deposit_processing.py

def get_balance_churn_limit(state: BeaconState) -> Gwei:
    """
    Return the churn limit for the current epoch.
    """
    churn = max(
        MIN_PER_EPOCH_CHURN_LIMIT_ELECTRA,
        get_total_active_balance(state) // CHURN_LIMIT_QUOTIENT
    )
    return churn - churn % EFFECTIVE_BALANCE_INCREMENT


def get_activation_exit_churn_limit(state: BeaconState) -> Gwei:
    """
    Return the churn limit for the current epoch dedicated to activations and exits.
    """
    return min(MAX_PER_EPOCH_ACTIVATION_EXIT_CHURN_LIMIT, get_balance_churn_limit(state))


def process_deposit(state: BeaconState, deposit: Deposit) -> None:
    # Verify the Merkle branch
    assert is_valid_merkle_branch(
        leaf=hash_tree_root(deposit.data),
        branch=deposit.proof,
        depth=DEPOSIT_CONTRACT_TREE_DEPTH + 1,  # Add 1 for the List length mix-in
        index=state.eth1_deposit_index,
        root=state.eth1_data.deposit_root,
    )

    # Deposits must be processed in order
    state.eth1_deposit_index += 1

    # [Modified in Electra:EIP7251]
    apply_deposit(
        state=state,
        pubkey=deposit.data.pubkey,
        withdrawal_credentials=deposit.data.withdrawal_credentials,
        amount=deposit.data.amount,
        signature=deposit.data.signature,
    )


def apply_deposit(state: BeaconState,
                  pubkey: BLSPubkey,
                  withdrawal_credentials: Bytes32,
                  amount: uint64,
                  signature: BLSSignature) -> None:
    validator_pubkeys = [v.pubkey for v in state.validators]
    if pubkey not in validator_pubkeys:
        # Verify the deposit signature (proof of possession) which is not checked by the deposit contract
        if is_valid_deposit_signature(pubkey, withdrawal_credentials, amount, signature):
            add_validator_to_registry(state, pubkey, withdrawal_credentials, Gwei(0))  # [Modified in Electra:EIP7251]
        else:
            return

    # Increase balance by deposit amount
    # [Modified in Electra:EIP7251]
    state.pending_deposits.append(PendingDeposit(
        pubkey=pubkey,
        withdrawal_credentials=withdrawal_credentials,
        amount=amount,
        signature=signature,
        slot=GENESIS_SLOT  # Use GENESIS_SLOT to distinguish from a pending deposit request
    ))


def process_deposit_request(state: BeaconState, deposit_request: DepositRequest) -> None:
    # Set deposit request start index
    if state.deposit_requests_start_index == UNSET_DEPOSIT_REQUESTS_START_INDEX:
        state.deposit_requests_start_index = deposit_request.index

    # Create pending deposit
    state.pending_deposits.append(PendingDeposit(
        pubkey=deposit_request.pubkey,
        withdrawal_credentials=deposit_request.withdrawal_credentials,
        amount=deposit_request.amount,
        signature=deposit_request.signature,
        slot=state.slot,
    ))


def process_pending_deposits(state: BeaconState) -> None:
    next_epoch = Epoch(get_current_epoch(state) + 1)
    available_for_processing = state.deposit_balance_to_consume + get_activation_exit_churn_limit(state)
    processed_amount = 0
    next_deposit_index = 0
    deposits_to_postpone = []
    is_churn_limit_reached = False
    finalized_slot = compute_start_slot_at_epoch(state.finalized_checkpoint.epoch)

    for deposit in state.pending_deposits:
        # Do not process deposit requests if Eth1 bridge deposits are not yet applied.
        if (
            # Is deposit request
            deposit.slot > GENESIS_SLOT and
            # There are pending Eth1 bridge deposits
            state.eth1_deposit_index < state.deposit_requests_start_index
        ):
            break

        # Check if deposit has been finalized, otherwise, stop processing.
        if deposit.slot > finalized_slot:
            break

        # Check if number of processed deposits has not reached the limit, otherwise, stop processing.
        if next_deposit_index >= MAX_PENDING_DEPOSITS_PER_EPOCH:  # MAX_PENDING_DEPOSITS_PER_EPOCH = 16
            break

        # Read validator state
        is_validator_exited = False
        is_validator_withdrawn = False
        validator_pubkeys = [v.pubkey for v in state.validators]
        if deposit.pubkey in validator_pubkeys:
            validator = state.validators[ValidatorIndex(validator_pubkeys.index(deposit.pubkey))]
            is_validator_exited = validator.exit_epoch < FAR_FUTURE_EPOCH
            is_validator_withdrawn = validator.withdrawable_epoch < next_epoch

        if is_validator_withdrawn:
            # Deposited balance will never become active. Increase balance but do not consume churn
            apply_pending_deposit(state, deposit)
        elif is_validator_exited:
            # Validator is exiting, postpone the deposit until after withdrawable epoch
            deposits_to_postpone.append(deposit)
        else:
            # Check if deposit fits in the churn, otherwise, do no more deposit processing in this epoch.
            is_churn_limit_reached = processed_amount + deposit.amount > available_for_processing
            if is_churn_limit_reached:
                break

            # Consume churn and apply deposit.
            processed_amount += deposit.amount
            apply_pending_deposit(state, deposit)

        # Regardless of how the deposit was handled, we move on in the queue.
        next_deposit_index += 1

    state.pending_deposits = state.pending_deposits[next_deposit_index:] + deposits_to_postpone

    # Accumulate churn only if the churn limit has been hit.
    if is_churn_limit_reached:
        state.deposit_balance_to_consume = available_for_processing - processed_amount
    else:
        state.deposit_balance_to_consume = Gwei(0)