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[mediawiki.git] / includes / parser / ParserCache.php

<?php
/**
 * Cache for outputs of the PHP parser
 *
 * 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 Cache Parser
 */

use MediaWiki\HookContainer\HookContainer;
use MediaWiki\HookContainer\HookRunner;
use MediaWiki\Json\JsonCodec;
use MediaWiki\Page\PageRecord;
use MediaWiki\Page\WikiPageFactory;
use MediaWiki\Parser\ParserCacheMetadata;
use MediaWiki\Title\TitleFactory;
use Psr\Log\LoggerInterface;

/**
 * Cache for ParserOutput objects corresponding to the latest page revisions.
 *
 * The ParserCache is a two-tiered cache backed by BagOStuff which supports
 * varying the stored content on the values of ParserOptions used during
 * a page parse.
 *
 * First tier is keyed by the page ID and stores ParserCacheMetadata, which
 * contains information about cache expiration and the list of ParserOptions
 * used during the parse of the page. For example, if only 'dateformat' and
 * 'userlang' options were accessed by the parser when producing output for the
 * page, array [ 'dateformat', 'userlang' ] will be stored in the metadata cache.
 * This means none of the other existing options had any effect on the output.
 *
 * The second tier of the cache contains ParserOutput objects. The key for the
 * second tier is constructed from the page ID and values of those ParserOptions
 * used during a page parse which affected the output. Upon cache lookup, the list
 * of used option names is retrieved from tier 1 cache, and only the values of
 * those options are hashed together with the page ID to produce a key, while
 * the rest of the options are ignored. Following the example above where
 * only [ 'dateformat', 'userlang' ] options changed the parser output for a
 * page, the key will look like 'page_id!dateformat=default:userlang=ru'.
 * Thus any cache lookup with dateformat=default and userlang=ru will hit the
 * same cache entry regardless of the values of the rest of the options, since they
 * were not accessed during a parse and thus did not change the output.
 *
 * @see ParserOutput::recordOption()
 * @see ParserOutput::getUsedOptions()
 * @see ParserOptions::allCacheVaryingOptions()
 * @ingroup Cache Parser
 */
class ParserCache {
        /**
         * Constants for self::getKey()
         * @since 1.30
         * @since 1.36 the constants were made public
         */

        /** Use only current data */
        public const USE_CURRENT_ONLY = 0;

        /** Use expired data if current data is unavailable */
        public const USE_EXPIRED = 1;

        /** Use expired data or data from different revisions if current data is unavailable */
        public const USE_OUTDATED = 2;

        /**
         * Use expired data and data from different revisions, and if all else
         * fails vary on all variable options
         */
        private const USE_ANYTHING = 3;

        /** @var string The name of this ParserCache. Used as a root of the cache key. */
        private $name;

        /** @var BagOStuff */
        private $cache;

        /**
         * Anything cached prior to this is invalidated
         *
         * @var string
         */
        private $cacheEpoch;

        /** @var HookRunner */
        private $hookRunner;

        /** @var JsonCodec */
        private $jsonCodec;

        /** @var IBufferingStatsdDataFactory */
        private $stats;

        /** @var LoggerInterface */
        private $logger;

        /** @var TitleFactory */
        private $titleFactory;

        /** @var WikiPageFactory */
        private $wikiPageFactory;

        /**
         * @var BagOStuff small in-process cache to store metadata.
         * It's needed multiple times during the request, for example
         * to build a PoolWorkArticleView key, and then to fetch the
         * actual ParserCache entry.
         */
        private $metadataProcCache;

        /**
         * Setup a cache pathway with a given back-end storage mechanism.
         *
         * This class use an invalidation strategy that is compatible with
         * MultiWriteBagOStuff in async replication mode.
         *
         * @param string $name
         * @param BagOStuff $cache
         * @param string $cacheEpoch Anything before this timestamp is invalidated
         * @param HookContainer $hookContainer
         * @param JsonCodec $jsonCodec
         * @param IBufferingStatsdDataFactory $stats
         * @param LoggerInterface $logger
         * @param TitleFactory $titleFactory
         * @param WikiPageFactory $wikiPageFactory
         */
        public function __construct(
                string $name,
                BagOStuff $cache,
                string $cacheEpoch,
                HookContainer $hookContainer,
                JsonCodec $jsonCodec,
                IBufferingStatsdDataFactory $stats,
                LoggerInterface $logger,
                TitleFactory $titleFactory,
                WikiPageFactory $wikiPageFactory
        ) {
                $this->name = $name;
                $this->cache = $cache;
                $this->cacheEpoch = $cacheEpoch;
                $this->hookRunner = new HookRunner( $hookContainer );
                $this->jsonCodec = $jsonCodec;
                $this->stats = $stats;
                $this->logger = $logger;
                $this->titleFactory = $titleFactory;
                $this->wikiPageFactory = $wikiPageFactory;
                $this->metadataProcCache = new HashBagOStuff( [ 'maxKeys' => 2 ] );
        }

        /**
         * @param PageRecord $page
         * @since 1.28
         */
        public function deleteOptionsKey( PageRecord $page ) {
                $page->assertWiki( PageRecord::LOCAL );
                $key = $this->makeMetadataKey( $page );
                $this->metadataProcCache->delete( $key );
                $this->cache->delete( $key );
        }

        /**
         * Retrieve the ParserOutput from ParserCache, even if it's outdated.
         * @param PageRecord $page
         * @param ParserOptions $popts
         * @return ParserOutput|false
         */
        public function getDirty( PageRecord $page, $popts ) {
                $page->assertWiki( PageRecord::LOCAL );
                $value = $this->get( $page, $popts, true );
                return is_object( $value ) ? $value : false;
        }

        /**
         * @param PageRecord $page
         * @param string $metricSuffix
         */
        private function incrementStats( PageRecord $page, $metricSuffix ) {
                $wikiPage = $this->wikiPageFactory->newFromTitle( $page );
                $contentModel = str_replace( '.', '_', $wikiPage->getContentModel() );
                $this->stats->increment( "{$this->name}.{$contentModel}.{$metricSuffix}" );
        }

        /**
         * Returns the ParserCache metadata about the given page
         * considering the given options.
         *
         * @note Which parser options influence the cache key
         * is controlled via ParserOutput::recordOption() or
         * ParserOptions::addExtraKey().
         *
         * @param PageRecord $page
         * @param int $staleConstraint one of the self::USE_ constants
         * @return ParserCacheMetadata|null
         * @since 1.36
         */
        public function getMetadata(
                PageRecord $page,
                int $staleConstraint = self::USE_ANYTHING
        ): ?ParserCacheMetadata {
                $page->assertWiki( PageRecord::LOCAL );

                $pageKey = $this->makeMetadataKey( $page );
                $metadata = $this->metadataProcCache->get( $pageKey );
                if ( !$metadata ) {
                        $metadata = $this->cache->get(
                                $pageKey,
                                BagOStuff::READ_VERIFIED
                        );
                }

                if ( $metadata === false ) {
                        $this->incrementStats( $page, "miss_absent_metadata" );
                        $this->logger->debug( 'ParserOutput metadata cache miss', [ 'name' => $this->name ] );
                        return null;
                }

                // NOTE: If the value wasn't serialized to JSON when being stored,
                //       we may already have a ParserOutput object here. This used
                //       to be the default behavior before 1.36. We need to retain
                //       support so we can handle cached objects after an update
                //       from an earlier revision.
                // NOTE: Support for reading string values from the cache must be
                //       deployed a while before starting to write JSON to the cache,
                //       in case we have to revert either change.
                if ( is_string( $metadata ) ) {
                        $metadata = $this->restoreFromJson( $metadata, $pageKey, CacheTime::class );
                }

                if ( !$metadata instanceof CacheTime ) {
                        $this->incrementStats( $page, 'miss_unserialize' );
                        return null;
                }

                if ( $this->checkExpired( $metadata, $page, $staleConstraint, 'metadata' ) ) {
                        return null;
                }

                if ( $this->checkOutdated( $metadata, $page, $staleConstraint, 'metadata' ) ) {
                        return null;
                }

                $this->logger->debug( 'Parser cache options found', [ 'name' => $this->name ] );
                return $metadata;
        }

        /**
         * @param PageRecord $page
         * @return string
         */
        private function makeMetadataKey( PageRecord $page ): string {
                return $this->cache->makeKey( $this->name, 'idoptions', $page->getId( PageRecord::LOCAL ) );
        }

        /**
         * Get a key that will be used by the ParserCache to store the content
         * for a given page considering the given options and the array of
         * used options.
         *
         * @warning The exact format of the key is considered internal and is subject
         * to change, thus should not be used as storage or long-term caching key.
         * This is intended to be used for logging or keying something transient.
         *
         * @param PageRecord $page
         * @param ParserOptions $options
         * @param array|null $usedOptions Defaults to all cache varying options.
         * @return string
         * @internal
         * @since 1.36
         */
        public function makeParserOutputKey(
                PageRecord $page,
                ParserOptions $options,
                array $usedOptions = null
        ): string {
                $usedOptions ??= ParserOptions::allCacheVaryingOptions();
                // idhash seem to mean 'page id' + 'rendering hash' (r3710)
                $pageid = $page->getId( PageRecord::LOCAL );
                $title = $this->titleFactory->newFromPageIdentity( $page );
                $hash = $options->optionsHash( $usedOptions, $title );
                // Before T263581 ParserCache was split between normal page views
                // and action=parse. -0 is left in the key to avoid invalidating the entire
                // cache when removing the cache split.
                return $this->cache->makeKey( $this->name, 'idhash', "{$pageid}-0!{$hash}" );
        }

        /**
         * Retrieve the ParserOutput from ParserCache.
         * false if not found or outdated.
         *
         * @param PageRecord $page
         * @param ParserOptions $popts
         * @param bool $useOutdated (default false)
         *
         * @return ParserOutput|false
         */
        public function get( PageRecord $page, $popts, $useOutdated = false ) {
                $page->assertWiki( PageRecord::LOCAL );

                if ( !$page->exists() ) {
                        $this->incrementStats( $page, 'miss_nonexistent' );
                        return false;
                }

                if ( $page->isRedirect() ) {
                        // It's a redirect now
                        $this->incrementStats( $page, 'miss_redirect' );
                        return false;
                }

                $staleConstraint = $useOutdated ? self::USE_OUTDATED : self::USE_CURRENT_ONLY;
                $parserOutputMetadata = $this->getMetadata( $page, $staleConstraint );
                if ( !$parserOutputMetadata ) {
                        return false;
                }

                if ( !$popts->isSafeToCache( $parserOutputMetadata->getUsedOptions() ) ) {
                        $this->incrementStats( $page, 'miss_unsafe' );
                        return false;
                }

                $parserOutputKey = $this->makeParserOutputKey(
                        $page,
                        $popts,
                        $parserOutputMetadata->getUsedOptions()
                );

                $value = $this->cache->get( $parserOutputKey, BagOStuff::READ_VERIFIED );
                if ( $value === false ) {
                        $this->incrementStats( $page, "miss_absent" );
                        $this->logger->debug( 'ParserOutput cache miss', [ 'name' => $this->name ] );
                        return false;
                }

                // NOTE: If the value wasn't serialized to JSON when being stored,
                //       we may already have a ParserOutput object here. This used
                //       to be the default behavior before 1.36. We need to retain
                //       support so we can handle cached objects after an update
                //       from an earlier revision.
                // NOTE: Support for reading string values from the cache must be
                //       deployed a while before starting to write JSON to the cache,
                //       in case we have to revert either change.
                if ( is_string( $value ) ) {
                        $value = $this->restoreFromJson( $value, $parserOutputKey, ParserOutput::class );
                }

                if ( !$value instanceof ParserOutput ) {
                        $this->incrementStats( $page, 'miss_unserialize' );
                        return false;
                }

                if ( $this->checkExpired( $value, $page, $staleConstraint, 'output' ) ) {
                        return false;
                }

                if ( $this->checkOutdated( $value, $page, $staleConstraint, 'output' ) ) {
                        return false;
                }

                $wikiPage = $this->wikiPageFactory->newFromTitle( $page );
                if ( $this->hookRunner->onRejectParserCacheValue( $value, $wikiPage, $popts ) === false ) {
                        $this->incrementStats( $page, 'miss_rejected' );
                        $this->logger->debug( 'key valid, but rejected by RejectParserCacheValue hook handler',
                                [ 'name' => $this->name ] );
                        return false;
                }

                $this->logger->debug( 'ParserOutput cache found', [ 'name' => $this->name ] );
                $this->incrementStats( $page, 'hit' );
                return $value;
        }

        /**
         * @param ParserOutput $parserOutput
         * @param PageRecord $page
         * @param ParserOptions $popts
         * @param string|null $cacheTime TS_MW timestamp when the cache was generated
         * @param int|null $revId Revision ID that was parsed
         */
        public function save(
                ParserOutput $parserOutput,
                PageRecord $page,
                $popts,
                $cacheTime = null,
                $revId = null
        ) {
                $page->assertWiki( PageRecord::LOCAL );

                if ( !$parserOutput->hasText() ) {
                        throw new InvalidArgumentException( 'Attempt to cache a ParserOutput with no text set!' );
                }

                $expire = $parserOutput->getCacheExpiry();

                if ( !$popts->isSafeToCache( $parserOutput->getUsedOptions() ) ) {
                        $this->logger->debug(
                                'Parser options are not safe to cache and has not been saved',
                                [ 'name' => $this->name ]
                        );
                        $this->incrementStats( $page, 'save_unsafe' );
                        return;
                }

                if ( $expire <= 0 ) {
                        $this->logger->debug(
                                'Parser output was marked as uncacheable and has not been saved',
                                [ 'name' => $this->name ]
                        );
                        $this->incrementStats( $page, 'save_uncacheable' );
                        return;
                }

                if ( $this->cache instanceof EmptyBagOStuff ) {
                        return;
                }

                $cacheTime = $cacheTime ?: wfTimestampNow();
                $revId = $revId ?: $page->getLatest( PageRecord::LOCAL );

                if ( !$revId ) {
                        $this->logger->debug(
                                'Parser output cannot be saved if the revision ID is not known',
                                [ 'name' => $this->name ]
                        );
                        $this->incrementStats( $page, 'save_norevid' );
                        return;
                }

                $metadata = new CacheTime;
                $metadata->recordOptions( $parserOutput->getUsedOptions() );
                $metadata->updateCacheExpiry( $expire );

                $metadata->setCacheTime( $cacheTime );
                $parserOutput->setCacheTime( $cacheTime );
                $metadata->setCacheRevisionId( $revId );
                $parserOutput->setCacheRevisionId( $revId );

                $parserOutputKey = $this->makeParserOutputKey(
                        $page,
                        $popts,
                        $metadata->getUsedOptions()
                );

                $msg = "Saved in parser cache with key $parserOutputKey" .
                        " and timestamp $cacheTime" .
                        " and revision id $revId.";

                $reason = $popts->getRenderReason();
                $msg .= " Rendering was triggered because: $reason";

                $parserOutput->addCacheMessage( $msg );

                $pageKey = $this->makeMetadataKey( $page );

                $parserOutputData = $this->convertForCache( $parserOutput, $parserOutputKey );
                $metadataData = $this->convertForCache( $metadata, $pageKey );

                if ( !$parserOutputData || !$metadataData ) {
                        $this->logger->warning(
                                'Parser output failed to serialize and was not saved',
                                [ 'name' => $this->name ]
                        );
                        $this->incrementStats( $page, 'save_nonserializable' );
                        return;
                }

                // Save the parser output
                $this->cache->set(
                        $parserOutputKey,
                        $parserOutputData,
                        $expire,
                        BagOStuff::WRITE_ALLOW_SEGMENTS
                );

                // ...and its pointer to the local cache.
                $this->metadataProcCache->set( $pageKey, $metadataData, $expire );
                // ...and to the global cache.
                $this->cache->set( $pageKey, $metadataData, $expire );

                $title = $this->titleFactory->newFromPageIdentity( $page );
                $this->hookRunner->onParserCacheSaveComplete( $this, $parserOutput, $title, $popts, $revId );

                $this->logger->debug( 'Saved in parser cache', [
                        'name' => $this->name,
                        'key' => $parserOutputKey,
                        'cache_time' => $cacheTime,
                        'rev_id' => $revId
                ] );
                $this->incrementStats( $page, 'save_success' );

                $reasonKey = preg_replace( '/\W+/', '_', $popts->getRenderReason() );
                $this->incrementStats( $page, "reason.$reasonKey" );
        }

        /**
         * Get the backend BagOStuff instance that
         * powers the parser cache
         *
         * @since 1.30
         * @internal
         * @return BagOStuff
         */
        public function getCacheStorage() {
                return $this->cache;
        }

        /**
         * Check if $entry expired for $page given the $staleConstraint
         * when fetching from $cacheTier.
         * @param CacheTime $entry
         * @param PageRecord $page
         * @param int $staleConstraint One of USE_* constants.
         * @param string $cacheTier
         * @return bool
         */
        private function checkExpired(
                CacheTime $entry,
                PageRecord $page,
                int $staleConstraint,
                string $cacheTier
        ): bool {
                if ( $staleConstraint < self::USE_EXPIRED && $entry->expired( $page->getTouched() ) ) {
                        $this->incrementStats( $page, 'miss_expired' );
                        $this->logger->debug( "{$cacheTier} key expired", [
                                'name' => $this->name,
                                'touched' => $page->getTouched(),
                                'epoch' => $this->cacheEpoch,
                                'cache_time' => $entry->getCacheTime()
                        ] );
                        return true;
                }
                return false;
        }

        /**
         * Check if $entry belongs to the latest revision of $page
         * given $staleConstraint when fetched from $cacheTier.
         * @param CacheTime $entry
         * @param PageRecord $page
         * @param int $staleConstraint One of USE_* constants.
         * @param string $cacheTier
         * @return bool
         */
        private function checkOutdated(
                CacheTime $entry,
                PageRecord $page,
                int $staleConstraint,
                string $cacheTier
        ): bool {
                $latestRevId = $page->getLatest( PageRecord::LOCAL );
                if ( $staleConstraint < self::USE_OUTDATED && $entry->isDifferentRevision( $latestRevId ) ) {
                        $this->incrementStats( $page, "miss_revid" );
                        $this->logger->debug( "{$cacheTier} key is for an old revision", [
                                'name' => $this->name,
                                'rev_id' => $latestRevId,
                                'cached_rev_id' => $entry->getCacheRevisionId()
                        ] );
                        return true;
                }
                return false;
        }

        /**
         * @param string $jsonData
         * @param string $key
         * @param string $expectedClass
         * @return CacheTime|ParserOutput|null
         */
        private function restoreFromJson( string $jsonData, string $key, string $expectedClass ) {
                try {
                        /** @var CacheTime $obj */
                        $obj = $this->jsonCodec->unserialize( $jsonData, $expectedClass );
                        return $obj;
                } catch ( InvalidArgumentException $e ) {
                        $this->logger->error( "Unable to unserialize JSON", [
                                'name' => $this->name,
                                'cache_key' => $key,
                                'message' => $e->getMessage()
                        ] );
                        return null;
                }
        }

        /**
         * @param CacheTime $obj
         * @param string $key
         * @return string|null
         */
        protected function convertForCache( CacheTime $obj, string $key ) {
                try {
                        return $this->jsonCodec->serialize( $obj );
                } catch ( InvalidArgumentException $e ) {
                        $this->logger->error( "Unable to serialize JSON", [
                                'name' => $this->name,
                                'cache_key' => $key,
                                'message' => $e->getMessage(),
                        ] );
                        return null;
                }
        }
}