Merge "rest: Return a 400 for invalid render IDs"

[mediawiki.git] / includes / libs / objectcache / MediumSpecificBagOStuff.php

<?php
/**
 * 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
 */
namespace Wikimedia\ObjectCache;

use InvalidArgumentException;
use JsonSerializable;
use stdClass;
use Wikimedia\WaitConditionLoop;

/**
 * Helper classs that implements most of BagOStuff for a backend.
 *
 * This should be used by concrete implementations only. Wrapper classes that
 * proxy another BagOStuff should extend and implement BagOStuff directly.
 *
 * @ingroup Cache
 * @since 1.34
 */
abstract class MediumSpecificBagOStuff extends BagOStuff {
        /** @var array<string,array> Map of (key => (class LOCK_* constant => value) */
        protected $locks = [];
        /** @var int Bytes; chunk size of segmented cache values */
        protected $segmentationSize;
        /** @var int Bytes; maximum total size of a segmented cache value */
        protected $segmentedValueMaxSize;

        /** @var float Seconds; maximum expected seconds for a lock ping to reach the backend */
        protected $maxLockSendDelay = 0.05;

        /** @var array */
        private $duplicateKeyLookups = [];
        /** @var bool */
        private $reportDupes = false;
        /** @var bool */
        private $dupeTrackScheduled = false;

        /** Component to use for key construction of blob segment keys */
        private const SEGMENT_COMPONENT = 'segment';

        /** Idiom for doGet() to return extra information by reference */
        protected const PASS_BY_REF = -1;

        protected const METRIC_OP_GET = 'get';
        protected const METRIC_OP_SET = 'set';
        protected const METRIC_OP_DELETE = 'delete';
        protected const METRIC_OP_CHANGE_TTL = 'change_ttl';
        protected const METRIC_OP_ADD = 'add';
        protected const METRIC_OP_INCR = 'incr';
        protected const METRIC_OP_DECR = 'decr';
        protected const METRIC_OP_CAS = 'cas';

        protected const LOCK_RCLASS = 0;
        protected const LOCK_DEPTH = 1;
        protected const LOCK_TIME = 2;
        protected const LOCK_EXPIRY = 3;

        /**
         * @see BagOStuff::__construct()
         * Additional $params options include:
         *   - logger: Psr\Log\LoggerInterface instance
         *   - reportDupes: Whether to emit warning log messages for all keys that were
         *      requested more than once (requires an asyncHandler).
         *   - segmentationSize: The chunk size, in bytes, of segmented values. The value should
         *      not exceed the maximum size of values in the storage backend, as configured by
         *      the site administrator.
         *   - segmentedValueMaxSize: The maximum total size, in bytes, of segmented values.
         *      This should be configured to a reasonable size give the site traffic and the
         *      amount of I/O between application and cache servers that the network can handle.
         *
         * @param array $params
         *
         * @phpcs:ignore Generic.Files.LineLength
         * @phan-param array{logger?:\Psr\Log\LoggerInterface,asyncHandler?:callable,reportDupes?:bool,segmentationSize?:int|float,segmentedValueMaxSize?:int} $params
         */
        public function __construct( array $params = [] ) {
                parent::__construct( $params );

                if ( !empty( $params['reportDupes'] ) && $this->asyncHandler ) {
                        $this->reportDupes = true;
                }

                // Default to 8MiB if segmentationSize is not set
                $this->segmentationSize = $params['segmentationSize'] ?? 8_388_608;
                // Default to 64MiB if segmentedValueMaxSize is not set
                $this->segmentedValueMaxSize = $params['segmentedValueMaxSize'] ?? 67_108_864;
        }

        /**
         * Get an item with the given key
         *
         * If the key includes a deterministic input hash (e.g. the key can only have
         * the correct value) or complete staleness checks are handled by the caller
         * (e.g. nothing relies on the TTL), then the READ_VERIFIED flag should be set.
         * This lets tiered backends know they can safely upgrade a cached value to
         * higher tiers using standard TTLs.
         *
         * @param string $key
         * @param int $flags Bitfield of BagOStuff::READ_* constants [optional]
         *
         * @return mixed Returns false on failure or if the item does not exist
         */
        public function get( $key, $flags = 0 ) {
                $this->trackDuplicateKeys( $key );

                return $this->resolveSegments( $key, $this->doGet( $key, $flags ) );
        }

        /**
         * Track the number of times that a given key has been used.
         *
         * @param string $key
         */
        private function trackDuplicateKeys( $key ) {
                if ( !$this->reportDupes ) {
                        return;
                }

                if ( !isset( $this->duplicateKeyLookups[$key] ) ) {
                        // Track that we have seen this key. This N-1 counting style allows
                        // easy filtering with array_filter() later.
                        $this->duplicateKeyLookups[$key] = 0;
                } else {
                        $this->duplicateKeyLookups[$key]++;

                        if ( $this->dupeTrackScheduled === false ) {
                                $this->dupeTrackScheduled = true;
                                // Schedule a callback that logs keys processed more than once by get().
                                call_user_func( $this->asyncHandler, function () {
                                        $dups = array_filter( $this->duplicateKeyLookups );
                                        foreach ( $dups as $key => $count ) {
                                                $this->logger->warning(
                                                        'Duplicate get(): "{key}" fetched {count} times',
                                                        // Count is N-1 of the actual lookup count
                                                        [ 'key' => $key, 'count' => $count + 1, ]
                                                );
                                        }
                                } );
                        }
                }
        }

        /**
         * Get an item
         *
         * The CAS token should be null if the key does not exist or the value is corrupt
         *
         * @param string $key
         * @param int $flags Bitfield of BagOStuff::READ_* constants [optional]
         * @param mixed &$casToken CAS token if MediumSpecificBagOStuff::PASS_BY_REF [returned]
         *
         * @return mixed Returns false on failure or if the item does not exist
         */
        abstract protected function doGet( $key, $flags = 0, &$casToken = null );

        public function set( $key, $value, $exptime = 0, $flags = 0 ) {
                $entry = $this->makeValueOrSegmentList( $key, $value, $exptime, $flags, $ok );

                // Only when all segments (if any) are stored should the main key be changed
                return $ok && $this->doSet( $key, $entry, $exptime, $flags );
        }

        /**
         * Set an item
         *
         * @param string $key
         * @param mixed $value
         * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
         * @param int $flags Bitfield of BagOStuff::WRITE_* constants
         *
         * @return bool Success
         */
        abstract protected function doSet( $key, $value, $exptime = 0, $flags = 0 );

        public function delete( $key, $flags = 0 ) {
                if ( !$this->fieldHasFlags( $flags, self::WRITE_ALLOW_SEGMENTS ) ) {
                        return $this->doDelete( $key, $flags );
                }

                $mainValue = $this->doGet( $key, self::READ_LATEST );
                if ( !$this->doDelete( $key, $flags ) ) {
                        return false;
                }

                if ( !SerializedValueContainer::isSegmented( $mainValue ) ) {
                        // no segments to delete
                        return true;
                }

                $orderedKeys = array_map(
                        function ( $segmentHash ) use ( $key ) {
                                return $this->makeGlobalKey( self::SEGMENT_COMPONENT, $key, $segmentHash );
                        },
                        $mainValue->{SerializedValueContainer::SEGMENTED_HASHES}
                );

                return $this->deleteMulti( $orderedKeys, $flags & ~self::WRITE_ALLOW_SEGMENTS );
        }

        /**
         * Delete an item
         *
         * @param string $key
         * @param int $flags Bitfield of BagOStuff::WRITE_* constants
         *
         * @return bool True if the item was deleted or not found, false on failure
         */
        abstract protected function doDelete( $key, $flags = 0 );

        public function add( $key, $value, $exptime = 0, $flags = 0 ) {
                $entry = $this->makeValueOrSegmentList( $key, $value, $exptime, $flags, $ok );

                // Only when all segments (if any) are stored should the main key be changed
                return $ok && $this->doAdd( $key, $entry, $exptime, $flags );
        }

        /**
         * Insert an item if it does not already exist
         *
         * @param string $key
         * @param mixed $value
         * @param int $exptime
         * @param int $flags Bitfield of BagOStuff::WRITE_* constants (since 1.33)
         *
         * @return bool Success
         */
        abstract protected function doAdd( $key, $value, $exptime = 0, $flags = 0 );

        /**
         * Merge changes into the existing cache value (possibly creating a new one)
         *
         * The callback function returns the new value given the current value
         * (which will be false if not present), and takes the arguments:
         * (this BagOStuff, cache key, current value, TTL).
         * The TTL parameter is reference set to $exptime. It can be overridden in the callback.
         * Nothing is stored nor deleted if the callback returns false.
         *
         * @param string $key
         * @param callable $callback Callback method to be executed
         * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
         * @param int $attempts The amount of times to attempt a merge in case of failure
         * @param int $flags Bitfield of BagOStuff::WRITE_* constants
         *
         * @return bool Success
         */
        public function merge( $key, callable $callback, $exptime = 0, $attempts = 10, $flags = 0 ) {
                return $this->mergeViaCas( $key, $callback, $exptime, $attempts, $flags );
        }

        /**
         * @param string $key
         * @param callable $callback Callback method to be executed
         * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
         * @param int $attempts The amount of times to attempt a merge in case of failure
         * @param int $flags Bitfield of BagOStuff::WRITE_* constants
         *
         * @return bool Success
         * @see BagOStuff::merge()
         */
        final protected function mergeViaCas( $key, callable $callback, $exptime, $attempts, $flags ) {
                $attemptsLeft = $attempts;
                do {
                        $token = self::PASS_BY_REF;
                        // Get the old value and CAS token from cache
                        $watchPoint = $this->watchErrors();
                        $currentValue = $this->resolveSegments(
                                $key,
                                $this->doGet( $key, $flags, $token )
                        );
                        if ( $this->getLastError( $watchPoint ) ) {
                                // Don't spam slow retries due to network problems (retry only on races)
                                $this->logger->warning(
                                        __METHOD__ . ' failed due to read I/O error on get() for {key}.', [ 'key' => $key ]
                                );
                                $success = false;
                                break;
                        }

                        // Derive the new value from the old value
                        $value = $callback( $this, $key, $currentValue, $exptime );
                        $keyWasNonexistent = ( $currentValue === false );
                        $valueMatchesOldValue = ( $value === $currentValue );
                        // free RAM in case the value is large
                        unset( $currentValue );

                        $watchPoint = $this->watchErrors();
                        if ( $value === false || $exptime < 0 ) {
                                // do nothing
                                $success = true;
                        } elseif ( $valueMatchesOldValue && $attemptsLeft !== $attempts ) {
                                // recently set by another thread to the same value
                                $success = true;
                        } elseif ( $keyWasNonexistent ) {
                                // Try to create the key, failing if it gets created in the meantime
                                $success = $this->add( $key, $value, $exptime, $flags );
                        } else {
                                // Try to update the key, failing if it gets changed in the meantime
                                $success = $this->cas( $token, $key, $value, $exptime, $flags );
                        }
                        if ( $this->getLastError( $watchPoint ) ) {
                                // Don't spam slow retries due to network problems (retry only on races)
                                $this->logger->warning(
                                        __METHOD__ . ' failed due to write I/O error for {key}.',
                                        [ 'key' => $key ]
                                );
                                $success = false;
                                break;
                        }

                } while ( !$success && --$attemptsLeft );

                return $success;
        }

        /**
         * Set an item if the current CAS token matches the provided CAS token
         *
         * @param mixed $casToken Only set the item if it still has this CAS token
         * @param string $key
         * @param mixed $value
         * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
         * @param int $flags Bitfield of BagOStuff::WRITE_* constants
         *
         * @return bool Success
         */
        protected function cas( $casToken, $key, $value, $exptime = 0, $flags = 0 ) {
                if ( $casToken === null ) {
                        $this->logger->warning(
                                __METHOD__ . ' got empty CAS token for {key}.',
                                [ 'key' => $key ]
                        );

                        // caller may have meant to use add()?
                        return false;
                }

                $entry = $this->makeValueOrSegmentList( $key, $value, $exptime, $flags, $ok );

                // Only when all segments (if any) are stored should the main key be changed
                return $ok && $this->doCas( $casToken, $key, $entry, $exptime, $flags );
        }

        /**
         * Set an item if the current CAS token matches the provided CAS token
         *
         * @param mixed $casToken CAS token from an existing version of the key
         * @param string $key
         * @param mixed $value
         * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
         * @param int $flags Bitfield of BagOStuff::WRITE_* constants
         *
         * @return bool Success
         */
        protected function doCas( $casToken, $key, $value, $exptime = 0, $flags = 0 ) {
                // @TODO: the use of lock() assumes that all other relevant sets() use a lock
                if ( !$this->lock( $key, 0 ) ) {
                        // non-blocking
                        return false;
                }

                $curCasToken = self::PASS_BY_REF;
                $watchPoint = $this->watchErrors();
                $exists = ( $this->doGet( $key, self::READ_LATEST, $curCasToken ) !== false );
                if ( $this->getLastError( $watchPoint ) ) {
                        // Fail if the old CAS token could not be read
                        $success = false;
                        $this->logger->warning(
                                __METHOD__ . ' failed due to write I/O error for {key}.',
                                [ 'key' => $key ]
                        );
                } elseif ( $exists && $this->tokensMatch( $casToken, $curCasToken ) ) {
                        $success = $this->doSet( $key, $value, $exptime, $flags );
                } else {
                        // mismatched or failed
                        $success = false;
                        $this->logger->info(
                                __METHOD__ . ' failed due to race condition for {key}.',
                                [ 'key' => $key, 'key_exists' => $exists ]
                        );
                }

                $this->unlock( $key );

                return $success;
        }

        /**
         * @param mixed $value CAS token for an existing key
         * @param mixed $otherValue CAS token for an existing key
         *
         * @return bool Whether the two tokens match
         */
        final protected function tokensMatch( $value, $otherValue ) {
                $type = gettype( $value );
                // Ideally, tokens are counters, timestamps, hashes, or serialized PHP values.
                // However, some classes might use the PHP values themselves.
                if ( $type !== gettype( $otherValue ) ) {
                        return false;
                }
                // Serialize both tokens to strictly compare objects or arrays (which might objects
                // nested inside). Note that this will not apply if integer/string CAS tokens are used.
                if ( $type === 'array' || $type === 'object' ) {
                        return ( serialize( $value ) === serialize( $otherValue ) );
                }

                // For string/integer tokens, use a simple comparison
                return ( $value === $otherValue );
        }

        /**
         * Change the expiration on a key if it exists
         *
         * If an expiry in the past is given then the key will immediately be expired
         *
         * For large values written using WRITE_ALLOW_SEGMENTS, this only changes the TTL of the
         * main segment list key. While lowering the TTL of the segment list key has the effect of
         * functionally lowering the TTL of the key, it might leave unused blobs in cache for longer.
         * Raising the TTL of such keys is not effective, since the expiration of a single segment
         * key effectively expires the entire value.
         *
         * @param string $key
         * @param int $exptime TTL or UNIX timestamp
         * @param int $flags Bitfield of BagOStuff::WRITE_* constants (since 1.33)
         *
         * @return bool Success Returns false on failure or if the item does not exist
         * @since 1.28
         */
        public function changeTTL( $key, $exptime = 0, $flags = 0 ) {
                return $this->doChangeTTL( $key, $exptime, $flags );
        }

        /**
         * @param string $key
         * @param int $exptime
         * @param int $flags
         *
         * @return bool
         */
        protected function doChangeTTL( $key, $exptime, $flags ) {
                // @TODO: the use of lock() assumes that all other relevant sets() use a lock
                if ( !$this->lock( $key, 0 ) ) {
                        return false;
                }

                $expiry = $this->getExpirationAsTimestamp( $exptime );
                $delete = ( $expiry != self::TTL_INDEFINITE && $expiry < $this->getCurrentTime() );

                // Use doGet() to avoid having to trigger resolveSegments()
                $blob = $this->doGet( $key, self::READ_LATEST );
                if ( $blob ) {
                        if ( $delete ) {
                                $ok = $this->doDelete( $key, $flags );
                        } else {
                                $ok = $this->doSet( $key, $blob, $exptime, $flags );
                        }
                } else {
                        $ok = false;
                }

                $this->unlock( $key );

                return $ok;
        }

        public function incrWithInit( $key, $exptime, $step = 1, $init = null, $flags = 0 ) {
                $step = (int)$step;
                $init = is_int( $init ) ? $init : $step;

                return $this->doIncrWithInit( $key, $exptime, $step, $init, $flags );
        }

        /**
         * @param string $key
         * @param int $exptime
         * @param int $step
         * @param int $init
         * @param int $flags
         *
         * @return int|bool New value or false on failure
         */
        abstract protected function doIncrWithInit( $key, $exptime, $step, $init, $flags );

        /**
         * @param string $key
         * @param int $timeout
         * @param int $exptime
         * @param string $rclass
         *
         * @return bool
         */
        public function lock( $key, $timeout = 6, $exptime = 6, $rclass = '' ) {
                $exptime = min( $exptime ?: INF, self::TTL_DAY );

                $acquired = false;

                if ( isset( $this->locks[$key] ) ) {
                        // Already locked; avoid deadlocks and allow lock reentry if specified
                        if ( $rclass != '' && $this->locks[$key][self::LOCK_RCLASS] === $rclass ) {
                                ++$this->locks[$key][self::LOCK_DEPTH];
                                $acquired = true;
                        }
                } else {
                        // Not already locked; acquire a lock on the backend
                        $lockTsUnix = $this->doLock( $key, $timeout, $exptime );
                        if ( $lockTsUnix !== null ) {
                                $this->locks[$key] = [
                                        self::LOCK_RCLASS => $rclass,
                                        self::LOCK_DEPTH  => 1,
                                        self::LOCK_TIME   => $lockTsUnix,
                                        self::LOCK_EXPIRY => $lockTsUnix + $exptime
                                ];
                                $acquired = true;
                        }
                }

                return $acquired;
        }

        /**
         * @see MediumSpecificBagOStuff::lock()
         *
         * @param string $key
         * @param int $timeout Lock wait timeout; 0 for non-blocking [optional]
         * @param int $exptime Lock time-to-live 1 day maximum [optional]
         *
         * @return float|null UNIX timestamp of acquisition; null on failure
         */
        protected function doLock( $key, $timeout, $exptime ) {
                $lockTsUnix = null;

                $fname = __METHOD__;
                $loop = new WaitConditionLoop(
                        function () use ( $key, $exptime, $fname, &$lockTsUnix ) {
                                $watchPoint = $this->watchErrors();
                                if ( $this->add( $this->makeLockKey( $key ), 1, $exptime ) ) {
                                        $lockTsUnix = microtime( true );

                                        return WaitConditionLoop::CONDITION_REACHED;
                                } elseif ( $this->getLastError( $watchPoint ) ) {
                                        $this->logger->warning(
                                                "$fname failed due to I/O error for {key}.",
                                                [ 'key' => $key ]
                                        );

                                        return WaitConditionLoop::CONDITION_ABORTED;
                                }

                                return WaitConditionLoop::CONDITION_CONTINUE;
                        },
                        $timeout
                );
                $code = $loop->invoke();

                if ( $code === $loop::CONDITION_TIMED_OUT ) {
                        $this->logger->warning(
                                "$fname failed due to timeout for {key}.",
                                [ 'key' => $key, 'timeout' => $timeout ]
                        );
                }

                return $lockTsUnix;
        }

        /**
         * Release an advisory lock on a key string
         *
         * @param string $key
         *
         * @return bool Success
         */
        public function unlock( $key ) {
                $released = false;

                if ( isset( $this->locks[$key] ) ) {
                        if ( --$this->locks[$key][self::LOCK_DEPTH] > 0 ) {
                                $released = true;
                        } else {
                                $released = $this->doUnlock( $key );
                                unset( $this->locks[$key] );
                                if ( !$released ) {
                                        $this->logger->warning(
                                                __METHOD__ . ' failed to release lock for {key}.',
                                                [ 'key' => $key ]
                                        );
                                }
                        }
                } else {
                        $this->logger->warning(
                                __METHOD__ . ' no lock to release for {key}.',
                                [ 'key' => $key ]
                        );
                }

                return $released;
        }

        /**
         * @see MediumSpecificBagOStuff::unlock()
         *
         * @param string $key
         *
         * @return bool Success
         */
        protected function doUnlock( $key ) {
                $released = false;

                // Estimate the remaining TTL of the lock key
                $curTTL = $this->locks[$key][self::LOCK_EXPIRY] - $this->getCurrentTime();

                // Check the risk of race conditions for key deletion
                if ( $this->getQoS( self::ATTR_DURABILITY ) <= self::QOS_DURABILITY_SCRIPT ) {
                        // Lock (and data) keys use memory specific to this request (e.g. HashBagOStuff)
                        $isSafe = true;
                } else {
                        // It is unsafe to delete the lock key if there is a serious risk of the key already
                        // being claimed by another thread before the delete operation reaches the backend
                        $isSafe = ( $curTTL > $this->maxLockSendDelay );
                }

                if ( $isSafe ) {
                        $released = $this->doDelete( $this->makeLockKey( $key ) );
                } else {
                        $this->logger->warning(
                                "Lock for {key} held too long ({age} sec).",
                                [ 'key' => $key, 'curTTL' => $curTTL ]
                        );
                }

                return $released;
        }

        /**
         * @param string $key
         *
         * @return string
         */
        protected function makeLockKey( $key ) {
                return "$key:lock";
        }

        public function deleteObjectsExpiringBefore(
                $timestamp,
                ?callable $progress = null,
                $limit = INF,
                ?string $tag = null
        ) {
                return false;
        }

        /**
         * Get an associative array containing the item for each of the keys that have items.
         *
         * @param string[] $keys List of keys; can be a map of (unused => key) for convenience
         * @param int $flags Bitfield; supports READ_LATEST [optional]
         *
         * @return mixed[] Map of (key => value) for existing keys; preserves the order of $keys
         */
        public function getMulti( array $keys, $flags = 0 ) {
                $foundByKey = $this->doGetMulti( $keys, $flags );

                $res = [];
                foreach ( $keys as $key ) {
                        // Resolve one blob at a time (avoids too much I/O at once)
                        if ( array_key_exists( $key, $foundByKey ) ) {
                                // A value should not appear in the key if a segment is missing
                                $value = $this->resolveSegments( $key, $foundByKey[$key] );
                                if ( $value !== false ) {
                                        $res[$key] = $value;
                                }
                        }
                }

                return $res;
        }

        /**
         * Get an associative array containing the item for each of the keys that have items.
         *
         * @param string[] $keys List of keys
         * @param int $flags Bitfield; supports READ_LATEST [optional]
         *
         * @return array Map of (key => value) for existing keys; preserves the order of $keys
         */
        protected function doGetMulti( array $keys, $flags = 0 ) {
                $res = [];
                foreach ( $keys as $key ) {
                        $val = $this->doGet( $key, $flags );
                        if ( $val !== false ) {
                                $res[$key] = $val;
                        }
                }

                return $res;
        }

        /**
         * Batch insertion/replace
         *
         * This does not support WRITE_ALLOW_SEGMENTS to avoid excessive read I/O
         *
         * @param mixed[] $valueByKey Map of (key => value)
         * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
         * @param int $flags Bitfield of BagOStuff::WRITE_* constants (since 1.33)
         *
         * @return bool Success
         * @since 1.24
         */
        public function setMulti( array $valueByKey, $exptime = 0, $flags = 0 ) {
                if ( $this->fieldHasFlags( $flags, self::WRITE_ALLOW_SEGMENTS ) ) {
                        throw new InvalidArgumentException( __METHOD__ . ' got WRITE_ALLOW_SEGMENTS' );
                }

                return $this->doSetMulti( $valueByKey, $exptime, $flags );
        }

        /**
         * @param mixed[] $data Map of (key => value)
         * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
         * @param int $flags Bitfield of BagOStuff::WRITE_* constants
         *
         * @return bool Success
         */
        protected function doSetMulti( array $data, $exptime = 0, $flags = 0 ) {
                $res = true;
                foreach ( $data as $key => $value ) {
                        $res = $this->doSet( $key, $value, $exptime, $flags ) && $res;
                }

                return $res;
        }

        public function deleteMulti( array $keys, $flags = 0 ) {
                if ( $this->fieldHasFlags( $flags, self::WRITE_ALLOW_SEGMENTS ) ) {
                        throw new InvalidArgumentException( __METHOD__ . ' got WRITE_ALLOW_SEGMENTS' );
                }

                return $this->doDeleteMulti( $keys, $flags );
        }

        /**
         * @param string[] $keys List of keys
         * @param int $flags Bitfield of BagOStuff::WRITE_* constants
         *
         * @return bool Success
         */
        protected function doDeleteMulti( array $keys, $flags = 0 ) {
                $res = true;
                foreach ( $keys as $key ) {
                        $res = $this->doDelete( $key, $flags ) && $res;
                }

                return $res;
        }

        /**
         * Change the expiration of multiple keys that exist
         *
         * @param string[] $keys List of keys
         * @param int $exptime TTL or UNIX timestamp
         * @param int $flags Bitfield of BagOStuff::WRITE_* constants (since 1.33)
         *
         * @return bool Success
         *
         * @since 1.34
         */
        public function changeTTLMulti( array $keys, $exptime, $flags = 0 ) {
                return $this->doChangeTTLMulti( $keys, $exptime, $flags );
        }

        /**
         * @param string[] $keys List of keys
         * @param int $exptime TTL or UNIX timestamp
         * @param int $flags Bitfield of BagOStuff::WRITE_* constants
         *
         * @return bool Success
         */
        protected function doChangeTTLMulti( array $keys, $exptime, $flags = 0 ) {
                $res = true;
                foreach ( $keys as $key ) {
                        $res = $this->doChangeTTL( $key, $exptime, $flags ) && $res;
                }

                return $res;
        }

        /**
         * Get and reassemble the chunks of blob at the given key
         *
         * @param string $key
         * @param mixed $mainValue
         *
         * @return string|null|bool The combined string, false if missing, null on error
         */
        final protected function resolveSegments( $key, $mainValue ) {
                if ( SerializedValueContainer::isSegmented( $mainValue ) ) {
                        $orderedKeys = array_map(
                                function ( $segmentHash ) use ( $key ) {
                                        return $this->makeGlobalKey( self::SEGMENT_COMPONENT, $key, $segmentHash );
                                },
                                $mainValue->{SerializedValueContainer::SEGMENTED_HASHES}
                        );

                        $segmentsByKey = $this->doGetMulti( $orderedKeys );

                        $parts = [];
                        foreach ( $orderedKeys as $segmentKey ) {
                                if ( isset( $segmentsByKey[$segmentKey] ) ) {
                                        $parts[] = $segmentsByKey[$segmentKey];
                                } else {
                                        // missing segment
                                        return false;
                                }
                        }

                        return $this->unserialize( implode( '', $parts ) );
                }

                return $mainValue;
        }

        /**
         * Check if a value should use a segmentation wrapper due to its size
         *
         * In order to avoid extra serialization and/or twice-serialized wrappers, just check if
         * the value is a large string. Support cache wrappers (e.g. WANObjectCache) that use 2D
         * arrays to wrap values. This does not recurse in order to avoid overhead from complex
         * structures and the risk of infinite loops (due to references).
         *
         * @param mixed $value
         * @param int $flags
         *
         * @return bool
         */
        private function useSegmentationWrapper( $value, $flags ) {
                if (
                        $this->segmentationSize === INF ||
                        !$this->fieldHasFlags( $flags, self::WRITE_ALLOW_SEGMENTS )
                ) {
                        return false;
                }

                if ( is_string( $value ) ) {
                        return ( strlen( $value ) >= $this->segmentationSize );
                }

                if ( is_array( $value ) ) {
                        // Expect that the contained value will be one of the first array entries
                        foreach ( array_slice( $value, 0, 4 ) as $v ) {
                                if ( is_string( $v ) && strlen( $v ) >= $this->segmentationSize ) {
                                        return true;
                                }
                        }
                }

                // Avoid breaking functions for incrementing/decrementing integer key values
                return false;
        }

        /**
         * Make the entry to store at a key (inline or segment list), storing any segments
         *
         * @param string $key
         * @param mixed $value
         * @param int $exptime
         * @param int $flags
         * @param mixed|null &$ok Whether the entry is usable (e.g. no missing segments) [returned]
         *
         * @return mixed The entry (inline value, wrapped inline value, or wrapped segment list)
         * @since 1.34
         */
        final protected function makeValueOrSegmentList( $key, $value, $exptime, $flags, &$ok ) {
                $entry = $value;
                $ok = true;

                if ( $this->useSegmentationWrapper( $value, $flags ) ) {
                        $segmentSize = $this->segmentationSize;
                        $maxTotalSize = $this->segmentedValueMaxSize;
                        $serialized = $this->getSerialized( $value, $key );
                        $size = strlen( $serialized );
                        if ( $size > $maxTotalSize ) {
                                $this->logger->warning(
                                        "Value for {key} exceeds $maxTotalSize bytes; cannot segment.",
                                        [ 'key' => $key ]
                                );
                        } else {
                                // Split the serialized value into chunks and store them at different keys
                                $chunksByKey = [];
                                $segmentHashes = [];
                                $count = intdiv( $size, $segmentSize ) + ( ( $size % $segmentSize ) ? 1 : 0 );
                                for ( $i = 0; $i < $count; ++$i ) {
                                        $segment = substr( $serialized, $i * $segmentSize, $segmentSize );
                                        $hash = sha1( $segment );
                                        $chunkKey = $this->makeGlobalKey( self::SEGMENT_COMPONENT, $key, $hash );
                                        $chunksByKey[$chunkKey] = $segment;
                                        $segmentHashes[] = $hash;
                                }
                                $flags &= ~self::WRITE_ALLOW_SEGMENTS;
                                $ok = $this->setMulti( $chunksByKey, $exptime, $flags );
                                $entry = SerializedValueContainer::newSegmented( $segmentHashes );
                        }
                }

                return $entry;
        }

        /**
         * @param int|float $exptime
         *
         * @return bool Whether the expiry is non-infinite, and, negative or not a UNIX timestamp
         * @since 1.34
         */
        final protected function isRelativeExpiration( $exptime ) {
                return ( $exptime !== self::TTL_INDEFINITE && $exptime < ( 10 * self::TTL_YEAR ) );
        }

        /**
         * Convert an optionally relative timestamp to an absolute time
         *
         * The input value will be cast to an integer and interpreted as follows:
         *   - zero: no expiry; return zero (e.g. TTL_INDEFINITE)
         *   - negative: relative TTL; return UNIX timestamp offset by this value
         *   - positive (< 10 years): relative TTL; return UNIX timestamp offset by this value
         *   - positive (>= 10 years): absolute UNIX timestamp; return this value
         *
         * @param int $exptime
         *
         * @return int Expiration timestamp or TTL_INDEFINITE for indefinite
         * @since 1.34
         */
        final protected function getExpirationAsTimestamp( $exptime ) {
                if ( $exptime == self::TTL_INDEFINITE ) {
                        return $exptime;
                }

                return $this->isRelativeExpiration( $exptime )
                        ? intval( $this->getCurrentTime() + $exptime )
                        : $exptime;
        }

        /**
         * Convert an optionally absolute expiry time to a relative time. If an
         * absolute time is specified which is in the past, use a short expiry time.
         *
         * The input value will be cast to an integer and interpreted as follows:
         *   - zero: no expiry; return zero (e.g. TTL_INDEFINITE)
         *   - negative: relative TTL; return a short expiry time (1 second)
         *   - positive (< 10 years): relative TTL; return this value
         *   - positive (>= 10 years): absolute UNIX timestamp; return offset to current time
         *
         * @param int $exptime
         *
         * @return int Relative TTL or TTL_INDEFINITE for indefinite
         * @since 1.34
         */
        final protected function getExpirationAsTTL( $exptime ) {
                if ( $exptime == self::TTL_INDEFINITE ) {
                        return $exptime;
                }

                return $this->isRelativeExpiration( $exptime )
                        ? $exptime
                        : (int)max( $exptime - $this->getCurrentTime(), 1 );
        }

        /**
         * Check if a value is an integer
         *
         * @param mixed $value
         *
         * @return bool
         */
        final protected function isInteger( $value ) {
                if ( is_int( $value ) ) {
                        return true;
                } elseif ( !is_string( $value ) ) {
                        return false;
                }

                $integer = (int)$value;

                return ( $value === (string)$integer );
        }

        public function getQoS( $flag ) {
                return $this->attrMap[$flag] ?? self::QOS_UNKNOWN;
        }

        /**
         * @deprecated since 1.43, not used anywhere.
         */
        public function getSegmentationSize() {
                wfDeprecated( __METHOD__, '1.43' );

                return $this->segmentationSize;
        }

        /**
         * @deprecated since 1.43, not used anywhere.
         */
        public function getSegmentedValueMaxSize() {
                wfDeprecated( __METHOD__, '1.43' );

                return $this->segmentedValueMaxSize;
        }

        /**
         * Get the serialized form a value, logging a warning if it involves custom classes
         *
         * @param mixed $value
         * @param string $key
         *
         * @return string|int String/integer representation of value
         * @since 1.35
         */
        protected function getSerialized( $value, $key ) {
                $this->checkValueSerializability( $value, $key );

                return $this->serialize( $value );
        }

        /**
         * Log if a new cache value does not appear suitable for serialization at a quick glance
         *
         * This aids migration of values to JSON-like structures and the debugging of exceptions
         * due to serialization failure.
         *
         * This does not recurse more than one level into container structures.
         *
         * A proper cache key value is one of the following:
         *  - null
         *  - a scalar
         *  - an array with scalar/null values
         *  - an array tree with scalar/null "leaf" values
         *  - an stdClass instance with scalar/null field values
         *  - an stdClass instance tree with scalar/null "leaf" values
         *  - an instance of a class that implements JsonSerializable
         *
         * @param mixed $value Result of the value generation callback for the key
         * @param string $key Cache key
         */
        private function checkValueSerializability( $value, $key ) {
                if ( is_array( $value ) ) {
                        $this->checkIterableMapSerializability( $value, $key );
                } elseif ( is_object( $value ) ) {
                        // Note that Closure instances count as objects
                        if ( $value instanceof stdClass ) {
                                $this->checkIterableMapSerializability( $value, $key );
                        } elseif ( !( $value instanceof JsonSerializable ) ) {
                                $this->logger->warning(
                                        "{class} value for '{cachekey}'; serialization is suspect.",
                                        [ 'cachekey' => $key, 'class' => get_class( $value ) ]
                                );
                        }
                }
        }

        /**
         * @param array|stdClass $value Result of the value generation callback for the key
         * @param string $key Cache key
         */
        private function checkIterableMapSerializability( $value, $key ) {
                foreach ( $value as $index => $entry ) {
                        if ( is_object( $entry ) ) {
                                // Note that Closure instances count as objects
                                if (
                                        !( $entry instanceof \stdClass ) &&
                                        !( $entry instanceof \JsonSerializable )
                                ) {
                                        $this->logger->warning(
                                                "{class} value for '{cachekey}' at '$index'; serialization is suspect.",
                                                [ 'cachekey' => $key, 'class' => get_class( $entry ) ]
                                        );

                                        return;
                                }
                        }
                }
        }

        /**
         * @param mixed $value
         *
         * @return string|int|false String/integer representation
         * @note Special handling is usually needed for integers so incr()/decr() work
         */
        protected function serialize( $value ) {
                return is_int( $value ) ? $value : serialize( $value );
        }

        /**
         * @param string|int|false $value
         *
         * @return mixed Original value or false on error
         * @note Special handling is usually needed for integers so incr()/decr() work
         */
        protected function unserialize( $value ) {
                return $this->isInteger( $value ) ? (int)$value : unserialize( $value );
        }

        /**
         * @param string $text
         */
        protected function debug( $text ) {
                $this->logger->debug( "{class} debug: $text", [ 'class' => static::class ] );
        }

        /**
         * @param string $key Key generated by BagOStuff::makeKeyInternal
         *
         * @return string A stats prefix to describe this class of key (e.g. "objectcache.file")
         */
        private function determinekeyGroupForStats( $key ): string {
                // Key came directly from BagOStuff::makeKey() or BagOStuff::makeGlobalKey()
                // and thus has the format of "<scope>:<collection>[:<constant or variable>]..."
                $components = explode( ':', $key, 3 );
                // Handle legacy callers that fail to use the key building methods
                $keygroup = $components[1] ?? 'UNKNOWN';

                return strtr( $keygroup, '.', '_' );
        }

        /**
         * @param string $op Operation name as a MediumSpecificBagOStuff::METRIC_OP_* constant
         * @param array<int,string>|array<string,int[]> $keyInfo Key list, if payload sizes are not
         *  applicable, otherwise, map of (key => (send payload size, receive payload size)); send
         *  and receive sizes are 0 where not applicable and receive sizes are "false" for keys
         *  that were not found during read operations
         */
        protected function updateOpStats( string $op, array $keyInfo ) {
                $deltasByMetric = [];

                foreach ( $keyInfo as $indexOrKey => $keyOrSizes ) {
                        if ( is_array( $keyOrSizes ) ) {
                                $key = $indexOrKey;
                                [ $sPayloadSize, $rPayloadSize ] = $keyOrSizes;
                        } else {
                                $key = $keyOrSizes;
                                $sPayloadSize = 0;
                                $rPayloadSize = 0;
                        }

                        // Metric prefix for the cache wrapper and key collection name
                        $keygroup = $this->determinekeyGroupForStats( $key );

                        if ( $op === self::METRIC_OP_GET ) {
                                // This operation was either a "hit" or "miss" for this key
                                if ( $rPayloadSize === false ) {
                                        $statsdName = "objectcache.{$keygroup}.{$op}_miss_rate";
                                        $statsName = "bagostuff_miss_total";
                                } else {
                                        $statsdName = "objectcache.{$keygroup}.{$op}_hit_rate";
                                        $statsName = "bagostuff_hit_total";
                                }
                        } else {
                                // There is no concept of "hit" or "miss" for this operation
                                $statsdName = "objectcache.{$keygroup}.{$op}_call_rate";
                                $statsName = "bagostuff_call_total";
                        }
                        $deltasByMetric[$statsdName] = [
                                'delta' => ( $deltasByMetric[$statsdName]['delta'] ?? 0 ) + 1,
                                'metric' => $statsName,
                                'keygroup' => $keygroup,
                                'operation' => $op,
                        ];

                        if ( $sPayloadSize > 0 ) {
                                $statsdName = "objectcache.{$keygroup}.{$op}_bytes_sent";
                                $statsName = "bagostuff_bytes_sent_total";
                                $deltasByMetric[$statsdName] = [
                                        'delta' => ( $deltasByMetric[$statsdName]['delta'] ?? 0 ) + $sPayloadSize,
                                        'metric' => $statsName,
                                        'keygroup' => $keygroup,
                                        'operation' => $op,
                                ];
                        }

                        if ( $rPayloadSize > 0 ) {
                                $statsdName = "objectcache.{$keygroup}.{$op}_bytes_read";
                                $statsName = "bagostuff_bytes_read_total";
                                $deltasByMetric[$statsdName] = [
                                        'delta' => ( $deltasByMetric[$statsdName]['delta'] ?? 0 ) + $rPayloadSize,
                                        'metric' => $statsName,
                                        'keygroup' => $keygroup,
                                        'operation' => $op,
                                ];
                        }
                }

                foreach ( $deltasByMetric as $statsdName => $delta ) {
                        $this->stats->getCounter( $delta['metric'] )
                                ->setLabel( 'keygroup', $delta['keygroup'] )
                                ->setLabel( 'operation', $delta['operation'] )
                                ->copyToStatsdAt( $statsdName )
                                ->incrementBy( $delta['delta'] );
                }
        }
}

/** @deprecated class alias since 1.43 */
class_alias( MediumSpecificBagOStuff::class, 'MediumSpecificBagOStuff' );