Merge pull request #13760 from ahrtr/fix_raftexample_snapshot

Update the confstate before sending snapshot

contrib/raftexample/raft.go

@@ -456,7 +456,7 @@ func (rc *raftNode) serveChannels() {
 				rc.publishSnapshot(rd.Snapshot)
 			}
 			rc.raftStorage.Append(rd.Entries)
-			rc.transport.Send(rd.Messages)
+			rc.transport.Send(rc.processMessages(rd.Messages))
 			applyDoneC, ok := rc.publishEntries(rc.entriesToApply(rd.CommittedEntries))
 			if !ok {
 				rc.stop()
@@ -476,6 +476,18 @@ func (rc *raftNode) serveChannels() {
 	}
 }
 
+// When there is a `raftpb.EntryConfChange` after creating the snapshot,
+// then the confState included in the snapshot is out of date. so We need
+// to update the confState before sending a snapshot to a follower.
+func (rc *raftNode) processMessages(ms []raftpb.Message) []raftpb.Message {
+	for i := 0; i < len(ms); i++ {
+		if ms[i].Type == raftpb.MsgSnap {
+			ms[i].Snapshot.Metadata.ConfState = rc.confState
+		}
+	}
+	return ms
+}
+
 func (rc *raftNode) serveRaft() {
 	url, err := url.Parse(rc.peers[rc.id-1])
 	if err != nil {

contrib/raftexample/raft_test.go

@@ -0,0 +1,129 @@
+// Copyright 2022 The etcd Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package main
+
+import (
+	"go.etcd.io/etcd/raft/v3/raftpb"
+	"reflect"
+	"testing"
+)
+
+func TestProcessMessages(t *testing.T) {
+	cases := []struct {
+		name             string
+		confState        raftpb.ConfState
+		InputMessages    []raftpb.Message
+		ExpectedMessages []raftpb.Message
+	}{
+		{
+			name: "only one snapshot message",
+			confState: raftpb.ConfState{
+				Voters: []uint64{2, 6, 8, 10},
+			},
+			InputMessages: []raftpb.Message{
+				{
+					Type: raftpb.MsgSnap,
+					To:   8,
+					Snapshot: raftpb.Snapshot{
+						Metadata: raftpb.SnapshotMetadata{
+							Index: 100,
+							Term:  3,
+							ConfState: raftpb.ConfState{
+								Voters:    []uint64{2, 6, 8},
+								AutoLeave: true,
+							},
+						},
+					},
+				},
+			},
+			ExpectedMessages: []raftpb.Message{
+				{
+					Type: raftpb.MsgSnap,
+					To:   8,
+					Snapshot: raftpb.Snapshot{
+						Metadata: raftpb.SnapshotMetadata{
+							Index: 100,
+							Term:  3,
+							ConfState: raftpb.ConfState{
+								Voters: []uint64{2, 6, 8, 10},
+							},
+						},
+					},
+				},
+			},
+		},
+		{
+			name: "one snapshot message and one other message",
+			confState: raftpb.ConfState{
+				Voters: []uint64{2, 7, 8, 12},
+			},
+			InputMessages: []raftpb.Message{
+				{
+					Type: raftpb.MsgSnap,
+					To:   8,
+					Snapshot: raftpb.Snapshot{
+						Metadata: raftpb.SnapshotMetadata{
+							Index: 100,
+							Term:  3,
+							ConfState: raftpb.ConfState{
+								Voters:    []uint64{2, 6, 8},
+								AutoLeave: true,
+							},
+						},
+					},
+				},
+				{
+					Type: raftpb.MsgApp,
+					From: 6,
+					To:   8,
+				},
+			},
+			ExpectedMessages: []raftpb.Message{
+				{
+					Type: raftpb.MsgSnap,
+					To:   8,
+					Snapshot: raftpb.Snapshot{
+						Metadata: raftpb.SnapshotMetadata{
+							Index: 100,
+							Term:  3,
+							ConfState: raftpb.ConfState{
+								Voters: []uint64{2, 7, 8, 12},
+							},
+						},
+					},
+				},
+				{
+					Type: raftpb.MsgApp,
+					From: 6,
+					To:   8,
+				},
+			},
+		},
+	}
+
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			rn := &raftNode{
+				confState: tc.confState,
+			}
+
+			outputMessages := rn.processMessages(tc.InputMessages)
+
+			if !reflect.DeepEqual(outputMessages, tc.ExpectedMessages) {
+				t.Fatalf("Unexpected messages, expected: %v, got %v", tc.ExpectedMessages, outputMessages)
+			}
+		})
+	}
+}