@@ -36,10 +36,17 @@ type (

 		NoLchown    bool

 		Name        string

 	}

+

+	// Archiver allows the reuse of most utility functions of this package

+	// with a pluggable Untar function.

+	Archiver struct {

+		Untar func(io.Reader, string, *TarOptions) error

+	}

 )

 var (

 	ErrNotImplemented = errors.New("Function not implemented")

+	defaultArchiver   = &Archiver{Untar}

 )

 const (

@@ -549,45 +556,47 @@ loop:

 	return nil

 }

-// TarUntar is a convenience function which calls Tar and Untar, with

-// the output of one piped into the other. If either Tar or Untar fails,

-// TarUntar aborts and returns the error.

-func TarUntar(src string, dst string) error {

+func (archiver *Archiver) TarUntar(src, dst string) error {

 	log.Debugf("TarUntar(%s %s)", src, dst)

 	archive, err := TarWithOptions(src, &TarOptions{Compression: Uncompressed})

 	if err != nil {

 		return err

 	}

 	defer archive.Close()

-	return Untar(archive, dst, nil)

+	return archiver.Untar(archive, dst, nil)

 }

-// UntarPath is a convenience function which looks for an archive

-// at filesystem path `src`, and unpacks it at `dst`.

-func UntarPath(src, dst string) error {

+// TarUntar is a convenience function which calls Tar and Untar, with the output of one piped into the other.

+// If either Tar or Untar fails, TarUntar aborts and returns the error.

+func TarUntar(src, dst string) error {

+	return defaultArchiver.TarUntar(src, dst)

+}

+

+func (archiver *Archiver) UntarPath(src, dst string) error {

 	archive, err := os.Open(src)

 	if err != nil {

 		return err

 	}

 	defer archive.Close()

-	if err := Untar(archive, dst, nil); err != nil {

+	if err := archiver.Untar(archive, dst, nil); err != nil {

 		return err

 	}

 	return nil

 }

-// CopyWithTar creates a tar archive of filesystem path `src`, and

-// unpacks it at filesystem path `dst`.

-// The archive is streamed directly with fixed buffering and no

-// intermediary disk IO.

-//

-func CopyWithTar(src, dst string) error {

+// UntarPath is a convenience function which looks for an archive

+// at filesystem path `src`, and unpacks it at `dst`.

+func UntarPath(src, dst string) error {

+	return defaultArchiver.UntarPath(src, dst)

+}

+

+func (archiver *Archiver) CopyWithTar(src, dst string) error {

 	srcSt, err := os.Stat(src)

 	if err != nil {

 		return err

 	}

 	if !srcSt.IsDir() {

-		return CopyFileWithTar(src, dst)

+		return archiver.CopyFileWithTar(src, dst)

 	}

 	// Create dst, copy src's content into it

 	log.Debugf("Creating dest directory: %s", dst)

@@ -595,16 +604,18 @@ func CopyWithTar(src, dst string) error {

 		return err

 	}

 	log.Debugf("Calling TarUntar(%s, %s)", src, dst)

-	return TarUntar(src, dst)

+	return archiver.TarUntar(src, dst)

 }

-// CopyFileWithTar emulates the behavior of the 'cp' command-line

-// for a single file. It copies a regular file from path `src` to

-// path `dst`, and preserves all its metadata.

-//

-// If `dst` ends with a trailing slash '/', the final destination path

-// will be `dst/base(src)`.

-func CopyFileWithTar(src, dst string) (err error) {

+// CopyWithTar creates a tar archive of filesystem path `src`, and

+// unpacks it at filesystem path `dst`.

+// The archive is streamed directly with fixed buffering and no

+// intermediary disk IO.

+func CopyWithTar(src, dst string) error {

+	return defaultArchiver.CopyWithTar(src, dst)

+}

+

+func (archiver *Archiver) CopyFileWithTar(src, dst string) (err error) {

 	log.Debugf("CopyFileWithTar(%s, %s)", src, dst)

 	srcSt, err := os.Stat(src)

 	if err != nil {

@@ -652,7 +663,17 @@ func CopyFileWithTar(src, dst string) (err error) {

 			err = er

 		}

 	}()

-	return Untar(r, filepath.Dir(dst), nil)

+	return archiver.Untar(r, filepath.Dir(dst), nil)

+}

+

+// CopyFileWithTar emulates the behavior of the 'cp' command-line

+// for a single file. It copies a regular file from path `src` to

+// path `dst`, and preserves all its metadata.

+//

+// If `dst` ends with a trailing slash '/', the final destination path

+// will be `dst/base(src)`.

+func CopyFileWithTar(src, dst string) (err error) {

+	return defaultArchiver.CopyFileWithTar(src, dst)

 }

 // CmdStream executes a command, and returns its stdout as a stream.