Merge "Optimize HashRing to avoid hashing for the common single-location case"

[lhc/web/wiklou.git] / includes / libs / filebackend / FileBackendStore.php

<?php
/**
 * Base class for all backends using particular storage medium.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, write to the Free Software Foundation, Inc.,
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 * http://www.gnu.org/copyleft/gpl.html
 *
 * @file
 * @ingroup FileBackend
 */

use Wikimedia\AtEase\AtEase;
use Wikimedia\Timestamp\ConvertibleTimestamp;

/**
 * @brief Base class for all backends using particular storage medium.
 *
 * This class defines the methods as abstract that subclasses must implement.
 * Outside callers should *not* use functions with "Internal" in the name.
 *
 * The FileBackend operations are implemented using basic functions
 * such as storeInternal(), copyInternal(), deleteInternal() and the like.
 * This class is also responsible for path resolution and sanitization.
 *
 * @ingroup FileBackend
 * @since 1.19
 */
abstract class FileBackendStore extends FileBackend {
        /** @var WANObjectCache */
        protected $memCache;
        /** @var BagOStuff */
        protected $srvCache;
        /** @var MapCacheLRU Map of paths to small (RAM/disk) cache items */
        protected $cheapCache;
        /** @var MapCacheLRU Map of paths to large (RAM/disk) cache items */
        protected $expensiveCache;

        /** @var array Map of container names to sharding config */
        protected $shardViaHashLevels = [];

        /** @var callable Method to get the MIME type of files */
        protected $mimeCallback;

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

        const CACHE_TTL = 10; // integer; TTL in seconds for process cache entries
        const CACHE_CHEAP_SIZE = 500; // integer; max entries in "cheap cache"
        const CACHE_EXPENSIVE_SIZE = 5; // integer; max entries in "expensive cache"

        /**
         * @see FileBackend::__construct()
         * Additional $config params include:
         *   - srvCache     : BagOStuff cache to APC or the like.
         *   - wanCache     : WANObjectCache object to use for persistent caching.
         *   - mimeCallback : Callback that takes (storage path, content, file system path) and
         *                    returns the MIME type of the file or 'unknown/unknown'. The file
         *                    system path parameter should be used if the content one is null.
         *
         * @param array $config
         */
        public function __construct( array $config ) {
                parent::__construct( $config );
                $this->mimeCallback = $config['mimeCallback'] ?? null;
                $this->srvCache = new EmptyBagOStuff(); // disabled by default
                $this->memCache = WANObjectCache::newEmpty(); // disabled by default
                $this->cheapCache = new MapCacheLRU( self::CACHE_CHEAP_SIZE );
                $this->expensiveCache = new MapCacheLRU( self::CACHE_EXPENSIVE_SIZE );
        }

        /**
         * Get the maximum allowable file size given backend
         * medium restrictions and basic performance constraints.
         * Do not call this function from places outside FileBackend and FileOp.
         *
         * @return int Bytes
         */
        final public function maxFileSizeInternal() {
                return $this->maxFileSize;
        }

        /**
         * Check if a file can be created or changed at a given storage path.
         * FS backends should check if the parent directory exists, files can be
         * written under it, and that any file already there is writable.
         * Backends using key/value stores should check if the container exists.
         *
         * @param string $storagePath
         * @return bool
         */
        abstract public function isPathUsableInternal( $storagePath );

        /**
         * Create a file in the backend with the given contents.
         * This will overwrite any file that exists at the destination.
         * Do not call this function from places outside FileBackend and FileOp.
         *
         * $params include:
         *   - content     : the raw file contents
         *   - dst         : destination storage path
         *   - headers     : HTTP header name/value map
         *   - async       : StatusValue will be returned immediately if supported.
         *                   If the StatusValue is OK, then its value field will be
         *                   set to a FileBackendStoreOpHandle object.
         *   - dstExists   : Whether a file exists at the destination (optimization).
         *                   Callers can use "false" if no existing file is being changed.
         *
         * @param array $params
         * @return StatusValue
         */
        final public function createInternal( array $params ) {
                /** @noinspection PhpUnusedLocalVariableInspection */
                $ps = $this->scopedProfileSection( __METHOD__ . "-{$this->name}" );
                if ( strlen( $params['content'] ) > $this->maxFileSizeInternal() ) {
                        $status = $this->newStatus( 'backend-fail-maxsize',
                                $params['dst'], $this->maxFileSizeInternal() );
                } else {
                        $status = $this->doCreateInternal( $params );
                        $this->clearCache( [ $params['dst'] ] );
                        if ( !isset( $params['dstExists'] ) || $params['dstExists'] ) {
                                $this->deleteFileCache( $params['dst'] ); // persistent cache
                        }
                }

                return $status;
        }

        /**
         * @see FileBackendStore::createInternal()
         * @param array $params
         * @return StatusValue
         */
        abstract protected function doCreateInternal( array $params );

        /**
         * Store a file into the backend from a file on disk.
         * This will overwrite any file that exists at the destination.
         * Do not call this function from places outside FileBackend and FileOp.
         *
         * $params include:
         *   - src         : source path on disk
         *   - dst         : destination storage path
         *   - headers     : HTTP header name/value map
         *   - async       : StatusValue will be returned immediately if supported.
         *                   If the StatusValue is OK, then its value field will be
         *                   set to a FileBackendStoreOpHandle object.
         *   - dstExists   : Whether a file exists at the destination (optimization).
         *                   Callers can use "false" if no existing file is being changed.
         *
         * @param array $params
         * @return StatusValue
         */
        final public function storeInternal( array $params ) {
                /** @noinspection PhpUnusedLocalVariableInspection */
                $ps = $this->scopedProfileSection( __METHOD__ . "-{$this->name}" );
                if ( filesize( $params['src'] ) > $this->maxFileSizeInternal() ) {
                        $status = $this->newStatus( 'backend-fail-maxsize',
                                $params['dst'], $this->maxFileSizeInternal() );
                } else {
                        $status = $this->doStoreInternal( $params );
                        $this->clearCache( [ $params['dst'] ] );
                        if ( !isset( $params['dstExists'] ) || $params['dstExists'] ) {
                                $this->deleteFileCache( $params['dst'] ); // persistent cache
                        }
                }

                return $status;
        }

        /**
         * @see FileBackendStore::storeInternal()
         * @param array $params
         * @return StatusValue
         */
        abstract protected function doStoreInternal( array $params );

        /**
         * Copy a file from one storage path to another in the backend.
         * This will overwrite any file that exists at the destination.
         * Do not call this function from places outside FileBackend and FileOp.
         *
         * $params include:
         *   - src                 : source storage path
         *   - dst                 : destination storage path
         *   - ignoreMissingSource : do nothing if the source file does not exist
         *   - headers             : HTTP header name/value map
         *   - async               : StatusValue will be returned immediately if supported.
         *                           If the StatusValue is OK, then its value field will be
         *                           set to a FileBackendStoreOpHandle object.
         *   - dstExists           : Whether a file exists at the destination (optimization).
         *                           Callers can use "false" if no existing file is being changed.
         *
         * @param array $params
         * @return StatusValue
         */
        final public function copyInternal( array $params ) {
                /** @noinspection PhpUnusedLocalVariableInspection */
                $ps = $this->scopedProfileSection( __METHOD__ . "-{$this->name}" );
                $status = $this->doCopyInternal( $params );
                $this->clearCache( [ $params['dst'] ] );
                if ( !isset( $params['dstExists'] ) || $params['dstExists'] ) {
                        $this->deleteFileCache( $params['dst'] ); // persistent cache
                }

                return $status;
        }

        /**
         * @see FileBackendStore::copyInternal()
         * @param array $params
         * @return StatusValue
         */
        abstract protected function doCopyInternal( array $params );

        /**
         * Delete a file at the storage path.
         * Do not call this function from places outside FileBackend and FileOp.
         *
         * $params include:
         *   - src                 : source storage path
         *   - ignoreMissingSource : do nothing if the source file does not exist
         *   - async               : StatusValue will be returned immediately if supported.
         *                           If the StatusValue is OK, then its value field will be
         *                           set to a FileBackendStoreOpHandle object.
         *
         * @param array $params
         * @return StatusValue
         */
        final public function deleteInternal( array $params ) {
                /** @noinspection PhpUnusedLocalVariableInspection */
                $ps = $this->scopedProfileSection( __METHOD__ . "-{$this->name}" );
                $status = $this->doDeleteInternal( $params );
                $this->clearCache( [ $params['src'] ] );
                $this->deleteFileCache( $params['src'] ); // persistent cache
                return $status;
        }

        /**
         * @see FileBackendStore::deleteInternal()
         * @param array $params
         * @return StatusValue
         */
        abstract protected function doDeleteInternal( array $params );

        /**
         * Move a file from one storage path to another in the backend.
         * This will overwrite any file that exists at the destination.
         * Do not call this function from places outside FileBackend and FileOp.
         *
         * $params include:
         *   - src                 : source storage path
         *   - dst                 : destination storage path
         *   - ignoreMissingSource : do nothing if the source file does not exist
         *   - headers             : HTTP header name/value map
         *   - async               : StatusValue will be returned immediately if supported.
         *                           If the StatusValue is OK, then its value field will be
         *                           set to a FileBackendStoreOpHandle object.
         *   - dstExists           : Whether a file exists at the destination (optimization).
         *                           Callers can use "false" if no existing file is being changed.
         *
         * @param array $params
         * @return StatusValue
         */
        final public function moveInternal( array $params ) {
                /** @noinspection PhpUnusedLocalVariableInspection */
                $ps = $this->scopedProfileSection( __METHOD__ . "-{$this->name}" );
                $status = $this->doMoveInternal( $params );
                $this->clearCache( [ $params['src'], $params['dst'] ] );
                $this->deleteFileCache( $params['src'] ); // persistent cache
                if ( !isset( $params['dstExists'] ) || $params['dstExists'] ) {
                        $this->deleteFileCache( $params['dst'] ); // persistent cache
                }

                return $status;
        }

        /**
         * @see FileBackendStore::moveInternal()
         * @param array $params
         * @return StatusValue
         */
        protected function doMoveInternal( array $params ) {
                unset( $params['async'] ); // two steps, won't work here :)
                $nsrc = FileBackend::normalizeStoragePath( $params['src'] );
                $ndst = FileBackend::normalizeStoragePath( $params['dst'] );
                // Copy source to dest
                $status = $this->copyInternal( $params );
                if ( $nsrc !== $ndst && $status->isOK() ) {
                        // Delete source (only fails due to races or network problems)
                        $status->merge( $this->deleteInternal( [ 'src' => $params['src'] ] ) );
                        $status->setResult( true, $status->value ); // ignore delete() errors
                }

                return $status;
        }

        /**
         * Alter metadata for a file at the storage path.
         * Do not call this function from places outside FileBackend and FileOp.
         *
         * $params include:
         *   - src           : source storage path
         *   - headers       : HTTP header name/value map
         *   - async         : StatusValue will be returned immediately if supported.
         *                     If the StatusValue is OK, then its value field will be
         *                     set to a FileBackendStoreOpHandle object.
         *
         * @param array $params
         * @return StatusValue
         */
        final public function describeInternal( array $params ) {
                /** @noinspection PhpUnusedLocalVariableInspection */
                $ps = $this->scopedProfileSection( __METHOD__ . "-{$this->name}" );
                if ( count( $params['headers'] ) ) {
                        $status = $this->doDescribeInternal( $params );
                        $this->clearCache( [ $params['src'] ] );
                        $this->deleteFileCache( $params['src'] ); // persistent cache
                } else {
                        $status = $this->newStatus(); // nothing to do
                }

                return $status;
        }

        /**
         * @see FileBackendStore::describeInternal()
         * @param array $params
         * @return StatusValue
         */
        protected function doDescribeInternal( array $params ) {
                return $this->newStatus();
        }

        /**
         * No-op file operation that does nothing.
         * Do not call this function from places outside FileBackend and FileOp.
         *
         * @param array $params
         * @return StatusValue
         */
        final public function nullInternal( array $params ) {
                return $this->newStatus();
        }

        final public function concatenate( array $params ) {
                /** @noinspection PhpUnusedLocalVariableInspection */
                $ps = $this->scopedProfileSection( __METHOD__ . "-{$this->name}" );
                $status = $this->newStatus();

                // Try to lock the source files for the scope of this function
                /** @noinspection PhpUnusedLocalVariableInspection */
                $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() ) {
                                $this->logger->error( static::class . "-{$this->name}" .
                                        " failed to concatenate " . count( $params['srcs'] ) . " file(s) [$sec sec]" );
                        }
                }

                return $status;
        }

        /**
         * @see FileBackendStore::concatenate()
         * @param array $params
         * @return StatusValue
         */
        protected function doConcatenate( array $params ) {
                $status = $this->newStatus();
                $tmpPath = $params['dst']; // convenience
                unset( $params['latest'] ); // sanity

                // Check that the specified temp file is valid...
                AtEase::suppressWarnings();
                $ok = ( is_file( $tmpPath ) && filesize( $tmpPath ) == 0 );
                AtEase::restoreWarnings();
                if ( !$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( [ '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 ) {
                /** @noinspection PhpUnusedLocalVariableInspection */
                $ps = $this->scopedProfileSection( __METHOD__ . "-{$this->name}" );
                $status = $this->newStatus();

                list( $fullCont, $dir, $shard ) = $this->resolveStoragePath( $params['dir'] );
                if ( $dir === null ) {
                        $status->fatal( 'backend-fail-invalidpath', $params['dir'] );

                        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
                        $this->logger->debug( __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 ) );
                        }
                }

                return $status;
        }

        /**
         * @see FileBackendStore::doPrepare()
         * @param string $container
         * @param string $dir
         * @param array $params
         * @return StatusValue
         */
        protected function doPrepareInternal( $container, $dir, array $params ) {
                return $this->newStatus();
        }

        final protected function doSecure( array $params ) {
                /** @noinspection PhpUnusedLocalVariableInspection */
                $ps = $this->scopedProfileSection( __METHOD__ . "-{$this->name}" );
                $status = $this->newStatus();

                list( $fullCont, $dir, $shard ) = $this->resolveStoragePath( $params['dir'] );
                if ( $dir === null ) {
                        $status->fatal( 'backend-fail-invalidpath', $params['dir'] );

                        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
                        $this->logger->debug( __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 ) );
                        }
                }

                return $status;
        }

        /**
         * @see FileBackendStore::doSecure()
         * @param string $container
         * @param string $dir
         * @param array $params
         * @return StatusValue
         */
        protected function doSecureInternal( $container, $dir, array $params ) {
                return $this->newStatus();
        }

        final protected function doPublish( array $params ) {
                /** @noinspection PhpUnusedLocalVariableInspection */
                $ps = $this->scopedProfileSection( __METHOD__ . "-{$this->name}" );
                $status = $this->newStatus();

                list( $fullCont, $dir, $shard ) = $this->resolveStoragePath( $params['dir'] );
                if ( $dir === null ) {
                        $status->fatal( 'backend-fail-invalidpath', $params['dir'] );

                        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
                        $this->logger->debug( __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 ) );
                        }
                }

                return $status;
        }

        /**
         * @see FileBackendStore::doPublish()
         * @param string $container
         * @param string $dir
         * @param array $params
         * @return StatusValue
         */
        protected function doPublishInternal( $container, $dir, array $params ) {
                return $this->newStatus();
        }

        final protected function doClean( array $params ) {
                /** @noinspection PhpUnusedLocalVariableInspection */
                $ps = $this->scopedProfileSection( __METHOD__ . "-{$this->name}" );
                $status = $this->newStatus();

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

                        return $status; // invalid storage path
                }

                // Attempt to lock this directory...
                $filesLockEx = [ $params['dir'] ];
                /** @noinspection PhpUnusedLocalVariableInspection */
                $scopedLockE = $this->getScopedFileLocks( $filesLockEx, LockManager::LOCK_EX, $status );
                if ( !$status->isOK() ) {
                        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
                        $this->logger->debug( __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
                        }
                }

                return $status;
        }

        /**
         * @see FileBackendStore::doClean()
         * @param string $container
         * @param string $dir
         * @param array $params
         * @return StatusValue
         */
        protected function doCleanInternal( $container, $dir, array $params ) {
                return $this->newStatus();
        }

        final public function fileExists( array $params ) {
                /** @noinspection PhpUnusedLocalVariableInspection */
                $ps = $this->scopedProfileSection( __METHOD__ . "-{$this->name}" );
                $stat = $this->getFileStat( $params );

                return ( $stat === self::UNKNOWN ) ? self::UNKNOWN : (bool)$stat;
        }

        final public function getFileTimestamp( array $params ) {
                /** @noinspection PhpUnusedLocalVariableInspection */
                $ps = $this->scopedProfileSection( __METHOD__ . "-{$this->name}" );
                $stat = $this->getFileStat( $params );

                return $stat ? $stat['mtime'] : false;
        }

        final public function getFileSize( array $params ) {
                /** @noinspection PhpUnusedLocalVariableInspection */
                $ps = $this->scopedProfileSection( __METHOD__ . "-{$this->name}" );
                $stat = $this->getFileStat( $params );

                return $stat ? $stat['size'] : false;
        }

        final public function getFileStat( array $params ) {
                $path = self::normalizeStoragePath( $params['src'] );
                if ( $path === null ) {
                        return false; // invalid storage path
                }
                /** @noinspection PhpUnusedLocalVariableInspection */
                $ps = $this->scopedProfileSection( __METHOD__ . "-{$this->name}" );

                $latest = !empty( $params['latest'] ); // use latest data?
                $requireSHA1 = !empty( $params['requireSHA1'] ); // require SHA-1 if file exists?

                if ( !$latest ) {
                        $stat = $this->cheapCache->getField( $path, 'stat', self::CACHE_TTL );
                        // Note that some backends, like SwiftFileBackend, sometimes set file stat process
                        // cache entries from mass object listings that do not include the SHA-1. In that
                        // case, loading the persistent stat cache will likely yield the SHA-1.
                        if (
                                $stat === self::UNKNOWN ||
                                ( $requireSHA1 && is_array( $stat ) && !isset( $stat['sha1'] ) )
                        ) {
                                $this->primeFileCache( [ $path ] ); // check persistent cache
                        }
                }

                $stat = $this->cheapCache->getField( $path, 'stat', self::CACHE_TTL );
                // 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 || $stat['latest'] ) &&
                                ( !$requireSHA1 || isset( $stat['sha1'] ) )
                        ) {
                                return $stat;
                        }
                } elseif ( in_array( $stat, [ 'NOT_EXIST', 'NOT_EXIST_LATEST' ], true ) ) {
                        if ( !$latest || $stat === 'NOT_EXIST_LATEST' ) {
                                return false;
                        }
                }

                $stat = $this->doGetFileStat( $params );

                if ( is_array( $stat ) ) { // file exists
                        // Strongly consistent backends can automatically set "latest"
                        $stat['latest'] = $stat['latest'] ?? $latest;
                        $this->cheapCache->setField( $path, 'stat', $stat );
                        $this->setFileCache( $path, $stat ); // update persistent cache
                        if ( isset( $stat['sha1'] ) ) { // some backends store SHA-1 as metadata
                                $this->cheapCache->setField( $path, 'sha1',
                                        [ 'hash' => $stat['sha1'], 'latest' => $latest ] );
                        }
                        if ( isset( $stat['xattr'] ) ) { // some backends store headers/metadata
                                $stat['xattr'] = self::normalizeXAttributes( $stat['xattr'] );
                                $this->cheapCache->setField( $path, 'xattr',
                                        [ 'map' => $stat['xattr'], 'latest' => $latest ] );
                        }
                } elseif ( $stat === false ) { // file does not exist
                        $this->cheapCache->setField( $path, 'stat', $latest ? 'NOT_EXIST_LATEST' : 'NOT_EXIST' );
                        $this->cheapCache->setField( $path, 'xattr', [ 'map' => false, 'latest' => $latest ] );
                        $this->cheapCache->setField( $path, 'sha1', [ 'hash' => false, 'latest' => $latest ] );
                        $this->logger->debug( __METHOD__ . ': File {path} does not exist', [
                                'path' => $path,
                        ] );
                } else { // an error occurred
                        $this->logger->warning( __METHOD__ . ': Could not stat file {path}', [
                                'path' => $path,
                        ] );
                }

                return $stat;
        }

        /**
         * @see FileBackendStore::getFileStat()
         * @param array $params
         */
        abstract protected function doGetFileStat( array $params );

        public function getFileContentsMulti( array $params ) {
                /** @noinspection PhpUnusedLocalVariableInspection */
                $ps = $this->scopedProfileSection( __METHOD__ . "-{$this->name}" );

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

                return $contents;
        }

        /**
         * @see FileBackendStore::getFileContentsMulti()
         * @param array $params
         * @return array
         */
        protected function doGetFileContentsMulti( array $params ) {
                $contents = [];
                foreach ( $this->doGetLocalReferenceMulti( $params ) as $path => $fsFile ) {
                        AtEase::suppressWarnings();
                        $contents[$path] = $fsFile ? file_get_contents( $fsFile->getPath() ) : false;
                        AtEase::restoreWarnings();
                }

                return $contents;
        }

        final public function getFileXAttributes( array $params ) {
                $path = self::normalizeStoragePath( $params['src'] );
                if ( $path === null ) {
                        return false; // invalid storage path
                }
                /** @noinspection PhpUnusedLocalVariableInspection */
                $ps = $this->scopedProfileSection( __METHOD__ . "-{$this->name}" );
                $latest = !empty( $params['latest'] ); // use latest data?
                if ( $this->cheapCache->hasField( $path, 'xattr', self::CACHE_TTL ) ) {
                        $stat = $this->cheapCache->getField( $path, 'xattr' );
                        // If we want the latest data, check that this cached
                        // value was in fact fetched with the latest available data.
                        if ( !$latest || $stat['latest'] ) {
                                return $stat['map'];
                        }
                }
                $fields = $this->doGetFileXAttributes( $params );
                $fields = is_array( $fields ) ? self::normalizeXAttributes( $fields ) : false;
                $this->cheapCache->setField( $path, 'xattr', [ 'map' => $fields, 'latest' => $latest ] );

                return $fields;
        }

        /**
         * @see FileBackendStore::getFileXAttributes()
         * @param array $params
         * @return array[][]|false
         */
        protected function doGetFileXAttributes( array $params ) {
                return [ 'headers' => [], 'metadata' => [] ]; // not supported
        }

        final public function getFileSha1Base36( array $params ) {
                $path = self::normalizeStoragePath( $params['src'] );
                if ( $path === null ) {
                        return false; // invalid storage path
                }
                /** @noinspection PhpUnusedLocalVariableInspection */
                $ps = $this->scopedProfileSection( __METHOD__ . "-{$this->name}" );
                $latest = !empty( $params['latest'] ); // use latest data?
                if ( $this->cheapCache->hasField( $path, 'sha1', self::CACHE_TTL ) ) {
                        $stat = $this->cheapCache->getField( $path, 'sha1' );
                        // If we want the latest data, check that this cached
                        // value was in fact fetched with the latest available data.
                        if ( !$latest || $stat['latest'] ) {
                                return $stat['hash'];
                        }
                }
                $hash = $this->doGetFileSha1Base36( $params );
                $this->cheapCache->setField( $path, 'sha1', [ 'hash' => $hash, 'latest' => $latest ] );

                return $hash;
        }

        /**
         * @see FileBackendStore::getFileSha1Base36()
         * @param array $params
         * @return bool|string
         */
        protected function doGetFileSha1Base36( array $params ) {
                $fsFile = $this->getLocalReference( $params );
                if ( !$fsFile ) {
                        return false;
                } else {
                        return $fsFile->getSha1Base36();
                }
        }

        final public function getFileProps( array $params ) {
                /** @noinspection PhpUnusedLocalVariableInspection */
                $ps = $this->scopedProfileSection( __METHOD__ . "-{$this->name}" );
                $fsFile = $this->getLocalReference( $params );
                $props = $fsFile ? $fsFile->getProps() : FSFile::placeholderProps();

                return $props;
        }

        final public function getLocalReferenceMulti( array $params ) {
                /** @noinspection PhpUnusedLocalVariableInspection */
                $ps = $this->scopedProfileSection( __METHOD__ . "-{$this->name}" );

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

                $fsFiles = []; // (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->hasField( $path, 'localRef' ) ) {
                                $val = $this->expensiveCache->getField( $path, 'localRef' );
                                // If we want the latest data, check that this cached
                                // value was in fact fetched with the latest available data.
                                if ( !$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->setField( $path, 'localRef',
                                        [ 'object' => $fsFile, 'latest' => $latest ] );
                        }
                }

                return $fsFiles;
        }

        /**
         * @see FileBackendStore::getLocalReferenceMulti()
         * @param array $params
         * @return array
         */
        protected function doGetLocalReferenceMulti( array $params ) {
                return $this->doGetLocalCopyMulti( $params );
        }

        final public function getLocalCopyMulti( array $params ) {
                /** @noinspection PhpUnusedLocalVariableInspection */
                $ps = $this->scopedProfileSection( __METHOD__ . "-{$this->name}" );

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

                return $tmpFiles;
        }

        /**
         * @see FileBackendStore::getLocalCopyMulti()
         * @param array $params
         * @return array
         */
        abstract protected function doGetLocalCopyMulti( array $params );

        /**
         * @see FileBackend::getFileHttpUrl()
         * @param array $params
         * @return string|null
         */
        public function getFileHttpUrl( array $params ) {
                return null; // not supported
        }

        final public function streamFile( array $params ) {
                /** @noinspection PhpUnusedLocalVariableInspection */
                $ps = $this->scopedProfileSection( __METHOD__ . "-{$this->name}" );
                $status = $this->newStatus();

                // Always set some fields for subclass convenience
                $params['options'] = $params['options'] ?? [];
                $params['headers'] = $params['headers'] ?? [];

                // Don't stream it out as text/html if there was a PHP error
                if ( ( empty( $params['headless'] ) || $params['headers'] ) && headers_sent() ) {
                        print "Headers already sent, terminating.\n";
                        $status->fatal( 'backend-fail-stream', $params['src'] );
                        return $status;
                }

                $status->merge( $this->doStreamFile( $params ) );

                return $status;
        }

        /**
         * @see FileBackendStore::streamFile()
         * @param array $params
         * @return StatusValue
         */
        protected function doStreamFile( array $params ) {
                $status = $this->newStatus();

                $flags = 0;
                $flags |= !empty( $params['headless'] ) ? HTTPFileStreamer::STREAM_HEADLESS : 0;
                $flags |= !empty( $params['allowOB'] ) ? HTTPFileStreamer::STREAM_ALLOW_OB : 0;

                $fsFile = $this->getLocalReference( $params );
                if ( $fsFile ) {
                        $streamer = new HTTPFileStreamer(
                                $fsFile->getPath(),
                                [
                                        'obResetFunc' => $this->obResetFunc,
                                        'streamMimeFunc' => $this->streamMimeFunc
                                ]
                        );
                        $res = $streamer->stream( $params['headers'], true, $params['options'], $flags );
                } else {
                        $res = false;
                        HTTPFileStreamer::send404Message( $params['src'], $flags );
                }

                if ( !$res ) {
                        $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
                        $this->logger->debug( __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 = self::UNKNOWN; // if we don't find anything, it is indeterminate
                                }
                        }

                        return $res;
                }
        }

        /**
         * @see FileBackendStore::directoryExists()
         *
         * @param string $container Resolved container name
         * @param string $dir Resolved path relative to container
         * @param array $params
         * @return bool|null
         */
        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 self::UNKNOWN;
                }
                if ( $shard !== null ) {
                        // File listing is confined to a single container/shard
                        return $this->getDirectoryListInternal( $fullCont, $dir, $params );
                } else {
                        $this->logger->debug( __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 );
                }
        }

        /**
         * Do not call this function from places outside FileBackend
         *
         * @see FileBackendStore::getDirectoryList()
         *
         * @param string $container Resolved container name
         * @param string $dir Resolved path relative to container
         * @param array $params
         * @return Traversable|array|null Returns null on failure
         */
        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 self::UNKNOWN;
                }
                if ( $shard !== null ) {
                        // File listing is confined to a single container/shard
                        return $this->getFileListInternal( $fullCont, $dir, $params );
                } else {
                        $this->logger->debug( __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 );
                }
        }

        /**
         * Do not call this function from places outside FileBackend
         *
         * @see FileBackendStore::getFileList()
         *
         * @param string $container Resolved container name
         * @param string $dir Resolved path relative to container
         * @param array $params
         * @return Traversable|string[]|null Returns null on failure
         */
        abstract public function getFileListInternal( $container, $dir, array $params );

        /**
         * Return a list of FileOp objects from a list of operations.
         * Do not call this function from places outside FileBackend.
         *
         * The result must have the same number of items as the input.
         * An exception is thrown if an unsupported operation is requested.
         *
         * @param array $ops Same format as doOperations()
         * @return FileOp[] List of FileOp objects
         * @throws FileBackendError
         */
        final public function getOperationsInternal( array $ops ) {
                $supportedOps = [
                        'store' => StoreFileOp::class,
                        'copy' => CopyFileOp::class,
                        'move' => MoveFileOp::class,
                        'delete' => DeleteFileOp::class,
                        'create' => CreateFileOp::class,
                        'describe' => DescribeFileOp::class,
                        'null' => NullFileOp::class
                ];

                $performOps = []; // 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, $this->logger );
                        } else {
                                throw new FileBackendError( "Operation '$opName' is not supported." );
                        }
                }

                return $performOps;
        }

        /**
         * Get a list of storage paths to lock for a list of operations
         * Returns an array with LockManager::LOCK_UW (shared locks) and
         * LockManager::LOCK_EX (exclusive locks) keys, each corresponding
         * to a list of storage paths to be locked. All returned paths are
         * normalized.
         *
         * @param array $performOps List of FileOp objects
         * @return array (LockManager::LOCK_UW => path list, LockManager::LOCK_EX => path list)
         */
        final public function getPathsToLockForOpsInternal( array $performOps ) {
                // Build up a list of files to lock...
                $paths = [ 'sh' => [], 'ex' => [] ];
                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 [
                        LockManager::LOCK_UW => $paths['sh'],
                        LockManager::LOCK_EX => $paths['ex']
                ];
        }

        public function getScopedLocksForOps( array $ops, StatusValue $status ) {
                $paths = $this->getPathsToLockForOpsInternal( $this->getOperationsInternal( $ops ) );

                return $this->getScopedFileLocks( $paths, 'mixed', $status );
        }

        final protected function doOperationsInternal( array $ops, array $opts ) {
                /** @noinspection PhpUnusedLocalVariableInspection */
                $ps = $this->scopedProfileSection( __METHOD__ . "-{$this->name}" );
                $status = $this->newStatus();

                // Fix up custom header name/value pairs...
                $ops = array_map( [ $this, 'sanitizeOpHeaders' ], $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...
                        /** @noinspection PhpUnusedLocalVariableInspection */
                        $scopeLock = $this->getScopedFileLocks( $paths, 'mixed', $status );
                        if ( !$status->isOK() ) {
                                return $status; // abort
                        }
                }

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

                // Build the list of paths involved
                $paths = [];
                foreach ( $performOps as $performOp ) {
                        $paths = array_merge( $paths, $performOp->storagePathsRead() );
                        $paths = array_merge( $paths, $performOp->storagePathsChanged() );
                }

                // Enlarge the cache to fit the stat entries of these files
                $this->cheapCache->setMaxSize( max( 2 * count( $paths ), self::CACHE_CHEAP_SIZE ) );

                // Load from the persistent container caches
                $this->primeContainerCache( $paths );
                // Get the latest stat info for all the files (having locked them)
                $ok = $this->preloadFileStat( [ 'srcs' => $paths, 'latest' => true ] );

                if ( $ok ) {
                        // Actually attempt the operation batch...
                        $opts = $this->setConcurrencyFlags( $opts );
                        $subStatus = FileOpBatch::attempt( $performOps, $opts, $this->fileJournal );
                } else {
                        // If we could not even stat some files, then bail out...
                        $subStatus = $this->newStatus( 'backend-fail-internal', $this->name );
                        foreach ( $ops as $i => $op ) { // mark each op as failed
                                $subStatus->success[$i] = false;
                                ++$subStatus->failCount;
                        }
                        $this->logger->error( static::class . "-{$this->name} " .
                                " stat failure; aborted operations: " . FormatJson::encode( $ops ) );
                }

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

                // Shrink the stat cache back to normal size
                $this->cheapCache->setMaxSize( self::CACHE_CHEAP_SIZE );

                return $status;
        }

        final protected function doQuickOperationsInternal( array $ops ) {
                /** @noinspection PhpUnusedLocalVariableInspection */
                $ps = $this->scopedProfileSection( __METHOD__ . "-{$this->name}" );
                $status = $this->newStatus();

                // Fix up custom header name/value pairs...
                $ops = array_map( [ $this, 'sanitizeOpHeaders' ], $ops );

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

                $supportedOps = [ 'create', 'store', 'copy', 'move', 'delete', 'describe', 'null' ];
                // Parallel ops may be disabled in config due to dependencies (e.g. needing popen())
                $async = ( $this->parallelize === 'implicit' && count( $ops ) > 1 );
                $maxConcurrency = $this->concurrency; // throttle
                /** @var StatusValue[] $statuses */
                $statuses = []; // array of (index => StatusValue)
                $fileOpHandles = []; // list of (index => handle) arrays
                $curFileOpHandles = []; // 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'], $supportedOps ) ) {
                                throw new FileBackendError( "Operation '{$params['op']}' is not supported." );
                        }
                        $method = $params['op'] . 'Internal'; // e.g. "storeInternal"
                        $subStatus = $this->$method( [ 'async' => $async ] + $params );
                        if ( $subStatus->value instanceof FileBackendStoreOpHandle ) { // async
                                if ( count( $curFileOpHandles ) >= $maxConcurrency ) {
                                        $fileOpHandles[] = $curFileOpHandles; // push this batch
                                        $curFileOpHandles = [];
                                }
                                $curFileOpHandles[$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;
                        }
                }

                return $status;
        }

        /**
         * Execute a list of FileBackendStoreOpHandle handles in parallel.
         * The resulting StatusValue object fields will correspond
         * to the order in which the handles where given.
         *
         * @param FileBackendStoreOpHandle[] $fileOpHandles
         * @return StatusValue[] Map of StatusValue objects
         * @throws FileBackendError
         */
        final public function executeOpHandlesInternal( array $fileOpHandles ) {
                /** @noinspection PhpUnusedLocalVariableInspection */
                $ps = $this->scopedProfileSection( __METHOD__ . "-{$this->name}" );

                foreach ( $fileOpHandles as $fileOpHandle ) {
                        if ( !( $fileOpHandle instanceof FileBackendStoreOpHandle ) ) {
                                throw new InvalidArgumentException( "Expected FileBackendStoreOpHandle object." );
                        } elseif ( $fileOpHandle->backend->getName() !== $this->getName() ) {
                                throw new InvalidArgumentException( "Expected handle for this file backend." );
                        }
                }

                $res = $this->doExecuteOpHandlesInternal( $fileOpHandles );
                foreach ( $fileOpHandles as $fileOpHandle ) {
                        $fileOpHandle->closeResources();
                }

                return $res;
        }

        /**
         * @see FileBackendStore::executeOpHandlesInternal()
         *
         * @param FileBackendStoreOpHandle[] $fileOpHandles
         *
         * @throws FileBackendError
         * @return StatusValue[] List of corresponding StatusValue objects
         */
        protected function doExecuteOpHandlesInternal( array $fileOpHandles ) {
                if ( count( $fileOpHandles ) ) {
                        throw new FileBackendError( "Backend does not support asynchronous operations." );
                }

                return [];
        }

        /**
         * Normalize and filter HTTP headers from a file operation
         *
         * This normalizes and strips long HTTP headers from a file operation.
         * Most headers are just numbers, but some are allowed to be long.
         * This function is useful for cleaning up headers and avoiding backend
         * specific errors, especially in the middle of batch file operations.
         *
         * @param array $op Same format as doOperation()
         * @return array
         */
        protected function sanitizeOpHeaders( array $op ) {
                static $longs = [ 'content-disposition' ];

                if ( isset( $op['headers'] ) ) { // op sets HTTP headers
                        $newHeaders = [];
                        foreach ( $op['headers'] as $name => $value ) {
                                $name = strtolower( $name );
                                $maxHVLen = in_array( $name, $longs ) ? INF : 255;
                                if ( strlen( $name ) > 255 || strlen( $value ) > $maxHVLen ) {
                                        trigger_error( "Header '$name: $value' is too long." );
                                } else {
                                        $newHeaders[$name] = strlen( $value ) ? $value : ''; // null/false => ""
                                }
                        }
                        $op['headers'] = $newHeaders;
                }

                return $op;
        }

        final public function preloadCache( array $paths ) {
                $fullConts = []; // 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 );
        }

        /**
         * Clears any additional stat caches for storage paths
         *
         * @see FileBackend::clearCache()
         *
         * @param array|null $paths Storage paths (optional)
         */
        protected function doClearCache( array $paths = null ) {
        }

        final public function preloadFileStat( array $params ) {
                /** @noinspection PhpUnusedLocalVariableInspection */
                $ps = $this->scopedProfileSection( __METHOD__ . "-{$this->name}" );
                $success = true; // no network errors

                $params['concurrency'] = ( $this->parallelize !== 'off' ) ? $this->concurrency : 1;
                $stats = $this->doGetFileStatMulti( $params );
                if ( $stats === null ) {
                        return true; // not supported
                }

                $latest = !empty( $params['latest'] ); // use latest data?
                foreach ( $stats as $path => $stat ) {
                        $path = FileBackend::normalizeStoragePath( $path );
                        if ( $path === null ) {
                                continue; // this shouldn't happen
                        }
                        if ( is_array( $stat ) ) { // file exists
                                // Strongly consistent backends can automatically set "latest"
                                $stat['latest'] = $stat['latest'] ?? $latest;
                                $this->cheapCache->setField( $path, 'stat', $stat );
                                $this->setFileCache( $path, $stat ); // update persistent cache
                                if ( isset( $stat['sha1'] ) ) { // some backends store SHA-1 as metadata
                                        $this->cheapCache->setField( $path, 'sha1',
                                                [ 'hash' => $stat['sha1'], 'latest' => $latest ] );
                                }
                                if ( isset( $stat['xattr'] ) ) { // some backends store headers/metadata
                                        $stat['xattr'] = self::normalizeXAttributes( $stat['xattr'] );
                                        $this->cheapCache->setField( $path, 'xattr',
                                                [ 'map' => $stat['xattr'], 'latest' => $latest ] );
                                }
                        } elseif ( $stat === false ) { // file does not exist
                                $this->cheapCache->setField( $path, 'stat',
                                        $latest ? 'NOT_EXIST_LATEST' : 'NOT_EXIST' );
                                $this->cheapCache->setField( $path, 'xattr',
                                        [ 'map' => false, 'latest' => $latest ] );
                                $this->cheapCache->setField( $path, 'sha1',
                                        [ 'hash' => false, 'latest' => $latest ] );
                                $this->logger->debug( __METHOD__ . ': File {path} does not exist', [
                                        'path' => $path,
                                ] );
                        } else { // an error occurred
                                $success = false;
                                $this->logger->warning( __METHOD__ . ': Could not stat file {path}', [
                                        'path' => $path,
                                ] );
                        }
                }

                return $success;
        }

        /**
         * Get file stat information (concurrently if possible) for several files
         *
         * @see FileBackend::getFileStat()
         *
         * @param array $params Parameters include:
         *   - srcs        : list of source storage paths
         *   - latest      : use the latest available data
         * @return array|null Map of storage paths to array|bool|null (returns null if not supported)
         * @since 1.23
         */
        protected function doGetFileStatMulti( array $params ) {
                return null; // not supported
        }

        /**
         * Is this a key/value store where directories are just virtual?
         * Virtual directories exists in so much as files exists that are
         * prefixed with the directory path followed by a forward slash.
         *
         * @return bool
         */
        abstract protected function directoriesAreVirtual();

        /**
         * Check if a short container name is valid
         *
         * This checks for length and illegal characters.
         * This may disallow certain characters that can appear
         * in the prefix used to make the full container name.
         *
         * @param string $container
         * @return bool
         */
        final protected static function isValidShortContainerName( $container ) {
                // Suffixes like '.xxx' (hex shard chars) or '.seg' (file segments)
                // might be used by subclasses. Reserve the dot character for sanity.
                // The only way dots end up in containers (e.g. resolveStoragePath)
                // is due to the wikiId container prefix or the above suffixes.
                return self::isValidContainerName( $container ) && !preg_match( '/[.]/', $container );
        }

        /**
         * Check if a full container name is valid
         *
         * This checks for length and illegal characters.
         * Limiting the characters makes migrations to other stores easier.
         *
         * @param string $container
         * @return bool
         */
        final protected static function isValidContainerName( $container ) {
                // This accounts for NTFS, Swift, and Ceph restrictions
                // and disallows directory separators or traversal characters.
                // Note that matching strings URL encode to the same string;
                // in Swift/Ceph, the length restriction is *after* URL encoding.
                return (bool)preg_match( '/^[a-z0-9][a-z0-9-_.]{0,199}$/i', $container );
        }

        /**
         * Splits a storage path into an internal container name,
         * an internal relative file name, and a container shard suffix.
         * Any shard suffix is already appended to the internal container name.
         * This also checks that the storage path is valid and within this backend.
         *
         * If the container is sharded but a suffix could not be determined,
         * this means that the path can only refer to a directory and can only
         * be scanned by looking in all the container shards.
         *
         * @param string $storagePath
         * @return array (container, path, container suffix) or (null, null, null) if invalid
         */
        final protected function resolveStoragePath( $storagePath ) {
                list( $backend, $shortCont, $relPath ) = self::splitStoragePath( $storagePath );
                if ( $backend === $this->name ) { // must be for this backend
                        $relPath = self::normalizeContainerPath( $relPath );
                        if ( $relPath !== null && self::isValidShortContainerName( $shortCont ) ) {
                                // Get shard for the normalized path if this container is sharded
                                $cShard = $this->getContainerShard( $shortCont, $relPath );
                                // Validate and sanitize the relative path (backend-specific)
                                $relPath = $this->resolveContainerPath( $shortCont, $relPath );
                                if ( $relPath !== null ) {
                                        // Prepend any wiki ID prefix to the container name
                                        $container = $this->fullContainerName( $shortCont );
                                        if ( self::isValidContainerName( $container ) ) {
                                                // Validate and sanitize the container name (backend-specific)
                                                $container = $this->resolveContainerName( "{$container}{$cShard}" );
                                                if ( $container !== null ) {
                                                        return [ $container, $relPath, $cShard ];
                                                }
                                        }
                                }
                        }
                }

                return [ null, null, null ];
        }

        /**
         * Like resolveStoragePath() except null values are returned if
         * the container is sharded and the shard could not be determined
         * or if the path ends with '/'. The latter case is illegal for FS
         * backends and can confuse listings for object store backends.
         *
         * This function is used when resolving paths that must be valid
         * locations for files. Directory and listing functions should
         * generally just use resolveStoragePath() instead.
         *
         * @see FileBackendStore::resolveStoragePath()
         *
         * @param string $storagePath
         * @return array (container, path) or (null, null) if invalid
         */
        final protected function resolveStoragePathReal( $storagePath ) {
                list( $container, $relPath, $cShard ) = $this->resolveStoragePath( $storagePath );
                if ( $cShard !== null && substr( $relPath, -1 ) !== '/' ) {
                        return [ $container, $relPath ];
                }

                return [ null, null ];
        }

        /**
         * Get the container name shard suffix for a given path.
         * Any empty suffix means the container is not sharded.
         *
         * @param string $container Container name
         * @param string $relPath Storage path relative to the container
         * @return string|null Returns null if shard could not be determined
         */
        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.
                        $m = [];
                        if ( preg_match( "!^(?:[^/]{2,}/)*$hashDirRegex(?:/|$)!", $relPath, $m ) ) {
                                return '.' . implode( '', array_slice( $m, 1 ) );
                        }

                        return null; // failed to match
                }

                return ''; // no sharding
        }

        /**
         * Check if a storage path maps to a single shard.
         * Container dirs like "a", where the container shards on "x/xy",
         * can reside on several shards. Such paths are tricky to handle.
         *
         * @param string $storagePath Storage path
         * @return bool
         */
        final public function isSingleShardPathInternal( $storagePath ) {
                list( , , $shard ) = $this->resolveStoragePath( $storagePath );

                return ( $shard !== null );
        }

        /**
         * Get the sharding config for a container.
         * If greater than 0, then all file storage paths within
         * the container are required to be hashed accordingly.
         *
         * @param string $container
         * @return array (integer levels, integer base, repeat flag) or (0, 0, false)
         */
        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 [ $hashLevels, $hashBase, $config['repeat'] ];
                                }
                        }
                }

                return [ 0, 0, false ]; // no sharding
        }

        /**
         * Get a list of full container shard suffixes for a container
         *
         * @param string $container
         * @return array
         */
        final protected function getContainerSuffixes( $container ) {
                $shards = [];
                list( $digits, $base ) = $this->getContainerHashLevels( $container );
                if ( $digits > 0 ) {
                        $numShards = $base ** $digits;
                        for ( $index = 0; $index < $numShards; $index++ ) {
                                $shards[] = '.' . Wikimedia\base_convert( $index, 10, $base, $digits );
                        }
                }

                return $shards;
        }

        /**
         * Get the full container name, including the wiki ID prefix
         *
         * @param string $container
         * @return string
         */
        final protected function fullContainerName( $container ) {
                if ( $this->domainId != '' ) {
                        return "{$this->domainId}-$container";
                } else {
                        return $container;
                }
        }

        /**
         * Resolve a container name, checking if it's allowed by the backend.
         * This is intended for internal use, such as encoding illegal chars.
         * Subclasses can override this to be more restrictive.
         *
         * @param string $container
         * @return string|null
         */
        protected function resolveContainerName( $container ) {
                return $container;
        }

        /**
         * Resolve a relative storage path, checking if it's allowed by the backend.
         * This is intended for internal use, such as encoding illegal chars or perhaps
         * getting absolute paths (e.g. FS based backends). Note that the relative path
         * may be the empty string (e.g. the path is simply to the container).
         *
         * @param string $container Container name
         * @param string $relStoragePath Storage path relative to the container
         * @return string|null Path or null if not valid
         */
        protected function resolveContainerPath( $container, $relStoragePath ) {
                return $relStoragePath;
        }

        /**
         * Get the cache key for a container
         *
         * @param string $container Resolved container name
         * @return string
         */
        private function containerCacheKey( $container ) {
                return "filebackend:{$this->name}:{$this->domainId}:container:{$container}";
        }

        /**
         * Set the cached info for a container
         *
         * @param string $container Resolved container name
         * @param array $val Information to cache
         */
        final protected function setContainerCache( $container, array $val ) {
                $this->memCache->set( $this->containerCacheKey( $container ), $val, 14 * 86400 );
        }

        /**
         * Delete the cached info for a container.
         * The cache key is salted for a while to prevent race conditions.
         *
         * @param string $container Resolved container name
         */
        final protected function deleteContainerCache( $container ) {
                if ( !$this->memCache->delete( $this->containerCacheKey( $container ), 300 ) ) {
                        trigger_error( "Unable to delete stat cache for container $container." );
                }
        }

        /**
         * Do a batch lookup from cache for container stats for all containers
         * used in a list of container names or storage paths objects.
         * This loads the persistent cache values into the process cache.
         *
         * @param array $items
         */
        final protected function primeContainerCache( array $items ) {
                /** @noinspection PhpUnusedLocalVariableInspection */
                $ps = $this->scopedProfileSection( __METHOD__ . "-{$this->name}" );

                $paths = []; // list of storage paths
                $contNames = []; // (cache key => resolved container name)
                // Get all the paths/containers from the items...
                foreach ( $items as $item ) {
                        if ( 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 = []; // (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' ) );
        }

        /**
         * Fill the backend-specific process cache given an array of
         * resolved container names and their corresponding cached info.
         * Only containers that actually exist should appear in the map.
         *
         * @param array $containerInfo Map of resolved container names to cached info
         */
        protected function doPrimeContainerCache( array $containerInfo ) {
        }

        /**
         * Get the cache key for a file path
         *
         * @param string $path Normalized storage path
         * @return string
         */
        private function fileCacheKey( $path ) {
                return "filebackend:{$this->name}:{$this->domainId}:file:" . sha1( $path );
        }

        /**
         * Set the cached stat info for a file path.
         * Negatives (404s) are not cached. By not caching negatives, we can skip cache
         * salting for the case when a file is created at a path were there was none before.
         *
         * @param string $path Storage path
         * @param array $val Stat information to cache
         */
        final protected function setFileCache( $path, array $val ) {
                $path = FileBackend::normalizeStoragePath( $path );
                if ( $path === null ) {
                        return; // invalid storage path
                }
                $mtime = ConvertibleTimestamp::convert( TS_UNIX, $val['mtime'] );
                $ttl = $this->memCache->adaptiveTTL( $mtime, 7 * 86400, 300, 0.1 );
                $key = $this->fileCacheKey( $path );
                // Set the cache unless it is currently salted.
                $this->memCache->set( $key, $val, $ttl );
        }

        /**
         * Delete the cached stat info for a file path.
         * The cache key is salted for a while to prevent race conditions.
         * Since negatives (404s) are not cached, this does not need to be called when
         * a file is created at a path were there was none before.
         *
         * @param string $path Storage path
         */
        final protected function deleteFileCache( $path ) {
                $path = FileBackend::normalizeStoragePath( $path );
                if ( $path === null ) {
                        return; // invalid storage path
                }
                if ( !$this->memCache->delete( $this->fileCacheKey( $path ), 300 ) ) {
                        trigger_error( "Unable to delete stat cache for file $path." );
                }
        }

        /**
         * Do a batch lookup from cache for file stats for all paths
         * used in a list of storage paths or FileOp objects.
         * This loads the persistent cache values into the process cache.
         *
         * @param array $items List of storage paths
         */
        final protected function primeFileCache( array $items ) {
                /** @noinspection PhpUnusedLocalVariableInspection */
                $ps = $this->scopedProfileSection( __METHOD__ . "-{$this->name}" );

                $paths = []; // list of storage paths
                $pathNames = []; // (cache key => storage path)
                // Get all the paths/containers from the items...
                foreach ( $items as $item ) {
                        if ( 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 file cache keys...
                $values = $this->memCache->getMulti( array_keys( $pathNames ) );
                foreach ( $values as $cacheKey => $val ) {
                        $path = $pathNames[$cacheKey];
                        if ( is_array( $val ) ) {
                                $val['latest'] = false; // never completely trust cache
                                $this->cheapCache->setField( $path, 'stat', $val );
                                if ( isset( $val['sha1'] ) ) { // some backends store SHA-1 as metadata
                                        $this->cheapCache->setField( $path, 'sha1',
                                                [ 'hash' => $val['sha1'], 'latest' => false ] );
                                }
                                if ( isset( $val['xattr'] ) ) { // some backends store headers/metadata
                                        $val['xattr'] = self::normalizeXAttributes( $val['xattr'] );
                                        $this->cheapCache->setField( $path, 'xattr',
                                                [ 'map' => $val['xattr'], 'latest' => false ] );
                                }
                        }
                }
        }

        /**
         * Normalize file headers/metadata to the FileBackend::getFileXAttributes() format
         *
         * @param array $xattr
         * @return array
         * @since 1.22
         */
        final protected static function normalizeXAttributes( array $xattr ) {
                $newXAttr = [ 'headers' => [], 'metadata' => [] ];

                foreach ( $xattr['headers'] as $name => $value ) {
                        $newXAttr['headers'][strtolower( $name )] = $value;
                }

                foreach ( $xattr['metadata'] as $name => $value ) {
                        $newXAttr['metadata'][strtolower( $name )] = $value;
                }

                return $newXAttr;
        }

        /**
         * Set the 'concurrency' option from a list of operation options
         *
         * @param array $opts Map of operation options
         * @return array
         */
        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;
        }

        /**
         * Get the content type to use in HEAD/GET requests for a file
         *
         * @param string $storagePath
         * @param string|null $content File data
         * @param string|null $fsPath File system path
         * @return string MIME type
         */
        protected function getContentType( $storagePath, $content, $fsPath ) {
                if ( $this->mimeCallback ) {
                        return call_user_func_array( $this->mimeCallback, func_get_args() );
                }

                $mime = ( $fsPath !== null ) ? mime_content_type( $fsPath ) : false;
                return $mime ?: 'unknown/unknown';
        }
}