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contracts: Cap the surcharge reward by the amount of rent that way payed by a contract (#7870)

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* Add rent_payed field to the contract info

* Don't pay out more as reward as was spent in rent

* Make successful evictions free

* Add tests to check that surcharge reward is capped by rent payed

* review: Fixed docs
This commit is contained in:
Alexander Theißen
2021-01-14 13:45:13 +01:00
committed by GitHub
parent c2ebcae0a6
commit ad1717293d
5 changed files with 112 additions and 40 deletions
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substrate/frame/contracts/src/lib.rs
+19 -5
View File
@@ -122,6 +122,7 @@ use frame_support::{
storage::child::ChildInfo,
dispatch::{DispatchResult, DispatchResultWithPostInfo},
traits::{OnUnbalanced, Currency, Get, Time, Randomness},
weights::Pays,
};
use frame_system::{ensure_signed, ensure_root, Module as System};
use pallet_contracts_primitives::{
@@ -211,6 +212,10 @@ pub struct RawAliveContractInfo<CodeHash, Balance, BlockNumber> {
pub code_hash: CodeHash,
/// Pay rent at most up to this value.
pub rent_allowance: Balance,
/// The amount of rent that was payed by the contract over its whole lifetime.
///
/// A restored contract starts with a value of zero just like a new contract.
pub rent_payed: Balance,
/// Last block rent has been payed.
pub deduct_block: BlockNumber,
/// Last block child storage has been written.
@@ -602,8 +607,12 @@ decl_module! {
gas_meter.into_dispatch_result(result)
}
/// Allows block producers to claim a small reward for evicting a contract. If a block producer
/// fails to do so, a regular users will be allowed to claim the reward.
/// Allows block producers to claim a small reward for evicting a contract. If a block
/// producer fails to do so, a regular users will be allowed to claim the reward.
///
/// In case of a successful eviction no fees are charged from the sender. However, the
/// reward is capped by the total amount of rent that was payed by the contract while
/// it was alive.
///
/// If contract is not evicted as a result of this call, [`Error::ContractNotEvictable`]
/// is returned and the sender is not eligible for the reward.
@@ -612,7 +621,7 @@ decl_module! {
origin,
dest: T::AccountId,
aux_sender: Option<T::AccountId>
) -> DispatchResult {
) -> DispatchResultWithPostInfo {
let origin = origin.into();
let (signed, rewarded) = match (origin, aux_sender) {
(Ok(frame_system::RawOrigin::Signed(account)), None) => {
@@ -634,8 +643,13 @@ decl_module! {
};
// If poking the contract has lead to eviction of the contract, give out the rewards.
if Rent::<T>::snitch_contract_should_be_evicted(&dest, handicap)? {
T::Currency::deposit_into_existing(&rewarded, T::SurchargeReward::get()).map(|_| ())
if let Some(rent_payed) = Rent::<T>::try_eviction(&dest, handicap)? {
T::Currency::deposit_into_existing(
&rewarded,
T::SurchargeReward::get().min(rent_payed),
)
.map(|_| Pays::No.into())
.map_err(Into::into)
} else {
Err(Error::<T>::ContractNotEvictable.into())
}