Ticket #44302: 44302.diff

src/wp-includes/default-filters.php

@@ -268 +268 @@
 // Actions
 add_action( 'wp_head', '_wp_render_title_tag', 1 );
 add_action( 'wp_head', 'wp_enqueue_scripts', 1 );
+add_action( 'template_redirect', 'wp_dns_prefetch_control_header', 11, 0 );
 add_action( 'wp_head', 'wp_resource_hints', 2 );
 add_action( 'wp_head', 'feed_links', 2 );
 add_action( 'wp_head', 'feed_links_extra', 3 );

src/wp-includes/general-template.php

@@ -2913 +2913 @@
 }
 
 /**
- * Prints resource hints to browsers for pre-fetching, pre-rendering
- * and pre-connecting to web sites.
+ * Returns the unique list of URLs and hosts that can be used for resource hints.
  *
- * Gives hints to browsers to prefetch specific pages or render them
+ * Resource hints suggest browsers to prefetch specific pages or render them
  * in the background, to perform DNS lookups or to begin the connection
  * handshake (DNS, TCP, TLS) in the background.
  *
- * These performance improving indicators work by using `<link rel"…">`.
- *
- * @since 4.6.0
+ * @since 5.0.0
  */
-function wp_resource_hints() {
+function wp_get_resource_hints() {
         $hints = array(
                 'dns-prefetch' => wp_dependencies_unique_hosts(),
                 'preconnect'   => array(),
@@ -2995 +2992 @@
                         $unique_urls[ $url ] = $atts;
                 }
 
-                foreach ( $unique_urls as $atts ) {
-                        $html = '';
+                return $unique_urls;
+        }
+}
 
-                        foreach ( $atts as $attr => $value ) {
-                                if ( ! is_scalar( $value ) ||
-                                        ( ! in_array( $attr, array( 'as', 'crossorigin', 'href', 'pr', 'rel', 'type' ), true ) && ! is_numeric( $attr ) ) ) {
+/**
+ * Sends an X-DNS-Prefetch-Control response header.
+ *
+ * By default, the header is only sent if dns-prefetch resource hints are added.
+ *
+ * @since 5.0.0
+ */
+function wp_dns_prefetch_control_header() {
+        $unique_urls = wp_get_resource_hints();
 
-                                        continue;
-                                }
+        /**
+         * Filters whether WordPress should send an X-DNS-Prefetch-Control header.
+         *
+         * @since 5.0.0
+         *
+         * @param bool $send_header Whether the header should be sent or not.
+         *                          True if dns-prefetch resource hints are added, false otherwise.
+         */
+        $send_header = apply_filters( 'dns_prefetch_control_header', ! empty( $unique_urls['dns-prefetch'] ) );
 
-                                $value = ( 'href' === $attr ) ? esc_url( $value ) : esc_attr( $value );
+        if (!$send_header) {
+                return;
+        }
 
-                                if ( ! is_string( $attr ) ) {
-                                        $html .= " $value";
-                                } else {
-                                        $html .= " $attr='$value'";
-                                }
+        header( 'X-DNS-Prefetch-Control: on', false );
+}
+
+/**
+ * Prints resource hints to browsers for pre-fetching, pre-rendering
+ * and pre-connecting to web sites.
+ *
+ * Gives hints to browsers to prefetch specific pages or render them
+ * in the background, to perform DNS lookups or to begin the connection
+ * handshake (DNS, TCP, TLS) in the background.
+ *
+ * These performance improving indicators work by using `<link rel"…">`.
+ *
+ * @since 4.6.0
+ */
+function wp_resource_hints() {
+        $unique_urls = wp_get_resource_hints();
+
+        foreach ( $unique_urls as $atts ) {
+                $html = '';
+
+                foreach ( $atts as $attr => $value ) {
+                        if ( ! is_scalar( $value ) ||
+                                ( ! in_array( $attr, array( 'as', 'crossorigin', 'href', 'pr', 'rel', 'type' ), true ) && ! is_numeric( $attr ) ) ) {
+
+                                continue;
                         }
 
-                        $html = trim( $html );
+                        $value = ( 'href' === $attr ) ? esc_url( $value ) : esc_attr( $value );
 
-                        echo "<link $html />\n";
+                        if ( ! is_string( $attr ) ) {
+                                $html .= " $value";
+                        } else {
+                                $html .= " $attr='$value'";
+                        }
                 }
+
+                $html = trim( $html );
+
+                echo "<link $html />\n";
         }
 }