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         const FOR_UPDATE = 1; // force message reload
  54
  55         /**
  56          * Process local cache of loaded messages that are defined in
  57          * MediaWiki namespace. First array level is a language code,
  58          * second level is message key and the values are either message
  59          * content prefixed with space, or !NONEXISTENT for negative
  60          * caching.
  61          */
  62         protected $mCache;
  63
  64         /**
  65          * Should  mean that database cannot be used, but check
  66          * @var bool $mDisable
  67          */
  68         protected $mDisable;
  69
  70         /**
  71          * Lifetime for cache, used by object caching.
  72          * Set on construction, see __construct().
  73          */
  74         protected $mExpiry;
  75
  76         /**
  77          * Message cache has its own parser which it uses to transform
  78          * messages.
  79          */
  80         protected $mParserOptions, $mParser;
  81
  82         /**
  83          * Variable for tracking which variables are already loaded
  84          * @var array $mLoadedLanguages
  85          */
  86         protected $mLoadedLanguages = array();
  87
  88         /**
  89          * Singleton instance
  90          *
  91          * @var MessageCache $instance
  92          */
  93         private static $instance;
  94
  95         /**
  96          * @var bool $mInParser
  97          */
  98         protected $mInParser = false;
  99
 100         /**
 101          * Get the signleton instance of this class
 102          *
 103          * @since 1.18
 104          * @return MessageCache
 105          */
 106         public static function singleton() {
 107                 if ( is_null( self::$instance ) ) {
 108                         global $wgUseDatabaseMessages, $wgMsgCacheExpiry;
 109                         self::$instance = new self(
 110                                 wfGetMessageCacheStorage(),
 111                                 $wgUseDatabaseMessages,
 112                                 $wgMsgCacheExpiry
 113                         );
 114                 }
 115
 116                 return self::$instance;
 117         }
 118
 119         /**
 120          * Destroy the singleton instance
 121          *
 122          * @since 1.18
 123          */
 124         public static function destroyInstance() {
 125                 self::$instance = null;
 126         }
 127
 128         /**
 129          * @param BagOStuff $memCached A cache instance. If none, fall back to CACHE_NONE.
 130          * @param bool $useDB
 131          * @param int $expiry Lifetime for cache. @see $mExpiry.
 132          */
 133         function __construct( $memCached, $useDB, $expiry ) {
 134                 if ( !$memCached ) {
 135                         $memCached = wfGetCache( CACHE_NONE );
 136                 }
 137
 138                 $this->mMemc = $memCached;
 139                 $this->mDisable = !$useDB;
 140                 $this->mExpiry = $expiry;
 141         }
 142
 143         /**
 144          * ParserOptions is lazy initialised.
 145          *
 146          * @return ParserOptions
 147          */
 148         function getParserOptions() {
 149                 if ( !$this->mParserOptions ) {
 150                         $this->mParserOptions = new ParserOptions;
 151                         $this->mParserOptions->setEditSection( false );
 152                 }
 153
 154                 return $this->mParserOptions;
 155         }
 156
 157         /**
 158          * Try to load the cache from a local file.
 159          *
 160          * @param string $hash The hash of contents, to check validity.
 161          * @param string $code Optional language code, see documenation of load().
 162          * @return array The cache array
 163          */
 164         function getLocalCache( $hash, $code ) {
 165                 global $wgCacheDirectory;
 166
 167                 $filename = "$wgCacheDirectory/messages-" . wfWikiID() . "-$code";
 168
 169                 # Check file existence
 170                 wfSuppressWarnings();
 171                 $file = fopen( $filename, 'r' );
 172                 wfRestoreWarnings();
 173                 if ( !$file ) {
 174                         return false; // No cache file
 175                 }
 176
 177                 // Check to see if the file has the hash specified
 178                 $localHash = fread( $file, 32 );
 179                 if ( $hash === $localHash ) {
 180                         // All good, get the rest of it
 181                         $serialized = '';
 182                         while ( !feof( $file ) ) {
 183                                 $serialized .= fread( $file, 100000 );
 184                         }
 185                         fclose( $file );
 186
 187                         return unserialize( $serialized );
 188                 } else {
 189                         fclose( $file );
 190
 191                         return false; // Wrong hash
 192                 }
 193         }
 194
 195         /**
 196          * Save the cache to a local file.
 197          * @param string $serialized
 198          * @param string $hash
 199          * @param string $code
 200          */
 201         function saveToLocal( $serialized, $hash, $code ) {
 202                 global $wgCacheDirectory;
 203
 204                 $filename = "$wgCacheDirectory/messages-" . wfWikiID() . "-$code";
 205                 wfMkdirParents( $wgCacheDirectory, null, __METHOD__ ); // might fail
 206
 207                 wfSuppressWarnings();
 208                 $file = fopen( $filename, 'w' );
 209                 wfRestoreWarnings();
 210
 211                 if ( !$file ) {
 212                         wfDebug( "Unable to open local cache file for writing\n" );
 213
 214                         return;
 215                 }
 216
 217                 fwrite( $file, $hash . $serialized );
 218                 fclose( $file );
 219                 wfSuppressWarnings();
 220                 chmod( $filename, 0666 );
 221                 wfRestoreWarnings();
 222         }
 223
 224         /**
 225          * Loads messages from caches or from database in this order:
 226          * (1) local message cache (if $wgUseLocalMessageCache is enabled)
 227          * (2) memcached
 228          * (3) from the database.
 229          *
 230          * When succesfully loading from (2) or (3), all higher level caches are
 231          * updated for the newest version.
 232          *
 233          * Nothing is loaded if member variable mDisable is true, either manually
 234          * set by calling code or if message loading fails (is this possible?).
 235          *
 236          * Returns true if cache is already populated or it was succesfully populated,
 237          * or false if populating empty cache fails. Also returns true if MessageCache
 238          * is disabled.
 239          *
 240          * @param bool|string $code Language to which load messages
 241          * @param integer $mode Use MessageCache::FOR_UPDATE to skip process cache
 242          * @throws MWException
 243          * @return bool
 244          */
 245         function load( $code = false, $mode = null ) {
 246                 global $wgUseLocalMessageCache;
 247
 248                 if ( !is_string( $code ) ) {
 249                         # This isn't really nice, so at least make a note about it and try to
 250                         # fall back
 251                         wfDebug( __METHOD__ . " called without providing a language code\n" );
 252                         $code = 'en';
 253                 }
 254
 255                 # Don't do double loading...
 256                 if ( isset( $this->mLoadedLanguages[$code] ) && $mode != self::FOR_UPDATE ) {
 257                         return true;
 258                 }
 259
 260                 # 8 lines of code just to say (once) that message cache is disabled
 261                 if ( $this->mDisable ) {
 262                         static $shownDisabled = false;
 263                         if ( !$shownDisabled ) {
 264                                 wfDebug( __METHOD__ . ": disabled\n" );
 265                                 $shownDisabled = true;
 266                         }
 267
 268                         return true;
 269                 }
 270
 271                 # Loading code starts
 272                 $success = false; # Keep track of success
 273                 $staleCache = false; # a cache array with expired data, or false if none has been loaded
 274                 $where = array(); # Debug info, delayed to avoid spamming debug log too much
 275                 $cacheKey = wfMemcKey( 'messages', $code ); # Key in memc for messages
 276
 277                 # Local cache
 278                 # Hash of the contents is stored in memcache, to detect if local cache goes
 279                 # out of date (e.g. due to replace() on some other server)
 280                 if ( $wgUseLocalMessageCache ) {
 281                         $hash = $this->mMemc->get( wfMemcKey( 'messages', $code, 'hash' ) );
 282                         if ( $hash ) {
 283                                 $cache = $this->getLocalCache( $hash, $code );
 284                                 if ( !$cache ) {
 285                                         $where[] = 'local cache is empty or has the wrong hash';
 286                                 } elseif ( $this->isCacheExpired( $cache ) ) {
 287                                         $where[] = 'local cache is expired';
 288                                         $staleCache = $cache;
 289                                 } else {
 290                                         $where[] = 'got from local cache';
 291                                         $success = true;
 292                                         $this->mCache[$code] = $cache;
 293                                 }
 294                         }
 295                 }
 296
 297                 if ( !$success ) {
 298                         # Try the global cache. If it is empty, try to acquire a lock. If
 299                         # the lock can't be acquired, wait for the other thread to finish
 300                         # and then try the global cache a second time.
 301                         for ( $failedAttempts = 0; $failedAttempts < 2; $failedAttempts++ ) {
 302                                 $cache = $this->mMemc->get( $cacheKey );
 303                                 if ( !$cache ) {
 304                                         $where[] = 'global cache is empty';
 305                                 } elseif ( $this->isCacheExpired( $cache ) ) {
 306                                         $where[] = 'global cache is expired';
 307                                         $staleCache = $cache;
 308                                 } else {
 309                                         $where[] = 'got from global cache';
 310                                         $this->mCache[$code] = $cache;
 311                                         $this->saveToCaches( $cache, 'local-only', $code );
 312                                         $success = true;
 313                                 }
 314
 315                                 if ( $success ) {
 316                                         # Done, no need to retry
 317                                         break;
 318                                 }
 319
 320                                 # We need to call loadFromDB. Limit the concurrency to a single
 321                                 # process. This prevents the site from going down when the cache
 322                                 # expires.
 323                                 $statusKey = wfMemcKey( 'messages', $code, 'status' );
 324                                 $acquired = $this->mMemc->add( $statusKey, 'loading', MSG_LOAD_TIMEOUT );
 325                                 if ( $acquired ) {
 326                                         # Unlock the status key if there is an exception
 327                                         $that = $this;
 328                                         $statusUnlocker = new ScopedCallback( function () use ( $that, $statusKey ) {
 329                                                 $that->mMemc->delete( $statusKey );
 330                                         } );
 331
 332                                         # Now let's regenerate
 333                                         $where[] = 'loading from database';
 334
 335                                         # Lock the cache to prevent conflicting writes
 336                                         # If this lock fails, it doesn't really matter, it just means the
 337                                         # write is potentially non-atomic, e.g. the results of a replace()
 338                                         # may be discarded.
 339                                         if ( $this->lock( $cacheKey ) ) {
 340                                                 $mainUnlocker = new ScopedCallback( function () use ( $that, $cacheKey ) {
 341                                                         $that->unlock( $cacheKey );
 342                                                 } );
 343                                         } else {
 344                                                 $mainUnlocker = null;
 345                                                 $where[] = 'could not acquire main lock';
 346                                         }
 347
 348                                         $cache = $this->loadFromDB( $code );
 349                                         $this->mCache[$code] = $cache;
 350                                         $success = true;
 351                                         $saveSuccess = $this->saveToCaches( $cache, 'all', $code );
 352
 353                                         # Unlock
 354                                         ScopedCallback::consume( $mainUnlocker );
 355                                         ScopedCallback::consume( $statusUnlocker );
 356
 357                                         if ( !$saveSuccess ) {
 358                                                 # Cache save has failed.
 359                                                 # There are two main scenarios where this could be a problem:
 360                                                 #
 361                                                 #   - The cache is more than the maximum size (typically
 362                                                 #     1MB compressed).
 363                                                 #
 364                                                 #   - Memcached has no space remaining in the relevant slab
 365                                                 #     class. This is unlikely with recent versions of
 366                                                 #     memcached.
 367                                                 #
 368                                                 # Either way, if there is a local cache, nothing bad will
 369                                                 # happen. If there is no local cache, disabling the message
 370                                                 # cache for all requests avoids incurring a loadFromDB()
 371                                                 # overhead on every request, and thus saves the wiki from
 372                                                 # complete downtime under moderate traffic conditions.
 373                                                 if ( !$wgUseLocalMessageCache ) {
 374                                                         $this->mMemc->set( $statusKey, 'error', 60 * 5 );
 375                                                         $where[] = 'could not save cache, disabled globally for 5 minutes';
 376                                                 } else {
 377                                                         $where[] = "could not save global cache";
 378                                                 }
 379                                         }
 380
 381                                         # Load from DB complete, no need to retry
 382                                         break;
 383                                 } elseif ( $staleCache ) {
 384                                         # Use the stale cache while some other thread constructs the new one
 385                                         $where[] = 'using stale cache';
 386                                         $this->mCache[$code] = $staleCache;
 387                                         $success = true;
 388                                         break;
 389                                 } elseif ( $failedAttempts > 0 ) {
 390                                         # Already retried once, still failed, so don't do another lock/unlock cycle
 391                                         # This case will typically be hit if memcached is down, or if
 392                                         # loadFromDB() takes longer than MSG_WAIT_TIMEOUT
 393                                         $where[] = "could not acquire status key.";
 394                                         break;
 395                                 } else {
 396                                         $status = $this->mMemc->get( $statusKey );
 397                                         if ( $status === 'error' ) {
 398                                                 # Disable cache
 399                                                 break;
 400                                         } else {
 401                                                 # Wait for the other thread to finish, then retry
 402                                                 $where[] = 'waited for other thread to complete';
 403                                                 $this->lock( $cacheKey );
 404                                                 $this->unlock( $cacheKey );
 405                                         }
 406                                 }
 407                         }
 408                 }
 409
 410                 if ( !$success ) {
 411                         $where[] = 'loading FAILED - cache is disabled';
 412                         $this->mDisable = true;
 413                         $this->mCache = false;
 414                         # This used to throw an exception, but that led to nasty side effects like
 415                         # the whole wiki being instantly down if the memcached server died
 416                 } else {
 417                         # All good, just record the success
 418                         $this->mLoadedLanguages[$code] = true;
 419                 }
 420                 $info = implode( ', ', $where );
 421                 wfDebugLog( 'MessageCache', __METHOD__ . ": Loading $code... $info\n" );
 422
 423                 return $success;
 424         }
 425
 426         /**
 427          * Loads cacheable messages from the database. Messages bigger than
 428          * $wgMaxMsgCacheEntrySize are assigned a special value, and are loaded
 429          * on-demand from the database later.
 430          *
 431          * @param string $code Language code.
 432          * @return array Loaded messages for storing in caches.
 433          */
 434         function loadFromDB( $code ) {
 435                 global $wgMaxMsgCacheEntrySize, $wgLanguageCode, $wgAdaptiveMessageCache;
 436
 437                 $dbr = wfGetDB( DB_SLAVE );
 438                 $cache = array();
 439
 440                 # Common conditions
 441                 $conds = array(
 442                         'page_is_redirect' => 0,
 443                         'page_namespace' => NS_MEDIAWIKI,
 444                 );
 445
 446                 $mostused = array();
 447                 if ( $wgAdaptiveMessageCache && $code !== $wgLanguageCode ) {
 448                         if ( !isset( $this->mCache[$wgLanguageCode] ) ) {
 449                                 $this->load( $wgLanguageCode );
 450                         }
 451                         $mostused = array_keys( $this->mCache[$wgLanguageCode] );
 452                         foreach ( $mostused as $key => $value ) {
 453                                 $mostused[$key] = "$value/$code";
 454                         }
 455                 }
 456
 457                 if ( count( $mostused ) ) {
 458                         $conds['page_title'] = $mostused;
 459                 } elseif ( $code !== $wgLanguageCode ) {
 460                         $conds[] = 'page_title' . $dbr->buildLike( $dbr->anyString(), '/', $code );
 461                 } else {
 462                         # Effectively disallows use of '/' character in NS_MEDIAWIKI for uses
 463                         # other than language code.
 464                         $conds[] = 'page_title NOT' . $dbr->buildLike( $dbr->anyString(), '/', $dbr->anyString() );
 465                 }
 466
 467                 # Conditions to fetch oversized pages to ignore them
 468                 $bigConds = $conds;
 469                 $bigConds[] = 'page_len > ' . intval( $wgMaxMsgCacheEntrySize );
 470
 471                 # Load titles for all oversized pages in the MediaWiki namespace
 472                 $res = $dbr->select( 'page', 'page_title', $bigConds, __METHOD__ . "($code)-big" );
 473                 foreach ( $res as $row ) {
 474                         $cache[$row->page_title] = '!TOO BIG';
 475                 }
 476
 477                 # Conditions to load the remaining pages with their contents
 478                 $smallConds = $conds;
 479                 $smallConds[] = 'page_latest=rev_id';
 480                 $smallConds[] = 'rev_text_id=old_id';
 481                 $smallConds[] = 'page_len <= ' . intval( $wgMaxMsgCacheEntrySize );
 482
 483                 $res = $dbr->select(
 484                         array( 'page', 'revision', 'text' ),
 485                         array( 'page_title', 'old_text', 'old_flags' ),
 486                         $smallConds,
 487                         __METHOD__ . "($code)-small"
 488                 );
 489
 490                 foreach ( $res as $row ) {
 491                         $text = Revision::getRevisionText( $row );
 492                         if ( $text === false ) {
 493                                 // Failed to fetch data; possible ES errors?
 494                                 // Store a marker to fetch on-demand as a workaround...
 495                                 $entry = '!TOO BIG';
 496                                 wfDebugLog(
 497                                         'MessageCache',
 498                                         __METHOD__
 499                                                 . ": failed to load message page text for {$row->page_title} ($code)"
 500                                 );
 501                         } else {
 502                                 $entry = ' ' . $text;
 503                         }
 504                         $cache[$row->page_title] = $entry;
 505                 }
 506
 507                 $cache['VERSION'] = MSG_CACHE_VERSION;
 508                 $cache['EXPIRY'] = wfTimestamp( TS_MW, time() + $this->mExpiry );
 509
 510                 return $cache;
 511         }
 512
 513         /**
 514          * Updates cache as necessary when message page is changed
 515          *
 516          * @param string $title Name of the page changed.
 517          * @param mixed $text New contents of the page.
 518          */
 519         public function replace( $title, $text ) {
 520                 global $wgMaxMsgCacheEntrySize, $wgContLang;
 521
 522                 if ( $this->mDisable ) {
 523                         return;
 524                 }
 525
 526                 list( $msg, $code ) = $this->figureMessage( $title );
 527
 528                 $cacheKey = wfMemcKey( 'messages', $code );
 529                 $this->lock( $cacheKey );
 530                 $this->load( $code, self::FOR_UPDATE );
 531
 532                 $titleKey = wfMemcKey( 'messages', 'individual', $title );
 533
 534                 if ( $text === false ) {
 535                         # Article was deleted
 536                         $this->mCache[$code][$title] = '!NONEXISTENT';
 537                         $this->mMemc->delete( $titleKey );
 538                 } elseif ( strlen( $text ) > $wgMaxMsgCacheEntrySize ) {
 539                         # Check for size
 540                         $this->mCache[$code][$title] = '!TOO BIG';
 541                         $this->mMemc->set( $titleKey, ' ' . $text, $this->mExpiry );
 542                 } else {
 543                         $this->mCache[$code][$title] = ' ' . $text;
 544                         $this->mMemc->delete( $titleKey );
 545                 }
 546
 547                 # Update caches
 548                 $this->saveToCaches( $this->mCache[$code], 'all', $code );
 549                 $this->unlock( $cacheKey );
 550
 551                 // Also delete cached sidebar... just in case it is affected
 552                 $codes = array( $code );
 553                 if ( $code === 'en' ) {
 554                         // Delete all sidebars, like for example on action=purge on the
 555                         // sidebar messages
 556                         $codes = array_keys( Language::fetchLanguageNames() );
 557                 }
 558
 559                 $cache = ObjectCache::getMainWANInstance();
 560                 foreach ( $codes as $code ) {
 561                         $sidebarKey = wfMemcKey( 'sidebar', $code );
 562                         $cache->delete( $sidebarKey, 5 );
 563                 }
 564
 565                 // Update the message in the message blob store
 566                 $blobStore = new MessageBlobStore();
 567                 $blobStore->updateMessage( $wgContLang->lcfirst( $msg ) );
 568
 569                 Hooks::run( 'MessageCacheReplace', array( $title, $text ) );
 570
 571         }
 572
 573         /**
 574          * Is the given cache array expired due to time passing or a version change?
 575          *
 576          * @param array $cache
 577          * @return bool
 578          */
 579         protected function isCacheExpired( $cache ) {
 580                 if ( !isset( $cache['VERSION'] ) || !isset( $cache['EXPIRY'] ) ) {
 581                         return true;
 582                 }
 583                 if ( $cache['VERSION'] != MSG_CACHE_VERSION ) {
 584                         return true;
 585                 }
 586                 if ( wfTimestampNow() >= $cache['EXPIRY'] ) {
 587                         return true;
 588                 }
 589
 590                 return false;
 591         }
 592
 593         /**
 594          * Shortcut to update caches.
 595          *
 596          * @param array $cache Cached messages with a version.
 597          * @param string $dest Either "local-only" to save to local caches only
 598          *   or "all" to save to all caches.
 599          * @param string|bool $code Language code (default: false)
 600          * @return bool
 601          */
 602         protected function saveToCaches( $cache, $dest, $code = false ) {
 603                 global $wgUseLocalMessageCache;
 604
 605                 $cacheKey = wfMemcKey( 'messages', $code );
 606
 607                 if ( $dest === 'all' ) {
 608                         $success = $this->mMemc->set( $cacheKey, $cache );
 609                 } else {
 610                         $success = true;
 611                 }
 612
 613                 # Save to local cache
 614                 if ( $wgUseLocalMessageCache ) {
 615                         $serialized = serialize( $cache );
 616                         $hash = md5( $serialized );
 617                         $this->mMemc->set( wfMemcKey( 'messages', $code, 'hash' ), $hash );
 618                         $this->saveToLocal( $serialized, $hash, $code );
 619                 }
 620
 621                 return $success;
 622         }
 623
 624         /**
 625          * Represents a write lock on the messages key.
 626          *
 627          * Will retry MessageCache::MSG_WAIT_TIMEOUT times, each operations having
 628          * a timeout of MessageCache::MSG_LOCK_TIMEOUT.
 629          *
 630          * @param string $key
 631          * @return bool Success
 632          */
 633         function lock( $key ) {
 634                 $lockKey = $key . ':lock';
 635                 $acquired = false;
 636                 $testDone = false;
 637                 for ( $i = 0; $i < MSG_WAIT_TIMEOUT && !$acquired; $i++ ) {
 638                         $acquired = $this->mMemc->add( $lockKey, 1, MSG_LOCK_TIMEOUT );
 639                         if ( $acquired ) {
 640                                 break;
 641                         }
 642
 643                         # Fail fast if memcached is totally down
 644                         if ( !$testDone ) {
 645                                 $testDone = true;
 646                                 if ( !$this->mMemc->set( wfMemcKey( 'test' ), 'test', 1 ) ) {
 647                                         break;
 648                                 }
 649                         }
 650                         sleep( 1 );
 651                 }
 652
 653                 return $acquired;
 654         }
 655
 656         function unlock( $key ) {
 657                 $lockKey = $key . ':lock';
 658                 $this->mMemc->delete( $lockKey );
 659         }
 660
 661         /**
 662          * Get a message from either the content language or the user language.
 663          *
 664          * First, assemble a list of languages to attempt getting the message from. This
 665          * chain begins with the requested language and its fallbacks and then continues with
 666          * the content language and its fallbacks. For each language in the chain, the following
 667          * process will occur (in this order):
 668          *  1. If a language-specific override, i.e., [[MW:msg/lang]], is available, use that.
 669          *     Note: for the content language, there is no /lang subpage.
 670          *  2. Fetch from the static CDB cache.
 671          *  3. If available, check the database for fallback language overrides.
 672          *
 673          * This process provides a number of guarantees. When changing this code, make sure all
 674          * of these guarantees are preserved.
 675          *  * If the requested language is *not* the content language, then the CDB cache for that
 676          *    specific language will take precedence over the root database page ([[MW:msg]]).
 677          *  * Fallbacks will be just that: fallbacks. A fallback language will never be reached if
 678          *    the message is available *anywhere* in the language for which it is a fallback.
 679          *
 680          * @param string $key The message key
 681          * @param bool $useDB If true, look for the message in the DB, false
 682          *   to use only the compiled l10n cache.
 683          * @param bool|string|object $langcode Code of the language to get the message for.
 684          *   - If string and a valid code, will create a standard language object
 685          *   - If string but not a valid code, will create a basic language object
 686          *   - If boolean and false, create object from the current users language
 687          *   - If boolean and true, create object from the wikis content language
 688          *   - If language object, use it as given
 689          * @param bool $isFullKey Specifies whether $key is a two part key "msg/lang".
 690          *
 691          * @throws MWException When given an invalid key
 692          * @return string|bool False if the message doesn't exist, otherwise the
 693          *   message (which can be empty)
 694          */
 695         function get( $key, $useDB = true, $langcode = true, $isFullKey = false ) {
 696                 global $wgContLang;
 697
 698                 if ( is_int( $key ) ) {
 699                         // Fix numerical strings that somehow become ints
 700                         // on their way here
 701                         $key = (string)$key;
 702                 } elseif ( !is_string( $key ) ) {
 703                         throw new MWException( 'Non-string key given' );
 704                 } elseif ( $key === '' ) {
 705                         // Shortcut: the empty key is always missing
 706                         return false;
 707                 }
 708
 709                 // For full keys, get the language code from the key
 710                 $pos = strrpos( $key, '/' );
 711                 if ( $isFullKey && $pos !== false ) {
 712                         $langcode = substr( $key, $pos + 1 );
 713                         $key = substr( $key, 0, $pos );
 714                 }
 715
 716                 // Normalise title-case input (with some inlining)
 717                 $lckey = strtr( $key, ' ', '_' );
 718                 if ( ord( $lckey ) < 128 ) {
 719                         $lckey[0] = strtolower( $lckey[0] );
 720                 } else {
 721                         $lckey = $wgContLang->lcfirst( $lckey );
 722                 }
 723
 724                 Hooks::run( 'MessageCache::get', array( &$lckey ) );
 725
 726                 if ( ord( $lckey ) < 128 ) {
 727                         $uckey = ucfirst( $lckey );
 728                 } else {
 729                         $uckey = $wgContLang->ucfirst( $lckey );
 730                 }
 731
 732                 // Loop through each language in the fallback list until we find something useful
 733                 $lang = wfGetLangObj( $langcode );
 734                 $message = $this->getMessageFromFallbackChain(
 735                         $lang,
 736                         $lckey,
 737                         $uckey,
 738                         !$this->mDisable && $useDB
 739                 );
 740
 741                 // If we still have no message, maybe the key was in fact a full key so try that
 742                 if ( $message === false ) {
 743                         $parts = explode( '/', $lckey );
 744                         // We may get calls for things that are http-urls from sidebar
 745                         // Let's not load nonexistent languages for those
 746                         // They usually have more than one slash.
 747                         if ( count( $parts ) == 2 && $parts[1] !== '' ) {
 748                                 $message = Language::getMessageFor( $parts[0], $parts[1] );
 749                                 if ( $message === null ) {
 750                                         $message = false;
 751                                 }
 752                         }
 753                 }
 754
 755                 // Post-processing if the message exists
 756                 if ( $message !== false ) {
 757                         // Fix whitespace
 758                         $message = str_replace(
 759                                 array(
 760                                         # Fix for trailing whitespace, removed by textarea
 761                                         '&#32;',
 762                                         # Fix for NBSP, converted to space by firefox
 763                                         '&nbsp;',
 764                                         '&#160;',
 765                                 ),
 766                                 array(
 767                                         ' ',
 768                                         "\xc2\xa0",
 769                                         "\xc2\xa0"
 770                                 ),
 771                                 $message
 772                         );
 773                 }
 774
 775                 return $message;
 776         }
 777
 778         /**
 779          * Given a language, try and fetch a message from that language, then the
 780          * fallbacks of that language, then the site language, then the fallbacks for the
 781          * site language.
 782          *
 783          * @param Language $lang Requested language
 784          * @param string $lckey Lowercase key for the message
 785          * @param string $uckey Uppercase key for the message
 786          * @param bool $useDB Whether to use the database
 787          *
 788          * @see MessageCache::get
 789          * @return string|bool The message, or false if not found
 790          */
 791         protected function getMessageFromFallbackChain( $lang, $lckey, $uckey, $useDB ) {
 792                 global $wgLanguageCode, $wgContLang;
 793
 794                 $langcode = $lang->getCode();
 795                 $message = false;
 796
 797                 // First try the requested language.
 798                 if ( $useDB ) {
 799                         if ( $langcode === $wgLanguageCode ) {
 800                                 // Messages created in the content language will not have the /lang extension
 801                                 $message = $this->getMsgFromNamespace( $uckey, $langcode );
 802                         } else {
 803                                 $message = $this->getMsgFromNamespace( "$uckey/$langcode", $langcode );
 804                         }
 805                 }
 806
 807                 if ( $message !== false ) {
 808                         return $message;
 809                 }
 810
 811                 // Check the CDB cache
 812                 $message = $lang->getMessage( $lckey );
 813                 if ( $message !== null ) {
 814                         return $message;
 815                 }
 816
 817                 list( $fallbackChain, $siteFallbackChain ) =
 818                         Language::getFallbacksIncludingSiteLanguage( $langcode );
 819
 820                 // Next try checking the database for all of the fallback languages of the requested language.
 821                 if ( $useDB ) {
 822                         foreach ( $fallbackChain as $code ) {
 823                                 if ( $code === $wgLanguageCode ) {
 824                                         // Messages created in the content language will not have the /lang extension
 825                                         $message = $this->getMsgFromNamespace( $uckey, $code );
 826                                 } else {
 827                                         $message = $this->getMsgFromNamespace( "$uckey/$code", $code );
 828                                 }
 829
 830                                 if ( $message !== false ) {
 831                                         // Found the message.
 832                                         return $message;
 833                                 }
 834                         }
 835                 }
 836
 837                 // Now try checking the site language.
 838                 if ( $useDB ) {
 839                         $message = $this->getMsgFromNamespace( $uckey, $wgLanguageCode );
 840                         if ( $message !== false ) {
 841                                 return $message;
 842                         }
 843                 }
 844
 845                 $message = $wgContLang->getMessage( $lckey );
 846                 if ( $message !== null ) {
 847                         return $message;
 848                 }
 849
 850                 // Finally try the DB for the site language's fallbacks.
 851                 if ( $useDB ) {
 852                         foreach ( $siteFallbackChain as $code ) {
 853                                 $message = $this->getMsgFromNamespace( "$uckey/$code", $code );
 854                                 if ( $message === false && $code === $wgLanguageCode ) {
 855                                         // Messages created in the content language will not have the /lang extension
 856                                         $message = $this->getMsgFromNamespace( $uckey, $code );
 857                                 }
 858
 859                                 if ( $message !== false ) {
 860                                         // Found the message.
 861                                         return $message;
 862                                 }
 863                         }
 864                 }
 865
 866                 return false;
 867         }
 868
 869         /**
 870          * Get a message from the MediaWiki namespace, with caching. The key must
 871          * first be converted to two-part lang/msg form if necessary.
 872          *
 873          * Unlike self::get(), this function doesn't resolve fallback chains, and
 874          * some callers require this behavior. LanguageConverter::parseCachedTable()
 875          * and self::get() are some examples in core.
 876          *
 877          * @param string $title Message cache key with initial uppercase letter.
 878          * @param string $code Code denoting the language to try.
 879          * @return string|bool The message, or false if it does not exist or on error
 880          */
 881         function getMsgFromNamespace( $title, $code ) {
 882                 $this->load( $code );
 883                 if ( isset( $this->mCache[$code][$title] ) ) {
 884                         $entry = $this->mCache[$code][$title];
 885                         if ( substr( $entry, 0, 1 ) === ' ' ) {
 886                                 // The message exists, so make sure a string
 887                                 // is returned.
 888                                 return (string)substr( $entry, 1 );
 889                         } elseif ( $entry === '!NONEXISTENT' ) {
 890                                 return false;
 891                         } elseif ( $entry === '!TOO BIG' ) {
 892                                 // Fall through and try invididual message cache below
 893                         }
 894                 } else {
 895                         // XXX: This is not cached in process cache, should it?
 896                         $message = false;
 897                         Hooks::run( 'MessagesPreLoad', array( $title, &$message ) );
 898                         if ( $message !== false ) {
 899                                 return $message;
 900                         }
 901
 902                         return false;
 903                 }
 904
 905                 # Try the individual message cache
 906                 $titleKey = wfMemcKey( 'messages', 'individual', $title );
 907                 $entry = $this->mMemc->get( $titleKey );
 908                 if ( $entry ) {
 909                         if ( substr( $entry, 0, 1 ) === ' ' ) {
 910                                 $this->mCache[$code][$title] = $entry;
 911
 912                                 // The message exists, so make sure a string
 913                                 // is returned.
 914                                 return (string)substr( $entry, 1 );
 915                         } elseif ( $entry === '!NONEXISTENT' ) {
 916                                 $this->mCache[$code][$title] = '!NONEXISTENT';
 917
 918                                 return false;
 919                         } else {
 920                                 # Corrupt/obsolete entry, delete it
 921                                 $this->mMemc->delete( $titleKey );
 922                         }
 923                 }
 924
 925                 # Try loading it from the database
 926                 $revision = Revision::newFromTitle(
 927                         Title::makeTitle( NS_MEDIAWIKI, $title ), false, Revision::READ_LATEST
 928                 );
 929                 if ( $revision ) {
 930                         $content = $revision->getContent();
 931                         if ( !$content ) {
 932                                 // A possibly temporary loading failure.
 933                                 wfDebugLog(
 934                                         'MessageCache',
 935                                         __METHOD__ . ": failed to load message page text for {$title} ($code)"
 936                                 );
 937                                 $message = null; // no negative caching
 938                         } else {
 939                                 // XXX: Is this the right way to turn a Content object into a message?
 940                                 // NOTE: $content is typically either WikitextContent, JavaScriptContent or
 941                                 //       CssContent. MessageContent is *not* used for storing messages, it's
 942                                 //       only used for wrapping them when needed.
 943                                 $message = $content->getWikitextForTransclusion();
 944
 945                                 if ( $message === false || $message === null ) {
 946                                         wfDebugLog(
 947                                                 'MessageCache',
 948                                                 __METHOD__ . ": message content doesn't provide wikitext "
 949                                                         . "(content model: " . $content->getContentHandler() . ")"
 950                                         );
 951
 952                                         $message = false; // negative caching
 953                                 } else {
 954                                         $this->mCache[$code][$title] = ' ' . $message;
 955                                         $this->mMemc->set( $titleKey, ' ' . $message, $this->mExpiry );
 956                                 }
 957                         }
 958                 } else {
 959                         $message = false; // negative caching
 960                 }
 961
 962                 if ( $message === false ) { // negative caching
 963                         $this->mCache[$code][$title] = '!NONEXISTENT';
 964                         $this->mMemc->set( $titleKey, '!NONEXISTENT', $this->mExpiry );
 965                 }
 966
 967                 return $message;
 968         }
 969
 970         /**
 971          * @param string $message
 972          * @param bool $interface
 973          * @param string $language Language code
 974          * @param Title $title
 975          * @return string
 976          */
 977         function transform( $message, $interface = false, $language = null, $title = null ) {
 978                 // Avoid creating parser if nothing to transform
 979                 if ( strpos( $message, '{{' ) === false ) {
 980                         return $message;
 981                 }
 982
 983                 if ( $this->mInParser ) {
 984                         return $message;
 985                 }
 986
 987                 $parser = $this->getParser();
 988                 if ( $parser ) {
 989                         $popts = $this->getParserOptions();
 990                         $popts->setInterfaceMessage( $interface );
 991                         $popts->setTargetLanguage( $language );
 992
 993                         $userlang = $popts->setUserLang( $language );
 994                         $this->mInParser = true;
 995                         $message = $parser->transformMsg( $message, $popts, $title );
 996                         $this->mInParser = false;
 997                         $popts->setUserLang( $userlang );
 998                 }
 999
1000                 return $message;
1001         }
1002
1003         /**
1004          * @return Parser
1005          */
1006         function getParser() {
1007                 global $wgParser, $wgParserConf;
1008                 if ( !$this->mParser && isset( $wgParser ) ) {
1009                         # Do some initialisation so that we don't have to do it twice
1010                         $wgParser->firstCallInit();
1011                         # Clone it and store it
1012                         $class = $wgParserConf['class'];
1013                         if ( $class == 'ParserDiffTest' ) {
1014                                 # Uncloneable
1015                                 $this->mParser = new $class( $wgParserConf );
1016                         } else {
1017                                 $this->mParser = clone $wgParser;
1018                         }
1019                 }
1020
1021                 return $this->mParser;
1022         }
1023
1024         /**
1025          * @param string $text
1026          * @param Title $title
1027          * @param bool $linestart Whether or not this is at the start of a line
1028          * @param bool $interface Whether this is an interface message
1029          * @param string $language Language code
1030          * @return ParserOutput|string
1031          */
1032         public function parse( $text, $title = null, $linestart = true,
1033                 $interface = false, $language = null
1034         ) {
1035                 if ( $this->mInParser ) {
1036                         return htmlspecialchars( $text );
1037                 }
1038
1039                 $parser = $this->getParser();
1040                 $popts = $this->getParserOptions();
1041                 $popts->setInterfaceMessage( $interface );
1042                 $popts->setTargetLanguage( $language );
1043
1044                 if ( !$title || !$title instanceof Title ) {
1045                         global $wgTitle;
1046                         wfDebugLog( 'GlobalTitleFail', __METHOD__ . ' called by ' . wfGetAllCallers( 5 ) . ' with no title set.' );
1047                         $title = $wgTitle;
1048                 }
1049                 // Sometimes $wgTitle isn't set either...
1050                 if ( !$title ) {
1051                         # It's not uncommon having a null $wgTitle in scripts. See r80898
1052                         # Create a ghost title in such case
1053                         $title = Title::makeTitle( NS_SPECIAL, 'Badtitle/title not set in ' . __METHOD__ );
1054                 }
1055
1056                 $this->mInParser = true;
1057                 $res = $parser->parse( $text, $title, $popts, $linestart );
1058                 $this->mInParser = false;
1059
1060                 return $res;
1061         }
1062
1063         function disable() {
1064                 $this->mDisable = true;
1065         }
1066
1067         function enable() {
1068                 $this->mDisable = false;
1069         }
1070
1071         /**
1072          * Clear all stored messages. Mainly used after a mass rebuild.
1073          */
1074         function clear() {
1075                 $langs = Language::fetchLanguageNames( null, 'mw' );
1076                 foreach ( array_keys( $langs ) as $code ) {
1077                         # Global cache
1078                         $this->mMemc->delete( wfMemcKey( 'messages', $code ) );
1079                         # Invalidate all local caches
1080                         $this->mMemc->delete( wfMemcKey( 'messages', $code, 'hash' ) );
1081                 }
1082                 $this->mLoadedLanguages = array();
1083         }
1084
1085         /**
1086          * @param string $key
1087          * @return array
1088          */
1089         public function figureMessage( $key ) {
1090                 global $wgLanguageCode;
1091                 $pieces = explode( '/', $key );
1092                 if ( count( $pieces ) < 2 ) {
1093                         return array( $key, $wgLanguageCode );
1094                 }
1095
1096                 $lang = array_pop( $pieces );
1097                 if ( !Language::fetchLanguageName( $lang, null, 'mw' ) ) {
1098                         return array( $key, $wgLanguageCode );
1099                 }
1100
1101                 $message = implode( '/', $pieces );
1102
1103                 return array( $message, $lang );
1104         }
1105
1106         /**
1107          * Get all message keys stored in the message cache for a given language.
1108          * If $code is the content language code, this will return all message keys
1109          * for which MediaWiki:msgkey exists. If $code is another language code, this
1110          * will ONLY return message keys for which MediaWiki:msgkey/$code exists.
1111          * @param string $code Language code
1112          * @return array Array of message keys (strings)
1113          */
1114         public function getAllMessageKeys( $code ) {
1115                 global $wgContLang;
1116                 $this->load( $code );
1117                 if ( !isset( $this->mCache[$code] ) ) {
1118                         // Apparently load() failed
1119                         return null;
1120                 }
1121                 // Remove administrative keys
1122                 $cache = $this->mCache[$code];
1123                 unset( $cache['VERSION'] );
1124                 unset( $cache['EXPIRY'] );
1125                 // Remove any !NONEXISTENT keys
1126                 $cache = array_diff( $cache, array( '!NONEXISTENT' ) );
1127
1128                 // Keys may appear with a capital first letter. lcfirst them.
1129                 return array_map( array( $wgContLang, 'lcfirst' ), array_keys( $cache ) );
1130         }
1131 }