includes/filerepo/backend/FileBackend.php

   1 <?php
   2 /**
   3  * @defgroup FileBackend File backend
   4  * @ingroup  FileRepo
   5  *
   6  * File backend is used to interact with file storage systems,
   7  * such as the local file system, NFS, or cloud storage systems.
   8  */
   9
  10 /**
  11  * @file
  12  * @ingroup FileBackend
  13  * @author Aaron Schulz
  14  */
  15
  16 /**
  17  * @brief Base class for all file backend classes (including multi-write backends).
  18  *
  19  * This class defines the methods as abstract that subclasses must implement.
  20  * Outside callers can assume that all backends will have these functions.
  21  *
  22  * All "storage paths" are of the format "mwstore://<backend>/<container>/<path>".
  23  * The <path> portion is a relative path that uses UNIX file system (FS) notation,
  24  * though any particular backend may not actually be using a local filesystem.
  25  * Therefore, the relative paths are only virtual.
  26  *
  27  * Backend contents are stored under wiki-specific container names by default.
  28  * For legacy reasons, this has no effect for the FS backend class, and per-wiki
  29  * segregation must be done by setting the container paths appropriately.
  30  *
  31  * FS-based backends are somewhat more restrictive due to the existence of real
  32  * directory files; a regular file cannot have the same name as a directory. Other
  33  * backends with virtual directories may not have this limitation. Callers should
  34  * store files in such a way that no files and directories are under the same path.
  35  *
  36  * Methods should avoid throwing exceptions at all costs.
  37  * As a corollary, external dependencies should be kept to a minimum.
  38  *
  39  * @ingroup FileBackend
  40  * @since 1.19
  41  */
  42 abstract class FileBackend {
  43         protected $name; // string; unique backend name
  44         protected $wikiId; // string; unique wiki name
  45         protected $readOnly; // string; read-only explanation message
  46         /** @var LockManager */
  47         protected $lockManager;
  48
  49         /**
  50          * Create a new backend instance from configuration.
  51          * This should only be called from within FileBackendGroup.
  52          *
  53          * $config includes:
  54          *     'name'        : The unique name of this backend.
  55          *                     This should consist of alphanumberic, '-', and '_' characters.
  56          *                     This name should not be changed after use.
  57          *     'wikiId'      : Prefix to container names that is unique to this wiki.
  58          *                     This should consist of alphanumberic, '-', and '_' characters.
  59          *     'lockManager' : Registered name of a file lock manager to use.
  60          *     'readOnly'    : Write operations are disallowed if this is a non-empty string.
  61          *                     It should be an explanation for the backend being read-only.
  62          *
  63          * @param $config Array
  64          */
  65         public function __construct( array $config ) {
  66                 $this->name = $config['name'];
  67                 if ( !preg_match( '!^[a-zA-Z0-9-_]{1,255}$!', $this->name ) ) {
  68                         throw new MWException( "Backend name `{$this->name}` is invalid." );
  69                 }
  70                 $this->wikiId = isset( $config['wikiId'] )
  71                         ? $config['wikiId']
  72                         : wfWikiID(); // e.g. "my_wiki-en_"
  73                 $this->lockManager = ( $config['lockManager'] instanceof LockManager )
  74                         ? $config['lockManager']
  75                         : LockManagerGroup::singleton()->get( $config['lockManager'] );
  76                 $this->readOnly = isset( $config['readOnly'] )
  77                         ? (string)$config['readOnly']
  78                         : '';
  79         }
  80
  81         /**
  82          * Get the unique backend name.
  83          * We may have multiple different backends of the same type.
  84          * For example, we can have two Swift backends using different proxies.
  85          *
  86          * @return string
  87          */
  88         final public function getName() {
  89                 return $this->name;
  90         }
  91
  92         /**
  93          * Check if this backend is read-only
  94          *
  95          * @return bool
  96          */
  97         final public function isReadOnly() {
  98                 return ( $this->readOnly != '' );
  99         }
 100
 101         /**
 102          * Get an explanatory message if this backend is read-only
 103          *
 104          * @return string|bool Returns falls if the backend is not read-only
 105          */
 106         final public function getReadOnlyReason() {
 107                 return ( $this->readOnly != '' ) ? $this->readOnly : false;
 108         }
 109
 110         /**
 111          * This is the main entry point into the backend for write operations.
 112          * Callers supply an ordered list of operations to perform as a transaction.
 113          * Files will be locked, the stat cache cleared, and then the operations attempted.
 114          * If any serious errors occur, all attempted operations will be rolled back.
 115          *
 116          * $ops is an array of arrays. The outer array holds a list of operations.
 117          * Each inner array is a set of key value pairs that specify an operation.
 118          *
 119          * Supported operations and their parameters:
 120          * a) Create a new file in storage with the contents of a string
 121          *     array(
 122          *         'op'                  => 'create',
 123          *         'dst'                 => <storage path>,
 124          *         'content'             => <string of new file contents>,
 125          *         'overwrite'           => <boolean>,
 126          *         'overwriteSame'       => <boolean>
 127          *     )
 128          * b) Copy a file system file into storage
 129          *     array(
 130          *         'op'                  => 'store',
 131          *         'src'                 => <file system path>,
 132          *         'dst'                 => <storage path>,
 133          *         'overwrite'           => <boolean>,
 134          *         'overwriteSame'       => <boolean>
 135          *     )
 136          * c) Copy a file within storage
 137          *     array(
 138          *         'op'                  => 'copy',
 139          *         'src'                 => <storage path>,
 140          *         'dst'                 => <storage path>,
 141          *         'overwrite'           => <boolean>,
 142          *         'overwriteSame'       => <boolean>
 143          *     )
 144          * d) Move a file within storage
 145          *     array(
 146          *         'op'                  => 'move',
 147          *         'src'                 => <storage path>,
 148          *         'dst'                 => <storage path>,
 149          *         'overwrite'           => <boolean>,
 150          *         'overwriteSame'       => <boolean>
 151          *     )
 152          * e) Delete a file within storage
 153          *     array(
 154          *         'op'                  => 'delete',
 155          *         'src'                 => <storage path>,
 156          *         'ignoreMissingSource' => <boolean>
 157          *     )
 158          * f) Do nothing (no-op)
 159          *     array(
 160          *         'op'                  => 'null',
 161          *     )
 162          *
 163          * Boolean flags for operations (operation-specific):
 164          * 'ignoreMissingSource' : The operation will simply succeed and do
 165          *                         nothing if the source file does not exist.
 166          * 'overwrite'           : Any destination file will be overwritten.
 167          * 'overwriteSame'       : An error will not be given if a file already
 168          *                         exists at the destination that has the same
 169          *                         contents as the new contents to be written there.
 170          *
 171          * $opts is an associative of boolean flags, including:
 172          * 'force'               : Errors that would normally cause a rollback do not.
 173          *                         The remaining operations are still attempted if any fail.
 174          * 'nonLocking'          : No locks are acquired for the operations.
 175          *                         This can increase performance for non-critical writes.
 176          *                         This has no effect unless the 'force' flag is set.
 177          * 'allowStale'          : Don't require the latest available data.
 178          *                         This can increase performance for non-critical writes.
 179          *                         This has no effect unless the 'force' flag is set.
 180          *
 181          * Remarks on locking:
 182          * File system paths given to operations should refer to files that are
 183          * already locked or otherwise safe from modification from other processes.
 184          * Normally these files will be new temp files, which should be adequate.
 185          *
 186          * Return value:
 187          * This returns a Status, which contains all warnings and fatals that occured
 188          * during the operation. The 'failCount', 'successCount', and 'success' members
 189          * will reflect each operation attempted. The status will be "OK" unless any
 190          * of the operations failed and the 'force' parameter was not set.
 191          *
 192          * @param $ops Array List of operations to execute in order
 193          * @param $opts Array Batch operation options
 194          * @return Status
 195          */
 196         final public function doOperations( array $ops, array $opts = array() ) {
 197                 if ( $this->isReadOnly() ) {
 198                         return Status::newFatal( 'backend-fail-readonly', $this->name, $this->readOnly );
 199                 }
 200                 if ( empty( $opts['force'] ) ) { // sanity
 201                         unset( $opts['nonLocking'] );
 202                         unset( $opts['allowStale'] );
 203                 }
 204                 return $this->doOperationsInternal( $ops, $opts );
 205         }
 206
 207         /**
 208          * @see FileBackend::doOperations()
 209          */
 210         abstract protected function doOperationsInternal( array $ops, array $opts );
 211
 212         /**
 213          * Same as doOperations() except it takes a single operation.
 214          * If you are doing a batch of operations that should either
 215          * all succeed or all fail, then use that function instead.
 216          *
 217          * @see FileBackend::doOperations()
 218          *
 219          * @param $op Array Operation
 220          * @param $opts Array Operation options
 221          * @return Status
 222          */
 223         final public function doOperation( array $op, array $opts = array() ) {
 224                 return $this->doOperations( array( $op ), $opts );
 225         }
 226
 227         /**
 228          * Performs a single create operation.
 229          * This sets $params['op'] to 'create' and passes it to doOperation().
 230          *
 231          * @see FileBackend::doOperation()
 232          *
 233          * @param $params Array Operation parameters
 234          * @param $opts Array Operation options
 235          * @return Status
 236          */
 237         final public function create( array $params, array $opts = array() ) {
 238                 $params['op'] = 'create';
 239                 return $this->doOperation( $params, $opts );
 240         }
 241
 242         /**
 243          * Performs a single store operation.
 244          * This sets $params['op'] to 'store' and passes it to doOperation().
 245          *
 246          * @see FileBackend::doOperation()
 247          *
 248          * @param $params Array Operation parameters
 249          * @param $opts Array Operation options
 250          * @return Status
 251          */
 252         final public function store( array $params, array $opts = array() ) {
 253                 $params['op'] = 'store';
 254                 return $this->doOperation( $params, $opts );
 255         }
 256
 257         /**
 258          * Performs a single copy operation.
 259          * This sets $params['op'] to 'copy' and passes it to doOperation().
 260          *
 261          * @see FileBackend::doOperation()
 262          *
 263          * @param $params Array Operation parameters
 264          * @param $opts Array Operation options
 265          * @return Status
 266          */
 267         final public function copy( array $params, array $opts = array() ) {
 268                 $params['op'] = 'copy';
 269                 return $this->doOperation( $params, $opts );
 270         }
 271
 272         /**
 273          * Performs a single move operation.
 274          * This sets $params['op'] to 'move' and passes it to doOperation().
 275          *
 276          * @see FileBackend::doOperation()
 277          *
 278          * @param $params Array Operation parameters
 279          * @param $opts Array Operation options
 280          * @return Status
 281          */
 282         final public function move( array $params, array $opts = array() ) {
 283                 $params['op'] = 'move';
 284                 return $this->doOperation( $params, $opts );
 285         }
 286
 287         /**
 288          * Performs a single delete operation.
 289          * This sets $params['op'] to 'delete' and passes it to doOperation().
 290          *
 291          * @see FileBackend::doOperation()
 292          *
 293          * @param $params Array Operation parameters
 294          * @param $opts Array Operation options
 295          * @return Status
 296          */
 297         final public function delete( array $params, array $opts = array() ) {
 298                 $params['op'] = 'delete';
 299                 return $this->doOperation( $params, $opts );
 300         }
 301
 302         /**
 303          * Concatenate a list of storage files into a single file system file.
 304          * The target path should refer to a file that is already locked or
 305          * otherwise safe from modification from other processes. Normally,
 306          * the file will be a new temp file, which should be adequate.
 307          * $params include:
 308          *     srcs          : ordered source storage paths (e.g. chunk1, chunk2, ...)
 309          *     dst           : file system path to 0-byte temp file
 310          *
 311          * @param $params Array Operation parameters
 312          * @return Status
 313          */
 314         abstract public function concatenate( array $params );
 315
 316         /**
 317          * Prepare a storage directory for usage.
 318          * This will create any required containers and parent directories.
 319          * Backends using key/value stores only need to create the container.
 320          *
 321          * $params include:
 322          *     dir : storage directory
 323          *
 324          * @param $params Array
 325          * @return Status
 326          */
 327         final public function prepare( array $params ) {
 328                 if ( $this->isReadOnly() ) {
 329                         return Status::newFatal( 'backend-fail-readonly', $this->name, $this->readOnly );
 330                 }
 331                 return $this->doPrepare( $params );
 332         }
 333
 334         /**
 335          * @see FileBackend::prepare()
 336          */
 337         abstract protected function doPrepare( array $params );
 338
 339         /**
 340          * Take measures to block web access to a storage directory and
 341          * the container it belongs to. FS backends might add .htaccess
 342          * files whereas key/value store backends might restrict container
 343          * access to the auth user that represents end-users in web request.
 344          * This is not guaranteed to actually do anything.
 345          *
 346          * $params include:
 347          *     dir       : storage directory
 348          *     noAccess  : try to deny file access
 349          *     noListing : try to deny file listing
 350          *
 351          * @param $params Array
 352          * @return Status
 353          */
 354         final public function secure( array $params ) {
 355                 if ( $this->isReadOnly() ) {
 356                         return Status::newFatal( 'backend-fail-readonly', $this->name, $this->readOnly );
 357                 }
 358                 $status = $this->doPrepare( $params ); // dir must exist to restrict it
 359                 if ( $status->isOK() ) {
 360                         $status->merge( $this->doSecure( $params ) );
 361                 }
 362                 return $status;
 363         }
 364
 365         /**
 366          * @see FileBackend::secure()
 367          */
 368         abstract protected function doSecure( array $params );
 369
 370         /**
 371          * Delete a storage directory if it is empty.
 372          * Backends using key/value stores may do nothing unless the directory
 373          * is that of an empty container, in which case it should be deleted.
 374          *
 375          * $params include:
 376          *     dir : storage directory
 377          *
 378          * @param $params Array
 379          * @return Status
 380          */
 381         final public function clean( array $params ) {
 382                 if ( $this->isReadOnly() ) {
 383                         return Status::newFatal( 'backend-fail-readonly', $this->name, $this->readOnly );
 384                 }
 385                 return $this->doClean( $params );
 386         }
 387
 388         /**
 389          * @see FileBackend::clean()
 390          */
 391         abstract protected function doClean( array $params );
 392
 393         /**
 394          * Check if a file exists at a storage path in the backend.
 395          * This returns false if only a directory exists at the path.
 396          *
 397          * $params include:
 398          *     src    : source storage path
 399          *     latest : use the latest available data
 400          *
 401          * @param $params Array
 402          * @return bool|null Returns null on failure
 403          */
 404         abstract public function fileExists( array $params );
 405
 406         /**
 407          * Get the last-modified timestamp of the file at a storage path.
 408          *
 409          * $params include:
 410          *     src    : source storage path
 411          *     latest : use the latest available data
 412          *
 413          * @param $params Array
 414          * @return string|bool TS_MW timestamp or false on failure
 415          */
 416         abstract public function getFileTimestamp( array $params );
 417
 418         /**
 419          * Get the contents of a file at a storage path in the backend.
 420          * This should be avoided for potentially large files.
 421          *
 422          * $params include:
 423          *     src    : source storage path
 424          *     latest : use the latest available data
 425          *
 426          * @param $params Array
 427          * @return string|bool Returns false on failure
 428          */
 429         abstract public function getFileContents( array $params );
 430
 431         /**
 432          * Get the size (bytes) of a file at a storage path in the backend.
 433          *
 434          * $params include:
 435          *     src    : source storage path
 436          *     latest : use the latest available data
 437          *
 438          * @param $params Array
 439          * @return integer|bool Returns false on failure
 440          */
 441         abstract public function getFileSize( array $params );
 442
 443         /**
 444          * Get quick information about a file at a storage path in the backend.
 445          * If the file does not exist, then this returns false.
 446          * Otherwise, the result is an associative array that includes:
 447          *     mtime  : the last-modified timestamp (TS_MW)
 448          *     size   : the file size (bytes)
 449          * Additional values may be included for internal use only.
 450          *
 451          * $params include:
 452          *     src    : source storage path
 453          *     latest : use the latest available data
 454          *
 455          * @param $params Array
 456          * @return Array|bool|null Returns null on failure
 457          */
 458         abstract public function getFileStat( array $params );
 459
 460         /**
 461          * Get a SHA-1 hash of the file at a storage path in the backend.
 462          *
 463          * $params include:
 464          *     src    : source storage path
 465          *     latest : use the latest available data
 466          *
 467          * @param $params Array
 468          * @return string|bool Hash string or false on failure
 469          */
 470         abstract public function getFileSha1Base36( array $params );
 471
 472         /**
 473          * Get the properties of the file at a storage path in the backend.
 474          * Returns FSFile::placeholderProps() on failure.
 475          *
 476          * $params include:
 477          *     src    : source storage path
 478          *     latest : use the latest available data
 479          *
 480          * @param $params Array
 481          * @return Array
 482          */
 483         abstract public function getFileProps( array $params );
 484
 485         /**
 486          * Stream the file at a storage path in the backend.
 487          * If the file does not exists, a 404 error will be given.
 488          * Appropriate HTTP headers (Status, Content-Type, Content-Length)
 489          * must be sent if streaming began, while none should be sent otherwise.
 490          * Implementations should flush the output buffer before sending data.
 491          *
 492          * $params include:
 493          *     src     : source storage path
 494          *     headers : additional HTTP headers to send on success
 495          *     latest  : use the latest available data
 496          *
 497          * @param $params Array
 498          * @return Status
 499          */
 500         abstract public function streamFile( array $params );
 501
 502         /**
 503          * Returns a file system file, identical to the file at a storage path.
 504          * The file returned is either:
 505          * a) A local copy of the file at a storage path in the backend.
 506          *    The temporary copy will have the same extension as the source.
 507          * b) An original of the file at a storage path in the backend.
 508          * Temporary files may be purged when the file object falls out of scope.
 509          *
 510          * Write operations should *never* be done on this file as some backends
 511          * may do internal tracking or may be instances of FileBackendMultiWrite.
 512          * In that later case, there are copies of the file that must stay in sync.
 513          * Additionally, further calls to this function may return the same file.
 514          *
 515          * $params include:
 516          *     src    : source storage path
 517          *     latest : use the latest available data
 518          *
 519          * @param $params Array
 520          * @return FSFile|null Returns null on failure
 521          */
 522         abstract public function getLocalReference( array $params );
 523
 524         /**
 525          * Get a local copy on disk of the file at a storage path in the backend.
 526          * The temporary copy will have the same file extension as the source.
 527          * Temporary files may be purged when the file object falls out of scope.
 528          *
 529          * $params include:
 530          *     src    : source storage path
 531          *     latest : use the latest available data
 532          *
 533          * @param $params Array
 534          * @return TempFSFile|null Returns null on failure
 535          */
 536         abstract public function getLocalCopy( array $params );
 537
 538         /**
 539          * Get an iterator to list out all stored files under a storage directory.
 540          * If the directory is of the form "mwstore://backend/container",
 541          * then all files in the container should be listed.
 542          * If the directory is of form "mwstore://backend/container/dir",
 543          * then all files under that container directory should be listed.
 544          * Results should be storage paths relative to the given directory.
 545          *
 546          * Storage backends with eventual consistency might return stale data.
 547          *
 548          * $params include:
 549          *     dir : storage path directory
 550          *
 551          * @return Traversable|Array|null Returns null on failure
 552          */
 553         abstract public function getFileList( array $params );
 554
 555         /**
 556          * Invalidate any in-process file existence and property cache.
 557          * If $paths is given, then only the cache for those files will be cleared.
 558          *
 559          * @param $paths Array Storage paths (optional)
 560          * @return void
 561          */
 562         public function clearCache( array $paths = null ) {}
 563
 564         /**
 565          * Lock the files at the given storage paths in the backend.
 566          * This will either lock all the files or none (on failure).
 567          *
 568          * Callers should consider using getScopedFileLocks() instead.
 569          *
 570          * @param $paths Array Storage paths
 571          * @param $type integer LockManager::LOCK_* constant
 572          * @return Status
 573          */
 574         final public function lockFiles( array $paths, $type ) {
 575                 return $this->lockManager->lock( $paths, $type );
 576         }
 577
 578         /**
 579          * Unlock the files at the given storage paths in the backend.
 580          *
 581          * @param $paths Array Storage paths
 582          * @param $type integer LockManager::LOCK_* constant
 583          * @return Status
 584          */
 585         final public function unlockFiles( array $paths, $type ) {
 586                 return $this->lockManager->unlock( $paths, $type );
 587         }
 588
 589         /**
 590          * Lock the files at the given storage paths in the backend.
 591          * This will either lock all the files or none (on failure).
 592          * On failure, the status object will be updated with errors.
 593          *
 594          * Once the return value goes out scope, the locks will be released and
 595          * the status updated. Unlock fatals will not change the status "OK" value.
 596          *
 597          * @param $paths Array Storage paths
 598          * @param $type integer LockManager::LOCK_* constant
 599          * @param $status Status Status to update on lock/unlock
 600          * @return ScopedLock|null Returns null on failure
 601          */
 602         final public function getScopedFileLocks( array $paths, $type, Status $status ) {
 603                 return ScopedLock::factory( $this->lockManager, $paths, $type, $status );
 604         }
 605
 606         /**
 607          * Check if a given path is a "mwstore://" path.
 608          * This does not do any further validation or any existence checks.
 609          *
 610          * @param $path string
 611          * @return bool
 612          */
 613         final public static function isStoragePath( $path ) {
 614                 return ( strpos( $path, 'mwstore://' ) === 0 );
 615         }
 616
 617         /**
 618          * Split a storage path into a backend name, a container name,
 619          * and a relative file path. The relative path may be the empty string.
 620          * This does not do any path normalization or traversal checks.
 621          *
 622          * @param $storagePath string
 623          * @return Array (backend, container, rel object) or (null, null, null)
 624          */
 625         final public static function splitStoragePath( $storagePath ) {
 626                 if ( self::isStoragePath( $storagePath ) ) {
 627                         // Remove the "mwstore://" prefix and split the path
 628                         $parts = explode( '/', substr( $storagePath, 10 ), 3 );
 629                         if ( count( $parts ) >= 2 && $parts[0] != '' && $parts[1] != '' ) {
 630                                 if ( count( $parts ) == 3 ) {
 631                                         return $parts; // e.g. "backend/container/path"
 632                                 } else {
 633                                         return array( $parts[0], $parts[1], '' ); // e.g. "backend/container"
 634                                 }
 635                         }
 636                 }
 637                 return array( null, null, null );
 638         }
 639
 640         /**
 641          * Normalize a storage path by cleaning up directory separators.
 642          * Returns null if the path is not of the format of a valid storage path.
 643          *
 644          * @param $storagePath string
 645          * @return string|null
 646          */
 647         final public static function normalizeStoragePath( $storagePath ) {
 648                 list( $backend, $container, $relPath ) = self::splitStoragePath( $storagePath );
 649                 if ( $relPath !== null ) { // must be for this backend
 650                         $relPath = self::normalizeContainerPath( $relPath );
 651                         if ( $relPath !== null ) {
 652                                 return ( $relPath != '' )
 653                                         ? "mwstore://{$backend}/{$container}/{$relPath}"
 654                                         : "mwstore://{$backend}/{$container}";
 655                         }
 656                 }
 657                 return null;
 658         }
 659
 660         /**
 661          * Get the parent storage directory of a storage path.
 662          * This returns a path like "mwstore://backend/container",
 663          * "mwstore://backend/container/...", or null if there is no parent.
 664          *
 665          * @param $storagePath string
 666          * @return string|null
 667          */
 668         final public static function parentStoragePath( $storagePath ) {
 669                 $storagePath = dirname( $storagePath );
 670                 list( $b, $cont, $rel ) = self::splitStoragePath( $storagePath );
 671                 return ( $rel === null ) ? null : $storagePath;
 672         }
 673
 674         /**
 675          * Get the final extension from a storage or FS path
 676          *
 677          * @param $path string
 678          * @return string
 679          */
 680         final public static function extensionFromPath( $path ) {
 681                 $i = strrpos( $path, '.' );
 682                 return strtolower( $i ? substr( $path, $i + 1 ) : '' );
 683         }
 684
 685         /**
 686          * Validate and normalize a relative storage path.
 687          * Null is returned if the path involves directory traversal.
 688          * Traversal is insecure for FS backends and broken for others.
 689          *
 690          * @param $path string Storage path relative to a container
 691          * @return string|null
 692          */
 693         final protected static function normalizeContainerPath( $path ) {
 694                 // Normalize directory separators
 695                 $path = strtr( $path, '\\', '/' );
 696                 // Collapse any consecutive directory separators
 697                 $path = preg_replace( '![/]{2,}!', '/', $path );
 698                 // Remove any leading directory separator
 699                 $path = ltrim( $path, '/' );
 700                 // Use the same traversal protection as Title::secureAndSplit()
 701                 if ( strpos( $path, '.' ) !== false ) {
 702                         if (
 703                                 $path === '.' ||
 704                                 $path === '..' ||
 705                                 strpos( $path, './' ) === 0 ||
 706                                 strpos( $path, '../' ) === 0 ||
 707                                 strpos( $path, '/./' ) !== false ||
 708                                 strpos( $path, '/../' ) !== false
 709                         ) {
 710                                 return null;
 711                         }
 712                 }
 713                 return $path;
 714         }
 715 }