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  * Cache of messages that are defined by MediaWiki namespace pages or by hooks
  36  *
  37  * Performs various MediaWiki namespace-related functions
  38  * @ingroup Cache
  39  */
  40 class MessageCache {
  41         const FOR_UPDATE = 1; // force message reload
  42
  43         /** How long to wait for memcached locks */
  44         const WAIT_SEC = 15;
  45         /** How long memcached locks last */
  46         const LOCK_TTL = 30;
  47
  48         /**
  49          * Process cache of loaded messages that are defined in MediaWiki namespace
  50          *
  51          * @var MapCacheLRU Map of (language code => key => " <MESSAGE>" or "!TOO BIG")
  52          */
  53         protected $cache;
  54
  55         /**
  56          * @var bool[] Map of (language code => boolean)
  57          */
  58         protected $cacheVolatile = [];
  59
  60         /**
  61          * Should mean that database cannot be used, but check
  62          * @var bool $mDisable
  63          */
  64         protected $mDisable;
  65
  66         /**
  67          * Lifetime for cache, used by object caching.
  68          * Set on construction, see __construct().
  69          */
  70         protected $mExpiry;
  71
  72         /**
  73          * Message cache has its own parser which it uses to transform messages
  74          * @var ParserOptions
  75          */
  76         protected $mParserOptions;
  77         /** @var Parser */
  78         protected $mParser;
  79
  80         /**
  81          * @var bool $mInParser
  82          */
  83         protected $mInParser = false;
  84
  85         /** @var WANObjectCache */
  86         protected $wanCache;
  87         /** @var BagOStuff */
  88         protected $clusterCache;
  89         /** @var BagOStuff */
  90         protected $srvCache;
  91
  92         /**
  93          * Singleton instance
  94          *
  95          * @var MessageCache $instance
  96          */
  97         private static $instance;
  98
  99         /**
 100          * Get the signleton instance of this class
 101          *
 102          * @since 1.18
 103          * @return MessageCache
 104          */
 105         public static function singleton() {
 106                 if ( self::$instance === null ) {
 107                         global $wgUseDatabaseMessages, $wgMsgCacheExpiry, $wgUseLocalMessageCache;
 108                         self::$instance = new self(
 109                                 MediaWikiServices::getInstance()->getMainWANObjectCache(),
 110                                 wfGetMessageCacheStorage(),
 111                                 $wgUseLocalMessageCache
 112                                         ? MediaWikiServices::getInstance()->getLocalServerObjectCache()
 113                                         : new EmptyBagOStuff(),
 114                                 $wgUseDatabaseMessages,
 115                                 $wgMsgCacheExpiry
 116                         );
 117                 }
 118
 119                 return self::$instance;
 120         }
 121
 122         /**
 123          * Destroy the singleton instance
 124          *
 125          * @since 1.18
 126          */
 127         public static function destroyInstance() {
 128                 self::$instance = null;
 129         }
 130
 131         /**
 132          * Normalize message key input
 133          *
 134          * @param string $key Input message key to be normalized
 135          * @return string Normalized message key
 136          */
 137         public static function normalizeKey( $key ) {
 138                 global $wgContLang;
 139
 140                 $lckey = strtr( $key, ' ', '_' );
 141                 if ( ord( $lckey ) < 128 ) {
 142                         $lckey[0] = strtolower( $lckey[0] );
 143                 } else {
 144                         $lckey = $wgContLang->lcfirst( $lckey );
 145                 }
 146
 147                 return $lckey;
 148         }
 149
 150         /**
 151          * @param WANObjectCache $wanCache
 152          * @param BagOStuff $clusterCache
 153          * @param BagOStuff $serverCache
 154          * @param bool $useDB Whether to look for message overrides (e.g. MediaWiki: pages)
 155          * @param int $expiry Lifetime for cache. @see $mExpiry.
 156          */
 157         public function __construct(
 158                 WANObjectCache $wanCache,
 159                 BagOStuff $clusterCache,
 160                 BagOStuff $serverCache,
 161                 $useDB,
 162                 $expiry
 163         ) {
 164                 $this->wanCache = $wanCache;
 165                 $this->clusterCache = $clusterCache;
 166                 $this->srvCache = $serverCache;
 167
 168                 $this->cache = new MapCacheLRU( 5 ); // limit size for sanity
 169
 170                 $this->mDisable = !$useDB;
 171                 $this->mExpiry = $expiry;
 172         }
 173
 174         /**
 175          * ParserOptions is lazy initialised.
 176          *
 177          * @return ParserOptions
 178          */
 179         function getParserOptions() {
 180                 global $wgUser;
 181
 182                 if ( !$this->mParserOptions ) {
 183                         if ( !$wgUser->isSafeToLoad() ) {
 184                                 // $wgUser isn't unstubbable yet, so don't try to get a
 185                                 // ParserOptions for it. And don't cache this ParserOptions
 186                                 // either.
 187                                 $po = ParserOptions::newFromAnon();
 188                                 $po->setAllowUnsafeRawHtml( false );
 189                                 return $po;
 190                         }
 191
 192                         $this->mParserOptions = new ParserOptions;
 193                         // Messages may take parameters that could come
 194                         // from malicious sources. As a precaution, disable
 195                         // the <html> parser tag when parsing messages.
 196                         $this->mParserOptions->setAllowUnsafeRawHtml( false );
 197                 }
 198
 199                 return $this->mParserOptions;
 200         }
 201
 202         /**
 203          * Try to load the cache from APC.
 204          *
 205          * @param string $code Optional language code, see documenation of load().
 206          * @return array|bool The cache array, or false if not in cache.
 207          */
 208         protected function getLocalCache( $code ) {
 209                 $cacheKey = $this->srvCache->makeKey( __CLASS__, $code );
 210
 211                 return $this->srvCache->get( $cacheKey );
 212         }
 213
 214         /**
 215          * Save the cache to APC.
 216          *
 217          * @param string $code
 218          * @param array $cache The cache array
 219          */
 220         protected function saveToLocalCache( $code, $cache ) {
 221                 $cacheKey = $this->srvCache->makeKey( __CLASS__, $code );
 222                 $this->srvCache->set( $cacheKey, $cache );
 223         }
 224
 225         /**
 226          * Loads messages from caches or from database in this order:
 227          * (1) local message cache (if $wgUseLocalMessageCache is enabled)
 228          * (2) memcached
 229          * (3) from the database.
 230          *
 231          * When succesfully loading from (2) or (3), all higher level caches are
 232          * updated for the newest version.
 233          *
 234          * Nothing is loaded if member variable mDisable is true, either manually
 235          * set by calling code or if message loading fails (is this possible?).
 236          *
 237          * Returns true if cache is already populated or it was succesfully populated,
 238          * or false if populating empty cache fails. Also returns true if MessageCache
 239          * is disabled.
 240          *
 241          * @param string $code Language to which load messages
 242          * @param int|null $mode Use MessageCache::FOR_UPDATE to skip process cache [optional]
 243          * @throws InvalidArgumentException
 244          * @return bool
 245          */
 246         protected function load( $code, $mode = null ) {
 247                 if ( !is_string( $code ) ) {
 248                         throw new InvalidArgumentException( "Missing language code" );
 249                 }
 250
 251                 # Don't do double loading...
 252                 if ( $this->cache->has( $code ) && $mode != self::FOR_UPDATE ) {
 253                         return true;
 254                 }
 255
 256                 # 8 lines of code just to say (once) that message cache is disabled
 257                 if ( $this->mDisable ) {
 258                         static $shownDisabled = false;
 259                         if ( !$shownDisabled ) {
 260                                 wfDebug( __METHOD__ . ": disabled\n" );
 261                                 $shownDisabled = true;
 262                         }
 263
 264                         return true;
 265                 }
 266
 267                 # Loading code starts
 268                 $success = false; # Keep track of success
 269                 $staleCache = false; # a cache array with expired data, or false if none has been loaded
 270                 $where = []; # Debug info, delayed to avoid spamming debug log too much
 271
 272                 # Hash of the contents is stored in memcache, to detect if data-center cache
 273                 # or local cache goes out of date (e.g. due to replace() on some other server)
 274                 list( $hash, $hashVolatile ) = $this->getValidationHash( $code );
 275                 $this->cacheVolatile[$code] = $hashVolatile;
 276
 277                 # Try the local cache and check against the cluster hash key...
 278                 $cache = $this->getLocalCache( $code );
 279                 if ( !$cache ) {
 280                         $where[] = 'local cache is empty';
 281                 } elseif ( !isset( $cache['HASH'] ) || $cache['HASH'] !== $hash ) {
 282                         $where[] = 'local cache has the wrong hash';
 283                         $staleCache = $cache;
 284                 } elseif ( $this->isCacheExpired( $cache ) ) {
 285                         $where[] = 'local cache is expired';
 286                         $staleCache = $cache;
 287                 } elseif ( $hashVolatile ) {
 288                         $where[] = 'local cache validation key is expired/volatile';
 289                         $staleCache = $cache;
 290                 } else {
 291                         $where[] = 'got from local cache';
 292                         $this->cache->set( $code, $cache );
 293                         $success = true;
 294                 }
 295
 296                 if ( !$success ) {
 297                         $cacheKey = $this->clusterCache->makeKey( 'messages', $code );
 298                         # Try the global cache. If it is empty, try to acquire a lock. If
 299                         # the lock can't be acquired, wait for the other thread to finish
 300                         # and then try the global cache a second time.
 301                         for ( $failedAttempts = 0; $failedAttempts <= 1; $failedAttempts++ ) {
 302                                 if ( $hashVolatile && $staleCache ) {
 303                                         # Do not bother fetching the whole cache blob to avoid I/O.
 304                                         # Instead, just try to get the non-blocking $statusKey lock
 305                                         # below, and use the local stale value if it was not acquired.
 306                                         $where[] = 'global cache is presumed expired';
 307                                 } else {
 308                                         $cache = $this->clusterCache->get( $cacheKey );
 309                                         if ( !$cache ) {
 310                                                 $where[] = 'global cache is empty';
 311                                         } elseif ( $this->isCacheExpired( $cache ) ) {
 312                                                 $where[] = 'global cache is expired';
 313                                                 $staleCache = $cache;
 314                                         } elseif ( $hashVolatile ) {
 315                                                 # DB results are replica DB lag prone until the holdoff TTL passes.
 316                                                 # By then, updates should be reflected in loadFromDBWithLock().
 317                                                 # One thread renerates the cache while others use old values.
 318                                                 $where[] = 'global cache is expired/volatile';
 319                                                 $staleCache = $cache;
 320                                         } else {
 321                                                 $where[] = 'got from global cache';
 322                                                 $this->cache->set( $code, $cache );
 323                                                 $this->saveToCaches( $cache, 'local-only', $code );
 324                                                 $success = true;
 325                                         }
 326                                 }
 327
 328                                 if ( $success ) {
 329                                         # Done, no need to retry
 330                                         break;
 331                                 }
 332
 333                                 # We need to call loadFromDB. Limit the concurrency to one process.
 334                                 # This prevents the site from going down when the cache expires.
 335                                 # Note that the DB slam protection lock here is non-blocking.
 336                                 $loadStatus = $this->loadFromDBWithLock( $code, $where, $mode );
 337                                 if ( $loadStatus === true ) {
 338                                         $success = true;
 339                                         break;
 340                                 } elseif ( $staleCache ) {
 341                                         # Use the stale cache while some other thread constructs the new one
 342                                         $where[] = 'using stale cache';
 343                                         $this->cache->set( $code, $staleCache );
 344                                         $success = true;
 345                                         break;
 346                                 } elseif ( $failedAttempts > 0 ) {
 347                                         # Already blocked once, so avoid another lock/unlock cycle.
 348                                         # This case will typically be hit if memcached is down, or if
 349                                         # loadFromDB() takes longer than LOCK_WAIT.
 350                                         $where[] = "could not acquire status key.";
 351                                         break;
 352                                 } elseif ( $loadStatus === 'cantacquire' ) {
 353                                         # Wait for the other thread to finish, then retry. Normally,
 354                                         # the memcached get() will then yeild the other thread's result.
 355                                         $where[] = 'waited for other thread to complete';
 356                                         $this->getReentrantScopedLock( $cacheKey );
 357                                 } else {
 358                                         # Disable cache; $loadStatus is 'disabled'
 359                                         break;
 360                                 }
 361                         }
 362                 }
 363
 364                 if ( !$success ) {
 365                         $where[] = 'loading FAILED - cache is disabled';
 366                         $this->mDisable = true;
 367                         $this->cache->set( $code, null );
 368                         wfDebugLog( 'MessageCacheError', __METHOD__ . ": Failed to load $code\n" );
 369                         # This used to throw an exception, but that led to nasty side effects like
 370                         # the whole wiki being instantly down if the memcached server died
 371                 }
 372
 373                 if ( !$this->cache->has( $code ) ) { // sanity
 374                         throw new LogicException( "Process cache for '$code' should be set by now." );
 375                 }
 376
 377                 $info = implode( ', ', $where );
 378                 wfDebugLog( 'MessageCache', __METHOD__ . ": Loading $code... $info\n" );
 379
 380                 return $success;
 381         }
 382
 383         /**
 384          * @param string $code
 385          * @param array &$where List of wfDebug() comments
 386          * @param int|null $mode Use MessageCache::FOR_UPDATE to use DB_MASTER
 387          * @return bool|string True on success or one of ("cantacquire", "disabled")
 388          */
 389         protected function loadFromDBWithLock( $code, array &$where, $mode = null ) {
 390                 # If cache updates on all levels fail, give up on message overrides.
 391                 # This is to avoid easy site outages; see $saveSuccess comments below.
 392                 $statusKey = $this->clusterCache->makeKey( 'messages', $code, 'status' );
 393                 $status = $this->clusterCache->get( $statusKey );
 394                 if ( $status === 'error' ) {
 395                         $where[] = "could not load; method is still globally disabled";
 396                         return 'disabled';
 397                 }
 398
 399                 # Now let's regenerate
 400                 $where[] = 'loading from database';
 401
 402                 # Lock the cache to prevent conflicting writes.
 403                 # This lock is non-blocking so stale cache can quickly be used.
 404                 # Note that load() will call a blocking getReentrantScopedLock()
 405                 # after this if it really need to wait for any current thread.
 406                 $cacheKey = $this->clusterCache->makeKey( 'messages', $code );
 407                 $scopedLock = $this->getReentrantScopedLock( $cacheKey, 0 );
 408                 if ( !$scopedLock ) {
 409                         $where[] = 'could not acquire main lock';
 410                         return 'cantacquire';
 411                 }
 412
 413                 $cache = $this->loadFromDB( $code, $mode );
 414                 $this->cache->set( $code, $cache );
 415                 $saveSuccess = $this->saveToCaches( $cache, 'all', $code );
 416
 417                 if ( !$saveSuccess ) {
 418                         /**
 419                          * Cache save has failed.
 420                          *
 421                          * There are two main scenarios where this could be a problem:
 422                          * - The cache is more than the maximum size (typically 1MB compressed).
 423                          * - Memcached has no space remaining in the relevant slab class. This is
 424                          *   unlikely with recent versions of memcached.
 425                          *
 426                          * Either way, if there is a local cache, nothing bad will happen. If there
 427                          * is no local cache, disabling the message cache for all requests avoids
 428                          * incurring a loadFromDB() overhead on every request, and thus saves the
 429                          * wiki from complete downtime under moderate traffic conditions.
 430                          */
 431                         if ( $this->srvCache instanceof EmptyBagOStuff ) {
 432                                 $this->clusterCache->set( $statusKey, 'error', 60 * 5 );
 433                                 $where[] = 'could not save cache, disabled globally for 5 minutes';
 434                         } else {
 435                                 $where[] = "could not save global cache";
 436                         }
 437                 }
 438
 439                 return true;
 440         }
 441
 442         /**
 443          * Loads cacheable messages from the database. Messages bigger than
 444          * $wgMaxMsgCacheEntrySize are assigned a special value, and are loaded
 445          * on-demand from the database later.
 446          *
 447          * @param string $code Language code
 448          * @param int|null $mode Use MessageCache::FOR_UPDATE to skip process cache
 449          * @return array Loaded messages for storing in caches
 450          */
 451         protected function loadFromDB( $code, $mode = null ) {
 452                 global $wgMaxMsgCacheEntrySize, $wgLanguageCode, $wgAdaptiveMessageCache;
 453
 454                 // (T164666) The query here performs really poorly on WMF's
 455                 // contributions replicas. We don't have a way to say "any group except
 456                 // contributions", so for the moment let's specify 'api'.
 457                 // @todo: Get rid of this hack.
 458                 $dbr = wfGetDB( ( $mode == self::FOR_UPDATE ) ? DB_MASTER : DB_REPLICA, 'api' );
 459
 460                 $cache = [];
 461
 462                 # Common conditions
 463                 $conds = [
 464                         'page_is_redirect' => 0,
 465                         'page_namespace' => NS_MEDIAWIKI,
 466                 ];
 467
 468                 $mostused = [];
 469                 if ( $wgAdaptiveMessageCache && $code !== $wgLanguageCode ) {
 470                         if ( !$this->cache->has( $wgLanguageCode ) ) {
 471                                 $this->load( $wgLanguageCode );
 472                         }
 473                         $mostused = array_keys( $this->cache->get( $wgLanguageCode ) );
 474                         foreach ( $mostused as $key => $value ) {
 475                                 $mostused[$key] = "$value/$code";
 476                         }
 477                 }
 478
 479                 if ( count( $mostused ) ) {
 480                         $conds['page_title'] = $mostused;
 481                 } elseif ( $code !== $wgLanguageCode ) {
 482                         $conds[] = 'page_title' . $dbr->buildLike( $dbr->anyString(), '/', $code );
 483                 } else {
 484                         # Effectively disallows use of '/' character in NS_MEDIAWIKI for uses
 485                         # other than language code.
 486                         $conds[] = 'page_title NOT' .
 487                                 $dbr->buildLike( $dbr->anyString(), '/', $dbr->anyString() );
 488                 }
 489
 490                 # Conditions to fetch oversized pages to ignore them
 491                 $bigConds = $conds;
 492                 $bigConds[] = 'page_len > ' . intval( $wgMaxMsgCacheEntrySize );
 493
 494                 # Load titles for all oversized pages in the MediaWiki namespace
 495                 $res = $dbr->select(
 496                         'page',
 497                         [ 'page_title', 'page_latest' ],
 498                         $bigConds,
 499                         __METHOD__ . "($code)-big"
 500                 );
 501                 foreach ( $res as $row ) {
 502                         $cache[$row->page_title] = '!TOO BIG';
 503                         // At least include revision ID so page changes are reflected in the hash
 504                         $cache['EXCESSIVE'][$row->page_title] = $row->page_latest;
 505                 }
 506
 507                 # Conditions to load the remaining pages with their contents
 508                 $smallConds = $conds;
 509                 $smallConds[] = 'page_len <= ' . intval( $wgMaxMsgCacheEntrySize );
 510
 511                 $res = $dbr->select(
 512                         [ 'page', 'revision', 'text' ],
 513                         [ 'page_title', 'old_id', 'old_text', 'old_flags' ],
 514                         $smallConds,
 515                         __METHOD__ . "($code)-small",
 516                         [],
 517                         [
 518                                 'revision' => [ 'JOIN', 'page_latest=rev_id' ],
 519                                 'text' => [ 'JOIN', 'rev_text_id=old_id' ],
 520                         ]
 521                 );
 522
 523                 foreach ( $res as $row ) {
 524                         $text = Revision::getRevisionText( $row );
 525                         if ( $text === false ) {
 526                                 // Failed to fetch data; possible ES errors?
 527                                 // Store a marker to fetch on-demand as a workaround...
 528                                 // TODO Use a differnt marker
 529                                 $entry = '!TOO BIG';
 530                                 wfDebugLog(
 531                                         'MessageCache',
 532                                         __METHOD__
 533                                         . ": failed to load message page text for {$row->page_title} ($code)"
 534                                 );
 535                         } else {
 536                                 $entry = ' ' . $text;
 537                         }
 538                         $cache[$row->page_title] = $entry;
 539                 }
 540
 541                 $cache['VERSION'] = MSG_CACHE_VERSION;
 542                 ksort( $cache );
 543
 544                 # Hash for validating local cache (APC). No need to take into account
 545                 # messages larger than $wgMaxMsgCacheEntrySize, since those are only
 546                 # stored and fetched from memcache.
 547                 $cache['HASH'] = md5( serialize( $cache ) );
 548                 $cache['EXPIRY'] = wfTimestamp( TS_MW, time() + $this->mExpiry );
 549
 550                 return $cache;
 551         }
 552
 553         /**
 554          * Updates cache as necessary when message page is changed
 555          *
 556          * @param string $title Message cache key with initial uppercase letter
 557          * @param string|bool $text New contents of the page (false if deleted)
 558          */
 559         public function replace( $title, $text ) {
 560                 global $wgLanguageCode;
 561
 562                 if ( $this->mDisable ) {
 563                         return;
 564                 }
 565
 566                 list( $msg, $code ) = $this->figureMessage( $title );
 567                 if ( strpos( $title, '/' ) !== false && $code === $wgLanguageCode ) {
 568                         // Content language overrides do not use the /<code> suffix
 569                         return;
 570                 }
 571
 572                 // (a) Update the process cache with the new message text
 573                 if ( $text === false ) {
 574                         // Page deleted
 575                         $this->cache->setField( $code, $title, '!NONEXISTENT' );
 576                 } else {
 577                         // Ignore $wgMaxMsgCacheEntrySize so the process cache is up to date
 578                         $this->cache->setField( $code, $title, ' ' . $text );
 579                 }
 580
 581                 // (b) Update the shared caches in a deferred update with a fresh DB snapshot
 582                 DeferredUpdates::addCallableUpdate(
 583                         function () use ( $title, $msg, $code ) {
 584                                 global $wgContLang, $wgMaxMsgCacheEntrySize;
 585                                 // Allow one caller at a time to avoid race conditions
 586                                 $scopedLock = $this->getReentrantScopedLock(
 587                                         $this->clusterCache->makeKey( 'messages', $code )
 588                                 );
 589                                 if ( !$scopedLock ) {
 590                                         LoggerFactory::getInstance( 'MessageCache' )->error(
 591                                                 __METHOD__ . ': could not acquire lock to update {title} ({code})',
 592                                                 [ 'title' => $title, 'code' => $code ] );
 593                                         return;
 594                                 }
 595                                 // Load the messages from the master DB to avoid race conditions
 596                                 $cache = $this->loadFromDB( $code, self::FOR_UPDATE );
 597                                 // Check if an individual cache key should exist and update cache accordingly
 598                                 $page = WikiPage::factory( Title::makeTitle( NS_MEDIAWIKI, $title ) );
 599                                 $page->loadPageData( $page::READ_LATEST );
 600                                 $text = $this->getMessageTextFromContent( $page->getContent() );
 601                                 if ( is_string( $text ) && strlen( $text ) > $wgMaxMsgCacheEntrySize ) {
 602                                         $this->wanCache->set(
 603                                                 $this->bigMessageCacheKey( $cache['HASH'], $title ),
 604                                                 ' ' . $text,
 605                                                 $this->mExpiry
 606                                         );
 607                                 }
 608                                 // Mark this cache as definitely being "latest" (non-volatile) so
 609                                 // load() calls do not try to refresh the cache with replica DB data
 610                                 $cache['LATEST'] = time();
 611                                 // Update the process cache
 612                                 $this->cache->set( $code, $cache );
 613                                 // Pre-emptively update the local datacenter cache so things like edit filter and
 614                                 // blacklist changes are reflected immediately; these often use MediaWiki: pages.
 615                                 // The datacenter handling replace() calls should be the same one handling edits
 616                                 // as they require HTTP POST.
 617                                 $this->saveToCaches( $cache, 'all', $code );
 618                                 // Release the lock now that the cache is saved
 619                                 ScopedCallback::consume( $scopedLock );
 620
 621                                 // Relay the purge. Touching this check key expires cache contents
 622                                 // and local cache (APC) validation hash across all datacenters.
 623                                 $this->wanCache->touchCheckKey( $this->getCheckKey( $code ) );
 624
 625                                 // Purge the message in the message blob store
 626                                 $resourceloader = RequestContext::getMain()->getOutput()->getResourceLoader();
 627                                 $blobStore = $resourceloader->getMessageBlobStore();
 628                                 $blobStore->updateMessage( $wgContLang->lcfirst( $msg ) );
 629
 630                                 Hooks::run( 'MessageCacheReplace', [ $title, $text ] );
 631                         },
 632                         DeferredUpdates::PRESEND
 633                 );
 634         }
 635
 636         /**
 637          * Is the given cache array expired due to time passing or a version change?
 638          *
 639          * @param array $cache
 640          * @return bool
 641          */
 642         protected function isCacheExpired( $cache ) {
 643                 if ( !isset( $cache['VERSION'] ) || !isset( $cache['EXPIRY'] ) ) {
 644                         return true;
 645                 }
 646                 if ( $cache['VERSION'] != MSG_CACHE_VERSION ) {
 647                         return true;
 648                 }
 649                 if ( wfTimestampNow() >= $cache['EXPIRY'] ) {
 650                         return true;
 651                 }
 652
 653                 return false;
 654         }
 655
 656         /**
 657          * Shortcut to update caches.
 658          *
 659          * @param array $cache Cached messages with a version.
 660          * @param string $dest Either "local-only" to save to local caches only
 661          *   or "all" to save to all caches.
 662          * @param string|bool $code Language code (default: false)
 663          * @return bool
 664          */
 665         protected function saveToCaches( array $cache, $dest, $code = false ) {
 666                 if ( $dest === 'all' ) {
 667                         $cacheKey = $this->clusterCache->makeKey( 'messages', $code );
 668                         $success = $this->clusterCache->set( $cacheKey, $cache );
 669                         $this->setValidationHash( $code, $cache );
 670                 } else {
 671                         $success = true;
 672                 }
 673
 674                 $this->saveToLocalCache( $code, $cache );
 675
 676                 return $success;
 677         }
 678
 679         /**
 680          * Get the md5 used to validate the local APC cache
 681          *
 682          * @param string $code
 683          * @return array (hash or false, bool expiry/volatility status)
 684          */
 685         protected function getValidationHash( $code ) {
 686                 $curTTL = null;
 687                 $value = $this->wanCache->get(
 688                         $this->wanCache->makeKey( 'messages', $code, 'hash', 'v1' ),
 689                         $curTTL,
 690                         [ $this->getCheckKey( $code ) ]
 691                 );
 692
 693                 if ( $value ) {
 694                         $hash = $value['hash'];
 695                         if ( ( time() - $value['latest'] ) < WANObjectCache::TTL_MINUTE ) {
 696                                 // Cache was recently updated via replace() and should be up-to-date.
 697                                 // That method is only called in the primary datacenter and uses FOR_UPDATE.
 698                                 // Also, it is unlikely that the current datacenter is *now* secondary one.
 699                                 $expired = false;
 700                         } else {
 701                                 // See if the "check" key was bumped after the hash was generated
 702                                 $expired = ( $curTTL < 0 );
 703                         }
 704                 } else {
 705                         // No hash found at all; cache must regenerate to be safe
 706                         $hash = false;
 707                         $expired = true;
 708                 }
 709
 710                 return [ $hash, $expired ];
 711         }
 712
 713         /**
 714          * Set the md5 used to validate the local disk cache
 715          *
 716          * If $cache has a 'LATEST' UNIX timestamp key, then the hash will not
 717          * be treated as "volatile" by getValidationHash() for the next few seconds.
 718          * This is triggered when $cache is generated using FOR_UPDATE mode.
 719          *
 720          * @param string $code
 721          * @param array $cache Cached messages with a version
 722          */
 723         protected function setValidationHash( $code, array $cache ) {
 724                 $this->wanCache->set(
 725                         $this->wanCache->makeKey( 'messages', $code, 'hash', 'v1' ),
 726                         [
 727                                 'hash' => $cache['HASH'],
 728                                 'latest' => $cache['LATEST'] ?? 0
 729                         ],
 730                         WANObjectCache::TTL_INDEFINITE
 731                 );
 732         }
 733
 734         /**
 735          * @param string $key A language message cache key that stores blobs
 736          * @param int $timeout Wait timeout in seconds
 737          * @return null|ScopedCallback
 738          */
 739         protected function getReentrantScopedLock( $key, $timeout = self::WAIT_SEC ) {
 740                 return $this->clusterCache->getScopedLock( $key, $timeout, self::LOCK_TTL, __METHOD__ );
 741         }
 742
 743         /**
 744          * Get a message from either the content language or the user language.
 745          *
 746          * First, assemble a list of languages to attempt getting the message from. This
 747          * chain begins with the requested language and its fallbacks and then continues with
 748          * the content language and its fallbacks. For each language in the chain, the following
 749          * process will occur (in this order):
 750          *  1. If a language-specific override, i.e., [[MW:msg/lang]], is available, use that.
 751          *     Note: for the content language, there is no /lang subpage.
 752          *  2. Fetch from the static CDB cache.
 753          *  3. If available, check the database for fallback language overrides.
 754          *
 755          * This process provides a number of guarantees. When changing this code, make sure all
 756          * of these guarantees are preserved.
 757          *  * If the requested language is *not* the content language, then the CDB cache for that
 758          *    specific language will take precedence over the root database page ([[MW:msg]]).
 759          *  * Fallbacks will be just that: fallbacks. A fallback language will never be reached if
 760          *    the message is available *anywhere* in the language for which it is a fallback.
 761          *
 762          * @param string $key The message key
 763          * @param bool $useDB If true, look for the message in the DB, false
 764          *   to use only the compiled l10n cache.
 765          * @param bool|string|object $langcode Code of the language to get the message for.
 766          *   - If string and a valid code, will create a standard language object
 767          *   - If string but not a valid code, will create a basic language object
 768          *   - If boolean and false, create object from the current users language
 769          *   - If boolean and true, create object from the wikis content language
 770          *   - If language object, use it as given
 771          * @param bool $isFullKey Specifies whether $key is a two part key "msg/lang".
 772          *
 773          * @throws MWException When given an invalid key
 774          * @return string|bool False if the message doesn't exist, otherwise the
 775          *   message (which can be empty)
 776          */
 777         function get( $key, $useDB = true, $langcode = true, $isFullKey = false ) {
 778                 if ( is_int( $key ) ) {
 779                         // Fix numerical strings that somehow become ints
 780                         // on their way here
 781                         $key = (string)$key;
 782                 } elseif ( !is_string( $key ) ) {
 783                         throw new MWException( 'Non-string key given' );
 784                 } elseif ( $key === '' ) {
 785                         // Shortcut: the empty key is always missing
 786                         return false;
 787                 }
 788
 789                 // For full keys, get the language code from the key
 790                 $pos = strrpos( $key, '/' );
 791                 if ( $isFullKey && $pos !== false ) {
 792                         $langcode = substr( $key, $pos + 1 );
 793                         $key = substr( $key, 0, $pos );
 794                 }
 795
 796                 // Normalise title-case input (with some inlining)
 797                 $lckey = self::normalizeKey( $key );
 798
 799                 Hooks::run( 'MessageCache::get', [ &$lckey ] );
 800
 801                 // Loop through each language in the fallback list until we find something useful
 802                 $lang = wfGetLangObj( $langcode );
 803                 $message = $this->getMessageFromFallbackChain(
 804                         $lang,
 805                         $lckey,
 806                         !$this->mDisable && $useDB
 807                 );
 808
 809                 // If we still have no message, maybe the key was in fact a full key so try that
 810                 if ( $message === false ) {
 811                         $parts = explode( '/', $lckey );
 812                         // We may get calls for things that are http-urls from sidebar
 813                         // Let's not load nonexistent languages for those
 814                         // They usually have more than one slash.
 815                         if ( count( $parts ) == 2 && $parts[1] !== '' ) {
 816                                 $message = Language::getMessageFor( $parts[0], $parts[1] );
 817                                 if ( $message === null ) {
 818                                         $message = false;
 819                                 }
 820                         }
 821                 }
 822
 823                 // Post-processing if the message exists
 824                 if ( $message !== false ) {
 825                         // Fix whitespace
 826                         $message = str_replace(
 827                                 [
 828                                         # Fix for trailing whitespace, removed by textarea
 829                                         '&#32;',
 830                                         # Fix for NBSP, converted to space by firefox
 831                                         '&nbsp;',
 832                                         '&#160;',
 833                                         '&shy;'
 834                                 ],
 835                                 [
 836                                         ' ',
 837                                         "\u{00A0}",
 838                                         "\u{00A0}",
 839                                         "\u{00AD}"
 840                                 ],
 841                                 $message
 842                         );
 843                 }
 844
 845                 return $message;
 846         }
 847
 848         /**
 849          * Given a language, try and fetch messages from that language.
 850          *
 851          * Will also consider fallbacks of that language, the site language, and fallbacks for
 852          * the site language.
 853          *
 854          * @see MessageCache::get
 855          * @param Language|StubObject $lang Preferred language
 856          * @param string $lckey Lowercase key for the message (as for localisation cache)
 857          * @param bool $useDB Whether to include messages from the wiki database
 858          * @return string|bool The message, or false if not found
 859          */
 860         protected function getMessageFromFallbackChain( $lang, $lckey, $useDB ) {
 861                 global $wgContLang;
 862
 863                 $alreadyTried = [];
 864
 865                 // First try the requested language.
 866                 $message = $this->getMessageForLang( $lang, $lckey, $useDB, $alreadyTried );
 867                 if ( $message !== false ) {
 868                         return $message;
 869                 }
 870
 871                 // Now try checking the site language.
 872                 $message = $this->getMessageForLang( $wgContLang, $lckey, $useDB, $alreadyTried );
 873                 return $message;
 874         }
 875
 876         /**
 877          * Given a language, try and fetch messages from that language and its fallbacks.
 878          *
 879          * @see MessageCache::get
 880          * @param Language|StubObject $lang Preferred language
 881          * @param string $lckey Lowercase key for the message (as for localisation cache)
 882          * @param bool $useDB Whether to include messages from the wiki database
 883          * @param bool[] $alreadyTried Contains true for each language that has been tried already
 884          * @return string|bool The message, or false if not found
 885          */
 886         private function getMessageForLang( $lang, $lckey, $useDB, &$alreadyTried ) {
 887                 global $wgContLang;
 888
 889                 $langcode = $lang->getCode();
 890
 891                 // Try checking the database for the requested language
 892                 if ( $useDB ) {
 893                         $uckey = $wgContLang->ucfirst( $lckey );
 894
 895                         if ( !isset( $alreadyTried[$langcode] ) ) {
 896                                 $message = $this->getMsgFromNamespace(
 897                                         $this->getMessagePageName( $langcode, $uckey ),
 898                                         $langcode
 899                                 );
 900
 901                                 if ( $message !== false ) {
 902                                         return $message;
 903                                 }
 904                                 $alreadyTried[$langcode] = true;
 905                         }
 906                 } else {
 907                         $uckey = null;
 908                 }
 909
 910                 // Check the CDB cache
 911                 $message = $lang->getMessage( $lckey );
 912                 if ( $message !== null ) {
 913                         return $message;
 914                 }
 915
 916                 // Try checking the database for all of the fallback languages
 917                 if ( $useDB ) {
 918                         $fallbackChain = Language::getFallbacksFor( $langcode );
 919
 920                         foreach ( $fallbackChain as $code ) {
 921                                 if ( isset( $alreadyTried[$code] ) ) {
 922                                         continue;
 923                                 }
 924
 925                                 $message = $this->getMsgFromNamespace(
 926                                         $this->getMessagePageName( $code, $uckey ), $code );
 927
 928                                 if ( $message !== false ) {
 929                                         return $message;
 930                                 }
 931                                 $alreadyTried[$code] = true;
 932                         }
 933                 }
 934
 935                 return false;
 936         }
 937
 938         /**
 939          * Get the message page name for a given language
 940          *
 941          * @param string $langcode
 942          * @param string $uckey Uppercase key for the message
 943          * @return string The page name
 944          */
 945         private function getMessagePageName( $langcode, $uckey ) {
 946                 global $wgLanguageCode;
 947
 948                 if ( $langcode === $wgLanguageCode ) {
 949                         // Messages created in the content language will not have the /lang extension
 950                         return $uckey;
 951                 } else {
 952                         return "$uckey/$langcode";
 953                 }
 954         }
 955
 956         /**
 957          * Get a message from the MediaWiki namespace, with caching. The key must
 958          * first be converted to two-part lang/msg form if necessary.
 959          *
 960          * Unlike self::get(), this function doesn't resolve fallback chains, and
 961          * some callers require this behavior. LanguageConverter::parseCachedTable()
 962          * and self::get() are some examples in core.
 963          *
 964          * @param string $title Message cache key with initial uppercase letter
 965          * @param string $code Code denoting the language to try
 966          * @return string|bool The message, or false if it does not exist or on error
 967          */
 968         public function getMsgFromNamespace( $title, $code ) {
 969                 // Load all MediaWiki page definitions into cache. Note that individual keys
 970                 // already loaded into cache during this request remain in the cache, which
 971                 // includes the value of hook-defined messages.
 972                 $this->load( $code );
 973
 974                 $entry = $this->cache->getField( $code, $title );
 975                 if ( $entry !== null ) {
 976                         if ( substr( $entry, 0, 1 ) === ' ' ) {
 977                                 // The message exists and is not '!TOO BIG'
 978                                 return (string)substr( $entry, 1 );
 979                         } elseif ( $entry === '!NONEXISTENT' ) {
 980                                 return false;
 981                         }
 982                         // Fall through and try invididual message cache below
 983                 } else {
 984                         // Message does not have a MediaWiki page definition
 985                         $message = false;
 986                         Hooks::run( 'MessagesPreLoad', [ $title, &$message, $code ] );
 987                         if ( $message !== false ) {
 988                                 $this->cache->setField( $code, $title, ' ' . $message );
 989                         } else {
 990                                 $this->cache->setField( $code, $title, '!NONEXISTENT' );
 991                         }
 992
 993                         return $message;
 994                 }
 995
 996                 if ( $this->cacheVolatile[$code] ) {
 997                         $entry = false;
 998                         // Make sure that individual keys respect the WAN cache holdoff period too
 999                         LoggerFactory::getInstance( 'MessageCache' )->debug(
1000                                 __METHOD__ . ': loading volatile key \'{titleKey}\'',
1001                                 [ 'titleKey' => $title, 'code' => $code ] );
1002                 } else {
1003                         // Try the individual message cache
1004                         $entry = $this->loadCachedMessagePageEntry(
1005                                 $title,
1006                                 $code,
1007                                 $this->cache->getField( $code, 'HASH' )
1008                         );
1009                 }
1010
1011                 if ( $entry !== false && substr( $entry, 0, 1 ) === ' ' ) {
1012                         $this->cache->setField( $code, $title, $entry );
1013                         // The message exists, so make sure a string is returned
1014                         return (string)substr( $entry, 1 );
1015                 }
1016
1017                 $this->cache->setField( $code, $title, '!NONEXISTENT' );
1018
1019                 return false;
1020         }
1021
1022         /**
1023          * @param string $dbKey
1024          * @param string $code
1025          * @param string $hash
1026          * @return string Either " <MESSAGE>" or "!NONEXISTANT"
1027          */
1028         private function loadCachedMessagePageEntry( $dbKey, $code, $hash ) {
1029                 return $this->wanCache->getWithSetCallback(
1030                         $this->bigMessageCacheKey( $hash, $dbKey ),
1031                         $this->mExpiry,
1032                         function ( $oldValue, &$ttl, &$setOpts ) use ( $dbKey, $code ) {
1033                                 // Try loading the message from the database
1034                                 $dbr = wfGetDB( DB_REPLICA );
1035                                 $setOpts += Database::getCacheSetOptions( $dbr );
1036                                 // Use newKnownCurrent() to avoid querying revision/user tables
1037                                 $title = Title::makeTitle( NS_MEDIAWIKI, $dbKey );
1038                                 $revision = Revision::newKnownCurrent( $dbr, $title );
1039                                 if ( !$revision ) {
1040                                         return '!NONEXISTENT';
1041                                 }
1042                                 $content = $revision->getContent();
1043                                 if ( $content ) {
1044                                         $message = $this->getMessageTextFromContent( $content );
1045                                 } else {
1046                                         LoggerFactory::getInstance( 'MessageCache' )->warning(
1047                                                 __METHOD__ . ': failed to load page text for \'{titleKey}\'',
1048                                                 [ 'titleKey' => $dbKey, 'code' => $code ]
1049                                         );
1050                                         $message = null;
1051                                 }
1052
1053                                 if ( is_string( $message ) ) {
1054                                         return ' ' . $message;
1055                                 }
1056
1057                                 $ttl = 5; // possibly a temporary loading failure
1058
1059                                 return '!NONEXISTENT';
1060                         }
1061                 );
1062         }
1063
1064         /**
1065          * @param string $message
1066          * @param bool $interface
1067          * @param Language|null $language
1068          * @param Title|null $title
1069          * @return string
1070          */
1071         public function transform( $message, $interface = false, $language = null, $title = null ) {
1072                 // Avoid creating parser if nothing to transform
1073                 if ( strpos( $message, '{{' ) === false ) {
1074                         return $message;
1075                 }
1076
1077                 if ( $this->mInParser ) {
1078                         return $message;
1079                 }
1080
1081                 $parser = $this->getParser();
1082                 if ( $parser ) {
1083                         $popts = $this->getParserOptions();
1084                         $popts->setInterfaceMessage( $interface );
1085                         $popts->setTargetLanguage( $language );
1086
1087                         $userlang = $popts->setUserLang( $language );
1088                         $this->mInParser = true;
1089                         $message = $parser->transformMsg( $message, $popts, $title );
1090                         $this->mInParser = false;
1091                         $popts->setUserLang( $userlang );
1092                 }
1093
1094                 return $message;
1095         }
1096
1097         /**
1098          * @return Parser
1099          */
1100         public function getParser() {
1101                 global $wgParser, $wgParserConf;
1102
1103                 if ( !$this->mParser && isset( $wgParser ) ) {
1104                         # Do some initialisation so that we don't have to do it twice
1105                         $wgParser->firstCallInit();
1106                         # Clone it and store it
1107                         $class = $wgParserConf['class'];
1108                         if ( $class == ParserDiffTest::class ) {
1109                                 # Uncloneable
1110                                 $this->mParser = new $class( $wgParserConf );
1111                         } else {
1112                                 $this->mParser = clone $wgParser;
1113                         }
1114                 }
1115
1116                 return $this->mParser;
1117         }
1118
1119         /**
1120          * @param string $text
1121          * @param Title|null $title
1122          * @param bool $linestart Whether or not this is at the start of a line
1123          * @param bool $interface Whether this is an interface message
1124          * @param Language|string|null $language Language code
1125          * @return ParserOutput|string
1126          */
1127         public function parse( $text, $title = null, $linestart = true,
1128                 $interface = false, $language = null
1129         ) {
1130                 global $wgTitle;
1131
1132                 if ( $this->mInParser ) {
1133                         return htmlspecialchars( $text );
1134                 }
1135
1136                 $parser = $this->getParser();
1137                 $popts = $this->getParserOptions();
1138                 $popts->setInterfaceMessage( $interface );
1139
1140                 if ( is_string( $language ) ) {
1141                         $language = Language::factory( $language );
1142                 }
1143                 $popts->setTargetLanguage( $language );
1144
1145                 if ( !$title || !$title instanceof Title ) {
1146                         wfDebugLog( 'GlobalTitleFail', __METHOD__ . ' called by ' .
1147                                 wfGetAllCallers( 6 ) . ' with no title set.' );
1148                         $title = $wgTitle;
1149                 }
1150                 // Sometimes $wgTitle isn't set either...
1151                 if ( !$title ) {
1152                         # It's not uncommon having a null $wgTitle in scripts. See r80898
1153                         # Create a ghost title in such case
1154                         $title = Title::makeTitle( NS_SPECIAL, 'Badtitle/title not set in ' . __METHOD__ );
1155                 }
1156
1157                 $this->mInParser = true;
1158                 $res = $parser->parse( $text, $title, $popts, $linestart );
1159                 $this->mInParser = false;
1160
1161                 return $res;
1162         }
1163
1164         public function disable() {
1165                 $this->mDisable = true;
1166         }
1167
1168         public function enable() {
1169                 $this->mDisable = false;
1170         }
1171
1172         /**
1173          * Whether DB/cache usage is disabled for determining messages
1174          *
1175          * If so, this typically indicates either:
1176          *   - a) load() failed to find a cached copy nor query the DB
1177          *   - b) we are in a special context or error mode that cannot use the DB
1178          * If the DB is ignored, any derived HTML output or cached objects may be wrong.
1179          * To avoid long-term cache pollution, TTLs can be adjusted accordingly.
1180          *
1181          * @return bool
1182          * @since 1.27
1183          */
1184         public function isDisabled() {
1185                 return $this->mDisable;
1186         }
1187
1188         /**
1189          * Clear all stored messages in global and local cache
1190          *
1191          * Mainly used after a mass rebuild
1192          */
1193         public function clear() {
1194                 $langs = Language::fetchLanguageNames( null, 'mw' );
1195                 foreach ( array_keys( $langs ) as $code ) {
1196                         $this->wanCache->touchCheckKey( $this->getCheckKey( $code ) );
1197                 }
1198                 $this->cache->clear();
1199         }
1200
1201         /**
1202          * @param string $key
1203          * @return array
1204          */
1205         public function figureMessage( $key ) {
1206                 global $wgLanguageCode;
1207
1208                 $pieces = explode( '/', $key );
1209                 if ( count( $pieces ) < 2 ) {
1210                         return [ $key, $wgLanguageCode ];
1211                 }
1212
1213                 $lang = array_pop( $pieces );
1214                 if ( !Language::fetchLanguageName( $lang, null, 'mw' ) ) {
1215                         return [ $key, $wgLanguageCode ];
1216                 }
1217
1218                 $message = implode( '/', $pieces );
1219
1220                 return [ $message, $lang ];
1221         }
1222
1223         /**
1224          * Get all message keys stored in the message cache for a given language.
1225          * If $code is the content language code, this will return all message keys
1226          * for which MediaWiki:msgkey exists. If $code is another language code, this
1227          * will ONLY return message keys for which MediaWiki:msgkey/$code exists.
1228          * @param string $code Language code
1229          * @return array Array of message keys (strings)
1230          */
1231         public function getAllMessageKeys( $code ) {
1232                 global $wgContLang;
1233
1234                 $this->load( $code );
1235                 if ( !$this->cache->has( $code ) ) {
1236                         // Apparently load() failed
1237                         return null;
1238                 }
1239                 // Remove administrative keys
1240                 $cache = $this->cache->get( $code );
1241                 unset( $cache['VERSION'] );
1242                 unset( $cache['EXPIRY'] );
1243                 unset( $cache['EXCESSIVE'] );
1244                 // Remove any !NONEXISTENT keys
1245                 $cache = array_diff( $cache, [ '!NONEXISTENT' ] );
1246
1247                 // Keys may appear with a capital first letter. lcfirst them.
1248                 return array_map( [ $wgContLang, 'lcfirst' ], array_keys( $cache ) );
1249         }
1250
1251         /**
1252          * Purge message caches when a MediaWiki: page is created, updated, or deleted
1253          *
1254          * @param Title $title Message page title
1255          * @param Content|null $content New content for edit/create, null on deletion
1256          * @since 1.29
1257          */
1258         public function updateMessageOverride( Title $title, Content $content = null ) {
1259                 global $wgContLang;
1260
1261                 $msgText = $this->getMessageTextFromContent( $content );
1262                 if ( $msgText === null ) {
1263                         $msgText = false; // treat as not existing
1264                 }
1265
1266                 $this->replace( $title->getDBkey(), $msgText );
1267
1268                 if ( $wgContLang->hasVariants() ) {
1269                         $wgContLang->updateConversionTable( $title );
1270                 }
1271         }
1272
1273         /**
1274          * @param string $code Language code
1275          * @return string WAN cache key usable as a "check key" against language page edits
1276          */
1277         public function getCheckKey( $code ) {
1278                 return $this->wanCache->makeKey( 'messages', $code );
1279         }
1280
1281         /**
1282          * @param Content|null $content Content or null if the message page does not exist
1283          * @return string|bool|null Returns false if $content is null and null on error
1284          */
1285         private function getMessageTextFromContent( Content $content = null ) {
1286                 // @TODO: could skip pseudo-messages like js/css here, based on content model
1287                 if ( $content ) {
1288                         // Message page exists...
1289                         // XXX: Is this the right way to turn a Content object into a message?
1290                         // NOTE: $content is typically either WikitextContent, JavaScriptContent or
1291                         //       CssContent. MessageContent is *not* used for storing messages, it's
1292                         //       only used for wrapping them when needed.
1293                         $msgText = $content->getWikitextForTransclusion();
1294                         if ( $msgText === false || $msgText === null ) {
1295                                 // This might be due to some kind of misconfiguration...
1296                                 $msgText = null;
1297                                 LoggerFactory::getInstance( 'MessageCache' )->warning(
1298                                         __METHOD__ . ": message content doesn't provide wikitext "
1299                                         . "(content model: " . $content->getModel() . ")" );
1300                         }
1301                 } else {
1302                         // Message page does not exist...
1303                         $msgText = false;
1304                 }
1305
1306                 return $msgText;
1307         }
1308
1309         /**
1310          * @param string $hash Hash for this version of the entire key/value overrides map
1311          * @param string $title Message cache key with initial uppercase letter
1312          * @return string
1313          */
1314         private function bigMessageCacheKey( $hash, $title ) {
1315                 return $this->wanCache->makeKey( 'messages-big', $hash, $title );
1316         }
1317 }