Support the subscription of every imported block

client/api/src/backend.rs

@@ -49,6 +49,19 @@ pub type TransactionForSB<B, Block> = <B as StateBackend<HashFor<Block>>>::Trans
 /// Extracts the transaction for the given backend.
 pub type TransactionFor<B, Block> = TransactionForSB<StateBackendFor<B, Block>, Block>;
 
+/// Describes which block import notification stream should be notified.
+#[derive(Debug, Clone)]
+pub enum ImportNotificationAction {
+	/// Notify only when the chain has synced to the tip or there is a re-org.
+	RecentBlock,
+	/// Notify for every single block no matter what the sync state is.
+	EveryBlock,
+	/// Both block import notifications above should be fired.
+	Both,
+	/// No block import notification should be fired.
+	None,
+}
+
 /// Import operation summary.
 ///
 /// Contains information about the block that just got imported,
@@ -68,6 +81,8 @@ pub struct ImportSummary<Block: BlockT> {
 	///
 	/// If `None`, there was no re-org while importing.
 	pub tree_route: Option<sp_blockchain::TreeRoute<Block>>,
+	/// What notify action to take for this import.
+	pub import_notification_action: ImportNotificationAction,
 }
 
 /// Finalization operation summary.

client/api/src/client.rs

@@ -63,6 +63,9 @@ pub trait BlockchainEvents<Block: BlockT> {
 	/// imported block.
 	fn import_notification_stream(&self) -> ImportNotifications<Block>;
 
+	/// Get a stream of every imported block.
+	fn every_import_notification_stream(&self) -> ImportNotifications<Block>;
+
 	/// Get a stream of finality notifications. Not guaranteed to be fired for every
 	/// finalized block.
 	fn finality_notification_stream(&self) -> FinalityNotifications<Block>;

client/merkle-mountain-range/src/test_utils.rs

@@ -264,6 +264,10 @@ impl BlockchainEvents<Block> for MockClient {
 		unimplemented!()
 	}
 
+	fn every_import_notification_stream(&self) -> ImportNotifications<Block> {
+		unimplemented!()
+	}
+
 	fn finality_notification_stream(&self) -> FinalityNotifications<Block> {
 		self.client.lock().finality_notification_stream()
 	}

client/service/src/client/client.rs

@@ -31,7 +31,7 @@ use sc_block_builder::{BlockBuilderApi, BlockBuilderProvider, RecordProof};
 use sc_client_api::{
 	backend::{
 		self, apply_aux, BlockImportOperation, ClientImportOperation, FinalizeSummary, Finalizer,
-		ImportSummary, LockImportRun, NewBlockState, StorageProvider,
+		ImportNotificationAction, ImportSummary, LockImportRun, NewBlockState, StorageProvider,
 	},
 	client::{
 		BadBlocks, BlockBackend, BlockImportNotification, BlockOf, BlockchainEvents, ClientInfo,
@@ -106,6 +106,7 @@ where
 	executor: E,
 	storage_notifications: StorageNotifications<Block>,
 	import_notification_sinks: NotificationSinks<BlockImportNotification<Block>>,
+	every_block_import_notification_sinks: NotificationSinks<BlockImportNotification<Block>>,
 	finality_notification_sinks: NotificationSinks<FinalityNotification<Block>>,
 	// Collects auxiliary operations to be performed atomically together with
 	// block import operations.
@@ -304,19 +305,22 @@ where
 				FinalityNotification::from_summary(summary, self.unpin_worker_sender.clone())
 			});
 
-			let (import_notification, storage_changes) = match notify_imported {
-				Some(mut summary) => {
-					let storage_changes = summary.storage_changes.take();
-					(
-						Some(BlockImportNotification::from_summary(
-							summary,
-							self.unpin_worker_sender.clone(),
-						)),
-						storage_changes,
-					)
-				},
-				None => (None, None),
-			};
+			let (import_notification, storage_changes, import_notification_action) =
+				match notify_imported {
+					Some(mut summary) => {
+						let import_notification_action = summary.import_notification_action.clone();
+						let storage_changes = summary.storage_changes.take();
+						(
+							Some(BlockImportNotification::from_summary(
+								summary,
+								self.unpin_worker_sender.clone(),
+							)),
+							storage_changes,
+							import_notification_action,
+						)
+					},
+					None => (None, None, ImportNotificationAction::None),
+				};
 
 			if let Some(ref notification) = finality_notification {
 				for action in self.finality_actions.lock().iter_mut() {
@@ -353,7 +357,24 @@ where
 			}
 
 			self.notify_finalized(finality_notification)?;
-			self.notify_imported(import_notification, storage_changes)?;
+
+			match import_notification_action {
+				ImportNotificationAction::Both => {
+					self.notify_imported(import_notification.clone(), storage_changes.clone())?;
+					self.notify_imported_for_every_block(import_notification, storage_changes)?;
+				},
+				ImportNotificationAction::RecentBlock =>
+					self.notify_imported(import_notification, storage_changes)?,
+				ImportNotificationAction::EveryBlock =>
+					self.notify_imported_for_every_block(import_notification, storage_changes)?,
+				ImportNotificationAction::None => {
+					// Cleanup any closed import notification sinks.
+					self.import_notification_sinks.lock().retain(|sink| !sink.is_closed());
+					self.every_block_import_notification_sinks
+						.lock()
+						.retain(|sink| !sink.is_closed());
+				},
+			}
 
 			Ok(r)
 		};
@@ -451,6 +472,7 @@ where
 			executor,
 			storage_notifications: StorageNotifications::new(prometheus_registry),
 			import_notification_sinks: Default::default(),
+			every_block_import_notification_sinks: Default::default(),
 			finality_notification_sinks: Default::default(),
 			import_actions: Default::default(),
 			finality_actions: Default::default(),
@@ -771,9 +793,14 @@ where
 
 		operation.op.insert_aux(aux)?;
 
-		// We only notify when we are already synced to the tip of the chain
+		let should_notify_every_block =
+			!self.every_block_import_notification_sinks.lock().is_empty();
+
+		// Notify when we are already synced to the tip of the chain
 		// or if this import triggers a re-org
-		if make_notifications || tree_route.is_some() {
+		let should_notify_recent_block = make_notifications || tree_route.is_some();
+
+		if should_notify_every_block || should_notify_recent_block {
 			let header = import_headers.into_post();
 			if finalized {
 				let mut summary = match operation.notify_finalized.take() {
@@ -812,13 +839,24 @@ where
 				operation.notify_finalized = Some(summary);
 			}
 
+			let import_notification_action = if should_notify_every_block {
+				if should_notify_recent_block {
+					ImportNotificationAction::Both
+				} else {
+					ImportNotificationAction::EveryBlock
+				}
+			} else {
+				ImportNotificationAction::RecentBlock
+			};
+
 			operation.notify_imported = Some(ImportSummary {
 				hash,
 				origin,
 				header,
 				is_new_best,
 				storage_changes,
 				tree_route,
+				import_notification_action,
 			})
 		}
 
@@ -1047,6 +1085,38 @@ where
 		Ok(())
 	}
 
+	fn notify_imported_for_every_block(
+		&self,
+		notification: Option<BlockImportNotification<Block>>,
+		storage_changes: Option<(StorageCollection, ChildStorageCollection)>,
+	) -> sp_blockchain::Result<()> {
+		let notification = match notification {
+			Some(notify_import) => notify_import,
+			None => {
+				// Cleanup any closed import notification sinks.
+				self.every_block_import_notification_sinks
+					.lock()
+					.retain(|sink| !sink.is_closed());
+				return Ok(())
+			},
+		};
+
+		if let Some(storage_changes) = storage_changes {
+			// TODO [ToDr] How to handle re-orgs? Should we re-emit all storage changes?
+			self.storage_notifications.trigger(
+				&notification.hash,
+				storage_changes.0.into_iter(),
+				storage_changes.1.into_iter().map(|(sk, v)| (sk, v.into_iter())),
+			);
+		}
+
+		self.every_block_import_notification_sinks
+			.lock()
+			.retain(|sink| sink.unbounded_send(notification.clone()).is_ok());
+
+		Ok(())
+	}
+
 	/// Attempts to revert the chain by `n` blocks guaranteeing that no block is
 	/// reverted past the last finalized block. Returns the number of blocks
 	/// that were successfully reverted.
@@ -1980,6 +2050,12 @@ where
 		stream
 	}
 
+	fn every_import_notification_stream(&self) -> ImportNotifications<Block> {
+		let (sink, stream) = tracing_unbounded("mpsc_every_import_notification_stream", 100_000);
+		self.every_block_import_notification_sinks.lock().push(sink);
+		stream
+	}
+
 	fn finality_notification_stream(&self) -> FinalityNotifications<Block> {
 		let (sink, stream) = tracing_unbounded("mpsc_finality_notification_stream", 100_000);
 		self.finality_notification_sinks.lock().push(sink);