grandpa: minor cleanups in communication module (#6371)

* grandpa: replace Result<(), ()> with Option<()>

* grandpa: replace &Option<T> with Option<&T>

* grandpa: cleanup local id and keystore usages

* grandpa: return bool on check_message_signature

* grandpa: fix erroneous log message on startup

* grandpa: fix test

substrate/client/finality-grandpa/src/communication/mod.rs

@@ -105,6 +105,34 @@ mod benefit {
 	pub(super) const PER_EQUIVOCATION: i32 = 10;
 }
 
+/// A type that ties together our local authority id and a keystore where it is
+/// available for signing.
+pub struct LocalIdKeystore((AuthorityId, BareCryptoStorePtr));
+
+impl LocalIdKeystore {
+	/// Returns a reference to our local authority id.
+	fn local_id(&self) -> &AuthorityId {
+		&(self.0).0
+	}
+
+	/// Returns a reference to the keystore.
+	fn keystore(&self) -> &BareCryptoStorePtr {
+		&(self.0).1
+	}
+}
+
+impl AsRef<BareCryptoStorePtr> for LocalIdKeystore {
+	fn as_ref(&self) -> &BareCryptoStorePtr {
+		self.keystore()
+	}
+}
+
+impl From<(AuthorityId, BareCryptoStorePtr)> for LocalIdKeystore {
+	fn from(inner: (AuthorityId, BareCryptoStorePtr)) -> LocalIdKeystore {
+		LocalIdKeystore(inner)
+	}
+}
+
 /// If the voter set is larger than this value some telemetry events are not
 /// sent to avoid increasing usage resource on the node and flooding the
 /// telemetry server (e.g. received votes, received commits.)
@@ -272,11 +300,10 @@ impl<B: BlockT, N: Network<B>> NetworkBridge<B, N> {
 	/// network all within the current set.
 	pub(crate) fn round_communication(
 		&self,
-		keystore: Option<BareCryptoStorePtr>,
+		keystore: Option<LocalIdKeystore>,
 		round: Round,
 		set_id: SetId,
 		voters: Arc<VoterSet<AuthorityId>>,
-		local_key: Option<AuthorityId>,
 		has_voted: HasVoted<B>,
 	) -> (
 		impl Stream<Item = SignedMessage<B>> + Unpin,
@@ -288,9 +315,10 @@ impl<B: BlockT, N: Network<B>> NetworkBridge<B, N> {
 			&*voters,
 		);
 
-		let local_id = local_key.and_then(|id| {
-			if voters.contains(&id) {
-				Some(id)
+		let keystore = keystore.and_then(|ks| {
+			let id = ks.local_id();
+			if voters.contains(id) {
+				Some(ks)
 			} else {
 				None
 			}
@@ -350,11 +378,10 @@ impl<B: BlockT, N: Network<B>> NetworkBridge<B, N> {
 
 		let (tx, out_rx) = mpsc::channel(0);
 		let outgoing = OutgoingMessages::<B> {
-			keystore: keystore.clone(),
+			keystore,
 			round: round.0,
 			set_id: set_id.0,
 			network: self.gossip_engine.clone(),
-			local_id,
 			sender: tx,
 			has_voted,
 		};
@@ -629,11 +656,10 @@ pub struct SetId(pub SetIdNumber);
 pub(crate) struct OutgoingMessages<Block: BlockT> {
 	round: RoundNumber,
 	set_id: SetIdNumber,
-	local_id: Option<AuthorityId>,
+	keystore: Option<LocalIdKeystore>,
 	sender: mpsc::Sender<SignedMessage<Block>>,
 	network: Arc<Mutex<GossipEngine<Block>>>,
 	has_voted: HasVoted<Block>,
-	keystore: Option<BareCryptoStorePtr>,
 }
 
 impl<B: BlockT> Unpin for OutgoingMessages<B> {}
@@ -667,19 +693,12 @@ impl<Block: BlockT> Sink<Message<Block>> for OutgoingMessages<Block>
 		}
 
 		// when locals exist, sign messages on import
-		if let Some(ref public) = self.local_id {
-			let keystore = match &self.keystore {
-				Some(keystore) => keystore.clone(),
-				None => {
-					return Err(Error::Signing("Cannot sign without a keystore".to_string()))
-				}
-			};
-
+		if let Some(ref keystore) = self.keystore {
 			let target_hash = *(msg.target().0);
 			let signed = sp_finality_grandpa::sign_message(
-				keystore,
+				keystore.as_ref(),
 				msg,
-				public.clone(),
+				keystore.local_id().clone(),
 				self.round,
 				self.set_id,
 			).ok_or(
@@ -774,7 +793,7 @@ fn check_compact_commit<Block: BlockT>(
 		use crate::communication::gossip::Misbehavior;
 		use finality_grandpa::Message as GrandpaMessage;
 
-		if let Err(()) = sp_finality_grandpa::check_message_signature_with_buffer(
+		if !sp_finality_grandpa::check_message_signature_with_buffer(
 			&GrandpaMessage::Precommit(precommit.clone()),
 			id,
 			sig,
@@ -862,7 +881,7 @@ fn check_catch_up<Block: BlockT>(
 		for (msg, id, sig) in messages {
 			signatures_checked += 1;
 
-			if let Err(()) = sp_finality_grandpa::check_message_signature_with_buffer(
+			if !sp_finality_grandpa::check_message_signature_with_buffer(
 				&msg,
 				id,
 				sig,