grandpa-rpc: allow proving finality of blocks from latest authority set (paritytech#8585)

* grandpa: use new latest stored justification in prove_finality

* grandpa: include end in range in FinalityProof::unknown_headers

* grandpa: typo in comment

* grandpa: remove ProvableJustification

* grandpa: revert unnecessary changes

* grandpa: extend AuthoritySetChangeId and cleanup get_set_id

* grandpa: move check_finality_proof to the test module

* grandpa: warn on missing authority set changes data

* grandpa: add missing use statement

* grandpa: simplify finality_proof tests

* grandpa: additional tests for finality_proof

Co-authored-by: André Silva <andrerfosilva@gmail.com>

Author: octol

client/finality-grandpa/src/authorities.rs

@@ -18,6 +18,10 @@
 
 //! Utilities for dealing with authorities, authority sets, and handoffs.
 
+use std::cmp::Ord;
+use std::fmt::Debug;
+use std::ops::Add;
+
 use fork_tree::ForkTree;
 use parking_lot::MappedMutexGuard;
 use finality_grandpa::voter_set::VoterSet;
@@ -27,9 +31,7 @@ use sc_telemetry::{telemetry, TelemetryHandle, CONSENSUS_INFO};
 use sp_finality_grandpa::{AuthorityId, AuthorityList};
 use sc_consensus::shared_data::{SharedData, SharedDataLocked};
 
-use std::cmp::Ord;
-use std::fmt::Debug;
-use std::ops::Add;
+use crate::SetId;
 
 /// Error type returned on operations on the `AuthoritySet`.
 #[derive(Debug, derive_more::Display)]
@@ -684,6 +686,20 @@ impl<H, N: Add<Output=N> + Clone> PendingChange<H, N> {
 #[derive(Debug, Encode, Decode, Clone, PartialEq)]
 pub struct AuthoritySetChanges<N>(Vec<(u64, N)>);
 
+/// The response when querying for a set id for a specific block. Either we get a set id
+/// together with a block number for the last block in the set, or that the requested block is in the
+/// latest set, or that we don't know what set id the given block belongs to.
+#[derive(Debug, PartialEq)]
+pub enum AuthoritySetChangeId<N> {
+	/// The requested block is in the latest set.
+	Latest,
+	/// Tuple containing the set id and the last block number of that set.
+	Set(SetId, N),
+	/// We don't know which set id the request block belongs to (this can only happen due to missing
+	/// data).
+	Unknown,
+}
+
 impl<N> From<Vec<(u64, N)>> for AuthoritySetChanges<N> {
 	fn from(changes: Vec<(u64, N)>) -> AuthoritySetChanges<N> {
 		AuthoritySetChanges(changes)
@@ -699,7 +715,15 @@ impl<N: Ord + Clone> AuthoritySetChanges<N> {
 		self.0.push((set_id, block_number));
 	}
 
-	pub(crate) fn get_set_id(&self, block_number: N) -> Option<(u64, N)> {
+	pub(crate) fn get_set_id(&self, block_number: N) -> AuthoritySetChangeId<N> {
+		if self.0
+			.last()
+			.map(|last_auth_change| last_auth_change.1 < block_number)
+			.unwrap_or(false)
+		{
+			return AuthoritySetChangeId::Latest;
+		}
+
 		let idx = self.0
 			.binary_search_by_key(&block_number, |(_, n)| n.clone())
 			.unwrap_or_else(|b| b);
@@ -711,16 +735,16 @@ impl<N: Ord + Clone> AuthoritySetChanges<N> {
 				let (prev_set_id, _) = self.0[idx - 1usize];
 				if set_id != prev_set_id + 1u64 {
 					// Without the preceding set_id we don't have a well-defined start.
-					return None;
+					return AuthoritySetChangeId::Unknown;
 				}
 			} else if set_id != 0 {
 				// If this is the first index, yet not the first set id then it's not well-defined
 				// that we are in the right set id.
-				return None;
+				return AuthoritySetChangeId::Unknown;
 			}
-			Some((set_id, block_number))
+			AuthoritySetChangeId::Set(set_id, block_number)
 		} else {
-			None
+			AuthoritySetChangeId::Unknown
 		}
 	}
 
@@ -1660,11 +1684,11 @@ mod tests {
 		authority_set_changes.append(1, 81);
 		authority_set_changes.append(2, 121);
 
-		assert_eq!(authority_set_changes.get_set_id(20), Some((0, 41)));
-		assert_eq!(authority_set_changes.get_set_id(40), Some((0, 41)));
-		assert_eq!(authority_set_changes.get_set_id(41), Some((0, 41)));
-		assert_eq!(authority_set_changes.get_set_id(42), Some((1, 81)));
-		assert_eq!(authority_set_changes.get_set_id(141), None);
+		assert_eq!(authority_set_changes.get_set_id(20), AuthoritySetChangeId::Set(0, 41));
+		assert_eq!(authority_set_changes.get_set_id(40), AuthoritySetChangeId::Set(0, 41));
+		assert_eq!(authority_set_changes.get_set_id(41), AuthoritySetChangeId::Set(0, 41));
+		assert_eq!(authority_set_changes.get_set_id(42), AuthoritySetChangeId::Set(1, 81));
+		assert_eq!(authority_set_changes.get_set_id(141), AuthoritySetChangeId::Latest);
 	}
 
 	#[test]
@@ -1674,11 +1698,11 @@ mod tests {
 		authority_set_changes.append(3, 81);
 		authority_set_changes.append(4, 121);
 
-		assert_eq!(authority_set_changes.get_set_id(20), None);
-		assert_eq!(authority_set_changes.get_set_id(40), None);
-		assert_eq!(authority_set_changes.get_set_id(41), None);
-		assert_eq!(authority_set_changes.get_set_id(42), Some((3, 81)));
-		assert_eq!(authority_set_changes.get_set_id(141), None);
+		assert_eq!(authority_set_changes.get_set_id(20), AuthoritySetChangeId::Unknown);
+		assert_eq!(authority_set_changes.get_set_id(40), AuthoritySetChangeId::Unknown);
+		assert_eq!(authority_set_changes.get_set_id(41), AuthoritySetChangeId::Unknown);
+		assert_eq!(authority_set_changes.get_set_id(42), AuthoritySetChangeId::Set(3, 81));
+		assert_eq!(authority_set_changes.get_set_id(141), AuthoritySetChangeId::Latest);
 	}
 
 	#[test]