title Message page title
1259          * @param Content|null $content New content for edit/create, null on deletion
1260          * @since 1.29
1261          */
1262         public function updateMessageOverride( Title $title, Content $content = null ) {
1263                 global $wgContLang;
1264
1265                 $msgText = $this->getMessageTextFromContent( $content );
1266                 if ( $msgText === null ) {
1267                         $msgText = false; // treat as not existing
1268                 }
1269
1270                 $this->replace( $title->getDBkey(), $msgText );
1271
1272                 if ( $wgContLang->hasVariants() ) {
1273                         $wgContLang->updateConversionTable( $title );
1274                 }
1275         }
1276
1277         /**
1278          * @param Content|null $content Content or null if the message page does not exist
1279          * @return string|bool|null Returns false if $content is null and null on error
1280          */
1281         private function getMessageTextFromContent( Content $content = null ) {
1282                 // @TODO: could skip pseudo-messages like js/css here, based on content model
1283                 if ( $content ) {
1284                         // Message page exists...
1285                         // XXX: Is this the right way to turn a Content object into a message?
1286                         // NOTE: $content is typically either WikitextContent, JavaScriptContent or
1287                         //       CssContent. MessageContent is *not* used for storing messages, it's
1288                         //       only used for wrapping them when needed.
1289                         $msgText = $content->getWikitextForTransclusion();
1290                         if ( $msgText === false || $msgText === null ) {
1291                                 // This might be due to some kind of misconfiguration...
1292                                 $msgText = null;
1293                                 LoggerFactory::getInstance( 'MessageCache' )->warning(
1294                                         __METHOD__ . ": message content doesn't provide wikitext "
1295                                         . "(content model: " . $content->getModel() . ")" );
1296                         }
1297                 } else {
1298                         // Message page does not exist...
1299                         $msgText = false;
1300                 }
1301
1302                 return $msgText;
1303         }
1304 }