REST API: Introduce the `rest_preload_api_request()` function.

This function helps perform multiple REST API requests, for the purpose of preloading data into a page.

See #45110.


Built from https://develop.svn.wordpress.org/branches/5.0@43763


git-svn-id: http://core.svn.wordpress.org/branches/5.0@43592 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/rest-api.php

@@ -1311,3 +1311,56 @@ function rest_sanitize_value_from_schema( $value, $args ) {
 
 	return $value;
 }
+
+/**
+ * Append result of internal request to REST API for purpose of preloading data to be attached to a page.
+ * Expected to be called in the context of `array_reduce`.
+ *
+ * @since 5.0.0
+ *
+ * @param  array  $memo Reduce accumulator.
+ * @param  string $path REST API path to preload.
+ * @return array        Modified reduce accumulator.
+ */
+function rest_preload_api_request( $memo, $path ) {
+	// array_reduce() doesn't support passing an array in PHP 5.2, so we need to make sure we start with one.
+	if ( ! is_array( $memo ) ) {
+		$memo = array();
+	}
+
+	if ( empty( $path ) ) {
+		return $memo;
+	}
+
+	$path_parts = parse_url( $path );
+	if ( false === $path_parts ) {
+		return $memo;
+	}
+
+	$request = new WP_REST_Request( 'GET', $path_parts['path'] );
+	if ( ! empty( $path_parts['query'] ) ) {
+		parse_str( $path_parts['query'], $query_params );
+		$request->set_query_params( $query_params );
+	}
+
+	$response = rest_do_request( $request );
+	if ( 200 === $response->status ) {
+		$server = rest_get_server();
+		$data   = (array) $response->get_data();
+		if ( method_exists( $server, 'get_compact_response_links' ) ) {
+			$links = call_user_func( array( $server, 'get_compact_response_links' ), $response );
+		} else {
+			$links = call_user_func( array( $server, 'get_response_links' ), $response );
+		}
+		if ( ! empty( $links ) ) {
+			$data['_links'] = $links;
+		}
+
+		$memo[ $path ] = array(
+			'body'    => $data,
+			'headers' => $response->headers,
+		);
+	}
+
+	return $memo;
+}

wp-includes/version.php

@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.0-alpha-43762';
+$wp_version = '5.0-alpha-43763';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.