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- <?php
- namespace Drupal\Core\Asset;
- use Drupal\Component\Utility\Html;
- use Drupal\Core\State\StateInterface;
- /**
- * Renders CSS assets.
- *
- * For production websites, LINK tags are preferable to STYLE tags with @import
- * statements, because:
- * - They are the standard tag intended for linking to a resource.
- * - On Firefox 2 and perhaps other browsers, CSS files included with @import
- * statements don't get saved when saving the complete web page for offline
- * use: https://www.drupal.org/node/145218.
- * - On IE, if only LINK tags and no @import statements are used, all the CSS
- * files are downloaded in parallel, resulting in faster page load, but if
- * @import statements are used and span across multiple STYLE tags, all the
- * ones from one STYLE tag must be downloaded before downloading begins for
- * the next STYLE tag. Furthermore, IE7 does not support media declaration on
- * the @import statement, so multiple STYLE tags must be used when different
- * files are for different media types. Non-IE browsers always download in
- * parallel, so this is an IE-specific performance quirk:
- * http://www.stevesouders.com/blog/2009/04/09/dont-use-import/.
- *
- * However, IE has an annoying limit of 31 total CSS inclusion tags
- * (https://www.drupal.org/node/228818) and LINK tags are limited to one file
- * per tag, whereas STYLE tags can contain multiple @import statements allowing
- * multiple files to be loaded per tag. When CSS aggregation is disabled, a
- * Drupal site can easily have more than 31 CSS files that need to be loaded, so
- * using LINK tags exclusively would result in a site that would display
- * incorrectly in IE. Depending on different needs, different strategies can be
- * employed to decide when to use LINK tags and when to use STYLE tags.
- *
- * The strategy employed by this class is to use LINK tags for all aggregate
- * files and for all files that cannot be aggregated (e.g., if 'preprocess' is
- * set to FALSE or the type is 'external'), and to use STYLE tags for groups
- * of files that could be aggregated together but aren't (e.g., if the site-wide
- * aggregation setting is disabled). This results in all LINK tags when
- * aggregation is enabled, a guarantee that as many or only slightly more tags
- * are used with aggregation disabled than enabled (so that if the limit were to
- * be crossed with aggregation enabled, the site developer would also notice the
- * problem while aggregation is disabled), and an easy way for a developer to
- * view HTML source while aggregation is disabled and know what files will be
- * aggregated together when aggregation becomes enabled.
- *
- * This class evaluates the aggregation enabled/disabled condition on a group
- * by group basis by testing whether an aggregate file has been made for the
- * group rather than by testing the site-wide aggregation setting. This allows
- * this class to work correctly even if modules have implemented custom
- * logic for grouping and aggregating files.
- */
- class CssCollectionRenderer implements AssetCollectionRendererInterface {
- /**
- * The state key/value store.
- *
- * @var \Drupal\Core\State\StateInterface
- */
- protected $state;
- /**
- * Constructs a CssCollectionRenderer.
- *
- * @param \Drupal\Core\State\StateInterface $state
- * The state key/value store.
- */
- public function __construct(StateInterface $state) {
- $this->state = $state;
- }
- /**
- * {@inheritdoc}
- */
- public function render(array $css_assets) {
- $elements = [];
- // A dummy query-string is added to filenames, to gain control over
- // browser-caching. The string changes on every update or full cache
- // flush, forcing browsers to load a new copy of the files, as the
- // URL changed.
- $query_string = $this->state->get('system.css_js_query_string') ?: '0';
- // Defaults for LINK and STYLE elements.
- $link_element_defaults = [
- '#type' => 'html_tag',
- '#tag' => 'link',
- '#attributes' => [
- 'rel' => 'stylesheet',
- ],
- ];
- $style_element_defaults = [
- '#type' => 'html_tag',
- '#tag' => 'style',
- ];
- // For filthy IE hack.
- $current_ie_group_keys = NULL;
- $get_ie_group_key = function ($css_asset) {
- return [$css_asset['type'], $css_asset['preprocess'], $css_asset['group'], $css_asset['media'], $css_asset['browsers']];
- };
- // Loop through all CSS assets, by key, to allow for the special IE
- // workaround.
- $css_assets_keys = array_keys($css_assets);
- for ($i = 0; $i < count($css_assets_keys); $i++) {
- $css_asset = $css_assets[$css_assets_keys[$i]];
- switch ($css_asset['type']) {
- // For file items, there are three possibilities.
- // - There are up to 31 CSS assets on the page (some of which may be
- // aggregated). In this case, output a LINK tag for file CSS assets.
- // - There are more than 31 CSS assets on the page, yet we must stay
- // below IE<10's limit of 31 total CSS inclusion tags, we handle this
- // in two ways:
- // - file CSS assets that are not eligible for aggregation (their
- // 'preprocess' flag has been set to FALSE): in this case, output a
- // LINK tag.
- // - file CSS assets that can be aggregated (and possibly have been):
- // in this case, figure out which subsequent file CSS assets share
- // the same key properties ('group', 'media' and 'browsers') and
- // output this group into as few STYLE tags as possible (a STYLE
- // tag may contain only 31 @import statements).
- case 'file':
- // The dummy query string needs to be added to the URL to control
- // browser-caching.
- $query_string_separator = (strpos($css_asset['data'], '?') !== FALSE) ? '&' : '?';
- // As long as the current page will not run into IE's limit for CSS
- // assets: output a LINK tag for a file CSS asset.
- if (count($css_assets) <= 31) {
- $element = $link_element_defaults;
- $element['#attributes']['href'] = file_url_transform_relative(file_create_url($css_asset['data'])) . $query_string_separator . $query_string;
- $element['#attributes']['media'] = $css_asset['media'];
- $element['#browsers'] = $css_asset['browsers'];
- $elements[] = $element;
- }
- // The current page will run into IE's limits for CSS assets: work
- // around these limits by performing a light form of grouping.
- // Once Drupal only needs to support IE10 and later, we can drop this.
- else {
- // The file CSS asset is ineligible for aggregation: output it in a
- // LINK tag.
- if (!$css_asset['preprocess']) {
- $element = $link_element_defaults;
- $element['#attributes']['href'] = file_url_transform_relative(file_create_url($css_asset['data'])) . $query_string_separator . $query_string;
- $element['#attributes']['media'] = $css_asset['media'];
- $element['#browsers'] = $css_asset['browsers'];
- $elements[] = $element;
- }
- // The file CSS asset can be aggregated, but hasn't been: combine
- // multiple items into as few STYLE tags as possible.
- else {
- $import = [];
- // Start with the current CSS asset, iterate over subsequent CSS
- // assets and find which ones have the same 'type', 'group',
- // 'preprocess', 'media' and 'browsers' properties.
- $j = $i;
- $next_css_asset = $css_asset;
- $current_ie_group_key = $get_ie_group_key($css_asset);
- do {
- // The dummy query string needs to be added to the URL to
- // control browser-caching. IE7 does not support a media type on
- // the @import statement, so we instead specify the media for
- // the group on the STYLE tag.
- $import[] = '@import url("' . Html::escape(file_url_transform_relative(file_create_url($next_css_asset['data'])) . '?' . $query_string) . '");';
- // Move the outer for loop skip the next item, since we
- // processed it here.
- $i = $j;
- // Retrieve next CSS asset, unless there is none: then break.
- if ($j + 1 < count($css_assets_keys)) {
- $j++;
- $next_css_asset = $css_assets[$css_assets_keys[$j]];
- }
- else {
- break;
- }
- } while ($get_ie_group_key($next_css_asset) == $current_ie_group_key);
- // In addition to IE's limit of 31 total CSS inclusion tags, it
- // also has a limit of 31 @import statements per STYLE tag.
- while (!empty($import)) {
- $import_batch = array_slice($import, 0, 31);
- $import = array_slice($import, 31);
- $element = $style_element_defaults;
- // This simplifies the JavaScript regex, allowing each line
- // (separated by \n) to be treated as a completely different
- // string. This means that we can use ^ and $ on one line at a
- // time, and not worry about style tags since they'll never
- // match the regex.
- $element['#value'] = "\n" . implode("\n", $import_batch) . "\n";
- $element['#attributes']['media'] = $css_asset['media'];
- $element['#browsers'] = $css_asset['browsers'];
- $elements[] = $element;
- }
- }
- }
- break;
- // Output a LINK tag for an external CSS asset. The asset's 'data'
- // property contains the full URL.
- case 'external':
- $element = $link_element_defaults;
- $element['#attributes']['href'] = $css_asset['data'];
- $element['#attributes']['media'] = $css_asset['media'];
- $element['#browsers'] = $css_asset['browsers'];
- $elements[] = $element;
- break;
- default:
- throw new \Exception('Invalid CSS asset type.');
- }
- }
- return $elements;
- }
- }
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