Whitelist the <wbr> element.

[mediawiki.git] / includes / resourceloader / ResourceLoader.php

<?php
/**
 * Base class for resource loading system.
 *
 * 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
 * @author Roan Kattouw
 * @author Trevor Parscal
 */

/**
 * Dynamic JavaScript and CSS resource loading system.
 *
 * Most of the documention is on the MediaWiki documentation wiki starting at:
 *    http://www.mediawiki.org/wiki/ResourceLoader
 */
class ResourceLoader {

        /* Protected Static Members */
        protected static $filterCacheVersion = 7;
        protected static $requiredSourceProperties = array( 'loadScript' );

        /** Array: List of module name/ResourceLoaderModule object pairs */
        protected $modules = array();

        /** Associative array mapping module name to info associative array */
        protected $moduleInfos = array();

        /** Associative array mapping framework ids to a list of names of test suite modules */
        /** like array( 'qunit' => array( 'mediawiki.tests.qunit.suites', 'ext.foo.tests', .. ), .. ) */
        protected $testModuleNames = array();

        /** array( 'source-id' => array( 'loadScript' => 'http://.../load.php' ) ) **/
        protected $sources = array();

        /** @var bool */
        protected $hasErrors = false;

        /* Protected Methods */

        /**
         * Loads information stored in the database about modules.
         *
         * This method grabs modules dependencies from the database and updates modules
         * objects.
         *
         * This is not inside the module code because it is much faster to
         * request all of the information at once than it is to have each module
         * requests its own information. This sacrifice of modularity yields a substantial
         * performance improvement.
         *
         * @param array $modules List of module names to preload information for
         * @param $context ResourceLoaderContext: Context to load the information within
         */
        public function preloadModuleInfo( array $modules, ResourceLoaderContext $context ) {
                if ( !count( $modules ) ) {
                        return; // or else Database*::select() will explode, plus it's cheaper!
                }
                $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 ) {
                        $this->getModule( $row->md_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 ) {
                        $this->getModule( $name )->setFileDependencies( $skin, array() );
                }

                // Get message blob mtimes. Only do this for modules with messages
                $modulesWithMessages = array();
                foreach ( $modules as $name ) {
                        if ( count( $this->getModule( $name )->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 ) {
                                $this->getModule( $row->mr_resource )->setMsgBlobMtime( $lang,
                                        wfTimestamp( TS_UNIX, $row->mr_timestamp ) );
                                unset( $modulesWithoutMessages[$row->mr_resource] );
                        }
                }
                foreach ( array_keys( $modulesWithoutMessages ) as $name ) {
                        $this->getModule( $name )->setMsgBlobMtime( $lang, 0 );
                }
        }

        /**
         * Runs JavaScript or CSS data through a filter, caching the filtered result for future calls.
         *
         * Available filters are:
         *  - minify-js \see JavaScriptMinifier::minify
         *  - minify-css \see CSSMin::minify
         *
         * If $data is empty, only contains whitespace or the filter was unknown,
         * $data is returned unmodified.
         *
         * @param string $filter Name of filter to run
         * @param string $data Text to filter, such as JavaScript or CSS text
         * @return String: Filtered data, or a comment containing an error message
         */
        protected function filter( $filter, $data ) {
                global $wgResourceLoaderMinifierStatementsOnOwnLine, $wgResourceLoaderMinifierMaxLineLength;
                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 ) ) {
                        wfProfileOut( __METHOD__ );
                        return $cacheEntry;
                }

                $result = '';
                // Run the filter - we've already verified one of these will work
                try {
                        switch ( $filter ) {
                                case 'minify-js':
                                        $result = JavaScriptMinifier::minify( $data,
                                                $wgResourceLoaderMinifierStatementsOnOwnLine,
                                                $wgResourceLoaderMinifierMaxLineLength
                                        );
                                        $result .= "\n/* cache key: $key */";
                                        break;
                                case 'minify-css':
                                        $result = CSSMin::minify( $data );
                                        $result .= "\n/* cache key: $key */";
                                        break;
                        }

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

                wfProfileOut( __METHOD__ );

                return $result;
        }

        /* Methods */

        /**
         * Registers core modules and runs registration hooks.
         */
        public function __construct() {
                global $IP, $wgResourceModules, $wgResourceLoaderSources, $wgLoadScript, $wgEnableJavaScriptTest;

                wfProfileIn( __METHOD__ );

                // Add 'local' source first
                $this->addSource( 'local', array( 'loadScript' => $wgLoadScript, 'apiScript' => wfScript( 'api' ) ) );

                // Add other sources
                $this->addSource( $wgResourceLoaderSources );

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

                if ( $wgEnableJavaScriptTest === true ) {
                        $this->registerTestModules();
                }

                wfProfileOut( __METHOD__ );
        }

        /**
         * Registers a module with the ResourceLoader system.
         *
         * @param $name Mixed: Name of module as a string or List of name/object pairs as an array
         * @param array $info Module info array. For backwards compatibility with 1.17alpha,
         *   this may also be a ResourceLoaderModule object. Optional when using
         *   multiple-registration calling style.
         * @throws MWException: If a duplicate module registration is attempted
         * @throws MWException: If a module name contains illegal characters (pipes or commas)
         * @throws MWException: If something other than a ResourceLoaderModule is being registered
         * @return Boolean: False if there were any errors, in which case one or more modules were not
         *     registered
         */
        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 ( is_object( $info ) ) {
                                // Old calling convention
                                // Validate the input
                                if ( !( $info instanceof ResourceLoaderModule ) ) {
                                        wfProfileOut( __METHOD__ );
                                        throw new MWException( 'ResourceLoader invalid module error. ' .
                                                'Instances of ResourceLoaderModule expected.' );
                                }

                                $this->moduleInfos[$name] = array( 'object' => $info );
                                $info->setName( $name );
                                $this->modules[$name] = $info;
                        } else {
                                // New calling convention
                                $this->moduleInfos[$name] = $info;
                        }
                }

                wfProfileOut( __METHOD__ );
        }

        /**
         */
        public function registerTestModules() {
                global $IP, $wgEnableJavaScriptTest;

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

                wfProfileIn( __METHOD__ );

                // Get core test suites
                $testModules = array();
                $testModules['qunit'] = include "$IP/tests/qunit/QUnitTestResources.php";
                // 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'][] = 'mediawiki.tests.qunit.testrunner';
                }

                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__ );
        }

        /**
         * Add a foreign source of modules.
         *
         * Source properties:
         * 'loadScript': URL (either fully-qualified or protocol-relative) of load.php for this source
         *
         * @param $id Mixed: source ID (string), or array( id1 => props1, id2 => props2, ... )
         * @param array $properties source properties
         * @throws MWException
         */
        public function addSource( $id, $properties = 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
                        );
                }

                // Validate properties
                foreach ( self::$requiredSourceProperties as $prop ) {
                        if ( !isset( $properties[$prop] ) ) {
                                throw new MWException( "Required property $prop missing from source ID $id" );
                        }
                }

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

        /**
         * Get a list of module names
         *
         * @return Array: List of module names
         */
        public function getModuleNames() {
                return array_keys( $this->moduleInfos );
        }

        /**
         * Get a list of test module names for one (or all) frameworks.
         * If the given framework id is unknkown, or if the in-object variable is not an array,
         * then it will return an empty array.
         *
         * @param string $framework Optional. Get only the test module names for one
         * particular framework.
         * @return Array
         */
        public function getTestModuleNames( $framework = 'all' ) {
                /// @todo api siteinfo prop testmodulenames modulenames
                if ( $framework == 'all' ) {
                        return $this->testModuleNames;
                } elseif ( isset( $this->testModuleNames[$framework] ) && is_array( $this->testModuleNames[$framework] ) ) {
                        return $this->testModuleNames[$framework];
                } else {
                        return array();
                }
        }

        /**
         * Get the ResourceLoaderModule object for a given module name.
         *
         * @param string $name Module name
         * @return ResourceLoaderModule if module has been registered, null otherwise
         */
        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];
                        /** @var ResourceLoaderModule $object */
                        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->setName( $name );
                        $this->modules[$name] = $object;
                }

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

        /**
         * Get the list of sources
         *
         * @return Array: array( id => array of properties, .. )
         */
        public function getSources() {
                return $this->sources;
        }

        /**
         * Outputs a response to a resource load-request, including a content-type header.
         *
         * @param $context ResourceLoaderContext: Context in which a response should be formed
         */
        public function respond( ResourceLoaderContext $context ) {
                global $wgCacheEpoch, $wgUseFileCache;

                // Use file cache if enabled and available...
                if ( $wgUseFileCache ) {
                        $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 = '';

                // Split requested modules into two groups, modules and missing
                $modules = array();
                $missing = array();
                foreach ( $context->getModules() as $name ) {
                        if ( isset( $this->moduleInfos[$name] ) ) {
                                $module = $this->getModule( $name );
                                // 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 .= $this->makeComment( "Cannot show private module \"$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 ) {
                        wfDebugLog( 'resourceloader', __METHOD__ . ": preloading module info failed: $e" );
                        $this->hasErrors = true;
                        // Add exception to the output as a comment
                        $errors .= $this->makeComment( $e->__toString() );
                }

                wfProfileIn( __METHOD__ . '-getModifiedTime' );

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

                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 = $this->makeComment( $warnings ) . $response;
                        $this->hasErrors = true;
                }

                // Save response to file cache unless there are errors
                if ( isset( $fileCache ) && !$errors && !$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__ );
        }

        /**
         * Send content type and last modified headers to the client.
         * @param $context ResourceLoaderContext
         * @param string $mtime TS_MW timestamp to use for last-modified
         * @param bool $errors Whether there are commented-out errors in the response
         * @return void
         */
        protected function sendResponseHeaders( ResourceLoaderContext $context, $mtime, $errors ) {
                global $wgResourceLoaderMaxage;
                // 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 = $wgResourceLoaderMaxage['unversioned']['client'];
                        $smaxage = $wgResourceLoaderMaxage['unversioned']['server'];
                // If a version was specified we can use a longer expiry time since changing
                // version numbers causes cache misses
                } else {
                        $maxage = $wgResourceLoaderMaxage['versioned']['client'];
                        $smaxage = $wgResourceLoaderMaxage['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() ) );
                }
        }

        /**
         * If there's an If-Modified-Since header, respond with a 304 appropriately
         * and clear out the output buffer. If the client cache is too old then do nothing.
         * @param $context ResourceLoaderContext
         * @param string $mtime The TS_MW timestamp to check the header against
         * @return bool True iff 304 header sent and output handled
         */
        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.
                                // On some setups, ob_get_level() doesn't seem to go down to zero
                                // no matter how often we call ob_get_clean(), so instead of doing
                                // the more intuitive while ( ob_get_level() > 0 ) ob_get_clean();
                                // we have to be safe here and avoid an infinite loop.
                                // Caching the level is not an option, need to allow it to
                                // shorten the loop on-the-fly (bug 46836)
                                for ( $i = 0; $i < ob_get_level(); $i++ ) {
                                        ob_end_clean();
                                }

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

        /**
         * Send out code for a response from file cache if possible
         *
         * @param $fileCache ResourceFileCache: Cache object for this request URL
         * @param $context ResourceLoaderContext: Context in which to generate a response
         * @return bool If this found a cache file and handled the response
         */
        protected function tryRespondFromFileCache(
                ResourceFileCache $fileCache, ResourceLoaderContext $context
        ) {
                global $wgResourceLoaderMaxage;
                // Buffer output to catch warnings.
                ob_start();
                // Get the maximum age the cache can be
                $maxage = is_null( $context->getVersion() )
                        ? $wgResourceLoaderMaxage['unversioned']['server']
                        : $wgResourceLoaderMaxage['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
        }

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

        /**
         * Generates code for a response
         *
         * @param $context ResourceLoaderContext: Context in which to generate a response
         * @param array $modules List of module objects keyed by module name
         * @param array $missing List of unavailable modules (optional)
         * @return String: Response data
         */
        public function makeModuleResponse( ResourceLoaderContext $context,
                array $modules, $missing = array()
        ) {
                $out = '';
                $exceptions = '';
                if ( $modules === array() && $missing === array() ) {
                        return '/* No modules requested. Max made me put this here */';
                }

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

                // Generate output
                $isRaw = false;
                foreach ( $modules as $name => $module ) {
                        /**
                         * @var $module ResourceLoaderModule
                         */

                        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 );
                                                if ( is_string( $scripts ) && strlen( $scripts ) && substr( $scripts, -1 ) !== ';' ) {
                                                        // bug 27054: Append semicolon to prevent weird bugs
                                                        // caused by files not terminating their statements right
                                                        $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 ) {
                                wfDebugLog( 'resourceloader', __METHOD__ . ": generating module package failed: $e" );
                                $this->hasErrors = true;
                                // Add exception to the output as a comment
                                $exceptions .= $this->makeComment( $e->__toString() );

                                // Register module as missing
                                $missing[] = $name;
                                unset( $modules[$name] );
                        }
                        $isRaw |= $module->isRaw();
                        wfProfileOut( __METHOD__ . '-' . $name );
                }

                // Update module states
                if ( $context->shouldIncludeScripts() && !$context->getRaw() && !$isRaw ) {
                        // Set the state of modules loaded as only scripts to ready
                        if ( count( $modules ) && $context->getOnly() === 'scripts' ) {
                                $out .= self::makeLoaderStateScript(
                                        array_fill_keys( array_keys( $modules ), 'ready' ) );
                        }
                        // Set the state of modules which were requested but unavailable as missing
                        if ( is_array( $missing ) && count( $missing ) ) {
                                $out .= self::makeLoaderStateScript( array_fill_keys( $missing, 'missing' ) );
                        }
                }

                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 */

        /**
         * Returns JS code to call to mw.loader.implement for a module with
         * given properties.
         *
         * @param string $name Module name
         * @param $scripts Mixed: List of URLs to JavaScript files or String of JavaScript code
         * @param $styles Mixed: Array of CSS strings keyed by media type, or an array of lists of URLs to
         * CSS files keyed by media type
         * @param $messages Mixed: List of messages associated with this module. May either be an
         *     associative array mapping message key to value, or a JSON-encoded message blob containing
         *     the same data, wrapped in an XmlJsCode object.
         *
         * @throws MWException
         * @return string
         */
        public static function makeLoaderImplementScript( $name, $scripts, $styles, $messages ) {
                if ( is_string( $scripts ) ) {
                        $scripts = new XmlJsCode( "function () {\n{$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()
                );
        }

        /**
         * Returns JS code which, when called, will register a given list of messages.
         *
         * @param $messages Mixed: Either an associative array mapping message key to value, or a
         *     JSON-encoded message blob containing the same data, wrapped in an XmlJsCode object.
         *
         * @return string
         */
        public static function makeMessageSetScript( $messages ) {
                return Xml::encodeJsCall( 'mw.messages.set', array( (object)$messages ) );
        }

        /**
         * Combines an associative array mapping media type to CSS into a
         * single stylesheet with "@media" blocks.
         *
         * @param array $stylePairs Array keyed by media type containing (arrays of) CSS strings.
         *
         * @return Array
         */
        private 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;
        }

        /**
         * Returns a JS call to mw.loader.state, which sets the state of a
         * module or modules to a given value. Has two calling conventions:
         *
         *    - ResourceLoader::makeLoaderStateScript( $name, $state ):
         *         Set the state of a single module called $name to $state
         *
         *    - ResourceLoader::makeLoaderStateScript( array( $name => $state, ... ) ):
         *         Set the state of modules with the given names to the given states
         *
         * @param $name string
         * @param $state
         *
         * @return string
         */
        public static function makeLoaderStateScript( $name, $state = null ) {
                if ( is_array( $name ) ) {
                        return Xml::encodeJsCall( 'mw.loader.state', array( $name ) );
                } else {
                        return Xml::encodeJsCall( 'mw.loader.state', array( $name, $state ) );
                }
        }

        /**
         * Returns JS code which calls the script given by $script. The script will
         * be called with local variables name, version, dependencies and group,
         * which will have values corresponding to $name, $version, $dependencies
         * and $group as supplied.
         *
         * @param string $name Module name
         * @param $version Integer: Module version number as a timestamp
         * @param array $dependencies List of module names on which this module depends
         * @param string $group Group which the module is in.
         * @param string $source Source of the module, or 'local' if not foreign.
         * @param string $script JavaScript code
         *
         * @return string
         */
        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 ) );
        }

        /**
         * Returns JS code which calls mw.loader.register with the given
         * parameters. Has three calling conventions:
         *
         *   - ResourceLoader::makeLoaderRegisterScript( $name, $version, $dependencies, $group, $source ):
         *       Register a single module.
         *
         *   - ResourceLoader::makeLoaderRegisterScript( array( $name1, $name2 ) ):
         *       Register modules with the given names.
         *
         *   - ResourceLoader::makeLoaderRegisterScript( array(
         *        array( $name1, $version1, $dependencies1, $group1, $source1 ),
         *        array( $name2, $version2, $dependencies1, $group2, $source2 ),
         *        ...
         *     ) ):
         *        Registers modules with the given names and parameters.
         *
         * @param string $name Module name
         * @param $version Integer: Module version number as a timestamp
         * @param array $dependencies List of module names on which this module depends
         * @param string $group group which the module is in.
         * @param string $source source of the module, or 'local' if not foreign
         *
         * @return string
         */
        public static function makeLoaderRegisterScript( $name, $version = null,
                $dependencies = null, $group = null, $source = null
        ) {
                if ( is_array( $name ) ) {
                        return Xml::encodeJsCall( 'mw.loader.register', array( $name ) );
                } else {
                        $version = (int)$version > 1 ? (int)$version : 1;
                        return Xml::encodeJsCall( 'mw.loader.register',
                                array( $name, $version, $dependencies, $group, $source ) );
                }
        }

        /**
         * Returns JS code which calls mw.loader.addSource() with the given
         * parameters. Has two calling conventions:
         *
         *   - ResourceLoader::makeLoaderSourcesScript( $id, $properties ):
         *       Register a single source
         *
         *   - ResourceLoader::makeLoaderSourcesScript( array( $id1 => $props1, $id2 => $props2, ... ) );
         *       Register sources with the given IDs and properties.
         *
         * @param string $id source ID
         * @param array $properties source properties (see addSource())
         *
         * @return string
         */
        public static function makeLoaderSourcesScript( $id, $properties = null ) {
                if ( is_array( $id ) ) {
                        return Xml::encodeJsCall( 'mw.loader.addSource', array( $id ) );
                } else {
                        return Xml::encodeJsCall( 'mw.loader.addSource', array( $id, $properties ) );
                }
        }

        /**
         * Returns JS code which runs given JS code if the client-side framework is
         * present.
         *
         * @param string $script JavaScript code
         *
         * @return string
         */
        public static function makeLoaderConditionalScript( $script ) {
                return "if(window.mw){\n" . trim( $script ) . "\n}";
        }

        /**
         * Returns JS code which will set the MediaWiki configuration array to
         * the given value.
         *
         * @param array $configuration List of configuration values keyed by variable name
         *
         * @return string
         */
        public static function makeConfigSetScript( array $configuration ) {
                return Xml::encodeJsCall( 'mw.config.set', array( $configuration ), ResourceLoader::inDebugMode() );
        }

        /**
         * Convert an array of module names to a packed query string.
         *
         * For example, array( 'foo.bar', 'foo.baz', 'bar.baz', 'bar.quux' )
         * becomes 'foo.bar,baz|bar.baz,quux'
         * @param array $modules of module names (strings)
         * @return string Packed query string
         */
        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;
        }

        /**
         * Determine whether debug mode was requested
         * Order of priority is 1) request param, 2) cookie, 3) $wg setting
         * @return bool
         */
        public static function inDebugMode() {
                global $wgRequest, $wgResourceLoaderDebug;
                static $retval = null;
                if ( !is_null( $retval ) ) {
                        return $retval;
                }
                return $retval = $wgRequest->getFuzzyBool( 'debug',
                        $wgRequest->getCookie( 'resourceLoaderDebug', '', $wgResourceLoaderDebug ) );
        }

        /**
         * Build a load.php URL
         * @param array $modules of module names (strings)
         * @param string $lang Language code
         * @param string $skin Skin name
         * @param string|null $user User name. If null, the &user= parameter is omitted
         * @param string|null $version Versioning timestamp
         * @param bool $debug Whether the request should be in debug mode
         * @param string|null $only &only= parameter
         * @param bool $printable Printable mode
         * @param bool $handheld Handheld mode
         * @param array $extraQuery Extra query parameters to add
         * @return string URL to load.php. May be protocol-relative (if $wgLoadScript is procol-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 );
        }

        /**
         * Build a query array (array representation of query string) for load.php. Helper
         * function for makeLoaderURL().
         *
         * @param array $modules
         * @param string $lang
         * @param string $skin
         * @param string $user
         * @param string $version
         * @param bool $debug
         * @param string $only
         * @param bool $printable
         * @param bool $handheld
         * @param array $extraQuery
         *
         * @return array
         */
        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;
        }

        /**
         * Check a module name for validity.
         *
         * Module names may not contain pipes (|), commas (,) or exclamation marks (!) and can be
         * at most 255 bytes.
         *
         * @param string $moduleName Module name to check
         * @return bool Whether $moduleName is a valid module name
         */
        public static function isValidModuleName( $moduleName ) {
                return !preg_match( '/[|,!]/', $moduleName ) && strlen( $moduleName ) <= 255;
        }
}