1<?php
  2/**
  3 * Speculative loading functions.
  4 *
  5 * @package WordPress
  6 * @subpackage Speculative Loading
  7 * @since 6.8.0
  8 */
  9
 10/**
 11 * Returns the speculation rules configuration.
 12 *
 13 * @since 6.8.0
 14 *
 15 * @return array<string, string>|null Associative array with 'mode' and 'eagerness' keys, or null if speculative
 16 *                                    loading is disabled.
 17 */
 18function wp_get_speculation_rules_configuration(): ?array {
 19	// By default, speculative loading is only enabled for sites with pretty permalinks when no user is logged in.
 20	if ( ! is_user_logged_in() && get_option( 'permalink_structure' ) ) {
 21		$config = array(
 22			'mode'      => 'auto',
 23			'eagerness' => 'auto',
 24		);
 25	} else {
 26		$config = null;
 27	}
 28
 29	/**
 30	 * Filters the way that speculation rules are configured.
 31	 *
 32	 * The Speculation Rules API is a web API that allows to automatically prefetch or prerender certain URLs on the
 33	 * page, which can lead to near-instant page load times. This is also referred to as speculative loading.
 34	 *
 35	 * There are two aspects to the configuration:
 36	 * * The "mode" (whether to "prefetch" or "prerender" URLs).
 37	 * * The "eagerness" (whether to speculatively load URLs in an "eager", "moderate", or "conservative" way).
 38	 *
 39	 * By default, the speculation rules configuration is decided by WordPress Core ("auto"). This filter can be used
 40	 * to force a certain configuration, which could for instance load URLs more or less eagerly.
 41	 *
 42	 * For logged-in users or for sites that are not configured to use pretty permalinks, the default value is `null`,
 43	 * indicating that speculative loading is entirely disabled.
 44	 *
 45	 * @since 6.8.0
 46	 * @see https://developer.chrome.com/docs/web-platform/prerender-pages
 47	 *
 48	 * @param array<string, string>|null $config Associative array with 'mode' and 'eagerness' keys, or `null`. The
 49	 *                                           default value for both of the keys is 'auto'. Other possible values
 50	 *                                           for 'mode' are 'prefetch' and 'prerender'. Other possible values for
 51	 *                                           'eagerness' are 'eager', 'moderate', and 'conservative'. The value
 52	 *                                           `null` is used to disable speculative loading entirely.
 53	 */
 54	$config = apply_filters( 'wp_speculation_rules_configuration', $config );
 55
 56	// Allow the value `null` to indicate that speculative loading is disabled.
 57	if ( null === $config ) {
 58		return null;
 59	}
 60
 61	// Sanitize the configuration and replace 'auto' with current defaults.
 62	$default_mode      = 'prefetch';
 63	$default_eagerness = 'conservative';
 64	if ( ! is_array( $config ) ) {
 65		return array(
 66			'mode'      => $default_mode,
 67			'eagerness' => $default_eagerness,
 68		);
 69	}
 70	if (
 71		! isset( $config['mode'] ) ||
 72		'auto' === $config['mode'] ||
 73		! WP_Speculation_Rules::is_valid_mode( $config['mode'] )
 74	) {
 75		$config['mode'] = $default_mode;
 76	}
 77	if (
 78		! isset( $config['eagerness'] ) ||
 79		'auto' === $config['eagerness'] ||
 80		! WP_Speculation_Rules::is_valid_eagerness( $config['eagerness'] ) ||
 81		// 'immediate' is a valid eagerness, but for safety WordPress does not allow it for document-level rules.
 82		'immediate' === $config['eagerness']
 83	) {
 84		$config['eagerness'] = $default_eagerness;
 85	}
 86
 87	return array(
 88		'mode'      => $config['mode'],
 89		'eagerness' => $config['eagerness'],
 90	);
 91}
 92
 93/**
 94 * Returns the full speculation rules data based on the configuration.
 95 *
 96 * Plugins with features that rely on frontend URLs to exclude from prefetching or prerendering should use the
 97 * {@see 'wp_speculation_rules_href_exclude_paths'} filter to ensure those URL patterns are excluded.
 98 *
 99 * Additional speculation rules other than the default rule from WordPress Core can be provided by using the
100 * {@see 'wp_load_speculation_rules'} action and amending the passed WP_Speculation_Rules object.
101 *
102 * @since 6.8.0
103 * @access private
104 *
105 * @return WP_Speculation_Rules|null Object representing the speculation rules to use, or null if speculative loading
106 *                                   is disabled in the current context.
107 */
108function wp_get_speculation_rules(): ?WP_Speculation_Rules {
109	$configuration = wp_get_speculation_rules_configuration();
110	if ( null === $configuration ) {
111		return null;
112	}
113
114	$mode      = $configuration['mode'];
115	$eagerness = $configuration['eagerness'];
116
117	$prefixer = new WP_URL_Pattern_Prefixer();
118
119	$base_href_exclude_paths = array(
120		$prefixer->prefix_path_pattern( '/wp-*.php', 'site' ),
121		$prefixer->prefix_path_pattern( '/wp-admin/*', 'site' ),
122		$prefixer->prefix_path_pattern( '/*', 'uploads' ),
123		$prefixer->prefix_path_pattern( '/*', 'content' ),
124		$prefixer->prefix_path_pattern( '/*', 'plugins' ),
125		$prefixer->prefix_path_pattern( '/*', 'template' ),
126		$prefixer->prefix_path_pattern( '/*', 'stylesheet' ),
127	);
128
129	/*
130	 * If pretty permalinks are enabled, exclude any URLs with query parameters.
131	 * Otherwise, exclude specifically the URLs with a `_wpnonce` query parameter or any other query parameter
132	 * containing the word `nonce`.
133	 */
134	if ( get_option( 'permalink_structure' ) ) {
135		$base_href_exclude_paths[] = $prefixer->prefix_path_pattern( '/*\\?(.+)', 'home' );
136	} else {
137		$base_href_exclude_paths[] = $prefixer->prefix_path_pattern( '/*\\?*(^|&)*nonce*=*', 'home' );
138	}
139
140	/**
141	 * Filters the paths for which speculative loading should be disabled.
142	 *
143	 * All paths should start in a forward slash, relative to the root document. The `*` can be used as a wildcard.
144	 * If the WordPress site is in a subdirectory, the exclude paths will automatically be prefixed as necessary.
145	 *
146	 * Note that WordPress always excludes certain path patterns such as `/wp-login.php` and `/wp-admin/*`, and those
147	 * cannot be modified using the filter.
148	 *
149	 * @since 6.8.0
150	 *
151	 * @param string[] $href_exclude_paths Additional path patterns to disable speculative loading for.
152	 * @param string   $mode               Mode used to apply speculative loading. Either 'prefetch' or 'prerender'.
153	 */
154	$href_exclude_paths = (array) apply_filters( 'wp_speculation_rules_href_exclude_paths', array(), $mode );
155
156	// Ensure that:
157	// 1. There are no duplicates.
158	// 2. The base paths cannot be removed.
159	// 3. The array has sequential keys (i.e. array_is_list()).
160	$href_exclude_paths = array_values(
161		array_unique(
162			array_merge(
163				$base_href_exclude_paths,
164				array_map(
165					static function ( string $href_exclude_path ) use ( $prefixer ): string {
166						return $prefixer->prefix_path_pattern( $href_exclude_path );
167					},
168					$href_exclude_paths
169				)
170			)
171		)
172	);
173
174	$speculation_rules = new WP_Speculation_Rules();
175
176	$main_rule_conditions = array(
177		// Include any URLs within the same site.
178		array(
179			'href_matches' => $prefixer->prefix_path_pattern( '/*' ),
180		),
181		// Except for excluded paths.
182		array(
183			'not' => array(
184				'href_matches' => $href_exclude_paths,
185			),
186		),
187		// Also exclude rel=nofollow links, as certain plugins use that on their links that perform an action.
188		array(
189			'not' => array(
190				'selector_matches' => 'a[rel~="nofollow"]',
191			),
192		),
193		// Also exclude links that are explicitly marked to opt out, either directly or via a parent element.
194		array(
195			'not' => array(
196				'selector_matches' => ".no-{$mode}, .no-{$mode} a",
197			),
198		),
199	);
200
201	// If using 'prerender', also exclude links that opt out of 'prefetch' because it's part of 'prerender'.
202	if ( 'prerender' === $mode ) {
203		$main_rule_conditions[] = array(
204			'not' => array(
205				'selector_matches' => '.no-prefetch, .no-prefetch a',
206			),
207		);
208	}
209
210	$speculation_rules->add_rule(
211		$mode,
212		'main',
213		array(
214			'source'    => 'document',
215			'where'     => array(
216				'and' => $main_rule_conditions,
217			),
218			'eagerness' => $eagerness,
219		)
220	);
221
222	/**
223	 * Fires when speculation rules data is loaded, allowing to amend the rules.
224	 *
225	 * @since 6.8.0
226	 *
227	 * @param WP_Speculation_Rules $speculation_rules Object representing the speculation rules to use.
228	 */
229	do_action( 'wp_load_speculation_rules', $speculation_rules );
230
231	return $speculation_rules;
232}
233
234/**
235 * Prints the speculation rules.
236 *
237 * For browsers that do not support speculation rules yet, the `script[type="speculationrules"]` tag will be ignored.
238 *
239 * @since 6.8.0
240 * @access private
241 */
242function wp_print_speculation_rules(): void {
243	$speculation_rules = wp_get_speculation_rules();
244	if ( null === $speculation_rules ) {
245		return;
246	}
247
248	wp_print_inline_script_tag(
249		(string) wp_json_encode(
250			$speculation_rules,
251			JSON_HEX_TAG | JSON_UNESCAPED_SLASHES
252		),
253		array( 'type' => 'speculationrules' )
254	);
255}
256