Adds ability to clear obsolete reports in Offences pallet

bin/node/runtime/src/lib.rs

@@ -529,6 +529,7 @@ impl pallet_session::Config for Runtime {
 	type NextSessionRotation = Babe;
 	type SessionManager = pallet_session::historical::NoteHistoricalRoot<Self, Staking>;
 	type SessionHandler = <SessionKeys as OpaqueKeys>::KeyTypeIdProviders;
+	type SessionChangeListener = Offences;
 	type Keys = SessionKeys;
 	type WeightInfo = pallet_session::weights::SubstrateWeight<Runtime>;
 }
@@ -1331,10 +1332,16 @@ impl pallet_im_online::Config for Runtime {
 	type MaxPeerDataEncodingSize = MaxPeerDataEncodingSize;
 }
 
+parameter_types! {
+	pub const MaxSessionReportAge: u32 = BondingDuration::get() * SessionsPerEra::get();
+}
+
 impl pallet_offences::Config for Runtime {
 	type RuntimeEvent = RuntimeEvent;
 	type IdentificationTuple = pallet_session::historical::IdentificationTuple<Self>;
 	type OnOffenceHandler = Staking;
+	type MaxSessionReportAge = MaxSessionReportAge;
+	type SessionInfoProvider = Session;
 }
 
 impl pallet_authority_discovery::Config for Runtime {

frame/authority-discovery/src/lib.rs

@@ -213,6 +213,7 @@ mod tests {
 		type ValidatorIdOf = ConvertInto;
 		type NextSessionRotation = pallet_session::PeriodicSessions<Period, Offset>;
 		type WeightInfo = ();
+		type SessionChangeListener = ();
 	}
 
 	impl pallet_session::historical::Config for Test {

frame/babe/src/mock.rs

@@ -114,6 +114,7 @@ impl pallet_session::Config for Test {
 	type SessionHandler = <MockSessionKeys as OpaqueKeys>::KeyTypeIdProviders;
 	type Keys = MockSessionKeys;
 	type WeightInfo = ();
+	type SessionChangeListener = ();
 }
 
 impl pallet_session::historical::Config for Test {
@@ -166,6 +167,7 @@ parameter_types! {
 	pub const SlashDeferDuration: EraIndex = 0;
 	pub const RewardCurve: &'static PiecewiseLinear<'static> = &REWARD_CURVE;
 	pub const OffendingValidatorsThreshold: Perbill = Perbill::from_percent(16);
+	pub const MaxSessionReportAge: SessionIndex = BondingDuration::get() * SessionsPerEra::get();
 }
 
 pub struct OnChainSeqPhragmen;
@@ -213,6 +215,8 @@ impl pallet_offences::Config for Test {
 	type RuntimeEvent = RuntimeEvent;
 	type IdentificationTuple = pallet_session::historical::IdentificationTuple<Self>;
 	type OnOffenceHandler = Staking;
+	type SessionInfoProvider = Session;
+	type MaxSessionReportAge = MaxSessionReportAge;
 }
 
 parameter_types! {

frame/beefy-mmr/src/mock.rs

@@ -99,6 +99,7 @@ impl pallet_session::Config for Test {
 	type SessionHandler = <MockSessionKeys as OpaqueKeys>::KeyTypeIdProviders;
 	type Keys = MockSessionKeys;
 	type WeightInfo = ();
+	type SessionChangeListener = ();
 }
 
 pub type MmrLeaf = sp_consensus_beefy::mmr::MmrLeaf<

frame/beefy/src/mock.rs

@@ -139,6 +139,7 @@ impl pallet_session::Config for Test {
 	type SessionHandler = <MockSessionKeys as OpaqueKeys>::KeyTypeIdProviders;
 	type Keys = MockSessionKeys;
 	type WeightInfo = ();
+	type SessionChangeListener = ();
 }
 
 impl pallet_session::historical::Config for Test {
@@ -190,6 +191,7 @@ parameter_types! {
 	pub const BondingDuration: EraIndex = 3;
 	pub const RewardCurve: &'static PiecewiseLinear<'static> = &REWARD_CURVE;
 	pub const OffendingValidatorsThreshold: Perbill = Perbill::from_percent(17);
+	pub const MaxSessionReportAge: SessionIndex = BondingDuration::get() * SessionsPerEra::get();
 }
 
 pub struct OnChainSeqPhragmen;
@@ -237,6 +239,8 @@ impl pallet_offences::Config for Test {
 	type RuntimeEvent = RuntimeEvent;
 	type IdentificationTuple = pallet_session::historical::IdentificationTuple<Self>;
 	type OnOffenceHandler = Staking;
+	type SessionInfoProvider = Session;
+	type MaxSessionReportAge = MaxSessionReportAge;
 }
 
 // Note, that we can't use `UintAuthorityId` here. Reason is that the implementation

frame/election-provider-multi-phase/test-staking-e2e/src/mock.rs

@@ -159,6 +159,7 @@ impl pallet_session::Config for Runtime {
 	type ValidatorId = AccountId;
 	type ValidatorIdOf = pallet_staking::StashOf<Runtime>;
 	type WeightInfo = ();
+	type SessionChangeListener = ();
 }
 impl pallet_session::historical::Config for Runtime {
 	type FullIdentification = pallet_staking::Exposure<AccountId, Balance>;

frame/grandpa/src/mock.rs

@@ -120,6 +120,7 @@ impl pallet_session::Config for Test {
 	type SessionHandler = <TestSessionKeys as OpaqueKeys>::KeyTypeIdProviders;
 	type Keys = TestSessionKeys;
 	type WeightInfo = ();
+	type SessionChangeListener = ();
 }
 
 impl pallet_session::historical::Config for Test {
@@ -171,6 +172,7 @@ parameter_types! {
 	pub const BondingDuration: EraIndex = 3;
 	pub const RewardCurve: &'static PiecewiseLinear<'static> = &REWARD_CURVE;
 	pub const OffendingValidatorsThreshold: Perbill = Perbill::from_percent(17);
+	pub const MaxSessionReportAge: SessionIndex = BondingDuration::get() * SessionsPerEra::get();
 }
 
 pub struct OnChainSeqPhragmen;
@@ -218,6 +220,8 @@ impl pallet_offences::Config for Test {
 	type RuntimeEvent = RuntimeEvent;
 	type IdentificationTuple = pallet_session::historical::IdentificationTuple<Self>;
 	type OnOffenceHandler = Staking;
+	type SessionInfoProvider = Session;
+	type MaxSessionReportAge = MaxSessionReportAge;
 }
 
 parameter_types! {

frame/im-online/src/mock.rs

@@ -160,6 +160,7 @@ impl pallet_session::Config for Runtime {
 	type RuntimeEvent = RuntimeEvent;
 	type NextSessionRotation = pallet_session::PeriodicSessions<Period, Offset>;
 	type WeightInfo = ();
+	type SessionChangeListener = ();
 }
 
 impl pallet_session::historical::Config for Runtime {

frame/offences/Cargo.toml

@@ -22,6 +22,7 @@ frame-system = { version = "4.0.0-dev", default-features = false, path = "../sys
 pallet-balances = { version = "4.0.0-dev", default-features = false, path = "../balances" }
 sp-runtime = { version = "7.0.0", default-features = false, path = "../../primitives/runtime" }
 sp-staking = { version = "4.0.0-dev", default-features = false, path = "../../primitives/staking" }
+sp-session = { version = "4.0.0-dev", default-features = false, path = "../../primitives/session" }
 sp-std = { version = "5.0.0", default-features = false, path = "../../primitives/std" }
 
 [dev-dependencies]

frame/offences/benchmarking/src/mock.rs

@@ -128,6 +128,7 @@ impl pallet_session::Config for Test {
 	type ValidatorId = AccountId;
 	type ValidatorIdOf = pallet_staking::StashOf<Test>;
 	type WeightInfo = ();
+	type SessionChangeListener = ();
 }
 
 pallet_staking_reward_curve::build! {
@@ -204,6 +205,8 @@ impl pallet_offences::Config for Test {
 	type RuntimeEvent = RuntimeEvent;
 	type IdentificationTuple = pallet_session::historical::IdentificationTuple<Self>;
 	type OnOffenceHandler = Staking;
+	type SessionInfoProvider = Session;
+	type MaxSessionReportAge = ConstU32<6>;
 }
 
 impl<T> frame_system::offchain::SendTransactionTypes<T> for Test

frame/offences/src/lib.rs

@@ -17,7 +17,24 @@
 
 //! # Offences Pallet
 //!
-//! Tracks reported offences
+//! The offences pallet tracks reported offences using 3 key storage types:
+//!
+//! - [Reports]: A storage map of a report hash to its details
+//! - [ConcurrentReportsIndex]: A storage double map that stores a vector of reports
+//! 	for a specific [Kind] and [OpaqueTimeSlot]
+//! - [SessionReports]: A storage map that keeps a vector of active reports for a [SessionIndex].
+//!
+//! When a new offence is reported using [ReportOffence::report_offence], its `session_index` is
+//! first compared against the current `session_index`.
+//!
+//! If older than [Config::MaxSessionReportAge], the report is rejected right away.
+//!
+//! Else, all concurrent reports are loaded to determine the slash fraction and updated.
+//! The report is also inserted in [SessionReports] at this time.
+//! Finally, [Config::OnOffenceHandler] is called to handle any actions for this report.
+//!
+//! On the start of a new session, `clear_obsolete_reports` clears all reports
+//! that are older than [Config::MaxSessionReportAge].
 
 // Ensure we're `no_std` when compiling for Wasm.
 #![cfg_attr(not(feature = "std"), no_std)]
@@ -26,21 +43,21 @@ pub mod migration;
 mod mock;
 mod tests;
 
+use codec::{Decode, Encode};
 use core::marker::PhantomData;
-
-use codec::Encode;
-use frame_support::weights::Weight;
+use frame_support::{traits::Get, weights::Weight};
 use sp_runtime::{traits::Hash, Perbill};
+use sp_session::{SessionChangeListener, SessionInfoProvider};
 use sp_staking::{
 	offence::{Kind, Offence, OffenceDetails, OffenceError, OnOffenceHandler, ReportOffence},
-	SessionIndex,
+	EraIndex, SessionIndex,
 };
 use sp_std::prelude::*;
 
 pub use pallet::*;
 
 /// A binary blob which represents a SCALE codec-encoded `O::TimeSlot`.
-type OpaqueTimeSlot = Vec<u8>;
+pub type OpaqueTimeSlot = Vec<u8>;
 
 /// A type alias for a report identifier.
 type ReportIdOf<T> = <T as frame_system::Config>::Hash;
@@ -68,6 +85,14 @@ pub mod pallet {
 		type IdentificationTuple: Parameter;
 		/// A handler called for every offence report.
 		type OnOffenceHandler: OnOffenceHandler<Self::AccountId, Self::IdentificationTuple, Weight>;
+
+		/// Number of sessions for which a report is stored.
+		/// Once it gets older than this value, it gets cleaned up at the start of a new session.
+		#[pallet::constant]
+		type MaxSessionReportAge: Get<EraIndex>;
+
+		/// A trait that provides information about the current session
+		type SessionInfoProvider: SessionInfoProvider;
 	}
 
 	/// The primary structure that holds all offence records keyed by report identifiers.
@@ -92,6 +117,22 @@ pub mod pallet {
 		ValueQuery,
 	>;
 
+	/// A map that stores all reports along with
+	/// their kind and time slot info for a`SessionIndex`.
+	///
+	/// On start of a new session, all reports with a session index older than
+	/// `MaxSessionReportAge` are removed.
+	///
+	/// Note that time_slot is encoded as stored as an opaque type.
+	#[pallet::storage]
+	pub type SessionReports<T: Config> = StorageMap<
+		_,
+		Twox64Concat,
+		SessionIndex,
+		Vec<u8>, // Vec<(Kind, OpaqueTimeSlot, ReportIdOf<T>)>
+		ValueQuery,
+	>;
+
 	/// Events type.
 	#[pallet::event]
 	#[pallet::generate_deposit(pub(super) fn deposit_event)]
@@ -103,6 +144,37 @@ pub mod pallet {
 	}
 }
 
+impl<T: Config> Pallet<T> {
+	/// This is called at the start of each new session. Hence, only one session becomes
+	/// obsolete in this call, whose data gets cleared up here.
+	///
+	/// For example, if the `current_session_index` is 10 and `MaxSessionReportAge` is 6,
+	/// this clears all reports for `obsolete_session_index` 4.
+	fn clear_obsolete_reports(current_session_index: SessionIndex) {
+		if current_session_index <= T::MaxSessionReportAge::get() {
+			return
+		}
+
+		let obsolete_session_index = current_session_index - T::MaxSessionReportAge::get();
+
+		let session_reports = SessionReports::<T>::take(obsolete_session_index);
+		let session_reports =
+			Vec::<(Kind, OpaqueTimeSlot, ReportIdOf<T>)>::decode(&mut &session_reports[..])
+				.unwrap_or_default();
+
+		for (kind, time_slot, report_id) in &session_reports {
+			ConcurrentReportsIndex::<T>::remove(kind, time_slot);
+			Reports::<T>::remove(report_id);
+		}
+	}
+}
+
+impl<T: Config> SessionChangeListener for Pallet<T> {
+	fn on_session_change(session_index: SessionIndex) {
+		Self::clear_obsolete_reports(session_index)
+	}
+}
+
 impl<T, O> ReportOffence<T::AccountId, T::IdentificationTuple, O> for Pallet<T>
 where
 	T: Config,
@@ -112,10 +184,20 @@ where
 		let offenders = offence.offenders();
 		let time_slot = offence.time_slot();
 
+		let session_index = offence.session_index();
+		let current_session_index = T::SessionInfoProvider::current_session_index();
+
+		if current_session_index > T::MaxSessionReportAge::get() &&
+			session_index < current_session_index - T::MaxSessionReportAge::get()
+		{
+			return Err(OffenceError::ObsoleteReport)
+		}
+
 		// Go through all offenders in the offence report and find all offenders that were spotted
 		// in unique reports.
 		let TriageOutcome { concurrent_offenders } =
-			match Self::triage_offence_report::<O>(reporters, &time_slot, offenders) {
+			match Self::triage_offence_report::<O>(reporters, &time_slot, session_index, offenders)
+			{
 				Some(triage) => triage,
 				// The report contained only duplicates, so there is no need to slash again.
 				None => return Err(OffenceError::DuplicateReport),
@@ -167,9 +249,10 @@ impl<T: Config> Pallet<T> {
 	fn triage_offence_report<O: Offence<T::IdentificationTuple>>(
 		reporters: Vec<T::AccountId>,
 		time_slot: &O::TimeSlot,
+		session_index: SessionIndex,
 		offenders: Vec<T::IdentificationTuple>,
 	) -> Option<TriageOutcome<T>> {
-		let mut storage = ReportIndexStorage::<T, O>::load(time_slot);
+		let mut storage = ReportIndexStorage::<T, O>::load(time_slot, session_index);
 
 		let mut any_new = false;
 		for offender in offenders {
@@ -182,7 +265,7 @@ impl<T: Config> Pallet<T> {
 					OffenceDetails { offender, reporters: reporters.clone() },
 				);
 
-				storage.insert(report_id);
+				storage.insert(report_id, &time_slot);
 			}
 		}
 
@@ -216,28 +299,45 @@ struct TriageOutcome<T: Config> {
 #[must_use = "The changes are not saved without called `save`"]
 struct ReportIndexStorage<T: Config, O: Offence<T::IdentificationTuple>> {
 	opaque_time_slot: OpaqueTimeSlot,
+	session_index: SessionIndex,
 	concurrent_reports: Vec<ReportIdOf<T>>,
+	session_reports: Vec<(Kind, OpaqueTimeSlot, ReportIdOf<T>)>,
 	_phantom: PhantomData<O>,
 }
 
 impl<T: Config, O: Offence<T::IdentificationTuple>> ReportIndexStorage<T, O> {
 	/// Preload indexes from the storage for the specific `time_slot` and the kind of the offence.
-	fn load(time_slot: &O::TimeSlot) -> Self {
+	fn load(time_slot: &O::TimeSlot, session_index: SessionIndex) -> Self {
 		let opaque_time_slot = time_slot.encode();
 
+		let session_reports = SessionReports::<T>::get(session_index);
+		let session_reports =
+			Vec::<(Kind, OpaqueTimeSlot, ReportIdOf<T>)>::decode(&mut &session_reports[..])
+				.unwrap_or_default();
+
 		let concurrent_reports = <ConcurrentReportsIndex<T>>::get(&O::ID, &opaque_time_slot);
 
-		Self { opaque_time_slot, concurrent_reports, _phantom: Default::default() }
+		Self {
+			opaque_time_slot,
+			session_index,
+			concurrent_reports,
+			session_reports,
+			_phantom: Default::default(),
+		}
 	}
 
 	/// Insert a new report to the index.
-	fn insert(&mut self, report_id: ReportIdOf<T>) {
+	fn insert(&mut self, report_id: ReportIdOf<T>, time_slot: &O::TimeSlot) {
+		let opaque_time_slot = time_slot.encode();
+		self.session_reports.push((O::ID, opaque_time_slot, report_id));
+
 		// Update the list of concurrent reports.
 		self.concurrent_reports.push(report_id);
 	}
 
 	/// Dump the indexes to the storage.
 	fn save(self) {
+		SessionReports::<T>::set(self.session_index, self.session_reports.encode());
 		<ConcurrentReportsIndex<T>>::insert(
 			&O::ID,
 			&self.opaque_time_slot,