You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: repair.go
    path of file: ./repos/etcd/server/storage/wal
    
    the code of the file until where you have to start completion: // 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"
	"io"
	"os"
	"path/filepath"
	"time"

	"go.uber.org/zap"

	"go.etcd.io/etcd/client/pkg/v3/fileutil"
	"go.etcd.io/etcd/server/v3/storage/wal/walpb"
)

// Repair tries to repair ErrUnexpectedEOF in the
// last wal file by truncating.
func Repair(lg *zap.Logger, dirpath string) boo
    
func Repair(lg *zap.Logger, dirpath string) bool {
	if lg == nil {
		lg = zap.NewNop()
	}
	f, err := openLast(lg, dirpath)
	if err != nil {
		return false
	}
	defer f.Close()

	lg.Info("repairing", zap.String("path", f.Name()))

	rec := &walpb.Record{}
	decoder := NewDecoder(fileutil.NewFileReader(f.File))
	for {
		lastOffset := decoder.LastOffset()
		err := decoder.Decode(rec)
		switch {
		case err == nil:
			// update crc of the decoder when necessary
			switch rec.Type {
			case CrcType:
				crc := decoder.LastCRC()
				// current crc of decoder must match the crc of the record.
				// do no need to match 0 crc, since the decoder is a new one at this case.
				if crc != 0 && rec.Validate(crc) != nil {
					return false
				}
				decoder.UpdateCRC(rec.Crc)
			}
			continue

		case errors.Is(err, io.EOF):
			lg.Info("repaired", zap.String("path", f.Name()), zap.Error(io.EOF))
			return true

		case errors.Is(err, io.ErrUnexpectedEOF):
			brokenName := f.Name() + ".broken"
			bf, bferr := os.Create(brokenName)
			if bferr != nil {
				lg.Warn("failed to create backup file", zap.String("path", brokenName), zap.Error(bferr))
				return false
			}
			defer bf.Close()

			if _, err = f.Seek(0, io.SeekStart); err != nil {
				lg.Warn("failed to read file", zap.String("path", f.Name()), zap.Error(err))
				return false
			}

			if _, err = io.Copy(bf, f); err != nil {
				lg.Warn("failed to copy", zap.String("from", f.Name()), zap.String("to", brokenName), zap.Error(err))
				return false
			}

			if err = f.Truncate(lastOffset); err != nil {
				lg.Warn("failed to truncate", zap.String("path", f.Name()), zap.Error(err))
				return false
			}

			start := time.Now()
			if err = fileutil.Fsync(f.File); err != nil {
				lg.Warn("failed to fsync", zap.String("path", f.Name()), zap.Error(err))
				return false
			}
			walFsyncSec.Observe(time.Since(start).Seconds())

			lg.Info("repaired", zap.String("path", f.Name()), zap.Error(io.ErrUnexpectedEOF))
			return true

		default:
			lg.Warn("failed to repair", zap.String("path", f.Name()), zap.Error(err))
			return false
		}
	}
}