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-maxsize',
 454                                 $this->params['dst'], $this->backend->maxFileSizeInternal() );
 455                         $status->fatal( 'backend-fail-store', $this->params['src'], $this->params['dst'] );
 456                         return $status;
 457                 // Check if a file can be placed at the destination
 458                 } elseif ( !$this->backend->isPathUsableInternal( $this->params['dst'] ) ) {
 459                         $status->fatal( 'backend-fail-usable', $this->params['dst'] );
 460                         $status->fatal( 'backend-fail-store', $this->params['src'], $this->params['dst'] );
 461                         return $status;
 462                 }
 463                 // Check if destination file exists
 464                 $status->merge( $this->precheckDestExistence( $predicates ) );
 465                 if ( $status->isOK() ) {
 466                         // Update file existence predicates
 467                         $predicates['exists'][$this->params['dst']] = true;
 468                         $predicates['sha1'][$this->params['dst']] = $this->sourceSha1;
 469                 }
 470                 return $status; // safe to call attempt()
 471         }
 472
 473         protected function doAttempt() {
 474                 // Store the file at the destination
 475                 if ( !$this->destSameAsSource ) {
 476                         return $this->backend->storeInternal( $this->setFlags( $this->params ) );
 477                 }
 478                 return Status::newGood();
 479         }
 480
 481         protected function getSourceSha1Base36() {
 482                 wfSuppressWarnings();
 483                 $hash = sha1_file( $this->params['src'] );
 484                 wfRestoreWarnings();
 485                 if ( $hash !== false ) {
 486                         $hash = wfBaseConvert( $hash, 16, 36, 31 );
 487                 }
 488                 return $hash;
 489         }
 490
 491         protected function doStoragePathsChanged() {
 492                 return array( $this->params['dst'] );
 493         }
 494 }
 495
 496 /**
 497  * Create a file in the backend with the given content.
 498  * Parameters similar to FileBackendStore::createInternal(), which include:
 499  *     content       : the raw file contents
 500  *     dst           : destination storage path
 501  *     overwrite     : do nothing and pass if an identical file exists at destination
 502  *     overwriteSame : override any existing file at destination
 503  */
 504 class CreateFileOp extends FileOp {
 505         protected function allowedParams() {
 506                 return array( array( 'content', 'dst' ), array( 'overwrite', 'overwriteSame' ) );
 507         }
 508
 509         protected function doPrecheck( array &$predicates ) {
 510                 $status = Status::newGood();
 511                 // Check if the source data is too big
 512                 if ( strlen( $this->getParam( 'content' ) ) > $this->backend->maxFileSizeInternal() ) {
 513                         $status->fatal( 'backend-fail-maxsize',
 514                                 $this->params['dst'], $this->backend->maxFileSizeInternal() );
 515                         $status->fatal( 'backend-fail-create', $this->params['dst'] );
 516                         return $status;
 517                 // Check if a file can be placed at the destination
 518                 } elseif ( !$this->backend->isPathUsableInternal( $this->params['dst'] ) ) {
 519                         $status->fatal( 'backend-fail-usable', $this->params['dst'] );
 520                         $status->fatal( 'backend-fail-create', $this->params['dst'] );
 521                         return $status;
 522                 }
 523                 // Check if destination file exists
 524                 $status->merge( $this->precheckDestExistence( $predicates ) );
 525                 if ( $status->isOK() ) {
 526                         // Update file existence predicates
 527                         $predicates['exists'][$this->params['dst']] = true;
 528                         $predicates['sha1'][$this->params['dst']] = $this->sourceSha1;
 529                 }
 530                 return $status; // safe to call attempt()
 531         }
 532
 533         protected function doAttempt() {
 534                 if ( !$this->destSameAsSource ) {
 535                         // Create the file at the destination
 536                         return $this->backend->createInternal( $this->setFlags( $this->params ) );
 537                 }
 538                 return Status::newGood();
 539         }
 540
 541         protected function getSourceSha1Base36() {
 542                 return wfBaseConvert( sha1( $this->params['content'] ), 16, 36, 31 );
 543         }
 544
 545         protected function doStoragePathsChanged() {
 546                 return array( $this->params['dst'] );
 547         }
 548 }
 549
 550 /**
 551  * Copy a file from one storage path to another in the backend.
 552  * Parameters similar to FileBackendStore::copyInternal(), which include:
 553  *     src           : source storage path
 554  *     dst           : destination storage path
 555  *     overwrite     : do nothing and pass if an identical file exists at destination
 556  *     overwriteSame : override any existing file at destination
 557  */
 558 class CopyFileOp extends FileOp {
 559         protected function allowedParams() {
 560                 return array( array( 'src', 'dst' ), array( 'overwrite', 'overwriteSame' ) );
 561         }
 562
 563         protected function doPrecheck( array &$predicates ) {
 564                 $status = Status::newGood();
 565                 // Check if the source file exists
 566                 if ( !$this->fileExists( $this->params['src'], $predicates ) ) {
 567                         $status->fatal( 'backend-fail-notexists', $this->params['src'] );
 568                         return $status;
 569                 // Check if a file can be placed at the destination
 570                 } elseif ( !$this->backend->isPathUsableInternal( $this->params['dst'] ) ) {
 571                         $status->fatal( 'backend-fail-usable', $this->params['dst'] );
 572                         $status->fatal( 'backend-fail-copy', $this->params['src'], $this->params['dst'] );
 573                         return $status;
 574                 }
 575                 // Check if destination file exists
 576                 $status->merge( $this->precheckDestExistence( $predicates ) );
 577                 if ( $status->isOK() ) {
 578                         // Update file existence predicates
 579                         $predicates['exists'][$this->params['dst']] = true;
 580                         $predicates['sha1'][$this->params['dst']] = $this->sourceSha1;
 581                 }
 582                 return $status; // safe to call attempt()
 583         }
 584
 585         protected function doAttempt() {
 586                 // Do nothing if the src/dst paths are the same
 587                 if ( $this->params['src'] !== $this->params['dst'] ) {
 588                         // Copy the file into the destination
 589                         if ( !$this->destSameAsSource ) {
 590                                 return $this->backend->copyInternal( $this->setFlags( $this->params ) );
 591                         }
 592                 }
 593                 return Status::newGood();
 594         }
 595
 596         protected function doStoragePathsRead() {
 597                 return array( $this->params['src'] );
 598         }
 599
 600         protected function doStoragePathsChanged() {
 601                 return array( $this->params['dst'] );
 602         }
 603 }
 604
 605 /**
 606  * Move a file from one storage path to another in the backend.
 607  * Parameters similar to FileBackendStore::moveInternal(), which include:
 608  *     src           : source storage path
 609  *     dst           : destination storage path
 610  *     overwrite     : do nothing and pass if an identical file exists at destination
 611  *     overwriteSame : override any existing file at destination
 612  */
 613 class MoveFileOp extends FileOp {
 614         protected function allowedParams() {
 615                 return array( array( 'src', 'dst' ), array( 'overwrite', 'overwriteSame' ) );
 616         }
 617
 618         protected function doPrecheck( array &$predicates ) {
 619                 $status = Status::newGood();
 620                 // Check if the source file exists
 621                 if ( !$this->fileExists( $this->params['src'], $predicates ) ) {
 622                         $status->fatal( 'backend-fail-notexists', $this->params['src'] );
 623                         return $status;
 624                 // Check if a file can be placed at the destination
 625                 } elseif ( !$this->backend->isPathUsableInternal( $this->params['dst'] ) ) {
 626                         $status->fatal( 'backend-fail-usable', $this->params['dst'] );
 627                         $status->fatal( 'backend-fail-move', $this->params['src'], $this->params['dst'] );
 628                         return $status;
 629                 }
 630                 // Check if destination file exists
 631                 $status->merge( $this->precheckDestExistence( $predicates ) );
 632                 if ( $status->isOK() ) {
 633                         // Update file existence predicates
 634                         $predicates['exists'][$this->params['src']] = false;
 635                         $predicates['sha1'][$this->params['src']] = false;
 636                         $predicates['exists'][$this->params['dst']] = true;
 637                         $predicates['sha1'][$this->params['dst']] = $this->sourceSha1;
 638                 }
 639                 return $status; // safe to call attempt()
 640         }
 641
 642         protected function doAttempt() {
 643                 // Do nothing if the src/dst paths are the same
 644                 if ( $this->params['src'] !== $this->params['dst'] ) {
 645                         if ( !$this->destSameAsSource ) {
 646                                 // Move the file into the destination
 647                                 return $this->backend->moveInternal( $this->setFlags( $this->params ) );
 648                         } else {
 649                                 // Just delete source as the destination needs no changes
 650                                 $params = array( 'src' => $this->params['src'] );
 651                                 return $this->backend->deleteInternal( $this->setFlags( $params ) );
 652                         }
 653                 }
 654                 return Status::newGood();
 655         }
 656
 657         protected function doStoragePathsRead() {
 658                 return array( $this->params['src'] );
 659         }
 660
 661         protected function doStoragePathsChanged() {
 662                 return array( $this->params['src'], $this->params['dst'] );
 663         }
 664 }
 665
 666 /**
 667  * Delete a file at the given storage path from the backend.
 668  * Parameters similar to FileBackendStore::deleteInternal(), which include:
 669  *     src                 : source storage path
 670  *     ignoreMissingSource : don't return an error if the file does not exist
 671  */
 672 class DeleteFileOp extends FileOp {
 673         protected function allowedParams() {
 674                 return array( array( 'src' ), array( 'ignoreMissingSource' ) );
 675         }
 676
 677         protected $needsDelete = true;
 678
 679         protected function doPrecheck( array &$predicates ) {
 680                 $status = Status::newGood();
 681                 // Check if the source file exists
 682                 if ( !$this->fileExists( $this->params['src'], $predicates ) ) {
 683                         if ( !$this->getParam( 'ignoreMissingSource' ) ) {
 684                                 $status->fatal( 'backend-fail-notexists', $this->params['src'] );
 685                                 return $status;
 686                         }
 687                         $this->needsDelete = false;
 688                 }
 689                 // Update file existence predicates
 690                 $predicates['exists'][$this->params['src']] = false;
 691                 $predicates['sha1'][$this->params['src']] = false;
 692                 return $status; // safe to call attempt()
 693         }
 694
 695         protected function doAttempt() {
 696                 if ( $this->needsDelete ) {
 697                         // Delete the source file
 698                         return $this->backend->deleteInternal( $this->setFlags( $this->params ) );
 699                 }
 700                 return Status::newGood();
 701         }
 702
 703         protected function doStoragePathsChanged() {
 704                 return array( $this->params['src'] );
 705         }
 706 }
 707
 708 /**
 709  * Placeholder operation that has no params and does nothing
 710  */
 711 class NullFileOp extends FileOp {}