RaftNova

// BEFORE: timer never reset on valid heartbeats
func (n *Node) handleAppendEntries(req *pb.AppendEntriesRequest) *pb.AppendEntriesResponse {
  // ... process entries ...
  return &pb.AppendEntriesResponse{Success: true}
}

// AFTER: one line fixes liveness
func (n *Node) handleAppendEntries(req *pb.AppendEntriesRequest) *pb.AppendEntriesResponse {
  n.resetElectionTimer() // ← this line was missing
  // ... process entries ...
  return &pb.AppendEntriesResponse{Success: true}
}

// BEFORE: duplicate replies double-counted
votesGranted := 1 // self-vote
for reply := range replyChan {
  if reply.VoteGranted {
    votesGranted++
  }
}

// AFTER: track per-peer, count once
votesGranted := 1
votesReceived := map[string]bool{}
for reply := range replyChan {
  if votesReceived[reply.PeerID] { continue }
  votesReceived[reply.PeerID] = true
  if reply.VoteGranted {
    votesGranted++
  }
}

// BEFORE: replay restored term but not votedFor
func (n *Node) replayWAL(entries []WALEntry) {
  for _, e := range entries {
    if e.Type == WALStateRecord {
      n.currentTerm = e.Term
      // votedFor never restored ← BUG
    }
  }
}

// AFTER: both fields restored together
func (n *Node) replayWAL(entries []WALEntry) {
  for _, e := range entries {
    if e.Type == WALStateRecord {
      n.currentTerm = e.Term
      n.votedFor = e.VotedFor // ← restored
    }
  }
}

// BEFORE: committed entries from any term
func (n *Node) advanceCommitIndex() {
  for idx := n.commitIndex + 1; idx <= n.log.LastIndex(); idx++ {
    if n.countMajority(idx) {
      n.commitIndex = idx // ← UNSAFE for old-term entries
    }
  }
}

// AFTER: only commit current-term entries
func (n *Node) advanceCommitIndex() {
  for idx := n.commitIndex + 1; idx <= n.log.LastIndex(); idx++ {
    if n.log.TermAt(idx) != n.currentTerm { continue } // ← Figure 8
    if n.countMajority(idx) {
      n.commitIndex = idx
    }
  }
}

// BEFORE: truncated valid follower entries
func applyAppendEntries(leaderPrevIdx int, entries []Entry) {
  n.log.Truncate(leaderPrevIdx + 1) // ← deleted committed entries
  n.log.Append(entries...)
}

// AFTER: only truncate conflicting entries
func applyAppendEntries(leaderPrevIdx int, entries []Entry) {
  for i, e := range entries {
    idx := leaderPrevIdx + 1 + i
    if idx < n.log.Length() && n.log.TermAt(idx) != e.Term {
      n.log.Truncate(idx) // only truncate at conflict
      break
    }
  }
  n.log.AppendIfMissing(entries...)
}