Function zebra_consensus::transaction::check::lock_time_has_passed

pub fn lock_time_has_passed(
    tx: &Transaction,
    block_height: Height,
    block_time: impl Into<Option<DateTime<Utc>>>,
) -> Result<(), TransactionError>

Checks if the transaction’s lock time allows this transaction to be included in a block.

Arguments:

• block_height: the height of the mined block, or the height of the next block for mempool transactions
• block_time: the time in the mined block header, or the median-time-past of the next block for the mempool. Optional if the lock time is a height.

Panics

If the lock time is a time, and block_time is None.

Consensus

The transaction must be finalized: either its locktime must be in the past (or less than or equal to the current block height), or all of its sequence numbers must be 0xffffffff.

Transaction::lock_time validates the transparent input sequence numbers, returning None if they indicate that the transaction is finalized by them. Otherwise, this function checks that the lock time is in the past.

Mempool Consensus for Block Templates

the nTime field MUST represent a time strictly greater than the median of the timestamps of the past PoWMedianBlockSpan blocks.

https://zips.z.cash/protocol/protocol.pdf#blockheader

The transaction can be added to any block whose block time is greater than the locktime.

https://developer.bitcoin.org/devguide/transactions.html#locktime-and-sequence-number

If the transaction’s lock time is less than the median-time-past, it will always be less than the next block’s time, because the next block’s time is strictly greater than the median-time-past. (That is, lock-time < median-time-past < block-header-time.)

Using median-time-past + 1s (the next block’s mintime) would also satisfy this consensus rule, but we prefer the rule implemented by zcashd’s mempool: https://github.com/zcash/zcash/blob/9e1efad2d13dca5ee094a38e6aa25b0f2464da94/src/main.cpp#L776-L784