A0-1823: add substrate specific chain status (#844)

* add substrate chain status

finality-aleph/src/sync/mod.rs

@@ -91,12 +91,17 @@ pub enum BlockStatus<J: Justification> {
 
 /// The knowledge about the chain status.
 pub trait ChainStatus<J: Justification> {
+    type Error: Display;
+
     /// The status of the block.
-    fn status_of(&self, id: <J::Header as Header>::Identifier) -> BlockStatus<J>;
+    fn status_of(
+        &self,
+        id: <J::Header as Header>::Identifier,
+    ) -> Result<BlockStatus<J>, Self::Error>;
 
     /// The header of the best block.
-    fn best_block(&self) -> J::Header;
+    fn best_block(&self) -> Result<J::Header, Self::Error>;
 
     /// The justification of the top finalized block.
-    fn top_finalized(&self) -> J;
+    fn top_finalized(&self) -> Result<J, Self::Error>;
 }

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

@@ -0,0 +1,162 @@
+use std::{
+    fmt::{Display, Error as FmtError, Formatter},
+    marker::PhantomData,
+};
+
+use aleph_primitives::{BlockNumber, ALEPH_ENGINE_ID};
+use log::warn;
+use sp_blockchain::{Backend, Error as ClientError};
+use sp_runtime::{
+    generic::BlockId as SubstrateBlockId,
+    traits::{Block as BlockT, Header as SubstrateHeader},
+};
+
+use crate::{
+    justification::backwards_compatible_decode,
+    sync::{substrate::Justification, BlockStatus, ChainStatus, Header, LOG_TARGET},
+    AlephJustification,
+};
+
+/// What can go wrong when checking chain status
+#[derive(Debug)]
+pub enum Error<B: BlockT> {
+    MissingHash(B::Hash),
+    MissingJustification(B::Hash),
+    Client(ClientError),
+}
+
+impl<B: BlockT> Display for Error<B> {
+    fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), FmtError> {
+        use Error::*;
+        match self {
+            MissingHash(hash) => {
+                write!(
+                    f,
+                    "data availability problem: no block for existing hash {:?}",
+                    hash
+                )
+            }
+            MissingJustification(hash) => {
+                write!(
+                    f,
+                    "data availability problem: no justification for finalized block with hash {:?}",
+                    hash
+                )
+            }
+            Client(e) => {
+                write!(f, "substrate client error {}", e)
+            }
+        }
+    }
+}
+
+impl<B: BlockT> From<ClientError> for Error<B> {
+    fn from(value: ClientError) -> Self {
+        Error::Client(value)
+    }
+}
+
+/// Substrate implementation of ChainStatus trait
+pub struct SubstrateChainStatus<B, BE>
+where
+    BE: Backend<B>,
+    B: BlockT,
+    B::Header: SubstrateHeader<Number = BlockNumber>,
+{
+    client: BE,
+    _phantom: PhantomData<B>,
+}
+
+impl<B, BE> SubstrateChainStatus<B, BE>
+where
+    BE: Backend<B>,
+    B: BlockT,
+    B::Header: SubstrateHeader<Number = BlockNumber>,
+{
+    fn header(&self, hash: B::Hash) -> Result<Option<B::Header>, ClientError> {
+        let id = SubstrateBlockId::<B>::Hash(hash);
+        self.client.header(id)
+    }
+
+    fn justification(&self, hash: B::Hash) -> Result<Option<AlephJustification>, ClientError> {
+        let id = SubstrateBlockId::<B>::Hash(hash);
+        let justification = match self
+            .client
+            .justifications(id)?
+            .and_then(|j| j.into_justification(ALEPH_ENGINE_ID))
+        {
+            Some(justification) => justification,
+            None => return Ok(None),
+        };
+
+        match backwards_compatible_decode(justification) {
+            Ok(justification) => Ok(Some(justification)),
+            // This should not happen, as we only import correctly encoded justification.
+            Err(e) => {
+                warn!(
+                    target: LOG_TARGET,
+                    "Could not decode stored justification for block {:?}: {}", hash, e
+                );
+                Ok(None)
+            }
+        }
+    }
+
+    fn best_hash(&self) -> B::Hash {
+        self.client.info().best_hash
+    }
+
+    fn finalized_hash(&self) -> B::Hash {
+        self.client.info().finalized_hash
+    }
+}
+
+impl<B, BE> ChainStatus<Justification<B::Header>> for SubstrateChainStatus<B, BE>
+where
+    BE: Backend<B>,
+    B: BlockT,
+    B::Header: SubstrateHeader<Number = BlockNumber>,
+{
+    type Error = Error<B>;
+
+    fn status_of(
+        &self,
+        id: <B::Header as Header>::Identifier,
+    ) -> Result<BlockStatus<Justification<B::Header>>, Self::Error> {
+        let header = match self.header(id.hash)? {
+            Some(header) => header,
+            None => return Ok(BlockStatus::Unknown),
+        };
+
+        if let Some(raw_justification) = self.justification(id.hash)? {
+            Ok(BlockStatus::Justified(Justification {
+                header,
+                raw_justification,
+            }))
+        } else {
+            Ok(BlockStatus::Present(header))
+        }
+    }
+
+    fn best_block(&self) -> Result<B::Header, Self::Error> {
+        let best_hash = self.best_hash();
+
+        self.header(best_hash)?.ok_or(Error::MissingHash(best_hash))
+    }
+
+    fn top_finalized(&self) -> Result<Justification<B::Header>, Self::Error> {
+        let finalized_hash = self.finalized_hash();
+
+        let header = self
+            .header(finalized_hash)?
+            .ok_or(Error::MissingHash(finalized_hash))?;
+        let raw_justification = self
+            .justification(finalized_hash)?
+            .ok_or(Error::MissingJustification(finalized_hash))?;
+
+        Ok(Justification {
+            header,
+            raw_justification,
+        })
+    }
+}

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

@@ -8,6 +8,7 @@ use crate::{
     AlephJustification,
 };
 
+mod chain_status;
 mod status_notifier;
 
 #[derive(Clone, Debug, PartialEq, Eq)]