removes all occurences of ident strings (Built by...) in .o and .a files of a msys2 installation

msysunindent.go

package main

import (
	"bytes"
	"flag"
	"fmt"
	"io"
	"io/ioutil"
	"log"
	"os"
	"os/exec"
	"path/filepath"
	"regexp"
	"strings"
)

const (
	IDENT = "Built by"
)

var (
	_msys    string
	_objcopy string
	_ar      string
)

func init() {
	flag.StringVar(&_msys, "m", "C:\\msys32\\mingw32", "msys dir")
	flag.StringVar(&_objcopy, "o", "objcopy", "objcopy executable")
	flag.StringVar(&_ar, "a", "ar", "ar executable")
	flag.Parse()
}

func copyFile(src, dst string) error {
	in, err := os.OpenFile(src, os.O_RDONLY, 0750)
	if err != nil {
		return err
	}
	out, err := os.OpenFile(dst, os.O_WRONLY|os.O_TRUNC|os.O_CREATE, 0750)
	if err != nil {
		in.Close()
		return err
	}
	io.Copy(out, in)
	in.Close()
	out.Close()
	return nil
}

func slowLibFallback(info os.FileInfo, path string) error {
	wd, _ := os.Getwd()
	tempdir := filepath.Join(os.TempDir(), "msysunident")
	os.Mkdir(tempdir, 0750)
	tempfile := filepath.Join(tempdir, info.Name())
	copyFile(path, tempfile)
	os.Chdir(tempdir)
	{
		cmd := exec.Command("ar", "x", tempfile)
		err := cmd.Run()
		if err != nil {
			os.Chdir(wd)
			os.RemoveAll(tempdir)
			log.Fatal("ar x: ", err)
			return err
		}
	}
	var fis []os.FileInfo
	{
		dfd, err := os.Open(tempdir)
		if err != nil {
			os.Chdir(wd)
			os.RemoveAll(tempdir)
			log.Fatal(err)
			return err
		}
		tfis, err := dfd.Readdir(-1)
		if err != nil {
			dfd.Close()
			os.Chdir(wd)
			os.RemoveAll(tempdir)
			log.Fatal(err)
			return err
		}
		dfd.Close()
		fis = tfis
	}
	objs := make([]string, 0, len(fis))
	for _, fi := range fis {
		if !strings.HasSuffix(fi.Name(), ".o") {
			continue
		}
		file := filepath.Join(tempdir, fi.Name())
		cmd := exec.Command(_objcopy, "-R", ".rdata$zzz", file)
		err := cmd.Run()
		if err != nil {
			os.Chdir(wd)
			os.RemoveAll(tempdir)
			log.Fatal("objcopy -R", fi.Name(), ": ", err)
			return err
		}
		objs = append(objs, fi.Name())
	}
	{
		os.Remove(tempfile)
		c := append([]string{"rcs", tempfile}, objs...)
		cmd := exec.Command("ar", c...)
		err := cmd.Run()
		if err != nil {
			os.Chdir(wd)
			os.RemoveAll(tempdir)
			log.Fatal("ar rcs: ", err)
			return err
		}
	}
	copyFile(tempfile, path)
	os.Chdir(wd)
	os.RemoveAll(tempdir)
	return nil
}

func main() {
	if _msys == "" {
		flag.Usage()
		return
	}
	reBinary := regexp.MustCompile("\\.([oa])$")
	bident := []byte(IDENT)
	err := filepath.Walk(_msys,
		func(path string, info os.FileInfo, err error) error {
			m := reBinary.FindStringSubmatch(path)
			if m == nil {
				return nil
			}
			data, err := ioutil.ReadFile(path)
			if err != nil {
				log.Fatal(err)
				return err
			}
			if !bytes.Contains(data, bident) {
				return nil
			}
			if m[1] == "o" {
				fmt.Println(path)
				cmd := exec.Command(_objcopy, "-R", ".rdata$zzz", path)
				err := cmd.Run()
				if err != nil {
					log.Fatal("objcopy -R: ", err)
					return err
				}
			} else if m[1] == "a" {
				fmt.Println(path)
				cmd := exec.Command(_objcopy, "-R", ".rdata$zzz", path)
				err := cmd.Run()
				if err != nil {
					err = slowLibFallback(info, path)
					if err != nil {
						return err
					}
				}
			}
			return nil
		})
	if err != nil {
		log.Fatal(err)
	}
}