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