includes/filebackend/FileBackendMultiWrite.php

   1 <?php
   2 /**
   3  * Proxy backend that mirrors writes to several internal backends.
   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 FileBackend
  22  * @author Aaron Schulz
  23  */
  24
  25 /**
  26  * @brief Proxy backend that mirrors writes to several internal backends.
  27  *
  28  * This class defines a multi-write backend. Multiple backends can be
  29  * registered to this proxy backend and it will act as a single backend.
  30  * Use this when all access to those backends is through this proxy backend.
  31  * At least one of the backends must be declared the "master" backend.
  32  *
  33  * Only use this class when transitioning from one storage system to another.
  34  *
  35  * Read operations are only done on the 'master' backend for consistency.
  36  * Write operations are performed on all backends, starting with the master.
  37  * This makes a best-effort to have transactional semantics, but since requests
  38  * may sometimes fail, the use of "autoResync" or background scripts to fix
  39  * inconsistencies is important.
  40  *
  41  * @ingroup FileBackend
  42  * @since 1.19
  43  */
  44 class FileBackendMultiWrite extends FileBackend {
  45         /** @var FileBackendStore[] Prioritized list of FileBackendStore objects */
  46         protected $backends = [];
  47
  48         /** @var int Index of master backend */
  49         protected $masterIndex = -1;
  50         /** @var int Index of read affinity backend */
  51         protected $readIndex = -1;
  52
  53         /** @var int Bitfield */
  54         protected $syncChecks = 0;
  55         /** @var string|bool */
  56         protected $autoResync = false;
  57
  58         /** @var bool */
  59         protected $asyncWrites = false;
  60
  61         /* Possible internal backend consistency checks */
  62         const CHECK_SIZE = 1;
  63         const CHECK_TIME = 2;
  64         const CHECK_SHA1 = 4;
  65
  66         /**
  67          * Construct a proxy backend that consists of several internal backends.
  68          * Locking, journaling, and read-only checks are handled by the proxy backend.
  69          *
  70          * Additional $config params include:
  71          *   - backends       : Array of backend config and multi-backend settings.
  72          *                      Each value is the config used in the constructor of a
  73          *                      FileBackendStore class, but with these additional settings:
  74          *                        - class         : The name of the backend class
  75          *                        - isMultiMaster : This must be set for one backend.
  76          *                        - readAffinity  : Use this for reads without 'latest' set.
  77          *                        - template:     : If given a backend name, this will use
  78          *                                          the config of that backend as a template.
  79          *                                          Values specified here take precedence.
  80          *   - syncChecks     : Integer bitfield of internal backend sync checks to perform.
  81          *                      Possible bits include the FileBackendMultiWrite::CHECK_* constants.
  82          *                      There are constants for SIZE, TIME, and SHA1.
  83          *                      The checks are done before allowing any file operations.
  84          *   - autoResync     : Automatically resync the clone backends to the master backend
  85          *                      when pre-operation sync checks fail. This should only be used
  86          *                      if the master backend is stable and not missing any files.
  87          *                      Use "conservative" to limit resyncing to copying newer master
  88          *                      backend files over older (or non-existing) clone backend files.
  89          *                      Cases that cannot be handled will result in operation abortion.
  90          *   - replication    : Set to 'async' to defer file operations on the non-master backends.
  91          *                      This will apply such updates post-send for web requests. Note that
  92          *                      any checks from "syncChecks" are still synchronous.
  93          *
  94          * @param array $config
  95          * @throws FileBackendError
  96          */
  97         public function __construct( array $config ) {
  98                 parent::__construct( $config );
  99                 $this->syncChecks = isset( $config['syncChecks'] )
 100                         ? $config['syncChecks']
 101                         : self::CHECK_SIZE;
 102                 $this->autoResync = isset( $config['autoResync'] )
 103                         ? $config['autoResync']
 104                         : false;
 105                 $this->asyncWrites = isset( $config['replication'] ) && $config['replication'] === 'async';
 106                 // Construct backends here rather than via registration
 107                 // to keep these backends hidden from outside the proxy.
 108                 $namesUsed = [];
 109                 foreach ( $config['backends'] as $index => $config ) {
 110                         if ( isset( $config['template'] ) ) {
 111                                 // Config is just a modified version of a registered backend's.
 112                                 // This should only be used when that config is used only by this backend.
 113                                 $config = $config + FileBackendGroup::singleton()->config( $config['template'] );
 114                         }
 115                         $name = $config['name'];
 116                         if ( isset( $namesUsed[$name] ) ) { // don't break FileOp predicates
 117                                 throw new FileBackendError( "Two or more backends defined with the name $name." );
 118                         }
 119                         $namesUsed[$name] = 1;
 120                         // Alter certain sub-backend settings for sanity
 121                         unset( $config['readOnly'] ); // use proxy backend setting
 122                         unset( $config['fileJournal'] ); // use proxy backend journal
 123                         unset( $config['lockManager'] ); // lock under proxy backend
 124                         $config['wikiId'] = $this->wikiId; // use the proxy backend wiki ID
 125                         if ( !empty( $config['isMultiMaster'] ) ) {
 126                                 if ( $this->masterIndex >= 0 ) {
 127                                         throw new FileBackendError( 'More than one master backend defined.' );
 128                                 }
 129                                 $this->masterIndex = $index; // this is the "master"
 130                                 $config['fileJournal'] = $this->fileJournal; // log under proxy backend
 131                         }
 132                         if ( !empty( $config['readAffinity'] ) ) {
 133                                 $this->readIndex = $index; // prefer this for reads
 134                         }
 135                         // Create sub-backend object
 136                         if ( !isset( $config['class'] ) ) {
 137                                 throw new FileBackendError( 'No class given for a backend config.' );
 138                         }
 139                         $class = $config['class'];
 140                         $this->backends[$index] = new $class( $config );
 141                 }
 142                 if ( $this->masterIndex < 0 ) { // need backends and must have a master
 143                         throw new FileBackendError( 'No master backend defined.' );
 144                 }
 145                 if ( $this->readIndex < 0 ) {
 146                         $this->readIndex = $this->masterIndex; // default
 147                 }
 148         }
 149
 150         final protected function doOperationsInternal( array $ops, array $opts ) {
 151                 $status = Status::newGood();
 152
 153                 $mbe = $this->backends[$this->masterIndex]; // convenience
 154
 155                 // Try to lock those files for the scope of this function...
 156                 $scopeLock = null;
 157                 if ( empty( $opts['nonLocking'] ) ) {
 158                         // Try to lock those files for the scope of this function...
 159                         /** @noinspection PhpUnusedLocalVariableInspection */
 160                         $scopeLock = $this->getScopedLocksForOps( $ops, $status );
 161                         if ( !$status->isOK() ) {
 162                                 return $status; // abort
 163                         }
 164                 }
 165                 // Clear any cache entries (after locks acquired)
 166                 $this->clearCache();
 167                 $opts['preserveCache'] = true; // only locked files are cached
 168                 // Get the list of paths to read/write...
 169                 $relevantPaths = $this->fileStoragePathsForOps( $ops );
 170                 // Check if the paths are valid and accessible on all backends...
 171                 $status->merge( $this->accessibilityCheck( $relevantPaths ) );
 172                 if ( !$status->isOK() ) {
 173                         return $status; // abort
 174                 }
 175                 // Do a consistency check to see if the backends are consistent...
 176                 $syncStatus = $this->consistencyCheck( $relevantPaths );
 177                 if ( !$syncStatus->isOK() ) {
 178                         wfDebugLog( 'FileOperation', get_class( $this ) .
 179                                 " failed sync check: " . FormatJson::encode( $relevantPaths ) );
 180                         // Try to resync the clone backends to the master on the spot...
 181                         if ( $this->autoResync === false
 182                                 || !$this->resyncFiles( $relevantPaths, $this->autoResync )->isOK()
 183                         ) {
 184                                 $status->merge( $syncStatus );
 185
 186                                 return $status; // abort
 187                         }
 188                 }
 189                 // Actually attempt the operation batch on the master backend...
 190                 $realOps = $this->substOpBatchPaths( $ops, $mbe );
 191                 $masterStatus = $mbe->doOperations( $realOps, $opts );
 192                 $status->merge( $masterStatus );
 193                 // Propagate the operations to the clone backends if there were no unexpected errors
 194                 // and if there were either no expected errors or if the 'force' option was used.
 195                 // However, if nothing succeeded at all, then don't replicate any of the operations.
 196                 // If $ops only had one operation, this might avoid backend sync inconsistencies.
 197                 if ( $masterStatus->isOK() && $masterStatus->successCount > 0 ) {
 198                         foreach ( $this->backends as $index => $backend ) {
 199                                 if ( $index === $this->masterIndex ) {
 200                                         continue; // done already
 201                                 }
 202
 203                                 $realOps = $this->substOpBatchPaths( $ops, $backend );
 204                                 if ( $this->asyncWrites && !$this->hasVolatileSources( $ops ) ) {
 205                                         // Bind $scopeLock to the callback to preserve locks
 206                                         DeferredUpdates::addCallableUpdate(
 207                                                 function() use ( $backend, $realOps, $opts, $scopeLock, $relevantPaths ) {
 208                                                         wfDebugLog( 'FileOperationReplication',
 209                                                                 "'{$backend->getName()}' async replication; paths: " .
 210                                                                 FormatJson::encode( $relevantPaths ) );
 211                                                         $backend->doOperations( $realOps, $opts );
 212                                                 }
 213                                         );
 214                                 } else {
 215                                         wfDebugLog( 'FileOperationReplication',
 216                                                 "'{$backend->getName()}' sync replication; paths: " .
 217                                                 FormatJson::encode( $relevantPaths ) );
 218                                         $status->merge( $backend->doOperations( $realOps, $opts ) );
 219                                 }
 220                         }
 221                 }
 222                 // Make 'success', 'successCount', and 'failCount' fields reflect
 223                 // the overall operation, rather than all the batches for each backend.
 224                 // Do this by only using success values from the master backend's batch.
 225                 $status->success = $masterStatus->success;
 226                 $status->successCount = $masterStatus->successCount;
 227                 $status->failCount = $masterStatus->failCount;
 228
 229                 return $status;
 230         }
 231
 232         /**
 233          * Check that a set of files are consistent across all internal backends
 234          *
 235          * @param array $paths List of storage paths
 236          * @return Status
 237          */
 238         public function consistencyCheck( array $paths ) {
 239                 $status = Status::newGood();
 240                 if ( $this->syncChecks == 0 || count( $this->backends ) <= 1 ) {
 241                         return $status; // skip checks
 242                 }
 243
 244                 // Preload all of the stat info in as few round trips as possible...
 245                 foreach ( $this->backends as $backend ) {
 246                         $realPaths = $this->substPaths( $paths, $backend );
 247                         $backend->preloadFileStat( [ 'srcs' => $realPaths, 'latest' => true ] );
 248                 }
 249
 250                 $mBackend = $this->backends[$this->masterIndex];
 251                 foreach ( $paths as $path ) {
 252                         $params = [ 'src' => $path, 'latest' => true ];
 253                         $mParams = $this->substOpPaths( $params, $mBackend );
 254                         // Stat the file on the 'master' backend
 255                         $mStat = $mBackend->getFileStat( $mParams );
 256                         if ( $this->syncChecks & self::CHECK_SHA1 ) {
 257                                 $mSha1 = $mBackend->getFileSha1Base36( $mParams );
 258                         } else {
 259                                 $mSha1 = false;
 260                         }
 261                         // Check if all clone backends agree with the master...
 262                         foreach ( $this->backends as $index => $cBackend ) {
 263                                 if ( $index === $this->masterIndex ) {
 264                                         continue; // master
 265                                 }
 266                                 $cParams = $this->substOpPaths( $params, $cBackend );
 267                                 $cStat = $cBackend->getFileStat( $cParams );
 268                                 if ( $mStat ) { // file is in master
 269                                         if ( !$cStat ) { // file should exist
 270                                                 $status->fatal( 'backend-fail-synced', $path );
 271                                                 continue;
 272                                         }
 273                                         if ( $this->syncChecks & self::CHECK_SIZE ) {
 274                                                 if ( $cStat['size'] != $mStat['size'] ) { // wrong size
 275                                                         $status->fatal( 'backend-fail-synced', $path );
 276                                                         continue;
 277                                                 }
 278                                         }
 279                                         if ( $this->syncChecks & self::CHECK_TIME ) {
 280                                                 $mTs = wfTimestamp( TS_UNIX, $mStat['mtime'] );
 281                                                 $cTs = wfTimestamp( TS_UNIX, $cStat['mtime'] );
 282                                                 if ( abs( $mTs - $cTs ) > 30 ) { // outdated file somewhere
 283                                                         $status->fatal( 'backend-fail-synced', $path );
 284                                                         continue;
 285                                                 }
 286                                         }
 287                                         if ( $this->syncChecks & self::CHECK_SHA1 ) {
 288                                                 if ( $cBackend->getFileSha1Base36( $cParams ) !== $mSha1 ) { // wrong SHA1
 289                                                         $status->fatal( 'backend-fail-synced', $path );
 290                                                         continue;
 291                                                 }
 292                                         }
 293                                 } else { // file is not in master
 294                                         if ( $cStat ) { // file should not exist
 295                                                 $status->fatal( 'backend-fail-synced', $path );
 296                                         }
 297                                 }
 298                         }
 299                 }
 300
 301                 return $status;
 302         }
 303
 304         /**
 305          * Check that a set of file paths are usable across all internal backends
 306          *
 307          * @param array $paths List of storage paths
 308          * @return Status
 309          */
 310         public function accessibilityCheck( array $paths ) {
 311                 $status = Status::newGood();
 312                 if ( count( $this->backends ) <= 1 ) {
 313                         return $status; // skip checks
 314                 }
 315
 316                 foreach ( $paths as $path ) {
 317                         foreach ( $this->backends as $backend ) {
 318                                 $realPath = $this->substPaths( $path, $backend );
 319                                 if ( !$backend->isPathUsableInternal( $realPath ) ) {
 320                                         $status->fatal( 'backend-fail-usable', $path );
 321                                 }
 322                         }
 323                 }
 324
 325                 return $status;
 326         }
 327
 328         /**
 329          * Check that a set of files are consistent across all internal backends
 330          * and re-synchronize those files against the "multi master" if needed.
 331          *
 332          * @param array $paths List of storage paths
 333          * @param string|bool $resyncMode False, True, or "conservative"; see __construct()
 334          * @return Status
 335          */
 336         public function resyncFiles( array $paths, $resyncMode = true ) {
 337                 $status = Status::newGood();
 338
 339                 $mBackend = $this->backends[$this->masterIndex];
 340                 foreach ( $paths as $path ) {
 341                         $mPath = $this->substPaths( $path, $mBackend );
 342                         $mSha1 = $mBackend->getFileSha1Base36( [ 'src' => $mPath, 'latest' => true ] );
 343                         $mStat = $mBackend->getFileStat( [ 'src' => $mPath, 'latest' => true ] );
 344                         if ( $mStat === null || ( $mSha1 !== false && !$mStat ) ) { // sanity
 345                                 $status->fatal( 'backend-fail-internal', $this->name );
 346                                 wfDebugLog( 'FileOperation', __METHOD__
 347                                         . ': File is not available on the master backend' );
 348                                 continue; // file is not available on the master backend...
 349                         }
 350                         // Check of all clone backends agree with the master...
 351                         foreach ( $this->backends as $index => $cBackend ) {
 352                                 if ( $index === $this->masterIndex ) {
 353                                         continue; // master
 354                                 }
 355                                 $cPath = $this->substPaths( $path, $cBackend );
 356                                 $cSha1 = $cBackend->getFileSha1Base36( [ 'src' => $cPath, 'latest' => true ] );
 357                                 $cStat = $cBackend->getFileStat( [ 'src' => $cPath, 'latest' => true ] );
 358                                 if ( $cStat === null || ( $cSha1 !== false && !$cStat ) ) { // sanity
 359                                         $status->fatal( 'backend-fail-internal', $cBackend->getName() );
 360                                         wfDebugLog( 'FileOperation', __METHOD__ .
 361                                                 ': File is not available on the clone backend' );
 362                                         continue; // file is not available on the clone backend...
 363                                 }
 364                                 if ( $mSha1 === $cSha1 ) {
 365                                         // already synced; nothing to do
 366                                 } elseif ( $mSha1 !== false ) { // file is in master
 367                                         if ( $resyncMode === 'conservative'
 368                                                 && $cStat && $cStat['mtime'] > $mStat['mtime']
 369                                         ) {
 370                                                 $status->fatal( 'backend-fail-synced', $path );
 371                                                 continue; // don't rollback data
 372                                         }
 373                                         $fsFile = $mBackend->getLocalReference(
 374                                                 [ 'src' => $mPath, 'latest' => true ] );
 375                                         $status->merge( $cBackend->quickStore(
 376                                                 [ 'src' => $fsFile->getPath(), 'dst' => $cPath ]
 377                                         ) );
 378                                 } elseif ( $mStat === false ) { // file is not in master
 379                                         if ( $resyncMode === 'conservative' ) {
 380                                                 $status->fatal( 'backend-fail-synced', $path );
 381                                                 continue; // don't delete data
 382                                         }
 383                                         $status->merge( $cBackend->quickDelete( [ 'src' => $cPath ] ) );
 384                                 }
 385                         }
 386                 }
 387
 388                 return $status;
 389         }
 390
 391         /**
 392          * Get a list of file storage paths to read or write for a list of operations
 393          *
 394          * @param array $ops Same format as doOperations()
 395          * @return array List of storage paths to files (does not include directories)
 396          */
 397         protected function fileStoragePathsForOps( array $ops ) {
 398                 $paths = [];
 399                 foreach ( $ops as $op ) {
 400                         if ( isset( $op['src'] ) ) {
 401                                 // For things like copy/move/delete with "ignoreMissingSource" and there
 402                                 // is no source file, nothing should happen and there should be no errors.
 403                                 if ( empty( $op['ignoreMissingSource'] )
 404                                         || $this->fileExists( [ 'src' => $op['src'] ] )
 405                                 ) {
 406                                         $paths[] = $op['src'];
 407                                 }
 408                         }
 409                         if ( isset( $op['srcs'] ) ) {
 410                                 $paths = array_merge( $paths, $op['srcs'] );
 411                         }
 412                         if ( isset( $op['dst'] ) ) {
 413                                 $paths[] = $op['dst'];
 414                         }
 415                 }
 416
 417                 return array_values( array_unique( array_filter( $paths, 'FileBackend::isStoragePath' ) ) );
 418         }
 419
 420         /**
 421          * Substitute the backend name in storage path parameters
 422          * for a set of operations with that of a given internal backend.
 423          *
 424          * @param array $ops List of file operation arrays
 425          * @param FileBackendStore $backend
 426          * @return array
 427          */
 428         protected function substOpBatchPaths( array $ops, FileBackendStore $backend ) {
 429                 $newOps = []; // operations
 430                 foreach ( $ops as $op ) {
 431                         $newOp = $op; // operation
 432                         foreach ( [ 'src', 'srcs', 'dst', 'dir' ] as $par ) {
 433                                 if ( isset( $newOp[$par] ) ) { // string or array
 434                                         $newOp[$par] = $this->substPaths( $newOp[$par], $backend );
 435                                 }
 436                         }
 437                         $newOps[] = $newOp;
 438                 }
 439
 440                 return $newOps;
 441         }
 442
 443         /**
 444          * Same as substOpBatchPaths() but for a single operation
 445          *
 446          * @param array $ops File operation array
 447          * @param FileBackendStore $backend
 448          * @return array
 449          */
 450         protected function substOpPaths( array $ops, FileBackendStore $backend ) {
 451                 $newOps = $this->substOpBatchPaths( [ $ops ], $backend );
 452
 453                 return $newOps[0];
 454         }
 455
 456         /**
 457          * Substitute the backend of storage paths with an internal backend's name
 458          *
 459          * @param array|string $paths List of paths or single string path
 460          * @param FileBackendStore $backend
 461          * @return array|string
 462          */
 463         protected function substPaths( $paths, FileBackendStore $backend ) {
 464                 return preg_replace(
 465                         '!^mwstore://' . preg_quote( $this->name, '!' ) . '/!',
 466                         StringUtils::escapeRegexReplacement( "mwstore://{$backend->getName()}/" ),
 467                         $paths // string or array
 468                 );
 469         }
 470
 471         /**
 472          * Substitute the backend of internal storage paths with the proxy backend's name
 473          *
 474          * @param array|string $paths List of paths or single string path
 475          * @return array|string
 476          */
 477         protected function unsubstPaths( $paths ) {
 478                 return preg_replace(
 479                         '!^mwstore://([^/]+)!',
 480                         StringUtils::escapeRegexReplacement( "mwstore://{$this->name}" ),
 481                         $paths // string or array
 482                 );
 483         }
 484
 485         /**
 486          * @param array $ops File operations for FileBackend::doOperations()
 487          * @return bool Whether there are file path sources with outside lifetime/ownership
 488          */
 489         protected function hasVolatileSources( array $ops ) {
 490                 foreach ( $ops as $op ) {
 491                         if ( $op['op'] === 'store' && !isset( $op['srcRef'] ) ) {
 492                                 return true; // source file might be deleted anytime after do*Operations()
 493                         }
 494                 }
 495
 496                 return false;
 497         }
 498
 499         protected function doQuickOperationsInternal( array $ops ) {
 500                 $status = Status::newGood();
 501                 // Do the operations on the master backend; setting Status fields...
 502                 $realOps = $this->substOpBatchPaths( $ops, $this->backends[$this->masterIndex] );
 503                 $masterStatus = $this->backends[$this->masterIndex]->doQuickOperations( $realOps );
 504                 $status->merge( $masterStatus );
 505                 // Propagate the operations to the clone backends...
 506                 foreach ( $this->backends as $index => $backend ) {
 507                         if ( $index === $this->masterIndex ) {
 508                                 continue; // done already
 509                         }
 510
 511                         $realOps = $this->substOpBatchPaths( $ops, $backend );
 512                         if ( $this->asyncWrites && !$this->hasVolatileSources( $ops ) ) {
 513                                 DeferredUpdates::addCallableUpdate(
 514                                         function() use ( $backend, $realOps ) {
 515                                                 $backend->doQuickOperations( $realOps );
 516                                         }
 517                                 );
 518                         } else {
 519                                 $status->merge( $backend->doQuickOperations( $realOps ) );
 520                         }
 521                 }
 522                 // Make 'success', 'successCount', and 'failCount' fields reflect
 523                 // the overall operation, rather than all the batches for each backend.
 524                 // Do this by only using success values from the master backend's batch.
 525                 $status->success = $masterStatus->success;
 526                 $status->successCount = $masterStatus->successCount;
 527                 $status->failCount = $masterStatus->failCount;
 528
 529                 return $status;
 530         }
 531
 532         protected function doPrepare( array $params ) {
 533                 return $this->doDirectoryOp( 'prepare', $params );
 534         }
 535
 536         protected function doSecure( array $params ) {
 537                 return $this->doDirectoryOp( 'secure', $params );
 538         }
 539
 540         protected function doPublish( array $params ) {
 541                 return $this->doDirectoryOp( 'publish', $params );
 542         }
 543
 544         protected function doClean( array $params ) {
 545                 return $this->doDirectoryOp( 'clean', $params );
 546         }
 547
 548         /**
 549          * @param string $method One of (doPrepare,doSecure,doPublish,doClean)
 550          * @param array $params Method arguments
 551          * @return Status
 552          */
 553         protected function doDirectoryOp( $method, array $params ) {
 554                 $status = Status::newGood();
 555
 556                 $realParams = $this->substOpPaths( $params, $this->backends[$this->masterIndex] );
 557                 $masterStatus = $this->backends[$this->masterIndex]->$method( $realParams );
 558                 $status->merge( $masterStatus );
 559
 560                 foreach ( $this->backends as $index => $backend ) {
 561                         if ( $index === $this->masterIndex ) {
 562                                 continue; // already done
 563                         }
 564
 565                         $realParams = $this->substOpPaths( $params, $backend );
 566                         if ( $this->asyncWrites ) {
 567                                 DeferredUpdates::addCallableUpdate(
 568                                         function() use ( $backend, $method, $realParams ) {
 569                                                 $backend->$method( $realParams );
 570                                         }
 571                                 );
 572                         } else {
 573                                 $status->merge( $backend->$method( $realParams ) );
 574                         }
 575                 }
 576
 577                 return $status;
 578         }
 579
 580         public function concatenate( array $params ) {
 581                 // We are writing to an FS file, so we don't need to do this per-backend
 582                 $index = $this->getReadIndexFromParams( $params );
 583                 $realParams = $this->substOpPaths( $params, $this->backends[$index] );
 584
 585                 return $this->backends[$index]->concatenate( $realParams );
 586         }
 587
 588         public function fileExists( array $params ) {
 589                 $index = $this->getReadIndexFromParams( $params );
 590                 $realParams = $this->substOpPaths( $params, $this->backends[$index] );
 591
 592                 return $this->backends[$index]->fileExists( $realParams );
 593         }
 594
 595         public function getFileTimestamp( array $params ) {
 596                 $index = $this->getReadIndexFromParams( $params );
 597                 $realParams = $this->substOpPaths( $params, $this->backends[$index] );
 598
 599                 return $this->backends[$index]->getFileTimestamp( $realParams );
 600         }
 601
 602         public function getFileSize( array $params ) {
 603                 $index = $this->getReadIndexFromParams( $params );
 604                 $realParams = $this->substOpPaths( $params, $this->backends[$index] );
 605
 606                 return $this->backends[$index]->getFileSize( $realParams );
 607         }
 608
 609         public function getFileStat( array $params ) {
 610                 $index = $this->getReadIndexFromParams( $params );
 611                 $realParams = $this->substOpPaths( $params, $this->backends[$index] );
 612
 613                 return $this->backends[$index]->getFileStat( $realParams );
 614         }
 615
 616         public function getFileXAttributes( array $params ) {
 617                 $index = $this->getReadIndexFromParams( $params );
 618                 $realParams = $this->substOpPaths( $params, $this->backends[$index] );
 619
 620                 return $this->backends[$index]->getFileXAttributes( $realParams );
 621         }
 622
 623         public function getFileContentsMulti( array $params ) {
 624                 $index = $this->getReadIndexFromParams( $params );
 625                 $realParams = $this->substOpPaths( $params, $this->backends[$index] );
 626
 627                 $contentsM = $this->backends[$index]->getFileContentsMulti( $realParams );
 628
 629                 $contents = []; // (path => FSFile) mapping using the proxy backend's name
 630                 foreach ( $contentsM as $path => $data ) {
 631                         $contents[$this->unsubstPaths( $path )] = $data;
 632                 }
 633
 634                 return $contents;
 635         }
 636
 637         public function getFileSha1Base36( array $params ) {
 638                 $index = $this->getReadIndexFromParams( $params );
 639                 $realParams = $this->substOpPaths( $params, $this->backends[$index] );
 640
 641                 return $this->backends[$index]->getFileSha1Base36( $realParams );
 642         }
 643
 644         public function getFileProps( array $params ) {
 645                 $index = $this->getReadIndexFromParams( $params );
 646                 $realParams = $this->substOpPaths( $params, $this->backends[$index] );
 647
 648                 return $this->backends[$index]->getFileProps( $realParams );
 649         }
 650
 651         public function streamFile( array $params ) {
 652                 $index = $this->getReadIndexFromParams( $params );
 653                 $realParams = $this->substOpPaths( $params, $this->backends[$index] );
 654
 655                 return $this->backends[$index]->streamFile( $realParams );
 656         }
 657
 658         public function getLocalReferenceMulti( array $params ) {
 659                 $index = $this->getReadIndexFromParams( $params );
 660                 $realParams = $this->substOpPaths( $params, $this->backends[$index] );
 661
 662                 $fsFilesM = $this->backends[$index]->getLocalReferenceMulti( $realParams );
 663
 664                 $fsFiles = []; // (path => FSFile) mapping using the proxy backend's name
 665                 foreach ( $fsFilesM as $path => $fsFile ) {
 666                         $fsFiles[$this->unsubstPaths( $path )] = $fsFile;
 667                 }
 668
 669                 return $fsFiles;
 670         }
 671
 672         public function getLocalCopyMulti( array $params ) {
 673                 $index = $this->getReadIndexFromParams( $params );
 674                 $realParams = $this->substOpPaths( $params, $this->backends[$index] );
 675
 676                 $tempFilesM = $this->backends[$index]->getLocalCopyMulti( $realParams );
 677
 678                 $tempFiles = []; // (path => TempFSFile) mapping using the proxy backend's name
 679                 foreach ( $tempFilesM as $path => $tempFile ) {
 680                         $tempFiles[$this->unsubstPaths( $path )] = $tempFile;
 681                 }
 682
 683                 return $tempFiles;
 684         }
 685
 686         public function getFileHttpUrl( array $params ) {
 687                 $index = $this->getReadIndexFromParams( $params );
 688                 $realParams = $this->substOpPaths( $params, $this->backends[$index] );
 689
 690                 return $this->backends[$index]->getFileHttpUrl( $realParams );
 691         }
 692
 693         public function directoryExists( array $params ) {
 694                 $realParams = $this->substOpPaths( $params, $this->backends[$this->masterIndex] );
 695
 696                 return $this->backends[$this->masterIndex]->directoryExists( $realParams );
 697         }
 698
 699         public function getDirectoryList( array $params ) {
 700                 $realParams = $this->substOpPaths( $params, $this->backends[$this->masterIndex] );
 701
 702                 return $this->backends[$this->masterIndex]->getDirectoryList( $realParams );
 703         }
 704
 705         public function getFileList( array $params ) {
 706                 $realParams = $this->substOpPaths( $params, $this->backends[$this->masterIndex] );
 707
 708                 return $this->backends[$this->masterIndex]->getFileList( $realParams );
 709         }
 710
 711         public function getFeatures() {
 712                 return $this->backends[$this->masterIndex]->getFeatures();
 713         }
 714
 715         public function clearCache( array $paths = null ) {
 716                 foreach ( $this->backends as $backend ) {
 717                         $realPaths = is_array( $paths ) ? $this->substPaths( $paths, $backend ) : null;
 718                         $backend->clearCache( $realPaths );
 719                 }
 720         }
 721
 722         public function preloadCache( array $paths ) {
 723                 $realPaths = $this->substPaths( $paths, $this->backends[$this->readIndex] );
 724                 $this->backends[$this->readIndex]->preloadCache( $realPaths );
 725         }
 726
 727         public function preloadFileStat( array $params ) {
 728                 $index = $this->getReadIndexFromParams( $params );
 729                 $realParams = $this->substOpPaths( $params, $this->backends[$index] );
 730
 731                 return $this->backends[$index]->preloadFileStat( $realParams );
 732         }
 733
 734         public function getScopedLocksForOps( array $ops, Status $status ) {
 735                 $realOps = $this->substOpBatchPaths( $ops, $this->backends[$this->masterIndex] );
 736                 $fileOps = $this->backends[$this->masterIndex]->getOperationsInternal( $realOps );
 737                 // Get the paths to lock from the master backend
 738                 $paths = $this->backends[$this->masterIndex]->getPathsToLockForOpsInternal( $fileOps );
 739                 // Get the paths under the proxy backend's name
 740                 $pbPaths = [
 741                         LockManager::LOCK_UW => $this->unsubstPaths( $paths[LockManager::LOCK_UW] ),
 742                         LockManager::LOCK_EX => $this->unsubstPaths( $paths[LockManager::LOCK_EX] )
 743                 ];
 744
 745                 // Actually acquire the locks
 746                 return $this->getScopedFileLocks( $pbPaths, 'mixed', $status );
 747         }
 748
 749         /**
 750          * @param array $params
 751          * @return int The master or read affinity backend index, based on $params['latest']
 752          */
 753         protected function getReadIndexFromParams( array $params ) {
 754                 return !empty( $params['latest'] ) ? $this->masterIndex : $this->readIndex;
 755         }
 756 }