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/subsystem-util/Cargo.toml

@@ -22,6 +22,7 @@ polkadot-node-jaeger = { path = "../jaeger" }
 polkadot-node-metrics = { path = "../metrics" }
 polkadot-node-network-protocol = { path = "../network/protocol" }
 polkadot-primitives = { path = "../../primitives" }
+polkadot-node-primitives = { path = "../primitives" }
 polkadot-overseer = { path = "../overseer" }
 metered-channel = { path = "../metered-channel" }
 
@@ -35,3 +36,4 @@ env_logger = "0.9.0"
 futures = { version = "0.3.17", features = ["thread-pool"] }
 log = "0.4.13"
 polkadot-node-subsystem-test-helpers = { path = "../subsystem-test-helpers" }
+lazy_static = "1.4.0"

polkadot/node/subsystem-util/src/lib.rs

@@ -209,6 +209,7 @@ specialize_requests! {
 	fn request_assumed_validation_data(para_id: ParaId, expected_persisted_validation_data_hash: Hash) -> Option<(PersistedValidationData, ValidationCodeHash)>; AssumedValidationData;
 	fn request_session_index_for_child() -> SessionIndex; SessionIndexForChild;
 	fn request_validation_code(para_id: ParaId, assumption: OccupiedCoreAssumption) -> Option<ValidationCode>; ValidationCode;
+	fn request_validation_code_by_hash(validation_code_hash: ValidationCodeHash) -> Option<ValidationCode>; ValidationCodeByHash;
 	fn request_candidate_pending_availability(para_id: ParaId) -> Option<CommittedCandidateReceipt>; CandidatePendingAvailability;
 	fn request_candidate_events() -> Vec<CandidateEvent>; CandidateEvents;
 	fn request_session_info(index: SessionIndex) -> Option<SessionInfo>; SessionInfo;

polkadot/node/subsystem-util/src/rolling_session_window.rs

@@ -19,6 +19,7 @@
 //! This is useful for consensus components which need to stay up-to-date about recent sessions but don't
 //! care about the state of particular blocks.
 
+pub use polkadot_node_primitives::{new_session_window_size, SessionWindowSize};
 use polkadot_primitives::v1::{Hash, SessionIndex, SessionInfo};
 
 use futures::channel::oneshot;
@@ -27,6 +28,7 @@ use polkadot_node_subsystem::{
 	messages::{RuntimeApiMessage, RuntimeApiRequest},
 	overseer, SubsystemContext,
 };
+use thiserror::Error;
 
 /// Sessions unavailable in state to cache.
 #[derive(Debug)]
@@ -51,7 +53,7 @@ pub struct SessionsUnavailableInfo {
 }
 
 /// Sessions were unavailable to fetch from the state for some reason.
-#[derive(Debug)]
+#[derive(Debug, Error)]
 pub struct SessionsUnavailable {
 	/// The error kind.
 	kind: SessionsUnavailableKind,
@@ -59,16 +61,15 @@ pub struct SessionsUnavailable {
 	info: Option<SessionsUnavailableInfo>,
 }
 
+impl core::fmt::Display for SessionsUnavailable {
+	fn fmt(&self, f: &mut core::fmt::Formatter) -> Result<(), core::fmt::Error> {
+		write!(f, "Sessions unavailable: {:?}, info: {:?}", self.kind, self.info)
+	}
+}
+
 /// An indicated update of the rolling session window.
 #[derive(Debug, PartialEq, Clone)]
 pub enum SessionWindowUpdate {
-	/// The session window was just initialized to the current values.
-	Initialized {
-		/// The start of the window (inclusive).
-		window_start: SessionIndex,
-		/// The end of the window (inclusive).
-		window_end: SessionIndex,
-	},
 	/// The session window was just advanced from one range to a new one.
 	Advanced {
 		/// The previous start of the window (inclusive).
@@ -85,49 +86,63 @@ pub enum SessionWindowUpdate {
 }
 
 /// A rolling window of sessions and cached session info.
-#[derive(Default)]
 pub struct RollingSessionWindow {
-	earliest_session: Option<SessionIndex>,
+	earliest_session: SessionIndex,
 	session_info: Vec<SessionInfo>,
-	window_size: SessionIndex,
+	window_size: SessionWindowSize,
 }
 
 impl RollingSessionWindow {
 	/// Initialize a new session info cache with the given window size.
-	pub fn new(window_size: SessionIndex) -> Self {
-		RollingSessionWindow { earliest_session: None, session_info: Vec::new(), window_size }
+	pub async fn new(
+		ctx: &mut (impl SubsystemContext + overseer::SubsystemContext),
+		window_size: SessionWindowSize,
+		block_hash: Hash,
+	) -> Result<Self, SessionsUnavailable> {
+		let session_index = get_session_index_for_head(ctx, block_hash).await?;
+
+		let window_start = session_index.saturating_sub(window_size.get() - 1);
+
+		match load_all_sessions(ctx, block_hash, window_start, session_index).await {
+			Err(kind) => Err(SessionsUnavailable {
+				kind,
+				info: Some(SessionsUnavailableInfo {
+					window_start,
+					window_end: session_index,
+					block_hash,
+				}),
+			}),
+			Ok(s) => Ok(Self { earliest_session: window_start, session_info: s, window_size }),
+		}
 	}
 
 	/// Initialize a new session info cache with the given window size and
 	/// initial data.
 	pub fn with_session_info(
-		window_size: SessionIndex,
+		window_size: SessionWindowSize,
 		earliest_session: SessionIndex,
 		session_info: Vec<SessionInfo>,
 	) -> Self {
-		RollingSessionWindow { earliest_session: Some(earliest_session), session_info, window_size }
+		RollingSessionWindow { earliest_session, session_info, window_size }
 	}
 
 	/// Access the session info for the given session index, if stored within the window.
 	pub fn session_info(&self, index: SessionIndex) -> Option<&SessionInfo> {
-		self.earliest_session.and_then(|earliest| {
-			if index < earliest {
-				None
-			} else {
-				self.session_info.get((index - earliest) as usize)
-			}
-		})
+		if index < self.earliest_session {
+			None
+		} else {
+			self.session_info.get((index - self.earliest_session) as usize)
+		}
 	}
 
-	/// Access the index of the earliest session, if the window is not empty.
-	pub fn earliest_session(&self) -> Option<SessionIndex> {
-		self.earliest_session.clone()
-	}
-
-	/// Access the index of the latest session, if the window is not empty.
-	pub fn latest_session(&self) -> Option<SessionIndex> {
+	/// Access the index of the earliest session.
+	pub fn earliest_session(&self) -> SessionIndex {
 		self.earliest_session
-			.map(|earliest| earliest + (self.session_info.len() as SessionIndex).saturating_sub(1))
+	}
+
+	/// Access the index of the latest session.
+	pub fn latest_session(&self) -> SessionIndex {
+		self.earliest_session + (self.session_info.len() as SessionIndex).saturating_sub(1)
 	}
 
 	/// When inspecting a new import notification, updates the session info cache to match
@@ -142,116 +157,86 @@ impl RollingSessionWindow {
 		ctx: &mut (impl SubsystemContext + overseer::SubsystemContext),
 		block_hash: Hash,
 	) -> Result<SessionWindowUpdate, SessionsUnavailable> {
-		if self.window_size == 0 {
+		let session_index = get_session_index_for_head(ctx, block_hash).await?;
+
+		let old_window_start = self.earliest_session;
+
+		let latest = self.latest_session();
+
+		// Either cached or ancient.
+		if session_index <= latest {
 			return Ok(SessionWindowUpdate::Unchanged)
 		}
 
-		let session_index = {
-			let (s_tx, s_rx) = oneshot::channel();
+		let old_window_end = latest;
 
-			// We're requesting session index of a child to populate the cache in advance.
-			ctx.send_message(RuntimeApiMessage::Request(
-				block_hash,
-				RuntimeApiRequest::SessionIndexForChild(s_tx),
-			))
-			.await;
+		let window_start = session_index.saturating_sub(self.window_size.get() - 1);
 
-			match s_rx.await {
-				Ok(Ok(s)) => s,
-				Ok(Err(e)) =>
-					return Err(SessionsUnavailable {
-						kind: SessionsUnavailableKind::RuntimeApi(e),
-						info: None,
-					}),
-				Err(e) =>
-					return Err(SessionsUnavailable {
-						kind: SessionsUnavailableKind::RuntimeApiUnavailable(e),
-						info: None,
-					}),
-			}
-		};
+		// keep some of the old window, if applicable.
+		let overlap_start = window_start.saturating_sub(old_window_start);
 
-		match self.earliest_session {
-			None => {
-				// First block processed on start-up.
+		let fresh_start = if latest < window_start { window_start } else { latest + 1 };
 
-				let window_start = session_index.saturating_sub(self.window_size - 1);
+		match load_all_sessions(ctx, block_hash, fresh_start, session_index).await {
+			Err(kind) => Err(SessionsUnavailable {
+				kind,
+				info: Some(SessionsUnavailableInfo {
+					window_start: fresh_start,
+					window_end: session_index,
+					block_hash,
+				}),
+			}),
+			Ok(s) => {
+				let update = SessionWindowUpdate::Advanced {
+					prev_window_start: old_window_start,
+					prev_window_end: old_window_end,
+					new_window_start: window_start,
+					new_window_end: session_index,
+				};
 
-				match load_all_sessions(ctx, block_hash, window_start, session_index).await {
-					Err(kind) => Err(SessionsUnavailable {
-						kind,
-						info: Some(SessionsUnavailableInfo {
-							window_start,
-							window_end: session_index,
-							block_hash,
-						}),
-					}),
-					Ok(s) => {
-						let update = SessionWindowUpdate::Initialized {
-							window_start,
-							window_end: session_index,
-						};
+				let outdated = std::cmp::min(overlap_start as usize, self.session_info.len());
+				self.session_info.drain(..outdated);
+				self.session_info.extend(s);
+				// we need to account for this case:
+				// window_start ................................... session_index
+				//              old_window_start ........... latest
+				let new_earliest = std::cmp::max(window_start, old_window_start);
+				self.earliest_session = new_earliest;
 
-						self.earliest_session = Some(window_start);
-						self.session_info = s;
-
-						Ok(update)
-					},
-				}
-			},
-			Some(old_window_start) => {
-				let latest =
-					self.latest_session().expect("latest always exists if earliest does; qed");
-
-				// Either cached or ancient.
-				if session_index <= latest {
-					return Ok(SessionWindowUpdate::Unchanged)
-				}
-
-				let old_window_end = latest;
-
-				let window_start = session_index.saturating_sub(self.window_size - 1);
-
-				// keep some of the old window, if applicable.
-				let overlap_start = window_start.saturating_sub(old_window_start);
-
-				let fresh_start = if latest < window_start { window_start } else { latest + 1 };
-
-				match load_all_sessions(ctx, block_hash, fresh_start, session_index).await {
-					Err(kind) => Err(SessionsUnavailable {
-						kind,
-						info: Some(SessionsUnavailableInfo {
-							window_start: fresh_start,
-							window_end: session_index,
-							block_hash,
-						}),
-					}),
-					Ok(s) => {
-						let update = SessionWindowUpdate::Advanced {
-							prev_window_start: old_window_start,
-							prev_window_end: old_window_end,
-							new_window_start: window_start,
-							new_window_end: session_index,
-						};
-
-						let outdated =
-							std::cmp::min(overlap_start as usize, self.session_info.len());
-						self.session_info.drain(..outdated);
-						self.session_info.extend(s);
-						// we need to account for this case:
-						// window_start ................................... session_index
-						//              old_window_start ........... latest
-						let new_earliest = std::cmp::max(window_start, old_window_start);
-						self.earliest_session = Some(new_earliest);
-
-						Ok(update)
-					},
-				}
+				Ok(update)
 			},
 		}
 	}
 }
 
+async fn get_session_index_for_head(
+	ctx: &mut (impl SubsystemContext + overseer::SubsystemContext),
+	block_hash: Hash,
+) -> Result<SessionIndex, SessionsUnavailable> {
+	let (s_tx, s_rx) = oneshot::channel();
+
+	// We're requesting session index of a child to populate the cache in advance.
+	ctx.send_message(RuntimeApiMessage::Request(
+		block_hash,
+		RuntimeApiRequest::SessionIndexForChild(s_tx),
+	))
+	.await;
+
+	match s_rx.await {
+		Ok(Ok(s)) => Ok(s),
+		Ok(Err(e)) =>
+			return Err(SessionsUnavailable {
+				kind: SessionsUnavailableKind::RuntimeApi(e),
+				info: None,
+			}),
+		Err(e) =>
+			return Err(SessionsUnavailable {
+				kind: SessionsUnavailableKind::RuntimeApiUnavailable(e),
+				info: None,
+			}),
+	}
+}
+
 async fn load_all_sessions(
 	ctx: &mut (impl SubsystemContext + overseer::SubsystemContext),
 	block_hash: Hash,
@@ -289,7 +274,7 @@ mod tests {
 	use polkadot_primitives::v1::Header;
 	use sp_core::testing::TaskExecutor;
 
-	const TEST_WINDOW_SIZE: SessionIndex = 6;
+	pub const TEST_WINDOW_SIZE: SessionWindowSize = new_session_window_size!(6);
 
 	fn dummy_session_info(index: SessionIndex) -> SessionInfo {
 		SessionInfo {
@@ -309,7 +294,7 @@ mod tests {
 	fn cache_session_info_test(
 		expected_start_session: SessionIndex,
 		session: SessionIndex,
-		mut window: RollingSessionWindow,
+		window: Option<RollingSessionWindow>,
 		expect_requests_from: SessionIndex,
 	) {
 		let header = Header {
@@ -328,9 +313,15 @@ mod tests {
 
 		let test_fut = {
 			Box::pin(async move {
-				window.cache_session_info_for_head(&mut ctx, hash).await.unwrap();
-
-				assert_eq!(window.earliest_session, Some(expected_start_session));
+				let window = match window {
+					None =>
+						RollingSessionWindow::new(&mut ctx, TEST_WINDOW_SIZE, hash).await.unwrap(),
+					Some(mut window) => {
+						window.cache_session_info_for_head(&mut ctx, hash).await.unwrap();
+						window
+					},
+				};
+				assert_eq!(window.earliest_session, expected_start_session);
 				assert_eq!(
 					window.session_info,
 					(expected_start_session..=session).map(dummy_session_info).collect::<Vec<_>>(),
@@ -370,34 +361,34 @@ mod tests {
 
 	#[test]
 	fn cache_session_info_first_early() {
-		cache_session_info_test(0, 1, RollingSessionWindow::new(TEST_WINDOW_SIZE), 0);
+		cache_session_info_test(0, 1, None, 0);
 	}
 
 	#[test]
 	fn cache_session_info_does_not_underflow() {
 		let window = RollingSessionWindow {
-			earliest_session: Some(1),
+			earliest_session: 1,
 			session_info: vec![dummy_session_info(1)],
 			window_size: TEST_WINDOW_SIZE,
 		};
 
-		cache_session_info_test(1, 2, window, 2);
+		cache_session_info_test(1, 2, Some(window), 2);
 	}
 
 	#[test]
 	fn cache_session_info_first_late() {
 		cache_session_info_test(
-			(100 as SessionIndex).saturating_sub(TEST_WINDOW_SIZE - 1),
+			(100 as SessionIndex).saturating_sub(TEST_WINDOW_SIZE.get() - 1),
 			100,
-			RollingSessionWindow::new(TEST_WINDOW_SIZE),
-			(100 as SessionIndex).saturating_sub(TEST_WINDOW_SIZE - 1),
+			None,
+			(100 as SessionIndex).saturating_sub(TEST_WINDOW_SIZE.get() - 1),
 		);
 	}
 
 	#[test]
 	fn cache_session_info_jump() {
 		let window = RollingSessionWindow {
-			earliest_session: Some(50),
+			earliest_session: 50,
 			session_info: vec![
 				dummy_session_info(50),
 				dummy_session_info(51),
@@ -407,43 +398,43 @@ mod tests {
 		};
 
 		cache_session_info_test(
-			(100 as SessionIndex).saturating_sub(TEST_WINDOW_SIZE - 1),
+			(100 as SessionIndex).saturating_sub(TEST_WINDOW_SIZE.get() - 1),
 			100,
-			window,
-			(100 as SessionIndex).saturating_sub(TEST_WINDOW_SIZE - 1),
+			Some(window),
+			(100 as SessionIndex).saturating_sub(TEST_WINDOW_SIZE.get() - 1),
 		);
 	}
 
 	#[test]
 	fn cache_session_info_roll_full() {
-		let start = 99 - (TEST_WINDOW_SIZE - 1);
+		let start = 99 - (TEST_WINDOW_SIZE.get() - 1);
 		let window = RollingSessionWindow {
-			earliest_session: Some(start),
+			earliest_session: start,
 			session_info: (start..=99).map(dummy_session_info).collect(),
 			window_size: TEST_WINDOW_SIZE,
 		};
 
 		cache_session_info_test(
-			(100 as SessionIndex).saturating_sub(TEST_WINDOW_SIZE - 1),
+			(100 as SessionIndex).saturating_sub(TEST_WINDOW_SIZE.get() - 1),
 			100,
-			window,
+			Some(window),
 			100, // should only make one request.
 		);
 	}
 
 	#[test]
 	fn cache_session_info_roll_many_full() {
-		let start = 97 - (TEST_WINDOW_SIZE - 1);
+		let start = 97 - (TEST_WINDOW_SIZE.get() - 1);
 		let window = RollingSessionWindow {
-			earliest_session: Some(start),
+			earliest_session: start,
 			session_info: (start..=97).map(dummy_session_info).collect(),
 			window_size: TEST_WINDOW_SIZE,
 		};
 
 		cache_session_info_test(
-			(100 as SessionIndex).saturating_sub(TEST_WINDOW_SIZE - 1),
+			(100 as SessionIndex).saturating_sub(TEST_WINDOW_SIZE.get() - 1),
 			100,
-			window,
+			Some(window),
 			98,
 		);
 	}
@@ -452,13 +443,16 @@ mod tests {
 	fn cache_session_info_roll_early() {
 		let start = 0;
 		let window = RollingSessionWindow {
-			earliest_session: Some(start),
+			earliest_session: start,
 			session_info: (0..=1).map(dummy_session_info).collect(),
 			window_size: TEST_WINDOW_SIZE,
 		};
 
 		cache_session_info_test(
-			0, 2, window, 2, // should only make one request.
+			0,
+			2,
+			Some(window),
+			2, // should only make one request.
 		);
 	}
 
@@ -466,18 +460,18 @@ mod tests {
 	fn cache_session_info_roll_many_early() {
 		let start = 0;
 		let window = RollingSessionWindow {
-			earliest_session: Some(start),
+			earliest_session: start,
 			session_info: (0..=1).map(dummy_session_info).collect(),
 			window_size: TEST_WINDOW_SIZE,
 		};
 
-		cache_session_info_test(0, 3, window, 2);
+		cache_session_info_test(0, 3, Some(window), 2);
 	}
 
 	#[test]
 	fn any_session_unavailable_for_caching_means_no_change() {
 		let session: SessionIndex = 6;
-		let start_session = session.saturating_sub(TEST_WINDOW_SIZE - 1);
+		let start_session = session.saturating_sub(TEST_WINDOW_SIZE.get() - 1);
 
 		let header = Header {
 			digest: Default::default(),
@@ -490,13 +484,11 @@ mod tests {
 		let pool = TaskExecutor::new();
 		let (mut ctx, mut handle) = make_subsystem_context::<(), _>(pool.clone());
 
-		let mut window = RollingSessionWindow::new(TEST_WINDOW_SIZE);
 		let hash = header.hash();
 
 		let test_fut = {
 			Box::pin(async move {
-				let res = window.cache_session_info_for_head(&mut ctx, hash).await;
-
+				let res = RollingSessionWindow::new(&mut ctx, TEST_WINDOW_SIZE, hash).await;
 				assert!(res.is_err());
 			})
 		};
@@ -551,14 +543,14 @@ mod tests {
 		let pool = TaskExecutor::new();
 		let (mut ctx, mut handle) = make_subsystem_context::<(), _>(pool.clone());
 
-		let mut window = RollingSessionWindow::new(TEST_WINDOW_SIZE);
 		let hash = header.hash();
 
 		let test_fut = {
 			Box::pin(async move {
-				window.cache_session_info_for_head(&mut ctx, hash).await.unwrap();
+				let window =
+					RollingSessionWindow::new(&mut ctx, TEST_WINDOW_SIZE, hash).await.unwrap();
 
-				assert_eq!(window.earliest_session, Some(session));
+				assert_eq!(window.earliest_session, session);
 				assert_eq!(window.session_info, vec![dummy_session_info(session)]);
 			})
 		};

polkadot/node/subsystem-util/src/runtime/error.rs

@@ -48,11 +48,11 @@ pub enum Fatal {
 pub enum NonFatal {
 	/// Some request to the runtime failed.
 	/// For example if we prune a block we're requesting info about.
-	#[error("Runtime API error")]
+	#[error("Runtime API error {0}")]
 	RuntimeRequest(RuntimeApiError),
 
 	/// We tried fetching a session info which was not available.
-	#[error("There was no session with the given index")]
+	#[error("There was no session with the given index {0}")]
 	NoSuchSession(SessionIndex),
 }
 

polkadot/node/subsystem-util/src/runtime/mod.rs

@@ -27,13 +27,14 @@ use sp_keystore::{CryptoStore, SyncCryptoStorePtr};
 
 use polkadot_node_subsystem::{SubsystemContext, SubsystemSender};
 use polkadot_primitives::v1::{
-	CoreState, EncodeAs, GroupIndex, GroupRotationInfo, Hash, OccupiedCore, SessionIndex,
-	SessionInfo, Signed, SigningContext, UncheckedSigned, ValidatorId, ValidatorIndex,
+	CandidateEvent, CoreState, EncodeAs, GroupIndex, GroupRotationInfo, Hash, OccupiedCore,
+	SessionIndex, SessionInfo, Signed, SigningContext, UncheckedSigned, ValidationCode,
+	ValidationCodeHash, ValidatorId, ValidatorIndex,
 };
 
 use crate::{
-	request_availability_cores, request_session_index_for_child, request_session_info,
-	request_validator_groups,
+	request_availability_cores, request_candidate_events, request_session_index_for_child,
+	request_session_info, request_validation_code_by_hash, request_validator_groups,
 };
 
 /// Errors that can happen on runtime fetches.
@@ -300,3 +301,27 @@ where
 		recv_runtime(request_validator_groups(relay_parent, ctx.sender()).await).await?;
 	Ok(info)
 }
+
+/// Get `CandidateEvent`s for the given `relay_parent`.
+pub async fn get_candidate_events<Sender>(
+	sender: &mut Sender,
+	relay_parent: Hash,
+) -> Result<Vec<CandidateEvent>>
+where
+	Sender: SubsystemSender,
+{
+	recv_runtime(request_candidate_events(relay_parent, sender).await).await
+}
+
+/// Fetch `ValidationCode` by hash from the runtime.
+pub async fn get_validation_code_by_hash<Sender>(
+	sender: &mut Sender,
+	relay_parent: Hash,
+	validation_code_hash: ValidationCodeHash,
+) -> Result<Option<ValidationCode>>
+where
+	Sender: SubsystemSender,
+{
+	recv_runtime(request_validation_code_by_hash(relay_parent, validation_code_hash, sender).await)
+		.await
+}