Runtime Fees

Runtime fees are measured in Gas. Gas price will be discussed separately.

When a transaction is converted into a receipt, the signer account is charged for the full cost of the transaction. This cost consists of extra attached gas, attached deposits and the transaction fee.

The total transaction fee is the sum of the following:

• A fee for creation of the receipt
• A fee for every action

Every Fee consists of 3 values measured in gas:

• send_sir and send_not_sir - the gas burned when the action is being created to be sent to a receiver.
  • send_sir is used when current_account_id == receiver_id (current_account_id is a signer_id for a signed transaction).
  • send_not_sir is used when current_account_id != receiver_id
• execution - the gas burned when the action is being executed on the receiver's account.

Receipt creation cost

There are 2 types of receipts:

• Action receipts ActionReceipt
• Data receipts DataReceipt

A transaction is converted into an ActionReceipt. Data receipts are used for data dependencies and will be discussed separately.

The Fee for an action receipt creation is described in the config action_receipt_creation_config.

Example: when a signed transaction is being converted into a receipt, the gas for action_receipt_creation_config.send is being burned immediately, while the gas for action_receipt_creation_config.execution is only charged, but not burned. It'll be burned when the newly created receipt is executed on the receiver's account.

Fees for actions

Every Action has a corresponding Fee(s) described in the config action_creation_config. Similar to a receipt creation costs, the send gas is burned when an action is added to a receipt to be sent, and the execution gas is only charged, but not burned.

Fees are either a base fee or a fee per byte of some data within the action.

Here is the list of actions and their corresponding fees:

• CreateAccount uses
  • the base fee create_account_cost
• DeployContract uses the sum of the following fees:
  • the base fee deploy_contract_cost
  • the fee per byte of the contract code to be deployed with the fee deploy_contract_cost_per_byte To compute the number of bytes for a deploy contract action deploy_contract_action use deploy_contract_action.code.len()
• FunctionCall uses the sum of the following fees:
  • the base fee function_call_cost
  • the fee per byte of method name string and per byte of arguments with the fee function_call_cost_per_byte. To compute the number of bytes for a function call action function_call_action use function_call_action.method_name.as_bytes().len() + function_call_action.args.len()
• Transfer uses one of the following fees:
  • if the receiver_id is an Implicit Account ID, then a sum of base fees is used:
    • the create account base fee create_account_cost
    • the transfer base fee transfer_cost
    • the add full access key base fee add_key_cost.full_access_cost
  • if the receiver_id is NOT an Implicit Account ID, then only the base fee is used:
    • the transfer base fee transfer_cost
• Stake uses
  • the base fee stake_cost
• AddKey uses one of the following fees:
  • if the access key is AccessKeyPermission::FullAccess the base fee is used
    • the add full access key base fee add_key_cost.full_access_cost
  • if the access key is AccessKeyPermission::FunctionCall the sum of the fees is used
    • the add function call permission access key base fee add_key_cost.function_call_cost
    • the fee per byte of method names with extra byte for every method with the fee add_key_cost.function_call_cost_per_byte To compute the number of bytes for function_call_permission use function_call_permission.method_names.iter().map(|name| name.as_bytes().len() as u64 + 1).sum::<u64>()
• DeleteKey uses
  • the base fee delete_key_cost
• DeleteAccount uses
  • the base fee delete_account_cost
  • action receipt creation fee for creating Transfer to send remaining funds to beneficiary_id
  • full transfer fee described in the corresponding item

Gas tracking

In Runtime, gas is tracked in the following fields of ActionResult struct:

• gas_burnt - irreversible amount of gas spent on computations.
• gas_used - includes burnt gas and gas attached to the new ActionReceipts created during the method execution.
• gas_burnt_for_function_call - stores gas burnt during function call execution. Later, contract account gets 30% of it as a reward for a possibility to invoke the function.

Initially runtime charges gas_used from the account. Some gas may be refunded later, see Refunds.

At first, we charge fees related to conversion from SignedTransaction to ActionReceipt and future execution of this receipt:

• costs of all SignedTransactions passed to Runtime::apply are computed in tx_cost function during validation;
• total_cost is deducted from signer, which is a sum of:
  • gas_to_balance(gas_burnt) where gas_burnt is action receipt send fee + total_send_fees(transaction.actions));
  • gas_to_balance(gas_remaining) where gas_remaining is action receipt exec fee + total_prepaid_exec_fees(transaction.actions) to pay all remaining fees caused by transaction;
  • total_deposit(transaction.actions);
• each transaction is converted to receipt and passed to Runtime::process_receipt.

Then each ActionReceipt is passed to Runtime::apply_action_receipt where gas is tracked as follows:

• ActionResult is created with ActionReceipt execution fee;
• all actions inside ActionReceipt are passed to Runtime::apply_action;
• ActionResult with charged base execution fees is created there;
• if action execution leads to new ActionReceipts creation, corresponding action_[action_name] function adds new fees to the ActionResult. E.g. action_delete_account also charges the following fees:
  • gas_burnt: send fee for new ActionReceipt creation + complex send fee for Transfer to beneficiary account
  • gas_used: gas_burnt + exec fee for created ActionReceipt + complex exec fee for Transfer
• all computed ActionResults are merged into one, where all gas values are summed up;
• unused gas is refunded in generate_refund_receipts.

Inside VMLogic, the fees are tracked in the GasCounter struct. The VM itself is called in the action_function_call inside Runtime. When all actions are processed, the result is returned as a VMOutcome, which is later merged with ActionResult.

Example

Let's say we have the following transaction:

Transaction {
    signer_id: "alice.near",
    public_key: "2onVGYTFwyaGetWckywk92ngBiZeNpBeEjuzSznEdhRE",
    nonce: 23,
    receiver_id: "lockup.alice.near",
    block_hash: "3CwEMonK6MmKgjKePiFYgydbAvxhhqCPHKuDMnUcGGTK",
    actions: [
        Action::CreateAccount(CreateAccountAction {}),
        Action::Transfer(TransferAction {
            deposit: 100000000000000000000000000,
        }),
        Action::DeployContract(DeployContractAction {
            code: vec![/*<...128000 bytes...>*/],
        }),
        Action::FunctionCall(FunctionCallAction {
            method_name: "new",
            args: b"{\"owner_id\": \"alice.near\"}".to_vec(),
            gas: 25000000000000,
            deposit: 0,
        }),
    ],
}

It has signer_id != receiver_id so it will use send_not_sir for send fees.

It contains 4 actions with 2 actions that requires to compute number of bytes. We assume code in DeployContractAction contains 128000 bytes. And FunctionCallAction has method_name with length of 3 and args length of 26, so total of 29.

First let's compute the amount that will be burned immediately for sending a receipt.

burnt_gas = \
    config.action_receipt_creation_config.send_not_sir + \
    config.action_creation_config.create_account_cost.send_not_sir + \
    config.action_creation_config.transfer_cost.send_not_sir + \
    config.action_creation_config.deploy_contract_cost.send_not_sir + \
    128000 * config.action_creation_config.deploy_contract_cost_per_byte.send_not_sir + \
    config.action_creation_config.function_call_cost.send_not_sir + \
    29 * config.action_creation_config.function_call_cost_per_byte.send_not_sir

Now, by using burnt_gas, we can calculate the total transaction fee

total_transaction_fee = burnt_gas + \
    config.action_receipt_creation_config.execution + \
    config.action_creation_config.create_account_cost.execution + \
    config.action_creation_config.transfer_cost.execution + \
    config.action_creation_config.deploy_contract_cost.execution + \
    128000 * config.action_creation_config.deploy_contract_cost_per_byte.execution + \
    config.action_creation_config.function_call_cost.execution + \
    29 * config.action_creation_config.function_call_cost_per_byte.execution

This total_transaction_fee is the amount of gas required to create a new receipt from the transaction.

NOTE: There are extra amounts required to prepay for deposit in TransferAction and gas in FunctionCallAction, but this is not part of the total transaction fee.