Heartbeats are not sent from authority nodes

Question

I was looking into the code of im-online pallet and found the following function here, if false is returned, a heartbeat is sent else AlreadyOnline Error is returned;

fn is_online_aux(authority_index: AuthIndex, authority: &ValidatorId<T>) -> bool {
        let current_session = T::ValidatorSet::session_index();

        ReceivedHeartbeats::<T>::contains_key(&current_session, &authority_index) ||
            AuthoredBlocks::<T>::get(&current_session, authority) != 0
    }

Every time in a session, this function returns true because of number of blocks authored is non-zero which prevents a heartbeat being sent. I speculate the heartbeats are never sent out from a node. Kindly someone help me better understand what exactly is happening here.

Answer 1

You don't need to send a heartbeat, if the node has produced a block. Producing a block is essentially the same and even better to "proof" that you were online in a session. So, im-online isn't sending a heartbeat in this case.

Answer 2

Here is some extended explanations base on bkchr's answer.

The most common case is:

Your node is ready, and it's trying to produce blocks. But due to the consensus algorithm, BABE or whatever chose the block producer randomly. And you are very unlucky today. You didn't produce any blocks in the previous session.

Should the consensus system punish you? You are offline and not responsible for the network. Or it's just because you are so unlucky today.

And the consensus system doesn't want to punish the honest/unlucky guy. So, your node needs to send a heartbeat to say, "I'm always online, but I didn't get any chances.".