EIP-4844: Implement gas accounting

[jangko]

Gas accounting

We introduce data gas as a new type of gas. It is independent of normal gas and follows its own targeting rule, similar to EIP-1559. We use the excess_data_gas header field to store persistent data needed to compute the data gas price. For now, only blobs are priced in data gas.

DATA_GAS_PER_BLOB: 2 ** 17
MIN_DATA_GASPRICE: 1
DATA_GASPRICE_UPDATE_FRACTION: 2225652

def calc_data_fee(tx: SignedBlobTransaction, parent: Header) -> int:
    return get_total_data_gas(tx) * get_data_gasprice(header)

def get_total_data_gas(tx: SignedBlobTransaction) -> int:
    return DATA_GAS_PER_BLOB * len(tx.message.blob_versioned_hashes)

def get_data_gasprice(header: Header) -> int:
    return fake_exponential(
        MIN_DATA_GASPRICE,
        header.excess_data_gas,
        DATA_GASPRICE_UPDATE_FRACTION
    )

def fake_exponential(factor: int, numerator: int, denominator: int) -> int:
    i = 1
    output = 0
    numerator_accum = factor * denominator
    while numerator_accum > 0:
        output += numerator_accum
        numerator_accum = (numerator_accum * numerator) // (denominator * i)
        i += 1
    return output // denominator

def validate_block(block: Block) -> None:
    ...

    for tx in block.transactions:
        ...

        # the signer must be able to afford the transaction
        assert signer(tx).balance >= tx.message.gas * tx.message.max_fee_per_gas + get_total_data_gas(tx) * tx.message.max_fee_per_data_gas

        # ensure that the user was willing to at least pay the current data gasprice
        assert tx.message.max_fee_per_data_gas >= get_data_gasprice(parent(block).header)

The actual data_fee as calculated via calc_data_fee is deducted from the sender balance before transaction execution and burned, and is not refunded in case of transaction failure. (meaning: calc_data_fee will be subtracted from sender near intrinsicGas)