FileBackendStore.php

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<?php
abstract class FileBackendStore extends FileBackend {
        protected $memCache;
        protected $cheapCache; // Map of paths to small (RAM/disk) cache items
        protected $expensiveCache; // Map of paths to large (RAM/disk) cache items

        protected $shardViaHashLevels = array(); // (container name => config array)

        protected $maxFileSize = 4294967296; // integer bytes (4GiB)

        const CACHE_TTL = 10; // integer; TTL in seconds for process cache entries

        public function __construct( array $config ) {
                parent::__construct( $config );
                $this->memCache = new EmptyBagOStuff(); // disabled by default
                $this->cheapCache = new ProcessCacheLRU( 300 );
                $this->expensiveCache = new ProcessCacheLRU( 5 );
        }

        final public function maxFileSizeInternal() {
                return $this->maxFileSize;
        }

        abstract public function isPathUsableInternal( $storagePath );

        final public function createInternal( array $params ) {
                wfProfileIn( __METHOD__ );
                wfProfileIn( __METHOD__ . '-' . $this->name );
                if ( strlen( $params['content'] ) > $this->maxFileSizeInternal() ) {
                        $status = Status::newFatal( 'backend-fail-maxsize',
                                $params['dst'], $this->maxFileSizeInternal() );
                } else {
                        $status = $this->doCreateInternal( $params );
                        $this->clearCache( array( $params['dst'] ) );
                        if ( !isset( $params['dstExists'] ) || $params['dstExists'] ) {
                                $this->deleteFileCache( $params['dst'] ); // persistent cache
                        }
                }
                wfProfileOut( __METHOD__ . '-' . $this->name );
                wfProfileOut( __METHOD__ );
                return $status;
        }

        abstract protected function doCreateInternal( array $params );

        final public function storeInternal( array $params ) {
                wfProfileIn( __METHOD__ );
                wfProfileIn( __METHOD__ . '-' . $this->name );
                if ( filesize( $params['src'] ) > $this->maxFileSizeInternal() ) {
                        $status = Status::newFatal( 'backend-fail-maxsize',
                                $params['dst'], $this->maxFileSizeInternal() );
                } else {
                        $status = $this->doStoreInternal( $params );
                        $this->clearCache( array( $params['dst'] ) );
                        if ( !isset( $params['dstExists'] ) || $params['dstExists'] ) {
                                $this->deleteFileCache( $params['dst'] ); // persistent cache
                        }
                }
                wfProfileOut( __METHOD__ . '-' . $this->name );
                wfProfileOut( __METHOD__ );
                return $status;
        }

        abstract protected function doStoreInternal( array $params );

        final public function copyInternal( array $params ) {
                wfProfileIn( __METHOD__ );
                wfProfileIn( __METHOD__ . '-' . $this->name );
                $status = $this->doCopyInternal( $params );
                $this->clearCache( array( $params['dst'] ) );
                if ( !isset( $params['dstExists'] ) || $params['dstExists'] ) {
                        $this->deleteFileCache( $params['dst'] ); // persistent cache
                }
                wfProfileOut( __METHOD__ . '-' . $this->name );
                wfProfileOut( __METHOD__ );
                return $status;
        }

        abstract protected function doCopyInternal( array $params );

        final public function deleteInternal( array $params ) {
                wfProfileIn( __METHOD__ );
                wfProfileIn( __METHOD__ . '-' . $this->name );
                $status = $this->doDeleteInternal( $params );
                $this->clearCache( array( $params['src'] ) );
                $this->deleteFileCache( $params['src'] ); // persistent cache
                wfProfileOut( __METHOD__ . '-' . $this->name );
                wfProfileOut( __METHOD__ );
                return $status;
        }

        abstract protected function doDeleteInternal( array $params );

        final public function moveInternal( array $params ) {
                wfProfileIn( __METHOD__ );
                wfProfileIn( __METHOD__ . '-' . $this->name );
                $status = $this->doMoveInternal( $params );
                $this->clearCache( array( $params['src'], $params['dst'] ) );
                $this->deleteFileCache( $params['src'] ); // persistent cache
                if ( !isset( $params['dstExists'] ) || $params['dstExists'] ) {
                        $this->deleteFileCache( $params['dst'] ); // persistent cache
                }
                wfProfileOut( __METHOD__ . '-' . $this->name );
                wfProfileOut( __METHOD__ );
                return $status;
        }

        protected function doMoveInternal( array $params ) {
                unset( $params['async'] ); // two steps, won't work here :)
                // Copy source to dest
                $status = $this->copyInternal( $params );
                if ( $status->isOK() ) {
                        // Delete source (only fails due to races or medium going down)
                        $status->merge( $this->deleteInternal( array( 'src' => $params['src'] ) ) );
                        $status->setResult( true, $status->value ); // ignore delete() errors
                }
                return $status;
        }

        final public function describeInternal( array $params ) {
                wfProfileIn( __METHOD__ );
                wfProfileIn( __METHOD__ . '-' . $this->name );
                $status = $this->doDescribeInternal( $params );
                $this->clearCache( array( $params['src'] ) );
                $this->deleteFileCache( $params['src'] ); // persistent cache
                wfProfileOut( __METHOD__ . '-' . $this->name );
                wfProfileOut( __METHOD__ );
                return $status;
        }

        protected function doDescribeInternal( array $params ) {
                return Status::newGood();
        }

        final public function nullInternal( array $params ) {
                return Status::newGood();
        }

        final public function concatenate( array $params ) {
                wfProfileIn( __METHOD__ );
                wfProfileIn( __METHOD__ . '-' . $this->name );
                $status = Status::newGood();

                // Try to lock the source files for the scope of this function
                $scopeLockS = $this->getScopedFileLocks( $params['srcs'], LockManager::LOCK_UW, $status );
                if ( $status->isOK() ) {
                        // Actually do the file concatenation...
                        $start_time = microtime( true );
                        $status->merge( $this->doConcatenate( $params ) );
                        $sec = microtime( true ) - $start_time;
                        if ( !$status->isOK() ) {
                                wfDebugLog( 'FileOperation', get_class( $this ) . " failed to concatenate " .
                                        count( $params['srcs'] ) . " file(s) [$sec sec]" );
                        }
                }

                wfProfileOut( __METHOD__ . '-' . $this->name );
                wfProfileOut( __METHOD__ );
                return $status;
        }

        protected function doConcatenate( array $params ) {
                $status = Status::newGood();
                $tmpPath = $params['dst']; // convenience
                unset( $params['latest'] ); // sanity

                // Check that the specified temp file is valid...
                wfSuppressWarnings();
                $ok = ( is_file( $tmpPath ) && filesize( $tmpPath ) == 0 );
                wfRestoreWarnings();
                if ( !$ok ) { // not present or not empty
                        $status->fatal( 'backend-fail-opentemp', $tmpPath );
                        return $status;
                }

                // Get local FS versions of the chunks needed for the concatenation...
                $fsFiles = $this->getLocalReferenceMulti( $params );
                foreach ( $fsFiles as $path => &$fsFile ) {
                        if ( !$fsFile ) { // chunk failed to download?
                                $fsFile = $this->getLocalReference( array( 'src' => $path ) );
                                if ( !$fsFile ) { // retry failed?
                                        $status->fatal( 'backend-fail-read', $path );
                                        return $status;
                                }
                        }
                }
                unset( $fsFile ); // unset reference so we can reuse $fsFile

                // Get a handle for the destination temp file
                $tmpHandle = fopen( $tmpPath, 'ab' );
                if ( $tmpHandle === false ) {
                        $status->fatal( 'backend-fail-opentemp', $tmpPath );
                        return $status;
                }

                // Build up the temp file using the source chunks (in order)...
                foreach ( $fsFiles as $virtualSource => $fsFile ) {
                        // Get a handle to the local FS version
                        $sourceHandle = fopen( $fsFile->getPath(), 'rb' );
                        if ( $sourceHandle === false ) {
                                fclose( $tmpHandle );
                                $status->fatal( 'backend-fail-read', $virtualSource );
                                return $status;
                        }
                        // Append chunk to file (pass chunk size to avoid magic quotes)
                        if ( !stream_copy_to_stream( $sourceHandle, $tmpHandle ) ) {
                                fclose( $sourceHandle );
                                fclose( $tmpHandle );
                                $status->fatal( 'backend-fail-writetemp', $tmpPath );
                                return $status;
                        }
                        fclose( $sourceHandle );
                }
                if ( !fclose( $tmpHandle ) ) {
                        $status->fatal( 'backend-fail-closetemp', $tmpPath );
                        return $status;
                }

                clearstatcache(); // temp file changed

                return $status;
        }

        final protected function doPrepare( array $params ) {
                wfProfileIn( __METHOD__ );
                wfProfileIn( __METHOD__ . '-' . $this->name );

                $status = Status::newGood();
                list( $fullCont, $dir, $shard ) = $this->resolveStoragePath( $params['dir'] );
                if ( $dir === null ) {
                        $status->fatal( 'backend-fail-invalidpath', $params['dir'] );
                        wfProfileOut( __METHOD__ . '-' . $this->name );
                        wfProfileOut( __METHOD__ );
                        return $status; // invalid storage path
                }

                if ( $shard !== null ) { // confined to a single container/shard
                        $status->merge( $this->doPrepareInternal( $fullCont, $dir, $params ) );
                } else { // directory is on several shards
                        wfDebug( __METHOD__ . ": iterating over all container shards.\n" );
                        list( , $shortCont, ) = self::splitStoragePath( $params['dir'] );
                        foreach ( $this->getContainerSuffixes( $shortCont ) as $suffix ) {
                                $status->merge( $this->doPrepareInternal( "{$fullCont}{$suffix}", $dir, $params ) );
                        }
                }

                wfProfileOut( __METHOD__ . '-' . $this->name );
                wfProfileOut( __METHOD__ );
                return $status;
        }

        protected function doPrepareInternal( $container, $dir, array $params ) {
                return Status::newGood();
        }

        final protected function doSecure( array $params ) {
                wfProfileIn( __METHOD__ );
                wfProfileIn( __METHOD__ . '-' . $this->name );
                $status = Status::newGood();

                list( $fullCont, $dir, $shard ) = $this->resolveStoragePath( $params['dir'] );
                if ( $dir === null ) {
                        $status->fatal( 'backend-fail-invalidpath', $params['dir'] );
                        wfProfileOut( __METHOD__ . '-' . $this->name );
                        wfProfileOut( __METHOD__ );
                        return $status; // invalid storage path
                }

                if ( $shard !== null ) { // confined to a single container/shard
                        $status->merge( $this->doSecureInternal( $fullCont, $dir, $params ) );
                } else { // directory is on several shards
                        wfDebug( __METHOD__ . ": iterating over all container shards.\n" );
                        list( , $shortCont, ) = self::splitStoragePath( $params['dir'] );
                        foreach ( $this->getContainerSuffixes( $shortCont ) as $suffix ) {
                                $status->merge( $this->doSecureInternal( "{$fullCont}{$suffix}", $dir, $params ) );
                        }
                }

                wfProfileOut( __METHOD__ . '-' . $this->name );
                wfProfileOut( __METHOD__ );
                return $status;
        }

        protected function doSecureInternal( $container, $dir, array $params ) {
                return Status::newGood();
        }

        final protected function doPublish( array $params ) {
                wfProfileIn( __METHOD__ );
                wfProfileIn( __METHOD__ . '-' . $this->name );
                $status = Status::newGood();

                list( $fullCont, $dir, $shard ) = $this->resolveStoragePath( $params['dir'] );
                if ( $dir === null ) {
                        $status->fatal( 'backend-fail-invalidpath', $params['dir'] );
                        wfProfileOut( __METHOD__ . '-' . $this->name );
                        wfProfileOut( __METHOD__ );
                        return $status; // invalid storage path
                }

                if ( $shard !== null ) { // confined to a single container/shard
                        $status->merge( $this->doPublishInternal( $fullCont, $dir, $params ) );
                } else { // directory is on several shards
                        wfDebug( __METHOD__ . ": iterating over all container shards.\n" );
                        list( , $shortCont, ) = self::splitStoragePath( $params['dir'] );
                        foreach ( $this->getContainerSuffixes( $shortCont ) as $suffix ) {
                                $status->merge( $this->doPublishInternal( "{$fullCont}{$suffix}", $dir, $params ) );
                        }
                }

                wfProfileOut( __METHOD__ . '-' . $this->name );
                wfProfileOut( __METHOD__ );
                return $status;
        }

        protected function doPublishInternal( $container, $dir, array $params ) {
                return Status::newGood();
        }

        final protected function doClean( array $params ) {
                wfProfileIn( __METHOD__ );
                wfProfileIn( __METHOD__ . '-' . $this->name );
                $status = Status::newGood();

                // Recursive: first delete all empty subdirs recursively
                if ( !empty( $params['recursive'] ) && !$this->directoriesAreVirtual() ) {
                        $subDirsRel = $this->getTopDirectoryList( array( 'dir' => $params['dir'] ) );
                        if ( $subDirsRel !== null ) { // no errors
                                foreach ( $subDirsRel as $subDirRel ) {
                                        $subDir = $params['dir'] . "/{$subDirRel}"; // full path
                                        $status->merge( $this->doClean( array( 'dir' => $subDir ) + $params ) );
                                }
                                unset( $subDirsRel ); // free directory for rmdir() on Windows (for FS backends)
                        }
                }

                list( $fullCont, $dir, $shard ) = $this->resolveStoragePath( $params['dir'] );
                if ( $dir === null ) {
                        $status->fatal( 'backend-fail-invalidpath', $params['dir'] );
                        wfProfileOut( __METHOD__ . '-' . $this->name );
                        wfProfileOut( __METHOD__ );
                        return $status; // invalid storage path
                }

                // Attempt to lock this directory...
                $filesLockEx = array( $params['dir'] );
                $scopedLockE = $this->getScopedFileLocks( $filesLockEx, LockManager::LOCK_EX, $status );
                if ( !$status->isOK() ) {
                        wfProfileOut( __METHOD__ . '-' . $this->name );
                        wfProfileOut( __METHOD__ );
                        return $status; // abort
                }

                if ( $shard !== null ) { // confined to a single container/shard
                        $status->merge( $this->doCleanInternal( $fullCont, $dir, $params ) );
                        $this->deleteContainerCache( $fullCont ); // purge cache
                } else { // directory is on several shards
                        wfDebug( __METHOD__ . ": iterating over all container shards.\n" );
                        list( , $shortCont, ) = self::splitStoragePath( $params['dir'] );
                        foreach ( $this->getContainerSuffixes( $shortCont ) as $suffix ) {
                                $status->merge( $this->doCleanInternal( "{$fullCont}{$suffix}", $dir, $params ) );
                                $this->deleteContainerCache( "{$fullCont}{$suffix}" ); // purge cache
                        }
                }

                wfProfileOut( __METHOD__ . '-' . $this->name );
                wfProfileOut( __METHOD__ );
                return $status;
        }

        protected function doCleanInternal( $container, $dir, array $params ) {
                return Status::newGood();
        }

        final public function fileExists( array $params ) {
                wfProfileIn( __METHOD__ );
                wfProfileIn( __METHOD__ . '-' . $this->name );
                $stat = $this->getFileStat( $params );
                wfProfileOut( __METHOD__ . '-' . $this->name );
                wfProfileOut( __METHOD__ );
                return ( $stat === null ) ? null : (bool)$stat; // null => failure
        }

        final public function getFileTimestamp( array $params ) {
                wfProfileIn( __METHOD__ );
                wfProfileIn( __METHOD__ . '-' . $this->name );
                $stat = $this->getFileStat( $params );
                wfProfileOut( __METHOD__ . '-' . $this->name );
                wfProfileOut( __METHOD__ );
                return $stat ? $stat['mtime'] : false;
        }

        final public function getFileSize( array $params ) {
                wfProfileIn( __METHOD__ );
                wfProfileIn( __METHOD__ . '-' . $this->name );
                $stat = $this->getFileStat( $params );
                wfProfileOut( __METHOD__ . '-' . $this->name );
                wfProfileOut( __METHOD__ );
                return $stat ? $stat['size'] : false;
        }

        final public function getFileStat( array $params ) {
                $path = self::normalizeStoragePath( $params['src'] );
                if ( $path === null ) {
                        return false; // invalid storage path
                }
                wfProfileIn( __METHOD__ );
                wfProfileIn( __METHOD__ . '-' . $this->name );
                $latest = !empty( $params['latest'] ); // use latest data?
                if ( !$this->cheapCache->has( $path, 'stat', self::CACHE_TTL ) ) {
                        $this->primeFileCache( array( $path ) ); // check persistent cache
                }
                if ( $this->cheapCache->has( $path, 'stat', self::CACHE_TTL ) ) {
                        $stat = $this->cheapCache->get( $path, 'stat' );
                        // If we want the latest data, check that this cached
                        // value was in fact fetched with the latest available data.
                        if ( is_array( $stat ) ) {
                                if ( !$latest || $stat['latest'] ) {
                                        wfProfileOut( __METHOD__ . '-' . $this->name );
                                        wfProfileOut( __METHOD__ );
                                        return $stat;
                                }
                        } elseif ( in_array( $stat, array( 'NOT_EXIST', 'NOT_EXIST_LATEST' ) ) ) {
                                if ( !$latest || $stat === 'NOT_EXIST_LATEST' ) {
                                        wfProfileOut( __METHOD__ . '-' . $this->name );
                                        wfProfileOut( __METHOD__ );
                                        return false;
                                }
                        }
                }
                wfProfileIn( __METHOD__ . '-miss' );
                wfProfileIn( __METHOD__ . '-miss-' . $this->name );
                $stat = $this->doGetFileStat( $params );
                wfProfileOut( __METHOD__ . '-miss-' . $this->name );
                wfProfileOut( __METHOD__ . '-miss' );
                if ( is_array( $stat ) ) { // file exists
                        $stat['latest'] = $latest;
                        $this->cheapCache->set( $path, 'stat', $stat );
                        $this->setFileCache( $path, $stat ); // update persistent cache
                        if ( isset( $stat['sha1'] ) ) { // some backends store SHA-1 as metadata
                                $this->cheapCache->set( $path, 'sha1',
                                        array( 'hash' => $stat['sha1'], 'latest' => $latest ) );
                        }
                } elseif ( $stat === false ) { // file does not exist
                        $this->cheapCache->set( $path, 'stat', $latest ? 'NOT_EXIST_LATEST' : 'NOT_EXIST' );
                        wfDebug( __METHOD__ . ": File $path does not exist.\n" );
                } else { // an error occurred
                        wfDebug( __METHOD__ . ": Could not stat file $path.\n" );
                }
                wfProfileOut( __METHOD__ . '-' . $this->name );
                wfProfileOut( __METHOD__ );
                return $stat;
        }

        abstract protected function doGetFileStat( array $params );

        public function getFileContentsMulti( array $params ) {
                wfProfileIn( __METHOD__ );
                wfProfileIn( __METHOD__ . '-' . $this->name );

                $params = $this->setConcurrencyFlags( $params );
                $contents = $this->doGetFileContentsMulti( $params );

                wfProfileOut( __METHOD__ . '-' . $this->name );
                wfProfileOut( __METHOD__ );
                return $contents;
        }

        protected function doGetFileContentsMulti( array $params ) {
                $contents = array();
                foreach ( $this->doGetLocalReferenceMulti( $params ) as $path => $fsFile ) {
                        wfSuppressWarnings();
                        $contents[$path] = $fsFile ? file_get_contents( $fsFile->getPath() ) : false;
                        wfRestoreWarnings();
                }
                return $contents;
        }

        final public function getFileSha1Base36( array $params ) {
                $path = self::normalizeStoragePath( $params['src'] );
                if ( $path === null ) {
                        return false; // invalid storage path
                }
                wfProfileIn( __METHOD__ );
                wfProfileIn( __METHOD__ . '-' . $this->name );
                $latest = !empty( $params['latest'] ); // use latest data?
                if ( $this->cheapCache->has( $path, 'sha1', self::CACHE_TTL ) ) {
                        $stat = $this->cheapCache->get( $path, 'sha1' );
                        // If we want the latest data, check that this cached
                        // value was in fact fetched with the latest available data.
                        if ( !$latest || $stat['latest'] ) {
                                wfProfileOut( __METHOD__ . '-' . $this->name );
                                wfProfileOut( __METHOD__ );
                                return $stat['hash'];
                        }
                }
                wfProfileIn( __METHOD__ . '-miss' );
                wfProfileIn( __METHOD__ . '-miss-' . $this->name );
                $hash = $this->doGetFileSha1Base36( $params );
                wfProfileOut( __METHOD__ . '-miss-' . $this->name );
                wfProfileOut( __METHOD__ . '-miss' );
                $this->cheapCache->set( $path, 'sha1', array( 'hash' => $hash, 'latest' => $latest ) );
                wfProfileOut( __METHOD__ . '-' . $this->name );
                wfProfileOut( __METHOD__ );
                return $hash;
        }

        protected function doGetFileSha1Base36( array $params ) {
                $fsFile = $this->getLocalReference( $params );
                if ( !$fsFile ) {
                        return false;
                } else {
                        return $fsFile->getSha1Base36();
                }
        }

        final public function getFileProps( array $params ) {
                wfProfileIn( __METHOD__ );
                wfProfileIn( __METHOD__ . '-' . $this->name );
                $fsFile = $this->getLocalReference( $params );
                $props = $fsFile ? $fsFile->getProps() : FSFile::placeholderProps();
                wfProfileOut( __METHOD__ . '-' . $this->name );
                wfProfileOut( __METHOD__ );
                return $props;
        }

        final public function getLocalReferenceMulti( array $params ) {
                wfProfileIn( __METHOD__ );
                wfProfileIn( __METHOD__ . '-' . $this->name );

                $params = $this->setConcurrencyFlags( $params );

                $fsFiles = array(); // (path => FSFile)
                $latest = !empty( $params['latest'] ); // use latest data?
                // Reuse any files already in process cache...
                foreach ( $params['srcs'] as $src ) {
                        $path = self::normalizeStoragePath( $src );
                        if ( $path === null ) {
                                $fsFiles[$src] = null; // invalid storage path
                        } elseif ( $this->expensiveCache->has( $path, 'localRef' ) ) {
                                $val = $this->expensiveCache->get( $path, 'localRef' );
                                // If we want the latest data, check that this cached
                                // value was in fact fetched with the latest available data.
                                if ( !$latest || $val['latest'] ) {
                                        $fsFiles[$src] = $val['object'];
                                }
                        }
                }
                // Fetch local references of any remaning files...
                $params['srcs'] = array_diff( $params['srcs'], array_keys( $fsFiles ) );
                foreach ( $this->doGetLocalReferenceMulti( $params ) as $path => $fsFile ) {
                        $fsFiles[$path] = $fsFile;
                        if ( $fsFile ) { // update the process cache...
                                $this->expensiveCache->set( $path, 'localRef',
                                        array( 'object' => $fsFile, 'latest' => $latest ) );
                        }
                }

                wfProfileOut( __METHOD__ . '-' . $this->name );
                wfProfileOut( __METHOD__ );
                return $fsFiles;
        }

        protected function doGetLocalReferenceMulti( array $params ) {
                return $this->doGetLocalCopyMulti( $params );
        }

        final public function getLocalCopyMulti( array $params ) {
                wfProfileIn( __METHOD__ );
                wfProfileIn( __METHOD__ . '-' . $this->name );

                $params = $this->setConcurrencyFlags( $params );
                $tmpFiles = $this->doGetLocalCopyMulti( $params );

                wfProfileOut( __METHOD__ . '-' . $this->name );
                wfProfileOut( __METHOD__ );
                return $tmpFiles;
        }

        abstract protected function doGetLocalCopyMulti( array $params );

        public function getFileHttpUrl( array $params ) {
                return null; // not supported
        }

        final public function streamFile( array $params ) {
                wfProfileIn( __METHOD__ );
                wfProfileIn( __METHOD__ . '-' . $this->name );
                $status = Status::newGood();

                $info = $this->getFileStat( $params );
                if ( !$info ) { // let StreamFile handle the 404
                        $status->fatal( 'backend-fail-notexists', $params['src'] );
                }

                // Set output buffer and HTTP headers for stream
                $extraHeaders = isset( $params['headers'] ) ? $params['headers'] : array();
                $res = StreamFile::prepareForStream( $params['src'], $info, $extraHeaders );
                if ( $res == StreamFile::NOT_MODIFIED ) {
                        // do nothing; client cache is up to date
                } elseif ( $res == StreamFile::READY_STREAM ) {
                        wfProfileIn( __METHOD__ . '-send' );
                        wfProfileIn( __METHOD__ . '-send-' . $this->name );
                        $status = $this->doStreamFile( $params );
                        wfProfileOut( __METHOD__ . '-send-' . $this->name );
                        wfProfileOut( __METHOD__ . '-send' );
                        if ( !$status->isOK() ) {
                                // Per bug 41113, nasty things can happen if bad cache entries get
                                // stuck in cache. It's also possible that this error can come up
                                // with simple race conditions. Clear out the stat cache to be safe.
                                $this->clearCache( array( $params['src'] ) );
                                $this->deleteFileCache( $params['src'] );
                                trigger_error( "Bad stat cache or race condition for file {$params['src']}." );
                        }
                } else {
                        $status->fatal( 'backend-fail-stream', $params['src'] );
                }

                wfProfileOut( __METHOD__ . '-' . $this->name );
                wfProfileOut( __METHOD__ );
                return $status;
        }

        protected function doStreamFile( array $params ) {
                $status = Status::newGood();

                $fsFile = $this->getLocalReference( $params );
                if ( !$fsFile ) {
                        $status->fatal( 'backend-fail-stream', $params['src'] );
                } elseif ( !readfile( $fsFile->getPath() ) ) {
                        $status->fatal( 'backend-fail-stream', $params['src'] );
                }

                return $status;
        }

        final public function directoryExists( array $params ) {
                list( $fullCont, $dir, $shard ) = $this->resolveStoragePath( $params['dir'] );
                if ( $dir === null ) {
                        return false; // invalid storage path
                }
                if ( $shard !== null ) { // confined to a single container/shard
                        return $this->doDirectoryExists( $fullCont, $dir, $params );
                } else { // directory is on several shards
                        wfDebug( __METHOD__ . ": iterating over all container shards.\n" );
                        list( , $shortCont, ) = self::splitStoragePath( $params['dir'] );
                        $res = false; // response
                        foreach ( $this->getContainerSuffixes( $shortCont ) as $suffix ) {
                                $exists = $this->doDirectoryExists( "{$fullCont}{$suffix}", $dir, $params );
                                if ( $exists ) {
                                        $res = true;
                                        break; // found one!
                                } elseif ( $exists === null ) { // error?
                                        $res = null; // if we don't find anything, it is indeterminate
                                }
                        }
                        return $res;
                }
        }

        abstract protected function doDirectoryExists( $container, $dir, array $params );

        final public function getDirectoryList( array $params ) {
                list( $fullCont, $dir, $shard ) = $this->resolveStoragePath( $params['dir'] );
                if ( $dir === null ) { // invalid storage path
                        return null;
                }
                if ( $shard !== null ) {
                        // File listing is confined to a single container/shard
                        return $this->getDirectoryListInternal( $fullCont, $dir, $params );
                } else {
                        wfDebug( __METHOD__ . ": iterating over all container shards.\n" );
                        // File listing spans multiple containers/shards
                        list( , $shortCont, ) = self::splitStoragePath( $params['dir'] );
                        return new FileBackendStoreShardDirIterator( $this,
                                $fullCont, $dir, $this->getContainerSuffixes( $shortCont ), $params );
                }
        }

        abstract public function getDirectoryListInternal( $container, $dir, array $params );

        final public function getFileList( array $params ) {
                list( $fullCont, $dir, $shard ) = $this->resolveStoragePath( $params['dir'] );
                if ( $dir === null ) { // invalid storage path
                        return null;
                }
                if ( $shard !== null ) {
                        // File listing is confined to a single container/shard
                        return $this->getFileListInternal( $fullCont, $dir, $params );
                } else {
                        wfDebug( __METHOD__ . ": iterating over all container shards.\n" );
                        // File listing spans multiple containers/shards
                        list( , $shortCont, ) = self::splitStoragePath( $params['dir'] );
                        return new FileBackendStoreShardFileIterator( $this,
                                $fullCont, $dir, $this->getContainerSuffixes( $shortCont ), $params );
                }
        }

        abstract public function getFileListInternal( $container, $dir, array $params );

        final public function getOperationsInternal( array $ops ) {
                $supportedOps = array(
                        'store'    => 'StoreFileOp',
                        'copy'     => 'CopyFileOp',
                        'move'     => 'MoveFileOp',
                        'delete'   => 'DeleteFileOp',
                        'create'   => 'CreateFileOp',
                        'describe' => 'DescribeFileOp',
                        'null'     => 'NullFileOp'
                );

                $performOps = array(); // array of FileOp objects
                // Build up ordered array of FileOps...
                foreach ( $ops as $operation ) {
                        $opName = $operation['op'];
                        if ( isset( $supportedOps[$opName] ) ) {
                                $class = $supportedOps[$opName];
                                // Get params for this operation
                                $params = $operation;
                                // Append the FileOp class
                                $performOps[] = new $class( $this, $params );
                        } else {
                                throw new MWException( "Operation '$opName' is not supported." );
                        }
                }

                return $performOps;
        }

        final public function getPathsToLockForOpsInternal( array $performOps ) {
                // Build up a list of files to lock...
                $paths = array( 'sh' => array(), 'ex' => array() );
                foreach ( $performOps as $fileOp ) {
                        $paths['sh'] = array_merge( $paths['sh'], $fileOp->storagePathsRead() );
                        $paths['ex'] = array_merge( $paths['ex'], $fileOp->storagePathsChanged() );
                }
                // Optimization: if doing an EX lock anyway, don't also set an SH one
                $paths['sh'] = array_diff( $paths['sh'], $paths['ex'] );
                // Get a shared lock on the parent directory of each path changed
                $paths['sh'] = array_merge( $paths['sh'], array_map( 'dirname', $paths['ex'] ) );

                return $paths;
        }

        public function getScopedLocksForOps( array $ops, Status $status ) {
                $paths = $this->getPathsToLockForOpsInternal( $this->getOperationsInternal( $ops ) );
                return array(
                        $this->getScopedFileLocks( $paths['sh'], LockManager::LOCK_UW, $status ),
                        $this->getScopedFileLocks( $paths['ex'], LockManager::LOCK_EX, $status )
                );
        }

        final protected function doOperationsInternal( array $ops, array $opts ) {
                wfProfileIn( __METHOD__ );
                wfProfileIn( __METHOD__ . '-' . $this->name );
                $status = Status::newGood();

                // Fix up custom header name/value pairs...
                $ops = array_map( array( $this, 'stripInvalidHeadersFromOp' ), $ops );

                // Build up a list of FileOps...
                $performOps = $this->getOperationsInternal( $ops );

                // Acquire any locks as needed...
                if ( empty( $opts['nonLocking'] ) ) {
                        // Build up a list of files to lock...
                        $paths = $this->getPathsToLockForOpsInternal( $performOps );
                        // Try to lock those files for the scope of this function...
                        $scopeLockS = $this->getScopedFileLocks( $paths['sh'], LockManager::LOCK_UW, $status );
                        $scopeLockE = $this->getScopedFileLocks( $paths['ex'], LockManager::LOCK_EX, $status );
                        if ( !$status->isOK() ) {
                                wfProfileOut( __METHOD__ . '-' . $this->name );
                                wfProfileOut( __METHOD__ );
                                return $status; // abort
                        }
                }

                // Clear any file cache entries (after locks acquired)
                if ( empty( $opts['preserveCache'] ) ) {
                        $this->clearCache();
                }

                // Load from the persistent file and container caches
                $this->primeFileCache( $performOps );
                $this->primeContainerCache( $performOps );

                // Actually attempt the operation batch...
                $opts = $this->setConcurrencyFlags( $opts );
                $subStatus = FileOpBatch::attempt( $performOps, $opts, $this->fileJournal );

                // Merge errors into status fields
                $status->merge( $subStatus );
                $status->success = $subStatus->success; // not done in merge()

                wfProfileOut( __METHOD__ . '-' . $this->name );
                wfProfileOut( __METHOD__ );
                return $status;
        }

        final protected function doQuickOperationsInternal( array $ops ) {
                wfProfileIn( __METHOD__ );
                wfProfileIn( __METHOD__ . '-' . $this->name );
                $status = Status::newGood();

                // Fix up custom header name/value pairs...
                $ops = array_map( array( $this, 'stripInvalidHeadersFromOp' ), $ops );

                // Clear any file cache entries
                $this->clearCache();

                $supportedOps = array( 'create', 'store', 'copy', 'move', 'delete', 'null' );
                $async = ( $this->parallelize === 'implicit' );
                $maxConcurrency = $this->concurrency; // throttle

                $statuses = array(); // array of (index => Status)
                $fileOpHandles = array(); // list of (index => handle) arrays
                $curFileOpHandles = array(); // current handle batch
                // Perform the sync-only ops and build up op handles for the async ops...
                foreach ( $ops as $index => $params ) {
                        if ( !in_array( $params['op'], $supportedOps ) ) {
                                wfProfileOut( __METHOD__ . '-' . $this->name );
                                wfProfileOut( __METHOD__ );
                                throw new MWException( "Operation '{$params['op']}' is not supported." );
                        }
                        $method = $params['op'] . 'Internal'; // e.g. "storeInternal"
                        $subStatus = $this->$method( array( 'async' => $async ) + $params );
                        if ( $subStatus->value instanceof FileBackendStoreOpHandle ) { // async
                                if ( count( $curFileOpHandles ) >= $maxConcurrency ) {
                                        $fileOpHandles[] = $curFileOpHandles; // push this batch
                                        $curFileOpHandles = array();
                                }
                                $curFileOpHandles[$index] = $subStatus->value; // keep index
                        } else { // error or completed
                                $statuses[$index] = $subStatus; // keep index
                        }
                }
                if ( count( $curFileOpHandles ) ) {
                        $fileOpHandles[] = $curFileOpHandles; // last batch
                }
                // Do all the async ops that can be done concurrently...
                foreach ( $fileOpHandles as $fileHandleBatch ) {
                        $statuses = $statuses + $this->executeOpHandlesInternal( $fileHandleBatch );
                }
                // Marshall and merge all the responses...
                foreach ( $statuses as $index => $subStatus ) {
                        $status->merge( $subStatus );
                        if ( $subStatus->isOK() ) {
                                $status->success[$index] = true;
                                ++$status->successCount;
                        } else {
                                $status->success[$index] = false;
                                ++$status->failCount;
                        }
                }

                wfProfileOut( __METHOD__ . '-' . $this->name );
                wfProfileOut( __METHOD__ );
                return $status;
        }

        final public function executeOpHandlesInternal( array $fileOpHandles ) {
                wfProfileIn( __METHOD__ );
                wfProfileIn( __METHOD__ . '-' . $this->name );
                foreach ( $fileOpHandles as $fileOpHandle ) {
                        if ( !( $fileOpHandle instanceof FileBackendStoreOpHandle ) ) {
                                throw new MWException( "Given a non-FileBackendStoreOpHandle object." );
                        } elseif ( $fileOpHandle->backend->getName() !== $this->getName() ) {
                                throw new MWException( "Given a FileBackendStoreOpHandle for the wrong backend." );
                        }
                }
                $res = $this->doExecuteOpHandlesInternal( $fileOpHandles );
                foreach ( $fileOpHandles as $fileOpHandle ) {
                        $fileOpHandle->closeResources();
                }
                wfProfileOut( __METHOD__ . '-' . $this->name );
                wfProfileOut( __METHOD__ );
                return $res;
        }

        protected function doExecuteOpHandlesInternal( array $fileOpHandles ) {
                foreach ( $fileOpHandles as $fileOpHandle ) { // OK if empty
                        throw new MWException( "This backend supports no asynchronous operations." );
                }
                return array();
        }

        protected function stripInvalidHeadersFromOp( array $op ) {
                if ( isset( $op['headers'] ) ) {
                        foreach ( $op['headers'] as $name => $value ) {
                                if ( strlen( $name ) > 255 || strlen( $value ) > 255 ) {
                                        trigger_error( "Header '$name: $value' is too long." );
                                        unset( $op['headers'][$name] );
                                } elseif ( !strlen( $value ) ) {
                                        $op['headers'][$name] = ''; // null/false => ""
                                }
                        }
                }
                return $op;
        }

        final public function preloadCache( array $paths ) {
                $fullConts = array(); // full container names
                foreach ( $paths as $path ) {
                        list( $fullCont, , ) = $this->resolveStoragePath( $path );
                        $fullConts[] = $fullCont;
                }
                // Load from the persistent file and container caches
                $this->primeContainerCache( $fullConts );
                $this->primeFileCache( $paths );
        }

        final public function clearCache( array $paths = null ) {
                if ( is_array( $paths ) ) {
                        $paths = array_map( 'FileBackend::normalizeStoragePath', $paths );
                        $paths = array_filter( $paths, 'strlen' ); // remove nulls
                }
                if ( $paths === null ) {
                        $this->cheapCache->clear();
                        $this->expensiveCache->clear();
                } else {
                        foreach ( $paths as $path ) {
                                $this->cheapCache->clear( $path );
                                $this->expensiveCache->clear( $path );
                        }
                }
                $this->doClearCache( $paths );
        }

        protected function doClearCache( array $paths = null ) {}

        abstract protected function directoriesAreVirtual();

        final protected static function isValidContainerName( $container ) {
                // This accounts for Swift and S3 restrictions while leaving room
                // for things like '.xxx' (hex shard chars) or '.seg' (segments).
                // This disallows directory separators or traversal characters.
                // Note that matching strings URL encode to the same string;
                // in Swift, the length restriction is *after* URL encoding.
                return preg_match( '/^[a-z0-9][a-z0-9-_]{0,199}$/i', $container );
        }

        final protected function resolveStoragePath( $storagePath ) {
                list( $backend, $container, $relPath ) = self::splitStoragePath( $storagePath );
                if ( $backend === $this->name ) { // must be for this backend
                        $relPath = self::normalizeContainerPath( $relPath );
                        if ( $relPath !== null ) {
                                // Get shard for the normalized path if this container is sharded
                                $cShard = $this->getContainerShard( $container, $relPath );
                                // Validate and sanitize the relative path (backend-specific)
                                $relPath = $this->resolveContainerPath( $container, $relPath );
                                if ( $relPath !== null ) {
                                        // Prepend any wiki ID prefix to the container name
                                        $container = $this->fullContainerName( $container );
                                        if ( self::isValidContainerName( $container ) ) {
                                                // Validate and sanitize the container name (backend-specific)
                                                $container = $this->resolveContainerName( "{$container}{$cShard}" );
                                                if ( $container !== null ) {
                                                        return array( $container, $relPath, $cShard );
                                                }
                                        }
                                }
                        }
                }
                return array( null, null, null );
        }

        final protected function resolveStoragePathReal( $storagePath ) {
                list( $container, $relPath, $cShard ) = $this->resolveStoragePath( $storagePath );
                if ( $cShard !== null ) {
                        return array( $container, $relPath );
                }
                return array( null, null );
        }

        final protected function getContainerShard( $container, $relPath ) {
                list( $levels, $base, $repeat ) = $this->getContainerHashLevels( $container );
                if ( $levels == 1 || $levels == 2 ) {
                        // Hash characters are either base 16 or 36
                        $char = ( $base == 36 ) ? '[0-9a-z]' : '[0-9a-f]';
                        // Get a regex that represents the shard portion of paths.
                        // The concatenation of the captures gives us the shard.
                        if ( $levels === 1 ) { // 16 or 36 shards per container
                                $hashDirRegex = '(' . $char . ')';
                        } else { // 256 or 1296 shards per container
                                if ( $repeat ) { // verbose hash dir format (e.g. "a/ab/abc")
                                        $hashDirRegex = $char . '/(' . $char . '{2})';
                                } else { // short hash dir format (e.g. "a/b/c")
                                        $hashDirRegex = '(' . $char . ')/(' . $char . ')';
                                }
                        }
                        // Allow certain directories to be above the hash dirs so as
                        // to work with FileRepo (e.g. "archive/a/ab" or "temp/a/ab").
                        // They must be 2+ chars to avoid any hash directory ambiguity.
                        $m = array();
                        if ( preg_match( "!^(?:[^/]{2,}/)*$hashDirRegex(?:/|$)!", $relPath, $m ) ) {
                                return '.' . implode( '', array_slice( $m, 1 ) );
                        }
                        return null; // failed to match
                }
                return ''; // no sharding
        }

        final public function isSingleShardPathInternal( $storagePath ) {
                list( , , $shard ) = $this->resolveStoragePath( $storagePath );
                return ( $shard !== null );
        }

        final protected function getContainerHashLevels( $container ) {
                if ( isset( $this->shardViaHashLevels[$container] ) ) {
                        $config = $this->shardViaHashLevels[$container];
                        $hashLevels = (int)$config['levels'];
                        if ( $hashLevels == 1 || $hashLevels == 2 ) {
                                $hashBase = (int)$config['base'];
                                if ( $hashBase == 16 || $hashBase == 36 ) {
                                        return array( $hashLevels, $hashBase, $config['repeat'] );
                                }
                        }
                }
                return array( 0, 0, false ); // no sharding
        }

        final protected function getContainerSuffixes( $container ) {
                $shards = array();
                list( $digits, $base ) = $this->getContainerHashLevels( $container );
                if ( $digits > 0 ) {
                        $numShards = pow( $base, $digits );
                        for ( $index = 0; $index < $numShards; $index++ ) {
                                $shards[] = '.' . wfBaseConvert( $index, 10, $base, $digits );
                        }
                }
                return $shards;
        }

        final protected function fullContainerName( $container ) {
                if ( $this->wikiId != '' ) {
                        return "{$this->wikiId}-$container";
                } else {
                        return $container;
                }
        }

        protected function resolveContainerName( $container ) {
                return $container;
        }

        protected function resolveContainerPath( $container, $relStoragePath ) {
                return $relStoragePath;
        }

        private function containerCacheKey( $container ) {
                return wfMemcKey( 'backend', $this->getName(), 'container', $container );
        }

        final protected function setContainerCache( $container, $val ) {
                $this->memCache->add( $this->containerCacheKey( $container ), $val, 14*86400 );
        }

        final protected function deleteContainerCache( $container ) {
                if ( !$this->memCache->set( $this->containerCacheKey( $container ), 'PURGED', 300 ) ) {
                        trigger_error( "Unable to delete stat cache for container $container." );
                }
        }

        final protected function primeContainerCache( array $items ) {
                wfProfileIn( __METHOD__ );
                wfProfileIn( __METHOD__ . '-' . $this->name );

                $paths = array(); // list of storage paths
                $contNames = array(); // (cache key => resolved container name)
                // Get all the paths/containers from the items...
                foreach ( $items as $item ) {
                        if ( $item instanceof FileOp ) {
                                $paths = array_merge( $paths, $item->storagePathsRead() );
                                $paths = array_merge( $paths, $item->storagePathsChanged() );
                        } elseif ( self::isStoragePath( $item ) ) {
                                $paths[] = $item;
                        } elseif ( is_string( $item ) ) { // full container name
                                $contNames[$this->containerCacheKey( $item )] = $item;
                        }
                }
                // Get all the corresponding cache keys for paths...
                foreach ( $paths as $path ) {
                        list( $fullCont, , ) = $this->resolveStoragePath( $path );
                        if ( $fullCont !== null ) { // valid path for this backend
                                $contNames[$this->containerCacheKey( $fullCont )] = $fullCont;
                        }
                }

                $contInfo = array(); // (resolved container name => cache value)
                // Get all cache entries for these container cache keys...
                $values = $this->memCache->getMulti( array_keys( $contNames ) );
                foreach ( $values as $cacheKey => $val ) {
                        $contInfo[$contNames[$cacheKey]] = $val;
                }

                // Populate the container process cache for the backend...
                $this->doPrimeContainerCache( array_filter( $contInfo, 'is_array' ) );

                wfProfileOut( __METHOD__ . '-' . $this->name );
                wfProfileOut( __METHOD__ );
        }

        protected function doPrimeContainerCache( array $containerInfo ) {}

        private function fileCacheKey( $path ) {
                return wfMemcKey( 'backend', $this->getName(), 'file', sha1( $path ) );
        }

        final protected function setFileCache( $path, $val ) {
                $path = FileBackend::normalizeStoragePath( $path );
                if ( $path === null ) {
                        return; // invalid storage path
                }
                $this->memCache->add( $this->fileCacheKey( $path ), $val, 7*86400 );
        }

        final protected function deleteFileCache( $path ) {
                $path = FileBackend::normalizeStoragePath( $path );
                if ( $path === null ) {
                        return; // invalid storage path
                }
                if ( !$this->memCache->set( $this->fileCacheKey( $path ), 'PURGED', 300 ) ) {
                        trigger_error( "Unable to delete stat cache for file $path." );
                }
        }

        final protected function primeFileCache( array $items ) {
                wfProfileIn( __METHOD__ );
                wfProfileIn( __METHOD__ . '-' . $this->name );

                $paths = array(); // list of storage paths
                $pathNames = array(); // (cache key => storage path)
                // Get all the paths/containers from the items...
                foreach ( $items as $item ) {
                        if ( $item instanceof FileOp ) {
                                $paths = array_merge( $paths, $item->storagePathsRead() );
                                $paths = array_merge( $paths, $item->storagePathsChanged() );
                        } elseif ( self::isStoragePath( $item ) ) {
                                $paths[] = FileBackend::normalizeStoragePath( $item );
                        }
                }
                // Get rid of any paths that failed normalization...
                $paths = array_filter( $paths, 'strlen' ); // remove nulls
                // Get all the corresponding cache keys for paths...
                foreach ( $paths as $path ) {
                        list( , $rel, ) = $this->resolveStoragePath( $path );
                        if ( $rel !== null ) { // valid path for this backend
                                $pathNames[$this->fileCacheKey( $path )] = $path;
                        }
                }
                // Get all cache entries for these container cache keys...
                $values = $this->memCache->getMulti( array_keys( $pathNames ) );
                foreach ( $values as $cacheKey => $val ) {
                        if ( is_array( $val ) ) {
                                $path = $pathNames[$cacheKey];
                                $this->cheapCache->set( $path, 'stat', $val );
                                if ( isset( $val['sha1'] ) ) { // some backends store SHA-1 as metadata
                                        $this->cheapCache->set( $path, 'sha1',
                                                array( 'hash' => $val['sha1'], 'latest' => $val['latest'] ) );
                                }
                        }
                }

                wfProfileOut( __METHOD__ . '-' . $this->name );
                wfProfileOut( __METHOD__ );
        }

        final protected function setConcurrencyFlags( array $opts ) {
                $opts['concurrency'] = 1; // off
                if ( $this->parallelize === 'implicit' ) {
                        if ( !isset( $opts['parallelize'] ) || $opts['parallelize'] ) {
                                $opts['concurrency'] = $this->concurrency;
                        }
                } elseif ( $this->parallelize === 'explicit' ) {
                        if ( !empty( $opts['parallelize'] ) ) {
                                $opts['concurrency'] = $this->concurrency;
                        }
                }
                return $opts;
        }
}

abstract class FileBackendStoreOpHandle {
        public $params = array(); // params to caller functions
        public $backend;
        public $resourcesToClose = array();

        public $call; // string; name that identifies the function called

        public function closeResources() {
                array_map( 'fclose', $this->resourcesToClose );
        }
}

abstract class FileBackendStoreShardListIterator implements Iterator {
        protected $backend;
        protected $params;
        protected $shardSuffixes;
        protected $container; // string; full container name
        protected $directory; // string; resolved relative path

        protected $iter;
        protected $curShard = 0; // integer
        protected $pos = 0; // integer

        protected $multiShardPaths = array(); // (rel path => 1)

        public function __construct(
                FileBackendStore $backend, $container, $dir, array $suffixes, array $params
        ) {
                $this->backend = $backend;
                $this->container = $container;
                $this->directory = $dir;
                $this->shardSuffixes = $suffixes;
                $this->params = $params;
        }

        public function key() {
                return $this->pos;
        }

        public function valid() {
                if ( $this->iter instanceof Iterator ) {
                        return $this->iter->valid();
                } elseif ( is_array( $this->iter ) ) {
                        return ( current( $this->iter ) !== false ); // no paths can have this value
                }
                return false; // some failure?
        }

        public function current() {
                return ( $this->iter instanceof Iterator )
                        ? $this->iter->current()
                        : current( $this->iter );
        }

        public function next() {
                ++$this->pos;
                ( $this->iter instanceof Iterator ) ? $this->iter->next() : next( $this->iter );
                do {
                        $continue = false; // keep scanning shards?
                        $this->filterViaNext(); // filter out duplicates
                        // Find the next non-empty shard if no elements are left
                        if ( !$this->valid() ) {
                                $this->nextShardIteratorIfNotValid();
                                $continue = $this->valid(); // re-filter unless we ran out of shards
                        }
                } while ( $continue );
        }

        public function rewind() {
                $this->pos = 0;
                $this->curShard = 0;
                $this->setIteratorFromCurrentShard();
                do {
                        $continue = false; // keep scanning shards?
                        $this->filterViaNext(); // filter out duplicates
                        // Find the next non-empty shard if no elements are left
                        if ( !$this->valid() ) {
                                $this->nextShardIteratorIfNotValid();
                                $continue = $this->valid(); // re-filter unless we ran out of shards
                        }
                } while ( $continue );
        }

        protected function filterViaNext() {
                while ( $this->valid() ) {
                        $rel = $this->iter->current(); // path relative to given directory
                        $path = $this->params['dir'] . "/{$rel}"; // full storage path
                        if ( $this->backend->isSingleShardPathInternal( $path ) ) {
                                break; // path is only on one shard; no issue with duplicates
                        } elseif ( isset( $this->multiShardPaths[$rel] ) ) {
                                // Don't keep listing paths that are on multiple shards
                                ( $this->iter instanceof Iterator ) ? $this->iter->next() : next( $this->iter );
                        } else {
                                $this->multiShardPaths[$rel] = 1;
                                break;
                        }
                }
        }

        protected function nextShardIteratorIfNotValid() {
                while ( !$this->valid() && ++$this->curShard < count( $this->shardSuffixes ) ) {
                        $this->setIteratorFromCurrentShard();
                }
        }

        protected function setIteratorFromCurrentShard() {
                $this->iter = $this->listFromShard(
                        $this->container . $this->shardSuffixes[$this->curShard],
                        $this->directory, $this->params );
                // Start loading results so that current() works
                if ( $this->iter ) {
                        ( $this->iter instanceof Iterator ) ? $this->iter->rewind() : reset( $this->iter );
                }
        }

        abstract protected function listFromShard( $container, $dir, array $params );
}

class FileBackendStoreShardDirIterator extends FileBackendStoreShardListIterator {
        protected function listFromShard( $container, $dir, array $params ) {
                return $this->backend->getDirectoryListInternal( $container, $dir, $params );
        }
}

class FileBackendStoreShardFileIterator extends FileBackendStoreShardListIterator {
        protected function listFromShard( $container, $dir, array $params ) {
                return $this->backend->getFileListInternal( $container, $dir, $params );
        }
}