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
  24 /**
  25  * MediaWiki message cache structure version.
  26  * Bump this whenever the message cache format has changed.
  27  */
  28 define( 'MSG_CACHE_VERSION', 1 );
  29
  30 /**
  31  * Memcached timeout when loading a key.
  32  * See MessageCache::load()
  33  */
  34 define( 'MSG_LOAD_TIMEOUT', 60 );
  35
  36 /**
  37  * Memcached timeout when locking a key for a writing operation.
  38  * See MessageCache::lock()
  39  */
  40 define( 'MSG_LOCK_TIMEOUT', 30 );
  41 /**
  42  * Number of times we will try to acquire a lock from Memcached.
  43  * This comes in addition to MSG_LOCK_TIMEOUT.
  44  */
  45 define( 'MSG_WAIT_TIMEOUT', 30 );
  46
  47 /**
  48  * Message cache
  49  * Performs various MediaWiki namespace-related functions
  50  * @ingroup Cache
  51  */
  52 class MessageCache {
  53         /**
  54          * Process local cache of loaded messages that are defined in
  55          * MediaWiki namespace. First array level is a language code,
  56          * second level is message key and the values are either message
  57          * content prefixed with space, or !NONEXISTENT for negative
  58          * caching.
  59          */
  60         protected $mCache;
  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 it's own parser which it uses to transform
  76          * messages.
  77          */
  78         protected $mParserOptions, $mParser;
  79
  80         /**
  81          * Variable for tracking which variables are already loaded
  82          * @var array $mLoadedLanguages
  83          */
  84         protected $mLoadedLanguages = array();
  85
  86         /**
  87          * Singleton instance
  88          *
  89          * @var MessageCache $instance
  90          */
  91         private static $instance;
  92
  93         /**
  94          * @var bool $mInParser
  95          */
  96         protected $mInParser = false;
  97
  98         /**
  99          * Get the signleton instance of this class
 100          *
 101          * @since 1.18
 102          * @return MessageCache
 103          */
 104         public static function singleton() {
 105                 if ( is_null( self::$instance ) ) {
 106                         global $wgUseDatabaseMessages, $wgMsgCacheExpiry;
 107                         self::$instance = new self(
 108                                 wfGetMessageCacheStorage(),
 109                                 $wgUseDatabaseMessages,
 110                                 $wgMsgCacheExpiry
 111                         );
 112                 }
 113                 return self::$instance;
 114         }
 115
 116         /**
 117          * Destroy the singleton instance
 118          *
 119          * @since 1.18
 120          */
 121         public static function destroyInstance() {
 122                 self::$instance = null;
 123         }
 124
 125         /**
 126          * @param ObjectCache $memCached A cache instance. If none, fall back to CACHE_NONE.
 127          * @param bool $useDB
 128          * @param int $expiry Lifetime for cache. @see $mExpiry.
 129          */
 130         function __construct( $memCached, $useDB, $expiry ) {
 131                 if ( !$memCached ) {
 132                         $memCached = wfGetCache( CACHE_NONE );
 133                 }
 134
 135                 $this->mMemc = $memCached;
 136                 $this->mDisable = !$useDB;
 137                 $this->mExpiry = $expiry;
 138         }
 139
 140         /**
 141          * ParserOptions is lazy initialised.
 142          *
 143          * @return ParserOptions
 144          */
 145         function getParserOptions() {
 146                 if ( !$this->mParserOptions ) {
 147                         $this->mParserOptions = new ParserOptions;
 148                         $this->mParserOptions->setEditSection( false );
 149                 }
 150                 return $this->mParserOptions;
 151         }
 152
 153         /**
 154          * Try to load the cache from a local file.
 155          *
 156          * @param string $hash the hash of contents, to check validity.
 157          * @param Mixed $code Optional language code, see documenation of load().
 158          * @return array The cache array
 159          */
 160         function getLocalCache( $hash, $code ) {
 161                 global $wgCacheDirectory;
 162
 163                 $filename = "$wgCacheDirectory/messages-" . wfWikiID() . "-$code";
 164
 165                 # Check file existence
 166                 wfSuppressWarnings();
 167                 $file = fopen( $filename, 'r' );
 168                 wfRestoreWarnings();
 169                 if ( !$file ) {
 170                         return false; // No cache file
 171                 }
 172
 173                 // Check to see if the file has the hash specified
 174                 $localHash = fread( $file, 32 );
 175                 if ( $hash === $localHash ) {
 176                         // All good, get the rest of it
 177                         $serialized = '';
 178                         while ( !feof( $file ) ) {
 179                                 $serialized .= fread( $file, 100000 );
 180                         }
 181                         fclose( $file );
 182                         return unserialize( $serialized );
 183                 } else {
 184                         fclose( $file );
 185                         return false; // Wrong hash
 186                 }
 187         }
 188
 189         /**
 190          * Save the cache to a local file.
 191          */
 192         function saveToLocal( $serialized, $hash, $code ) {
 193                 global $wgCacheDirectory;
 194
 195                 $filename = "$wgCacheDirectory/messages-" . wfWikiID() . "-$code";
 196                 wfMkdirParents( $wgCacheDirectory, null, __METHOD__ ); // might fail
 197
 198                 wfSuppressWarnings();
 199                 $file = fopen( $filename, 'w' );
 200                 wfRestoreWarnings();
 201
 202                 if ( !$file ) {
 203                         wfDebug( "Unable to open local cache file for writing\n" );
 204                         return;
 205                 }
 206
 207                 fwrite( $file, $hash . $serialized );
 208                 fclose( $file );
 209                 wfSuppressWarnings();
 210                 chmod( $filename, 0666 );
 211                 wfRestoreWarnings();
 212         }
 213
 214         /**
 215          * Loads messages from caches or from database in this order:
 216          * (1) local message cache (if $wgUseLocalMessageCache is enabled)
 217          * (2) memcached
 218          * (3) from the database.
 219          *
 220          * When succesfully loading from (2) or (3), all higher level caches are
 221          * updated for the newest version.
 222          *
 223          * Nothing is loaded if member variable mDisable is true, either manually
 224          * set by calling code or if message loading fails (is this possible?).
 225          *
 226          * Returns true if cache is already populated or it was succesfully populated,
 227          * or false if populating empty cache fails. Also returns true if MessageCache
 228          * is disabled.
 229          *
 230          * @param bool|String $code Language to which load messages
 231          * @throws MWException
 232          * @return bool
 233          */
 234         function load( $code = false ) {
 235                 global $wgUseLocalMessageCache;
 236
 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] ) ) {
 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                         return true;
 257                 }
 258
 259                 # Loading code starts
 260                 wfProfileIn( __METHOD__ );
 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 = array(); # Debug info, delayed to avoid spamming debug log too much
 264                 $cacheKey = wfMemcKey( 'messages', $code ); # Key in memc for messages
 265
 266                 # Local cache
 267                 # Hash of the contents is stored in memcache, to detect if local cache goes
 268                 # out of date (e.g. due to replace() on some other server)
 269                 if ( $wgUseLocalMessageCache ) {
 270                         wfProfileIn( __METHOD__ . '-fromlocal' );
 271
 272                         $hash = $this->mMemc->get( wfMemcKey( 'messages', $code, 'hash' ) );
 273                         if ( $hash ) {
 274                                 $cache = $this->getLocalCache( $hash, $code );
 275                                 if ( !$cache ) {
 276                                         $where[] = 'local cache is empty or has the wrong hash';
 277                                 } elseif ( $this->isCacheExpired( $cache ) ) {
 278                                         $where[] = 'local cache is expired';
 279                                         $staleCache = $cache;
 280                                 } else {
 281                                         $where[] = 'got from local cache';
 282                                         $success = true;
 283                                         $this->mCache[$code] = $cache;
 284                                 }
 285                         }
 286                         wfProfileOut( __METHOD__ . '-fromlocal' );
 287                 }
 288
 289                 if ( !$success ) {
 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 < 2; $failedAttempts++ ) {
 294                                 wfProfileIn( __METHOD__ . '-fromcache' );
 295                                 $cache = $this->mMemc->get( $cacheKey );
 296                                 if ( !$cache ) {
 297                                         $where[] = 'global cache is empty';
 298                                 } elseif ( $this->isCacheExpired( $cache ) ) {
 299                                         $where[] = 'global cache is expired';
 300                                         $staleCache = $cache;
 301                                 } else {
 302                                         $where[] = 'got from global cache';
 303                                         $this->mCache[$code] = $cache;
 304                                         $this->saveToCaches( $cache, 'local-only', $code );
 305                                         $success = true;
 306                                 }
 307
 308                                 wfProfileOut( __METHOD__ . '-fromcache' );
 309
 310                                 if ( $success ) {
 311                                         # Done, no need to retry
 312                                         break;
 313                                 }
 314
 315                                 # We need to call loadFromDB. Limit the concurrency to a single
 316                                 # process. This prevents the site from going down when the cache
 317                                 # expires.
 318                                 $statusKey = wfMemcKey( 'messages', $code, 'status' );
 319                                 $acquired = $this->mMemc->add( $statusKey, 'loading', MSG_LOAD_TIMEOUT );
 320                                 if ( $acquired ) {
 321                                         # Unlock the status key if there is an exception
 322                                         $that = $this;
 323                                         $statusUnlocker = new ScopedCallback( function () use ( $that, $statusKey ) {
 324                                                 $that->mMemc->delete( $statusKey );
 325                                         } );
 326
 327                                         # Now let's regenerate
 328                                         $where[] = 'loading from database';
 329
 330                                         # Lock the cache to prevent conflicting writes
 331                                         # If this lock fails, it doesn't really matter, it just means the
 332                                         # write is potentially non-atomic, e.g. the results of a replace()
 333                                         # may be discarded.
 334                                         if ( $this->lock( $cacheKey ) ) {
 335                                                 $mainUnlocker = new ScopedCallback( function () use ( $that, $cacheKey ) {
 336                                                         $that->unlock( $cacheKey );
 337                                                 } );
 338                                         } else {
 339                                                 $mainUnlocker = null;
 340                                                 $where[] = 'could not acquire main lock';
 341                                         }
 342
 343                                         $cache = $this->loadFromDB( $code );
 344                                         $this->mCache[$code] = $cache;
 345                                         $success = true;
 346                                         $saveSuccess = $this->saveToCaches( $cache, 'all', $code );
 347
 348                                         # Unlock
 349                                         ScopedCallback::consume( $mainUnlocker );
 350                                         ScopedCallback::consume( $statusUnlocker );
 351
 352                                         if ( !$saveSuccess ) {
 353                                                 # Cache save has failed.
 354                                                 # There are two main scenarios where this could be a problem:
 355                                                 #
 356                                                 #   - The cache is more than the maximum size (typically
 357                                                 #     1MB compressed).
 358                                                 #
 359                                                 #   - Memcached has no space remaining in the relevant slab
 360                                                 #     class. This is unlikely with recent versions of
 361                                                 #     memcached.
 362                                                 #
 363                                                 # Either way, if there is a local cache, nothing bad will
 364                                                 # happen. If there is no local cache, disabling the message
 365                                                 # cache for all requests avoids incurring a loadFromDB()
 366                                                 # overhead on every request, and thus saves the wiki from
 367                                                 # complete downtime under moderate traffic conditions.
 368                                                 if ( !$wgUseLocalMessageCache ) {
 369                                                         $this->mMemc->set( $statusKey, 'error', 60 * 5 );
 370                                                         $where[] = 'could not save cache, disabled globally for 5 minutes';
 371                                                 } else {
 372                                                         $where[] = "could not save global cache";
 373                                                 }
 374                                         }
 375
 376                                         # Load from DB complete, no need to retry
 377                                         break;
 378                                 } elseif ( $staleCache ) {
 379                                         # Use the stale cache while some other thread constructs the new one
 380                                         $where[] = 'using stale cache';
 381                                         $this->mCache[$code] = $staleCache;
 382                                         $success = true;
 383                                         break;
 384                                 } elseif ( $failedAttempts > 0 ) {
 385                                         # Already retried once, still failed, so don't do another lock/unlock cycle
 386                                         # This case will typically be hit if memcached is down, or if
 387                                         # loadFromDB() takes longer than MSG_WAIT_TIMEOUT
 388                                         $where[] = "could not acquire status key.";
 389                                         break;
 390                                 } else {
 391                                         $status = $this->mMemc->get( $statusKey );
 392                                         if ( $status === 'error' ) {
 393                                                 # Disable cache
 394                                                 break;
 395                                         } else {
 396                                                 # Wait for the other thread to finish, then retry
 397                                                 $where[] = 'waited for other thread to complete';
 398                                                 $this->lock( $cacheKey );
 399                                                 $this->unlock( $cacheKey );
 400                                         }
 401                                 }
 402                         }
 403                 }
 404
 405                 if ( !$success ) {
 406                         $where[] = 'loading FAILED - cache is disabled';
 407                         $this->mDisable = true;
 408                         $this->mCache = false;
 409                         # This used to throw an exception, but that led to nasty side effects like
 410                         # the whole wiki being instantly down if the memcached server died
 411                 } else {
 412                         # All good, just record the success
 413                         $this->mLoadedLanguages[$code] = true;
 414                 }
 415                 $info = implode( ', ', $where );
 416                 wfDebug( __METHOD__ . ": Loading $code... $info\n" );
 417                 wfProfileOut( __METHOD__ );
 418                 return $success;
 419         }
 420
 421         /**
 422          * Loads cacheable messages from the database. Messages bigger than
 423          * $wgMaxMsgCacheEntrySize are assigned a special value, and are loaded
 424          * on-demand from the database later.
 425          *
 426          * @param string $code Language code.
 427          * @return array Loaded messages for storing in caches.
 428          */
 429         function loadFromDB( $code ) {
 430                 wfProfileIn( __METHOD__ );
 431                 global $wgMaxMsgCacheEntrySize, $wgLanguageCode, $wgAdaptiveMessageCache;
 432                 $dbr = wfGetDB( DB_SLAVE );
 433                 $cache = array();
 434
 435                 # Common conditions
 436                 $conds = array(
 437                         'page_is_redirect' => 0,
 438                         'page_namespace' => NS_MEDIAWIKI,
 439                 );
 440
 441                 $mostused = array();
 442                 if ( $wgAdaptiveMessageCache && $code !== $wgLanguageCode ) {
 443                         if ( !isset( $this->mCache[$wgLanguageCode] ) ) {
 444                                 $this->load( $wgLanguageCode );
 445                         }
 446                         $mostused = array_keys( $this->mCache[$wgLanguageCode] );
 447                         foreach ( $mostused as $key => $value ) {
 448                                 $mostused[$key] = "$value/$code";
 449                         }
 450                 }
 451
 452                 if ( count( $mostused ) ) {
 453                         $conds['page_title'] = $mostused;
 454                 } elseif ( $code !== $wgLanguageCode ) {
 455                         $conds[] = 'page_title' . $dbr->buildLike( $dbr->anyString(), '/', $code );
 456                 } else {
 457                         # Effectively disallows use of '/' character in NS_MEDIAWIKI for uses
 458                         # other than language code.
 459                         $conds[] = 'page_title NOT' . $dbr->buildLike( $dbr->anyString(), '/', $dbr->anyString() );
 460                 }
 461
 462                 # Conditions to fetch oversized pages to ignore them
 463                 $bigConds = $conds;
 464                 $bigConds[] = 'page_len > ' . intval( $wgMaxMsgCacheEntrySize );
 465
 466                 # Load titles for all oversized pages in the MediaWiki namespace
 467                 $res = $dbr->select( 'page', 'page_title', $bigConds, __METHOD__ . "($code)-big" );
 468                 foreach ( $res as $row ) {
 469                         $cache[$row->page_title] = '!TOO BIG';
 470                 }
 471
 472                 # Conditions to load the remaining pages with their contents
 473                 $smallConds = $conds;
 474                 $smallConds[] = 'page_latest=rev_id';
 475                 $smallConds[] = 'rev_text_id=old_id';
 476                 $smallConds[] = 'page_len <= ' . intval( $wgMaxMsgCacheEntrySize );
 477
 478                 $res = $dbr->select(
 479                         array( 'page', 'revision', 'text' ),
 480                         array( 'page_title', 'old_text', 'old_flags' ),
 481                         $smallConds,
 482                         __METHOD__ . "($code)-small"
 483                 );
 484
 485                 foreach ( $res as $row ) {
 486                         $text = Revision::getRevisionText( $row );
 487                         if ( $text === false ) {
 488                                 // Failed to fetch data; possible ES errors?
 489                                 // Store a marker to fetch on-demand as a workaround...
 490                                 $entry = '!TOO BIG';
 491                                 wfDebugLog(
 492                                         'MessageCache',
 493                                         __METHOD__
 494                                                 . ": failed to load message page text for {$row->page_title} ($code)"
 495                                 );
 496                         } else {
 497                                 $entry = ' ' . $text;
 498                         }
 499                         $cache[$row->page_title] = $entry;
 500                 }
 501
 502                 $cache['VERSION'] = MSG_CACHE_VERSION;
 503                 $cache['EXPIRY'] = wfTimestamp( TS_MW, time() + $this->mExpiry );
 504                 wfProfileOut( __METHOD__ );
 505                 return $cache;
 506         }
 507
 508         /**
 509          * Updates cache as necessary when message page is changed
 510          *
 511          * @param string $title Name of the page changed.
 512          * @param mixed $text New contents of the page.
 513          */
 514         public function replace( $title, $text ) {
 515                 global $wgMaxMsgCacheEntrySize;
 516                 wfProfileIn( __METHOD__ );
 517
 518                 if ( $this->mDisable ) {
 519                         wfProfileOut( __METHOD__ );
 520                         return;
 521                 }
 522
 523                 list( $msg, $code ) = $this->figureMessage( $title );
 524
 525                 $cacheKey = wfMemcKey( 'messages', $code );
 526                 $this->load( $code );
 527                 $this->lock( $cacheKey );
 528
 529                 $titleKey = wfMemcKey( 'messages', 'individual', $title );
 530
 531                 if ( $text === false ) {
 532                         # Article was deleted
 533                         $this->mCache[$code][$title] = '!NONEXISTENT';
 534                         $this->mMemc->delete( $titleKey );
 535                 } elseif ( strlen( $text ) > $wgMaxMsgCacheEntrySize ) {
 536                         # Check for size
 537                         $this->mCache[$code][$title] = '!TOO BIG';
 538                         $this->mMemc->set( $titleKey, ' ' . $text, $this->mExpiry );
 539                 } else {
 540                         $this->mCache[$code][$title] = ' ' . $text;
 541                         $this->mMemc->delete( $titleKey );
 542                 }
 543
 544                 # Update caches
 545                 $this->saveToCaches( $this->mCache[$code], 'all', $code );
 546                 $this->unlock( $cacheKey );
 547
 548                 // Also delete cached sidebar... just in case it is affected
 549                 $codes = array( $code );
 550                 if ( $code === 'en' ) {
 551                         // Delete all sidebars, like for example on action=purge on the
 552                         // sidebar messages
 553                         $codes = array_keys( Language::fetchLanguageNames() );
 554                 }
 555
 556                 global $wgMemc;
 557                 foreach ( $codes as $code ) {
 558                         $sidebarKey = wfMemcKey( 'sidebar', $code );
 559                         $wgMemc->delete( $sidebarKey );
 560                 }
 561
 562                 // Update the message in the message blob store
 563                 global $wgContLang;
 564                 MessageBlobStore::updateMessage( $wgContLang->lcfirst( $msg ) );
 565
 566                 wfRunHooks( 'MessageCacheReplace', array( $title, $text ) );
 567
 568                 wfProfileOut( __METHOD__ );
 569         }
 570
 571         /**
 572          * Is the given cache array expired due to time passing or a version change?
 573          *
 574          * @param $cache
 575          * @return bool
 576          */
 577         protected function isCacheExpired( $cache ) {
 578                 if ( !isset( $cache['VERSION'] ) || !isset( $cache['EXPIRY'] ) ) {
 579                         return true;
 580                 }
 581                 if ( $cache['VERSION'] != MSG_CACHE_VERSION ) {
 582                         return true;
 583                 }
 584                 if ( wfTimestampNow() >= $cache['EXPIRY'] ) {
 585                         return true;
 586                 }
 587                 return false;
 588         }
 589
 590         /**
 591          * Shortcut to update caches.
 592          *
 593          * @param array $cache Cached messages with a version.
 594          * @param string $dest Either "local-only" to save to local caches only
 595          *   or "all" to save to all caches.
 596          * @param string|bool $code Language code (default: false)
 597          * @return bool
 598          */
 599         protected function saveToCaches( $cache, $dest, $code = false ) {
 600                 wfProfileIn( __METHOD__ );
 601                 global $wgUseLocalMessageCache;
 602
 603                 $cacheKey = wfMemcKey( 'messages', $code );
 604
 605                 if ( $dest === 'all' ) {
 606                         $success = $this->mMemc->set( $cacheKey, $cache );
 607                 } else {
 608                         $success = true;
 609                 }
 610
 611                 # Save to local cache
 612                 if ( $wgUseLocalMessageCache ) {
 613                         $serialized = serialize( $cache );
 614                         $hash = md5( $serialized );
 615                         $this->mMemc->set( wfMemcKey( 'messages', $code, 'hash' ), $hash );
 616                         $this->saveToLocal( $serialized, $hash, $code );
 617                 }
 618
 619                 wfProfileOut( __METHOD__ );
 620                 return $success;
 621         }
 622
 623         /**
 624          * Represents a write lock on the messages key.
 625          *
 626          * Will retry MessageCache::MSG_WAIT_TIMEOUT times, each operations having
 627          * a timeout of MessageCache::MSG_LOCK_TIMEOUT.
 628          *
 629          * @param string $key
 630          * @return Boolean: success
 631          */
 632         function lock( $key ) {
 633                 $lockKey = $key . ':lock';
 634                 $acquired = false;
 635                 $testDone = false;
 636                 for ( $i = 0; $i < MSG_WAIT_TIMEOUT && !$acquired; $i++ ) {
 637                         $acquired = $this->mMemc->add( $lockKey, 1, MSG_LOCK_TIMEOUT );
 638                         if ( $acquired ) {
 639                                 break;
 640                         }
 641
 642                         # Fail fast if memcached is totally down
 643                         if ( !$testDone ) {
 644                                 $testDone = true;
 645                                 if ( !$this->mMemc->set( wfMemcKey( 'test' ), 'test', 1 ) ) {
 646                                         break;
 647                                 }
 648                         }
 649                         sleep( 1 );
 650                 }
 651
 652                 return $acquired;
 653         }
 654
 655         function unlock( $key ) {
 656                 $lockKey = $key . ':lock';
 657                 $this->mMemc->delete( $lockKey );
 658         }
 659
 660         /**
 661          * Get a message from either the content language or the user language.
 662          *
 663          * First, assemble a list of languages to attempt getting the message from. This
 664          * chain begins with the requested language and its fallbacks and then continues with
 665          * the content language and its fallbacks. For each language in the chain, the following
 666          * process will occur (in this order):
 667          *  1. If a language-specific override, i.e., [[MW:msg/lang]], is available, use that.
 668          *     Note: for the content language, there is no /lang subpage.
 669          *  2. Fetch from the static CDB cache.
 670          *  3. If available, check the database for fallback language overrides.
 671          *
 672          * This process provides a number of guarantees. When changing this code, make sure all
 673          * of these guarantees are preserved.
 674          *  * If the requested language is *not* the content language, then the CDB cache for that
 675          *    specific language will take precedence over the root database page ([[MW:msg]]).
 676          *  * Fallbacks will be just that: fallbacks. A fallback language will never be reached if
 677          *    the message is available *anywhere* in the language for which it is a fallback.
 678          *
 679          * @param string $key the message key
 680          * @param bool $useDB If true, look for the message in the DB, false
 681          *                    to use only the compiled l10n cache.
 682          * @param bool|string|object $langcode Code of the language to get the message for.
 683          *        - If string and a valid code, will create a standard language object
 684          *        - If string but not a valid code, will create a basic language object
 685          *        - If boolean and false, create object from the current users language
 686          *        - If boolean and true, create object from the wikis content language
 687          *        - If language object, use it as given
 688          * @param bool $isFullKey specifies whether $key is a two part key
 689          *                   "msg/lang".
 690          *
 691          * @throws MWException when given an invalid key
 692          * @return string|bool False if the message doesn't exist, otherwise the message (which can be empty)
 693          */
 694         function get( $key, $useDB = true, $langcode = true, $isFullKey = false ) {
 695                 global $wgContLang;
 696
 697                 $section = new ProfileSection( __METHOD__ );
 698
 699                 if ( is_int( $key ) ) {
 700                         // Fix numerical strings that somehow become ints
 701                         // on their way here
 702                         $key = (string)$key;
 703                 } elseif ( !is_string( $key ) ) {
 704                         throw new MWException( 'Non-string key given' );
 705                 } elseif ( $key === '' ) {
 706                         // Shortcut: the empty key is always missing
 707                         return false;
 708                 }
 709
 710                 // For full keys, get the language code from the key
 711                 $pos = strrpos( $key, '/' );
 712                 if ( $isFullKey && $pos !== false ) {
 713                         $langcode = substr( $key, $pos + 1 );
 714                         $key = substr( $key, 0, $pos );
 715                 }
 716
 717                 // Normalise title-case input (with some inlining)
 718                 $lckey = strtr( $key, ' ', '_' );
 719                 if ( ord( $key ) < 128 ) {
 720                         $lckey[0] = strtolower( $lckey[0] );
 721                         $uckey = ucfirst( $lckey );
 722                 } else {
 723                         $lckey = $wgContLang->lcfirst( $lckey );
 724                         $uckey = $wgContLang->ucfirst( $lckey );
 725                 }
 726
 727                 // Loop through each language in the fallback list until we find something useful
 728                 $lang = wfGetLangObj( $langcode );
 729                 $message = $this->getMessageFromFallbackChain( $lang, $lckey, $uckey, !$this->mDisable && $useDB );
 730
 731                 // If we still have no message, maybe the key was in fact a full key so try that
 732                 if ( $message === false ) {
 733                         $parts = explode( '/', $lckey );
 734                         // We may get calls for things that are http-urls from sidebar
 735                         // Let's not load nonexistent languages for those
 736                         // They usually have more than one slash.
 737                         if ( count( $parts ) == 2 && $parts[1] !== '' ) {
 738                                 $message = Language::getMessageFor( $parts[0], $parts[1] );
 739                                 if ( $message === null ) {
 740                                         $message = false;
 741                                 }
 742                         }
 743                 }
 744
 745                 // Post-processing if the message exists
 746                 if ( $message !== false ) {
 747                         // Fix whitespace
 748                         $message = str_replace(
 749                                 array(
 750                                         # Fix for trailing whitespace, removed by textarea
 751                                         '&#32;',
 752                                         # Fix for NBSP, converted to space by firefox
 753                                         '&nbsp;',
 754                                         '&#160;',
 755                                 ),
 756                                 array(
 757                                         ' ',
 758                                         "\xc2\xa0",
 759                                         "\xc2\xa0"
 760                                 ),
 761                                 $message
 762                         );
 763                 }
 764
 765                 return $message;
 766         }
 767
 768         /**
 769          * Given a language, try and fetch a message from that language, then the
 770          * fallbacks of that language, then the site language, then the fallbacks for the
 771          * site language.
 772          *
 773          * @param Language $lang Requested language
 774          * @param string $lckey Lowercase key for the message
 775          * @param string $uckey Uppercase key for the message
 776          * @param bool $useDB Whether to use the database
 777          *
 778          * @see MessageCache::get
 779          * @return string|bool The message, or false if not found
 780          */
 781         protected function getMessageFromFallbackChain( $lang, $lckey, $uckey, $useDB ) {
 782                 global $wgLanguageCode, $wgContLang;
 783
 784                 $langcode = $lang->getCode();
 785                 $message = false;
 786
 787                 // First try the requested language.
 788                 if ( $useDB ) {
 789                         if ( $langcode === $wgLanguageCode ) {
 790                                 // Messages created in the content language will not have the /lang extension
 791                                 $message = $this->getMsgFromNamespace( $uckey, $langcode );
 792                         } else {
 793                                 $message = $this->getMsgFromNamespace( "$uckey/$langcode", $langcode );
 794                         }
 795                 }
 796
 797                 if ( $message !== false ) {
 798                         return $message;
 799                 }
 800
 801                 // Check the CDB cache
 802                 $message = $lang->getMessage( $lckey );
 803                 if ( $message !== null ) {
 804                         return $message;
 805                 }
 806
 807                 list( $fallbackChain, $siteFallbackChain ) = Language::getFallbacksIncludingSiteLanguage( $langcode );
 808
 809                 // Next try checking the database for all of the fallback languages of the requested language.
 810                 if ( $useDB ) {
 811                         foreach ( $fallbackChain as $code ) {
 812                                 if ( $code === $wgLanguageCode ) {
 813                                         // Messages created in the content language will not have the /lang extension
 814                                         $message = $this->getMsgFromNamespace( $uckey, $code );
 815                                 } else {
 816                                         $message = $this->getMsgFromNamespace( "$uckey/$code", $code );
 817                                 }
 818
 819                                 if ( $message !== false ) {
 820                                         // Found the message.
 821                                         return $message;
 822                                 }
 823                         }
 824                 }
 825
 826                 // Now try checking the site language.
 827                 if ( $useDB ) {
 828                         $message = $this->getMsgFromNamespace( $uckey, $wgLanguageCode );
 829                         if ( $message !== false ) {
 830                                 return $message;
 831                         }
 832                 }
 833
 834                 $message = $wgContLang->getMessage( $lckey );
 835                 if ( $message !== null ) {
 836                         return $message;
 837                 }
 838
 839                 // Finally try the DB for the site language's fallbacks.
 840                 if ( $useDB ) {
 841                         foreach ( $siteFallbackChain as $code ) {
 842                                 $message = $this->getMsgFromNamespace( "$uckey/$code", $code );
 843                                 if ( $message === false && $code === $wgLanguageCode ) {
 844                                         // Messages created in the content language will not have the /lang extension
 845                                         $message = $this->getMsgFromNamespace( $uckey, $code );
 846                                 }
 847
 848                                 if ( $message !== false ) {
 849                                         // Found the message.
 850                                         return $message;
 851                                 }
 852                         }
 853                 }
 854
 855                 return false;
 856         }
 857
 858         /**
 859          * Get a message from the MediaWiki namespace, with caching. The key must
 860          * first be converted to two-part lang/msg form if necessary.
 861          *
 862          * Unlike self::get(), this function doesn't resolve fallback chains, and
 863          * some callers require this behavior. LanguageConverter::parseCachedTable()
 864          * and self::get() are some examples in core.
 865          *
 866          * @param string $title Message cache key with initial uppercase letter.
 867          * @param string $code Code denoting the language to try.
 868          * @return string|bool The message, or false iff it does not exist or on error
 869          */
 870         function getMsgFromNamespace( $title, $code ) {
 871                 $this->load( $code );
 872                 if ( isset( $this->mCache[$code][$title] ) ) {
 873                         $entry = $this->mCache[$code][$title];
 874                         if ( substr( $entry, 0, 1 ) === ' ' ) {
 875                                 // The message exists, so make sure a string
 876                                 // is returned.
 877                                 return (string)substr( $entry, 1 );
 878                         } elseif ( $entry === '!NONEXISTENT' ) {
 879                                 return false;
 880                         } elseif ( $entry === '!TOO BIG' ) {
 881                                 // Fall through and try invididual message cache below
 882                         }
 883                 } else {
 884                         // XXX: This is not cached in process cache, should it?
 885                         $message = false;
 886                         wfRunHooks( 'MessagesPreLoad', array( $title, &$message ) );
 887                         if ( $message !== false ) {
 888                                 return $message;
 889                         }
 890
 891                         return false;
 892                 }
 893
 894                 # Try the individual message cache
 895                 $titleKey = wfMemcKey( 'messages', 'individual', $title );
 896                 $entry = $this->mMemc->get( $titleKey );
 897                 if ( $entry ) {
 898                         if ( substr( $entry, 0, 1 ) === ' ' ) {
 899                                 $this->mCache[$code][$title] = $entry;
 900                                 // The message exists, so make sure a string
 901                                 // is returned.
 902                                 return (string)substr( $entry, 1 );
 903                         } elseif ( $entry === '!NONEXISTENT' ) {
 904                                 $this->mCache[$code][$title] = '!NONEXISTENT';
 905                                 return false;
 906                         } else {
 907                                 # Corrupt/obsolete entry, delete it
 908                                 $this->mMemc->delete( $titleKey );
 909                         }
 910                 }
 911
 912                 # Try loading it from the database
 913                 $revision = Revision::newFromTitle(
 914                         Title::makeTitle( NS_MEDIAWIKI, $title ), false, Revision::READ_LATEST
 915                 );
 916                 if ( $revision ) {
 917                         $content = $revision->getContent();
 918                         if ( !$content ) {
 919                                 // A possibly temporary loading failure.
 920                                 wfDebugLog(
 921                                         'MessageCache',
 922                                         __METHOD__ . ": failed to load message page text for {$title} ($code)"
 923                                 );
 924                                 $message = null; // no negative caching
 925                         } else {
 926                                 // XXX: Is this the right way to turn a Content object into a message?
 927                                 // NOTE: $content is typically either WikitextContent, JavaScriptContent or
 928                                 //       CssContent. MessageContent is *not* used for storing messages, it's
 929                                 //       only used for wrapping them when needed.
 930                                 $message = $content->getWikitextForTransclusion();
 931
 932                                 if ( $message === false || $message === null ) {
 933                                         wfDebugLog(
 934                                                 'MessageCache',
 935                                                 __METHOD__ . ": message content doesn't provide wikitext "
 936                                                         . "(content model: " . $content->getContentHandler() . ")"
 937                                         );
 938
 939                                         $message = false; // negative caching
 940                                 } else {
 941                                         $this->mCache[$code][$title] = ' ' . $message;
 942                                         $this->mMemc->set( $titleKey, ' ' . $message, $this->mExpiry );
 943                                 }
 944                         }
 945                 } else {
 946                         $message = false; // negative caching
 947                 }
 948
 949                 if ( $message === false ) { // negative caching
 950                         $this->mCache[$code][$title] = '!NONEXISTENT';
 951                         $this->mMemc->set( $titleKey, '!NONEXISTENT', $this->mExpiry );
 952                 }
 953
 954                 return $message;
 955         }
 956
 957         /**
 958          * @param string $message
 959          * @param bool $interface
 960          * @param string $language Language code
 961          * @param Title $title
 962          * @return string
 963          */
 964         function transform( $message, $interface = false, $language = null, $title = null ) {
 965                 // Avoid creating parser if nothing to transform
 966                 if ( strpos( $message, '{{' ) === false ) {
 967                         return $message;
 968                 }
 969
 970                 if ( $this->mInParser ) {
 971                         return $message;
 972                 }
 973
 974                 $parser = $this->getParser();
 975                 if ( $parser ) {
 976                         $popts = $this->getParserOptions();
 977                         $popts->setInterfaceMessage( $interface );
 978                         $popts->setTargetLanguage( $language );
 979
 980                         $userlang = $popts->setUserLang( $language );
 981                         $this->mInParser = true;
 982                         $message = $parser->transformMsg( $message, $popts, $title );
 983                         $this->mInParser = false;
 984                         $popts->setUserLang( $userlang );
 985                 }
 986                 return $message;
 987         }
 988
 989         /**
 990          * @return Parser
 991          */
 992         function getParser() {
 993                 global $wgParser, $wgParserConf;
 994                 if ( !$this->mParser && isset( $wgParser ) ) {
 995                         # Do some initialisation so that we don't have to do it twice
 996                         $wgParser->firstCallInit();
 997                         # Clone it and store it
 998                         $class = $wgParserConf['class'];
 999                         if ( $class == 'Parser_DiffTest' ) {
1000                                 # Uncloneable
1001                                 $this->mParser = new $class( $wgParserConf );
1002                         } else {
1003                                 $this->mParser = clone $wgParser;
1004                         }
1005                 }
1006                 return $this->mParser;
1007         }
1008
1009         /**
1010          * @param string $text
1011          * @param Title $title
1012          * @param bool $linestart Whether or not this is at the start of a line
1013          * @param bool $interface Whether this is an interface message
1014          * @param string $language Language code
1015          * @return ParserOutput|string
1016          */
1017         public function parse( $text, $title = null, $linestart = true,
1018                 $interface = false, $language = null
1019         ) {
1020                 if ( $this->mInParser ) {
1021                         return htmlspecialchars( $text );
1022                 }
1023
1024                 $parser = $this->getParser();
1025                 $popts = $this->getParserOptions();
1026                 $popts->setInterfaceMessage( $interface );
1027                 $popts->setTargetLanguage( $language );
1028
1029                 wfProfileIn( __METHOD__ );
1030                 if ( !$title || !$title instanceof Title ) {
1031                         global $wgTitle;
1032                         $title = $wgTitle;
1033                 }
1034                 // Sometimes $wgTitle isn't set either...
1035                 if ( !$title ) {
1036                         # It's not uncommon having a null $wgTitle in scripts. See r80898
1037                         # Create a ghost title in such case
1038                         $title = Title::newFromText( 'Dwimmerlaik' );
1039                 }
1040
1041                 $this->mInParser = true;
1042                 $res = $parser->parse( $text, $title, $popts, $linestart );
1043                 $this->mInParser = false;
1044
1045                 wfProfileOut( __METHOD__ );
1046                 return $res;
1047         }
1048
1049         function disable() {
1050                 $this->mDisable = true;
1051         }
1052
1053         function enable() {
1054                 $this->mDisable = false;
1055         }
1056
1057         /**
1058          * Clear all stored messages. Mainly used after a mass rebuild.
1059          */
1060         function clear() {
1061                 $langs = Language::fetchLanguageNames( null, 'mw' );
1062                 foreach ( array_keys( $langs ) as $code ) {
1063                         # Global cache
1064                         $this->mMemc->delete( wfMemcKey( 'messages', $code ) );
1065                         # Invalidate all local caches
1066                         $this->mMemc->delete( wfMemcKey( 'messages', $code, 'hash' ) );
1067                 }
1068                 $this->mLoadedLanguages = array();
1069         }
1070
1071         /**
1072          * @param $key
1073          * @return array
1074          */
1075         public function figureMessage( $key ) {
1076                 global $wgLanguageCode;
1077                 $pieces = explode( '/', $key );
1078                 if ( count( $pieces ) < 2 ) {
1079                         return array( $key, $wgLanguageCode );
1080                 }
1081
1082                 $lang = array_pop( $pieces );
1083                 if ( !Language::fetchLanguageName( $lang, null, 'mw' ) ) {
1084                         return array( $key, $wgLanguageCode );
1085                 }
1086
1087                 $message = implode( '/', $pieces );
1088                 return array( $message, $lang );
1089         }
1090
1091         /**
1092          * Get all message keys stored in the message cache for a given language.
1093          * If $code is the content language code, this will return all message keys
1094          * for which MediaWiki:msgkey exists. If $code is another language code, this
1095          * will ONLY return message keys for which MediaWiki:msgkey/$code exists.
1096          * @param string $code Language code
1097          * @return array of message keys (strings)
1098          */
1099         public function getAllMessageKeys( $code ) {
1100                 global $wgContLang;
1101                 $this->load( $code );
1102                 if ( !isset( $this->mCache[$code] ) ) {
1103                         // Apparently load() failed
1104                         return null;
1105                 }
1106                 // Remove administrative keys
1107                 $cache = $this->mCache[$code];
1108                 unset( $cache['VERSION'] );
1109                 unset( $cache['EXPIRY'] );
1110                 // Remove any !NONEXISTENT keys
1111                 $cache = array_diff( $cache, array( '!NONEXISTENT' ) );
1112                 // Keys may appear with a capital first letter. lcfirst them.
1113                 return array_map( array( $wgContLang, 'lcfirst' ), array_keys( $cache ) );
1114         }
1115 }