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// This file is part of Substrate.
// Copyright (C) Parity Technologies (UK) Ltd.
// SPDX-License-Identifier: Apache-2.0
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
/// ! Traits and default implementation for paying transaction fees.
use crate::Config;
use core::marker::PhantomData;
use sp_runtime::{
traits::{DispatchInfoOf, PostDispatchInfoOf, Saturating, Zero},
transaction_validity::InvalidTransaction,
};
use frame_support::{
traits::{
fungible::{Balanced, Credit, Debt, Inspect},
tokens::Precision,
Currency, ExistenceRequirement, Imbalance, OnUnbalanced, WithdrawReasons,
},
unsigned::TransactionValidityError,
type NegativeImbalanceOf<C, T> =
<C as Currency<<T as frame_system::Config>::AccountId>>::NegativeImbalance;
/// Handle withdrawing, refunding and depositing of transaction fees.
pub trait OnChargeTransaction<T: Config> {
/// The underlying integer type in which fees are calculated.
type Balance: frame_support::traits::tokens::Balance;
type LiquidityInfo: Default;
/// Before the transaction is executed the payment of the transaction fees
/// need to be secured.
///
/// Note: The `fee` already includes the `tip`.
fn withdraw_fee(
who: &T::AccountId,
call: &T::RuntimeCall,
dispatch_info: &DispatchInfoOf<T::RuntimeCall>,
fee: Self::Balance,
tip: Self::Balance,
) -> Result<Self::LiquidityInfo, TransactionValidityError>;
/// After the transaction was executed the actual fee can be calculated.
/// This function should refund any overpaid fees and optionally deposit
/// the corrected amount.
fn correct_and_deposit_fee(
post_info: &PostDispatchInfoOf<T::RuntimeCall>,
corrected_fee: Self::Balance,
already_withdrawn: Self::LiquidityInfo,
) -> Result<(), TransactionValidityError>;
}
/// Implements transaction payment for a pallet implementing the [`frame_support::traits::fungible`]
/// trait (eg. pallet_balances) using an unbalance handler (implementing
/// [`OnUnbalanced`]).
/// The unbalance handler is given 2 unbalanceds in [`OnUnbalanced::on_unbalanceds`]: `fee` and
/// then `tip`.
pub struct FungibleAdapter<F, OU>(PhantomData<(F, OU)>);
impl<T, F, OU> OnChargeTransaction<T> for FungibleAdapter<F, OU>
where
T: Config,
F: Balanced<T::AccountId>,
OU: OnUnbalanced<Credit<T::AccountId, F>>,
{
type LiquidityInfo = Option<Credit<T::AccountId, F>>;
type Balance = <F as Inspect<<T as frame_system::Config>::AccountId>>::Balance;
who: &<T>::AccountId,
_call: &<T>::RuntimeCall,
_dispatch_info: &DispatchInfoOf<<T>::RuntimeCall>,
_tip: Self::Balance,
) -> Result<Self::LiquidityInfo, TransactionValidityError> {
if fee.is_zero() {
return Ok(None)
match F::withdraw(
who,
fee,
Precision::Exact,
frame_support::traits::tokens::Preservation::Preserve,
frame_support::traits::tokens::Fortitude::Polite,
) {
Ok(imbalance) => Ok(Some(imbalance)),
Err(_) => Err(InvalidTransaction::Payment.into()),
_post_info: &PostDispatchInfoOf<<T>::RuntimeCall>,
) -> Result<(), TransactionValidityError> {
if let Some(paid) = already_withdrawn {
// Calculate how much refund we should return
let refund_amount = paid.peek().saturating_sub(corrected_fee);
// refund to the the account that paid the fees if it exists. otherwise, don't refind
// anything.
let refund_imbalance = if F::total_balance(who) > F::Balance::zero() {
F::deposit(who, refund_amount, Precision::BestEffort)
.unwrap_or_else(|_| Debt::<T::AccountId, F>::zero())
} else {
Debt::<T::AccountId, F>::zero()
// merge the imbalance caused by paying the fees and refunding parts of it again.
let adjusted_paid: Credit<T::AccountId, F> = paid
.offset(refund_imbalance)
.same()
.map_err(|_| TransactionValidityError::Invalid(InvalidTransaction::Payment))?;
// Call someone else to handle the imbalance (fee and tip separately)
let (tip, fee) = adjusted_paid.split(tip);
OU::on_unbalanceds(Some(fee).into_iter().chain(Some(tip)));
Ok(())
/// Implements the transaction payment for a pallet implementing the [`Currency`]
/// trait (eg. the pallet_balances) using an unbalance handler (implementing
#[deprecated(
note = "Please use the fungible trait and FungibleAdapter. This struct will be removed some time after March 2024."
)]
pub struct CurrencyAdapter<C, OU>(PhantomData<(C, OU)>);
/// Default implementation for a Currency and an OnUnbalanced handler.
#[allow(deprecated)]
impl<T, C, OU> OnChargeTransaction<T> for CurrencyAdapter<C, OU>
C: Currency<<T as frame_system::Config>::AccountId>,
C::PositiveImbalance: Imbalance<
<C as Currency<<T as frame_system::Config>::AccountId>>::Balance,
Opposite = C::NegativeImbalance,
>,
C::NegativeImbalance: Imbalance<
Opposite = C::PositiveImbalance,
OU: OnUnbalanced<NegativeImbalanceOf<C, T>>,
type LiquidityInfo = Option<NegativeImbalanceOf<C, T>>;
type Balance = <C as Currency<<T as frame_system::Config>::AccountId>>::Balance;
/// Withdraw the predicted fee from the transaction origin.
_call: &T::RuntimeCall,
_info: &DispatchInfoOf<T::RuntimeCall>,
let withdraw_reason = if tip.is_zero() {
WithdrawReasons::TRANSACTION_PAYMENT
WithdrawReasons::TRANSACTION_PAYMENT | WithdrawReasons::TIP
match C::withdraw(who, fee, withdraw_reason, ExistenceRequirement::KeepAlive) {
/// Hand the fee and the tip over to the `[OnUnbalanced]` implementation.
/// Since the predicted fee might have been too high, parts of the fee may
/// be refunded.
/// Note: The `corrected_fee` already includes the `tip`.
_dispatch_info: &DispatchInfoOf<T::RuntimeCall>,
_post_info: &PostDispatchInfoOf<T::RuntimeCall>,
// refund to the the account that paid the fees. If this fails, the
// account might have dropped below the existential balance. In
// that case we don't refund anything.
let refund_imbalance = C::deposit_into_existing(who, refund_amount)
.unwrap_or_else(|_| C::PositiveImbalance::zero());
let adjusted_paid = paid