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ensure account of native token keeps alive after charge fee #1204

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Jul 14, 2021
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ensure account of native token keeps alive after charge fee #1204

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21 changes: 14 additions & 7 deletions modules/transaction-payment/src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -567,17 +567,24 @@ where
charge_fee_order.dedup();

let price_impact_limit = Some(T::MaxSlippageSwapWithDEX::get());
let native_existential_deposit = <T as Config>::Currency::minimum_balance();
let total_native = <T as Config>::Currency::total_balance(who);
// add the gap amount to keep account alive and have enough fee
let fee_and_alive_gap = if total_native < native_existential_deposit {
fee.saturating_add(native_existential_deposit.saturating_sub(total_native))
} else {
fee
};

// iterator charge fee order to get enough fee
for currency_id in charge_fee_order {
if currency_id == native_currency_id {
// check native balance if is enough
let native_is_enough =
<T as Config>::Currency::free_balance(who)
.checked_sub(&fee)
.map_or(false, |new_free_balance| {
<T as Config>::Currency::ensure_can_withdraw(who, fee, reason, new_free_balance).is_ok()
});
let native_is_enough = <T as Config>::Currency::free_balance(who)
.checked_sub(&fee_and_alive_gap)
.map_or(false, |new_free_balance| {
<T as Config>::Currency::ensure_can_withdraw(who, fee, reason, new_free_balance).is_ok()
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Suggested change
<T as Config>::Currency::ensure_can_withdraw(who, fee, reason, new_free_balance).is_ok()
<T as Config>::Currency::ensure_can_withdraw(who, fee, reason, fee_and_alive_gap).is_ok()

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@xlc The old code seems to be wrong.

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https://github.com/paritytech/substrate/blob/993907f9deb180795b291ba752b9c204165d74dc/frame/support/src/traits/tokens/currency.rs#L103

the last parameter is expected new balance after withdraw

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Ok, It's different from tokens.
https://github.com/open-web3-stack/open-runtime-module-library/blob/3d64077e5ac5539bde336a794308d85f6f5f2b82/tokens/src/lib.rs#L642

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Yes we removed the last parameter

});
if native_is_enough {
// native balance is enough, break iteration
break;
Expand All @@ -593,7 +600,7 @@ where
if T::DEX::swap_with_exact_target(
who,
&trading_path,
fee.unique_saturated_into(),
fee_and_alive_gap.unique_saturated_into(),
<T as Config>::MultiCurrency::free_balance(currency_id, who),
price_impact_limit,
)
Expand Down