Grandpa: save all completed prior rounds (#4203)

* Save concluded rounds.

* Doc nit

* Fix cargo

substrate/client/finality-grandpa/src/aux_schema.rs

@@ -36,6 +36,7 @@ use crate::NewAuthoritySet;
 
 const VERSION_KEY: &[u8] = b"grandpa_schema_version";
 const SET_STATE_KEY: &[u8] = b"grandpa_completed_round";
+const CONCLUDED_ROUNDS: &[u8] = b"grandpa_concluded_rounds";
 const AUTHORITY_SET_KEY: &[u8] = b"grandpa_voters";
 const CONSENSUS_CHANGES_KEY: &[u8] = b"grandpa_consensus_changes";
 
@@ -405,6 +406,18 @@ pub(crate) fn write_voter_set_state<Block: BlockT, B: AuxStore>(
 	)
 }
 
+/// Write concluded round.
+pub(crate) fn write_concluded_round<Block: BlockT, B: AuxStore>(
+	backend: &B,
+	round_data: &CompletedRound<Block>,
+) -> ClientResult<()> {
+	let mut key = CONCLUDED_ROUNDS.to_vec();
+	let round_number = round_data.number;
+	round_number.using_encoded(|n| key.extend(n));
+
+	backend.insert_aux(&[(&key[..], round_data.encode().as_slice())], &[])
+}
+
 /// Update the consensus changes.
 pub(crate) fn update_consensus_changes<H, N, F, R>(
 	set: &ConsensusChanges<H, N>,
@@ -608,4 +621,29 @@ mod test {
 			},
 		);
 	}
+
+	#[test]
+	fn write_read_concluded_rounds() {
+		let client = test_client::new();
+		let hash = H256::random();
+		let round_state = RoundState::genesis((hash, 0));
+
+		let completed_round = CompletedRound::<test_client::runtime::Block> {
+			number: 42,
+			state: round_state.clone(),
+			base: round_state.prevote_ghost.unwrap(),
+			votes: vec![],
+		};
+
+		assert!(write_concluded_round(&client, &completed_round).is_ok());
+
+		let round_number = completed_round.number;
+		let mut key = CONCLUDED_ROUNDS.to_vec();
+		round_number.using_encoded(|n| key.extend(n));
+
+		assert_eq!(
+			load_decode::<_, CompletedRound::<test_client::runtime::Block>>(&client, &key).unwrap(),
+			Some(completed_round),
+		);
+	}
 }

substrate/client/finality-grandpa/src/environment.rs

@@ -865,6 +865,7 @@ where
 					historical_votes.seen().iter().skip(n_existing_votes).cloned()
 				);
 				already_completed.state = state;
+				crate::aux_schema::write_concluded_round(&*self.client, &already_completed);
 			}
 
 			let set_state = VoterSetState::<Block>::Live {