Module fee_excess

Fee excesses associated with transactions or transitions.

These are represented as a ‘left’ and ‘right’ excess, which describe the unresolved fee excesses in the fee tokens of the first (or leftmost) and last (or rightmost) transactions in the transition.

Assumptions:

• Transactions are grouped by their fee token.
• The ‘fee transfer’ transaction to dispense those fees is part of this group.
• The fee excess for each token is 0 across the group.
• No transactions with fees paid in another token are executed while the previous fee token’s excess is non-zero.

By maintaining these assumptions, we can ensure that the un-settled fee excesses can be represented by excesses in (at most) 2 tokens. Consider, for example, any consecutive subsequence of the transactions

..[txn@2][ft@2][txn@3][txn@3][ft@3][txn@4][ft@4][txn@5][txn@5][ft@5][txn@6][ft@6]..

where [txn@i] and [ft@i] are transactions and fee transfers respectively paid in token i. The only groups which may have non-zero fee excesses are those which contain the start and end of the subsequence.

The code below also defines a canonical representation where fewer than 2 tokens have non-zero excesses. See the internal function FeeExcess::rebalance below for details and the implementation.

Port of the implementation from: https://github.com/MinaProtocol/mina/blob/2ee6e004ba8c6a0541056076aab22ea162f7eb3a/src/lib/mina_base/fee_excess.ml#L1

Structs

CheckedFeeExcess

FeeExcess

Functions

assert_equal_checked

eliminate_fee_excess 🔒

Eliminate a fee excess, either by combining it with one to the left/right, or by checking that it is zero.

eliminate_fee_excess_checked 🔒