Function follower_caught_up_credit 

pub fn follower_caught_up_credit(
    fetch_offset: i64,
    leader_log_end: i64,
    last_fetch_leader_log_end: i64,
) -> CaughtUpCredit

Kafka’s Replica.updateFetchStateOrThrow choice of lastCaughtUpTimeMs.

fetch_offset is the follower’s fetch offset, leader_log_end the leader’s log end offset when the fetch arrived, and last_fetch_leader_log_end the leader’s log end offset recorded at the follower’s previous fetch (-1 before the first). The host keeps the later of the credited time and the recorded one.