ResourceLoader.php

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<?php
class ResourceLoader {
    protected static $filterCacheVersion = 7;

    protected static $debugMode = null;

    protected $modules = array();

    protected $moduleInfos = array();

    private $config;

    protected $testModuleNames = array();

    protected $sources = array();

    protected $hasErrors = false;

    public function preloadModuleInfo( array $modules, ResourceLoaderContext $context ) {
        if ( !count( $modules ) ) {
            // Or else Database*::select() will explode, plus it's cheaper!
            return;
        }
        $dbr = wfGetDB( DB_SLAVE );
        $skin = $context->getSkin();
        $lang = $context->getLanguage();

        // Get file dependency information
        $res = $dbr->select( 'module_deps', array( 'md_module', 'md_deps' ), array(
                'md_module' => $modules,
                'md_skin' => $skin
            ), __METHOD__
        );

        // Set modules' dependencies
        $modulesWithDeps = array();
        foreach ( $res as $row ) {
            $module = $this->getModule( $row->md_module );
            if ( $module ) {
                $module->setFileDependencies( $skin, FormatJson::decode( $row->md_deps, true ) );
                $modulesWithDeps[] = $row->md_module;
            }
        }

        // Register the absence of a dependency row too
        foreach ( array_diff( $modules, $modulesWithDeps ) as $name ) {
            $module = $this->getModule( $name );
            if ( $module ) {
                $this->getModule( $name )->setFileDependencies( $skin, array() );
            }
        }

        // Get message blob mtimes. Only do this for modules with messages
        $modulesWithMessages = array();
        foreach ( $modules as $name ) {
            $module = $this->getModule( $name );
            if ( $module && count( $module->getMessages() ) ) {
                $modulesWithMessages[] = $name;
            }
        }
        $modulesWithoutMessages = array_flip( $modules ); // Will be trimmed down by the loop below
        if ( count( $modulesWithMessages ) ) {
            $res = $dbr->select( 'msg_resource', array( 'mr_resource', 'mr_timestamp' ), array(
                    'mr_resource' => $modulesWithMessages,
                    'mr_lang' => $lang
                ), __METHOD__
            );
            foreach ( $res as $row ) {
                $module = $this->getModule( $row->mr_resource );
                if ( $module ) {
                    $module->setMsgBlobMtime( $lang, wfTimestamp( TS_UNIX, $row->mr_timestamp ) );
                    unset( $modulesWithoutMessages[$row->mr_resource] );
                }
            }
        }
        foreach ( array_keys( $modulesWithoutMessages ) as $name ) {
            $module = $this->getModule( $name );
            if ( $module ) {
                $module->setMsgBlobMtime( $lang, 0 );
            }
        }
    }

    public function filter( $filter, $data, $cacheReport = true ) {
        wfProfileIn( __METHOD__ );

        // For empty/whitespace-only data or for unknown filters, don't perform
        // any caching or processing
        if ( trim( $data ) === '' || !in_array( $filter, array( 'minify-js', 'minify-css' ) ) ) {
            wfProfileOut( __METHOD__ );
            return $data;
        }

        // Try for cache hit
        // Use CACHE_ANYTHING since filtering is very slow compared to DB queries
        $key = wfMemcKey( 'resourceloader', 'filter', $filter, self::$filterCacheVersion, md5( $data ) );
        $cache = wfGetCache( CACHE_ANYTHING );
        $cacheEntry = $cache->get( $key );
        if ( is_string( $cacheEntry ) ) {
            wfIncrStats( "rl-$filter-cache-hits" );
            wfProfileOut( __METHOD__ );
            return $cacheEntry;
        }

        $result = '';
        // Run the filter - we've already verified one of these will work
        try {
            wfIncrStats( "rl-$filter-cache-misses" );
            switch ( $filter ) {
                case 'minify-js':
                    $result = JavaScriptMinifier::minify( $data,
                        $this->config->get( 'ResourceLoaderMinifierStatementsOnOwnLine' ),
                        $this->config->get( 'ResourceLoaderMinifierMaxLineLength' )
                    );
                    if ( $cacheReport ) {
                        $result .= "\n/* cache key: $key */";
                    }
                    break;
                case 'minify-css':
                    $result = CSSMin::minify( $data );
                    if ( $cacheReport ) {
                        $result .= "\n/* cache key: $key */";
                    }
                    break;
            }

            // Save filtered text to Memcached
            $cache->set( $key, $result );
        } catch ( Exception $e ) {
            MWExceptionHandler::logException( $e );
            wfDebugLog( 'resourceloader', __METHOD__ . ": minification failed: $e" );
            $this->hasErrors = true;
            // Return exception as a comment
            $result = self::formatException( $e );
        }

        wfProfileOut( __METHOD__ );

        return $result;
    }

    /* Methods */

    public function __construct( Config $config = null ) {
        global $IP;

        wfProfileIn( __METHOD__ );

        if ( $config === null ) {
            wfDebug( __METHOD__ . ' was called without providing a Config instance' );
            $config = ConfigFactory::getDefaultInstance()->makeConfig( 'main' );
        }

        $this->config = $config;

        // Add 'local' source first
        $this->addSource( 'local', wfScript( 'load' ) );

        // Add other sources
        $this->addSource( $config->get( 'ResourceLoaderSources' ) );

        // Register core modules
        $this->register( include "$IP/resources/Resources.php" );
        // Register extension modules
        wfRunHooks( 'ResourceLoaderRegisterModules', array( &$this ) );
        $this->register( $config->get( 'ResourceModules' ) );

        if ( $config->get( 'EnableJavaScriptTest' ) === true ) {
            $this->registerTestModules();
        }

        wfProfileOut( __METHOD__ );
    }

    public function getConfig() {
        return $this->config;
    }

    public function register( $name, $info = null ) {
        wfProfileIn( __METHOD__ );

        // Allow multiple modules to be registered in one call
        $registrations = is_array( $name ) ? $name : array( $name => $info );
        foreach ( $registrations as $name => $info ) {
            // Disallow duplicate registrations
            if ( isset( $this->moduleInfos[$name] ) ) {
                wfProfileOut( __METHOD__ );
                // A module has already been registered by this name
                throw new MWException(
                    'ResourceLoader duplicate registration error. ' .
                    'Another module has already been registered as ' . $name
                );
            }

            // Check $name for validity
            if ( !self::isValidModuleName( $name ) ) {
                wfProfileOut( __METHOD__ );
                throw new MWException( "ResourceLoader module name '$name' is invalid, "
                    . "see ResourceLoader::isValidModuleName()" );
            }

            // Attach module
            if ( $info instanceof ResourceLoaderModule ) {
                $this->moduleInfos[$name] = array( 'object' => $info );
                $info->setName( $name );
                $this->modules[$name] = $info;
            } elseif ( is_array( $info ) ) {
                // New calling convention
                $this->moduleInfos[$name] = $info;
            } else {
                wfProfileOut( __METHOD__ );
                throw new MWException(
                    'ResourceLoader module info type error for module \'' . $name .
                    '\': expected ResourceLoaderModule or array (got: ' . gettype( $info ) . ')'
                );
            }

            // Last-minute changes

            // Apply custom skin-defined styles to existing modules.
            if ( $this->isFileModule( $name ) ) {
                foreach ( $this->config->get( 'ResourceModuleSkinStyles' ) as $skinName => $skinStyles ) {
                    // If this module already defines skinStyles for this skin, ignore $wgResourceModuleSkinStyles.
                    if ( isset( $this->moduleInfos[$name]['skinStyles'][$skinName] ) ) {
                        continue;
                    }

                    // If $name is preceded with a '+', the defined style files will be added to 'default'
                    // skinStyles, otherwise 'default' will be ignored as it normally would be.
                    if ( isset( $skinStyles[$name] ) ) {
                        $paths = (array)$skinStyles[$name];
                        $styleFiles = array();
                    } elseif ( isset( $skinStyles['+' . $name] ) ) {
                        $paths = (array)$skinStyles['+' . $name];
                        $styleFiles = isset( $this->moduleInfos[$name]['skinStyles']['default'] ) ?
                            $this->moduleInfos[$name]['skinStyles']['default'] :
                            array();
                    } else {
                        continue;
                    }

                    // Add new file paths, remapping them to refer to our directories and not use settings
                    // from the module we're modifying. These can come from the base definition or be defined
                    // for each module.
                    list( $localBasePath, $remoteBasePath ) =
                        ResourceLoaderFileModule::extractBasePaths( $skinStyles );
                    list( $localBasePath, $remoteBasePath ) =
                        ResourceLoaderFileModule::extractBasePaths( $paths, $localBasePath, $remoteBasePath );

                    foreach ( $paths as $path ) {
                        $styleFiles[] = new ResourceLoaderFilePath( $path, $localBasePath, $remoteBasePath );
                    }

                    $this->moduleInfos[$name]['skinStyles'][$skinName] = $styleFiles;
                }
            }
        }

        wfProfileOut( __METHOD__ );
    }

    public function registerTestModules() {
        global $IP;

        if ( $this->config->get( 'EnableJavaScriptTest' ) !== true ) {
            throw new MWException( 'Attempt to register JavaScript test modules '
                . 'but <code>$wgEnableJavaScriptTest</code> is false. '
                . 'Edit your <code>LocalSettings.php</code> to enable it.' );
        }

        wfProfileIn( __METHOD__ );

        // Get core test suites
        $testModules = array();
        $testModules['qunit'] = array();
        // Get other test suites (e.g. from extensions)
        wfRunHooks( 'ResourceLoaderTestModules', array( &$testModules, &$this ) );

        // Add the testrunner (which configures QUnit) to the dependencies.
        // Since it must be ready before any of the test suites are executed.
        foreach ( $testModules['qunit'] as &$module ) {
            // Make sure all test modules are top-loading so that when QUnit starts
            // on document-ready, it will run once and finish. If some tests arrive
            // later (possibly after QUnit has already finished) they will be ignored.
            $module['position'] = 'top';
            $module['dependencies'][] = 'test.mediawiki.qunit.testrunner';
        }

        $testModules['qunit'] =
            ( include "$IP/tests/qunit/QUnitTestResources.php" ) + $testModules['qunit'];

        foreach ( $testModules as $id => $names ) {
            // Register test modules
            $this->register( $testModules[$id] );

            // Keep track of their names so that they can be loaded together
            $this->testModuleNames[$id] = array_keys( $testModules[$id] );
        }

        wfProfileOut( __METHOD__ );
    }

    public function addSource( $id, $loadUrl = null ) {
        // Allow multiple sources to be registered in one call
        if ( is_array( $id ) ) {
            foreach ( $id as $key => $value ) {
                $this->addSource( $key, $value );
            }
            return;
        }

        // Disallow duplicates
        if ( isset( $this->sources[$id] ) ) {
            throw new MWException(
                'ResourceLoader duplicate source addition error. ' .
                'Another source has already been registered as ' . $id
            );
        }

        // Pre 1.24 backwards-compatibility
        if ( is_array( $loadUrl ) ) {
            if ( !isset( $loadUrl['loadScript'] ) ) {
                throw new MWException(
                    __METHOD__ . ' was passed an array with no "loadScript" key.'
                );
            }

            $loadUrl = $loadUrl['loadScript'];
        }

        $this->sources[$id] = $loadUrl;
    }

    public function getModuleNames() {
        return array_keys( $this->moduleInfos );
    }

    public function getTestModuleNames( $framework = 'all' ) {
        if ( $framework == 'all' ) {
            return $this->testModuleNames;
        } elseif ( isset( $this->testModuleNames[$framework] )
            && is_array( $this->testModuleNames[$framework] )
        ) {
            return $this->testModuleNames[$framework];
        } else {
            return array();
        }
    }

    public function getModule( $name ) {
        if ( !isset( $this->modules[$name] ) ) {
            if ( !isset( $this->moduleInfos[$name] ) ) {
                // No such module
                return null;
            }
            // Construct the requested object
            $info = $this->moduleInfos[$name];
            if ( isset( $info['object'] ) ) {
                // Object given in info array
                $object = $info['object'];
            } else {
                if ( !isset( $info['class'] ) ) {
                    $class = 'ResourceLoaderFileModule';
                } else {
                    $class = $info['class'];
                }
                $object = new $class( $info );
                $object->setConfig( $this->getConfig() );
            }
            $object->setName( $name );
            $this->modules[$name] = $object;
        }

        return $this->modules[$name];
    }

    protected function isFileModule( $name ) {
        if ( !isset( $this->moduleInfos[$name] ) ) {
            return false;
        }
        $info = $this->moduleInfos[$name];
        if ( isset( $info['object'] ) || isset( $info['class'] ) ) {
            return false;
        }
        return true;
    }

    public function getSources() {
        return $this->sources;
    }

    public function getLoadScript( $source ) {
        if ( !isset( $this->sources[$source] ) ) {
            throw new MWException( "The $source source was never registered in ResourceLoader." );
        }
        return $this->sources[$source];
    }

    public function respond( ResourceLoaderContext $context ) {
        // Use file cache if enabled and available...
        if ( $this->config->get( 'UseFileCache' ) ) {
            $fileCache = ResourceFileCache::newFromContext( $context );
            if ( $this->tryRespondFromFileCache( $fileCache, $context ) ) {
                return; // output handled
            }
        }

        // Buffer output to catch warnings. Normally we'd use ob_clean() on the
        // top-level output buffer to clear warnings, but that breaks when ob_gzhandler
        // is used: ob_clean() will clear the GZIP header in that case and it won't come
        // back for subsequent output, resulting in invalid GZIP. So we have to wrap
        // the whole thing in our own output buffer to be sure the active buffer
        // doesn't use ob_gzhandler.
        // See http://bugs.php.net/bug.php?id=36514
        ob_start();

        wfProfileIn( __METHOD__ );
        $errors = '';

        // Find out which modules are missing and instantiate the others
        $modules = array();
        $missing = array();
        foreach ( $context->getModules() as $name ) {
            $module = $this->getModule( $name );
            if ( $module ) {
                // Do not allow private modules to be loaded from the web.
                // This is a security issue, see bug 34907.
                if ( $module->getGroup() === 'private' ) {
                    wfDebugLog( 'resourceloader', __METHOD__ . ": request for private module '$name' denied" );
                    $this->hasErrors = true;
                    // Add exception to the output as a comment
                    $errors .= self::makeComment( "Cannot show private module \"$name\"" );

                    continue;
                }
                $modules[$name] = $module;
            } else {
                $missing[] = $name;
            }
        }

        // Preload information needed to the mtime calculation below
        try {
            $this->preloadModuleInfo( array_keys( $modules ), $context );
        } catch ( Exception $e ) {
            MWExceptionHandler::logException( $e );
            wfDebugLog( 'resourceloader', __METHOD__ . ": preloading module info failed: $e" );
            $this->hasErrors = true;
            // Add exception to the output as a comment
            $errors .= self::formatException( $e );
        }

        wfProfileIn( __METHOD__ . '-getModifiedTime' );

        // To send Last-Modified and support If-Modified-Since, we need to detect
        // the last modified time
        $mtime = wfTimestamp( TS_UNIX, $this->config->get( 'CacheEpoch' ) );
        foreach ( $modules as $module ) {
            try {
                // Calculate maximum modified time
                $mtime = max( $mtime, $module->getModifiedTime( $context ) );
            } catch ( Exception $e ) {
                MWExceptionHandler::logException( $e );
                wfDebugLog( 'resourceloader', __METHOD__ . ": calculating maximum modified time failed: $e" );
                $this->hasErrors = true;
                // Add exception to the output as a comment
                $errors .= self::formatException( $e );
            }
        }

        wfProfileOut( __METHOD__ . '-getModifiedTime' );

        // If there's an If-Modified-Since header, respond with a 304 appropriately
        if ( $this->tryRespondLastModified( $context, $mtime ) ) {
            wfProfileOut( __METHOD__ );
            return; // output handled (buffers cleared)
        }

        // Generate a response
        $response = $this->makeModuleResponse( $context, $modules, $missing );

        // Prepend comments indicating exceptions
        $response = $errors . $response;

        // Capture any PHP warnings from the output buffer and append them to the
        // response in a comment if we're in debug mode.
        if ( $context->getDebug() && strlen( $warnings = ob_get_contents() ) ) {
            $response = self::makeComment( $warnings ) . $response;
            $this->hasErrors = true;
        }

        // Save response to file cache unless there are errors
        if ( isset( $fileCache ) && !$errors && !count( $missing ) ) {
            // Cache single modules...and other requests if there are enough hits
            if ( ResourceFileCache::useFileCache( $context ) ) {
                if ( $fileCache->isCacheWorthy() ) {
                    $fileCache->saveText( $response );
                } else {
                    $fileCache->incrMissesRecent( $context->getRequest() );
                }
            }
        }

        // Send content type and cache related headers
        $this->sendResponseHeaders( $context, $mtime, $this->hasErrors );

        // Remove the output buffer and output the response
        ob_end_clean();
        echo $response;

        wfProfileOut( __METHOD__ );
    }

    protected function sendResponseHeaders( ResourceLoaderContext $context, $mtime, $errors ) {
        $rlMaxage = $this->config->get( 'ResourceLoaderMaxage' );
        // If a version wasn't specified we need a shorter expiry time for updates
        // to propagate to clients quickly
        // If there were errors, we also need a shorter expiry time so we can recover quickly
        if ( is_null( $context->getVersion() ) || $errors ) {
            $maxage = $rlMaxage['unversioned']['client'];
            $smaxage = $rlMaxage['unversioned']['server'];
        // If a version was specified we can use a longer expiry time since changing
        // version numbers causes cache misses
        } else {
            $maxage = $rlMaxage['versioned']['client'];
            $smaxage = $rlMaxage['versioned']['server'];
        }
        if ( $context->getOnly() === 'styles' ) {
            header( 'Content-Type: text/css; charset=utf-8' );
            header( 'Access-Control-Allow-Origin: *' );
        } else {
            header( 'Content-Type: text/javascript; charset=utf-8' );
        }
        header( 'Last-Modified: ' . wfTimestamp( TS_RFC2822, $mtime ) );
        if ( $context->getDebug() ) {
            // Do not cache debug responses
            header( 'Cache-Control: private, no-cache, must-revalidate' );
            header( 'Pragma: no-cache' );
        } else {
            header( "Cache-Control: public, max-age=$maxage, s-maxage=$smaxage" );
            $exp = min( $maxage, $smaxage );
            header( 'Expires: ' . wfTimestamp( TS_RFC2822, $exp + time() ) );
        }
    }

    protected function tryRespondLastModified( ResourceLoaderContext $context, $mtime ) {
        // If there's an If-Modified-Since header, respond with a 304 appropriately
        // Some clients send "timestamp;length=123". Strip the part after the first ';'
        // so we get a valid timestamp.
        $ims = $context->getRequest()->getHeader( 'If-Modified-Since' );
        // Never send 304s in debug mode
        if ( $ims !== false && !$context->getDebug() ) {
            $imsTS = strtok( $ims, ';' );
            if ( $mtime <= wfTimestamp( TS_UNIX, $imsTS ) ) {
                // There's another bug in ob_gzhandler (see also the comment at
                // the top of this function) that causes it to gzip even empty
                // responses, meaning it's impossible to produce a truly empty
                // response (because the gzip header is always there). This is
                // a problem because 304 responses have to be completely empty
                // per the HTTP spec, and Firefox behaves buggily when they're not.
                // See also http://bugs.php.net/bug.php?id=51579
                // To work around this, we tear down all output buffering before
                // sending the 304.
                wfResetOutputBuffers( /* $resetGzipEncoding = */ true );

                header( 'HTTP/1.0 304 Not Modified' );
                header( 'Status: 304 Not Modified' );
                return true;
            }
        }
        return false;
    }

    protected function tryRespondFromFileCache(
        ResourceFileCache $fileCache, ResourceLoaderContext $context
    ) {
        $rlMaxage = $this->config->get( 'ResourceLoaderMaxage' );
        // Buffer output to catch warnings.
        ob_start();
        // Get the maximum age the cache can be
        $maxage = is_null( $context->getVersion() )
            ? $rlMaxage['unversioned']['server']
            : $rlMaxage['versioned']['server'];
        // Minimum timestamp the cache file must have
        $good = $fileCache->isCacheGood( wfTimestamp( TS_MW, time() - $maxage ) );
        if ( !$good ) {
            try { // RL always hits the DB on file cache miss...
                wfGetDB( DB_SLAVE );
            } catch ( DBConnectionError $e ) { // ...check if we need to fallback to cache
                $good = $fileCache->isCacheGood(); // cache existence check
            }
        }
        if ( $good ) {
            $ts = $fileCache->cacheTimestamp();
            // Send content type and cache headers
            $this->sendResponseHeaders( $context, $ts, false );
            // If there's an If-Modified-Since header, respond with a 304 appropriately
            if ( $this->tryRespondLastModified( $context, $ts ) ) {
                return false; // output handled (buffers cleared)
            }
            $response = $fileCache->fetchText();
            // Capture any PHP warnings from the output buffer and append them to the
            // response in a comment if we're in debug mode.
            if ( $context->getDebug() && strlen( $warnings = ob_get_contents() ) ) {
                $response = "/*\n$warnings\n*/\n" . $response;
            }
            // Remove the output buffer and output the response
            ob_end_clean();
            echo $response . "\n/* Cached {$ts} */";
            return true; // cache hit
        }
        // Clear buffer
        ob_end_clean();

        return false; // cache miss
    }

    public static function makeComment( $text ) {
        $encText = str_replace( '*/', '* /', $text );
        return "/*\n$encText\n*/\n";
    }

    public static function formatException( $e ) {
        global $wgShowExceptionDetails;

        if ( $wgShowExceptionDetails ) {
            return self::makeComment( $e->__toString() );
        } else {
            return self::makeComment( wfMessage( 'internalerror' )->text() );
        }
    }

    public function makeModuleResponse( ResourceLoaderContext $context,
        array $modules, array $missing = array()
    ) {
        $out = '';
        $exceptions = '';
        $states = array();

        if ( !count( $modules ) && !count( $missing ) ) {
            return "/* This file is the Web entry point for MediaWiki's ResourceLoader:
   <https://www.mediawiki.org/wiki/ResourceLoader>. In this request,
   no modules were requested. Max made me put this here. */";
        }

        wfProfileIn( __METHOD__ );

        // Pre-fetch blobs
        if ( $context->shouldIncludeMessages() ) {
            try {
                $blobs = MessageBlobStore::getInstance()->get( $this, $modules, $context->getLanguage() );
            } catch ( Exception $e ) {
                MWExceptionHandler::logException( $e );
                wfDebugLog(
                    'resourceloader',
                    __METHOD__ . ": pre-fetching blobs from MessageBlobStore failed: $e"
                );
                $this->hasErrors = true;
                // Add exception to the output as a comment
                $exceptions .= self::formatException( $e );
            }
        } else {
            $blobs = array();
        }

        foreach ( $missing as $name ) {
            $states[$name] = 'missing';
        }

        // Generate output
        $isRaw = false;
        foreach ( $modules as $name => $module ) {
            wfProfileIn( __METHOD__ . '-' . $name );
            try {
                $scripts = '';
                if ( $context->shouldIncludeScripts() ) {
                    // If we are in debug mode, we'll want to return an array of URLs if possible
                    // However, we can't do this if the module doesn't support it
                    // We also can't do this if there is an only= parameter, because we have to give
                    // the module a way to return a load.php URL without causing an infinite loop
                    if ( $context->getDebug() && !$context->getOnly() && $module->supportsURLLoading() ) {
                        $scripts = $module->getScriptURLsForDebug( $context );
                    } else {
                        $scripts = $module->getScript( $context );
                        // rtrim() because there are usually a few line breaks
                        // after the last ';'. A new line at EOF, a new line
                        // added by ResourceLoaderFileModule::readScriptFiles, etc.
                        if ( is_string( $scripts )
                            && strlen( $scripts )
                            && substr( rtrim( $scripts ), -1 ) !== ';'
                        ) {
                            // Append semicolon to prevent weird bugs caused by files not
                            // terminating their statements right (bug 27054)
                            $scripts .= ";\n";
                        }
                    }
                }
                // Styles
                $styles = array();
                if ( $context->shouldIncludeStyles() ) {
                    // Don't create empty stylesheets like array( '' => '' ) for modules
                    // that don't *have* any stylesheets (bug 38024).
                    $stylePairs = $module->getStyles( $context );
                    if ( count( $stylePairs ) ) {
                        // If we are in debug mode without &only= set, we'll want to return an array of URLs
                        // See comment near shouldIncludeScripts() for more details
                        if ( $context->getDebug() && !$context->getOnly() && $module->supportsURLLoading() ) {
                            $styles = array(
                                'url' => $module->getStyleURLsForDebug( $context )
                            );
                        } else {
                            // Minify CSS before embedding in mw.loader.implement call
                            // (unless in debug mode)
                            if ( !$context->getDebug() ) {
                                foreach ( $stylePairs as $media => $style ) {
                                    // Can be either a string or an array of strings.
                                    if ( is_array( $style ) ) {
                                        $stylePairs[$media] = array();
                                        foreach ( $style as $cssText ) {
                                            if ( is_string( $cssText ) ) {
                                                $stylePairs[$media][] = $this->filter( 'minify-css', $cssText );
                                            }
                                        }
                                    } elseif ( is_string( $style ) ) {
                                        $stylePairs[$media] = $this->filter( 'minify-css', $style );
                                    }
                                }
                            }
                            // Wrap styles into @media groups as needed and flatten into a numerical array
                            $styles = array(
                                'css' => self::makeCombinedStyles( $stylePairs )
                            );
                        }
                    }
                }

                // Messages
                $messagesBlob = isset( $blobs[$name] ) ? $blobs[$name] : '{}';

                // Append output
                switch ( $context->getOnly() ) {
                    case 'scripts':
                        if ( is_string( $scripts ) ) {
                            // Load scripts raw...
                            $out .= $scripts;
                        } elseif ( is_array( $scripts ) ) {
                            // ...except when $scripts is an array of URLs
                            $out .= self::makeLoaderImplementScript( $name, $scripts, array(), array() );
                        }
                        break;
                    case 'styles':
                        // We no longer seperate into media, they are all combined now with
                        // custom media type groups into @media .. {} sections as part of the css string.
                        // Module returns either an empty array or a numerical array with css strings.
                        $out .= isset( $styles['css'] ) ? implode( '', $styles['css'] ) : '';
                        break;
                    case 'messages':
                        $out .= self::makeMessageSetScript( new XmlJsCode( $messagesBlob ) );
                        break;
                    default:
                        $out .= self::makeLoaderImplementScript(
                            $name,
                            $scripts,
                            $styles,
                            new XmlJsCode( $messagesBlob )
                        );
                        break;
                }
            } catch ( Exception $e ) {
                MWExceptionHandler::logException( $e );
                wfDebugLog( 'resourceloader', __METHOD__ . ": generating module package failed: $e" );
                $this->hasErrors = true;
                // Add exception to the output as a comment
                $exceptions .= self::formatException( $e );

                // Respond to client with error-state instead of module implementation
                $states[$name] = 'error';
                unset( $modules[$name] );
            }
            $isRaw |= $module->isRaw();
            wfProfileOut( __METHOD__ . '-' . $name );
        }

        // Update module states
        if ( $context->shouldIncludeScripts() && !$context->getRaw() && !$isRaw ) {
            if ( count( $modules ) && $context->getOnly() === 'scripts' ) {
                // Set the state of modules loaded as only scripts to ready as
                // they don't have an mw.loader.implement wrapper that sets the state
                foreach ( $modules as $name => $module ) {
                    $states[$name] = 'ready';
                }
            }

            // Set the state of modules we didn't respond to with mw.loader.implement
            if ( count( $states ) ) {
                $out .= self::makeLoaderStateScript( $states );
            }
        } else {
            if ( count( $states ) ) {
                $exceptions .= self::makeComment(
                    'Problematic modules: ' . FormatJson::encode( $states, ResourceLoader::inDebugMode() )
                );
            }
        }

        if ( !$context->getDebug() ) {
            if ( $context->getOnly() === 'styles' ) {
                $out = $this->filter( 'minify-css', $out );
            } else {
                $out = $this->filter( 'minify-js', $out );
            }
        }

        wfProfileOut( __METHOD__ );
        return $exceptions . $out;
    }

    /* Static Methods */

    public static function makeLoaderImplementScript( $name, $scripts, $styles, $messages ) {
        if ( is_string( $scripts ) ) {
            $scripts = new XmlJsCode( "function ( $, jQuery ) {\n{$scripts}\n}" );
        } elseif ( !is_array( $scripts ) ) {
            throw new MWException( 'Invalid scripts error. Array of URLs or string of code expected.' );
        }
        return Xml::encodeJsCall(
            'mw.loader.implement',
            array(
                $name,
                $scripts,
                // Force objects. mw.loader.implement requires them to be javascript objects.
                // Although these variables are associative arrays, which become javascript
                // objects through json_encode. In many cases they will be empty arrays, and
                // PHP/json_encode() consider empty arrays to be numerical arrays and
                // output javascript "[]" instead of "{}". This fixes that.
                (object)$styles,
                (object)$messages
            ),
            ResourceLoader::inDebugMode()
        );
    }

    public static function makeMessageSetScript( $messages ) {
        return Xml::encodeJsCall(
            'mw.messages.set',
            array( (object)$messages ),
            ResourceLoader::inDebugMode()
        );
    }

    public static function makeCombinedStyles( array $stylePairs ) {
        $out = array();
        foreach ( $stylePairs as $media => $styles ) {
            // ResourceLoaderFileModule::getStyle can return the styles
            // as a string or an array of strings. This is to allow separation in
            // the front-end.
            $styles = (array)$styles;
            foreach ( $styles as $style ) {
                $style = trim( $style );
                // Don't output an empty "@media print { }" block (bug 40498)
                if ( $style !== '' ) {
                    // Transform the media type based on request params and config
                    // The way that this relies on $wgRequest to propagate request params is slightly evil
                    $media = OutputPage::transformCssMedia( $media );

                    if ( $media === '' || $media == 'all' ) {
                        $out[] = $style;
                    } elseif ( is_string( $media ) ) {
                        $out[] = "@media $media {\n" . str_replace( "\n", "\n\t", "\t" . $style ) . "}";
                    }
                    // else: skip
                }
            }
        }
        return $out;
    }

    public static function makeLoaderStateScript( $name, $state = null ) {
        if ( is_array( $name ) ) {
            return Xml::encodeJsCall(
                'mw.loader.state',
                array( $name ),
                ResourceLoader::inDebugMode()
            );
        } else {
            return Xml::encodeJsCall(
                'mw.loader.state',
                array( $name, $state ),
                ResourceLoader::inDebugMode()
            );
        }
    }

    public static function makeCustomLoaderScript( $name, $version, $dependencies,
        $group, $source, $script
    ) {
        $script = str_replace( "\n", "\n\t", trim( $script ) );
        return Xml::encodeJsCall(
            "( function ( name, version, dependencies, group, source ) {\n\t$script\n} )",
            array( $name, $version, $dependencies, $group, $source ),
            ResourceLoader::inDebugMode()
        );
    }

    public static function makeLoaderRegisterScript( $name, $version = null,
        $dependencies = null, $group = null, $source = null, $skip = null
    ) {
        if ( is_array( $name ) ) {
            return Xml::encodeJsCall(
                'mw.loader.register',
                array( $name ),
                ResourceLoader::inDebugMode()
            );
        } else {
            $version = (int)$version > 1 ? (int)$version : 1;
            return Xml::encodeJsCall(
                'mw.loader.register',
                array( $name, $version, $dependencies, $group, $source, $skip ),
                ResourceLoader::inDebugMode()
            );
        }
    }

    public static function makeLoaderSourcesScript( $id, $properties = null ) {
        if ( is_array( $id ) ) {
            return Xml::encodeJsCall(
                'mw.loader.addSource',
                array( $id ),
                ResourceLoader::inDebugMode()
            );
        } else {
            return Xml::encodeJsCall(
                'mw.loader.addSource',
                array( $id, $properties ),
                ResourceLoader::inDebugMode()
            );
        }
    }

    public static function makeLoaderConditionalScript( $script ) {
        return "if(window.mw){\n" . trim( $script ) . "\n}";
    }

    public static function makeConfigSetScript( array $configuration ) {
        return Xml::encodeJsCall(
            'mw.config.set',
            array( $configuration ),
            ResourceLoader::inDebugMode()
        );
    }

    public static function makePackedModulesString( $modules ) {
        $groups = array(); // array( prefix => array( suffixes ) )
        foreach ( $modules as $module ) {
            $pos = strrpos( $module, '.' );
            $prefix = $pos === false ? '' : substr( $module, 0, $pos );
            $suffix = $pos === false ? $module : substr( $module, $pos + 1 );
            $groups[$prefix][] = $suffix;
        }

        $arr = array();
        foreach ( $groups as $prefix => $suffixes ) {
            $p = $prefix === '' ? '' : $prefix . '.';
            $arr[] = $p . implode( ',', $suffixes );
        }
        $str = implode( '|', $arr );
        return $str;
    }

    public static function inDebugMode() {
        if ( self::$debugMode === null ) {
            global $wgRequest, $wgResourceLoaderDebug;
            self::$debugMode = $wgRequest->getFuzzyBool( 'debug',
                $wgRequest->getCookie( 'resourceLoaderDebug', '', $wgResourceLoaderDebug )
            );
        }
        return self::$debugMode;
    }

    public static function clearCache() {
        self::$debugMode = null;
    }

    public function createLoaderURL( $source, ResourceLoaderContext $context,
        $extraQuery = array()
    ) {
        $query = self::createLoaderQuery( $context, $extraQuery );
        $script = $this->getLoadScript( $source );

        // Prevent the IE6 extension check from being triggered (bug 28840)
        // by appending a character that's invalid in Windows extensions ('*')
        return wfExpandUrl( wfAppendQuery( $script, $query ) . '&*', PROTO_RELATIVE );
    }

    public static function makeLoaderURL( $modules, $lang, $skin, $user = null,
        $version = null, $debug = false, $only = null, $printable = false,
        $handheld = false, $extraQuery = array()
    ) {
        global $wgLoadScript;

        $query = self::makeLoaderQuery( $modules, $lang, $skin, $user, $version, $debug,
            $only, $printable, $handheld, $extraQuery
        );

        // Prevent the IE6 extension check from being triggered (bug 28840)
        // by appending a character that's invalid in Windows extensions ('*')
        return wfExpandUrl( wfAppendQuery( $wgLoadScript, $query ) . '&*', PROTO_RELATIVE );
    }

    public static function createLoaderQuery( ResourceLoaderContext $context, $extraQuery = array() ) {
        return self::makeLoaderQuery(
            $context->getModules(),
            $context->getLanguage(),
            $context->getSkin(),
            $context->getUser(),
            $context->getVersion(),
            $context->getDebug(),
            $context->getOnly(),
            $context->getRequest()->getBool( 'printable' ),
            $context->getRequest()->getBool( 'handheld' ),
            $extraQuery
        );
    }

    public static function makeLoaderQuery( $modules, $lang, $skin, $user = null,
        $version = null, $debug = false, $only = null, $printable = false,
        $handheld = false, $extraQuery = array()
    ) {
        $query = array(
            'modules' => self::makePackedModulesString( $modules ),
            'lang' => $lang,
            'skin' => $skin,
            'debug' => $debug ? 'true' : 'false',
        );
        if ( $user !== null ) {
            $query['user'] = $user;
        }
        if ( $version !== null ) {
            $query['version'] = $version;
        }
        if ( $only !== null ) {
            $query['only'] = $only;
        }
        if ( $printable ) {
            $query['printable'] = 1;
        }
        if ( $handheld ) {
            $query['handheld'] = 1;
        }
        $query += $extraQuery;

        // Make queries uniform in order
        ksort( $query );
        return $query;
    }

    public static function isValidModuleName( $moduleName ) {
        return !preg_match( '/[|,!]/', $moduleName ) && strlen( $moduleName ) <= 255;
    }

    public static function getLessCompiler( Config $config ) {
        // When called from the installer, it is possible that a required PHP extension
        // is missing (at least for now; see bug 47564). If this is the case, throw an
        // exception (caught by the installer) to prevent a fatal error later on.
        if ( !function_exists( 'ctype_digit' ) ) {
            throw new MWException( 'lessc requires the Ctype extension' );
        }

        $less = new lessc();
        $less->setPreserveComments( true );
        $less->setVariables( self::getLessVars( $config ) );
        $less->setImportDir( $config->get( 'ResourceLoaderLESSImportPaths' ) );
        foreach ( $config->get( 'ResourceLoaderLESSFunctions' ) as $name => $func ) {
            $less->registerFunction( $name, $func );
        }
        return $less;
    }

    public static function getLessVars( Config $config ) {
        $lessVars = $config->get( 'ResourceLoaderLESSVars' );
        // Sort by key to ensure consistent hashing for cache lookups.
        ksort( $lessVars );
        return $lessVars;
    }
}