LinkCache.php
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LinkCache.php
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	<?php
	/**
	* Page existence cache.
	*
	* 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
	*/

	namespace MediaWiki\Cache;

	use InvalidArgumentException;
	use MapCacheLRU;
	use MediaWiki\Linker\LinkTarget;
	use MediaWiki\MainConfigNames;
	use MediaWiki\MediaWikiServices;
	use MediaWiki\Page\PageIdentity;
	use MediaWiki\Page\PageReference;
	use MediaWiki\Page\PageStoreRecord;
	use MediaWiki\Title\NamespaceInfo;
	use MediaWiki\Title\TitleFormatter;
	use MediaWiki\Title\TitleValue;
	use Psr\Log\LoggerAwareInterface;
	use Psr\Log\LoggerInterface;
	use Psr\Log\NullLogger;
	use stdClass;
	use Wikimedia\ObjectCache\WANObjectCache;
	use Wikimedia\Rdbms\Database;
	use Wikimedia\Rdbms\IDBAccessObject;
	use Wikimedia\Rdbms\ILoadBalancer;
	use Wikimedia\Rdbms\IReadableDatabase;

	/**
	* Cache for article titles (prefixed DB keys) and ids linked from one source
	*
	* @ingroup Cache
	*/
	class LinkCache implements LoggerAwareInterface {
	/** @var MapCacheLRU */
	private $entries;
	/** @var WANObjectCache */
	private $wanCache;
	/** @var TitleFormatter */
	private $titleFormatter;
	/** @var NamespaceInfo */
	private $nsInfo;
	/** @var ILoadBalancer\|null */
	private $loadBalancer;
	/** @var LoggerInterface */
	private $logger;

	/** How many Titles to store */
	private const MAX_SIZE = 10000;

	/** Key to page row object or null */
	private const ROW = 0;
	/** Key to query READ_* flags */
	private const FLAGS = 1;

	/**
	* @param TitleFormatter $titleFormatter
	* @param WANObjectCache $cache
	* @param NamespaceInfo $nsInfo
	* @param ILoadBalancer\|null $loadBalancer Use null when no database is set up, for example on installation
	*/
	public function __construct(
	TitleFormatter $titleFormatter,
	WANObjectCache $cache,
	NamespaceInfo $nsInfo,
	?ILoadBalancer $loadBalancer = null
	) {
	$this->entries = new MapCacheLRU( self::MAX_SIZE );
	$this->wanCache = $cache;
	$this->titleFormatter = $titleFormatter;
	$this->nsInfo = $nsInfo;
	$this->loadBalancer = $loadBalancer;
	$this->logger = new NullLogger();
	}

	/**
	* @param LoggerInterface $logger
	*/
	public function setLogger( LoggerInterface $logger ) {
	$this->logger = $logger;
	}

	/**
	* @param LinkTarget\|PageReference\|array\|string $page
	* @param bool $passThrough Return $page if $page is a string
	* @return ?string the cache key
	*/
	private function getCacheKey( $page, $passThrough = false ) {
	if ( is_string( $page ) ) {
	if ( $passThrough ) {
	return $page;
	} else {
	throw new InvalidArgumentException( 'They key may not be given as a string here' );
	}
	}

	if ( is_array( $page ) ) {
	$namespace = $page['page_namespace'];
	$dbkey = $page['page_title'];
	return strtr( $this->titleFormatter->formatTitle( $namespace, $dbkey ), ' ', '_' );
	}

	if ( $page instanceof PageReference && $page->getWikiId() !== PageReference::LOCAL ) {
	// No cross-wiki support yet. Perhaps LinkCache can become wiki-aware in the future.
	$this->logger->info(
	'cross-wiki page reference',
	[
	'page-wiki' => $page->getWikiId(),
	'page-reference' => $this->titleFormatter->getFullText( $page )
	]
	);
	return null;
	}

	if ( $page instanceof PageIdentity && !$page->canExist() ) {
	// Non-proper page, perhaps a special page or interwiki link or relative section link.
	$this->logger->warning(
	'non-proper page reference: {page-reference}',
	[ 'page-reference' => $this->titleFormatter->getFullText( $page ) ]
	);
	return null;
	}

	if ( $page instanceof LinkTarget
	&& ( $page->isExternal() \|\| $page->getText() === '' \|\| $page->getNamespace() < 0 )
	) {
	// Interwiki link or relative section link. These do not have a page ID, so they
	// can neither be "good" nor "bad" in the sense of this class.
	$this->logger->warning(
	'link to non-proper page: {page-link}',
	[ 'page-link' => $this->titleFormatter->getFullText( $page ) ]
	);
	return null;
	}

	return $this->titleFormatter->getPrefixedDBkey( $page );
	}

	/**
	* Get the ID of a page known to the process cache
	*
	* @param LinkTarget\|PageReference\|array\|string $page The page to get the ID for,
	* as an object, an array containing the page_namespace and page_title fields,
	* or a prefixed DB key. In MediaWiki 1.36 and earlier, only a string was accepted.
	* @return int Page ID, or zero if the page was not cached or does not exist or is not a
	* proper page (e.g. a special page or an interwiki link).
	*/
	public function getGoodLinkID( $page ) {
	$key = $this->getCacheKey( $page, true );
	if ( $key === null ) {
	return 0;
	}

	$entry = $this->entries->get( $key );
	if ( !$entry ) {
	return 0;
	}

	$row = $entry[self::ROW];

	return $row ? (int)$row->page_id : 0;
	}

	/**
	* Get the field of a page known to the process cache
	*
	* If this link is not a cached good title, it will return NULL.
	* @param LinkTarget\|PageReference\|array $page The page to get cached info for.
	* Can be given as an object or an associative array containing the
	* page_namespace and page_title fields.
	* In MediaWiki 1.36 and earlier, only LinkTarget was accepted.
	* @param string $field ( 'id', 'length', 'redirect', 'revision', 'model', 'lang' )
	* @return string\|int\|null The field value, or null if the page was not cached or does not exist
	* or is not a proper page (e.g. a special page or interwiki link).
	*/
	public function getGoodLinkFieldObj( $page, string $field ) {
	$key = $this->getCacheKey( $page );
	if ( $key === null ) {
	return null;
	}

	$entry = $this->entries->get( $key );
	if ( !$entry ) {
	return null;
	}

	$row = $entry[self::ROW];
	if ( !$row ) {
	return null;
	}

	switch ( $field ) {
	case 'id':
	return (int)$row->page_id;
	case 'length':
	return (int)$row->page_len;
	case 'redirect':
	return (int)$row->page_is_redirect;
	case 'revision':
	return (int)$row->page_latest;
	case 'model':
	return !empty( $row->page_content_model )
	? (string)$row->page_content_model
	: null;
	case 'lang':
	return !empty( $row->page_lang )
	? (string)$row->page_lang
	: null;
	default:
	throw new InvalidArgumentException( "Unknown field: $field" );
	}
	}

	/**
	* Check if a page is known to be missing based on the process cache
	*
	* @param LinkTarget\|PageReference\|array\|string $page The page to get cached info for,
	* as an object, an array containing the page_namespace and page_title fields,
	* or a prefixed DB key. In MediaWiki 1.36 and earlier, only a string was accepted.
	* In MediaWiki 1.36 and earlier, only a string was accepted.
	* @return bool Whether the page is known to be missing based on the process cache
	*/
	public function isBadLink( $page ) {
	$key = $this->getCacheKey( $page, true );
	if ( $key === null ) {
	return false;
	}

	$entry = $this->entries->get( $key );

	return ( $entry && !$entry[self::ROW] );
	}

	/**
	* Add information about an existing page to the process cache
	*
	* Callers must set the READ_LATEST flag if the row came from a DB_PRIMARY source.
	* However, the use of such data is highly discouraged; most callers rely on seeing
	* consistent DB_REPLICA data (e.g. REPEATABLE-READ point-in-time snapshots) and the
	* accidental use of DB_PRIMARY data via LinkCache is prone to causing anomalies.
	*
	* @param LinkTarget\|PageReference\|array $page The page to set cached info for.
	* Can be given as an object or an associative array containing the
	* page_namespace and page_title fields.
	* In MediaWiki 1.36 and earlier, only LinkTarget was accepted.
	* @param stdClass $row Object which has all fields returned by getSelectFields().
	* @param int $queryFlags The query flags used to retrieve the row, IDBAccessObject::READ_*
	* @since 1.19
	*/
	public function addGoodLinkObjFromRow(
	$page,
	stdClass $row,
	int $queryFlags = IDBAccessObject::READ_NORMAL
	) {
	$key = $this->getCacheKey( $page );
	if ( $key === null ) {
	return;
	}

	foreach ( self::getSelectFields() as $field ) {
	if ( !property_exists( $row, $field ) ) {
	throw new InvalidArgumentException( "Missing field: $field" );
	}
	}

	$this->entries->set( $key, [ self::ROW => $row, self::FLAGS => $queryFlags ] );
	}

	/**
	* Add information about a missing page to the process cache
	*
	* Callers must set the READ_LATEST flag if the row came from a DB_PRIMARY source.
	* However, the use of such data is highly discouraged; most callers rely on seeing
	* consistent DB_REPLICA data (e.g. REPEATABLE-READ point-in-time snapshots) and the
	* accidental use of DB_PRIMARY data via LinkCache is prone to causing anomalies.
	*
	* @param LinkTarget\|PageReference\|array $page The page to set cached info for.
	* Can be given as an object or an associative array containing the
	* page_namespace and page_title fields.
	* In MediaWiki 1.36 and earlier, only LinkTarget was accepted.
	* @param int $queryFlags The query flags used to retrieve the row, IDBAccessObject::READ_*
	*/
	public function addBadLinkObj( $page, int $queryFlags = IDBAccessObject::READ_NORMAL ) {
	$key = $this->getCacheKey( $page );
	if ( $key === null ) {
	return;
	}

	$this->entries->set( $key, [ self::ROW => null, self::FLAGS => $queryFlags ] );
	}

	/**
	* Clear information about a page being missing from the process cache
	*
	* @param LinkTarget\|PageReference\|array\|string $page The page to clear cached info for,
	* as an object, an array containing the page_namespace and page_title fields,
	* or a prefixed DB key. In MediaWiki 1.36 and earlier, only a string was accepted.
	* In MediaWiki 1.36 and earlier, only a string was accepted.
	*/
	public function clearBadLink( $page ) {
	$key = $this->getCacheKey( $page, true );
	if ( $key === null ) {
	return;
	}

	$entry = $this->entries->get( $key );
	if ( $entry && !$entry[self::ROW] ) {
	$this->entries->clear( $key );
	}
	}

	/**
	* Clear information about a page from the process cache
	*
	* @param LinkTarget\|PageReference\|array $page The page to clear cached info for.
	* Can be given as an object or an associative array containing the
	* page_namespace and page_title fields.
	* In MediaWiki 1.36 and earlier, only LinkTarget was accepted.
	*/
	public function clearLink( $page ) {
	$key = $this->getCacheKey( $page );
	if ( $key !== null ) {
	$this->entries->clear( $key );
	}
	}

	/**
	* Fields that LinkCache needs to select
	*
	* @since 1.28
	* @return array
	*/
	public static function getSelectFields() {
	$pageLanguageUseDB = MediaWikiServices::getInstance()->getMainConfig()
	->get( MainConfigNames::PageLanguageUseDB );

	$fields = array_merge(
	PageStoreRecord::REQUIRED_FIELDS,
	[
	'page_len',
	'page_content_model',
	]
	);

	if ( $pageLanguageUseDB ) {
	$fields[] = 'page_lang';
	}

	return $fields;
	}

	/**
	* Add a title to the link cache, return the page_id or zero if non-existent.
	* This causes the link to be looked up in the database if it is not yet cached.
	*
	* @deprecated since 1.37, use PageStore::getPageForLink() instead.
	*
	* @param LinkTarget\|PageReference\|array $page The page to load.
	* Can be given as an object or an associative array containing the
	* page_namespace and page_title fields.
	* In MediaWiki 1.36 and earlier, only LinkTarget was accepted.
	* @param int $queryFlags IDBAccessObject::READ_XXX
	*
	* @return int Page ID or zero
	*/
	public function addLinkObj( $page, int $queryFlags = IDBAccessObject::READ_NORMAL ) {
	$row = $this->getGoodLinkRow(
	$page->getNamespace(),
	$page->getDBkey(),
	[ $this, 'fetchPageRow' ],
	$queryFlags
	);

	return $row ? (int)$row->page_id : 0;
	}

	/**
	* @param TitleValue $link
	* @param callable\|null $fetchCallback
	* @param int $queryFlags
	* @return array [ $shouldAddGoodLink, $row ], $shouldAddGoodLink is a bool indicating
	* whether addGoodLinkObjFromRow should be called, and $row is the row the caller was looking
	* for (or null, when it was not found).
	*/
	private function getGoodLinkRowInternal(
	TitleValue $link,
	?callable $fetchCallback = null,
	int $queryFlags = IDBAccessObject::READ_NORMAL
	): array {
	$callerShouldAddGoodLink = false;

	$key = $this->getCacheKey( $link );
	if ( $key === null ) {
	return [ $callerShouldAddGoodLink, null ];
	}

	$ns = $link->getNamespace();
	$dbkey = $link->getDBkey();

	$entry = $this->entries->get( $key );
	if ( $entry && $entry[self::FLAGS] >= $queryFlags ) {
	return [ $callerShouldAddGoodLink, $entry[self::ROW] ?: null ];
	}

	if ( !$fetchCallback ) {
	return [ $callerShouldAddGoodLink, null ];
	}

	$callerShouldAddGoodLink = true;

	$wanCacheKey = $this->getPersistentCacheKey( $link );
	if ( $wanCacheKey !== null && !( $queryFlags & IDBAccessObject::READ_LATEST ) ) {
	// Some pages are often transcluded heavily, so use persistent caching
	$row = $this->wanCache->getWithSetCallback(
	$wanCacheKey,
	WANObjectCache::TTL_DAY,
	function ( $curValue, &$ttl, array &$setOpts ) use ( $fetchCallback, $ns, $dbkey ) {
	$dbr = $this->loadBalancer->getConnection( ILoadBalancer::DB_REPLICA );
	$setOpts += Database::getCacheSetOptions( $dbr );

	$row = $fetchCallback( $dbr, $ns, $dbkey, [] );
	$mtime = $row ? (int)wfTimestamp( TS_UNIX, $row->page_touched ) : false;
	$ttl = $this->wanCache->adaptiveTTL( $mtime, $ttl );

	return $row;
	}
	);
	} else {
	// No persistent caching needed, but we can still use the callback.
	if ( ( $queryFlags & IDBAccessObject::READ_LATEST ) == IDBAccessObject::READ_LATEST ) {
	$dbr = $this->loadBalancer->getConnection( DB_PRIMARY );
	} else {
	$dbr = $this->loadBalancer->getConnection( DB_REPLICA );
	}
	$options = [];
	if ( ( $queryFlags & IDBAccessObject::READ_EXCLUSIVE ) == IDBAccessObject::READ_EXCLUSIVE ) {
	$options[] = 'FOR UPDATE';
	} elseif ( ( $queryFlags & IDBAccessObject::READ_LOCKING ) == IDBAccessObject::READ_LOCKING ) {
	$options[] = 'LOCK IN SHARE MODE';
	}
	$row = $fetchCallback( $dbr, $ns, $dbkey, $options );
	}

	return [ $callerShouldAddGoodLink, $row ?: null ];
	}

	/**
	* Returns the row for the page if the page exists (subject to race conditions).
	* The row will be returned from local cache or WAN cache if possible, or it
	* will be looked up using the callback provided.
	*
	* @param int $ns
	* @param string $dbkey
	* @param callable\|null $fetchCallback A callback that will retrieve the link row with the
	* signature ( IReadableDatabase $db, int $ns, string $dbkey, array $queryOptions ): ?stdObj.
	* @param int $queryFlags IDBAccessObject::READ_XXX
	*
	* @return stdClass\|null
	* @internal for use by PageStore. Other code should use a PageLookup instead.
	*/
	public function getGoodLinkRow(
	int $ns,
	string $dbkey,
	?callable $fetchCallback = null,
	int $queryFlags = IDBAccessObject::READ_NORMAL
	): ?stdClass {
	$link = TitleValue::tryNew( $ns, $dbkey );
	if ( $link === null ) {
	return null;
	}

	[ $shouldAddGoodLink, $row ] = $this->getGoodLinkRowInternal(
	$link,
	$fetchCallback,
	$queryFlags
	);

	if ( $row ) {
	if ( $shouldAddGoodLink ) {
	try {
	$this->addGoodLinkObjFromRow( $link, $row, $queryFlags );
	} catch ( InvalidArgumentException $e ) {
	// a field is missing from $row; maybe we used a cache?; invalidate it and try again
	$this->invalidateTitle( $link );
	[ , $row ] = $this->getGoodLinkRowInternal(
	$link,
	$fetchCallback,
	$queryFlags
	);
	$this->addGoodLinkObjFromRow( $link, $row, $queryFlags );
	}
	}
	} else {
	$this->addBadLinkObj( $link );
	}

	return $row ?: null;
	}

	/**
	* @param LinkTarget\|PageReference\|TitleValue $page
	* @return string\|null
	*/
	private function getPersistentCacheKey( $page ) {
	// if no key can be derived, the page isn't cacheable
	if ( $this->getCacheKey( $page ) === null \|\| !$this->usePersistentCache( $page ) ) {
	return null;
	}

	return $this->wanCache->makeKey(
	'page',
	$page->getNamespace(),
	sha1( $page->getDBkey()
	) );
	}

	/**
	* @param LinkTarget\|PageReference\|int $pageOrNamespace
	* @return bool
	*/
	private function usePersistentCache( $pageOrNamespace ) {
	$ns = is_int( $pageOrNamespace ) ? $pageOrNamespace : $pageOrNamespace->getNamespace();
	if ( in_array( $ns, [ NS_TEMPLATE, NS_FILE, NS_CATEGORY, NS_MEDIAWIKI ] ) ) {
	return true;
	}
	// Focus on transcluded pages more than the main content
	if ( $this->nsInfo->isContent( $ns ) ) {
	return false;
	}
	// Non-talk extension namespaces (e.g. NS_MODULE)
	return ( $ns >= 100 && $this->nsInfo->isSubject( $ns ) );
	}

	/**
	* @param IReadableDatabase $db
	* @param int $ns
	* @param string $dbkey
	* @param array $options Query options, see IDatabase::select() for details.
	* @return stdClass\|false
	*/
	private function fetchPageRow( IReadableDatabase $db, int $ns, string $dbkey, $options = [] ) {
	$queryBuilder = $db->newSelectQueryBuilder()
	->select( self::getSelectFields() )
	->from( 'page' )
	->where( [ 'page_namespace' => $ns, 'page_title' => $dbkey ] )
	->options( $options );

	return $queryBuilder->caller( __METHOD__ )->fetchRow();
	}

	/**
	* Purge the persistent link cache for a title
	*
	* @param LinkTarget\|PageReference $page
	* In MediaWiki 1.36 and earlier, only LinkTarget was accepted.
	* @since 1.28
	*/
	public function invalidateTitle( $page ) {
	$wanCacheKey = $this->getPersistentCacheKey( $page );
	if ( $wanCacheKey !== null ) {
	$this->wanCache->delete( $wanCacheKey );
	}

	$this->clearLink( $page );
	}

	/**
	* Clears cache
	*/
	public function clear() {
	$this->entries->clear();
	}
	}

	/** @deprecated class alias since 1.42 */
	class_alias( LinkCache::class, 'LinkCache' );

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