private function readSourceMethod(Request $request, Annotation $annotation): string
    {
        $method = 'read' . $this->source($annotation);
        if (!method_exists($request, $method)) {
            throw new \RuntimeException(
                    'Unknown source ' . $annotation->getSource() . ' for '
                    . $annotation . ' on ' . get_class($request)
            );
        }

        return $method;
    }