diff -r c7c34916027a -r 177826044cd9 wp/wp-includes/class-wp-oembed-controller.php
--- a/wp/wp-includes/class-wp-oembed-controller.php	Mon Oct 14 18:06:33 2019 +0200
+++ b/wp/wp-includes/class-wp-oembed-controller.php	Mon Oct 14 18:28:13 2019 +0200
@@ -31,67 +31,75 @@
 		 */
 		$maxwidth = apply_filters( 'oembed_default_width', 600 );
 
-		register_rest_route( 'oembed/1.0', '/embed', array(
+		register_rest_route(
+			'oembed/1.0',
+			'/embed',
 			array(
-				'methods'  => WP_REST_Server::READABLE,
-				'callback' => array( $this, 'get_item' ),
-				'args'     => array(
-					'url'      => array(
-						'required'          => true,
-						'sanitize_callback' => 'esc_url_raw',
-					),
-					'format'   => array(
-						'default'           => 'json',
-						'sanitize_callback' => 'wp_oembed_ensure_format',
-					),
-					'maxwidth' => array(
-						'default'           => $maxwidth,
-						'sanitize_callback' => 'absint',
+				array(
+					'methods'  => WP_REST_Server::READABLE,
+					'callback' => array( $this, 'get_item' ),
+					'args'     => array(
+						'url'      => array(
+							'required'          => true,
+							'sanitize_callback' => 'esc_url_raw',
+						),
+						'format'   => array(
+							'default'           => 'json',
+							'sanitize_callback' => 'wp_oembed_ensure_format',
+						),
+						'maxwidth' => array(
+							'default'           => $maxwidth,
+							'sanitize_callback' => 'absint',
+						),
 					),
 				),
-			),
-		) );
+			)
+		);
 
-		register_rest_route( 'oembed/1.0', '/proxy', array(
+		register_rest_route(
+			'oembed/1.0',
+			'/proxy',
 			array(
-				'methods'  => WP_REST_Server::READABLE,
-				'callback' => array( $this, 'get_proxy_item' ),
-				'permission_callback' => array( $this, 'get_proxy_item_permissions_check' ),
-				'args'     => array(
-					'url'      => array(
-						'description'       => __( 'The URL of the resource for which to fetch oEmbed data.' ),
-						'type'              => 'string',
-						'required'          => true,
-						'sanitize_callback' => 'esc_url_raw',
-					),
-					'format'   => array(
-						'description'       => __( 'The oEmbed format to use.' ),
-						'type'              => 'string',
-						'default'           => 'json',
-						'enum'              => array(
-							'json',
-							'xml',
+				array(
+					'methods'             => WP_REST_Server::READABLE,
+					'callback'            => array( $this, 'get_proxy_item' ),
+					'permission_callback' => array( $this, 'get_proxy_item_permissions_check' ),
+					'args'                => array(
+						'url'       => array(
+							'description'       => __( 'The URL of the resource for which to fetch oEmbed data.' ),
+							'type'              => 'string',
+							'required'          => true,
+							'sanitize_callback' => 'esc_url_raw',
+						),
+						'format'    => array(
+							'description' => __( 'The oEmbed format to use.' ),
+							'type'        => 'string',
+							'default'     => 'json',
+							'enum'        => array(
+								'json',
+								'xml',
+							),
+						),
+						'maxwidth'  => array(
+							'description'       => __( 'The maximum width of the embed frame in pixels.' ),
+							'type'              => 'integer',
+							'default'           => $maxwidth,
+							'sanitize_callback' => 'absint',
+						),
+						'maxheight' => array(
+							'description'       => __( 'The maximum height of the embed frame in pixels.' ),
+							'type'              => 'integer',
+							'sanitize_callback' => 'absint',
+						),
+						'discover'  => array(
+							'description' => __( 'Whether to perform an oEmbed discovery request for non-whitelisted providers.' ),
+							'type'        => 'boolean',
+							'default'     => true,
 						),
 					),
-					'maxwidth' => array(
-						'description'       => __( 'The maximum width of the embed frame in pixels.' ),
-						'type'              => 'integer',
-						'default'           => $maxwidth,
-						'sanitize_callback' => 'absint',
-					),
-					'maxheight' => array(
-						'description'       => __( 'The maximum height of the embed frame in pixels.' ),
-						'type'              => 'integer',
-						'sanitize_callback' => 'absint',
-					),
-					'discover' => array(
-						'description'       => __( 'Whether to perform an oEmbed discovery request for non-whitelisted providers.' ),
-						'type'              => 'boolean',
-						'default'           => true,
-					),
 				),
-			),
-		) );
+			)
+		);
 	}
 
 	/**
@@ -157,7 +165,7 @@
 		// Serve oEmbed data from cache if set.
 		unset( $args['_wpnonce'] );
 		$cache_key = 'oembed_' . md5( serialize( $args ) );
-		$data = get_transient( $cache_key );
+		$data      = get_transient( $cache_key );
 		if ( ! empty( $data ) ) {
 			return $data;
 		}
@@ -173,12 +181,22 @@
 			$args['height'] = $args['maxheight'];
 		}
 
+		// Short-circuit process for URLs belonging to the current site.
+		$data = get_oembed_response_data_for_url( $url, $args );
+
+		if ( $data ) {
+			return $data;
+		}
+
 		$data = _wp_oembed_get_object()->get_data( $url, $args );
 
 		if ( false === $data ) {
 			return new WP_Error( 'oembed_invalid_url', get_status_header_desc( 404 ), array( 'status' => 404 ) );
 		}
 
+		/** This filter is documented in wp-includes/class-oembed.php */
+		$data->html = apply_filters( 'oembed_result', _wp_oembed_get_object()->data2html( (object) $data, $url ), $url, $args );
+
 		/**
 		 * Filters the oEmbed TTL value (time to live).
 		 *