Send recent votes in Vote Transactions (#3734)

core/src/locktower.rs

@@ -10,6 +10,7 @@ use std::sync::Arc;
 
 pub const VOTE_THRESHOLD_DEPTH: usize = 8;
 pub const VOTE_THRESHOLD_SIZE: f64 = 2f64 / 3f64;
+const MAX_RECENT_VOTES: usize = 16;
 
 #[derive(Default)]
 pub struct EpochStakes {
@@ -253,6 +254,13 @@ impl Locktower {
         }
     }
 
+    pub fn recent_votes(&self) -> Vec<Vote> {
+        let start = self.lockouts.votes.len().saturating_sub(MAX_RECENT_VOTES);
+        (start..self.lockouts.votes.len())
+            .map(|i| Vote::new(self.lockouts.votes[i].slot))
+            .collect()
+    }
+
     pub fn root(&self) -> Option<u64> {
         self.lockouts.root_slot
     }
@@ -798,4 +806,29 @@ mod test {
             locktower.collect_vote_lockouts(vote_to_evaluate, accounts.into_iter(), &ancestors);
         assert!(!locktower.check_vote_stake_threshold(vote_to_evaluate, &stakes_lockouts));
     }
+
+    fn vote_and_check_recent(num_votes: usize) {
+        let mut locktower = Locktower::new(EpochStakes::new_for_tests(2), 1, 0.67);
+        let start = num_votes.saturating_sub(MAX_RECENT_VOTES);
+        let expected: Vec<_> = (start..num_votes).map(|i| Vote::new(i as u64)).collect();
+        for i in 0..num_votes {
+            locktower.record_vote(i as u64);
+        }
+        assert_eq!(expected, locktower.recent_votes())
+    }
+
+    #[test]
+    fn test_recent_votes_full() {
+        vote_and_check_recent(MAX_LOCKOUT_HISTORY)
+    }
+
+    #[test]
+    fn test_recent_votes_empty() {
+        vote_and_check_recent(0)
+    }
+
+    #[test]
+    fn test_recent_votes_exact() {
+        vote_and_check_recent(MAX_RECENT_VOTES)
+    }
 }