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 use Wikimedia\Rdbms\Database;
  27
  28 /**
  29  * MediaWiki message cache structure version.
  30  * Bump this whenever the message cache format has changed.
  31  */
  32 define( 'MSG_CACHE_VERSION', 2 );
  33
  34 /**
  35  * Message cache
  36  * Performs various MediaWiki namespace-related functions
  37  * @ingroup Cache
  38  */
  39 class MessageCache {
  40         const FOR_UPDATE = 1; // force message reload
  41
  42         /** How long to wait for memcached locks */
  43         const WAIT_SEC = 15;
  44         /** How long memcached locks last */
  45         const LOCK_TTL = 30;
  46
  47         /**
  48          * Process local cache of loaded messages that are defined in
  49          * MediaWiki namespace. First array level is a language code,
  50          * second level is message key and the values are either message
  51          * content prefixed with space, or !NONEXISTENT for negative
  52          * caching.
  53          * @var array $mCache
  54          */
  55         protected $mCache;
  56
  57         /**
  58          * @var bool[] Map of (language code => boolean)
  59          */
  60         protected $mCacheVolatile = [];
  61
  62         /**
  63          * Should mean that database cannot be used, but check
  64          * @var bool $mDisable
  65          */
  66         protected $mDisable;
  67
  68         /**
  69          * Lifetime for cache, used by object caching.
  70          * Set on construction, see __construct().
  71          */
  72         protected $mExpiry;
  73
  74         /**
  75          * Message cache has its own parser which it uses to transform messages
  76          * @var ParserOptions
  77          */
  78         protected $mParserOptions;
  79         /** @var Parser */
  80         protected $mParser;
  81
  82         /**
  83          * Variable for tracking which variables are already loaded
  84          * @var array $mLoadedLanguages
  85          */
  86         protected $mLoadedLanguages = [];
  87
  88         /**
  89          * @var bool $mInParser
  90          */
  91         protected $mInParser = false;
  92
  93         /** @var WANObjectCache */
  94         protected $wanCache;
  95         /** @var BagOStuff */
  96         protected $clusterCache;
  97         /** @var BagOStuff */
  98         protected $srvCache;
  99
 100         /**
 101          * Singleton instance
 102          *
 103          * @var MessageCache $instance
 104          */
 105         private static $instance;
 106
 107         /**
 108          * Get the signleton instance of this class
 109          *
 110          * @since 1.18
 111          * @return MessageCache
 112          */
 113         public static function singleton() {
 114                 if ( self::$instance === null ) {
 115                         global $wgUseDatabaseMessages, $wgMsgCacheExpiry, $wgUseLocalMessageCache;
 116                         self::$instance = new self(
 117                                 MediaWikiServices::getInstance()->getMainWANObjectCache(),
 118                                 wfGetMessageCacheStorage(),
 119                                 $wgUseLocalMessageCache
 120                                         ? MediaWikiServices::getInstance()->getLocalServerObjectCache()
 121                                         : new EmptyBagOStuff(),
 122                                 $wgUseDatabaseMessages,
 123                                 $wgMsgCacheExpiry
 124                         );
 125                 }
 126
 127                 return self::$instance;
 128         }
 129
 130         /**
 131          * Destroy the singleton instance
 132          *
 133          * @since 1.18
 134          */
 135         public static function destroyInstance() {
 136                 self::$instance = null;
 137         }
 138
 139         /**
 140          * Normalize message key input
 141          *
 142          * @param string $key Input message key to be normalized
 143          * @return string Normalized message key
 144          */
 145         public static function normalizeKey( $key ) {
 146                 global $wgContLang;
 147
 148                 $lckey = strtr( $key, ' ', '_' );
 149                 if ( ord( $lckey ) < 128 ) {
 150                         $lckey[0] = strtolower( $lckey[0] );
 151                 } else {
 152                         $lckey = $wgContLang->lcfirst( $lckey );
 153                 }
 154
 155                 return $lckey;
 156         }
 157
 158         /**
 159          * @param WANObjectCache $wanCache WAN cache instance
 160          * @param BagOStuff $clusterCache Cluster cache instance
 161          * @param BagOStuff $srvCache Server cache instance
 162          * @param bool $useDB Whether to look for message overrides (e.g. MediaWiki: pages)
 163          * @param int $expiry Lifetime for cache. @see $mExpiry.
 164          */
 165         public function __construct(
 166                 WANObjectCache $wanCache,
 167                 BagOStuff $clusterCache,
 168                 BagOStuff $srvCache,
 169                 $useDB,
 170                 $expiry
 171         ) {
 172                 $this->wanCache = $wanCache;
 173                 $this->clusterCache = $clusterCache;
 174                 $this->srvCache = $srvCache;
 175
 176                 $this->mDisable = !$useDB;
 177                 $this->mExpiry = $expiry;
 178         }
 179
 180         /**
 181          * ParserOptions is lazy initialised.
 182          *
 183          * @return ParserOptions
 184          */
 185         function getParserOptions() {
 186                 global $wgUser;
 187
 188                 if ( !$this->mParserOptions ) {
 189                         if ( !$wgUser->isSafeToLoad() ) {
 190                                 // $wgUser isn't unstubbable yet, so don't try to get a
 191                                 // ParserOptions for it. And don't cache this ParserOptions
 192                                 // either.
 193                                 $po = ParserOptions::newFromAnon();
 194                                 $po->setEditSection( false );
 195                                 $po->setAllowUnsafeRawHtml( false );
 196                                 $po->setWrapOutputClass( false );
 197                                 return $po;
 198                         }
 199
 200                         $this->mParserOptions = new ParserOptions;
 201                         $this->mParserOptions->setEditSection( false );
 202                         // Messages may take parameters that could come
 203                         // from malicious sources. As a precaution, disable
 204                         // the <html> parser tag when parsing messages.
 205                         $this->mParserOptions->setAllowUnsafeRawHtml( false );
 206                         // Wrapping messages in an extra <div> is probably not expected. If
 207                         // they're outside the content area they probably shouldn't be
 208                         // targeted by CSS that's targeting the parser output, and if
 209                         // they're inside they already are from the outer div.
 210                         $this->mParserOptions->setWrapOutputClass( false );
 211                 }
 212
 213                 return $this->mParserOptions;
 214         }
 215
 216         /**
 217          * Try to load the cache from APC.
 218          *
 219          * @param string $code Optional language code, see documenation of load().
 220          * @return array|bool The cache array, or false if not in cache.
 221          */
 222         protected function getLocalCache( $code ) {
 223                 $cacheKey = $this->srvCache->makeKey( __CLASS__, $code );
 224
 225                 return $this->srvCache->get( $cacheKey );
 226         }
 227
 228         /**
 229          * Save the cache to APC.
 230          *
 231          * @param string $code
 232          * @param array $cache The cache array
 233          */
 234         protected function saveToLocalCache( $code, $cache ) {
 235                 $cacheKey = $this->srvCache->makeKey( __CLASS__, $code );
 236                 $this->srvCache->set( $cacheKey, $cache );
 237         }
 238
 239         /**
 240          * Loads messages from caches or from database in this order:
 241          * (1) local message cache (if $wgUseLocalMessageCache is enabled)
 242          * (2) memcached
 243          * (3) from the database.
 244          *
 245          * When succesfully loading from (2) or (3), all higher level caches are
 246          * updated for the newest version.
 247          *
 248          * Nothing is loaded if member variable mDisable is true, either manually
 249          * set by calling code or if message loading fails (is this possible?).
 250          *
 251          * Returns true if cache is already populated or it was succesfully populated,
 252          * or false if populating empty cache fails. Also returns true if MessageCache
 253          * is disabled.
 254          *
 255          * @param string $code Language to which load messages
 256          * @param int $mode Use MessageCache::FOR_UPDATE to skip process cache [optional]
 257          * @throws MWException
 258          * @return bool
 259          */
 260         protected function load( $code, $mode = null ) {
 261                 if ( !is_string( $code ) ) {
 262                         throw new InvalidArgumentException( "Missing language code" );
 263                 }
 264
 265                 # Don't do double loading...
 266                 if ( isset( $this->mLoadedLanguages[$code] ) && $mode != self::FOR_UPDATE ) {
 267                         return true;
 268                 }
 269
 270                 # 8 lines of code just to say (once) that message cache is disabled
 271                 if ( $this->mDisable ) {
 272                         static $shownDisabled = false;
 273                         if ( !$shownDisabled ) {
 274                                 wfDebug( __METHOD__ . ": disabled\n" );
 275                                 $shownDisabled = true;
 276                         }
 277
 278                         return true;
 279                 }
 280
 281                 # Loading code starts
 282                 $success = false; # Keep track of success
 283                 $staleCache = false; # a cache array with expired data, or false if none has been loaded
 284                 $where = []; # Debug info, delayed to avoid spamming debug log too much
 285
 286                 # Hash of the contents is stored in memcache, to detect if data-center cache
 287                 # or local cache goes out of date (e.g. due to replace() on some other server)
 288                 list( $hash, $hashVolatile ) = $this->getValidationHash( $code );
 289                 $this->mCacheVolatile[$code] = $hashVolatile;
 290
 291                 # Try the local cache and check against the cluster hash key...
 292                 $cache = $this->getLocalCache( $code );
 293                 if ( !$cache ) {
 294                         $where[] = 'local cache is empty';
 295                 } elseif ( !isset( $cache['HASH'] ) || $cache['HASH'] !== $hash ) {
 296                         $where[] = 'local cache has the wrong hash';
 297                         $staleCache = $cache;
 298                 } elseif ( $this->isCacheExpired( $cache ) ) {
 299                         $where[] = 'local cache is expired';
 300                         $staleCache = $cache;
 301                 } elseif ( $hashVolatile ) {
 302                         $where[] = 'local cache validation key is expired/volatile';
 303                         $staleCache = $cache;
 304                 } else {
 305                         $where[] = 'got from local cache';
 306                         $success = true;
 307                         $this->mCache[$code] = $cache;
 308                 }
 309
 310                 if ( !$success ) {
 311                         $cacheKey = $this->clusterCache->makeKey( 'messages', $code ); # Key in memc for messages
 312                         # Try the global cache. If it is empty, try to acquire a lock. If
 313                         # the lock can't be acquired, wait for the other thread to finish
 314                         # and then try the global cache a second time.
 315                         for ( $failedAttempts = 0; $failedAttempts <= 1; $failedAttempts++ ) {
 316                                 if ( $hashVolatile && $staleCache ) {
 317                                         # Do not bother fetching the whole cache blob to avoid I/O.
 318                                         # Instead, just try to get the non-blocking $statusKey lock
 319                                         # below, and use the local stale value if it was not acquired.
 320                                         $where[] = 'global cache is presumed expired';
 321                                 } else {
 322                                         $cache = $this->clusterCache->get( $cacheKey );
 323                                         if ( !$cache ) {
 324                                                 $where[] = 'global cache is empty';
 325                                         } elseif ( $this->isCacheExpired( $cache ) ) {
 326                                                 $where[] = 'global cache is expired';
 327                                                 $staleCache = $cache;
 328                                         } elseif ( $hashVolatile ) {
 329                                                 # DB results are replica DB lag prone until the holdoff TTL passes.
 330                                                 # By then, updates should be reflected in loadFromDBWithLock().
 331                                                 # One thread renerates the cache while others use old values.
 332                                                 $where[] = 'global cache is expired/volatile';
 333                                                 $staleCache = $cache;
 334                                         } else {
 335                                                 $where[] = 'got from global cache';
 336                                                 $this->mCache[$code] = $cache;
 337                                                 $this->saveToCaches( $cache, 'local-only', $code );
 338                                                 $success = true;
 339                                         }
 340                                 }
 341
 342                                 if ( $success ) {
 343                                         # Done, no need to retry
 344                                         break;
 345                                 }
 346
 347                                 # We need to call loadFromDB. Limit the concurrency to one process.
 348                                 # This prevents the site from going down when the cache expires.
 349                                 # Note that the DB slam protection lock here is non-blocking.
 350                                 $loadStatus = $this->loadFromDBWithLock( $code, $where, $mode );
 351                                 if ( $loadStatus === true ) {
 352                                         $success = true;
 353                                         break;
 354                                 } elseif ( $staleCache ) {
 355                                         # Use the stale cache while some other thread constructs the new one
 356                                         $where[] = 'using stale cache';
 357                                         $this->mCache[$code] = $staleCache;
 358                                         $success = true;
 359                                         break;
 360                                 } elseif ( $failedAttempts > 0 ) {
 361                                         # Already blocked once, so avoid another lock/unlock cycle.
 362                                         # This case will typically be hit if memcached is down, or if
 363                                         # loadFromDB() takes longer than LOCK_WAIT.
 364                                         $where[] = "could not acquire status key.";
 365                                         break;
 366                                 } elseif ( $loadStatus === 'cantacquire' ) {
 367                                         # Wait for the other thread to finish, then retry. Normally,
 368                                         # the memcached get() will then yeild the other thread's result.
 369                                         $where[] = 'waited for other thread to complete';
 370                                         $this->getReentrantScopedLock( $cacheKey );
 371                                 } else {
 372                                         # Disable cache; $loadStatus is 'disabled'
 373                                         break;
 374                                 }
 375                         }
 376                 }
 377
 378                 if ( !$success ) {
 379                         $where[] = 'loading FAILED - cache is disabled';
 380                         $this->mDisable = true;
 381                         $this->mCache = false;
 382                         wfDebugLog( 'MessageCacheError', __METHOD__ . ": Failed to load $code\n" );
 383                         # This used to throw an exception, but that led to nasty side effects like
 384                         # the whole wiki being instantly down if the memcached server died
 385                 } else {
 386                         # All good, just record the success
 387                         $this->mLoadedLanguages[$code] = true;
 388                 }
 389
 390                 $info = implode( ', ', $where );
 391                 wfDebugLog( 'MessageCache', __METHOD__ . ": Loading $code... $info\n" );
 392
 393                 return $success;
 394         }
 395
 396         /**
 397          * @param string $code
 398          * @param array &$where List of wfDebug() comments
 399          * @param int $mode Use MessageCache::FOR_UPDATE to use DB_MASTER
 400          * @return bool|string True on success or one of ("cantacquire", "disabled")
 401          */
 402         protected function loadFromDBWithLock( $code, array &$where, $mode = null ) {
 403                 # If cache updates on all levels fail, give up on message overrides.
 404                 # This is to avoid easy site outages; see $saveSuccess comments below.
 405                 $statusKey = $this->clusterCache->makeKey( 'messages', $code, 'status' );
 406                 $status = $this->clusterCache->get( $statusKey );
 407                 if ( $status === 'error' ) {
 408                         $where[] = "could not load; method is still globally disabled";
 409                         return 'disabled';
 410                 }
 411
 412                 # Now let's regenerate
 413                 $where[] = 'loading from database';
 414
 415                 # Lock the cache to prevent conflicting writes.
 416                 # This lock is non-blocking so stale cache can quickly be used.
 417                 # Note that load() will call a blocking getReentrantScopedLock()
 418                 # after this if it really need to wait for any current thread.
 419                 $cacheKey = $this->clusterCache->makeKey( 'messages', $code );
 420                 $scopedLock = $this->getReentrantScopedLock( $cacheKey, 0 );
 421                 if ( !$scopedLock ) {
 422                         $where[] = 'could not acquire main lock';
 423                         return 'cantacquire';
 424                 }
 425
 426                 $cache = $this->loadFromDB( $code, $mode );
 427                 $this->mCache[$code] = $cache;
 428                 $saveSuccess = $this->saveToCaches( $cache, 'all', $code );
 429
 430                 if ( !$saveSuccess ) {
 431                         /**
 432                          * Cache save has failed.
 433                          *
 434                          * There are two main scenarios where this could be a problem:
 435                          * - The cache is more than the maximum size (typically 1MB compressed).
 436                          * - Memcached has no space remaining in the relevant slab class. This is
 437                          *   unlikely with recent versions of memcached.
 438                          *
 439                          * Either way, if there is a local cache, nothing bad will happen. If there
 440                          * is no local cache, disabling the message cache for all requests avoids
 441                          * incurring a loadFromDB() overhead on every request, and thus saves the
 442                          * wiki from complete downtime under moderate traffic conditions.
 443                          */
 444                         if ( $this->srvCache instanceof EmptyBagOStuff ) {
 445                                 $this->clusterCache->set( $statusKey, 'error', 60 * 5 );
 446                                 $where[] = 'could not save cache, disabled globally for 5 minutes';
 447                         } else {
 448                                 $where[] = "could not save global cache";
 449                         }
 450                 }
 451
 452                 return true;
 453         }
 454
 455         /**
 456          * Loads cacheable messages from the database. Messages bigger than
 457          * $wgMaxMsgCacheEntrySize are assigned a special value, and are loaded
 458          * on-demand from the database later.
 459          *
 460          * @param string $code Language code
 461          * @param int $mode Use MessageCache::FOR_UPDATE to skip process cache
 462          * @return array Loaded messages for storing in caches
 463          */
 464         protected function loadFromDB( $code, $mode = null ) {
 465                 global $wgMaxMsgCacheEntrySize, $wgLanguageCode, $wgAdaptiveMessageCache;
 466
 467                 // (T164666) The query here performs really poorly on WMF's
 468                 // contributions replicas. We don't have a way to say "any group except
 469                 // contributions", so for the moment let's specify 'api'.
 470                 // @todo: Get rid of this hack.
 471                 $dbr = wfGetDB( ( $mode == self::FOR_UPDATE ) ? DB_MASTER : DB_REPLICA, 'api' );
 472
 473                 $cache = [];
 474
 475                 # Common conditions
 476                 $conds = [
 477                         'page_is_redirect' => 0,
 478                         'page_namespace' => NS_MEDIAWIKI,
 479                 ];
 480
 481                 $mostused = [];
 482                 if ( $wgAdaptiveMessageCache && $code !== $wgLanguageCode ) {
 483                         if ( !isset( $this->mCache[$wgLanguageCode] ) ) {
 484                                 $this->load( $wgLanguageCode );
 485                         }
 486                         $mostused = array_keys( $this->mCache[$wgLanguageCode] );
 487                         foreach ( $mostused as $key => $value ) {
 488                                 $mostused[$key] = "$value/$code";
 489                         }
 490                 }
 491
 492                 if ( count( $mostused ) ) {
 493                         $conds['page_title'] = $mostused;
 494                 } elseif ( $code !== $wgLanguageCode ) {
 495                         $conds[] = 'page_title' . $dbr->buildLike( $dbr->anyString(), '/', $code );
 496                 } else {
 497                         # Effectively disallows use of '/' character in NS_MEDIAWIKI for uses
 498                         # other than language code.
 499                         $conds[] = 'page_title NOT' .
 500                                 $dbr->buildLike( $dbr->anyString(), '/', $dbr->anyString() );
 501                 }
 502
 503                 # Conditions to fetch oversized pages to ignore them
 504                 $bigConds = $conds;
 505                 $bigConds[] = 'page_len > ' . intval( $wgMaxMsgCacheEntrySize );
 506
 507                 # Load titles for all oversized pages in the MediaWiki namespace
 508                 $res = $dbr->select(
 509                         'page',
 510                         [ 'page_title', 'page_latest' ],
 511                         $bigConds,
 512                         __METHOD__ . "($code)-big"
 513                 );
 514                 foreach ( $res as $row ) {
 515                         $cache[$row->page_title] = '!TOO BIG';
 516                         // At least include revision ID so page changes are reflected in the hash
 517                         $cache['EXCESSIVE'][$row->page_title] = $row->page_latest;
 518                 }
 519
 520                 # Conditions to load the remaining pages with their contents
 521                 $smallConds = $conds;
 522                 $smallConds[] = 'page_len <= ' . intval( $wgMaxMsgCacheEntrySize );
 523
 524                 $res = $dbr->select(
 525                         [ 'page', 'revision', 'text' ],
 526                         [ 'page_title', 'old_id', 'old_text', 'old_flags' ],
 527                         $smallConds,
 528                         __METHOD__ . "($code)-small",
 529                         [],
 530                         [
 531                                 'revision' => [ 'JOIN', 'page_latest=rev_id' ],
 532                                 'text' => [ 'JOIN', 'rev_text_id=old_id' ],
 533                         ]
 534                 );
 535
 536                 foreach ( $res as $row ) {
 537                         $text = Revision::getRevisionText( $row );
 538                         if ( $text === false ) {
 539                                 // Failed to fetch data; possible ES errors?
 540                                 // Store a marker to fetch on-demand as a workaround...
 541                                 // TODO Use a differnt marker
 542                                 $entry = '!TOO BIG';
 543                                 wfDebugLog(
 544                                         'MessageCache',
 545                                         __METHOD__
 546                                         . ": failed to load message page text for {$row->page_title} ($code)"
 547                                 );
 548                         } else {
 549                                 $entry = ' ' . $text;
 550                         }
 551                         $cache[$row->page_title] = $entry;
 552                 }
 553
 554                 $cache['VERSION'] = MSG_CACHE_VERSION;
 555                 ksort( $cache );
 556
 557                 # Hash for validating local cache (APC). No need to take into account
 558                 # messages larger than $wgMaxMsgCacheEntrySize, since those are only
 559                 # stored and fetched from memcache.
 560                 $cache['HASH'] = md5( serialize( $cache ) );
 561                 $cache['EXPIRY'] = wfTimestamp( TS_MW, time() + $this->mExpiry );
 562
 563                 return $cache;
 564         }
 565
 566         /**
 567          * Updates cache as necessary when message page is changed
 568          *
 569          * @param string $title Message cache key with initial uppercase letter
 570          * @param string|bool $text New contents of the page (false if deleted)
 571          */
 572         public function replace( $title, $text ) {
 573                 global $wgLanguageCode;
 574
 575                 if ( $this->mDisable ) {
 576                         return;
 577                 }
 578
 579                 list( $msg, $code ) = $this->figureMessage( $title );
 580                 if ( strpos( $title, '/' ) !== false && $code === $wgLanguageCode ) {
 581                         // Content language overrides do not use the /<code> suffix
 582                         return;
 583                 }
 584
 585                 // (a) Update the process cache with the new message text
 586                 if ( $text === false ) {
 587                         // Page deleted
 588                         $this->mCache[$code][$title] = '!NONEXISTENT';
 589                 } else {
 590                         // Ignore $wgMaxMsgCacheEntrySize so the process cache is up to date
 591                         $this->mCache[$code][$title] = ' ' . $text;
 592                 }
 593
 594                 // (b) Update the shared caches in a deferred update with a fresh DB snapshot
 595                 DeferredUpdates::addCallableUpdate(
 596                         function () use ( $title, $msg, $code ) {
 597                                 global $wgContLang, $wgMaxMsgCacheEntrySize;
 598                                 // Allow one caller at a time to avoid race conditions
 599                                 $scopedLock = $this->getReentrantScopedLock(
 600                                         $this->clusterCache->makeKey( 'messages', $code )
 601                                 );
 602                                 if ( !$scopedLock ) {
 603                                         LoggerFactory::getInstance( 'MessageCache' )->error(
 604                                                 __METHOD__ . ': could not acquire lock to update {title} ({code})',
 605                                                 [ 'title' => $title, 'code' => $code ] );
 606                                         return;
 607                                 }
 608                                 // Load the messages from the master DB to avoid race conditions
 609                                 $cache = $this->loadFromDB( $code, self::FOR_UPDATE );
 610                                 $this->mCache[$code] = $cache;
 611                                 // Load the process cache values and set the per-title cache keys
 612                                 $page = WikiPage::factory( Title::makeTitle( NS_MEDIAWIKI, $title ) );
 613                                 $page->loadPageData( $page::READ_LATEST );
 614                                 $text = $this->getMessageTextFromContent( $page->getContent() );
 615                                 // Check if an individual cache key should exist and update cache accordingly
 616                                 if ( is_string( $text ) && strlen( $text ) > $wgMaxMsgCacheEntrySize ) {
 617                                         $titleKey = $this->bigMessageCacheKey( $this->mCache[$code]['HASH'], $title );
 618                                         $this->wanCache->set( $titleKey, ' ' . $text, $this->mExpiry );
 619                                 }
 620                                 // Mark this cache as definitely being "latest" (non-volatile) so
 621                                 // load() calls do try to refresh the cache with replica DB data
 622                                 $this->mCache[$code]['LATEST'] = time();
 623                                 // Pre-emptively update the local datacenter cache so things like edit filter and
 624                                 // blacklist changes are reflect immediately, as these often use MediaWiki: pages.
 625                                 // The datacenter handling replace() calls should be the same one handling edits
 626                                 // as they require HTTP POST.
 627                                 $this->saveToCaches( $this->mCache[$code], 'all', $code );
 628                                 // Release the lock now that the cache is saved
 629                                 ScopedCallback::consume( $scopedLock );
 630
 631                                 // Relay the purge. Touching this check key expires cache contents
 632                                 // and local cache (APC) validation hash across all datacenters.
 633                                 $this->wanCache->touchCheckKey( $this->wanCache->makeKey( 'messages', $code ) );
 634                                 // Also delete cached sidebar... just in case it is affected
 635                                 // @TODO: shouldn't this be $code === $wgLanguageCode?
 636                                 if ( $code === 'en' ) {
 637                                         // Purge all language sidebars, e.g. on ?action=purge to the sidebar messages
 638                                         $codes = array_keys( Language::fetchLanguageNames() );
 639                                 } else {
 640                                         // Purge only the sidebar for this language
 641                                         $codes = [ $code ];
 642                                 }
 643                                 foreach ( $codes as $code ) {
 644                                         $this->wanCache->delete( $this->wanCache->makeKey( 'sidebar', $code ) );
 645                                 }
 646
 647                                 // Purge the message in the message blob store
 648                                 $resourceloader = RequestContext::getMain()->getOutput()->getResourceLoader();
 649                                 $blobStore = $resourceloader->getMessageBlobStore();
 650                                 $blobStore->updateMessage( $wgContLang->lcfirst( $msg ) );
 651
 652                                 Hooks::run( 'MessageCacheReplace', [ $title, $text ] );
 653                         },
 654                         DeferredUpdates::PRESEND
 655                 );
 656         }
 657
 658         /**
 659          * Is the given cache array expired due to time passing or a version change?
 660          *
 661          * @param array $cache
 662          * @return bool
 663          */
 664         protected function isCacheExpired( $cache ) {
 665                 if ( !isset( $cache['VERSION'] ) || !isset( $cache['EXPIRY'] ) ) {
 666                         return true;
 667                 }
 668                 if ( $cache['VERSION'] != MSG_CACHE_VERSION ) {
 669                         return true;
 670                 }
 671                 if ( wfTimestampNow() >= $cache['EXPIRY'] ) {
 672                         return true;
 673                 }
 674
 675                 return false;
 676         }
 677
 678         /**
 679          * Shortcut to update caches.
 680          *
 681          * @param array $cache Cached messages with a version.
 682          * @param string $dest Either "local-only" to save to local caches only
 683          *   or "all" to save to all caches.
 684          * @param string|bool $code Language code (default: false)
 685          * @return bool
 686          */
 687         protected function saveToCaches( array $cache, $dest, $code = false ) {
 688                 if ( $dest === 'all' ) {
 689                         $cacheKey = $this->clusterCache->makeKey( 'messages', $code );
 690                         $success = $this->clusterCache->set( $cacheKey, $cache );
 691                         $this->setValidationHash( $code, $cache );
 692                 } else {
 693                         $success = true;
 694                 }
 695
 696                 $this->saveToLocalCache( $code, $cache );
 697
 698                 return $success;
 699         }
 700
 701         /**
 702          * Get the md5 used to validate the local APC cache
 703          *
 704          * @param string $code
 705          * @return array (hash or false, bool expiry/volatility status)
 706          */
 707         protected function getValidationHash( $code ) {
 708                 $curTTL = null;
 709                 $value = $this->wanCache->get(
 710                         $this->wanCache->makeKey( 'messages', $code, 'hash', 'v1' ),
 711                         $curTTL,
 712                         [ $this->wanCache->makeKey( 'messages', $code ) ]
 713                 );
 714
 715                 if ( $value ) {
 716                         $hash = $value['hash'];
 717                         if ( ( time() - $value['latest'] ) < WANObjectCache::TTL_MINUTE ) {
 718                                 // Cache was recently updated via replace() and should be up-to-date.
 719                                 // That method is only called in the primary datacenter and uses FOR_UPDATE.
 720                                 // Also, it is unlikely that the current datacenter is *now* secondary one.
 721                                 $expired = false;
 722                         } else {
 723                                 // See if the "check" key was bumped after the hash was generated
 724                                 $expired = ( $curTTL < 0 );
 725                         }
 726                 } else {
 727                         // No hash found at all; cache must regenerate to be safe
 728                         $hash = false;
 729                         $expired = true;
 730                 }
 731
 732                 return [ $hash, $expired ];
 733         }
 734
 735         /**
 736          * Set the md5 used to validate the local disk cache
 737          *
 738          * If $cache has a 'LATEST' UNIX timestamp key, then the hash will not
 739          * be treated as "volatile" by getValidationHash() for the next few seconds.
 740          * This is triggered when $cache is generated using FOR_UPDATE mode.
 741          *
 742          * @param string $code
 743          * @param array $cache Cached messages with a version
 744          */
 745         protected function setValidationHash( $code, array $cache ) {
 746                 $this->wanCache->set(
 747                         $this->wanCache->makeKey( 'messages', $code, 'hash', 'v1' ),
 748                         [
 749                                 'hash' => $cache['HASH'],
 750                                 'latest' => isset( $cache['LATEST'] ) ? $cache['LATEST'] : 0
 751                         ],
 752                         WANObjectCache::TTL_INDEFINITE
 753                 );
 754         }
 755
 756         /**
 757          * @param string $key A language message cache key that stores blobs
 758          * @param int $timeout Wait timeout in seconds
 759          * @return null|ScopedCallback
 760          */
 761         protected function getReentrantScopedLock( $key, $timeout = self::WAIT_SEC ) {
 762                 return $this->clusterCache->getScopedLock( $key, $timeout, self::LOCK_TTL, __METHOD__ );
 763         }
 764
 765         /**
 766          * Get a message from either the content language or the user language.
 767          *
 768          * First, assemble a list of languages to attempt getting the message from. This
 769          * chain begins with the requested language and its fallbacks and then continues with
 770          * the content language and its fallbacks. For each language in the chain, the following
 771          * process will occur (in this order):
 772          *  1. If a language-specific override, i.e., [[MW:msg/lang]], is available, use that.
 773          *     Note: for the content language, there is no /lang subpage.
 774          *  2. Fetch from the static CDB cache.
 775          *  3. If available, check the database for fallback language overrides.
 776          *
 777          * This process provides a number of guarantees. When changing this code, make sure all
 778          * of these guarantees are preserved.
 779          *  * If the requested language is *not* the content language, then the CDB cache for that
 780          *    specific language will take precedence over the root database page ([[MW:msg]]).
 781          *  * Fallbacks will be just that: fallbacks. A fallback language will never be reached if
 782          *    the message is available *anywhere* in the language for which it is a fallback.
 783          *
 784          * @param string $key The message key
 785          * @param bool $useDB If true, look for the message in the DB, false
 786          *   to use only the compiled l10n cache.
 787          * @param bool|string|object $langcode Code of the language to get the message for.
 788          *   - If string and a valid code, will create a standard language object
 789          *   - If string but not a valid code, will create a basic language object
 790          *   - If boolean and false, create object from the current users language
 791          *   - If boolean and true, create object from the wikis content language
 792          *   - If language object, use it as given
 793          * @param bool $isFullKey Specifies whether $key is a two part key "msg/lang".
 794          *
 795          * @throws MWException When given an invalid key
 796          * @return string|bool False if the message doesn't exist, otherwise the
 797          *   message (which can be empty)
 798          */
 799         function get( $key, $useDB = true, $langcode = true, $isFullKey = false ) {
 800                 if ( is_int( $key ) ) {
 801                         // Fix numerical strings that somehow become ints
 802                         // on their way here
 803                         $key = (string)$key;
 804                 } elseif ( !is_string( $key ) ) {
 805                         throw new MWException( 'Non-string key given' );
 806                 } elseif ( $key === '' ) {
 807                         // Shortcut: the empty key is always missing
 808                         return false;
 809                 }
 810
 811                 // For full keys, get the language code from the key
 812                 $pos = strrpos( $key, '/' );
 813                 if ( $isFullKey && $pos !== false ) {
 814                         $langcode = substr( $key, $pos + 1 );
 815                         $key = substr( $key, 0, $pos );
 816                 }
 817
 818                 // Normalise title-case input (with some inlining)
 819                 $lckey = self::normalizeKey( $key );
 820
 821                 Hooks::run( 'MessageCache::get', [ &$lckey ] );
 822
 823                 // Loop through each language in the fallback list until we find something useful
 824                 $lang = wfGetLangObj( $langcode );
 825                 $message = $this->getMessageFromFallbackChain(
 826                         $lang,
 827                         $lckey,
 828                         !$this->mDisable && $useDB
 829                 );
 830
 831                 // If we still have no message, maybe the key was in fact a full key so try that
 832                 if ( $message === false ) {
 833                         $parts = explode( '/', $lckey );
 834                         // We may get calls for things that are http-urls from sidebar
 835                         // Let's not load nonexistent languages for those
 836                         // They usually have more than one slash.
 837                         if ( count( $parts ) == 2 && $parts[1] !== '' ) {
 838                                 $message = Language::getMessageFor( $parts[0], $parts[1] );
 839                                 if ( $message === null ) {
 840                                         $message = false;
 841                                 }
 842                         }
 843                 }
 844
 845                 // Post-processing if the message exists
 846                 if ( $message !== false ) {
 847                         // Fix whitespace
 848                         $message = str_replace(
 849                                 [
 850                                         # Fix for trailing whitespace, removed by textarea
 851                                         '&#32;',
 852                                         # Fix for NBSP, converted to space by firefox
 853                                         '&nbsp;',
 854                                         '&#160;',
 855                                         '&shy;'
 856                                 ],
 857                                 [
 858                                         ' ',
 859                                         "\xc2\xa0",
 860                                         "\xc2\xa0",
 861                                         "\xc2\xad"
 862                                 ],
 863                                 $message
 864                         );
 865                 }
 866
 867                 return $message;
 868         }
 869
 870         /**
 871          * Given a language, try and fetch messages from that language.
 872          *
 873          * Will also consider fallbacks of that language, the site language, and fallbacks for
 874          * the site language.
 875          *
 876          * @see MessageCache::get
 877          * @param Language|StubObject $lang Preferred language
 878          * @param string $lckey Lowercase key for the message (as for localisation cache)
 879          * @param bool $useDB Whether to include messages from the wiki database
 880          * @return string|bool The message, or false if not found
 881          */
 882         protected function getMessageFromFallbackChain( $lang, $lckey, $useDB ) {
 883                 global $wgContLang;
 884
 885                 $alreadyTried = [];
 886
 887                 // First try the requested language.
 888                 $message = $this->getMessageForLang( $lang, $lckey, $useDB, $alreadyTried );
 889                 if ( $message !== false ) {
 890                         return $message;
 891                 }
 892
 893                 // Now try checking the site language.
 894                 $message = $this->getMessageForLang( $wgContLang, $lckey, $useDB, $alreadyTried );
 895                 return $message;
 896         }
 897
 898         /**
 899          * Given a language, try and fetch messages from that language and its fallbacks.
 900          *
 901          * @see MessageCache::get
 902          * @param Language|StubObject $lang Preferred language
 903          * @param string $lckey Lowercase key for the message (as for localisation cache)
 904          * @param bool $useDB Whether to include messages from the wiki database
 905          * @param bool[] $alreadyTried Contains true for each language that has been tried already
 906          * @return string|bool The message, or false if not found
 907          */
 908         private function getMessageForLang( $lang, $lckey, $useDB, &$alreadyTried ) {
 909                 global $wgContLang;
 910
 911                 $langcode = $lang->getCode();
 912
 913                 // Try checking the database for the requested language
 914                 if ( $useDB ) {
 915                         $uckey = $wgContLang->ucfirst( $lckey );
 916
 917                         if ( !isset( $alreadyTried[ $langcode ] ) ) {
 918                                 $message = $this->getMsgFromNamespace(
 919                                         $this->getMessagePageName( $langcode, $uckey ),
 920                                         $langcode
 921                                 );
 922
 923                                 if ( $message !== false ) {
 924                                         return $message;
 925                                 }
 926                                 $alreadyTried[ $langcode ] = true;
 927                         }
 928                 } else {
 929                         $uckey = null;
 930                 }
 931
 932                 // Check the CDB cache
 933                 $message = $lang->getMessage( $lckey );
 934                 if ( $message !== null ) {
 935                         return $message;
 936                 }
 937
 938                 // Try checking the database for all of the fallback languages
 939                 if ( $useDB ) {
 940                         $fallbackChain = Language::getFallbacksFor( $langcode );
 941
 942                         foreach ( $fallbackChain as $code ) {
 943                                 if ( isset( $alreadyTried[ $code ] ) ) {
 944                                         continue;
 945                                 }
 946
 947                                 $message = $this->getMsgFromNamespace(
 948                                         $this->getMessagePageName( $code, $uckey ), $code );
 949
 950                                 if ( $message !== false ) {
 951                                         return $message;
 952                                 }
 953                                 $alreadyTried[ $code ] = true;
 954                         }
 955                 }
 956
 957                 return false;
 958         }
 959
 960         /**
 961          * Get the message page name for a given language
 962          *
 963          * @param string $langcode
 964          * @param string $uckey Uppercase key for the message
 965          * @return string The page name
 966          */
 967         private function getMessagePageName( $langcode, $uckey ) {
 968                 global $wgLanguageCode;
 969
 970                 if ( $langcode === $wgLanguageCode ) {
 971                         // Messages created in the content language will not have the /lang extension
 972                         return $uckey;
 973                 } else {
 974                         return "$uckey/$langcode";
 975                 }
 976         }
 977
 978         /**
 979          * Get a message from the MediaWiki namespace, with caching. The key must
 980          * first be converted to two-part lang/msg form if necessary.
 981          *
 982          * Unlike self::get(), this function doesn't resolve fallback chains, and
 983          * some callers require this behavior. LanguageConverter::parseCachedTable()
 984          * and self::get() are some examples in core.
 985          *
 986          * @param string $title Message cache key with initial uppercase letter
 987          * @param string $code Code denoting the language to try
 988          * @return string|bool The message, or false if it does not exist or on error
 989          */
 990         public function getMsgFromNamespace( $title, $code ) {
 991                 $this->load( $code );
 992
 993                 if ( isset( $this->mCache[$code][$title] ) ) {
 994                         $entry = $this->mCache[$code][$title];
 995                         if ( substr( $entry, 0, 1 ) === ' ' ) {
 996                                 // The message exists, so make sure a string is returned.
 997                                 return (string)substr( $entry, 1 );
 998                         } elseif ( $entry === '!NONEXISTENT' ) {
 999                                 return false;
1000                         } elseif ( $entry === '!TOO BIG' ) {
1001                                 // Fall through and try invididual message cache below
1002                         }
1003                 } else {
1004                         // XXX: This is not cached in process cache, should it?
1005                         $message = false;
1006                         Hooks::run( 'MessagesPreLoad', [ $title, &$message, $code ] );
1007                         if ( $message !== false ) {
1008                                 return $message;
1009                         }
1010
1011                         return false;
1012                 }
1013
1014                 // Individual message cache key
1015                 $titleKey = $this->bigMessageCacheKey( $this->mCache[$code]['HASH'], $title );
1016
1017                 if ( $this->mCacheVolatile[$code] ) {
1018                         $entry = false;
1019                         // Make sure that individual keys respect the WAN cache holdoff period too
1020                         LoggerFactory::getInstance( 'MessageCache' )->debug(
1021                                 __METHOD__ . ': loading volatile key \'{titleKey}\'',
1022                                 [ 'titleKey' => $titleKey, 'code' => $code ] );
1023                 } else {
1024                         // Try the individual message cache
1025                         $entry = $this->wanCache->get( $titleKey );
1026                 }
1027
1028                 if ( $entry !== false ) {
1029                         if ( substr( $entry, 0, 1 ) === ' ' ) {
1030                                 $this->mCache[$code][$title] = $entry;
1031                                 // The message exists, so make sure a string is returned
1032                                 return (string)substr( $entry, 1 );
1033                         } elseif ( $entry === '!NONEXISTENT' ) {
1034                                 $this->mCache[$code][$title] = '!NONEXISTENT';
1035
1036                                 return false;
1037                         } else {
1038                                 // Corrupt/obsolete entry, delete it
1039                                 $this->wanCache->delete( $titleKey );
1040                         }
1041                 }
1042
1043                 // Try loading the message from the database
1044                 $dbr = wfGetDB( DB_REPLICA );
1045                 $cacheOpts = Database::getCacheSetOptions( $dbr );
1046                 // Use newKnownCurrent() to avoid querying revision/user tables
1047                 $titleObj = Title::makeTitle( NS_MEDIAWIKI, $title );
1048                 if ( $titleObj->getLatestRevID() ) {
1049                         $revision = Revision::newKnownCurrent(
1050                                 $dbr,
1051                                 $titleObj->getArticleID(),
1052                                 $titleObj->getLatestRevID()
1053                         );
1054                 } else {
1055                         $revision = false;
1056                 }
1057
1058                 if ( $revision ) {
1059                         $content = $revision->getContent();
1060                         if ( $content ) {
1061                                 $message = $this->getMessageTextFromContent( $content );
1062                                 if ( is_string( $message ) ) {
1063                                         $this->mCache[$code][$title] = ' ' . $message;
1064                                         $this->wanCache->set( $titleKey, ' ' . $message, $this->mExpiry, $cacheOpts );
1065                                 }
1066                         } else {
1067                                 // A possibly temporary loading failure
1068                                 LoggerFactory::getInstance( 'MessageCache' )->warning(
1069                                         __METHOD__ . ': failed to load message page text for \'{titleKey}\'',
1070                                         [ 'titleKey' => $titleKey, 'code' => $code ] );
1071                                 $message = null; // no negative caching
1072                         }
1073                 } else {
1074                         $message = false; // negative caching
1075                 }
1076
1077                 if ( $message === false ) {
1078                         // Negative caching in case a "too big" message is no longer available (deleted)
1079                         $this->mCache[$code][$title] = '!NONEXISTENT';
1080                         $this->wanCache->set( $titleKey, '!NONEXISTENT', $this->mExpiry, $cacheOpts );
1081                 }
1082
1083                 return $message;
1084         }
1085
1086         /**
1087          * @param string $message
1088          * @param bool $interface
1089          * @param string $language Language code
1090          * @param Title $title
1091          * @return string
1092          */
1093         function transform( $message, $interface = false, $language = null, $title = null ) {
1094                 // Avoid creating parser if nothing to transform
1095                 if ( strpos( $message, '{{' ) === false ) {
1096                         return $message;
1097                 }
1098
1099                 if ( $this->mInParser ) {
1100                         return $message;
1101                 }
1102
1103                 $parser = $this->getParser();
1104                 if ( $parser ) {
1105                         $popts = $this->getParserOptions();
1106                         $popts->setInterfaceMessage( $interface );
1107                         $popts->setTargetLanguage( $language );
1108
1109                         $userlang = $popts->setUserLang( $language );
1110                         $this->mInParser = true;
1111                         $message = $parser->transformMsg( $message, $popts, $title );
1112                         $this->mInParser = false;
1113                         $popts->setUserLang( $userlang );
1114                 }
1115
1116                 return $message;
1117         }
1118
1119         /**
1120          * @return Parser
1121          */
1122         function getParser() {
1123                 global $wgParser, $wgParserConf;
1124
1125                 if ( !$this->mParser && isset( $wgParser ) ) {
1126                         # Do some initialisation so that we don't have to do it twice
1127                         $wgParser->firstCallInit();
1128                         # Clone it and store it
1129                         $class = $wgParserConf['class'];
1130                         if ( $class == 'ParserDiffTest' ) {
1131                                 # Uncloneable
1132                                 $this->mParser = new $class( $wgParserConf );
1133                         } else {
1134                                 $this->mParser = clone $wgParser;
1135                         }
1136                 }
1137
1138                 return $this->mParser;
1139         }
1140
1141         /**
1142          * @param string $text
1143          * @param Title $title
1144          * @param bool $linestart Whether or not this is at the start of a line
1145          * @param bool $interface Whether this is an interface message
1146          * @param Language|string $language Language code
1147          * @return ParserOutput|string
1148          */
1149         public function parse( $text, $title = null, $linestart = true,
1150                 $interface = false, $language = null
1151         ) {
1152                 global $wgTitle;
1153
1154                 if ( $this->mInParser ) {
1155                         return htmlspecialchars( $text );
1156                 }
1157
1158                 $parser = $this->getParser();
1159                 $popts = $this->getParserOptions();
1160                 $popts->setInterfaceMessage( $interface );
1161
1162                 if ( is_string( $language ) ) {
1163                         $language = Language::factory( $language );
1164                 }
1165                 $popts->setTargetLanguage( $language );
1166
1167                 if ( !$title || !$title instanceof Title ) {
1168                         wfDebugLog( 'GlobalTitleFail', __METHOD__ . ' called by ' .
1169                                 wfGetAllCallers( 6 ) . ' with no title set.' );
1170                         $title = $wgTitle;
1171                 }
1172                 // Sometimes $wgTitle isn't set either...
1173                 if ( !$title ) {
1174                         # It's not uncommon having a null $wgTitle in scripts. See r80898
1175                         # Create a ghost title in such case
1176                         $title = Title::makeTitle( NS_SPECIAL, 'Badtitle/title not set in ' . __METHOD__ );
1177                 }
1178
1179                 $this->mInParser = true;
1180                 $res = $parser->parse( $text, $title, $popts, $linestart );
1181                 $this->mInParser = false;
1182
1183                 return $res;
1184         }
1185
1186         function disable() {
1187                 $this->mDisable = true;
1188         }
1189
1190         function enable() {
1191                 $this->mDisable = false;
1192         }
1193
1194         /**
1195          * Whether DB/cache usage is disabled for determining messages
1196          *
1197          * If so, this typically indicates either:
1198          *   - a) load() failed to find a cached copy nor query the DB
1199          *   - b) we are in a special context or error mode that cannot use the DB
1200          * If the DB is ignored, any derived HTML output or cached objects may be wrong.
1201          * To avoid long-term cache pollution, TTLs can be adjusted accordingly.
1202          *
1203          * @return bool
1204          * @since 1.27
1205          */
1206         public function isDisabled() {
1207                 return $this->mDisable;
1208         }
1209
1210         /**
1211          * Clear all stored messages. Mainly used after a mass rebuild.
1212          */
1213         function clear() {
1214                 $langs = Language::fetchLanguageNames( null, 'mw' );
1215                 foreach ( array_keys( $langs ) as $code ) {
1216                         # Global and local caches
1217                         $this->wanCache->touchCheckKey( $this->wanCache->makeKey( 'messages', $code ) );
1218                 }
1219
1220                 $this->mLoadedLanguages = [];
1221         }
1222
1223         /**
1224          * @param string $key
1225          * @return array
1226          */
1227         public function figureMessage( $key ) {
1228                 global $wgLanguageCode;
1229
1230                 $pieces = explode( '/', $key );
1231                 if ( count( $pieces ) < 2 ) {
1232                         return [ $key, $wgLanguageCode ];
1233                 }
1234
1235                 $lang = array_pop( $pieces );
1236                 if ( !Language::fetchLanguageName( $lang, null, 'mw' ) ) {
1237                         return [ $key, $wgLanguageCode ];
1238                 }
1239
1240                 $message = implode( '/', $pieces );
1241
1242                 return [ $message, $lang ];
1243         }
1244
1245         /**
1246          * Get all message keys stored in the message cache for a given language.
1247          * If $code is the content language code, this will return all message keys
1248          * for which MediaWiki:msgkey exists. If $code is another language code, this
1249          * will ONLY return message keys for which MediaWiki:msgkey/$code exists.
1250          * @param string $code Language code
1251          * @return array Array of message keys (strings)
1252          */
1253         public function getAllMessageKeys( $code ) {
1254                 global $wgContLang;
1255
1256                 $this->load( $code );
1257                 if ( !isset( $this->mCache[$code] ) ) {
1258                         // Apparently load() failed
1259                         return null;
1260                 }
1261                 // Remove administrative keys
1262                 $cache = $this->mCache[$code];
1263                 unset( $cache['VERSION'] );
1264                 unset( $cache['EXPIRY'] );
1265                 unset( $cache['EXCESSIVE'] );
1266                 // Remove any !NONEXISTENT keys
1267                 $cache = array_diff( $cache, [ '!NONEXISTENT' ] );
1268
1269                 // Keys may appear with a capital first letter. lcfirst them.
1270                 return array_map( [ $wgContLang, 'lcfirst' ], array_keys( $cache ) );
1271         }
1272
1273         /**
1274          * Purge message caches when a MediaWiki: page is created, updated, or deleted
1275          *
1276          * @param Title $title Message page title
1277          * @param Content|null $content New content for edit/create, null on deletion
1278          * @since 1.29
1279          */
1280         public function updateMessageOverride( Title $title, Content $content = null ) {
1281                 global $wgContLang;
1282
1283                 $msgText = $this->getMessageTextFromContent( $content );
1284                 if ( $msgText === null ) {
1285                         $msgText = false; // treat as not existing
1286                 }
1287
1288                 $this->replace( $title->getDBkey(), $msgText );
1289
1290                 if ( $wgContLang->hasVariants() ) {
1291                         $wgContLang->updateConversionTable( $title );
1292                 }
1293         }
1294
1295         /**
1296          * @param Content|null $content Content or null if the message page does not exist
1297          * @return string|bool|null Returns false if $content is null and null on error
1298          */
1299         private function getMessageTextFromContent( Content $content = null ) {
1300                 // @TODO: could skip pseudo-messages like js/css here, based on content model
1301                 if ( $content ) {
1302                         // Message page exists...
1303                         // XXX: Is this the right way to turn a Content object into a message?
1304                         // NOTE: $content is typically either WikitextContent, JavaScriptContent or
1305                         //       CssContent. MessageContent is *not* used for storing messages, it's
1306                         //       only used for wrapping them when needed.
1307                         $msgText = $content->getWikitextForTransclusion();
1308                         if ( $msgText === false || $msgText === null ) {
1309                                 // This might be due to some kind of misconfiguration...
1310                                 $msgText = null;
1311                                 LoggerFactory::getInstance( 'MessageCache' )->warning(
1312                                         __METHOD__ . ": message content doesn't provide wikitext "
1313                                         . "(content model: " . $content->getModel() . ")" );
1314                         }
1315                 } else {
1316                         // Message page does not exist...
1317                         $msgText = false;
1318                 }
1319
1320                 return $msgText;
1321         }
1322
1323         /**
1324          * @param string $hash Hash for this version of the entire key/value overrides map
1325          * @param string $title Message cache key with initial uppercase letter
1326          * @return string
1327          */
1328         private function bigMessageCacheKey( $hash, $title ) {
1329                 return $this->wanCache->makeKey( 'messages-big', $hash, $title );
1330         }
1331 }