consensus: handle justification sync for blocks authored locally (#8698)

* consensus: add trait to control justification sync process

* network: implement JustificationSyncLink for NetworkService

* slots: handle justification sync in slot worker

* babe: fix slot worker instantiation

* aura: fix slot worker instantiation

* pow: handle justification sync in miner

* babe: fix tests

* aura: fix tests

* node: fix compilation

* node-template: fix compilation

* consensus: rename justification sync link parameter

* aura: fix test compilation

* consensus: slots: move JustificationSyncLink out of on_slot

substrate/primitives/consensus/common/src/block_import.rs

@@ -68,6 +68,30 @@ impl ImportResult {
 
 		ImportResult::Imported(aux)
 	}
+
+	/// Handles any necessary request for justifications (or clearing of pending requests) based on
+	/// the outcome of this block import.
+	pub fn handle_justification<B>(
+		&self,
+		hash: &B::Hash,
+		number: NumberFor<B>,
+		justification_sync_link: &mut dyn JustificationSyncLink<B>,
+	) where
+		B: BlockT,
+	{
+		match self {
+			ImportResult::Imported(aux) => {
+				if aux.clear_justification_requests {
+					justification_sync_link.clear_justification_requests();
+				}
+
+				if aux.needs_justification {
+					justification_sync_link.request_justification(hash, number);
+				}
+			}
+			_ => {}
+		}
+	}
 }
 
 /// Block data origin.
@@ -354,3 +378,32 @@ pub trait JustificationImport<B: BlockT> {
 		justification: Justification,
 	) -> Result<(), Self::Error>;
 }
+
+/// Control the synchronization process of block justifications.
+///
+/// When importing blocks different consensus engines might require that
+/// additional finality data is provided (i.e. a justification for the block).
+/// This trait abstracts the required methods to issue those requests
+pub trait JustificationSyncLink<B: BlockT>: Send + Sync {
+	/// Request a justification for the given block.
+	fn request_justification(&self, hash: &B::Hash, number: NumberFor<B>);
+
+	/// Clear all pending justification requests.
+	fn clear_justification_requests(&self);
+}
+
+impl<B: BlockT> JustificationSyncLink<B> for () {
+	fn request_justification(&self, _hash: &B::Hash, _number: NumberFor<B>) {}
+
+	fn clear_justification_requests(&self) {}
+}
+
+impl<B: BlockT, L: JustificationSyncLink<B>> JustificationSyncLink<B> for Arc<L> {
+	fn request_justification(&self, hash: &B::Hash, number: NumberFor<B>) {
+		L::request_justification(&*self, hash, number);
+	}
+
+	fn clear_justification_requests(&self) {
+		L::clear_justification_requests(&*self);
+	}
+}

substrate/primitives/consensus/common/src/lib.rs

@@ -49,8 +49,8 @@ mod metrics;
 
 pub use self::error::Error;
 pub use block_import::{
-	BlockImport, BlockOrigin, ForkChoiceStrategy, ImportedAux, BlockImportParams, BlockCheckParams,
-	ImportResult, JustificationImport,
+	BlockCheckParams, BlockImport, BlockImportParams, BlockOrigin, ForkChoiceStrategy,
+	ImportResult, ImportedAux, JustificationImport, JustificationSyncLink,
 };
 pub use select_chain::SelectChain;
 pub use sp_state_machine::Backend as StateBackend;