3 namespace Drupal\Core\Asset;
5 use Drupal\Component\Utility\Html;
6 use Drupal\Core\State\StateInterface;
11 * For production websites, LINK tags are preferable to STYLE tags with @import
12 * statements, because:
13 * - They are the standard tag intended for linking to a resource.
14 * - On Firefox 2 and perhaps other browsers, CSS files included with @import
15 * statements don't get saved when saving the complete web page for offline
16 * use: https://www.drupal.org/node/145218.
17 * - On IE, if only LINK tags and no @import statements are used, all the CSS
18 * files are downloaded in parallel, resulting in faster page load, but if
19 * @import statements are used and span across multiple STYLE tags, all the
20 * ones from one STYLE tag must be downloaded before downloading begins for
21 * the next STYLE tag. Furthermore, IE7 does not support media declaration on
22 * the @import statement, so multiple STYLE tags must be used when different
23 * files are for different media types. Non-IE browsers always download in
24 * parallel, so this is an IE-specific performance quirk:
25 * http://www.stevesouders.com/blog/2009/04/09/dont-use-import/.
27 * However, IE has an annoying limit of 31 total CSS inclusion tags
28 * (https://www.drupal.org/node/228818) and LINK tags are limited to one file
29 * per tag, whereas STYLE tags can contain multiple @import statements allowing
30 * multiple files to be loaded per tag. When CSS aggregation is disabled, a
31 * Drupal site can easily have more than 31 CSS files that need to be loaded, so
32 * using LINK tags exclusively would result in a site that would display
33 * incorrectly in IE. Depending on different needs, different strategies can be
34 * employed to decide when to use LINK tags and when to use STYLE tags.
36 * The strategy employed by this class is to use LINK tags for all aggregate
37 * files and for all files that cannot be aggregated (e.g., if 'preprocess' is
38 * set to FALSE or the type is 'external'), and to use STYLE tags for groups
39 * of files that could be aggregated together but aren't (e.g., if the site-wide
40 * aggregation setting is disabled). This results in all LINK tags when
41 * aggregation is enabled, a guarantee that as many or only slightly more tags
42 * are used with aggregation disabled than enabled (so that if the limit were to
43 * be crossed with aggregation enabled, the site developer would also notice the
44 * problem while aggregation is disabled), and an easy way for a developer to
45 * view HTML source while aggregation is disabled and know what files will be
46 * aggregated together when aggregation becomes enabled.
48 * This class evaluates the aggregation enabled/disabled condition on a group
49 * by group basis by testing whether an aggregate file has been made for the
50 * group rather than by testing the site-wide aggregation setting. This allows
51 * this class to work correctly even if modules have implemented custom
52 * logic for grouping and aggregating files.
54 class CssCollectionRenderer implements AssetCollectionRendererInterface {
57 * The state key/value store.
59 * @var \Drupal\Core\State\StateInterface
64 * Constructs a CssCollectionRenderer.
66 * @param \Drupal\Core\State\StateInterface $state
67 * The state key/value store.
69 public function __construct(StateInterface $state) {
70 $this->state = $state;
76 public function render(array $css_assets) {
79 // A dummy query-string is added to filenames, to gain control over
80 // browser-caching. The string changes on every update or full cache
81 // flush, forcing browsers to load a new copy of the files, as the
83 $query_string = $this->state->get('system.css_js_query_string') ?: '0';
85 // Defaults for LINK and STYLE elements.
86 $link_element_defaults = [
87 '#type' => 'html_tag',
90 'rel' => 'stylesheet',
93 $style_element_defaults = [
94 '#type' => 'html_tag',
98 // For filthy IE hack.
99 $current_ie_group_keys = NULL;
100 $get_ie_group_key = function ($css_asset) {
101 return [$css_asset['type'], $css_asset['preprocess'], $css_asset['group'], $css_asset['media'], $css_asset['browsers']];
104 // Loop through all CSS assets, by key, to allow for the special IE
106 $css_assets_keys = array_keys($css_assets);
107 for ($i = 0; $i < count($css_assets_keys); $i++) {
108 $css_asset = $css_assets[$css_assets_keys[$i]];
109 switch ($css_asset['type']) {
110 // For file items, there are three possibilities.
111 // - There are up to 31 CSS assets on the page (some of which may be
112 // aggregated). In this case, output a LINK tag for file CSS assets.
113 // - There are more than 31 CSS assets on the page, yet we must stay
114 // below IE<10's limit of 31 total CSS inclusion tags, we handle this
116 // - file CSS assets that are not eligible for aggregation (their
117 // 'preprocess' flag has been set to FALSE): in this case, output a
119 // - file CSS assets that can be aggregated (and possibly have been):
120 // in this case, figure out which subsequent file CSS assets share
121 // the same key properties ('group', 'media' and 'browsers') and
122 // output this group into as few STYLE tags as possible (a STYLE
123 // tag may contain only 31 @import statements).
125 // The dummy query string needs to be added to the URL to control
127 $query_string_separator = (strpos($css_asset['data'], '?') !== FALSE) ? '&' : '?';
129 // As long as the current page will not run into IE's limit for CSS
130 // assets: output a LINK tag for a file CSS asset.
131 if (count($css_assets) <= 31) {
132 $element = $link_element_defaults;
133 $element['#attributes']['href'] = file_url_transform_relative(file_create_url($css_asset['data'])) . $query_string_separator . $query_string;
134 $element['#attributes']['media'] = $css_asset['media'];
135 $element['#browsers'] = $css_asset['browsers'];
136 $elements[] = $element;
138 // The current page will run into IE's limits for CSS assets: work
139 // around these limits by performing a light form of grouping.
140 // Once Drupal only needs to support IE10 and later, we can drop this.
142 // The file CSS asset is ineligible for aggregation: output it in a
144 if (!$css_asset['preprocess']) {
145 $element = $link_element_defaults;
146 $element['#attributes']['href'] = file_url_transform_relative(file_create_url($css_asset['data'])) . $query_string_separator . $query_string;
147 $element['#attributes']['media'] = $css_asset['media'];
148 $element['#browsers'] = $css_asset['browsers'];
149 $elements[] = $element;
151 // The file CSS asset can be aggregated, but hasn't been: combine
152 // multiple items into as few STYLE tags as possible.
155 // Start with the current CSS asset, iterate over subsequent CSS
156 // assets and find which ones have the same 'type', 'group',
157 // 'preprocess', 'media' and 'browsers' properties.
159 $next_css_asset = $css_asset;
160 $current_ie_group_key = $get_ie_group_key($css_asset);
162 // The dummy query string needs to be added to the URL to
163 // control browser-caching. IE7 does not support a media type on
164 // the @import statement, so we instead specify the media for
165 // the group on the STYLE tag.
166 $import[] = '@import url("' . Html::escape(file_url_transform_relative(file_create_url($next_css_asset['data'])) . '?' . $query_string) . '");';
167 // Move the outer for loop skip the next item, since we
168 // processed it here.
170 // Retrieve next CSS asset, unless there is none: then break.
171 if ($j + 1 < count($css_assets_keys)) {
173 $next_css_asset = $css_assets[$css_assets_keys[$j]];
178 } while ($get_ie_group_key($next_css_asset) == $current_ie_group_key);
180 // In addition to IE's limit of 31 total CSS inclusion tags, it
181 // also has a limit of 31 @import statements per STYLE tag.
182 while (!empty($import)) {
183 $import_batch = array_slice($import, 0, 31);
184 $import = array_slice($import, 31);
185 $element = $style_element_defaults;
186 // This simplifies the JavaScript regex, allowing each line
187 // (separated by \n) to be treated as a completely different
188 // string. This means that we can use ^ and $ on one line at a
189 // time, and not worry about style tags since they'll never
191 $element['#value'] = "\n" . implode("\n", $import_batch) . "\n";
192 $element['#attributes']['media'] = $css_asset['media'];
193 $element['#browsers'] = $css_asset['browsers'];
194 $elements[] = $element;
200 // Output a LINK tag for an external CSS asset. The asset's 'data'
201 // property contains the full URL.
203 $element = $link_element_defaults;
204 $element['#attributes']['href'] = $css_asset['data'];
205 $element['#attributes']['media'] = $css_asset['media'];
206 $element['#browsers'] = $css_asset['browsers'];
207 $elements[] = $element;
211 throw new \Exception('Invalid CSS asset type.');