unzip.go

package unzip

import (
	"archive/zip"
	"context"
	"fmt"
	"io"
	"os"
	"path/filepath"
	"runtime"
	"strings"

	"golang.org/x/sync/errgroup"
)

func unzipInto(ctx context.Context, dirName string, arch *zip.Reader) (rerr error) {
	numProcs := runtime.GOMAXPROCS(-1)
	step := len(arch.File) / numProcs
	if step < 1 {
		step = 1
	}
	eg, ctx := errgroup.WithContext(ctx)
	for i := 0; i < len(arch.File); i += step {
		shard := arch.File[i:]
		if len(shard) > step {
			shard = shard[:step]
		}
		eg.Go(func() error {
			var un unzipper
			for _, zf := range shard {
				if err := ctx.Err(); err != nil {
					return nil
				}
				if err := un.unzipFile(zf, dirName); err != nil {
					return err
				}
			}
			return nil
		})
	}
	return eg.Wait()
}

type unzipper struct {
	copyBuffer [32 * 1024]byte
}

func (un *unzipper) unzipFile(zf *zip.File, destDir string) (rerr error) {
	// check that zip file path does not try to "slip" out of the destination directory
	path := filepath.Join(destDir, zf.Name)
	if prefix := filepath.Clean(destDir) + string(os.PathSeparator); !strings.HasPrefix(path, prefix) {
		return fmt.Errorf("illegal zip file name %q", zf.Name)
	}

	// ensure parent directory
	if err := os.MkdirAll(filepath.Dir(path), os.ModePerm); err != nil && os.IsNotExist(err) {
		return err
	}

	// create directory entry
	info := zf.FileInfo()
	if info.IsDir() {
		return os.Mkdir(path, info.Mode())
	}

	// extract file contents
	rc, err := zf.Open()
	if err != nil {
		return err
	}
	defer func() {
		if cerr := rc.Close(); rerr == nil {
			rerr = cerr
		}
	}()

	// exclusively create output file, and copy contents out of the archive
	out, err := os.OpenFile(path, os.O_WRONLY|os.O_CREATE|os.O_EXCL, info.Mode())
	if err != nil {
		return err
	}
	_, err = io.CopyBuffer(out, rc, un.copyBuffer[:])
	if cerr := out.Close(); err == nil {
		err = cerr
	}
	return err
}