if err != nil {
		return err
	}
	if msg.Flags&FlagSubroute != 0 {
		if m.subroute == nil {
			return fmt.Errorf("internal error: subroute not defined on client")
		}
		hid := m.subroute.withHandler(msg.Handler)
		before := len(dst)
		dst = append(dst, hid[:]...)
		if debugPrint {
			fmt.Println("Added subroute", hid.String(), "to message", msg, "len", len(dst)-before)
		}
	}