@Override
        public String toString() {
            return "InFlightRequest(header=" + header +
                    ", destination=" + destination +
                    ", expectResponse=" + expectResponse +
                    ", createdTimeMs=" + createdTimeMs +
                    ", sendTimeMs=" + sendTimeMs +
                    ", isInternalRequest=" + isInternalRequest +
                    ", request=" + request +
                    ", callback=" + callback +
                    ", send=" + send + ")";
        }
Add a metadata request to the list of sends if we can make one
clients/src/main/java/org/apache/kafka/clients/NetworkClient.java