public function get_namespace_index( $request ) {
		$namespace = $request['namespace'];

		if ( ! isset( $this->namespaces[ $namespace ] ) ) {
			return new WP_Error( 'rest_invalid_namespace', __( 'The specified namespace could not be found.' ), array( 'status' => 404 ) );
		}

		$routes    = $this->namespaces[ $namespace ];
		$endpoints = array_intersect_key( $this->get_routes(), $routes );

		$data     = array(
			'namespace' => $namespace,
			'routes'    => $this->get_data_for_routes( $endpoints, $request['context'] ),
		);
		$response = rest_ensure_response( $data );

		// Link to the root index.
		$response->add_link( 'up', rest_url( '/' ) );

		/**
		 * Filters the namespace index data.
		 *
		 * This typically is just the route data for the namespace, but you can
		 * add any data you'd like here.
		 *
		 * @since 4.4.0
		 *
		 * @param WP_REST_Response $response Response data.
		 * @param WP_REST_Request  $request  Request data. The namespace is passed as the 'namespace' parameter.
		 */
		return apply_filters( 'rest_namespace_index', $response, $request );
	}