Function polkadot_node_subsystem_util::determine_new_blocks

pub async fn determine_new_blocks<E, Sender>(
    sender: &mut Sender,
    is_known: impl Fn(&Hash) -> Result<bool, E>,
    head: Hash,
    header: &Header,
    lower_bound_number: BlockNumber
) -> Result<Vec<(Hash, Header)>, E>where
    Sender: SubsystemSender<ChainApiMessage>,

Given a new chain-head hash, this determines the hashes of all new blocks we should track metadata for, given this head.

This is guaranteed to be a subset of the (inclusive) ancestry of head determined as all blocks above the lower bound or above the highest known block, whichever is higher. This is formatted in descending order by block height.

An implication of this is that if head itself is known or not above the lower bound, then the returned list will be empty.

This may be somewhat expensive when first recovering from major sync.