includes/filerepo/backend/FileBackend.php

   1 <?php
   2 /**
   3  * @file
   4  * @ingroup FileBackend
   5  * @author Aaron Schulz
   6  */
   7
   8 /**
   9  * Base class for all file backend classes (including multi-write backends).
  10  * This class defines the methods as abstract that subclasses must implement.
  11  * Outside callers can assume that all backends will have these functions.
  12  *
  13  * All "storage paths" are of the format "mwstore://backend/container/path".
  14  * The paths use UNIX file system (FS) notation, though any particular backend may
  15  * not actually be using a local filesystem. Therefore, the paths are only virtual.
  16  *
  17  * Backend contents are stored under wiki-specific container names by default.
  18  * For legacy reasons, this has no effect for the FS backend class, and per-wiki
  19  * segregation must be done by setting the container paths appropriately.
  20  *
  21  * FS-based backends are somewhat more restrictive due to the existence of real
  22  * directory files; a regular file cannot have the same name as a directory. Other
  23  * backends with virtual directories may not have this limitation. Callers should
  24  * store files in such a way that no files and directories are under the same path.
  25  *
  26  * Methods should avoid throwing exceptions at all costs.
  27  * As a corollary, external dependencies should be kept to a minimum.
  28  *
  29  * @ingroup FileBackend
  30  * @since 1.19
  31  */
  32 abstract class FileBackendBase {
  33         protected $name; // unique backend name
  34         protected $wikiId; // unique wiki name
  35         protected $readOnly; // string
  36         /** @var LockManager */
  37         protected $lockManager;
  38
  39         /**
  40          * Create a new backend instance from configuration.
  41          * This should only be called from within FileBackendGroup.
  42          *
  43          * $config includes:
  44          *     'name'        : The unique name of this backend.
  45          *     'wikiId'      : Prefix to container names that is unique to this wiki.
  46          *                     This should consist of alphanumberic, '-', and '_' chars.
  47          *     'lockManager' : Registered name of a file lock manager to use.
  48          *     'readOnly'    : Write operations are disallowed if this is a non-empty string.
  49          *                     It should be an explanation for the backend being read-only.
  50          *
  51          * @param $config Array
  52          */
  53         public function __construct( array $config ) {
  54                 $this->name = $config['name'];
  55                 $this->wikiId = isset( $config['wikiId'] )
  56                         ? $config['wikiId']
  57                         : wfWikiID(); // e.g. "my_wiki-en_"
  58                 $this->wikiId = $this->resolveWikiId( $this->wikiId );
  59                 $this->lockManager = LockManagerGroup::singleton()->get( $config['lockManager'] );
  60                 $this->readOnly = isset( $config['readOnly'] )
  61                         ? (string)$config['readOnly']
  62                         : '';
  63         }
  64
  65         /**
  66          * Normalize a wiki ID by replacing characters that are
  67          * not supported by the backend as part of container names.
  68          *
  69          * @param $wikiId string
  70          * @return string
  71          */
  72         protected function resolveWikiId( $wikiId ) {
  73                 return $wikiId;
  74         }
  75
  76         /**
  77          * Get the unique backend name.
  78          *
  79          * We may have multiple different backends of the same type.
  80          * For example, we can have two Swift backends using different proxies.
  81          *
  82          * @return string
  83          */
  84         final public function getName() {
  85                 return $this->name;
  86         }
  87
  88         /**
  89          * This is the main entry point into the backend for write operations.
  90          * Callers supply an ordered list of operations to perform as a transaction.
  91          * If any serious errors occur, all attempted operations will be rolled back.
  92          *
  93          * $ops is an array of arrays. The outer array holds a list of operations.
  94          * Each inner array is a set of key value pairs that specify an operation.
  95          *
  96          * Supported operations and their parameters:
  97          * a) Create a new file in storage with the contents of a string
  98          *     array(
  99          *         'op'                  => 'create',
 100          *         'dst'                 => <storage path>,
 101          *         'content'             => <string of new file contents>,
 102          *         'overwriteDest'       => <boolean>,
 103          *         'overwriteSame'       => <boolean>
 104          *     )
 105          * b) Copy a file system file into storage
 106          *     array(
 107          *         'op'                  => 'store',
 108          *         'src'                 => <file system path>,
 109          *         'dst'                 => <storage path>,
 110          *         'overwriteDest'       => <boolean>,
 111          *         'overwriteSame'       => <boolean>
 112          *     )
 113          * c) Copy a file within storage
 114          *     array(
 115          *         'op'                  => 'copy',
 116          *         'src'                 => <storage path>,
 117          *         'dst'                 => <storage path>,
 118          *         'overwriteDest'       => <boolean>,
 119          *         'overwriteSame'       => <boolean>
 120          *     )
 121          * d) Move a file within storage
 122          *     array(
 123          *         'op'                  => 'move',
 124          *         'src'                 => <storage path>,
 125          *         'dst'                 => <storage path>,
 126          *         'overwriteDest'       => <boolean>,
 127          *         'overwriteSame'       => <boolean>
 128          *     )
 129          * e) Delete a file within storage
 130          *     array(
 131          *         'op'                  => 'delete',
 132          *         'src'                 => <storage path>,
 133          *         'ignoreMissingSource' => <boolean>
 134          *     )
 135          * f) Concatenate a list of files within storage into a single temp file
 136          *     array(
 137          *         'op'                  => 'concatenate',
 138          *         'srcs'                => <ordered array of storage paths>,
 139          *         'dst'                 => <file system path to 0-byte temp file>
 140          *     )
 141          * g) Do nothing (no-op)
 142          *     array(
 143          *         'op'                  => 'null',
 144          *     )
 145          *
 146          * Boolean flags for operations (operation-specific):
 147          * 'ignoreMissingSource' : The operation will simply succeed and do
 148          *                         nothing if the source file does not exist.
 149          * 'overwriteDest'       : Any destination file will be overwritten.
 150          * 'overwriteSame'       : An error will not be given if a file already
 151          *                         exists at the destination that has the same
 152          *                         contents as the new contents to be written there.
 153          *
 154          * $opts is an associative of boolean flags, including:
 155          * 'ignoreErrors'        : Errors that would normally cause a rollback do not.
 156          *                         The remaining operations are still attempted if any fail.
 157          * 'nonLocking'          : No locks are acquired for the operations.
 158          *                         This can increase performance for non-critical writes.
 159          *                         This has no effect unless the 'ignoreErrors' flag is set.
 160          * 'allowStale'          : Don't require the latest available data.
 161          *                         This can increase performance for non-critical writes.
 162          *                         This has no effect unless the 'ignoreErrors' flag is set.
 163          *
 164          * Return value:
 165          * This returns a Status, which contains all warnings and fatals that occured
 166          * during the operation. The 'failCount', 'successCount', and 'success' members
 167          * will reflect each operation attempted. The status will be "OK" unless any
 168          * of the operations failed and the 'ignoreErrors' parameter was not set.
 169          *
 170          * @param $ops Array List of operations to execute in order
 171          * @param $opts Array Batch operation options
 172          * @return Status
 173          */
 174         final public function doOperations( array $ops, array $opts = array() ) {
 175                 if ( $this->readOnly != '' ) {
 176                         return Status::newFatal( 'backend-fail-readonly', $this->name, $this->readOnly );
 177                 }
 178                 if ( empty( $opts['ignoreErrors'] ) ) { // sanity
 179                         unset( $opts['nonLocking'] );
 180                         unset( $opts['allowStale'] );
 181                 }
 182                 return $this->doOperationsInternal( $ops, $opts );
 183         }
 184
 185         /**
 186          * @see FileBackendBase::doOperations()
 187          */
 188         abstract protected function doOperationsInternal( array $ops, array $opts );
 189
 190         /**
 191          * Same as doOperations() except it takes a single operation.
 192          * If you are doing a batch of operations that should either
 193          * all succeed or all fail, then use that function instead.
 194          *
 195          * @see FileBackendBase::doOperations()
 196          *
 197          * @param $op Array Operation
 198          * @param $opts Array Operation options
 199          * @return Status
 200          */
 201         final public function doOperation( array $op, array $opts = array() ) {
 202                 return $this->doOperations( array( $op ), $opts );
 203         }
 204
 205         /**
 206          * Performs a single store operation.
 207          * This sets $params['op'] to 'store' and passes it to doOperation().
 208          *
 209          * @see FileBackendBase::doOperation()
 210          *
 211          * @param $params Array Operation parameters
 212          * @param $opts Array Operation options
 213          * @return Status
 214          */
 215         final public function store( array $params, array $opts = array() ) {
 216                 $params['op'] = 'store';
 217                 return $this->doOperation( $params, $opts );
 218         }
 219
 220         /**
 221          * Performs a single copy operation.
 222          * This sets $params['op'] to 'copy' and passes it to doOperation().
 223          *
 224          * @see FileBackendBase::doOperation()
 225          *
 226          * @param $params Array Operation parameters
 227          * @param $opts Array Operation options
 228          * @return Status
 229          */
 230         final public function copy( array $params, array $opts = array() ) {
 231                 $params['op'] = 'copy';
 232                 return $this->doOperation( $params, $opts );
 233         }
 234
 235         /**
 236          * Performs a single move operation.
 237          * This sets $params['op'] to 'move' and passes it to doOperation().
 238          *
 239          * @see FileBackendBase::doOperation()
 240          *
 241          * @param $params Array Operation parameters
 242          * @param $opts Array Operation options
 243          * @return Status
 244          */
 245         final public function move( array $params, array $opts = array() ) {
 246                 $params['op'] = 'move';
 247                 return $this->doOperation( $params, $opts );
 248         }
 249
 250         /**
 251          * Performs a single delete operation.
 252          * This sets $params['op'] to 'delete' and passes it to doOperation().
 253          *
 254          * @see FileBackendBase::doOperation()
 255          *
 256          * @param $params Array Operation parameters
 257          * @param $opts Array Operation options
 258          * @return Status
 259          */
 260         final public function delete( array $params, array $opts = array() ) {
 261                 $params['op'] = 'delete';
 262                 return $this->doOperation( $params, $opts );
 263         }
 264
 265         /**
 266          * Performs a single create operation.
 267          * This sets $params['op'] to 'create' and passes it to doOperation().
 268          *
 269          * @see FileBackendBase::doOperation()
 270          *
 271          * @param $params Array Operation parameters
 272          * @param $opts Array Operation options
 273          * @return Status
 274          */
 275         final public function create( array $params, array $opts = array() ) {
 276                 $params['op'] = 'create';
 277                 return $this->doOperation( $params, $opts );
 278         }
 279
 280         /**
 281          * Performs a single concatenate operation.
 282          * This sets $params['op'] to 'concatenate' and passes it to doOperation().
 283          *
 284          * @see FileBackendBase::doOperation()
 285          *
 286          * @param $params Array Operation parameters
 287          * @param $opts Array Operation options
 288          * @return Status
 289          */
 290         final public function concatenate( array $params, array $opts = array() ) {
 291                 $params['op'] = 'concatenate';
 292                 return $this->doOperation( $params, $opts );
 293         }
 294
 295         /**
 296          * Prepare a storage path for usage. This will create containers
 297          * that don't yet exist or, on FS backends, create parent directories.
 298          *
 299          * $params include:
 300          *     dir : storage directory
 301          *
 302          * @param $params Array
 303          * @return Status
 304          */
 305         abstract public function prepare( array $params );
 306
 307         /**
 308          * Take measures to block web access to a directory and
 309          * the container it belongs to. FS backends might add .htaccess
 310          * files wheras backends like Swift this might restrict container
 311          * access to backend user that represents end-users in web request.
 312          * This is not guaranteed to actually do anything.
 313          *
 314          * $params include:
 315          *     dir       : storage directory
 316          *     noAccess  : try to deny file access
 317          *     noListing : try to deny file listing
 318          *
 319          * @param $params Array
 320          * @return Status
 321          */
 322         abstract public function secure( array $params );
 323
 324         /**
 325          * Clean up an empty storage directory.
 326          * On FS backends, the directory will be deleted. Others may do nothing.
 327          *
 328          * $params include:
 329          *     dir : storage directory
 330          *
 331          * @param $params Array
 332          * @return Status
 333          */
 334         abstract public function clean( array $params );
 335
 336         /**
 337          * Check if a file exists at a storage path in the backend.
 338          * This returns false if only a directory exists at the path.
 339          *
 340          * $params include:
 341          *     src    : source storage path
 342          *     latest : use the latest available data
 343          *
 344          * @param $params Array
 345          * @return bool|null Returns null on failure
 346          */
 347         abstract public function fileExists( array $params );
 348
 349         /**
 350          * Get the last-modified timestamp of the file at a storage path.
 351          *
 352          * $params include:
 353          *     src    : source storage path
 354          *     latest : use the latest available data
 355          *
 356          * @param $params Array
 357          * @return string|false TS_MW timestamp or false on failure
 358          */
 359         abstract public function getFileTimestamp( array $params );
 360
 361         /**
 362          * Get the contents of a file at a storage path in the backend.
 363          * This should be avoided for potentially large files.
 364          *
 365          * $params include:
 366          *     src    : source storage path
 367          *     latest : use the latest available data
 368          *
 369          * @param $params Array
 370          * @return string|false Returns false on failure
 371          */
 372         abstract public function getFileContents( array $params );
 373
 374         /**
 375          * Get a SHA-1 hash of the file at a storage path in the backend.
 376          *
 377          * $params include:
 378          *     src    : source storage path
 379          *     latest : use the latest available data
 380          *
 381          * @param $params Array
 382          * @return string|false Hash string or false on failure
 383          */
 384         abstract public function getFileSha1Base36( array $params );
 385
 386         /**
 387          * Get the properties of the file at a storage path in the backend.
 388          * Returns FSFile::placeholderProps() on failure.
 389          *
 390          * $params include:
 391          *     src    : source storage path
 392          *     latest : use the latest available data
 393          *
 394          * @param $params Array
 395          * @return Array
 396          */
 397         abstract public function getFileProps( array $params );
 398
 399         /**
 400          * Stream the file at a storage path in the backend.
 401          * Appropriate HTTP headers (Status, Content-Type, Content-Length)
 402          * must be sent if streaming began, while none should be sent otherwise.
 403          * Implementations should flush the output buffer before sending data.
 404          *
 405          * $params include:
 406          *     src     : source storage path
 407          *     headers : additional HTTP headers to send on success
 408          *     latest  : use the latest available data
 409          *
 410          * @param $params Array
 411          * @return Status
 412          */
 413         abstract public function streamFile( array $params );
 414
 415         /**
 416          * Returns a file system file, identical to the file at a storage path.
 417          * The file returned is either:
 418          * a) A local copy of the file at a storage path in the backend.
 419          *    The temporary copy will have the same extension as the source.
 420          * b) An original of the file at a storage path in the backend.
 421          * Temporary files may be purged when the file object falls out of scope.
 422          *
 423          * Write operations should *never* be done on this file as some backends
 424          * may do internal tracking or may be instances of FileBackendMultiWrite.
 425          * In that later case, there are copies of the file that must stay in sync.
 426          *
 427          * $params include:
 428          *     src    : source storage path
 429          *     latest : use the latest available data
 430          *
 431          * @param $params Array
 432          * @return FSFile|null Returns null on failure
 433          */
 434         abstract public function getLocalReference( array $params );
 435
 436         /**
 437          * Get a local copy on disk of the file at a storage path in the backend.
 438          * The temporary copy will have the same file extension as the source.
 439          * Temporary files may be purged when the file object falls out of scope.
 440          *
 441          * $params include:
 442          *     src    : source storage path
 443          *     latest : use the latest available data
 444          *
 445          * @param $params Array
 446          * @return TempFSFile|null Returns null on failure
 447          */
 448         abstract public function getLocalCopy( array $params );
 449
 450         /**
 451          * Get an iterator to list out all stored files under a storage directory.
 452          * If the directory is of the form "mwstore://container", then all items in
 453          * the container should be listed. If of the form "mwstore://container/dir",
 454          * then all items under that container directory should be listed.
 455          * Results should be storage paths relative to the given directory.
 456          *
 457          * $params include:
 458          *     dir : storage path directory
 459          *
 460          * @return Traversable|Array|null Returns null on failure
 461          */
 462         abstract public function getFileList( array $params );
 463
 464         /**
 465          * Lock the files at the given storage paths in the backend.
 466          * This will either lock all the files or none (on failure).
 467          *
 468          * Callers should consider using getScopedFileLocks() instead.
 469          *
 470          * @param $paths Array Storage paths
 471          * @param $type integer LockManager::LOCK_* constant
 472          * @return Status
 473          */
 474         final public function lockFiles( array $paths, $type ) {
 475                 return $this->lockManager->lock( $paths, $type );
 476         }
 477
 478         /**
 479          * Unlock the files at the given storage paths in the backend.
 480          *
 481          * @param $paths Array Storage paths
 482          * @param $type integer LockManager::LOCK_* constant
 483          * @return Status
 484          */
 485         final public function unlockFiles( array $paths, $type ) {
 486                 return $this->lockManager->unlock( $paths, $type );
 487         }
 488
 489         /**
 490          * Lock the files at the given storage paths in the backend.
 491          * This will either lock all the files or none (on failure).
 492          * On failure, the status object will be updated with errors.
 493          *
 494          * Once the return value goes out scope, the locks will be released and
 495          * the status updated. Unlock fatals will not change the status "OK" value.
 496          *
 497          * @param $paths Array Storage paths
 498          * @param $type integer LockManager::LOCK_* constant
 499          * @param $status Status Status to update on lock/unlock
 500          * @return ScopedLock|null Returns null on failure
 501          */
 502         final public function getScopedFileLocks( array $paths, $type, Status $status ) {
 503                 return ScopedLock::factory( $this->lockManager, $paths, $type, $status );
 504         }
 505 }
 506
 507 /**
 508  * Base class for all single-write backends.
 509  * This class defines the methods as abstract that subclasses must implement.
 510  * Callers outside of FileBackend and its helper classes, such as FileOp,
 511  * should only call functions that are present in FileBackendBase.
 512  *
 513  * The FileBackendBase operations are implemented using primitive functions
 514  * such as storeInternal(), copyInternal(), deleteInternal() and the like.
 515  * This class is also responsible for path resolution and sanitization.
 516  *
 517  * @ingroup FileBackend
 518  * @since 1.19
 519  */
 520 abstract class FileBackend extends FileBackendBase {
 521         /** @var Array */
 522         protected $cache = array(); // (storage path => key => value)
 523         protected $maxCacheSize = 75; // integer; max paths with entries
 524         /** @var Array */
 525         protected $shardViaHashLevels = array(); // (container name => integer)
 526
 527         /**
 528          * Create a file in the backend with the given contents.
 529          * Do not call this function from places outside FileBackend and FileOp.
 530          *
 531          * $params include:
 532          *     content       : the raw file contents
 533          *     dst           : destination storage path
 534          *     overwriteDest : overwrite any file that exists at the destination
 535          *
 536          * @param $params Array
 537          * @return Status
 538          */
 539         final public function createInternal( array $params ) {
 540                 $status = $this->doCreateInternal( $params );
 541                 $this->clearCache( array( $params['dst'] ) );
 542                 return $status;
 543         }
 544
 545         /**
 546          * @see FileBackend::createInternal()
 547          */
 548         abstract protected function doCreateInternal( array $params );
 549
 550         /**
 551          * Store a file into the backend from a file on disk.
 552          * Do not call this function from places outside FileBackend and FileOp.
 553          *
 554          * $params include:
 555          *     src           : source path on disk
 556          *     dst           : destination storage path
 557          *     overwriteDest : overwrite any file that exists at the destination
 558          *
 559          * @param $params Array
 560          * @return Status
 561          */
 562         final public function storeInternal( array $params ) {
 563                 $status = $this->doStoreInternal( $params );
 564                 $this->clearCache( array( $params['dst'] ) );
 565                 return $status;
 566         }
 567
 568         /**
 569          * @see FileBackend::storeInternal()
 570          */
 571         abstract protected function doStoreInternal( array $params );
 572
 573         /**
 574          * Copy a file from one storage path to another in the backend.
 575          * Do not call this function from places outside FileBackend and FileOp.
 576          *
 577          * $params include:
 578          *     src           : source storage path
 579          *     dst           : destination storage path
 580          *     overwriteDest : overwrite any file that exists at the destination
 581          *
 582          * @param $params Array
 583          * @return Status
 584          */
 585         final public function copyInternal( array $params ) {
 586                 $status = $this->doCopyInternal( $params );
 587                 $this->clearCache( array( $params['dst'] ) );
 588                 return $status;
 589         }
 590
 591         /**
 592          * @see FileBackend::copyInternal()
 593          */
 594         abstract protected function doCopyInternal( array $params );
 595
 596         /**
 597          * Delete a file at the storage path.
 598          * Do not call this function from places outside FileBackend and FileOp.
 599          *
 600          * $params include:
 601          *     src                 : source storage path
 602          *     ignoreMissingSource : do nothing if the source file does not exist
 603          *
 604          * @param $params Array
 605          * @return Status
 606          */
 607         final public function deleteInternal( array $params ) {
 608                 $status = $this->doDeleteInternal( $params );
 609                 $this->clearCache( array( $params['src'] ) );
 610                 return $status;
 611         }
 612
 613         /**
 614          * @see FileBackend::deleteInternal()
 615          */
 616         abstract protected function doDeleteInternal( array $params );
 617
 618         /**
 619          * Move a file from one storage path to another in the backend.
 620          * Do not call this function from places outside FileBackend and FileOp.
 621          *
 622          * $params include:
 623          *     src           : source storage path
 624          *     dst           : destination storage path
 625          *     overwriteDest : overwrite any file that exists at the destination
 626          *
 627          * @param $params Array
 628          * @return Status
 629          */
 630         final public function moveInternal( array $params ) {
 631                 $status = $this->doMoveInternal( $params );
 632                 $this->clearCache( array( $params['src'], $params['dst'] ) );
 633                 return $status;
 634         }
 635
 636         /**
 637          * @see FileBackend::moveInternal()
 638          */
 639         protected function doMoveInternal( array $params ) {
 640                 // Copy source to dest
 641                 $status = $this->copyInternal( $params );
 642                 if ( !$status->isOK() ) {
 643                         return $status;
 644                 }
 645                 // Delete source (only fails due to races or medium going down)
 646                 $status->merge( $this->deleteInternal( array( 'src' => $params['src'] ) ) );
 647                 $status->setResult( true, $status->value ); // ignore delete() errors
 648                 return $status;
 649         }
 650
 651         /**
 652          * Combines files from several storage paths into a new file in the backend.
 653          * Do not call this function from places outside FileBackend and FileOp.
 654          * $params include:
 655          *     srcs          : ordered source storage paths (e.g. chunk1, chunk2, ...)
 656          *     dst           : file system path to 0-byte temp file
 657          *
 658          * @param $params Array
 659          * @return Status
 660          */
 661         final public function concatenateInternal( array $params ) {
 662                 $status = $this->doConcatenateInternal( $params );
 663                 return $status;
 664         }
 665
 666         /**
 667          * @see FileBackend::concatenateInternal()
 668          */
 669         protected function doConcatenateInternal( array $params ) {
 670                 $status = Status::newGood();
 671                 $tmpPath = $params['dst']; // convenience
 672
 673                 // Check that the specified temp file is valid...
 674                 wfSuppressWarnings();
 675                 $ok = ( is_file( $tmpPath ) && !filesize( $tmpPath ) );
 676                 wfRestoreWarnings();
 677                 if ( !$ok ) { // not present or not empty
 678                         $status->fatal( 'backend-fail-opentemp', $tmpPath );
 679                         return $status;
 680                 }
 681
 682                 // Build up the temp file using the source chunks (in order)...
 683                 $tmpHandle = fopen( $tmpPath, 'a' );
 684                 if ( $tmpHandle === false ) {
 685                         $status->fatal( 'backend-fail-opentemp', $tmpPath );
 686                         return $status;
 687                 }
 688                 foreach ( $params['srcs'] as $virtualSource ) {
 689                         // Get a local FS version of the chunk
 690                         $tmpFile = $this->getLocalReference( array( 'src' => $virtualSource ) );
 691                         if ( !$tmpFile ) {
 692                                 $status->fatal( 'backend-fail-read', $virtualSource );
 693                                 return $status;
 694                         }
 695                         // Get a handle to the local FS version
 696                         $sourceHandle = fopen( $tmpFile->getPath(), 'r' );
 697                         if ( $sourceHandle === false ) {
 698                                 fclose( $tmpHandle );
 699                                 $status->fatal( 'backend-fail-read', $virtualSource );
 700                                 return $status;
 701                         }
 702                         // Append chunk to file (pass chunk size to avoid magic quotes)
 703                         if ( !stream_copy_to_stream( $sourceHandle, $tmpHandle ) ) {
 704                                 fclose( $sourceHandle );
 705                                 fclose( $tmpHandle );
 706                                 $status->fatal( 'backend-fail-writetemp', $tmpPath );
 707                                 return $status;
 708                         }
 709                         fclose( $sourceHandle );
 710                 }
 711                 if ( !fclose( $tmpHandle ) ) {
 712                         $status->fatal( 'backend-fail-closetemp', $tmpPath );
 713                         return $status;
 714                 }
 715
 716                 return $status;
 717         }
 718
 719         /**
 720          * @see FileBackendBase::prepare()
 721          */
 722         final public function prepare( array $params ) {
 723                 $status = Status::newGood();
 724                 list( $fullCont, $dir, $shard ) = $this->resolveStoragePath( $params['dir'] );
 725                 if ( $dir === null ) {
 726                         $status->fatal( 'backend-fail-invalidpath', $params['dir'] );
 727                         return $status; // invalid storage path
 728                 }
 729                 if ( $shard !== null ) { // confined to a single container/shard
 730                         $status->merge( $this->doPrepare( $fullCont, $dir, $params ) );
 731                 } else { // directory is on several shards
 732                         wfDebug( __METHOD__ . ": iterating over all container shards.\n" );
 733                         list( $b, $shortCont, $r ) = self::splitStoragePath( $params['dir'] );
 734                         foreach ( $this->getContainerSuffixes( $shortCont ) as $suffix ) {
 735                                 $status->merge( $this->doPrepare( "{$fullCont}{$suffix}", $dir, $params ) );
 736                         }
 737                 }
 738                 return $status;
 739         }
 740
 741         /**
 742          * @see FileBackend::prepare()
 743          */
 744         protected function doPrepare( $container, $dir, array $params ) {
 745                 return Status::newGood();
 746         }
 747
 748         /**
 749          * @see FileBackendBase::secure()
 750          */
 751         final public function secure( array $params ) {
 752                 $status = Status::newGood();
 753                 list( $fullCont, $dir, $shard ) = $this->resolveStoragePath( $params['dir'] );
 754                 if ( $dir === null ) {
 755                         $status->fatal( 'backend-fail-invalidpath', $params['dir'] );
 756                         return $status; // invalid storage path
 757                 }
 758                 if ( $shard !== null ) { // confined to a single container/shard
 759                         $status->merge( $this->doSecure( $fullCont, $dir, $params ) );
 760                 } else { // directory is on several shards
 761                         wfDebug( __METHOD__ . ": iterating over all container shards.\n" );
 762                         list( $b, $shortCont, $r ) = self::splitStoragePath( $params['dir'] );
 763                         foreach ( $this->getContainerSuffixes( $shortCont ) as $suffix ) {
 764                                 $status->merge( $this->doSecure( "{$fullCont}{$suffix}", $dir, $params ) );
 765                         }
 766                 }
 767                 return $status;
 768         }
 769
 770         /**
 771          * @see FileBackend::secure()
 772          */
 773         protected function doSecure( $container, $dir, array $params ) {
 774                 return Status::newGood();
 775         }
 776
 777         /**
 778          * @see FileBackendBase::clean()
 779          */
 780         final public function clean( array $params ) {
 781                 $status = Status::newGood();
 782                 list( $fullCont, $dir, $shard ) = $this->resolveStoragePath( $params['dir'] );
 783                 if ( $dir === null ) {
 784                         $status->fatal( 'backend-fail-invalidpath', $params['dir'] );
 785                         return $status; // invalid storage path
 786                 }
 787                 if ( $shard !== null ) { // confined to a single container/shard
 788                         $status->merge( $this->doClean( $fullCont, $dir, $params ) );
 789                 } else { // directory is on several shards
 790                         wfDebug( __METHOD__ . ": iterating over all container shards.\n" );
 791                         list( $b, $shortCont, $r ) = self::splitStoragePath( $params['dir'] );
 792                         foreach ( $this->getContainerSuffixes( $shortCont ) as $suffix ) {
 793                                 $status->merge( $this->doClean( "{$fullCont}{$suffix}", $dir, $params ) );
 794                         }
 795                 }
 796                 return $status;
 797         }
 798
 799         /**
 800          * @see FileBackend::clean()
 801          */
 802         protected function doClean( $container, $dir, array $params ) {
 803                 return Status::newGood();
 804         }
 805
 806         /**
 807          * @see FileBackendBase::fileExists()
 808          */
 809         final public function fileExists( array $params ) {
 810                 $path = $params['src'];
 811                 if ( isset( $this->cache[$path]['exists'] ) ) {
 812                         return $this->cache[$path]['exists'];
 813                 }
 814                 $exists = $this->doFileExists( $params );
 815                 if ( $exists ) { // don't cache negatives
 816                         $this->trimCache(); // limit memory
 817                         $this->cache[$path]['exists'] = $exists;
 818                 }
 819                 return $exists;
 820         }
 821
 822         /**
 823          * @see FileBackend::fileExists()
 824          */
 825         abstract protected function doFileExists( array $params );
 826
 827         /**
 828          * @see FileBackendBase::getFileTimestamp()
 829          */
 830         final public function getFileTimestamp( array $params ) {
 831                 $path = $params['src'];
 832                 if ( isset( $this->cache[$path]['timestamp'] ) ) {
 833                         return $this->cache[$path]['timestamp'];
 834                 }
 835                 $timestamp = $this->doGetFileTimestamp( $params );
 836                 if ( $timestamp ) { // don't cache negatives
 837                         $this->trimCache(); // limit memory
 838                         $this->cache[$path]['timestamp'] = $timestamp;
 839                 }
 840                 return $timestamp;
 841         }
 842
 843         /**
 844          * @see FileBackend::getFileTimestamp()
 845          */
 846         abstract protected function doGetFileTimestamp( array $params );
 847
 848         /**
 849          * @see FileBackendBase::getFileContents()
 850          */
 851         public function getFileContents( array $params ) {
 852                 $tmpFile = $this->getLocalReference( $params );
 853                 if ( !$tmpFile ) {
 854                         return false;
 855                 }
 856                 wfSuppressWarnings();
 857                 $data = file_get_contents( $tmpFile->getPath() );
 858                 wfRestoreWarnings();
 859                 return $data;
 860         }
 861
 862         /**
 863          * @see FileBackendBase::getFileSha1Base36()
 864          */
 865         public function getFileSha1Base36( array $params ) {
 866                 $path = $params['src'];
 867                 if ( isset( $this->cache[$path]['sha1'] ) ) {
 868                         return $this->cache[$path]['sha1'];
 869                 }
 870                 $hash = $this->doGetFileSha1Base36( $params );
 871                 if ( $hash ) { // don't cache negatives
 872                         $this->trimCache(); // limit memory
 873                         $this->cache[$path]['sha1'] = $hash;
 874                 }
 875                 return $hash;
 876         }
 877
 878         /**
 879          * @see FileBackend::getFileSha1Base36()
 880          */
 881         protected function doGetFileSha1Base36( array $params ) {
 882                 $fsFile = $this->getLocalReference( $params );
 883                 if ( !$fsFile ) {
 884                         return false;
 885                 } else {
 886                         return $fsFile->getSha1Base36();
 887                 }
 888         }
 889
 890         /**
 891          * @see FileBackendBase::getFileProps()
 892          */
 893         public function getFileProps( array $params ) {
 894                 $fsFile = $this->getLocalReference( $params );
 895                 if ( !$fsFile ) {
 896                         return FSFile::placeholderProps();
 897                 } else {
 898                         return $fsFile->getProps();
 899                 }
 900         }
 901
 902         /**
 903          * @see FileBackendBase::getLocalReference()
 904          */
 905         public function getLocalReference( array $params ) {
 906                 $path = $params['src'];
 907                 if ( isset( $this->cache[$path]['localRef'] ) ) {
 908                         return $this->cache[$path]['localRef'];
 909                 }
 910                 $tmpFile = $this->getLocalCopy( $params );
 911                 if ( $tmpFile ) { // don't cache negatives
 912                         $this->trimCache(); // limit memory
 913                         $this->cache[$path]['localRef'] = $tmpFile;
 914                 }
 915                 return $tmpFile;
 916         }
 917
 918         /**
 919          * @see FileBackendBase::streamFile()
 920          */
 921         public function streamFile( array $params ) {
 922                 $status = Status::newGood();
 923
 924                 $fsFile = $this->getLocalReference( $params );
 925                 if ( !$fsFile ) {
 926                         $status->fatal( 'backend-fail-stream', $params['src'] );
 927                         return $status;
 928                 }
 929
 930                 $extraHeaders = isset( $params['headers'] )
 931                         ? $params['headers']
 932                         : array();
 933
 934                 $ok = StreamFile::stream( $fsFile->getPath(), $extraHeaders, false );
 935                 if ( !$ok ) {
 936                         $status->fatal( 'backend-fail-stream', $params['src'] );
 937                         return $status;
 938                 }
 939
 940                 return $status;
 941         }
 942
 943         /**
 944          * @see FileBackendBase::getFileList()
 945          */
 946         final public function getFileList( array $params ) {
 947                 list( $fullCont, $dir, $shard ) = $this->resolveStoragePath( $params['dir'] );
 948                 if ( $dir === null ) { // invalid storage path
 949                         return null;
 950                 }
 951                 if ( $shard !== null ) {
 952                         // File listing is confined to a single container/shard
 953                         return $this->getFileListInternal( $fullCont, $dir, $params );
 954                 } else {
 955                         wfDebug( __METHOD__ . ": iterating over all container shards.\n" );
 956                         // File listing spans multiple containers/shards
 957                         list( $b, $shortCont, $r ) = self::splitStoragePath( $params['dir'] );
 958                         return new ContainerShardListIterator( $this,
 959                                 $fullCont, $this->getContainerSuffixes( $shortCont ), $params );
 960                 }
 961         }
 962
 963         /**
 964          * Do not call this function from places outside FileBackend and ContainerFileListIterator
 965          *
 966          * @param $container string Resolved container name
 967          * @param $dir string Resolved path relative to container
 968          * @param $params Array
 969          * @see FileBackend::getFileList()
 970          */
 971         abstract public function getFileListInternal( $container, $dir, array $params );
 972
 973         /**
 974          * Get the list of supported operations and their corresponding FileOp classes.
 975          *
 976          * @return Array
 977          */
 978         protected function supportedOperations() {
 979                 return array(
 980                         'store'       => 'StoreFileOp',
 981                         'copy'        => 'CopyFileOp',
 982                         'move'        => 'MoveFileOp',
 983                         'delete'      => 'DeleteFileOp',
 984                         'concatenate' => 'ConcatenateFileOp',
 985                         'create'      => 'CreateFileOp',
 986                         'null'        => 'NullFileOp'
 987                 );
 988         }
 989
 990         /**
 991          * Return a list of FileOp objects from a list of operations.
 992          * Do not call this function from places outside FileBackend.
 993          *
 994          * The result must have the same number of items as the input.
 995          * An exception is thrown if an unsupported operation is requested.
 996          *
 997          * @param $ops Array Same format as doOperations()
 998          * @return Array List of FileOp objects
 999          * @throws MWException
1000          */
1001         final public function getOperations( array $ops ) {
1002                 $supportedOps = $this->supportedOperations();
1003
1004                 $performOps = array(); // array of FileOp objects
1005                 // Build up ordered array of FileOps...
1006                 foreach ( $ops as $operation ) {
1007                         $opName = $operation['op'];
1008                         if ( isset( $supportedOps[$opName] ) ) {
1009                                 $class = $supportedOps[$opName];
1010                                 // Get params for this operation
1011                                 $params = $operation;
1012                                 // Append the FileOp class
1013                                 $performOps[] = new $class( $this, $params );
1014                         } else {
1015                                 throw new MWException( "Operation `$opName` is not supported." );
1016                         }
1017                 }
1018
1019                 return $performOps;
1020         }
1021
1022         /**
1023          * @see FileBackendBase::doOperationsInternal()
1024          */
1025         protected function doOperationsInternal( array $ops, array $opts ) {
1026                 $status = Status::newGood();
1027
1028                 // Build up a list of FileOps...
1029                 $performOps = $this->getOperations( $ops );
1030
1031                 // Acquire any locks as needed...
1032                 if ( empty( $opts['nonLocking'] ) ) {
1033                         // Build up a list of files to lock...
1034                         $filesLockEx = $filesLockSh = array();
1035                         foreach ( $performOps as $fileOp ) {
1036                                 $filesLockSh = array_merge( $filesLockSh, $fileOp->storagePathsRead() );
1037                                 $filesLockEx = array_merge( $filesLockEx, $fileOp->storagePathsChanged() );
1038                         }
1039                         // Optimization: if doing an EX lock anyway, don't also set an SH one
1040                         $filesLockSh = array_diff( $filesLockSh, $filesLockEx );
1041                         // Try to lock those files for the scope of this function...
1042                         $scopeLockS = $this->getScopedFileLocks( $filesLockSh, LockManager::LOCK_UW, $status );
1043                         $scopeLockE = $this->getScopedFileLocks( $filesLockEx, LockManager::LOCK_EX, $status );
1044                         if ( !$status->isOK() ) {
1045                                 return $status; // abort
1046                         }
1047                 }
1048
1049                 // Clear any cache entries (after locks acquired)
1050                 $this->clearCache();
1051                 // Actually attempt the operation batch...
1052                 $status->merge( FileOp::attemptBatch( $performOps, $opts ) );
1053
1054                 return $status;
1055         }
1056
1057         /**
1058          * Invalidate the file existence and property cache
1059          *
1060          * @param $paths Array Clear cache for specific files
1061          * @return void
1062          */
1063         final public function clearCache( array $paths = null ) {
1064                 if ( $paths === null ) {
1065                         $this->cache = array();
1066                 } else {
1067                         foreach ( $paths as $path ) {
1068                                 unset( $this->cache[$path] );
1069                         }
1070                 }
1071         }
1072
1073         /**
1074          * Prune the cache if it is too big to add an item
1075          *
1076          * @return void
1077          */
1078         protected function trimCache() {
1079                 if ( count( $this->cache ) >= $this->maxCacheSize ) {
1080                         reset( $this->cache );
1081                         $key = key( $this->cache );
1082                         unset( $this->cache[$key] );
1083                 }
1084         }
1085
1086         /**
1087          * Check if a given path is a mwstore:// path.
1088          * This does not do any actual validation or existence checks.
1089          *
1090          * @param $path string
1091          * @return bool
1092          */
1093         final public static function isStoragePath( $path ) {
1094                 return ( strpos( $path, 'mwstore://' ) === 0 );
1095         }
1096
1097         /**
1098          * Split a storage path (e.g. "mwstore://backend/container/path/to/object")
1099          * into a backend name, a container name, and a relative object path.
1100          *
1101          * @param $storagePath string
1102          * @return Array (backend, container, rel object) or (null, null, null)
1103          */
1104         final public static function splitStoragePath( $storagePath ) {
1105                 if ( self::isStoragePath( $storagePath ) ) {
1106                         // Note: strlen( 'mwstore://' ) = 10
1107                         $parts = explode( '/', substr( $storagePath, 10 ), 3 );
1108                         if ( count( $parts ) == 3 ) {
1109                                 return $parts; // e.g. "backend/container/path"
1110                         } elseif ( count( $parts ) == 2 ) {
1111                                 return array( $parts[0], $parts[1], '' ); // e.g. "backend/container"
1112                         }
1113                 }
1114                 return array( null, null, null );
1115         }
1116
1117         /**
1118          * Check if a container name is valid.
1119          * This checks for for length and illegal characters.
1120          *
1121          * @param $container string
1122          * @return bool
1123          */
1124         final protected static function isValidContainerName( $container ) {
1125                 // This accounts for Swift and S3 restrictions while leaving room
1126                 // for things like '.xxx' (hex shard chars) or '.seg' (segments).
1127                 // Note that matching strings URL encode to the same string;
1128                 // in Swift, the length resriction is *after* URL encoding.
1129                 return preg_match( '/^[a-z0-9][a-z0-9-_]{0,199}$/i', $container );
1130         }
1131
1132         /**
1133          * Validate and normalize a relative storage path.
1134          * Null is returned if the path involves directory traversal.
1135          * Traversal is insecure for FS backends and broken for others.
1136          *
1137          * @param $path string
1138          * @return string|null
1139          */
1140         final protected static function normalizeStoragePath( $path ) {
1141                 // Normalize directory separators
1142                 $path = strtr( $path, '\\', '/' );
1143                 // Use the same traversal protection as Title::secureAndSplit()
1144                 if ( strpos( $path, '.' ) !== false ) {
1145                         if (
1146                                 $path === '.' ||
1147                                 $path === '..' ||
1148                                 strpos( $path, './' ) === 0 ||
1149                                 strpos( $path, '../' ) === 0 ||
1150                                 strpos( $path, '/./' ) !== false ||
1151                                 strpos( $path, '/../' ) !== false
1152                         ) {
1153                                 return null;
1154                         }
1155                 }
1156                 return $path;
1157         }
1158
1159         /**
1160          * Splits a storage path into an internal container name,
1161          * an internal relative file name, and a container shard suffix.
1162          * Any shard suffix is already appended to the internal container name.
1163          * This also checks that the storage path is valid and within this backend.
1164          *
1165          * If the container is sharded but a suffix could not be determined,
1166          * this means that the path can only refer to a directory and can only
1167          * be scanned by looking in all the container shards.
1168          *
1169          * @param $storagePath string
1170          * @return Array (container, path, container suffix) or (null, null, null) if invalid
1171          */
1172         final protected function resolveStoragePath( $storagePath ) {
1173                 list( $backend, $container, $relPath ) = self::splitStoragePath( $storagePath );
1174                 if ( $backend === $this->name ) { // must be for this backend
1175                         $relPath = self::normalizeStoragePath( $relPath );
1176                         if ( $relPath !== null ) {
1177                                 // Get shard for the normalized path if this container is sharded
1178                                 $cShard = $this->getContainerShard( $container, $relPath );
1179                                 // Validate and sanitize the relative path (backend-specific)
1180                                 $relPath = $this->resolveContainerPath( $container, $relPath );
1181                                 if ( $relPath !== null ) {
1182                                         // Prepend any wiki ID prefix to the container name
1183                                         $container = $this->fullContainerName( $container );
1184                                         if ( self::isValidContainerName( $container ) ) {
1185                                                 // Validate and sanitize the container name (backend-specific)
1186                                                 $container = $this->resolveContainerName( "{$container}{$cShard}" );
1187                                                 if ( $container !== null ) {
1188                                                         return array( $container, $relPath, $cShard );
1189                                                 }
1190                                         }
1191                                 }
1192                         }
1193                 }
1194                 return array( null, null, null );
1195         }
1196
1197         /**
1198          * Like resolveStoragePath() except null values are returned if
1199          * the container is sharded and the shard could not be determined.
1200          *
1201          * @see FileBackend::resolveStoragePath()
1202          *
1203          * @param $storagePath string
1204          * @return Array (container, path) or (null, null) if invalid
1205          */
1206         final protected function resolveStoragePathReal( $storagePath ) {
1207                 list( $container, $relPath, $cShard ) = $this->resolveStoragePath( $storagePath );
1208                 if ( $cShard !== null ) {
1209                         return array( $container, $relPath );
1210                 }
1211                 return array( null, null );
1212         }
1213
1214         /**
1215          * Get the container name shard suffix for a given path.
1216          * Any empty suffix means the container is not sharded.
1217          *
1218          * @param $container string Container name
1219          * @param $relStoragePath string Storage path relative to the container
1220          * @return string|null Returns null if shard could not be determined
1221          */
1222         final protected function getContainerShard( $container, $relPath ) {
1223                 $hashLevels = $this->getContainerHashLevels( $container );
1224                 if ( $hashLevels === 1 ) { // 16 shards per container
1225                         $hashDirRegex = '(?P<shard>[0-9a-f])';
1226                 } elseif ( $hashLevels === 2 ) { // 256 shards per container
1227                         $hashDirRegex = '[0-9a-f]/(?P<shard>[0-9a-f]{2})';
1228                 } else {
1229                         return ''; // no sharding
1230                 }
1231                 // Allow certain directories to be above the hash dirs so as
1232                 // to work with FileRepo (e.g. "archive/a/ab" or "temp/a/ab").
1233                 // They must be 2+ chars to avoid any hash directory ambiguity.
1234                 if ( preg_match( "!^(?:[^/]{2,}/)*$hashDirRegex(?:/|$)!", $relPath, $m ) ) {
1235                         return '.' . str_pad( $m['shard'], $hashLevels, '0', STR_PAD_LEFT );
1236                 }
1237                 return null; // failed to match
1238         }
1239
1240         /**
1241          * Get the number of hash levels for a container.
1242          * If greater than 0, then all file storage paths within
1243          * the container are required to be hashed accordingly.
1244          *
1245          * @param $container string
1246          * @return integer
1247          */
1248         final protected function getContainerHashLevels( $container ) {
1249                 if ( isset( $this->shardViaHashLevels[$container] ) ) {
1250                         $hashLevels = (int)$this->shardViaHashLevels[$container];
1251                         if ( $hashLevels >= 0 && $hashLevels <= 2 ) {
1252                                 return $hashLevels;
1253                         }
1254                 }
1255                 return 0; // no sharding
1256         }
1257
1258         /**
1259          * Get a list of full container shard suffixes for a container
1260          *
1261          * @param $container string
1262          * @return Array
1263          */
1264         final protected function getContainerSuffixes( $container ) {
1265                 $shards = array();
1266                 $digits = $this->getContainerHashLevels( $container );
1267                 if ( $digits > 0 ) {
1268                         $numShards = 1 << ( $digits * 4 );
1269                         for ( $index = 0; $index < $numShards; $index++ ) {
1270                                 $shards[] = '.' . str_pad( dechex( $index ), $digits, '0', STR_PAD_LEFT );
1271                         }
1272                 }
1273                 return $shards;
1274         }
1275
1276         /**
1277          * Get the full container name, including the wiki ID prefix
1278          *
1279          * @param $container string
1280          * @return string
1281          */
1282         final protected function fullContainerName( $container ) {
1283                 if ( $this->wikiId != '' ) {
1284                         return "{$this->wikiId}-$container";
1285                 } else {
1286                         return $container;
1287                 }
1288         }
1289
1290         /**
1291          * Resolve a container name, checking if it's allowed by the backend.
1292          * This is intended for internal use, such as encoding illegal chars.
1293          * Subclasses can override this to be more restrictive.
1294          *
1295          * @param $container string
1296          * @return string|null
1297          */
1298         protected function resolveContainerName( $container ) {
1299                 return $container;
1300         }
1301
1302         /**
1303          * Resolve a relative storage path, checking if it's allowed by the backend.
1304          * This is intended for internal use, such as encoding illegal chars or perhaps
1305          * getting absolute paths (e.g. FS based backends). Note that the relative path
1306          * may be the empty string (e.g. the path is simply to the container).
1307          *
1308          * @param $container string Container name
1309          * @param $relStoragePath string Storage path relative to the container
1310          * @return string|null Path or null if not valid
1311          */
1312         protected function resolveContainerPath( $container, $relStoragePath ) {
1313                 return $relStoragePath;
1314         }
1315
1316         /**
1317          * Get the final extension from a storage or FS path
1318          *
1319          * @param $path string
1320          * @return string
1321          */
1322         final public static function extensionFromPath( $path ) {
1323                 $i = strrpos( $path, '.' );
1324                 return strtolower( $i ? substr( $path, $i + 1 ) : '' );
1325         }
1326 }
1327
1328 /**
1329  * FileBackend helper function to handle file listings that span container shards.
1330  * Do not use this class from places outside of FileBackend.
1331  *
1332  * @ingroup FileBackend
1333  */
1334 class ContainerShardListIterator implements Iterator {
1335         /* @var FileBackend */
1336         protected $backend;
1337         /* @var Array */
1338         protected $params;
1339         /* @var Array */
1340         protected $shardSuffixes;
1341         protected $container; // string
1342         protected $directory; // string
1343
1344         /* @var Traversable */
1345         protected $iter;
1346         protected $curShard = 0; // integer
1347         protected $pos = 0; // integer
1348
1349         /**
1350          * @param $backend FileBackend
1351          * @param $container string Full storage container name
1352          * @param $dir string Storage directory relative to container
1353          * @param $suffixes Array List of container shard suffixes
1354          * @param $params Array
1355          */
1356         public function __construct(
1357                 FileBackend $backend, $container, $dir, array $suffixes, array $params
1358         ) {
1359                 $this->backend = $backend;
1360                 $this->container = $container;
1361                 $this->directory = $dir;
1362                 $this->shardSuffixes = $suffixes;
1363                 $this->params = $params;
1364         }
1365
1366         public function current() {
1367                 if ( is_array( $this->iter ) ) {
1368                         return current( $this->iter );
1369                 } else {
1370                         return $this->iter->current();
1371                 }
1372         }
1373
1374         public function key() {
1375                 return $this->pos;
1376         }
1377
1378         public function next() {
1379                 ++$this->pos;
1380                 if ( is_array( $this->iter ) ) {
1381                         next( $this->iter );
1382                 } else {
1383                         $this->iter->next();
1384                 }
1385                 // Find the next non-empty shard if no elements are left
1386                 $this->nextShardIteratorIfNotValid();
1387         }
1388
1389         /**
1390          * If the iterator for this container shard is out of items,
1391          * then move on to the next container that has items.
1392          * If there are none, then it advances to the last container.
1393          */
1394         protected function nextShardIteratorIfNotValid() {
1395                 while ( !$this->valid() ) {
1396                         if ( ++$this->curShard >= count( $this->shardSuffixes ) ) {
1397                                 break; // no more container shards
1398                         }
1399                         $this->setIteratorFromCurrentShard();
1400                 }
1401         }
1402
1403         protected function setIteratorFromCurrentShard() {
1404                 $suffix = $this->shardSuffixes[$this->curShard];
1405                 $this->iter = $this->backend->getFileListInternal(
1406                         "{$this->container}{$suffix}", $this->directory, $this->params );
1407         }
1408
1409         public function rewind() {
1410                 $this->pos = 0;
1411                 $this->curShard = 0;
1412                 $this->setIteratorFromCurrentShard();
1413                 // Find the next non-empty shard if this one has no elements
1414                 $this->nextShardIteratorIfNotValid();
1415         }
1416
1417         public function valid() {
1418                 if ( $this->iter == null ) {
1419                         return false; // some failure?
1420                 } elseif ( is_array( $this->iter ) ) {
1421                         return ( current( $this->iter ) !== false ); // no paths can have this value
1422                 } else {
1423                         return $this->iter->valid();
1424                 }
1425         }
1426 }