diff --git a/vendor/go.etcd.io/etcd/wal/util.go b/vendor/go.etcd.io/etcd/wal/util.go
new file mode 100644
index 0000000..a3f314b
--- /dev/null
+++ b/vendor/go.etcd.io/etcd/wal/util.go
@@ -0,0 +1,124 @@
+// Copyright 2015 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 wal
+
+import (
+	"errors"
+	"fmt"
+	"strings"
+
+	"go.etcd.io/etcd/pkg/fileutil"
+
+	"go.uber.org/zap"
+)
+
+var errBadWALName = errors.New("bad wal name")
+
+// Exist returns true if there are any files in a given directory.
+func Exist(dir string) bool {
+	names, err := fileutil.ReadDir(dir, fileutil.WithExt(".wal"))
+	if err != nil {
+		return false
+	}
+	return len(names) != 0
+}
+
+// searchIndex returns the last array index of names whose raft index section is
+// equal to or smaller than the given index.
+// The given names MUST be sorted.
+func searchIndex(lg *zap.Logger, names []string, index uint64) (int, bool) {
+	for i := len(names) - 1; i >= 0; i-- {
+		name := names[i]
+		_, curIndex, err := parseWALName(name)
+		if err != nil {
+			if lg != nil {
+				lg.Panic("failed to parse WAL file name", zap.String("path", name), zap.Error(err))
+			} else {
+				plog.Panicf("parse correct name should never fail: %v", err)
+			}
+		}
+		if index >= curIndex {
+			return i, true
+		}
+	}
+	return -1, false
+}
+
+// names should have been sorted based on sequence number.
+// isValidSeq checks whether seq increases continuously.
+func isValidSeq(lg *zap.Logger, names []string) bool {
+	var lastSeq uint64
+	for _, name := range names {
+		curSeq, _, err := parseWALName(name)
+		if err != nil {
+			if lg != nil {
+				lg.Panic("failed to parse WAL file name", zap.String("path", name), zap.Error(err))
+			} else {
+				plog.Panicf("parse correct name should never fail: %v", err)
+			}
+		}
+		if lastSeq != 0 && lastSeq != curSeq-1 {
+			return false
+		}
+		lastSeq = curSeq
+	}
+	return true
+}
+
+func readWALNames(lg *zap.Logger, dirpath string) ([]string, error) {
+	names, err := fileutil.ReadDir(dirpath)
+	if err != nil {
+		return nil, err
+	}
+	wnames := checkWalNames(lg, names)
+	if len(wnames) == 0 {
+		return nil, ErrFileNotFound
+	}
+	return wnames, nil
+}
+
+func checkWalNames(lg *zap.Logger, names []string) []string {
+	wnames := make([]string, 0)
+	for _, name := range names {
+		if _, _, err := parseWALName(name); err != nil {
+			// don't complain about left over tmp files
+			if !strings.HasSuffix(name, ".tmp") {
+				if lg != nil {
+					lg.Warn(
+						"ignored file in WAL directory",
+						zap.String("path", name),
+					)
+				} else {
+					plog.Warningf("ignored file %v in wal", name)
+				}
+			}
+			continue
+		}
+		wnames = append(wnames, name)
+	}
+	return wnames
+}
+
+func parseWALName(str string) (seq, index uint64, err error) {
+	if !strings.HasSuffix(str, ".wal") {
+		return 0, 0, errBadWALName
+	}
+	_, err = fmt.Sscanf(str, "%016x-%016x.wal", &seq, &index)
+	return seq, index, err
+}
+
+func walName(seq, index uint64) string {
+	return fmt.Sprintf("%016x-%016x.wal", seq, index)
+}