Runtime API for checking validation outputs (#1842)

* annoying whitespaces

* update guide

Add `CheckValidationOutputs` runtime api and also change the
candidate-validation stuff

* promote ValidationOutputs to global primitives

i.e. move it from node specific primitives to global v1 primitives. This
will be needed when we share it later in the runtime inclusion module

* refactor acceptance checks in the inclusion module

factor out the common code to share it during the block inclusion and
for the forthcoming CheckValidationOutputs runtime api.

Also note that the acceptance criteria was updated to incorporate checks
that exist now in candidate-validation

* plumb the runtime api outside

* extract validation_data from ValidationOutputs

* use runtime-api to check validation outputs

apart from that refactor, update docs and tidy a bit

* Update the maxium code size

This is to fix a test that performs an upgrade.

polkadot/runtime/parachains/src/inclusion.rs

@@ -131,8 +131,12 @@ decl_error! {
 		WrongCollator,
 		/// Scheduled cores out of order.
 		ScheduledOutOfOrder,
+		/// Head data exceeds the configured maximum.
+		HeadDataTooLarge,
 		/// Code upgrade prematurely.
 		PrematureCodeUpgrade,
+		/// Output code is too large
+		NewCodeTooLarge,
 		/// Candidate not in parent context.
 		CandidateNotInParentContext,
 		/// The bitfield contains a bit relating to an unassigned availability core.
@@ -345,9 +349,7 @@ impl<T: Trait> Module<T> {
 		candidates: Vec<BackedCandidate<T::Hash>>,
 		scheduled: Vec<CoreAssignment>,
 		group_validators: impl Fn(GroupIndex) -> Option<Vec<ValidatorIndex>>,
-	)
-		-> Result<Vec<CoreIndex>, DispatchError>
-	{
+	) -> Result<Vec<CoreIndex>, DispatchError> {
 		ensure!(candidates.len() <= scheduled.len(), Error::<T>::UnscheduledCandidate);
 
 		if scheduled.is_empty() {
@@ -356,9 +358,7 @@ impl<T: Trait> Module<T> {
 
 		let validators = Validators::get();
 		let parent_hash = <frame_system::Module<T>>::parent_hash();
-		let config = <configuration::Module<T>>::config();
-		let now = <frame_system::Module<T>>::block_number();
-		let relay_parent_number = now - One::one();
+		let check_cx = CandidateCheckContext::<T>::new();
 
 		// do all checks before writing storage.
 		let core_indices = {
@@ -400,27 +400,17 @@ impl<T: Trait> Module<T> {
 					candidate.descriptor().relay_parent == parent_hash,
 					Error::<T>::CandidateNotInParentContext,
 				);
-
-				// if any, the code upgrade attempt is allowed.
-				let valid_upgrade_attempt =
-					candidate.candidate.commitments.new_validation_code.is_none() ||
-					<paras::Module<T>>::last_code_upgrade(para_id, true)
-						.map_or(
-							true,
-							|last| last <= relay_parent_number &&
-								relay_parent_number.saturating_sub(last)
-									>= config.validation_upgrade_frequency,
-						);
-
-				ensure!(
-					valid_upgrade_attempt,
-					Error::<T>::PrematureCodeUpgrade,
-				);
 				ensure!(
 					candidate.descriptor().check_collator_signature().is_ok(),
 					Error::<T>::NotCollatorSigned,
 				);
 
+				check_cx.check_validation_outputs(
+					para_id,
+					&candidate.candidate.commitments.head_data,
+					&candidate.candidate.commitments.new_validation_code,
+				)?;
+
 				for (i, assignment) in scheduled[skip..].iter().enumerate() {
 					check_assignment_in_order(assignment)?;
 
@@ -498,7 +488,7 @@ impl<T: Trait> Module<T> {
 					false,
 					Error::<T>::UnscheduledCandidate,
 				);
-			};
+			}
 
 			// check remainder of scheduled cores, if any.
 			for assignment in scheduled[skip..].iter() {
@@ -530,8 +520,8 @@ impl<T: Trait> Module<T> {
 				core,
 				descriptor,
 				availability_votes,
-				relay_parent_number,
-				backed_in_number: now,
+				relay_parent_number: check_cx.relay_parent_number,
+				backed_in_number: check_cx.now,
 			});
 			<PendingAvailabilityCommitments>::insert(&para_id, commitments);
 		}
@@ -539,6 +529,20 @@ impl<T: Trait> Module<T> {
 		Ok(core_indices)
 	}
 
+	/// Run the acceptance criteria checks on the given candidate commitments.
+	///
+	/// Returns an 'Err` if any of the checks doesn't pass.
+	pub(crate) fn check_validation_outputs(
+		para_id: ParaId,
+		validation_outputs: primitives::v1::ValidationOutputs,
+	) -> Result<(), DispatchError> {
+		CandidateCheckContext::<T>::new().check_validation_outputs(
+			para_id,
+			&validation_outputs.head_data,
+			&validation_outputs.new_validation_code,
+		)
+	}
+
 	fn enact_candidate(
 		relay_parent_number: T::BlockNumber,
 		receipt: CommittedCandidateReceipt<T::Hash>,
@@ -654,6 +658,57 @@ const fn availability_threshold(n_validators: usize) -> usize {
 	threshold
 }
 
+/// A collection of data required for checking a candidate.
+struct CandidateCheckContext<T: Trait> {
+	config: configuration::HostConfiguration<T::BlockNumber>,
+	now: T::BlockNumber,
+	relay_parent_number: T::BlockNumber,
+}
+
+impl<T: Trait> CandidateCheckContext<T> {
+	fn new() -> Self {
+		let now = <frame_system::Module<T>>::block_number();
+		Self {
+			config: <configuration::Module<T>>::config(),
+			now,
+			relay_parent_number: now - One::one(),
+		}
+	}
+
+	/// Check the given outputs after candidate validation on whether it passes the acceptance
+	/// criteria.
+	fn check_validation_outputs(
+		&self,
+		para_id: ParaId,
+		head_data: &HeadData,
+		new_validation_code: &Option<primitives::v1::ValidationCode>,
+	) -> Result<(), DispatchError> {
+		ensure!(
+			head_data.0.len() <= self.config.max_head_data_size as _,
+			Error::<T>::HeadDataTooLarge
+		);
+
+		// if any, the code upgrade attempt is allowed.
+		if let Some(new_validation_code) = new_validation_code {
+			let valid_upgrade_attempt = <paras::Module<T>>::last_code_upgrade(para_id, true)
+				.map_or(true, |last| {
+					last <= self.relay_parent_number
+						&& self.relay_parent_number.saturating_sub(last)
+							>= self.config.validation_upgrade_frequency
+				});
+			ensure!(valid_upgrade_attempt, Error::<T>::PrematureCodeUpgrade);
+			ensure!(
+				new_validation_code.0.len() <= self.config.max_code_size as _,
+				Error::<T>::NewCodeTooLarge
+			);
+		}
+
+		// TODO: messaging acceptance criteria rules will go here.
+
+		Ok(())
+	}
+}
+
 #[cfg(test)]
 mod tests {
 	use super::*;
@@ -682,6 +737,7 @@ mod tests {
 	fn default_config() -> HostConfiguration<BlockNumber> {
 		let mut config = HostConfiguration::default();
 		config.parathread_cores = 1;
+		config.max_code_size = 3;
 		config
 	}
 

polkadot/runtime/parachains/src/runtime_api_impl/v1.rs

@@ -216,6 +216,15 @@ pub fn persisted_validation_data<T: initializer::Trait>(
 	)
 }
 
+/// Implementation for the `check_validation_outputs` function of the runtime API.
+pub fn check_validation_outputs<T: initializer::Trait>(
+	para_id: ParaId,
+	outputs: primitives::v1::ValidationOutputs,
+) -> bool {
+	// we strip detailed information from error here for the sake of simplicity of runtime API.
+	<inclusion::Module<T>>::check_validation_outputs(para_id, outputs).is_ok()
+}
+
 /// Implementation for the `session_index_for_child` function of the runtime API.
 pub fn session_index_for_child<T: initializer::Trait>() -> SessionIndex {
 	// Just returns the session index from `inclusion`. Runtime APIs follow
@@ -268,7 +277,7 @@ where
 }
 
 /// Get the `AuthorityDiscoveryId`s corresponding to the given `ValidatorId`s.
-/// Currently this request is limited to validators in the current session. 
+/// Currently this request is limited to validators in the current session.
 ///
 /// We assume that every validator runs authority discovery,
 /// which would allow us to establish point-to-point connection to given validators.