Update etcdutl migrate command: load wal records from the latest snapshot

etcdutl/etcdutl/migrate_command.go

@@ -15,6 +15,7 @@
 package etcdutl
 
 import (
+	"errors"
 	"fmt"
 	"strings"
 
@@ -24,6 +25,7 @@
 
 	"go.etcd.io/etcd/api/v3/version"
 	"go.etcd.io/etcd/pkg/v3/cobrautl"
+	"go.etcd.io/etcd/server/v3/etcdserver/api/snap"
 	"go.etcd.io/etcd/server/v3/storage/backend"
 	"go.etcd.io/etcd/server/v3/storage/datadir"
 	"go.etcd.io/etcd/server/v3/storage/schema"
@@ -95,7 +97,11 @@
 	c.be = backend.NewDefaultBackend(GetLogger(), dbPath)
 
 	walPath := datadir.ToWALDir(o.dataDir)
-	w, err := wal.OpenForRead(c.lg, walPath, walpb.Snapshot{})
+	walSnap, err := getLatestWALSnap(c.lg, o.dataDir)
+	if err != nil {
+		return nil, fmt.Errorf("failed to get the lastest snapshot: %w", err)
+	}
+	w, err := wal.OpenForRead(c.lg, walPath, walSnap)
 	if err != nil {
 		return nil, fmt.Errorf(`failed to open wal: %w`, err)
 	}
@@ -108,6 +114,26 @@
 	return c, nil
 }
 
+func getLatestWALSnap(lg *zap.Logger, dataDir string) (walpb.Snapshot, error) {
+	walPath := datadir.ToWALDir(dataDir)
+	walSnaps, err := wal.ValidSnapshotEntries(lg, walPath)
+	if err != nil {
+		return walpb.Snapshot{}, err
+	}
+
+	ss := snap.New(lg, datadir.ToSnapDir(dataDir))
+	snapshot, err := ss.LoadNewestAvailable(walSnaps)
+	if err != nil && !errors.Is(err, snap.ErrNoSnapshot) {
+		return walpb.Snapshot{}, err
+	}
+
+	var walsnap walpb.Snapshot
+	if snapshot != nil {
+		walsnap.Index, walsnap.Term = snapshot.Metadata.Index, snapshot.Metadata.Term
+	}
+	return walsnap, nil
+}
+
 type migrateConfig struct {
 	lg            *zap.Logger
 	be            backend.Backend

etcdutl/etcdutl/migrate_command_test.go

@@ -0,0 +1,143 @@
+// Copyright 2025 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 etcdutl
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+	"go.uber.org/zap"
+
+	"go.etcd.io/etcd/api/v3/etcdserverpb"
+	"go.etcd.io/etcd/client/pkg/v3/fileutil"
+	"go.etcd.io/etcd/pkg/v3/pbutil"
+	"go.etcd.io/etcd/server/v3/etcdserver/api/snap"
+	"go.etcd.io/etcd/server/v3/storage/datadir"
+	"go.etcd.io/etcd/server/v3/storage/wal"
+	"go.etcd.io/etcd/server/v3/storage/wal/walpb"
+	"go.etcd.io/raft/v3/raftpb"
+)
+
+func TestGetLatestWalSnap(t *testing.T) {
+	testCases := []struct {
+		name                  string
+		walSnaps              []walpb.Snapshot
+		snapshots             []raftpb.Snapshot
+		expectedLatestWALSnap walpb.Snapshot
+	}{
+		{
+			name: "wal snapshot records match the snapshot files",
+			walSnaps: []walpb.Snapshot{
+				{Index: 10, Term: 2},
+				{Index: 20, Term: 3},
+				{Index: 30, Term: 5},
+			},
+			snapshots: []raftpb.Snapshot{
+				{Metadata: raftpb.SnapshotMetadata{Index: 10, Term: 2}},
+				{Metadata: raftpb.SnapshotMetadata{Index: 20, Term: 3}},
+				{Metadata: raftpb.SnapshotMetadata{Index: 30, Term: 5}},
+			},
+			expectedLatestWALSnap: walpb.Snapshot{Index: 30, Term: 5},
+		},
+		{
+			name: "there are orphan snapshot files",
+			walSnaps: []walpb.Snapshot{
+				{Index: 10, Term: 2},
+				{Index: 20, Term: 3},
+				{Index: 35, Term: 5},
+			},
+			snapshots: []raftpb.Snapshot{
+				{Metadata: raftpb.SnapshotMetadata{Index: 10, Term: 2}},
+				{Metadata: raftpb.SnapshotMetadata{Index: 20, Term: 3}},
+				{Metadata: raftpb.SnapshotMetadata{Index: 35, Term: 5}},
+				{Metadata: raftpb.SnapshotMetadata{Index: 40, Term: 6}},
+				{Metadata: raftpb.SnapshotMetadata{Index: 50, Term: 7}},
+			},
+			expectedLatestWALSnap: walpb.Snapshot{Index: 35, Term: 5},
+		},
+		{
+			name: "there are orphan snapshot records in wal file",
+			walSnaps: []walpb.Snapshot{
+				{Index: 10, Term: 2},
+				{Index: 20, Term: 3},
+				{Index: 30, Term: 4},
+				{Index: 45, Term: 5},
+				{Index: 55, Term: 6},
+			},
+			snapshots: []raftpb.Snapshot{
+				{Metadata: raftpb.SnapshotMetadata{Index: 10, Term: 2}},
+				{Metadata: raftpb.SnapshotMetadata{Index: 20, Term: 3}},
+				{Metadata: raftpb.SnapshotMetadata{Index: 30, Term: 4}},
+			},
+			expectedLatestWALSnap: walpb.Snapshot{Index: 30, Term: 4},
+		},
+		{
+			name: "wal snapshot records do not match the snapshot files at all",
+			walSnaps: []walpb.Snapshot{
+				{Index: 10, Term: 2},
+				{Index: 20, Term: 3},
+				{Index: 30, Term: 4},
+			},
+			snapshots: []raftpb.Snapshot{
+				{Metadata: raftpb.SnapshotMetadata{Index: 40, Term: 5}},
+				{Metadata: raftpb.SnapshotMetadata{Index: 50, Term: 6}},
+			},
+			expectedLatestWALSnap: walpb.Snapshot{},
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			dataDir := t.TempDir()
+			lg := zap.NewNop()
+
+			require.NoError(t, fileutil.TouchDirAll(lg, datadir.ToMemberDir(dataDir)))
+			require.NoError(t, fileutil.TouchDirAll(lg, datadir.ToWALDir(dataDir)))
+			require.NoError(t, fileutil.TouchDirAll(lg, datadir.ToSnapDir(dataDir)))
+
+			// populate wal file
+			w, err := wal.Create(lg, datadir.ToWALDir(dataDir), pbutil.MustMarshal(
+				&etcdserverpb.Metadata{
+					NodeID:    1,
+					ClusterID: 2,
+				},
+			))
+			require.NoError(t, err)
+
+			for _, walSnap := range tc.walSnaps {
+				walSnap.ConfState = &raftpb.ConfState{Voters: []uint64{1}}
+				walErr := w.SaveSnapshot(walSnap)
+				require.NoError(t, walErr)
+				walErr = w.Save(raftpb.HardState{Term: walSnap.Term, Commit: walSnap.Index, Vote: 1}, nil)
+				require.NoError(t, walErr)
+			}
+			err = w.Close()
+			require.NoError(t, err)
+
+			// generate snapshot files
+			ss := snap.New(lg, datadir.ToSnapDir(dataDir))
+			for _, snap := range tc.snapshots {
+				snap.Metadata.ConfState = raftpb.ConfState{Voters: []uint64{1}}
+				snapErr := ss.SaveSnap(snap)
+				require.NoError(t, snapErr)
+			}
+
+			walSnap, err := getLatestWALSnap(lg, dataDir)
+			require.NoError(t, err)
+
+			require.Equal(t, tc.expectedLatestWALSnap, walSnap)
+		})
+	}
+}

tests/e2e/utl_migrate_test.go

@@ -90,16 +90,10 @@ func TestEtctlutlMigrate(t *testing.T) {
 			expectStorageVersion: &version.V3_6,
 		},
 		{
-			name:                 "Downgrade v3.6 to v3.5 should fail until it's implemented",
+			name:                 "Downgrade v3.6 to v3.5 should work",
 			targetVersion:        "3.5",
-			expectLogsSubString:  "cannot downgrade storage, WAL contains newer entries",
-			expectStorageVersion: &version.V3_6,
-		},
-		{
-			name:                "Downgrade v3.6 to v3.5 with force should work",
-			targetVersion:       "3.5",
-			force:               true,
-			expectLogsSubString: "forcefully cleared storage version",
+			expectLogsSubString:  "updated storage version",
+			expectStorageVersion: nil, // 3.5 doesn't have the field `storageVersion`, so it returns nil.
 		},
 		{
 			name:                 "Upgrade v3.6 to v3.7 with force should work",