private long maybeSendAnyVoterFetch(long currentTimeMs) {
        Optional<Node> readyNode = requestManager.findReadyBootstrapServer(currentTimeMs);
        if (readyNode.isPresent()) {
            return maybeSendRequest(
                currentTimeMs,
                readyNode.get(),
                this::buildFetchRequest
            );
        } else {
            return requestManager.backoffBeforeAvailableBootstrapServer(currentTimeMs);
        }
    }
Attempt to send a request. Return the time to wait before the request can be retried.
raft/src/main/java/org/apache/kafka/raft/KafkaRaftClient.java