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