fix: make fuzz run without fuzzy harness errors

fuzzy/cluster.go

@@ -5,6 +5,7 @@ package fuzzy
 
 import (
 	"bytes"
+	"errors"
 	"fmt"
 	"io"
 	"os"
@@ -22,6 +23,14 @@ type appliedItem struct {
 	data  []byte
 }
 
+type staticErrorFuture struct {
+	err error
+}
+
+func (s staticErrorFuture) Error() error {
+	return s.err
+}
+
 type cluster struct {
 	nodes            []*raftNode
 	removedNodes     []*raftNode
@@ -230,6 +239,9 @@ func (c *cluster) generateNApplies(s *applySource, n uint) [][]byte {
 
 func (c *cluster) leadershipTransfer(leaderTimeout time.Duration) raft.Future {
 	ldr := c.Leader(leaderTimeout)
+	if ldr == nil {
+		return staticErrorFuture{err: errors.New("no leader elected before leadership transfer")}
+	}
 	return ldr.raft.LeadershipTransfer()
 }
 

fuzzy/leadershiptransfer_test.go

@@ -19,15 +19,21 @@ func TestRaft_FuzzyLeadershipTransfer(t *testing.T) {
 	s := newApplySource("LeadershipTransfer")
 	data := cluster.generateNApplies(s, uint(r.Intn(10000)))
 	futures := cluster.sendNApplies(time.Minute, data)
-	cluster.leadershipTransfer(time.Minute)
+	if err := cluster.leadershipTransfer(time.Minute).Error(); err != nil {
+		t.Fatalf("leadership transfer failed: %v", err)
+	}
 
 	data = cluster.generateNApplies(s, uint(r.Intn(10000)))
 	futures = append(futures, cluster.sendNApplies(time.Minute, data)...)
-	cluster.leadershipTransfer(time.Minute)
+	if err := cluster.leadershipTransfer(time.Minute).Error(); err != nil {
+		t.Fatalf("leadership transfer failed: %v", err)
+	}
 
 	data = cluster.generateNApplies(s, uint(r.Intn(10000)))
 	futures = append(futures, cluster.sendNApplies(time.Minute, data)...)
-	cluster.leadershipTransfer(time.Minute)
+	if err := cluster.leadershipTransfer(time.Minute).Error(); err != nil {
+		t.Fatalf("leadership transfer failed: %v", err)
+	}
 
 	data = cluster.generateNApplies(s, uint(r.Intn(10000)))
 	futures = append(futures, cluster.sendNApplies(time.Minute, data)...)
@@ -39,6 +45,20 @@ func TestRaft_FuzzyLeadershipTransfer(t *testing.T) {
 	cluster.VerifyFSM(t)
 }
 
+func TestRaft_FuzzyLeadershipTransferWithoutLeader(t *testing.T) {
+	cluster := newRaftCluster(t, testLogWriter, "lt_no_leader", 5, nil)
+
+	if err := cluster.leadershipTransfer(0).Error(); err == nil {
+		t.Fatal("expected leadership transfer to fail when no leader can be elected")
+	}
+
+	for _, n := range cluster.nodes {
+		if err := n.raft.Shutdown().Error(); err != nil {
+			t.Fatalf("shutdown failed for %s: %v", n.name, err)
+		}
+	}
+}
+
 type LeadershipTransferMode int
 
 type LeadershipTransfer struct {

fuzzy/transport.go

@@ -113,6 +113,7 @@ func (t *transport) sendRPC(target string, req interface{}, resp interface{}) er
 	}
 	rpc := raft.RPC{RespChan: rc}
 	var reqVote raft.RequestVoteRequest
+	var reqPreVote raft.RequestPreVoteRequest
 	var timeoutNow raft.TimeoutNowRequest
 	var appEnt raft.AppendEntriesRequest
 	dec := codec.NewDecoderBytes(buff.Bytes(), &codecHandle)
@@ -127,6 +128,11 @@ func (t *transport) sendRPC(target string, req interface{}, resp interface{}) er
 			return err
 		}
 		rpc.Command = &reqVote
+	case *raft.RequestPreVoteRequest:
+		if err := dec.Decode(&reqPreVote); err != nil {
+			return err
+		}
+		rpc.Command = &reqPreVote
 	case *raft.AppendEntriesRequest:
 		if err := dec.Decode(&appEnt); err != nil {
 			return err