extract files from android backup

unab.go

package main

import (
	"compress/zlib"
	"flag"
	"io"
	"log"
	"os"
)

var (
	_ab  string
	_tar string
)

func init() {
	flag.StringVar(&_ab, "ab", "", "ab file")
	flag.StringVar(&_tar, "tar", "", "tar file")
	flag.Parse()
}

func main() {
	if _ab == "" || _tar == "" {
		flag.Usage()
		return
	}
	in, err := os.Open(_ab)
	if err != nil {
		log.Fatal(err)
	}
	defer in.Close()
	out, err := os.OpenFile(_tar, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0750)
	if err != nil {
		log.Fatal(err)
	}
	defer out.Close()
	const BACKUP_HEADER_LENGTH = 24
	if _, err := in.Seek(BACKUP_HEADER_LENGTH, os.SEEK_SET); err != nil {
		log.Fatal(err)
	}
	gzin, err := zlib.NewReader(in)
	if err != nil {
		log.Fatal(err)
	}
	if _, err := io.Copy(out, gzin); err != nil {
		log.Fatal(err)
	}
}