public ActivateClusterStateVersionRequest.Reply getReply(Request req) {
        NodeInfo info = request.getNodeInfo();
        if (req.isError()) {
            return new ActivateClusterStateVersionRequest.Reply(req.errorCode(), req.errorMessage());
        } else if (!req.checkReturnTypes("i")) {
            return new ActivateClusterStateVersionRequest.Reply(ErrorCode.BAD_REPLY, "Got RPC response with invalid return types from " + info);
        }
        int actualVersion = req.returnValues().get(0).asInt32();
        return ActivateClusterStateVersionRequest.Reply.withActualVersion(actualVersion);
    }
Binds together the reply received for a particular cluster state activation RPC and
the cluster controller-internal callback handler which expects to receive it.
clustercontroller-core/src/main/java/com/yahoo/vespa/clustercontroller/core/rpc/RPCActivateClusterStateVersionWaiter.java