public NetworkClient.InFlightRequest completeNext(String node) {
        NetworkClient.InFlightRequest inFlightRequest = requestQueue(node).pollLast();
        inFlightRequestCount.decrementAndGet();
        return inFlightRequest;
    }
Get the oldest request (the one that will be completed next) for the given node
clients/src/main/java/org/apache/kafka/clients/InFlightRequests.java