controller_middleware.php

function the_real_all(ServerRequestInterface $req, callable $next) {
  $action = $req->getAttribute('_action');
  $args = $req->getAttribute('_arguments);

  $result = $action(...$args);

  if (! $result instanceof ResponseInterface) {
    $responder = resolve_responder(get_class($result));
    $result = $responder($result);
  }

  return $next($req, $result);
}