Learner needs to respond vote requests.

Cargo.toml

@@ -13,7 +13,7 @@ categories = ["algorithms", "database-implementations"]
 
 [dependencies]
 log = "0.4.1"
-protobuf = "1.2"
+protobuf = "~1.5"
 quick-error = "1.2.1"
 rand = "0.4"
 fxhash = "0.2.1"

src/raft.rs

@@ -828,6 +828,7 @@ impl<T: Storage> Raft<T> {
             return;
         }
 
+        // Only send vote request to voters.
         let prs = self.take_prs();
         prs.voters()
             .keys()
@@ -1016,24 +1017,6 @@ impl<T: Storage> Raft<T> {
                 debug!("{} ignoring MsgHup because already leader", self.tag);
             },
             MessageType::MsgRequestVote | MessageType::MsgRequestPreVote => {
-                if self.is_learner {
-                    // TODO: learner may need to vote, in case of node down when confchange.
-                    info!(
-                        "{} [logterm: {}, index: {}, vote: {}] ignored {:?} from {} \
-                         [logterm: {}, index: {}] at term {}: learner can not vote",
-                        self.tag,
-                        self.raft_log.last_term(),
-                        self.raft_log.last_index(),
-                        self.vote,
-                        m.get_msg_type(),
-                        m.get_from(),
-                        m.get_log_term(),
-                        m.get_index(),
-                        self.term,
-                    );
-                    return Ok(());
-                }
-
                 // We can vote if this is a repeat of a vote we've already cast...
                 let can_vote = (self.vote == m.get_from()) ||
                     // ...we haven't voted and we don't think there's a leader yet in this term...

tests/cases/test_raft.rs

@@ -3784,21 +3784,6 @@ fn test_learner_promotion() {
     assert_eq!(network.peers[&2].state, StateRole::Leader);
 }
 
-// TestLearnerCannotVote checks that a learner can't vote even it receives a valid Vote request.
-#[test]
-fn test_learner_cannot_vote() {
-    let mut n2 = new_test_learner_raft(2, vec![1], vec![2], 10, 1, new_storage());
-    n2.become_follower(1, INVALID_ID);
-
-    let mut msg_vote = new_message(1, 2, MessageType::MsgRequestVote, 0);
-    msg_vote.set_term(2);
-    msg_vote.set_log_term(11);
-    msg_vote.set_index(11);
-    n2.step(msg_vote).unwrap();
-
-    assert_eq!(n2.msgs.len(), 0);
-}
-
 // TestLearnerLogReplication tests that a learner can receive entries from the leader.
 #[test]
 fn test_learner_log_replication() {
@@ -3964,3 +3949,31 @@ fn test_remove_learner() {
     assert!(n1.prs().nodes().is_empty());
     assert!(n1.prs().learner_nodes().is_empty());
 }
+
+#[test]
+fn test_learner_respond_vote() {
+    let mut n1 = new_test_learner_raft(1, vec![1, 2], vec![3], 10, 1, new_storage());
+    n1.become_follower(1, INVALID_ID);
+    n1.reset_randomized_election_timeout();
+
+    let mut n3 = new_test_learner_raft(3, vec![1, 2], vec![3], 10, 1, new_storage());
+    n3.become_follower(1, INVALID_ID);
+    n3.reset_randomized_election_timeout();
+
+    let do_campaign = |nw: &mut Network| {
+        let msg = new_message(1, 1, MessageType::MsgHup, 0);
+        nw.send(vec![msg]);
+    };
+
+    let mut network = Network::new(vec![Some(n1), None, Some(n3)]);
+    network.isolate(2);
+
+    // Can't elect new leader because 1 won't send MsgRequestVote to 3.
+    do_campaign(&mut network);
+    assert_eq!(network.peers[&1].state, StateRole::Candidate);
+
+    // After promote 3 to voter, election should success.
+    network.peers.get_mut(&1).unwrap().add_node(3);
+    do_campaign(&mut network);
+    assert_eq!(network.peers[&1].state, StateRole::Leader);
+}