archive.Extract Race

main.go

package main

import (
	"archive/tar"
	"bytes"
	"compress/gzip"
	"flag"
	"fmt"
	"io"
	"net/http"
	"os"
	"sync"

	"github.com/buildpacks/lifecycle/archive"
	"golang.org/x/sys/unix"
)

func main() {
	var order string
	flag.StringVar(&order, "order", "serial", "run archive.Extract serially or in parallel (serial|parallel)")
	flag.Parse()

	umask := unix.Umask(0022)
	defer unix.Umask(umask)

	fmt.Printf("umask before: %o\n", umask)

	var tarballs []*archive.NormalizingTarReader
	for i := 0; i < 10; i++ {
		response, err := http.Get("https://github.com/paketo-buildpacks/go-build/releases/download/v0.4.1/go-build-0.4.1.tgz")
		if err != nil {
			panic(err)
		}

		buffer := bytes.NewBuffer(nil)
		_, err = io.Copy(buffer, response.Body)

		err = response.Body.Close()
		if err != nil {
			panic(err)
		}

		gzr, err := gzip.NewReader(buffer)
		if err != nil {
			panic(err)
		}

		tmpDir, err := os.MkdirTemp("", "")
		if err != nil {
			panic(err)
		}

		tr := archive.NewNormalizingTarReader(tar.NewReader(gzr))
		tr.PrependDir(tmpDir)

		tarballs = append(tarballs, tr)
	}

	var err error
	if order == "serial" {
		err = serial(tarballs)
	} else {
		err = parallel(tarballs)
	}
	if err != nil {
		panic(err)
	}

	val := unix.Umask(0)
	_ = unix.Umask(val)
	fmt.Printf("umask after: %o\n", val)
}

func serial(tarballs []*archive.NormalizingTarReader) error {
	for _, tarball := range tarballs {
		err := archive.Extract(tarball)
		if err != nil {
			return err
		}
	}

	return nil
}

func parallel(tarballs []*archive.NormalizingTarReader) error {
	wg := &sync.WaitGroup{}
	for _, tarball := range tarballs {
		wg.Add(1)

		go func(tr *archive.NormalizingTarReader, waitGroup *sync.WaitGroup) {
			err := archive.Extract(tr)
			if err != nil {
				panic(err)
			}

			waitGroup.Done()
		}(tarball, wg)
	}

	wg.Wait()

	return nil
}