includes/filerepo/backend/FileOp.php

   1 <?php
   2 /**
   3  * Helper class for representing operations with transaction support.
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License as published by
   7  * the Free Software Foundation; either version 2 of the License, or
   8  * (at your option) any later version.
   9  *
  10  * This program is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  13  * GNU General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU General Public License along
  16  * with this program; if not, write to the Free Software Foundation, Inc.,
  17  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  18  * http://www.gnu.org/copyleft/gpl.html
  19  *
  20  * @file
  21  * @ingroup FileBackend
  22  * @author Aaron Schulz
  23  */
  24
  25 /**
  26  * FileBackend helper class for representing operations.
  27  * Do not use this class from places outside FileBackend.
  28  *
  29  * Methods called from FileOpBatch::attempt() should avoid throwing
  30  * exceptions at all costs. FileOp objects should be lightweight in order
  31  * to support large arrays in memory and serialization.
  32  *
  33  * @ingroup FileBackend
  34  * @since 1.19
  35  */
  36 abstract class FileOp {
  37         /** @var Array */
  38         protected $params = array();
  39         /** @var FileBackendStore */
  40         protected $backend;
  41
  42         protected $state = self::STATE_NEW; // integer
  43         protected $failed = false; // boolean
  44         protected $async = false; // boolean
  45         protected $useLatest = true; // boolean
  46         protected $batchId; // string
  47
  48         protected $sourceSha1; // string
  49         protected $destSameAsSource; // boolean
  50
  51         /* Object life-cycle */
  52         const STATE_NEW = 1;
  53         const STATE_CHECKED = 2;
  54         const STATE_ATTEMPTED = 3;
  55
  56         /**
  57          * Build a new file operation transaction
  58          *
  59          * @param $backend FileBackendStore
  60          * @param $params Array
  61          * @throws MWException
  62          */
  63         final public function __construct( FileBackendStore $backend, array $params ) {
  64                 $this->backend = $backend;
  65                 list( $required, $optional ) = $this->allowedParams();
  66                 foreach ( $required as $name ) {
  67                         if ( isset( $params[$name] ) ) {
  68                                 $this->params[$name] = $params[$name];
  69                         } else {
  70                                 throw new MWException( "File operation missing parameter '$name'." );
  71                         }
  72                 }
  73                 foreach ( $optional as $name ) {
  74                         if ( isset( $params[$name] ) ) {
  75                                 $this->params[$name] = $params[$name];
  76                         }
  77                 }
  78                 $this->params = $params;
  79         }
  80
  81         /**
  82          * Set the batch UUID this operation belongs to
  83          *
  84          * @param $batchId string
  85          * @return void
  86          */
  87         final public function setBatchId( $batchId ) {
  88                 $this->batchId = $batchId;
  89         }
  90
  91         /**
  92          * Whether to allow stale data for file reads and stat checks
  93          *
  94          * @param $allowStale bool
  95          * @return void
  96          */
  97         final public function allowStaleReads( $allowStale ) {
  98                 $this->useLatest = !$allowStale;
  99         }
 100
 101         /**
 102          * Get the value of the parameter with the given name
 103          *
 104          * @param $name string
 105          * @return mixed Returns null if the parameter is not set
 106          */
 107         final public function getParam( $name ) {
 108                 return isset( $this->params[$name] ) ? $this->params[$name] : null;
 109         }
 110
 111         /**
 112          * Check if this operation failed precheck() or attempt()
 113          *
 114          * @return bool
 115          */
 116         final public function failed() {
 117                 return $this->failed;
 118         }
 119
 120         /**
 121          * Get a new empty predicates array for precheck()
 122          *
 123          * @return Array
 124          */
 125         final public static function newPredicates() {
 126                 return array( 'exists' => array(), 'sha1' => array() );
 127         }
 128
 129         /**
 130          * Get a new empty dependency tracking array for paths read/written to
 131          *
 132          * @return Array
 133          */
 134         final public static function newDependencies() {
 135                 return array( 'read' => array(), 'write' => array() );
 136         }
 137
 138         /**
 139          * Update a dependency tracking array to account for this operation
 140          *
 141          * @param $deps Array Prior path reads/writes; format of FileOp::newPredicates()
 142          * @return Array
 143          */
 144         final public function applyDependencies( array $deps ) {
 145                 $deps['read']  += array_fill_keys( $this->storagePathsRead(), 1 );
 146                 $deps['write'] += array_fill_keys( $this->storagePathsChanged(), 1 );
 147                 return $deps;
 148         }
 149
 150         /**
 151          * Check if this operation changes files listed in $paths
 152          *
 153          * @param $paths Array Prior path reads/writes; format of FileOp::newPredicates()
 154          * @return boolean
 155          */
 156         final public function dependsOn( array $deps ) {
 157                 foreach ( $this->storagePathsChanged() as $path ) {
 158                         if ( isset( $deps['read'][$path] ) || isset( $deps['write'][$path] ) ) {
 159                                 return true; // "output" or "anti" dependency
 160                         }
 161                 }
 162                 foreach ( $this->storagePathsRead() as $path ) {
 163                         if ( isset( $deps['write'][$path] ) ) {
 164                                 return true; // "flow" dependency
 165                         }
 166                 }
 167                 return false;
 168         }
 169
 170         /**
 171          * Get the file journal entries for this file operation
 172          *
 173          * @param $oPredicates Array Pre-op info about files (format of FileOp::newPredicates)
 174          * @param $nPredicates Array Post-op info about files (format of FileOp::newPredicates)
 175          * @return Array
 176          */
 177         final public function getJournalEntries( array $oPredicates, array $nPredicates ) {
 178                 $nullEntries = array();
 179                 $updateEntries = array();
 180                 $deleteEntries = array();
 181                 $pathsUsed = array_merge( $this->storagePathsRead(), $this->storagePathsChanged() );
 182                 foreach ( $pathsUsed as $path ) {
 183                         $nullEntries[] = array( // assertion for recovery
 184                                 'op'      => 'null',
 185                                 'path'    => $path,
 186                                 'newSha1' => $this->fileSha1( $path, $oPredicates )
 187                         );
 188                 }
 189                 foreach ( $this->storagePathsChanged() as $path ) {
 190                         if ( $nPredicates['sha1'][$path] === false ) { // deleted
 191                                 $deleteEntries[] = array(
 192                                         'op'      => 'delete',
 193                                         'path'    => $path,
 194                                         'newSha1' => ''
 195                                 );
 196                         } else { // created/updated
 197                                 $updateEntries[] = array(
 198                                         'op'      => $this->fileExists( $path, $oPredicates ) ? 'update' : 'create',
 199                                         'path'    => $path,
 200                                         'newSha1' => $nPredicates['sha1'][$path]
 201                                 );
 202                         }
 203                 }
 204                 return array_merge( $nullEntries, $updateEntries, $deleteEntries );
 205         }
 206
 207         /**
 208          * Check preconditions of the operation without writing anything
 209          *
 210          * @param $predicates Array
 211          * @return Status
 212          */
 213         final public function precheck( array &$predicates ) {
 214                 if ( $this->state !== self::STATE_NEW ) {
 215                         return Status::newFatal( 'fileop-fail-state', self::STATE_NEW, $this->state );
 216                 }
 217                 $this->state = self::STATE_CHECKED;
 218                 $status = $this->doPrecheck( $predicates );
 219                 if ( !$status->isOK() ) {
 220                         $this->failed = true;
 221                 }
 222                 return $status;
 223         }
 224
 225         /**
 226          * @return Status
 227          */
 228         protected function doPrecheck( array &$predicates ) {
 229                 return Status::newGood();
 230         }
 231
 232         /**
 233          * Attempt the operation
 234          *
 235          * @return Status
 236          */
 237         final public function attempt() {
 238                 if ( $this->state !== self::STATE_CHECKED ) {
 239                         return Status::newFatal( 'fileop-fail-state', self::STATE_CHECKED, $this->state );
 240                 } elseif ( $this->failed ) { // failed precheck
 241                         return Status::newFatal( 'fileop-fail-attempt-precheck' );
 242                 }
 243                 $this->state = self::STATE_ATTEMPTED;
 244                 $status = $this->doAttempt();
 245                 if ( !$status->isOK() ) {
 246                         $this->failed = true;
 247                         $this->logFailure( 'attempt' );
 248                 }
 249                 return $status;
 250         }
 251
 252         /**
 253          * @return Status
 254          */
 255         protected function doAttempt() {
 256                 return Status::newGood();
 257         }
 258
 259         /**
 260          * Attempt the operation in the background
 261          *
 262          * @return Status
 263          */
 264         final public function attemptAsync() {
 265                 $this->async = true;
 266                 $result = $this->attempt();
 267                 $this->async = false;
 268                 return $result;
 269         }
 270
 271         /**
 272          * Get the file operation parameters
 273          *
 274          * @return Array (required params list, optional params list)
 275          */
 276         protected function allowedParams() {
 277                 return array( array(), array() );
 278         }
 279
 280         /**
 281          * Adjust params to FileBackendStore internal file calls
 282          *
 283          * @param $params Array
 284          * @return Array (required params list, optional params list)
 285          */
 286         protected function setFlags( array $params ) {
 287                 return array( 'async' => $this->async ) + $params;
 288         }
 289
 290         /**
 291          * Get a list of storage paths read from for this operation
 292          *
 293          * @return Array
 294          */
 295         final public function storagePathsRead() {
 296                 return array_map( 'FileBackend::normalizeStoragePath', $this->doStoragePathsRead() );
 297         }
 298
 299         /**
 300          * @see FileOp::storagePathsRead()
 301          * @return Array
 302          */
 303         protected function doStoragePathsRead() {
 304                 return array();
 305         }
 306
 307         /**
 308          * Get a list of storage paths written to for this operation
 309          *
 310          * @return Array
 311          */
 312         final public function storagePathsChanged() {
 313                 return array_map( 'FileBackend::normalizeStoragePath', $this->doStoragePathsChanged() );
 314         }
 315
 316         /**
 317          * @see FileOp::storagePathsChanged()
 318          * @return Array
 319          */
 320         protected function doStoragePathsChanged() {
 321                 return array();
 322         }
 323
 324         /**
 325          * Check for errors with regards to the destination file already existing.
 326          * This also updates the destSameAsSource and sourceSha1 member variables.
 327          * A bad status will be returned if there is no chance it can be overwritten.
 328          *
 329          * @param $predicates Array
 330          * @return Status
 331          */
 332         protected function precheckDestExistence( array $predicates ) {
 333                 $status = Status::newGood();
 334                 // Get hash of source file/string and the destination file
 335                 $this->sourceSha1 = $this->getSourceSha1Base36(); // FS file or data string
 336                 if ( $this->sourceSha1 === null ) { // file in storage?
 337                         $this->sourceSha1 = $this->fileSha1( $this->params['src'], $predicates );
 338                 }
 339                 $this->destSameAsSource = false;
 340                 if ( $this->fileExists( $this->params['dst'], $predicates ) ) {
 341                         if ( $this->getParam( 'overwrite' ) ) {
 342                                 return $status; // OK
 343                         } elseif ( $this->getParam( 'overwriteSame' ) ) {
 344                                 $dhash = $this->fileSha1( $this->params['dst'], $predicates );
 345                                 // Check if hashes are valid and match each other...
 346                                 if ( !strlen( $this->sourceSha1 ) || !strlen( $dhash ) ) {
 347                                         $status->fatal( 'backend-fail-hashes' );
 348                                 } elseif ( $this->sourceSha1 !== $dhash ) {
 349                                         // Give an error if the files are not identical
 350                                         $status->fatal( 'backend-fail-notsame', $this->params['dst'] );
 351                                 } else {
 352                                         $this->destSameAsSource = true; // OK
 353                                 }
 354                                 return $status; // do nothing; either OK or bad status
 355                         } else {
 356                                 $status->fatal( 'backend-fail-alreadyexists', $this->params['dst'] );
 357                                 return $status;
 358                         }
 359                 }
 360                 return $status;
 361         }
 362
 363         /**
 364          * precheckDestExistence() helper function to get the source file SHA-1.
 365          * Subclasses should overwride this iff the source is not in storage.
 366          *
 367          * @return string|bool Returns false on failure
 368          */
 369         protected function getSourceSha1Base36() {
 370                 return null; // N/A
 371         }
 372
 373         /**
 374          * Check if a file will exist in storage when this operation is attempted
 375          *
 376          * @param $source string Storage path
 377          * @param $predicates Array
 378          * @return bool
 379          */
 380         final protected function fileExists( $source, array $predicates ) {
 381                 if ( isset( $predicates['exists'][$source] ) ) {
 382                         return $predicates['exists'][$source]; // previous op assures this
 383                 } else {
 384                         $params = array( 'src' => $source, 'latest' => $this->useLatest );
 385                         return $this->backend->fileExists( $params );
 386                 }
 387         }
 388
 389         /**
 390          * Get the SHA-1 of a file in storage when this operation is attempted
 391          *
 392          * @param $source string Storage path
 393          * @param $predicates Array
 394          * @return string|bool False on failure
 395          */
 396         final protected function fileSha1( $source, array $predicates ) {
 397                 if ( isset( $predicates['sha1'][$source] ) ) {
 398                         return $predicates['sha1'][$source]; // previous op assures this
 399                 } else {
 400                         $params = array( 'src' => $source, 'latest' => $this->useLatest );
 401                         return $this->backend->getFileSha1Base36( $params );
 402                 }
 403         }
 404
 405         /**
 406          * Get the backend this operation is for
 407          *
 408          * @return FileBackendStore
 409          */
 410         public function getBackend() {
 411                 return $this->backend;
 412         }
 413
 414         /**
 415          * Log a file operation failure and preserve any temp files
 416          *
 417          * @param $action string
 418          * @return void
 419          */
 420         final public function logFailure( $action ) {
 421                 $params = $this->params;
 422                 $params['failedAction'] = $action;
 423                 try {
 424                         wfDebugLog( 'FileOperation', get_class( $this ) .
 425                                 " failed (batch #{$this->batchId}): " . FormatJson::encode( $params ) );
 426                 } catch ( Exception $e ) {
 427                         // bad config? debug log error?
 428                 }
 429         }
 430 }
 431
 432 /**
 433  * Store a file into the backend from a file on the file system.
 434  * Parameters similar to FileBackendStore::storeInternal(), which include:
 435  *     src           : source path on file system
 436  *     dst           : destination storage path
 437  *     overwrite     : do nothing and pass if an identical file exists at destination
 438  *     overwriteSame : override any existing file at destination
 439  */
 440 class StoreFileOp extends FileOp {
 441         protected function allowedParams() {
 442                 return array( array( 'src', 'dst' ), array( 'overwrite', 'overwriteSame' ) );
 443         }
 444
 445         protected function doPrecheck( array &$predicates ) {
 446                 $status = Status::newGood();
 447                 // Check if the source file exists on the file system
 448                 if ( !is_file( $this->params['src'] ) ) {
 449                         $status->fatal( 'backend-fail-notexists', $this->params['src'] );
 450                         return $status;
 451                 // Check if the source file is too big
 452                 } elseif ( filesize( $this->params['src'] ) > $this->backend->maxFileSizeInternal() ) {
 453                         $status->fatal( 'backend-fail-store', $this->params['src'], $this->params['dst'] );
 454                         return $status;
 455                 // Check if a file can be placed at the destination
 456                 } elseif ( !$this->backend->isPathUsableInternal( $this->params['dst'] ) ) {
 457                         $status->fatal( 'backend-fail-store', $this->params['src'], $this->params['dst'] );
 458                         return $status;
 459                 }
 460                 // Check if destination file exists
 461                 $status->merge( $this->precheckDestExistence( $predicates ) );
 462                 if ( $status->isOK() ) {
 463                         // Update file existence predicates
 464                         $predicates['exists'][$this->params['dst']] = true;
 465                         $predicates['sha1'][$this->params['dst']] = $this->sourceSha1;
 466                 }
 467                 return $status; // safe to call attempt()
 468         }
 469
 470         protected function doAttempt() {
 471                 // Store the file at the destination
 472                 if ( !$this->destSameAsSource ) {
 473                         return $this->backend->storeInternal( $this->setFlags( $this->params ) );
 474                 }
 475                 return Status::newGood();
 476         }
 477
 478         protected function getSourceSha1Base36() {
 479                 wfSuppressWarnings();
 480                 $hash = sha1_file( $this->params['src'] );
 481                 wfRestoreWarnings();
 482                 if ( $hash !== false ) {
 483                         $hash = wfBaseConvert( $hash, 16, 36, 31 );
 484                 }
 485                 return $hash;
 486         }
 487
 488         protected function doStoragePathsChanged() {
 489                 return array( $this->params['dst'] );
 490         }
 491 }
 492
 493 /**
 494  * Create a file in the backend with the given content.
 495  * Parameters similar to FileBackendStore::createInternal(), which include:
 496  *     content       : the raw file contents
 497  *     dst           : destination storage path
 498  *     overwrite     : do nothing and pass if an identical file exists at destination
 499  *     overwriteSame : override any existing file at destination
 500  */
 501 class CreateFileOp extends FileOp {
 502         protected function allowedParams() {
 503                 return array( array( 'content', 'dst' ), array( 'overwrite', 'overwriteSame' ) );
 504         }
 505
 506         protected function doPrecheck( array &$predicates ) {
 507                 $status = Status::newGood();
 508                 // Check if the source data is too big
 509                 if ( strlen( $this->getParam( 'content' ) ) > $this->backend->maxFileSizeInternal() ) {
 510                         $status->fatal( 'backend-fail-create', $this->params['dst'] );
 511                         return $status;
 512                 // Check if a file can be placed at the destination
 513                 } elseif ( !$this->backend->isPathUsableInternal( $this->params['dst'] ) ) {
 514                         $status->fatal( 'backend-fail-create', $this->params['dst'] );
 515                         return $status;
 516                 }
 517                 // Check if destination file exists
 518                 $status->merge( $this->precheckDestExistence( $predicates ) );
 519                 if ( $status->isOK() ) {
 520                         // Update file existence predicates
 521                         $predicates['exists'][$this->params['dst']] = true;
 522                         $predicates['sha1'][$this->params['dst']] = $this->sourceSha1;
 523                 }
 524                 return $status; // safe to call attempt()
 525         }
 526
 527         protected function doAttempt() {
 528                 if ( !$this->destSameAsSource ) {
 529                         // Create the file at the destination
 530                         return $this->backend->createInternal( $this->setFlags( $this->params ) );
 531                 }
 532                 return Status::newGood();
 533         }
 534
 535         protected function getSourceSha1Base36() {
 536                 return wfBaseConvert( sha1( $this->params['content'] ), 16, 36, 31 );
 537         }
 538
 539         protected function doStoragePathsChanged() {
 540                 return array( $this->params['dst'] );
 541         }
 542 }
 543
 544 /**
 545  * Copy a file from one storage path to another in the backend.
 546  * Parameters similar to FileBackendStore::copyInternal(), which include:
 547  *     src           : source storage path
 548  *     dst           : destination storage path
 549  *     overwrite     : do nothing and pass if an identical file exists at destination
 550  *     overwriteSame : override any existing file at destination
 551  */
 552 class CopyFileOp extends FileOp {
 553         protected function allowedParams() {
 554                 return array( array( 'src', 'dst' ), array( 'overwrite', 'overwriteSame' ) );
 555         }
 556
 557         protected function doPrecheck( array &$predicates ) {
 558                 $status = Status::newGood();
 559                 // Check if the source file exists
 560                 if ( !$this->fileExists( $this->params['src'], $predicates ) ) {
 561                         $status->fatal( 'backend-fail-notexists', $this->params['src'] );
 562                         return $status;
 563                 // Check if a file can be placed at the destination
 564                 } elseif ( !$this->backend->isPathUsableInternal( $this->params['dst'] ) ) {
 565                         $status->fatal( 'backend-fail-copy', $this->params['src'], $this->params['dst'] );
 566                         return $status;
 567                 }
 568                 // Check if destination file exists
 569                 $status->merge( $this->precheckDestExistence( $predicates ) );
 570                 if ( $status->isOK() ) {
 571                         // Update file existence predicates
 572                         $predicates['exists'][$this->params['dst']] = true;
 573                         $predicates['sha1'][$this->params['dst']] = $this->sourceSha1;
 574                 }
 575                 return $status; // safe to call attempt()
 576         }
 577
 578         protected function doAttempt() {
 579                 // Do nothing if the src/dst paths are the same
 580                 if ( $this->params['src'] !== $this->params['dst'] ) {
 581                         // Copy the file into the destination
 582                         if ( !$this->destSameAsSource ) {
 583                                 return $this->backend->copyInternal( $this->setFlags( $this->params ) );
 584                         }
 585                 }
 586                 return Status::newGood();
 587         }
 588
 589         protected function doStoragePathsRead() {
 590                 return array( $this->params['src'] );
 591         }
 592
 593         protected function doStoragePathsChanged() {
 594                 return array( $this->params['dst'] );
 595         }
 596 }
 597
 598 /**
 599  * Move a file from one storage path to another in the backend.
 600  * Parameters similar to FileBackendStore::moveInternal(), which include:
 601  *     src           : source storage path
 602  *     dst           : destination storage path
 603  *     overwrite     : do nothing and pass if an identical file exists at destination
 604  *     overwriteSame : override any existing file at destination
 605  */
 606 class MoveFileOp extends FileOp {
 607         protected function allowedParams() {
 608                 return array( array( 'src', 'dst' ), array( 'overwrite', 'overwriteSame' ) );
 609         }
 610
 611         protected function doPrecheck( array &$predicates ) {
 612                 $status = Status::newGood();
 613                 // Check if the source file exists
 614                 if ( !$this->fileExists( $this->params['src'], $predicates ) ) {
 615                         $status->fatal( 'backend-fail-notexists', $this->params['src'] );
 616                         return $status;
 617                 // Check if a file can be placed at the destination
 618                 } elseif ( !$this->backend->isPathUsableInternal( $this->params['dst'] ) ) {
 619                         $status->fatal( 'backend-fail-move', $this->params['src'], $this->params['dst'] );
 620                         return $status;
 621                 }
 622                 // Check if destination file exists
 623                 $status->merge( $this->precheckDestExistence( $predicates ) );
 624                 if ( $status->isOK() ) {
 625                         // Update file existence predicates
 626                         $predicates['exists'][$this->params['src']] = false;
 627                         $predicates['sha1'][$this->params['src']] = false;
 628                         $predicates['exists'][$this->params['dst']] = true;
 629                         $predicates['sha1'][$this->params['dst']] = $this->sourceSha1;
 630                 }
 631                 return $status; // safe to call attempt()
 632         }
 633
 634         protected function doAttempt() {
 635                 // Do nothing if the src/dst paths are the same
 636                 if ( $this->params['src'] !== $this->params['dst'] ) {
 637                         if ( !$this->destSameAsSource ) {
 638                                 // Move the file into the destination
 639                                 return $this->backend->moveInternal( $this->setFlags( $this->params ) );
 640                         } else {
 641                                 // Just delete source as the destination needs no changes
 642                                 $params = array( 'src' => $this->params['src'] );
 643                                 return $this->backend->deleteInternal( $this->setFlags( $params ) );
 644                         }
 645                 }
 646                 return Status::newGood();
 647         }
 648
 649         protected function doStoragePathsRead() {
 650                 return array( $this->params['src'] );
 651         }
 652
 653         protected function doStoragePathsChanged() {
 654                 return array( $this->params['src'], $this->params['dst'] );
 655         }
 656 }
 657
 658 /**
 659  * Delete a file at the given storage path from the backend.
 660  * Parameters similar to FileBackendStore::deleteInternal(), which include:
 661  *     src                 : source storage path
 662  *     ignoreMissingSource : don't return an error if the file does not exist
 663  */
 664 class DeleteFileOp extends FileOp {
 665         protected function allowedParams() {
 666                 return array( array( 'src' ), array( 'ignoreMissingSource' ) );
 667         }
 668
 669         protected $needsDelete = true;
 670
 671         protected function doPrecheck( array &$predicates ) {
 672                 $status = Status::newGood();
 673                 // Check if the source file exists
 674                 if ( !$this->fileExists( $this->params['src'], $predicates ) ) {
 675                         if ( !$this->getParam( 'ignoreMissingSource' ) ) {
 676                                 $status->fatal( 'backend-fail-notexists', $this->params['src'] );
 677                                 return $status;
 678                         }
 679                         $this->needsDelete = false;
 680                 }
 681                 // Update file existence predicates
 682                 $predicates['exists'][$this->params['src']] = false;
 683                 $predicates['sha1'][$this->params['src']] = false;
 684                 return $status; // safe to call attempt()
 685         }
 686
 687         protected function doAttempt() {
 688                 if ( $this->needsDelete ) {
 689                         // Delete the source file
 690                         return $this->backend->deleteInternal( $this->setFlags( $this->params ) );
 691                 }
 692                 return Status::newGood();
 693         }
 694
 695         protected function doStoragePathsChanged() {
 696                 return array( $this->params['src'] );
 697         }
 698 }
 699
 700 /**
 701  * Placeholder operation that has no params and does nothing
 702  */
 703 class NullFileOp extends FileOp {}