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