election-provider-multi-phase: Add extrinsic to challenge signed submissions

bin/node/runtime/src/lib.rs

@@ -571,8 +571,10 @@ parameter_types! {
 
 	// signed config
 	pub const SignedRewardBase: Balance = 1 * DOLLARS;
+	pub const ChallengeRewardBase: Balance = 1 * CENTS;
 	pub const SignedDepositBase: Balance = 1 * DOLLARS;
 	pub const SignedDepositByte: Balance = 1 * CENTS;
+	pub const MinimumSlashableAmount: Balance = 1 * DOLLARS;
 
 	pub SolutionImprovementThreshold: Perbill = Perbill::from_rational(1u32, 10_000);
 
@@ -670,6 +672,7 @@ impl pallet_election_provider_multi_phase::Config for Runtime {
 	type MinerTxPriority = MultiPhaseUnsignedPriority;
 	type SignedMaxSubmissions = ConstU32<10>;
 	type SignedRewardBase = SignedRewardBase;
+	type ChallengeRewardBase = ChallengeRewardBase;
 	type SignedDepositBase = SignedDepositBase;
 	type SignedDepositByte = SignedDepositByte;
 	type SignedDepositWeight = ();
@@ -685,7 +688,13 @@ impl pallet_election_provider_multi_phase::Config for Runtime {
 	type MaxElectableTargets = ConstU16<{ u16::MAX }>;
 	type MaxElectingVoters = MaxElectingVoters;
 	type BenchmarkingConfig = ElectionProviderBenchmarkConfig;
+	// BagsList allows a practically unbounded count of nominators to participate in NPoS elections.
+	// To ensure we respect memory limits when using the BagsList this must be set to a number of
+	// voters we know can fit into a single vec allocation.
+	type VoterSnapshotPerBlock = ConstU32<10_000>;
+	type MinimumSlashableAmount = MinimumSlashableAmount;
 	type WeightInfo = pallet_election_provider_multi_phase::weights::SubstrateWeight<Self>;
+
 }
 
 parameter_types! {

frame/election-provider-multi-phase/src/lib.rs

@@ -627,6 +627,10 @@ pub mod pallet {
 		#[pallet::constant]
 		type SignedRewardBase: Get<BalanceOf<Self>>;
 
+		// Base reward for a challenger
+		#[pallet::constant]
+		type ChallengeRewardBase: Get<BalanceOf<Self>>;
+
 		/// Base deposit for a signed solution.
 		#[pallet::constant]
 		type SignedDepositBase: Get<BalanceOf<Self>>;
@@ -708,6 +712,11 @@ pub mod pallet {
 
 		/// The weight of the pallet.
 		type WeightInfo: WeightInfo;
+
+		/// The minimum amount a solution challenger must have to execute
+		/// `challange_submission`
+		#[pallet::constant]
+		type MinimumSlashableAmount: Get<BalanceOf<Self>>;
 	}
 
 	#[pallet::hooks]
@@ -850,7 +859,7 @@ pub mod pallet {
 	impl<T: Config> Pallet<T> {
 		/// Submit a solution for the unsigned phase.
 		///
-		/// The dispatch origin fo this call must be __none__.
+		/// The dispatch origin for this call must be __none__.
 		///
 		/// This submission is checked on the fly. Moreover, this unsigned solution is only
 		/// validated when submitted to the pool from the **local** node. Effectively, this means
@@ -1055,6 +1064,44 @@ pub mod pallet {
 			<QueuedSolution<T>>::put(solution);
 			Ok(())
 		}
+
+		#[pallet::weight(100)]
+		pub fn challenge_solution(origin: OriginFor<T>, index: u32) -> DispatchResult {
+			let who = ensure_signed(origin)?;
+			// TODO: Create custom error
+			ensure!(
+				T::Currency::can_slash(&who, T::MinimumSlashableAmount::get()),
+				<Error<T>>::CallNotAllowed
+			);
+			// TODO: Add an `else` for a None result
+			if let Some(submission) = SignedSubmissionsMap::<T>::get(index) {
+				match Self::feasibility_check(
+					submission.raw_solution.clone(),
+					ElectionCompute::Signed,
+				) {
+					Ok(solution) => {
+						let _ = T::Currency::slash(&who, T::MinimumSlashableAmount::get());
+						CheckedSolutions::<T>::insert(submission, solution);
+						Ok(())
+					},
+					Err(_error) => {
+						T::Currency::slash_reserved(&who, submission.deposit);
+						SignedSubmissionsMap::<T>::remove(index);
+						let reward = {
+							let call = Call::challenge_solution::<T> { index };
+							let call_fee =
+								T::EstimateCallFee::estimate_call_fee(&call, None.into());
+							T::ChallengeRewardBase::get().saturating_add(call_fee)
+						};
+						let positive_imbalance = T::Currency::deposit_creating(&who, reward);
+						T::RewardHandler::on_unbalanced(positive_imbalance);
+						Err(Error::<T>::CallNotAllowed.into())
+					},
+				}
+			} else {
+				return Err(Error::<T>::CallNotAllowed.into())
+			}
+		}
 	}
 
 	#[pallet::event]
@@ -1240,6 +1287,10 @@ pub mod pallet {
 	pub type SignedSubmissionsMap<T: Config> =
 		StorageMap<_, Twox64Concat, u32, SignedSubmissionOf<T>, OptionQuery>;
 
+	#[pallet::storage]
+	pub type CheckedSolutions<T: Config> =
+		StorageMap<_, Twox64Concat, SignedSubmissionOf<T>, ReadySolution<T::AccountId>>;
+
 	// `SignedSubmissions` items end here.
 
 	/// The minimum score that each 'untrusted' solution must attain in order to be considered

frame/election-provider-multi-phase/src/mock.rs

@@ -258,6 +258,7 @@ parameter_types! {
 	pub static UnsignedPhase: BlockNumber = 5;
 	pub static SignedMaxSubmissions: u32 = 5;
 	pub static SignedDepositBase: Balance = 5;
+	pub static ChallengeRewardBase: Balance = 6;
 	pub static SignedDepositByte: Balance = 0;
 	pub static SignedDepositWeight: Balance = 0;
 	pub static SignedRewardBase: Balance = 7;
@@ -272,7 +273,9 @@ parameter_types! {
 	pub static MaxElectableTargets: TargetIndex = TargetIndex::max_value();
 
 	pub static EpochLength: u64 = 30;
-	pub static OnChainFallback: bool = true;
+
+	pub static OnChianFallback: bool = true;
+	pub static MinimumSlashableAmount: Balance = 3;
 }
 
 pub struct OnChainSeqPhragmen;
@@ -419,6 +422,7 @@ impl crate::Config for Runtime {
 	type MinerMaxLength = MinerMaxLength;
 	type MinerTxPriority = MinerTxPriority;
 	type SignedRewardBase = SignedRewardBase;
+	type ChallengeRewardBase = ChallengeRewardBase;
 	type SignedDepositBase = SignedDepositBase;
 	type SignedDepositByte = ();
 	type SignedDepositWeight = ();
@@ -436,6 +440,7 @@ impl crate::Config for Runtime {
 	type MaxElectingVoters = MaxElectingVoters;
 	type MaxElectableTargets = MaxElectableTargets;
 	type Solver = SequentialPhragmen<AccountId, SolutionAccuracyOf<Runtime>, Balancing>;
+	type MinimumSlashableAmount = MinimumSlashableAmount;
 }
 
 impl<LocalCall> frame_system::offchain::SendTransactionTypes<LocalCall> for Runtime