A0-1822: add substrate chain status notifier (#839)

* add substrate chain status notifier

finality-aleph/src/sync/mod.rs

@@ -59,23 +59,25 @@ pub trait Finalizer<J: Justification> {
     fn finalize(&self, justification: J) -> Result<(), Self::Error>;
 }
 
-/// A notification about the chain state changing.
-pub enum ChainStateNotification<BI: BlockIdentifier> {
+/// A notification about the chain status changing.
+pub enum ChainStatusNotification<BI: BlockIdentifier> {
     /// A block has been imported.
     BlockImported(BI),
     /// A block has been finalized.
     BlockFinalized(BI),
 }
 
-/// A stream of notifications about the chain state in the database changing.
+/// A stream of notifications about the chain status in the database changing.
 #[async_trait::async_trait]
-pub trait ChainStateNotifier<BI: BlockIdentifier> {
-    /// Returns a chain state notification when it is available.
-    async fn next(&self) -> ChainStateNotification<BI>;
+pub trait ChainStatusNotifier<BI: BlockIdentifier> {
+    type Error: Display;
+
+    /// Returns a chain status notification when it is available.
+    async fn next(&mut self) -> Result<ChainStatusNotification<BI>, Self::Error>;
 }
 
-/// The state of a block in the database.
-pub enum BlockState<J: Justification> {
+/// The status of a block in the database.
+pub enum BlockStatus<J: Justification> {
     /// The block is justified and thus finalized.
     Justified(J),
     /// The block is present, might be finalized if a descendant is justified.
@@ -84,10 +86,10 @@ pub enum BlockState<J: Justification> {
     Unknown,
 }
 
-/// The knowledge about the chain state.
-pub trait ChainState<J: Justification> {
-    /// The state of the block.
-    fn state_of(&self, id: <J::Header as Header>::Identifier) -> BlockState<J>;
+/// The knowledge about the chain status.
+pub trait ChainStatus<J: Justification> {
+    /// The status of the block.
+    fn status_of(&self, id: <J::Header as Header>::Identifier) -> BlockStatus<J>;
 
     /// The header of the best block.
     fn best_block(&self) -> J::Header;

finality-aleph/src/sync/substrate.rs → finality-aleph/src/sync/substrate/mod.rs

@@ -5,6 +5,8 @@ use sp_runtime::traits::{CheckedSub, Header as SubstrateHeader, One};
 
 use crate::sync::{BlockIdentifier, Header};
 
+mod status_notifier;
+
 #[derive(Clone, Debug, PartialEq, Eq)]
 pub struct BlockId<H: SubstrateHeader<Number = BlockNumber>> {
     hash: H::Hash,

finality-aleph/src/sync/substrate/status_notifier.rs

@@ -0,0 +1,78 @@
+use std::fmt::{Display, Error as FmtError, Formatter};
+
+use aleph_primitives::BlockNumber;
+use futures::StreamExt;
+use sc_client_api::client::{FinalityNotifications, ImportNotifications};
+use sp_runtime::traits::{Block as BlockT, Header as SubstrateHeader};
+use tokio::select;
+
+use crate::sync::{substrate::BlockId, ChainStatusNotification, ChainStatusNotifier, Header};
+
+/// What can go wrong when waiting for next chain status notification.
+#[derive(Debug)]
+pub enum Error {
+    JustificationStreamClosed,
+    ImportStreamClosed,
+}
+
+impl Display for Error {
+    fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), FmtError> {
+        use Error::*;
+        match self {
+            JustificationStreamClosed => {
+                write!(f, "finalization notification stream has ended")
+            }
+            ImportStreamClosed => {
+                write!(f, "import notification stream has ended")
+            }
+        }
+    }
+}
+
+/// Substrate specific implementation of `ChainStatusNotifier`.
+pub struct SubstrateChainStatusNotifier<B>
+where
+    B: BlockT,
+{
+    finality_notifications: FinalityNotifications<B>,
+    import_notifications: ImportNotifications<B>,
+}
+
+impl<B> SubstrateChainStatusNotifier<B>
+where
+    B: BlockT,
+{
+    fn new(
+        finality_notifications: FinalityNotifications<B>,
+        import_notifications: ImportNotifications<B>,
+    ) -> Self {
+        Self {
+            finality_notifications,
+            import_notifications,
+        }
+    }
+}
+
+#[async_trait::async_trait]
+impl<B> ChainStatusNotifier<BlockId<B::Header>> for SubstrateChainStatusNotifier<B>
+where
+    B: BlockT,
+    B::Header: SubstrateHeader<Number = BlockNumber>,
+{
+    type Error = Error;
+
+    async fn next(&mut self) -> Result<ChainStatusNotification<BlockId<B::Header>>, Self::Error> {
+        select! {
+            maybe_block = self.finality_notifications.next() => {
+                maybe_block
+                    .map(|block| ChainStatusNotification::BlockFinalized(block.header.id()))
+                    .ok_or(Error::JustificationStreamClosed)
+            },
+            maybe_block = self.import_notifications.next() => {
+                maybe_block
+                .map(|block| ChainStatusNotification::BlockImported(block.header.id()))
+                .ok_or(Error::ImportStreamClosed)
+            }
+        }
+    }
+}