[lhc/web/wiklou.git] / includes / api / ApiStashEdit.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
 */

use MediaWiki\Logger\LoggerFactory;
use MediaWiki\MediaWikiServices;
use Wikimedia\ScopedCallback;

/**
 * Prepare an edit in shared cache so that it can be reused on edit
 *
 * This endpoint can be called via AJAX as the user focuses on the edit
 * summary box. By the time of submission, the parse may have already
 * finished, and can be immediately used on page save. Certain parser
 * functions like {{REVISIONID}} or {{CURRENTTIME}} may cause the cache
 * to not be used on edit. Template and files used are check for changes
 * since the output was generated. The cache TTL is also kept low for sanity.
 *
 * @ingroup API
 * @since 1.25
 */
class ApiStashEdit extends ApiBase {
        const ERROR_NONE = 'stashed';
        const ERROR_PARSE = 'error_parse';
        const ERROR_CACHE = 'error_cache';
        const ERROR_UNCACHEABLE = 'uncacheable';
        const ERROR_BUSY = 'busy';

        const PRESUME_FRESH_TTL_SEC = 30;
        const MAX_CACHE_TTL = 300; // 5 minutes
        const MAX_SIGNATURE_TTL = 60;

        public function execute() {
                $user = $this->getUser();
                $params = $this->extractRequestParams();

                if ( $user->isBot() ) { // sanity
                        $this->dieWithError( 'apierror-botsnotsupported' );
                }

                $cache = ObjectCache::getLocalClusterInstance();
                $page = $this->getTitleOrPageId( $params );
                $title = $page->getTitle();

                if ( !ContentHandler::getForModelID( $params['contentmodel'] )
                        ->isSupportedFormat( $params['contentformat'] )
                ) {
                        $this->dieWithError(
                                [ 'apierror-badformat-generic', $params['contentformat'], $params['contentmodel'] ],
                                'badmodelformat'
                        );
                }

                $this->requireAtLeastOneParameter( $params, 'stashedtexthash', 'text' );

                $text = null;
                $textHash = null;
                if ( strlen( $params['stashedtexthash'] ) ) {
                        // Load from cache since the client indicates the text is the same as last stash
                        $textHash = $params['stashedtexthash'];
                        if ( !preg_match( '/^[0-9a-f]{40}$/', $textHash ) ) {
                                $this->dieWithError( 'apierror-stashedit-missingtext', 'missingtext' );
                        }
                        $textKey = $cache->makeKey( 'stashedit', 'text', $textHash );
                        $text = $cache->get( $textKey );
                        if ( !is_string( $text ) ) {
                                $this->dieWithError( 'apierror-stashedit-missingtext', 'missingtext' );
                        }
                } elseif ( $params['text'] !== null ) {
                        // Trim and fix newlines so the key SHA1's match (see WebRequest::getText())
                        $text = rtrim( str_replace( "\r\n", "\n", $params['text'] ) );
                        $textHash = sha1( $text );
                } else {
                        $this->dieWithError( [
                                'apierror-missingparam-at-least-one-of',
                                Message::listParam( [ '<var>stashedtexthash</var>', '<var>text</var>' ] ),
                                2,
                        ], 'missingparam' );
                }

                $textContent = ContentHandler::makeContent(
                        $text, $title, $params['contentmodel'], $params['contentformat'] );

                $page = WikiPage::factory( $title );
                if ( $page->exists() ) {
                        // Page exists: get the merged content with the proposed change
                        $baseRev = Revision::newFromPageId( $page->getId(), $params['baserevid'] );
                        if ( !$baseRev ) {
                                $this->dieWithError( [ 'apierror-nosuchrevid', $params['baserevid'] ] );
                        }
                        $currentRev = $page->getRevision();
                        if ( !$currentRev ) {
                                $this->dieWithError( [ 'apierror-missingrev-pageid', $page->getId() ], 'missingrev' );
                        }
                        // Merge in the new version of the section to get the proposed version
                        $editContent = $page->replaceSectionAtRev(
                                $params['section'],
                                $textContent,
                                $params['sectiontitle'],
                                $baseRev->getId()
                        );
                        if ( !$editContent ) {
                                $this->dieWithError( 'apierror-sectionreplacefailed', 'replacefailed' );
                        }
                        if ( $currentRev->getId() == $baseRev->getId() ) {
                                // Base revision was still the latest; nothing to merge
                                $content = $editContent;
                        } else {
                                // Merge the edit into the current version
                                $baseContent = $baseRev->getContent();
                                $currentContent = $currentRev->getContent();
                                if ( !$baseContent || !$currentContent ) {
                                        $this->dieWithError( [ 'apierror-missingcontent-pageid', $page->getId() ], 'missingrev' );
                                }
                                $handler = ContentHandler::getForModelID( $baseContent->getModel() );
                                $content = $handler->merge3( $baseContent, $editContent, $currentContent );
                        }
                } else {
                        // New pages: use the user-provided content model
                        $content = $textContent;
                }

                if ( !$content ) { // merge3() failed
                        $this->getResult()->addValue( null,
                                $this->getModuleName(), [ 'status' => 'editconflict' ] );
                        return;
                }

                // The user will abort the AJAX request by pressing "save", so ignore that
                ignore_user_abort( true );

                if ( $user->pingLimiter( 'stashedit' ) ) {
                        $status = 'ratelimited';
                } else {
                        $status = self::parseAndStash( $page, $content, $user, $params['summary'] );
                        $textKey = $cache->makeKey( 'stashedit', 'text', $textHash );
                        $cache->set( $textKey, $text, self::MAX_CACHE_TTL );
                }

                $stats = MediaWikiServices::getInstance()->getStatsdDataFactory();
                $stats->increment( "editstash.cache_stores.$status" );

                $this->getResult()->addValue(
                        null,
                        $this->getModuleName(),
                        [
                                'status' => $status,
                                'texthash' => $textHash
                        ]
                );
        }

        /**
         * @param WikiPage $page
         * @param Content $content Edit content
         * @param User $user
         * @param string $summary Edit summary
         * @return string ApiStashEdit::ERROR_* constant
         * @since 1.25
         */
        public static function parseAndStash( WikiPage $page, Content $content, User $user, $summary ) {
                $cache = ObjectCache::getLocalClusterInstance();
                $logger = LoggerFactory::getInstance( 'StashEdit' );

                $title = $page->getTitle();
                $key = self::getStashKey( $title, self::getContentHash( $content ), $user );

                // Use the master DB to allow for fast blocking locks on the "save path" where this
                // value might actually be used to complete a page edit. If the edit submission request
                // happens before this edit stash requests finishes, then the submission will block until
                // the stash request finishes parsing. For the lock acquisition below, there is not much
                // need to duplicate parsing of the same content/user/summary bundle, so try to avoid
                // blocking at all here.
                $dbw = wfGetDB( DB_MASTER );
                if ( !$dbw->lock( $key, __METHOD__, 0 ) ) {
                        // De-duplicate requests on the same key
                        return self::ERROR_BUSY;
                }
                /** @noinspection PhpUnusedLocalVariableInspection */
                $unlocker = new ScopedCallback( function () use ( $dbw, $key ) {
                        $dbw->unlock( $key, __METHOD__ );
                } );

                $cutoffTime = time() - self::PRESUME_FRESH_TTL_SEC;

                // Reuse any freshly build matching edit stash cache
                $editInfo = $cache->get( $key );
                if ( $editInfo && wfTimestamp( TS_UNIX, $editInfo->timestamp ) >= $cutoffTime ) {
                        $alreadyCached = true;
                } else {
                        $format = $content->getDefaultFormat();
                        $editInfo = $page->prepareContentForEdit( $content, null, $user, $format, false );
                        $alreadyCached = false;
                }

                if ( $editInfo && $editInfo->output ) {
                        // Let extensions add ParserOutput metadata or warm other caches
                        Hooks::run( 'ParserOutputStashForEdit',
                                [ $page, $content, $editInfo->output, $summary, $user ] );

                        $titleStr = (string)$title;
                        if ( $alreadyCached ) {
                                $logger->debug( "Already cached parser output for key '{cachekey}' ('{title}').",
                                        [ 'cachekey' => $key, 'title' => $titleStr ] );
                                return self::ERROR_NONE;
                        }

                        list( $stashInfo, $ttl, $code ) = self::buildStashValue(
                                $editInfo->pstContent,
                                $editInfo->output,
                                $editInfo->timestamp,
                                $user
                        );

                        if ( $stashInfo ) {
                                $ok = $cache->set( $key, $stashInfo, $ttl );
                                if ( $ok ) {
                                        $logger->debug( "Cached parser output for key '{cachekey}' ('{title}').",
                                                [ 'cachekey' => $key, 'title' => $titleStr ] );
                                        return self::ERROR_NONE;
                                } else {
                                        $logger->error( "Failed to cache parser output for key '{cachekey}' ('{title}').",
                                                [ 'cachekey' => $key, 'title' => $titleStr ] );
                                        return self::ERROR_CACHE;
                                }
                        } else {
                                $logger->info( "Uncacheable parser output for key '{cachekey}' ('{title}') [{code}].",
                                        [ 'cachekey' => $key, 'title' => $titleStr, 'code' => $code ] );
                                return self::ERROR_UNCACHEABLE;
                        }
                }

                return self::ERROR_PARSE;
        }

        /**
         * Check that a prepared edit is in cache and still up-to-date
         *
         * This method blocks if the prepared edit is already being rendered,
         * waiting until rendering finishes before doing final validity checks.
         *
         * The cache is rejected if template or file changes are detected.
         * Note that foreign template or file transclusions are not checked.
         *
         * The result is a map (pstContent,output,timestamp) with fields
         * extracted directly from WikiPage::prepareContentForEdit().
         *
         * @param Title $title
         * @param Content $content
         * @param User $user User to get parser options from
         * @return stdClass|bool Returns false on cache miss
         */
        public static function checkCache( Title $title, Content $content, User $user ) {
                if ( $user->isBot() ) {
                        return false; // bots never stash - don't pollute stats
                }

                $cache = ObjectCache::getLocalClusterInstance();
                $logger = LoggerFactory::getInstance( 'StashEdit' );
                $stats = MediaWikiServices::getInstance()->getStatsdDataFactory();

                $key = self::getStashKey( $title, self::getContentHash( $content ), $user );
                $editInfo = $cache->get( $key );
                if ( !is_object( $editInfo ) ) {
                        $start = microtime( true );
                        // We ignore user aborts and keep parsing. Block on any prior parsing
                        // so as to use its results and make use of the time spent parsing.
                        // Skip this logic if there no master connection in case this method
                        // is called on an HTTP GET request for some reason.
                        $lb = MediaWikiServices::getInstance()->getDBLoadBalancer();
                        $dbw = $lb->getAnyOpenConnection( $lb->getWriterIndex() );
                        if ( $dbw && $dbw->lock( $key, __METHOD__, 30 ) ) {
                                $editInfo = $cache->get( $key );
                                $dbw->unlock( $key, __METHOD__ );
                        }

                        $timeMs = 1000 * max( 0, microtime( true ) - $start );
                        $stats->timing( 'editstash.lock_wait_time', $timeMs );
                }

                if ( !is_object( $editInfo ) || !$editInfo->output ) {
                        $stats->increment( 'editstash.cache_misses.no_stash' );
                        $logger->debug( "Empty cache for key '$key' ('$title'); user '{$user->getName()}'." );
                        return false;
                }

                $age = time() - wfTimestamp( TS_UNIX, $editInfo->output->getCacheTime() );
                if ( $age <= self::PRESUME_FRESH_TTL_SEC ) {
                        // Assume nothing changed in this time
                        $stats->increment( 'editstash.cache_hits.presumed_fresh' );
                        $logger->debug( "Timestamp-based cache hit for key '$key' (age: $age sec)." );
                } elseif ( isset( $editInfo->edits ) && $editInfo->edits === $user->getEditCount() ) {
                        // Logged-in user made no local upload/template edits in the meantime
                        $stats->increment( 'editstash.cache_hits.presumed_fresh' );
                        $logger->debug( "Edit count based cache hit for key '$key' (age: $age sec)." );
                } elseif ( $user->isAnon()
                        && self::lastEditTime( $user ) < $editInfo->output->getCacheTime()
                ) {
                        // Logged-out user made no local upload/template edits in the meantime
                        $stats->increment( 'editstash.cache_hits.presumed_fresh' );
                        $logger->debug( "Edit check based cache hit for key '$key' (age: $age sec)." );
                } else {
                        // User may have changed included content
                        $editInfo = false;
                }

                if ( !$editInfo ) {
                        $stats->increment( 'editstash.cache_misses.proven_stale' );
                        $logger->info( "Stale cache for key '$key'; old key with outside edits. (age: $age sec)" );
                } elseif ( $editInfo->output->getFlag( 'vary-revision' ) ) {
                        // This can be used for the initial parse, e.g. for filters or doEditContent(),
                        // but a second parse will be triggered in doEditUpdates(). This is not optimal.
                        $logger->info( "Cache for key '$key' ('$title') has vary_revision." );
                } elseif ( $editInfo->output->getFlag( 'vary-revision-id' ) ) {
                        // Similar to the above if we didn't guess the ID correctly.
                        $logger->info( "Cache for key '$key' ('$title') has vary_revision_id." );
                }

                return $editInfo;
        }

        /**
         * @param User $user
         * @return string|null TS_MW timestamp or null
         */
        private static function lastEditTime( User $user ) {
                $time = wfGetDB( DB_REPLICA )->selectField(
                        'recentchanges',
                        'MAX(rc_timestamp)',
                        [ 'rc_user_text' => $user->getName() ],
                        __METHOD__
                );

                return wfTimestampOrNull( TS_MW, $time );
        }

        /**
         * Get hash of the content, factoring in model/format
         *
         * @param Content $content
         * @return string
         */
        private static function getContentHash( Content $content ) {
                return sha1( implode( "\n", [
                        $content->getModel(),
                        $content->getDefaultFormat(),
                        $content->serialize( $content->getDefaultFormat() )
                ] ) );
        }

        /**
         * Get the temporary prepared edit stash key for a user
         *
         * This key can be used for caching prepared edits provided:
         *   - a) The $user was used for PST options
         *   - b) The parser output was made from the PST using cannonical matching options
         *
         * @param Title $title
         * @param string $contentHash Result of getContentHash()
         * @param User $user User to get parser options from
         * @return string
         */
        private static function getStashKey( Title $title, $contentHash, User $user ) {
                return ObjectCache::getLocalClusterInstance()->makeKey(
                        'prepared-edit',
                        md5( $title->getPrefixedDBkey() ),
                        // Account for the edit model/text
                        $contentHash,
                        // Account for user name related variables like signatures
                        md5( $user->getId() . "\n" . $user->getName() )
                );
        }

        /**
         * Build a value to store in memcached based on the PST content and parser output
         *
         * This makes a simple version of WikiPage::prepareContentForEdit() as stash info
         *
         * @param Content $pstContent Pre-Save transformed content
         * @param ParserOutput $parserOutput
         * @param string $timestamp TS_MW
         * @param User $user
         * @return array (stash info array, TTL in seconds, info code) or (null, 0, info code)
         */
        private static function buildStashValue(
                Content $pstContent, ParserOutput $parserOutput, $timestamp, User $user
        ) {
                // If an item is renewed, mind the cache TTL determined by config and parser functions.
                // Put an upper limit on the TTL for sanity to avoid extreme template/file staleness.
                $since = time() - wfTimestamp( TS_UNIX, $parserOutput->getTimestamp() );
                $ttl = min( $parserOutput->getCacheExpiry() - $since, self::MAX_CACHE_TTL );

                // Avoid extremely stale user signature timestamps (T84843)
                if ( $parserOutput->getFlag( 'user-signature' ) ) {
                        $ttl = min( $ttl, self::MAX_SIGNATURE_TTL );
                }

                if ( $ttl <= 0 ) {
                        return [ null, 0, 'no_ttl' ];
                }

                // Only store what is actually needed
                $stashInfo = (object)[
                        'pstContent' => $pstContent,
                        'output'     => $parserOutput,
                        'timestamp'  => $timestamp,
                        'edits'      => $user->getEditCount()
                ];

                return [ $stashInfo, $ttl, 'ok' ];
        }

        public function getAllowedParams() {
                return [
                        'title' => [
                                ApiBase::PARAM_TYPE => 'string',
                                ApiBase::PARAM_REQUIRED => true
                        ],
                        'section' => [
                                ApiBase::PARAM_TYPE => 'string',
                        ],
                        'sectiontitle' => [
                                ApiBase::PARAM_TYPE => 'string'
                        ],
                        'text' => [
                                ApiBase::PARAM_TYPE => 'text',
                                ApiBase::PARAM_DFLT => null
                        ],
                        'stashedtexthash' => [
                                ApiBase::PARAM_TYPE => 'string',
                                ApiBase::PARAM_DFLT => null
                        ],
                        'summary' => [
                                ApiBase::PARAM_TYPE => 'string',
                        ],
                        'contentmodel' => [
                                ApiBase::PARAM_TYPE => ContentHandler::getContentModels(),
                                ApiBase::PARAM_REQUIRED => true
                        ],
                        'contentformat' => [
                                ApiBase::PARAM_TYPE => ContentHandler::getAllContentFormats(),
                                ApiBase::PARAM_REQUIRED => true
                        ],
                        'baserevid' => [
                                ApiBase::PARAM_TYPE => 'integer',
                                ApiBase::PARAM_REQUIRED => true
                        ]
                ];
        }

        public function needsToken() {
                return 'csrf';
        }

        public function mustBePosted() {
                return true;
        }

        public function isWriteMode() {
                return true;
        }

        public function isInternal() {
                return true;
        }
}