includes/libs/filebackend/FileBackend.php

   1 <?php
   2 /**
   3  * @defgroup FileBackend File backend
   4  *
   5  * File backend is used to interact with file storage systems,
   6  * such as the local file system, NFS, or cloud storage systems.
   7  */
   8
   9 /**
  10  * Base class for all file backends.
  11  *
  12  * This program is free software; you can redistribute it and/or modify
  13  * it under the terms of the GNU General Public License as published by
  14  * the Free Software Foundation; either version 2 of the License, or
  15  * (at your option) any later version.
  16  *
  17  * This program is distributed in the hope that it will be useful,
  18  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  19  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  20  * GNU General Public License for more details.
  21  *
  22  * You should have received a copy of the GNU General Public License along
  23  * with this program; if not, write to the Free Software Foundation, Inc.,
  24  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  25  * http://www.gnu.org/copyleft/gpl.html
  26  *
  27  * @file
  28  * @ingroup FileBackend
  29  */
  30 use Psr\Log\LoggerAwareInterface;
  31 use Psr\Log\LoggerInterface;
  32 use Wikimedia\ScopedCallback;
  33
  34 /**
  35  * @brief Base class for all file backend classes (including multi-write backends).
  36  *
  37  * This class defines the methods as abstract that subclasses must implement.
  38  * Outside callers can assume that all backends will have these functions.
  39  *
  40  * All "storage paths" are of the format "mwstore://<backend>/<container>/<path>".
  41  * The "backend" portion is unique name for the application to refer to a backend, while
  42  * the "container" portion is a top-level directory of the backend. The "path" portion
  43  * is a relative path that uses UNIX file system (FS) notation, though any particular
  44  * backend may not actually be using a local filesystem. Therefore, the relative paths
  45  * are only virtual.
  46  *
  47  * Backend contents are stored under "domain"-specific container names by default.
  48  * A domain is simply a logical umbrella for entities, such as those belonging to a certain
  49  * application or portion of a website, for example. A domain can be local or global.
  50  * Global (qualified) backends are achieved by configuring the "domain ID" to a constant.
  51  * Global domains are simpler, but local domains can be used by choosing a domain ID based on
  52  * the current context, such as which language of a website is being used.
  53  *
  54  * For legacy reasons, the FSFileBackend class allows manually setting the paths of
  55  * containers to ones that do not respect the "domain ID".
  56  *
  57  * In key/value (object) stores, containers are the only hierarchy (the rest is emulated).
  58  * FS-based backends are somewhat more restrictive due to the existence of real
  59  * directory files; a regular file cannot have the same name as a directory. Other
  60  * backends with virtual directories may not have this limitation. Callers should
  61  * store files in such a way that no files and directories are under the same path.
  62  *
  63  * In general, this class allows for callers to access storage through the same
  64  * interface, without regard to the underlying storage system. However, calling code
  65  * must follow certain patterns and be aware of certain things to ensure compatibility:
  66  *   - a) Always call prepare() on the parent directory before trying to put a file there;
  67  *        key/value stores only need the container to exist first, but filesystems need
  68  *        all the parent directories to exist first (prepare() is aware of all this)
  69  *   - b) Always call clean() on a directory when it might become empty to avoid empty
  70  *        directory buildup on filesystems; key/value stores never have empty directories,
  71  *        so doing this helps preserve consistency in both cases
  72  *   - c) Likewise, do not rely on the existence of empty directories for anything;
  73  *        calling directoryExists() on a path that prepare() was previously called on
  74  *        will return false for key/value stores if there are no files under that path
  75  *   - d) Never alter the resulting FSFile returned from getLocalReference(), as it could
  76  *        either be a copy of the source file in /tmp or the original source file itself
  77  *   - e) Use a file layout that results in never attempting to store files over directories
  78  *        or directories over files; key/value stores allow this but filesystems do not
  79  *   - f) Use ASCII file names (e.g. base32, IDs, hashes) to avoid Unicode issues in Windows
  80  *   - g) Do not assume that move operations are atomic (difficult with key/value stores)
  81  *   - h) Do not assume that file stat or read operations always have immediate consistency;
  82  *        various methods have a "latest" flag that should always be used if up-to-date
  83  *        information is required (this trades performance for correctness as needed)
  84  *   - i) Do not assume that directory listings have immediate consistency
  85  *
  86  * Methods of subclasses should avoid throwing exceptions at all costs.
  87  * As a corollary, external dependencies should be kept to a minimum.
  88  *
  89  * @ingroup FileBackend
  90  * @since 1.19
  91  */
  92 abstract class FileBackend implements LoggerAwareInterface {
  93         /** @var string Unique backend name */
  94         protected $name;
  95
  96         /** @var string Unique domain name */
  97         protected $domainId;
  98
  99         /** @var string Read-only explanation message */
 100         protected $readOnly;
 101
 102         /** @var string When to do operations in parallel */
 103         protected $parallelize;
 104
 105         /** @var int How many operations can be done in parallel */
 106         protected $concurrency;
 107
 108         /** @var string Temporary file directory */
 109         protected $tmpDirectory;
 110
 111         /** @var LockManager */
 112         protected $lockManager;
 113         /** @var FileJournal */
 114         protected $fileJournal;
 115         /** @var LoggerInterface */
 116         protected $logger;
 117         /** @var object|string Class name or object With profileIn/profileOut methods */
 118         protected $profiler;
 119
 120         /** @var callable */
 121         protected $obResetFunc;
 122         /** @var callable */
 123         protected $streamMimeFunc;
 124         /** @var callable */
 125         protected $statusWrapper;
 126
 127         /** Bitfield flags for supported features */
 128         const ATTR_HEADERS = 1; // files can be tagged with standard HTTP headers
 129         const ATTR_METADATA = 2; // files can be stored with metadata key/values
 130         const ATTR_UNICODE_PATHS = 4; // files can have Unicode paths (not just ASCII)
 131
 132         /**
 133          * Create a new backend instance from configuration.
 134          * This should only be called from within FileBackendGroup.
 135          *
 136          * @param array $config Parameters include:
 137          *   - name : The unique name of this backend.
 138          *      This should consist of alphanumberic, '-', and '_' characters.
 139          *      This name should not be changed after use (e.g. with journaling).
 140          *      Note that the name is *not* used in actual container names.
 141          *   - domainId : Prefix to container names that is unique to this backend.
 142          *      It should only consist of alphanumberic, '-', and '_' characters.
 143          *      This ID is what avoids collisions if multiple logical backends
 144          *      use the same storage system, so this should be set carefully.
 145          *   - lockManager : LockManager object to use for any file locking.
 146          *      If not provided, then no file locking will be enforced.
 147          *   - fileJournal : FileJournal object to use for logging changes to files.
 148          *      If not provided, then change journaling will be disabled.
 149          *   - readOnly : Write operations are disallowed if this is a non-empty string.
 150          *      It should be an explanation for the backend being read-only.
 151          *   - parallelize : When to do file operations in parallel (when possible).
 152          *      Allowed values are "implicit", "explicit" and "off".
 153          *   - concurrency : How many file operations can be done in parallel.
 154          *   - tmpDirectory : Directory to use for temporary files. If this is not set or null,
 155          *      then the backend will try to discover a usable temporary directory.
 156          *   - obResetFunc : alternative callback to clear the output buffer
 157          *   - streamMimeFunc : alternative method to determine the content type from the path
 158          *   - logger : Optional PSR logger object.
 159          *   - profiler : Optional class name or object With profileIn/profileOut methods.
 160          * @throws InvalidArgumentException
 161          */
 162         public function __construct( array $config ) {
 163                 $this->name = $config['name'];
 164                 $this->domainId = isset( $config['domainId'] )
 165                         ? $config['domainId'] // e.g. "my_wiki-en_"
 166                         : $config['wikiId']; // b/c alias
 167                 if ( !preg_match( '!^[a-zA-Z0-9-_]{1,255}$!', $this->name ) ) {
 168                         throw new InvalidArgumentException( "Backend name '{$this->name}' is invalid." );
 169                 } elseif ( !is_string( $this->domainId ) ) {
 170                         throw new InvalidArgumentException(
 171                                 "Backend domain ID not provided for '{$this->name}'." );
 172                 }
 173                 $this->lockManager = isset( $config['lockManager'] )
 174                         ? $config['lockManager']
 175                         : new NullLockManager( [] );
 176                 $this->fileJournal = isset( $config['fileJournal'] )
 177                         ? $config['fileJournal']
 178                         : FileJournal::factory( [ 'class' => NullFileJournal::class ], $this->name );
 179                 $this->readOnly = isset( $config['readOnly'] )
 180                         ? (string)$config['readOnly']
 181                         : '';
 182                 $this->parallelize = isset( $config['parallelize'] )
 183                         ? (string)$config['parallelize']
 184                         : 'off';
 185                 $this->concurrency = isset( $config['concurrency'] )
 186                         ? (int)$config['concurrency']
 187                         : 50;
 188                 $this->obResetFunc = isset( $config['obResetFunc'] )
 189                         ? $config['obResetFunc']
 190                         : [ $this, 'resetOutputBuffer' ];
 191                 $this->streamMimeFunc = isset( $config['streamMimeFunc'] )
 192                         ? $config['streamMimeFunc']
 193                         : null;
 194                 $this->statusWrapper = isset( $config['statusWrapper'] ) ? $config['statusWrapper'] : null;
 195
 196                 $this->profiler = isset( $config['profiler'] ) ? $config['profiler'] : null;
 197                 $this->logger = isset( $config['logger'] ) ? $config['logger'] : new \Psr\Log\NullLogger();
 198                 $this->statusWrapper = isset( $config['statusWrapper'] ) ? $config['statusWrapper'] : null;
 199                 $this->tmpDirectory = isset( $config['tmpDirectory'] ) ? $config['tmpDirectory'] : null;
 200         }
 201
 202         public function setLogger( LoggerInterface $logger ) {
 203                 $this->logger = $logger;
 204         }
 205
 206         /**
 207          * Get the unique backend name.
 208          * We may have multiple different backends of the same type.
 209          * For example, we can have two Swift backends using different proxies.
 210          *
 211          * @return string
 212          */
 213         final public function getName() {
 214                 return $this->name;
 215         }
 216
 217         /**
 218          * Get the domain identifier used for this backend (possibly empty).
 219          *
 220          * @return string
 221          * @since 1.28
 222          */
 223         final public function getDomainId() {
 224                 return $this->domainId;
 225         }
 226
 227         /**
 228          * Alias to getDomainId()
 229          * @return string
 230          * @since 1.20
 231          */
 232         final public function getWikiId() {
 233                 return $this->getDomainId();
 234         }
 235
 236         /**
 237          * Check if this backend is read-only
 238          *
 239          * @return bool
 240          */
 241         final public function isReadOnly() {
 242                 return ( $this->readOnly != '' );
 243         }
 244
 245         /**
 246          * Get an explanatory message if this backend is read-only
 247          *
 248          * @return string|bool Returns false if the backend is not read-only
 249          */
 250         final public function getReadOnlyReason() {
 251                 return ( $this->readOnly != '' ) ? $this->readOnly : false;
 252         }
 253
 254         /**
 255          * Get the a bitfield of extra features supported by the backend medium
 256          *
 257          * @return int Bitfield of FileBackend::ATTR_* flags
 258          * @since 1.23
 259          */
 260         public function getFeatures() {
 261                 return self::ATTR_UNICODE_PATHS;
 262         }
 263
 264         /**
 265          * Check if the backend medium supports a field of extra features
 266          *
 267          * @param int $bitfield Bitfield of FileBackend::ATTR_* flags
 268          * @return bool
 269          * @since 1.23
 270          */
 271         final public function hasFeatures( $bitfield ) {
 272                 return ( $this->getFeatures() & $bitfield ) === $bitfield;
 273         }
 274
 275         /**
 276          * This is the main entry point into the backend for write operations.
 277          * Callers supply an ordered list of operations to perform as a transaction.
 278          * Files will be locked, the stat cache cleared, and then the operations attempted.
 279          * If any serious errors occur, all attempted operations will be rolled back.
 280          *
 281          * $ops is an array of arrays. The outer array holds a list of operations.
 282          * Each inner array is a set of key value pairs that specify an operation.
 283          *
 284          * Supported operations and their parameters. The supported actions are:
 285          *  - create
 286          *  - store
 287          *  - copy
 288          *  - move
 289          *  - delete
 290          *  - describe (since 1.21)
 291          *  - null
 292          *
 293          * FSFile/TempFSFile object support was added in 1.27.
 294          *
 295          * a) Create a new file in storage with the contents of a string
 296          * @code
 297          *     [
 298          *         'op'                  => 'create',
 299          *         'dst'                 => <storage path>,
 300          *         'content'             => <string of new file contents>,
 301          *         'overwrite'           => <boolean>,
 302          *         'overwriteSame'       => <boolean>,
 303          *         'headers'             => <HTTP header name/value map> # since 1.21
 304          *     ]
 305          * @endcode
 306          *
 307          * b) Copy a file system file into storage
 308          * @code
 309          *     [
 310          *         'op'                  => 'store',
 311          *         'src'                 => <file system path, FSFile, or TempFSFile>,
 312          *         'dst'                 => <storage path>,
 313          *         'overwrite'           => <boolean>,
 314          *         'overwriteSame'       => <boolean>,
 315          *         'headers'             => <HTTP header name/value map> # since 1.21
 316          *     ]
 317          * @endcode
 318          *
 319          * c) Copy a file within storage
 320          * @code
 321          *     [
 322          *         'op'                  => 'copy',
 323          *         'src'                 => <storage path>,
 324          *         'dst'                 => <storage path>,
 325          *         'overwrite'           => <boolean>,
 326          *         'overwriteSame'       => <boolean>,
 327          *         'ignoreMissingSource' => <boolean>, # since 1.21
 328          *         'headers'             => <HTTP header name/value map> # since 1.21
 329          *     ]
 330          * @endcode
 331          *
 332          * d) Move a file within storage
 333          * @code
 334          *     [
 335          *         'op'                  => 'move',
 336          *         'src'                 => <storage path>,
 337          *         'dst'                 => <storage path>,
 338          *         'overwrite'           => <boolean>,
 339          *         'overwriteSame'       => <boolean>,
 340          *         'ignoreMissingSource' => <boolean>, # since 1.21
 341          *         'headers'             => <HTTP header name/value map> # since 1.21
 342          *     ]
 343          * @endcode
 344          *
 345          * e) Delete a file within storage
 346          * @code
 347          *     [
 348          *         'op'                  => 'delete',
 349          *         'src'                 => <storage path>,
 350          *         'ignoreMissingSource' => <boolean>
 351          *     ]
 352          * @endcode
 353          *
 354          * f) Update metadata for a file within storage
 355          * @code
 356          *     [
 357          *         'op'                  => 'describe',
 358          *         'src'                 => <storage path>,
 359          *         'headers'             => <HTTP header name/value map>
 360          *     ]
 361          * @endcode
 362          *
 363          * g) Do nothing (no-op)
 364          * @code
 365          *     [
 366          *         'op'                  => 'null',
 367          *     ]
 368          * @endcode
 369          *
 370          * Boolean flags for operations (operation-specific):
 371          *   - ignoreMissingSource : The operation will simply succeed and do
 372          *                           nothing if the source file does not exist.
 373          *   - overwrite           : Any destination file will be overwritten.
 374          *   - overwriteSame       : If a file already exists at the destination with the
 375          *                           same contents, then do nothing to the destination file
 376          *                           instead of giving an error. This does not compare headers.
 377          *                           This option is ignored if 'overwrite' is already provided.
 378          *   - headers             : If supplied, the result of merging these headers with any
 379          *                           existing source file headers (replacing conflicting ones)
 380          *                           will be set as the destination file headers. Headers are
 381          *                           deleted if their value is set to the empty string. When a
 382          *                           file has headers they are included in responses to GET and
 383          *                           HEAD requests to the backing store for that file.
 384          *                           Header values should be no larger than 255 bytes, except for
 385          *                           Content-Disposition. The system might ignore or truncate any
 386          *                           headers that are too long to store (exact limits will vary).
 387          *                           Backends that don't support metadata ignore this. (since 1.21)
 388          *
 389          * $opts is an associative of boolean flags, including:
 390          *   - force               : Operation precondition errors no longer trigger an abort.
 391          *                           Any remaining operations are still attempted. Unexpected
 392          *                           failures may still cause remaining operations to be aborted.
 393          *   - nonLocking          : No locks are acquired for the operations.
 394          *                           This can increase performance for non-critical writes.
 395          *                           This has no effect unless the 'force' flag is set.
 396          *   - nonJournaled        : Don't log this operation batch in the file journal.
 397          *                           This limits the ability of recovery scripts.
 398          *   - parallelize         : Try to do operations in parallel when possible.
 399          *   - bypassReadOnly      : Allow writes in read-only mode. (since 1.20)
 400          *   - preserveCache       : Don't clear the process cache before checking files.
 401          *                           This should only be used if all entries in the process
 402          *                           cache were added after the files were already locked. (since 1.20)
 403          *
 404          * @remarks Remarks on locking:
 405          * File system paths given to operations should refer to files that are
 406          * already locked or otherwise safe from modification from other processes.
 407          * Normally these files will be new temp files, which should be adequate.
 408          *
 409          * @par Return value:
 410          *
 411          * This returns a Status, which contains all warnings and fatals that occurred
 412          * during the operation. The 'failCount', 'successCount', and 'success' members
 413          * will reflect each operation attempted.
 414          *
 415          * The StatusValue will be "OK" unless:
 416          *   - a) unexpected operation errors occurred (network partitions, disk full...)
 417          *   - b) significant operation errors occurred and 'force' was not set
 418          *
 419          * @param array $ops List of operations to execute in order
 420          * @param array $opts Batch operation options
 421          * @return StatusValue
 422          */
 423         final public function doOperations( array $ops, array $opts = [] ) {
 424                 if ( empty( $opts['bypassReadOnly'] ) && $this->isReadOnly() ) {
 425                         return $this->newStatus( 'backend-fail-readonly', $this->name, $this->readOnly );
 426                 }
 427                 if ( !count( $ops ) ) {
 428                         return $this->newStatus(); // nothing to do
 429                 }
 430
 431                 $ops = $this->resolveFSFileObjects( $ops );
 432                 if ( empty( $opts['force'] ) ) { // sanity
 433                         unset( $opts['nonLocking'] );
 434                 }
 435
 436                 /** @noinspection PhpUnusedLocalVariableInspection */
 437                 $scope = $this->getScopedPHPBehaviorForOps(); // try to ignore client aborts
 438
 439                 return $this->doOperationsInternal( $ops, $opts );
 440         }
 441
 442         /**
 443          * @see FileBackend::doOperations()
 444          * @param array $ops
 445          * @param array $opts
 446          */
 447         abstract protected function doOperationsInternal( array $ops, array $opts );
 448
 449         /**
 450          * Same as doOperations() except it takes a single operation.
 451          * If you are doing a batch of operations that should either
 452          * all succeed or all fail, then use that function instead.
 453          *
 454          * @see FileBackend::doOperations()
 455          *
 456          * @param array $op Operation
 457          * @param array $opts Operation options
 458          * @return StatusValue
 459          */
 460         final public function doOperation( array $op, array $opts = [] ) {
 461                 return $this->doOperations( [ $op ], $opts );
 462         }
 463
 464         /**
 465          * Performs a single create operation.
 466          * This sets $params['op'] to 'create' and passes it to doOperation().
 467          *
 468          * @see FileBackend::doOperation()
 469          *
 470          * @param array $params Operation parameters
 471          * @param array $opts Operation options
 472          * @return StatusValue
 473          */
 474         final public function create( array $params, array $opts = [] ) {
 475                 return $this->doOperation( [ 'op' => 'create' ] + $params, $opts );
 476         }
 477
 478         /**
 479          * Performs a single store operation.
 480          * This sets $params['op'] to 'store' and passes it to doOperation().
 481          *
 482          * @see FileBackend::doOperation()
 483          *
 484          * @param array $params Operation parameters
 485          * @param array $opts Operation options
 486          * @return StatusValue
 487          */
 488         final public function store( array $params, array $opts = [] ) {
 489                 return $this->doOperation( [ 'op' => 'store' ] + $params, $opts );
 490         }
 491
 492         /**
 493          * Performs a single copy operation.
 494          * This sets $params['op'] to 'copy' and passes it to doOperation().
 495          *
 496          * @see FileBackend::doOperation()
 497          *
 498          * @param array $params Operation parameters
 499          * @param array $opts Operation options
 500          * @return StatusValue
 501          */
 502         final public function copy( array $params, array $opts = [] ) {
 503                 return $this->doOperation( [ 'op' => 'copy' ] + $params, $opts );
 504         }
 505
 506         /**
 507          * Performs a single move operation.
 508          * This sets $params['op'] to 'move' and passes it to doOperation().
 509          *
 510          * @see FileBackend::doOperation()
 511          *
 512          * @param array $params Operation parameters
 513          * @param array $opts Operation options
 514          * @return StatusValue
 515          */
 516         final public function move( array $params, array $opts = [] ) {
 517                 return $this->doOperation( [ 'op' => 'move' ] + $params, $opts );
 518         }
 519
 520         /**
 521          * Performs a single delete operation.
 522          * This sets $params['op'] to 'delete' and passes it to doOperation().
 523          *
 524          * @see FileBackend::doOperation()
 525          *
 526          * @param array $params Operation parameters
 527          * @param array $opts Operation options
 528          * @return StatusValue
 529          */
 530         final public function delete( array $params, array $opts = [] ) {
 531                 return $this->doOperation( [ 'op' => 'delete' ] + $params, $opts );
 532         }
 533
 534         /**
 535          * Performs a single describe operation.
 536          * This sets $params['op'] to 'describe' and passes it to doOperation().
 537          *
 538          * @see FileBackend::doOperation()
 539          *
 540          * @param array $params Operation parameters
 541          * @param array $opts Operation options
 542          * @return StatusValue
 543          * @since 1.21
 544          */
 545         final public function describe( array $params, array $opts = [] ) {
 546                 return $this->doOperation( [ 'op' => 'describe' ] + $params, $opts );
 547         }
 548
 549         /**
 550          * Perform a set of independent file operations on some files.
 551          *
 552          * This does no locking, nor journaling, and possibly no stat calls.
 553          * Any destination files that already exist will be overwritten.
 554          * This should *only* be used on non-original files, like cache files.
 555          *
 556          * Supported operations and their parameters:
 557          *  - create
 558          *  - store
 559          *  - copy
 560          *  - move
 561          *  - delete
 562          *  - describe (since 1.21)
 563          *  - null
 564          *
 565          * FSFile/TempFSFile object support was added in 1.27.
 566          *
 567          * a) Create a new file in storage with the contents of a string
 568          * @code
 569          *     [
 570          *         'op'                  => 'create',
 571          *         'dst'                 => <storage path>,
 572          *         'content'             => <string of new file contents>,
 573          *         'headers'             => <HTTP header name/value map> # since 1.21
 574          *     ]
 575          * @endcode
 576          *
 577          * b) Copy a file system file into storage
 578          * @code
 579          *     [
 580          *         'op'                  => 'store',
 581          *         'src'                 => <file system path, FSFile, or TempFSFile>,
 582          *         'dst'                 => <storage path>,
 583          *         'headers'             => <HTTP header name/value map> # since 1.21
 584          *     ]
 585          * @endcode
 586          *
 587          * c) Copy a file within storage
 588          * @code
 589          *     [
 590          *         'op'                  => 'copy',
 591          *         'src'                 => <storage path>,
 592          *         'dst'                 => <storage path>,
 593          *         'ignoreMissingSource' => <boolean>, # since 1.21
 594          *         'headers'             => <HTTP header name/value map> # since 1.21
 595          *     ]
 596          * @endcode
 597          *
 598          * d) Move a file within storage
 599          * @code
 600          *     [
 601          *         'op'                  => 'move',
 602          *         'src'                 => <storage path>,
 603          *         'dst'                 => <storage path>,
 604          *         'ignoreMissingSource' => <boolean>, # since 1.21
 605          *         'headers'             => <HTTP header name/value map> # since 1.21
 606          *     ]
 607          * @endcode
 608          *
 609          * e) Delete a file within storage
 610          * @code
 611          *     [
 612          *         'op'                  => 'delete',
 613          *         'src'                 => <storage path>,
 614          *         'ignoreMissingSource' => <boolean>
 615          *     ]
 616          * @endcode
 617          *
 618          * f) Update metadata for a file within storage
 619          * @code
 620          *     [
 621          *         'op'                  => 'describe',
 622          *         'src'                 => <storage path>,
 623          *         'headers'             => <HTTP header name/value map>
 624          *     ]
 625          * @endcode
 626          *
 627          * g) Do nothing (no-op)
 628          * @code
 629          *     [
 630          *         'op'                  => 'null',
 631          *     ]
 632          * @endcode
 633          *
 634          * @par Boolean flags for operations (operation-specific):
 635          *   - ignoreMissingSource : The operation will simply succeed and do
 636          *                           nothing if the source file does not exist.
 637          *   - headers             : If supplied with a header name/value map, the backend will
 638          *                           reply with these headers when GETs/HEADs of the destination
 639          *                           file are made. Header values should be smaller than 256 bytes.
 640          *                           Content-Disposition headers can be longer, though the system
 641          *                           might ignore or truncate ones that are too long to store.
 642          *                           Existing headers will remain, but these will replace any
 643          *                           conflicting previous headers, and headers will be removed
 644          *                           if they are set to an empty string.
 645          *                           Backends that don't support metadata ignore this. (since 1.21)
 646          *
 647          * $opts is an associative of boolean flags, including:
 648          *   - bypassReadOnly      : Allow writes in read-only mode (since 1.20)
 649          *
 650          * @par Return value:
 651          * This returns a Status, which contains all warnings and fatals that occurred
 652          * during the operation. The 'failCount', 'successCount', and 'success' members
 653          * will reflect each operation attempted for the given files. The StatusValue will be
 654          * considered "OK" as long as no fatal errors occurred.
 655          *
 656          * @param array $ops Set of operations to execute
 657          * @param array $opts Batch operation options
 658          * @return StatusValue
 659          * @since 1.20
 660          */
 661         final public function doQuickOperations( array $ops, array $opts = [] ) {
 662                 if ( empty( $opts['bypassReadOnly'] ) && $this->isReadOnly() ) {
 663                         return $this->newStatus( 'backend-fail-readonly', $this->name, $this->readOnly );
 664                 }
 665                 if ( !count( $ops ) ) {
 666                         return $this->newStatus(); // nothing to do
 667                 }
 668
 669                 $ops = $this->resolveFSFileObjects( $ops );
 670                 foreach ( $ops as &$op ) {
 671                         $op['overwrite'] = true; // avoids RTTs in key/value stores
 672                 }
 673
 674                 /** @noinspection PhpUnusedLocalVariableInspection */
 675                 $scope = $this->getScopedPHPBehaviorForOps(); // try to ignore client aborts
 676
 677                 return $this->doQuickOperationsInternal( $ops );
 678         }
 679
 680         /**
 681          * @see FileBackend::doQuickOperations()
 682          * @param array $ops
 683          * @since 1.20
 684          */
 685         abstract protected function doQuickOperationsInternal( array $ops );
 686
 687         /**
 688          * Same as doQuickOperations() except it takes a single operation.
 689          * If you are doing a batch of operations, then use that function instead.
 690          *
 691          * @see FileBackend::doQuickOperations()
 692          *
 693          * @param array $op Operation
 694          * @return StatusValue
 695          * @since 1.20
 696          */
 697         final public function doQuickOperation( array $op ) {
 698                 return $this->doQuickOperations( [ $op ] );
 699         }
 700
 701         /**
 702          * Performs a single quick create operation.
 703          * This sets $params['op'] to 'create' and passes it to doQuickOperation().
 704          *
 705          * @see FileBackend::doQuickOperation()
 706          *
 707          * @param array $params Operation parameters
 708          * @return StatusValue
 709          * @since 1.20
 710          */
 711         final public function quickCreate( array $params ) {
 712                 return $this->doQuickOperation( [ 'op' => 'create' ] + $params );
 713         }
 714
 715         /**
 716          * Performs a single quick store operation.
 717          * This sets $params['op'] to 'store' and passes it to doQuickOperation().
 718          *
 719          * @see FileBackend::doQuickOperation()
 720          *
 721          * @param array $params Operation parameters
 722          * @return StatusValue
 723          * @since 1.20
 724          */
 725         final public function quickStore( array $params ) {
 726                 return $this->doQuickOperation( [ 'op' => 'store' ] + $params );
 727         }
 728
 729         /**
 730          * Performs a single quick copy operation.
 731          * This sets $params['op'] to 'copy' and passes it to doQuickOperation().
 732          *
 733          * @see FileBackend::doQuickOperation()
 734          *
 735          * @param array $params Operation parameters
 736          * @return StatusValue
 737          * @since 1.20
 738          */
 739         final public function quickCopy( array $params ) {
 740                 return $this->doQuickOperation( [ 'op' => 'copy' ] + $params );
 741         }
 742
 743         /**
 744          * Performs a single quick move operation.
 745          * This sets $params['op'] to 'move' and passes it to doQuickOperation().
 746          *
 747          * @see FileBackend::doQuickOperation()
 748          *
 749          * @param array $params Operation parameters
 750          * @return StatusValue
 751          * @since 1.20
 752          */
 753         final public function quickMove( array $params ) {
 754                 return $this->doQuickOperation( [ 'op' => 'move' ] + $params );
 755         }
 756
 757         /**
 758          * Performs a single quick delete operation.
 759          * This sets $params['op'] to 'delete' and passes it to doQuickOperation().
 760          *
 761          * @see FileBackend::doQuickOperation()
 762          *
 763          * @param array $params Operation parameters
 764          * @return StatusValue
 765          * @since 1.20
 766          */
 767         final public function quickDelete( array $params ) {
 768                 return $this->doQuickOperation( [ 'op' => 'delete' ] + $params );
 769         }
 770
 771         /**
 772          * Performs a single quick describe operation.
 773          * This sets $params['op'] to 'describe' and passes it to doQuickOperation().
 774          *
 775          * @see FileBackend::doQuickOperation()
 776          *
 777          * @param array $params Operation parameters
 778          * @return StatusValue
 779          * @since 1.21
 780          */
 781         final public function quickDescribe( array $params ) {
 782                 return $this->doQuickOperation( [ 'op' => 'describe' ] + $params );
 783         }
 784
 785         /**
 786          * Concatenate a list of storage files into a single file system file.
 787          * The target path should refer to a file that is already locked or
 788          * otherwise safe from modification from other processes. Normally,
 789          * the file will be a new temp file, which should be adequate.
 790          *
 791          * @param array $params Operation parameters, include:
 792          *   - srcs        : ordered source storage paths (e.g. chunk1, chunk2, ...)
 793          *   - dst         : file system path to 0-byte temp file
 794          *   - parallelize : try to do operations in parallel when possible
 795          * @return StatusValue
 796          */
 797         abstract public function concatenate( array $params );
 798
 799         /**
 800          * Prepare a storage directory for usage.
 801          * This will create any required containers and parent directories.
 802          * Backends using key/value stores only need to create the container.
 803          *
 804          * The 'noAccess' and 'noListing' parameters works the same as in secure(),
 805          * except they are only applied *if* the directory/container had to be created.
 806          * These flags should always be set for directories that have private files.
 807          * However, setting them is not guaranteed to actually do anything.
 808          * Additional server configuration may be needed to achieve the desired effect.
 809          *
 810          * @param array $params Parameters include:
 811          *   - dir            : storage directory
 812          *   - noAccess       : try to deny file access (since 1.20)
 813          *   - noListing      : try to deny file listing (since 1.20)
 814          *   - bypassReadOnly : allow writes in read-only mode (since 1.20)
 815          * @return StatusValue
 816          */
 817         final public function prepare( array $params ) {
 818                 if ( empty( $params['bypassReadOnly'] ) && $this->isReadOnly() ) {
 819                         return $this->newStatus( 'backend-fail-readonly', $this->name, $this->readOnly );
 820                 }
 821                 /** @noinspection PhpUnusedLocalVariableInspection */
 822                 $scope = $this->getScopedPHPBehaviorForOps(); // try to ignore client aborts
 823                 return $this->doPrepare( $params );
 824         }
 825
 826         /**
 827          * @see FileBackend::prepare()
 828          * @param array $params
 829          */
 830         abstract protected function doPrepare( array $params );
 831
 832         /**
 833          * Take measures to block web access to a storage directory and
 834          * the container it belongs to. FS backends might add .htaccess
 835          * files whereas key/value store backends might revoke container
 836          * access to the storage user representing end-users in web requests.
 837          *
 838          * This is not guaranteed to actually make files or listings publically hidden.
 839          * Additional server configuration may be needed to achieve the desired effect.
 840          *
 841          * @param array $params Parameters include:
 842          *   - dir            : storage directory
 843          *   - noAccess       : try to deny file access
 844          *   - noListing      : try to deny file listing
 845          *   - bypassReadOnly : allow writes in read-only mode (since 1.20)
 846          * @return StatusValue
 847          */
 848         final public function secure( array $params ) {
 849                 if ( empty( $params['bypassReadOnly'] ) && $this->isReadOnly() ) {
 850                         return $this->newStatus( 'backend-fail-readonly', $this->name, $this->readOnly );
 851                 }
 852                 /** @noinspection PhpUnusedLocalVariableInspection */
 853                 $scope = $this->getScopedPHPBehaviorForOps(); // try to ignore client aborts
 854                 return $this->doSecure( $params );
 855         }
 856
 857         /**
 858          * @see FileBackend::secure()
 859          * @param array $params
 860          */
 861         abstract protected function doSecure( array $params );
 862
 863         /**
 864          * Remove measures to block web access to a storage directory and
 865          * the container it belongs to. FS backends might remove .htaccess
 866          * files whereas key/value store backends might grant container
 867          * access to the storage user representing end-users in web requests.
 868          * This essentially can undo the result of secure() calls.
 869          *
 870          * This is not guaranteed to actually make files or listings publically viewable.
 871          * Additional server configuration may be needed to achieve the desired effect.
 872          *
 873          * @param array $params Parameters include:
 874          *   - dir            : storage directory
 875          *   - access         : try to allow file access
 876          *   - listing        : try to allow file listing
 877          *   - bypassReadOnly : allow writes in read-only mode (since 1.20)
 878          * @return StatusValue
 879          * @since 1.20
 880          */
 881         final public function publish( array $params ) {
 882                 if ( empty( $params['bypassReadOnly'] ) && $this->isReadOnly() ) {
 883                         return $this->newStatus( 'backend-fail-readonly', $this->name, $this->readOnly );
 884                 }
 885                 /** @noinspection PhpUnusedLocalVariableInspection */
 886                 $scope = $this->getScopedPHPBehaviorForOps(); // try to ignore client aborts
 887                 return $this->doPublish( $params );
 888         }
 889
 890         /**
 891          * @see FileBackend::publish()
 892          * @param array $params
 893          */
 894         abstract protected function doPublish( array $params );
 895
 896         /**
 897          * Delete a storage directory if it is empty.
 898          * Backends using key/value stores may do nothing unless the directory
 899          * is that of an empty container, in which case it will be deleted.
 900          *
 901          * @param array $params Parameters include:
 902          *   - dir            : storage directory
 903          *   - recursive      : recursively delete empty subdirectories first (since 1.20)
 904          *   - bypassReadOnly : allow writes in read-only mode (since 1.20)
 905          * @return StatusValue
 906          */
 907         final public function clean( array $params ) {
 908                 if ( empty( $params['bypassReadOnly'] ) && $this->isReadOnly() ) {
 909                         return $this->newStatus( 'backend-fail-readonly', $this->name, $this->readOnly );
 910                 }
 911                 /** @noinspection PhpUnusedLocalVariableInspection */
 912                 $scope = $this->getScopedPHPBehaviorForOps(); // try to ignore client aborts
 913                 return $this->doClean( $params );
 914         }
 915
 916         /**
 917          * @see FileBackend::clean()
 918          * @param array $params
 919          */
 920         abstract protected function doClean( array $params );
 921
 922         /**
 923          * Enter file operation scope.
 924          * This just makes PHP ignore user aborts/disconnects until the return
 925          * value leaves scope. This returns null and does nothing in CLI mode.
 926          *
 927          * @return ScopedCallback|null
 928          */
 929         final protected function getScopedPHPBehaviorForOps() {
 930                 if ( PHP_SAPI != 'cli' ) { // https://bugs.php.net/bug.php?id=47540
 931                         $old = ignore_user_abort( true ); // avoid half-finished operations
 932                         return new ScopedCallback( function () use ( $old ) {
 933                                 ignore_user_abort( $old );
 934                         } );
 935                 }
 936
 937                 return null;
 938         }
 939
 940         /**
 941          * Check if a file exists at a storage path in the backend.
 942          * This returns false if only a directory exists at the path.
 943          *
 944          * @param array $params Parameters include:
 945          *   - src    : source storage path
 946          *   - latest : use the latest available data
 947          * @return bool|null Returns null on failure
 948          */
 949         abstract public function fileExists( array $params );
 950
 951         /**
 952          * Get the last-modified timestamp of the file at a storage path.
 953          *
 954          * @param array $params Parameters include:
 955          *   - src    : source storage path
 956          *   - latest : use the latest available data
 957          * @return string|bool TS_MW timestamp or false on failure
 958          */
 959         abstract public function getFileTimestamp( array $params );
 960
 961         /**
 962          * Get the contents of a file at a storage path in the backend.
 963          * This should be avoided for potentially large files.
 964          *
 965          * @param array $params Parameters include:
 966          *   - src    : source storage path
 967          *   - latest : use the latest available data
 968          * @return string|bool Returns false on failure
 969          */
 970         final public function getFileContents( array $params ) {
 971                 $contents = $this->getFileContentsMulti(
 972                         [ 'srcs' => [ $params['src'] ] ] + $params );
 973
 974                 return $contents[$params['src']];
 975         }
 976
 977         /**
 978          * Like getFileContents() except it takes an array of storage paths
 979          * and returns a map of storage paths to strings (or null on failure).
 980          * The map keys (paths) are in the same order as the provided list of paths.
 981          *
 982          * @see FileBackend::getFileContents()
 983          *
 984          * @param array $params Parameters include:
 985          *   - srcs        : list of source storage paths
 986          *   - latest      : use the latest available data
 987          *   - parallelize : try to do operations in parallel when possible
 988          * @return array Map of (path name => string or false on failure)
 989          * @since 1.20
 990          */
 991         abstract public function getFileContentsMulti( array $params );
 992
 993         /**
 994          * Get metadata about a file at a storage path in the backend.
 995          * If the file does not exist, then this returns false.
 996          * Otherwise, the result is an associative array that includes:
 997          *   - headers  : map of HTTP headers used for GET/HEAD requests (name => value)
 998          *   - metadata : map of file metadata (name => value)
 999          * Metadata keys and headers names will be returned in all lower-case.
1000          * Additional values may be included for internal use only.
1001          *
1002          * Use FileBackend::hasFeatures() to check how well this is supported.
1003          *
1004          * @param array $params
1005          * $params include:
1006          *   - src    : source storage path
1007          *   - latest : use the latest available data
1008          * @return array|bool Returns false on failure
1009          * @since 1.23
1010          */
1011         abstract public function getFileXAttributes( array $params );
1012
1013         /**
1014          * Get the size (bytes) of a file at a storage path in the backend.
1015          *
1016          * @param array $params Parameters include:
1017          *   - src    : source storage path
1018          *   - latest : use the latest available data
1019          * @return int|bool Returns false on failure
1020          */
1021         abstract public function getFileSize( array $params );
1022
1023         /**
1024          * Get quick information about a file at a storage path in the backend.
1025          * If the file does not exist, then this returns false.
1026          * Otherwise, the result is an associative array that includes:
1027          *   - mtime  : the last-modified timestamp (TS_MW)
1028          *   - size   : the file size (bytes)
1029          * Additional values may be included for internal use only.
1030          *
1031          * @param array $params Parameters include:
1032          *   - src    : source storage path
1033          *   - latest : use the latest available data
1034          * @return array|bool|null Returns null on failure
1035          */
1036         abstract public function getFileStat( array $params );
1037
1038         /**
1039          * Get a SHA-1 hash of the file at a storage path in the backend.
1040          *
1041          * @param array $params Parameters include:
1042          *   - src    : source storage path
1043          *   - latest : use the latest available data
1044          * @return string|bool Hash string or false on failure
1045          */
1046         abstract public function getFileSha1Base36( array $params );
1047
1048         /**
1049          * Get the properties of the file at a storage path in the backend.
1050          * This gives the result of FSFile::getProps() on a local copy of the file.
1051          *
1052          * @param array $params Parameters include:
1053          *   - src    : source storage path
1054          *   - latest : use the latest available data
1055          * @return array Returns FSFile::placeholderProps() on failure
1056          */
1057         abstract public function getFileProps( array $params );
1058
1059         /**
1060          * Stream the file at a storage path in the backend.
1061          *
1062          * If the file does not exists, an HTTP 404 error will be given.
1063          * Appropriate HTTP headers (Status, Content-Type, Content-Length)
1064          * will be sent if streaming began, while none will be sent otherwise.
1065          * Implementations should flush the output buffer before sending data.
1066          *
1067          * @param array $params Parameters include:
1068          *   - src      : source storage path
1069          *   - headers  : list of additional HTTP headers to send if the file exists
1070          *   - options  : HTTP request header map with lower case keys (since 1.28). Supports:
1071          *                range             : format is "bytes=(\d*-\d*)"
1072          *                if-modified-since : format is an HTTP date
1073          *   - headless : only include the body (and headers from "headers") (since 1.28)
1074          *   - latest   : use the latest available data
1075          *   - allowOB  : preserve any output buffers (since 1.28)
1076          * @return StatusValue
1077          */
1078         abstract public function streamFile( array $params );
1079
1080         /**
1081          * Returns a file system file, identical to the file at a storage path.
1082          * The file returned is either:
1083          *   - a) A local copy of the file at a storage path in the backend.
1084          *        The temporary copy will have the same extension as the source.
1085          *   - b) An original of the file at a storage path in the backend.
1086          * Temporary files may be purged when the file object falls out of scope.
1087          *
1088          * Write operations should *never* be done on this file as some backends
1089          * may do internal tracking or may be instances of FileBackendMultiWrite.
1090          * In that latter case, there are copies of the file that must stay in sync.
1091          * Additionally, further calls to this function may return the same file.
1092          *
1093          * @param array $params Parameters include:
1094          *   - src    : source storage path
1095          *   - latest : use the latest available data
1096          * @return FSFile|null Returns null on failure
1097          */
1098         final public function getLocalReference( array $params ) {
1099                 $fsFiles = $this->getLocalReferenceMulti(
1100                         [ 'srcs' => [ $params['src'] ] ] + $params );
1101
1102                 return $fsFiles[$params['src']];
1103         }
1104
1105         /**
1106          * Like getLocalReference() except it takes an array of storage paths
1107          * and returns a map of storage paths to FSFile objects (or null on failure).
1108          * The map keys (paths) are in the same order as the provided list of paths.
1109          *
1110          * @see FileBackend::getLocalReference()
1111          *
1112          * @param array $params Parameters include:
1113          *   - srcs        : list of source storage paths
1114          *   - latest      : use the latest available data
1115          *   - parallelize : try to do operations in parallel when possible
1116          * @return array Map of (path name => FSFile or null on failure)
1117          * @since 1.20
1118          */
1119         abstract public function getLocalReferenceMulti( array $params );
1120
1121         /**
1122          * Get a local copy on disk of the file at a storage path in the backend.
1123          * The temporary copy will have the same file extension as the source.
1124          * Temporary files may be purged when the file object falls out of scope.
1125          *
1126          * @param array $params Parameters include:
1127          *   - src    : source storage path
1128          *   - latest : use the latest available data
1129          * @return TempFSFile|null Returns null on failure
1130          */
1131         final public function getLocalCopy( array $params ) {
1132                 $tmpFiles = $this->getLocalCopyMulti(
1133                         [ 'srcs' => [ $params['src'] ] ] + $params );
1134
1135                 return $tmpFiles[$params['src']];
1136         }
1137
1138         /**
1139          * Like getLocalCopy() except it takes an array of storage paths and
1140          * returns a map of storage paths to TempFSFile objects (or null on failure).
1141          * The map keys (paths) are in the same order as the provided list of paths.
1142          *
1143          * @see FileBackend::getLocalCopy()
1144          *
1145          * @param array $params Parameters include:
1146          *   - srcs        : list of source storage paths
1147          *   - latest      : use the latest available data
1148          *   - parallelize : try to do operations in parallel when possible
1149          * @return array Map of (path name => TempFSFile or null on failure)
1150          * @since 1.20
1151          */
1152         abstract public function getLocalCopyMulti( array $params );
1153
1154         /**
1155          * Return an HTTP URL to a given file that requires no authentication to use.
1156          * The URL may be pre-authenticated (via some token in the URL) and temporary.
1157          * This will return null if the backend cannot make an HTTP URL for the file.
1158          *
1159          * This is useful for key/value stores when using scripts that seek around
1160          * large files and those scripts (and the backend) support HTTP Range headers.
1161          * Otherwise, one would need to use getLocalReference(), which involves loading
1162          * the entire file on to local disk.
1163          *
1164          * @param array $params Parameters include:
1165          *   - src : source storage path
1166          *   - ttl : lifetime (seconds) if pre-authenticated; default is 1 day
1167          * @return string|null
1168          * @since 1.21
1169          */
1170         abstract public function getFileHttpUrl( array $params );
1171
1172         /**
1173          * Check if a directory exists at a given storage path.
1174          * Backends using key/value stores will check if the path is a
1175          * virtual directory, meaning there are files under the given directory.
1176          *
1177          * Storage backends with eventual consistency might return stale data.
1178          *
1179          * @param array $params Parameters include:
1180          *   - dir : storage directory
1181          * @return bool|null Returns null on failure
1182          * @since 1.20
1183          */
1184         abstract public function directoryExists( array $params );
1185
1186         /**
1187          * Get an iterator to list *all* directories under a storage directory.
1188          * If the directory is of the form "mwstore://backend/container",
1189          * then all directories in the container will be listed.
1190          * If the directory is of form "mwstore://backend/container/dir",
1191          * then all directories directly under that directory will be listed.
1192          * Results will be storage directories relative to the given directory.
1193          *
1194          * Storage backends with eventual consistency might return stale data.
1195          *
1196          * Failures during iteration can result in FileBackendError exceptions (since 1.22).
1197          *
1198          * @param array $params Parameters include:
1199          *   - dir     : storage directory
1200          *   - topOnly : only return direct child dirs of the directory
1201          * @return Traversable|array|null Returns null on failure
1202          * @since 1.20
1203          */
1204         abstract public function getDirectoryList( array $params );
1205
1206         /**
1207          * Same as FileBackend::getDirectoryList() except only lists
1208          * directories that are immediately under the given directory.
1209          *
1210          * Storage backends with eventual consistency might return stale data.
1211          *
1212          * Failures during iteration can result in FileBackendError exceptions (since 1.22).
1213          *
1214          * @param array $params Parameters include:
1215          *   - dir : storage directory
1216          * @return Traversable|array|null Returns null on failure
1217          * @since 1.20
1218          */
1219         final public function getTopDirectoryList( array $params ) {
1220                 return $this->getDirectoryList( [ 'topOnly' => true ] + $params );
1221         }
1222
1223         /**
1224          * Get an iterator to list *all* stored files under a storage directory.
1225          * If the directory is of the form "mwstore://backend/container",
1226          * then all files in the container will be listed.
1227          * If the directory is of form "mwstore://backend/container/dir",
1228          * then all files under that directory will be listed.
1229          * Results will be storage paths relative to the given directory.
1230          *
1231          * Storage backends with eventual consistency might return stale data.
1232          *
1233          * Failures during iteration can result in FileBackendError exceptions (since 1.22).
1234          *
1235          * @param array $params Parameters include:
1236          *   - dir        : storage directory
1237          *   - topOnly    : only return direct child files of the directory (since 1.20)
1238          *   - adviseStat : set to true if stat requests will be made on the files (since 1.22)
1239          * @return Traversable|array|null Returns null on failure
1240          */
1241         abstract public function getFileList( array $params );
1242
1243         /**
1244          * Same as FileBackend::getFileList() except only lists
1245          * files that are immediately under the given directory.
1246          *
1247          * Storage backends with eventual consistency might return stale data.
1248          *
1249          * Failures during iteration can result in FileBackendError exceptions (since 1.22).
1250          *
1251          * @param array $params Parameters include:
1252          *   - dir        : storage directory
1253          *   - adviseStat : set to true if stat requests will be made on the files (since 1.22)
1254          * @return Traversable|array|null Returns null on failure
1255          * @since 1.20
1256          */
1257         final public function getTopFileList( array $params ) {
1258                 return $this->getFileList( [ 'topOnly' => true ] + $params );
1259         }
1260
1261         /**
1262          * Preload persistent file stat cache and property cache into in-process cache.
1263          * This should be used when stat calls will be made on a known list of a many files.
1264          *
1265          * @see FileBackend::getFileStat()
1266          *
1267          * @param array $paths Storage paths
1268          */
1269         abstract public function preloadCache( array $paths );
1270
1271         /**
1272          * Invalidate any in-process file stat and property cache.
1273          * If $paths is given, then only the cache for those files will be cleared.
1274          *
1275          * @see FileBackend::getFileStat()
1276          *
1277          * @param array $paths Storage paths (optional)
1278          */
1279         abstract public function clearCache( array $paths = null );
1280
1281         /**
1282          * Preload file stat information (concurrently if possible) into in-process cache.
1283          *
1284          * This should be used when stat calls will be made on a known list of a many files.
1285          * This does not make use of the persistent file stat cache.
1286          *
1287          * @see FileBackend::getFileStat()
1288          *
1289          * @param array $params Parameters include:
1290          *   - srcs        : list of source storage paths
1291          *   - latest      : use the latest available data
1292          * @return bool All requests proceeded without I/O errors (since 1.24)
1293          * @since 1.23
1294          */
1295         abstract public function preloadFileStat( array $params );
1296
1297         /**
1298          * Lock the files at the given storage paths in the backend.
1299          * This will either lock all the files or none (on failure).
1300          *
1301          * Callers should consider using getScopedFileLocks() instead.
1302          *
1303          * @param array $paths Storage paths
1304          * @param int $type LockManager::LOCK_* constant
1305          * @param int $timeout Timeout in seconds (0 means non-blocking) (since 1.24)
1306          * @return StatusValue
1307          */
1308         final public function lockFiles( array $paths, $type, $timeout = 0 ) {
1309                 $paths = array_map( 'FileBackend::normalizeStoragePath', $paths );
1310
1311                 return $this->wrapStatus( $this->lockManager->lock( $paths, $type, $timeout ) );
1312         }
1313
1314         /**
1315          * Unlock the files at the given storage paths in the backend.
1316          *
1317          * @param array $paths Storage paths
1318          * @param int $type LockManager::LOCK_* constant
1319          * @return StatusValue
1320          */
1321         final public function unlockFiles( array $paths, $type ) {
1322                 $paths = array_map( 'FileBackend::normalizeStoragePath', $paths );
1323
1324                 return $this->wrapStatus( $this->lockManager->unlock( $paths, $type ) );
1325         }
1326
1327         /**
1328          * Lock the files at the given storage paths in the backend.
1329          * This will either lock all the files or none (on failure).
1330          * On failure, the StatusValue object will be updated with errors.
1331          *
1332          * Once the return value goes out scope, the locks will be released and
1333          * the StatusValue updated. Unlock fatals will not change the StatusValue "OK" value.
1334          *
1335          * @see ScopedLock::factory()
1336          *
1337          * @param array $paths List of storage paths or map of lock types to path lists
1338          * @param int|string $type LockManager::LOCK_* constant or "mixed"
1339          * @param StatusValue $status StatusValue to update on lock/unlock
1340          * @param int $timeout Timeout in seconds (0 means non-blocking) (since 1.24)
1341          * @return ScopedLock|null Returns null on failure
1342          */
1343         final public function getScopedFileLocks(
1344                 array $paths, $type, StatusValue $status, $timeout = 0
1345         ) {
1346                 if ( $type === 'mixed' ) {
1347                         foreach ( $paths as &$typePaths ) {
1348                                 $typePaths = array_map( 'FileBackend::normalizeStoragePath', $typePaths );
1349                         }
1350                 } else {
1351                         $paths = array_map( 'FileBackend::normalizeStoragePath', $paths );
1352                 }
1353
1354                 return ScopedLock::factory( $this->lockManager, $paths, $type, $status, $timeout );
1355         }
1356
1357         /**
1358          * Get an array of scoped locks needed for a batch of file operations.
1359          *
1360          * Normally, FileBackend::doOperations() handles locking, unless
1361          * the 'nonLocking' param is passed in. This function is useful if you
1362          * want the files to be locked for a broader scope than just when the
1363          * files are changing. For example, if you need to update DB metadata,
1364          * you may want to keep the files locked until finished.
1365          *
1366          * @see FileBackend::doOperations()
1367          *
1368          * @param array $ops List of file operations to FileBackend::doOperations()
1369          * @param StatusValue $status StatusValue to update on lock/unlock
1370          * @return ScopedLock|null
1371          * @since 1.20
1372          */
1373         abstract public function getScopedLocksForOps( array $ops, StatusValue $status );
1374
1375         /**
1376          * Get the root storage path of this backend.
1377          * All container paths are "subdirectories" of this path.
1378          *
1379          * @return string Storage path
1380          * @since 1.20
1381          */
1382         final public function getRootStoragePath() {
1383                 return "mwstore://{$this->name}";
1384         }
1385
1386         /**
1387          * Get the storage path for the given container for this backend
1388          *
1389          * @param string $container Container name
1390          * @return string Storage path
1391          * @since 1.21
1392          */
1393         final public function getContainerStoragePath( $container ) {
1394                 return $this->getRootStoragePath() . "/{$container}";
1395         }
1396
1397         /**
1398          * Get the file journal object for this backend
1399          *
1400          * @return FileJournal
1401          */
1402         final public function getJournal() {
1403                 return $this->fileJournal;
1404         }
1405
1406         /**
1407          * Convert FSFile 'src' paths to string paths (with an 'srcRef' field set to the FSFile)
1408          *
1409          * The 'srcRef' field keeps any TempFSFile objects in scope for the backend to have it
1410          * around as long it needs (which may vary greatly depending on configuration)
1411          *
1412          * @param array $ops File operation batch for FileBaclend::doOperations()
1413          * @return array File operation batch
1414          */
1415         protected function resolveFSFileObjects( array $ops ) {
1416                 foreach ( $ops as &$op ) {
1417                         $src = isset( $op['src'] ) ? $op['src'] : null;
1418                         if ( $src instanceof FSFile ) {
1419                                 $op['srcRef'] = $src;
1420                                 $op['src'] = $src->getPath();
1421                         }
1422                 }
1423                 unset( $op );
1424
1425                 return $ops;
1426         }
1427
1428         /**
1429          * Check if a given path is a "mwstore://" path.
1430          * This does not do any further validation or any existence checks.
1431          *
1432          * @param string $path
1433          * @return bool
1434          */
1435         final public static function isStoragePath( $path ) {
1436                 return ( strpos( $path, 'mwstore://' ) === 0 );
1437         }
1438
1439         /**
1440          * Split a storage path into a backend name, a container name,
1441          * and a relative file path. The relative path may be the empty string.
1442          * This does not do any path normalization or traversal checks.
1443          *
1444          * @param string $storagePath
1445          * @return array (backend, container, rel object) or (null, null, null)
1446          */
1447         final public static function splitStoragePath( $storagePath ) {
1448                 if ( self::isStoragePath( $storagePath ) ) {
1449                         // Remove the "mwstore://" prefix and split the path
1450                         $parts = explode( '/', substr( $storagePath, 10 ), 3 );
1451                         if ( count( $parts ) >= 2 && $parts[0] != '' && $parts[1] != '' ) {
1452                                 if ( count( $parts ) == 3 ) {
1453                                         return $parts; // e.g. "backend/container/path"
1454                                 } else {
1455                                         return [ $parts[0], $parts[1], '' ]; // e.g. "backend/container"
1456                                 }
1457                         }
1458                 }
1459
1460                 return [ null, null, null ];
1461         }
1462
1463         /**
1464          * Normalize a storage path by cleaning up directory separators.
1465          * Returns null if the path is not of the format of a valid storage path.
1466          *
1467          * @param string $storagePath
1468          * @return string|null
1469          */
1470         final public static function normalizeStoragePath( $storagePath ) {
1471                 list( $backend, $container, $relPath ) = self::splitStoragePath( $storagePath );
1472                 if ( $relPath !== null ) { // must be for this backend
1473                         $relPath = self::normalizeContainerPath( $relPath );
1474                         if ( $relPath !== null ) {
1475                                 return ( $relPath != '' )
1476                                         ? "mwstore://{$backend}/{$container}/{$relPath}"
1477                                         : "mwstore://{$backend}/{$container}";
1478                         }
1479                 }
1480
1481                 return null;
1482         }
1483
1484         /**
1485          * Get the parent storage directory of a storage path.
1486          * This returns a path like "mwstore://backend/container",
1487          * "mwstore://backend/container/...", or null if there is no parent.
1488          *
1489          * @param string $storagePath
1490          * @return string|null
1491          */
1492         final public static function parentStoragePath( $storagePath ) {
1493                 $storagePath = dirname( $storagePath );
1494                 list( , , $rel ) = self::splitStoragePath( $storagePath );
1495
1496                 return ( $rel === null ) ? null : $storagePath;
1497         }
1498
1499         /**
1500          * Get the final extension from a storage or FS path
1501          *
1502          * @param string $path
1503          * @param string $case One of (rawcase, uppercase, lowercase) (since 1.24)
1504          * @return string
1505          */
1506         final public static function extensionFromPath( $path, $case = 'lowercase' ) {
1507                 $i = strrpos( $path, '.' );
1508                 $ext = $i ? substr( $path, $i + 1 ) : '';
1509
1510                 if ( $case === 'lowercase' ) {
1511                         $ext = strtolower( $ext );
1512                 } elseif ( $case === 'uppercase' ) {
1513                         $ext = strtoupper( $ext );
1514                 }
1515
1516                 return $ext;
1517         }
1518
1519         /**
1520          * Check if a relative path has no directory traversals
1521          *
1522          * @param string $path
1523          * @return bool
1524          * @since 1.20
1525          */
1526         final public static function isPathTraversalFree( $path ) {
1527                 return ( self::normalizeContainerPath( $path ) !== null );
1528         }
1529
1530         /**
1531          * Build a Content-Disposition header value per RFC 6266.
1532          *
1533          * @param string $type One of (attachment, inline)
1534          * @param string $filename Suggested file name (should not contain slashes)
1535          * @throws FileBackendError
1536          * @return string
1537          * @since 1.20
1538          */
1539         final public static function makeContentDisposition( $type, $filename = '' ) {
1540                 $parts = [];
1541
1542                 $type = strtolower( $type );
1543                 if ( !in_array( $type, [ 'inline', 'attachment' ] ) ) {
1544                         throw new InvalidArgumentException( "Invalid Content-Disposition type '$type'." );
1545                 }
1546                 $parts[] = $type;
1547
1548                 if ( strlen( $filename ) ) {
1549                         $parts[] = "filename*=UTF-8''" . rawurlencode( basename( $filename ) );
1550                 }
1551
1552                 return implode( ';', $parts );
1553         }
1554
1555         /**
1556          * Validate and normalize a relative storage path.
1557          * Null is returned if the path involves directory traversal.
1558          * Traversal is insecure for FS backends and broken for others.
1559          *
1560          * This uses the same traversal protection as Title::secureAndSplit().
1561          *
1562          * @param string $path Storage path relative to a container
1563          * @return string|null
1564          */
1565         final protected static function normalizeContainerPath( $path ) {
1566                 // Normalize directory separators
1567                 $path = strtr( $path, '\\', '/' );
1568                 // Collapse any consecutive directory separators
1569                 $path = preg_replace( '![/]{2,}!', '/', $path );
1570                 // Remove any leading directory separator
1571                 $path = ltrim( $path, '/' );
1572                 // Use the same traversal protection as Title::secureAndSplit()
1573                 if ( strpos( $path, '.' ) !== false ) {
1574                         if (
1575                                 $path === '.' ||
1576                                 $path === '..' ||
1577                                 strpos( $path, './' ) === 0 ||
1578                                 strpos( $path, '../' ) === 0 ||
1579                                 strpos( $path, '/./' ) !== false ||
1580                                 strpos( $path, '/../' ) !== false
1581                         ) {
1582                                 return null;
1583                         }
1584                 }
1585
1586                 return $path;
1587         }
1588
1589         /**
1590          * Yields the result of the status wrapper callback on either:
1591          *   - StatusValue::newGood() if this method is called without parameters
1592          *   - StatusValue::newFatal() with all parameters to this method if passed in
1593          *
1594          * @param string $args,...
1595          * @return StatusValue
1596          */
1597         final protected function newStatus() {
1598                 $args = func_get_args();
1599                 if ( count( $args ) ) {
1600                         $sv = call_user_func_array( [ StatusValue::class, 'newFatal' ], $args );
1601                 } else {
1602                         $sv = StatusValue::newGood();
1603                 }
1604
1605                 return $this->wrapStatus( $sv );
1606         }
1607
1608         /**
1609          * @param StatusValue $sv
1610          * @return StatusValue Modified status or StatusValue subclass
1611          */
1612         final protected function wrapStatus( StatusValue $sv ) {
1613                 return $this->statusWrapper ? call_user_func( $this->statusWrapper, $sv ) : $sv;
1614         }
1615
1616         /**
1617          * @param string $section
1618          * @return ScopedCallback|null
1619          */
1620         protected function scopedProfileSection( $section ) {
1621                 if ( $this->profiler ) {
1622                         call_user_func( [ $this->profiler, 'profileIn' ], $section );
1623                         return new ScopedCallback( [ $this->profiler, 'profileOut' ], [ $section ] );
1624                 }
1625
1626                 return null;
1627         }
1628
1629         protected function resetOutputBuffer() {
1630                 while ( ob_get_status() ) {
1631                         if ( !ob_end_clean() ) {
1632                                 // Could not remove output buffer handler; abort now
1633                                 // to avoid getting in some kind of infinite loop.
1634                                 break;
1635                         }
1636                 }
1637         }
1638 }