Dispute spam protection (#4134)

* Mostly notes.

* Better error messages.

* Introduce Fatal/NonFatal + drop back channel participation

- Fatal/NonFatal - in order to make it easier to use utility functions.
- We drop the back channel in dispute participation as it won't be
needed any more.

* Better error messages.

* Utility function for receiving `CandidateEvent`s.

* Ordering module typechecks.

* cargo fmt

* Prepare spam slots module.

* Implement SpamSlots mechanism.

* Implement queues.

* cargo fmt

* Participation.

* Participation taking shape.

* Finish participation.

* cargo fmt

* Cleanup.

* WIP: Cleanup + Integration.

* Make `RollingSessionWindow` initialized by default.

* Make approval voting typecheck.

* Get rid of lazy_static & fix approval voting tests

* Move `SessionWindowSize` to node primitives.

* Implement dispute coordinator initialization.

* cargo fmt

* Make queues return error instead of boolean.

* Initialized: WIP

* Introduce chain api for getting finalized block.

* Fix ordering to only prune candidates on finalized events.

* Pruning of old sessions in spam slots.

* New import logic.

* Make everything typecheck.

* Fix warnings.

* Get rid of obsolete dispute-participation.

* Fixes.

* Add back accidentelly deleted Cargo.lock

* Deliver disputes in an ordered fashion.

* Add module docs for errors

* Use type synonym.

* hidden docs.

* Fix overseer tests.

* Ordering provider taking `CandidateReceipt`.

... To be kicked on one next commit.

* Fix ordering to use relay_parent

as included block is not unique per candidate.

* Add comment in ordering.rs.

* Take care of duplicate entries in queues.

* Better spam slots.

* Review remarks + docs.

* Fix db tests.

* Participation tests.

* Also scrape votes on first leaf for good measure.

* Make tests typecheck.

* Spelling.

* Only participate in actual disputes, not on every import.

* Don't account backing votes to spam slots.

* Fix more tests.

* Don't participate if we don't have keys.

* Fix tests, typos and warnings.

* Fix merge error.

* Spelling fixes.

* Add missing docs.

* Queue tests.

* More tests.

* Add metrics + don't short circuit import.

* Basic test for ordering provider.

* Import fix.

* Remove dead link.

* One more dead link.

Co-authored-by: Lldenaurois <Ljdenaurois@gmail.com>

polkadot/node/core/approval-voting/src/import.rs

@@ -76,7 +76,7 @@ struct ImportedBlockInfo {
 }
 
 struct ImportedBlockInfoEnv<'a> {
-	session_window: &'a RollingSessionWindow,
+	session_window: &'a Option<RollingSessionWindow>,
 	assignment_criteria: &'a (dyn AssignmentCriteria + Send + Sync),
 	keystore: &'a LocalKeystore,
 }
@@ -133,7 +133,11 @@ async fn imported_block_info(
 			Err(_) => return Ok(None),
 		};
 
-		if env.session_window.earliest_session().map_or(true, |e| session_index < e) {
+		if env
+			.session_window
+			.as_ref()
+			.map_or(true, |s| session_index < s.earliest_session())
+		{
 			tracing::debug!(
 				target: LOG_TARGET,
 				"Block {} is from ancient session {}. Skipping",
@@ -180,7 +184,8 @@ async fn imported_block_info(
 		}
 	};
 
-	let session_info = match env.session_window.session_info(session_index) {
+	let session_info = match env.session_window.as_ref().and_then(|s| s.session_info(session_index))
+	{
 		Some(s) => s,
 		None => {
 			tracing::debug!(
@@ -324,7 +329,7 @@ pub(crate) async fn handle_new_head(
 		}
 	};
 
-	match state.session_window.cache_session_info_for_head(ctx, head).await {
+	match state.cache_session_info_for_head(ctx, head).await {
 		Err(e) => {
 			tracing::debug!(
 				target: LOG_TARGET,
@@ -335,7 +340,7 @@ pub(crate) async fn handle_new_head(
 
 			return Ok(Vec::new())
 		},
-		Ok(a @ SessionWindowUpdate::Advanced { .. }) => {
+		Ok(Some(a @ SessionWindowUpdate::Advanced { .. })) => {
 			tracing::info!(
 				target: LOG_TARGET,
 				update = ?a,
@@ -431,8 +436,9 @@ pub(crate) async fn handle_new_head(
 
 		let session_info = state
 			.session_window
-			.session_info(session_index)
-			.expect("imported_block_info requires session to be available; qed");
+			.as_ref()
+			.and_then(|s| s.session_info(session_index))
+			.expect("imported_block_info requires session info to be available; qed");
 
 		let (block_tick, no_show_duration) = {
 			let block_tick = slot_number_to_tick(state.slot_duration_millis, slot);
@@ -608,7 +614,7 @@ pub(crate) mod tests {
 
 	fn blank_state() -> State {
 		State {
-			session_window: RollingSessionWindow::new(APPROVAL_SESSIONS),
+			session_window: None,
 			keystore: Arc::new(LocalKeystore::in_memory()),
 			slot_duration_millis: 6_000,
 			clock: Box::new(MockClock::default()),
@@ -618,11 +624,11 @@ pub(crate) mod tests {
 
 	fn single_session_state(index: SessionIndex, info: SessionInfo) -> State {
 		State {
-			session_window: RollingSessionWindow::with_session_info(
+			session_window: Some(RollingSessionWindow::with_session_info(
 				APPROVAL_SESSIONS,
 				index,
 				vec![info],
-			),
+			)),
 			..blank_state()
 		}
 	}
@@ -740,7 +746,7 @@ pub(crate) mod tests {
 			let header = header.clone();
 			Box::pin(async move {
 				let env = ImportedBlockInfoEnv {
-					session_window: &session_window,
+					session_window: &Some(session_window),
 					assignment_criteria: &MockAssignmentCriteria,
 					keystore: &LocalKeystore::in_memory(),
 				};
@@ -849,7 +855,7 @@ pub(crate) mod tests {
 			let header = header.clone();
 			Box::pin(async move {
 				let env = ImportedBlockInfoEnv {
-					session_window: &session_window,
+					session_window: &Some(session_window),
 					assignment_criteria: &MockAssignmentCriteria,
 					keystore: &LocalKeystore::in_memory(),
 				};
@@ -942,7 +948,7 @@ pub(crate) mod tests {
 			.collect::<Vec<_>>();
 
 		let test_fut = {
-			let session_window = RollingSessionWindow::new(APPROVAL_SESSIONS);
+			let session_window = None;
 
 			let header = header.clone();
 			Box::pin(async move {
@@ -1037,11 +1043,11 @@ pub(crate) mod tests {
 				.map(|(r, c, g)| (r.hash(), r.clone(), *c, *g))
 				.collect::<Vec<_>>();
 
-			let session_window = RollingSessionWindow::with_session_info(
+			let session_window = Some(RollingSessionWindow::with_session_info(
 				APPROVAL_SESSIONS,
 				session,
 				vec![session_info],
-			);
+			));
 
 			let header = header.clone();
 			Box::pin(async move {

polkadot/node/core/approval-voting/src/lib.rs

@@ -44,7 +44,10 @@ use polkadot_node_subsystem::{
 };
 use polkadot_node_subsystem_util::{
 	metrics::{self, prometheus},
-	rolling_session_window::RollingSessionWindow,
+	rolling_session_window::{
+		new_session_window_size, RollingSessionWindow, SessionWindowSize, SessionWindowUpdate,
+		SessionsUnavailable,
+	},
 	TimeoutExt,
 };
 use polkadot_primitives::v1::{
@@ -92,7 +95,8 @@ use crate::{
 #[cfg(test)]
 mod tests;
 
-const APPROVAL_SESSIONS: SessionIndex = 6;
+pub const APPROVAL_SESSIONS: SessionWindowSize = new_session_window_size!(6);
+
 const APPROVAL_CHECKING_TIMEOUT: Duration = Duration::from_secs(120);
 const APPROVAL_CACHE_SIZE: usize = 1024;
 const TICK_TOO_FAR_IN_FUTURE: Tick = 20; // 10 seconds.
@@ -568,7 +572,7 @@ impl CurrentlyCheckingSet {
 }
 
 struct State {
-	session_window: RollingSessionWindow,
+	session_window: Option<RollingSessionWindow>,
 	keystore: Arc<LocalKeystore>,
 	slot_duration_millis: u64,
 	clock: Box<dyn Clock + Send + Sync>,
@@ -577,9 +581,30 @@ struct State {
 
 impl State {
 	fn session_info(&self, i: SessionIndex) -> Option<&SessionInfo> {
-		self.session_window.session_info(i)
+		self.session_window.as_ref().and_then(|w| w.session_info(i))
 	}
 
+	/// Bring `session_window` up to date.
+	pub async fn cache_session_info_for_head(
+		&mut self,
+		ctx: &mut (impl SubsystemContext + overseer::SubsystemContext),
+		head: Hash,
+	) -> Result<Option<SessionWindowUpdate>, SessionsUnavailable> {
+		let session_window = self.session_window.take();
+		match session_window {
+			None => {
+				self.session_window =
+					Some(RollingSessionWindow::new(ctx, APPROVAL_SESSIONS, head).await?);
+				Ok(None)
+			},
+			Some(mut session_window) => {
+				let r =
+					session_window.cache_session_info_for_head(ctx, head).await.map(Option::Some);
+				self.session_window = Some(session_window);
+				r
+			},
+		}
+	}
 	// Compute the required tranches for approval for this block and candidate combo.
 	// Fails if there is no approval entry for the block under the candidate or no candidate entry
 	// under the block, or if the session is out of bounds.
@@ -671,7 +696,7 @@ where
 	B: Backend,
 {
 	let mut state = State {
-		session_window: RollingSessionWindow::new(APPROVAL_SESSIONS),
+		session_window: None,
 		keystore: subsystem.keystore,
 		slot_duration_millis: subsystem.slot_duration_millis,
 		clock,