func writeTarFromLayer(r hcsshim.LayerReader, w io.Writer) error {
t := tar.NewWriter(w)
for {
name, size, fileInfo, err := r.Next()
if err == io.EOF {
break
}
if err != nil {
return err
}
if fileInfo == nil {
// Write a whiteout file.
hdr := &tar.Header{
Name: filepath.ToSlash(filepath.Join(filepath.Dir(name), archive.WhiteoutPrefix+filepath.Base(name))),
}
err := t.WriteHeader(hdr)
if err != nil {
return err
}
} else {
err = backuptar.WriteTarFileFromBackupStream(t, r, name, size, fileInfo)
if err != nil {
return err
}
}
}
return t.Close()
}
// exportLayer generates an archive from a layer based on the given ID.
func (d *Driver) exportLayer(id string, parentLayerPaths []string) (archive.Archive, error) {
if hcsshim.IsTP4() {
// Export in TP4 format to maintain compatibility with existing images and
// because ExportLayer is somewhat broken on TP4 and can't work with the new
// scheme.
tempFolder, err := ioutil.TempDir("", "hcs")
if err != nil {
return nil, err
}
defer func() {
if err != nil {
os.RemoveAll(tempFolder)
}
}()
if err = hcsshim.ExportLayer(d.info, id, tempFolder, parentLayerPaths); err != nil {
return nil, err
}
archive, err := archive.Tar(tempFolder, archive.Uncompressed)
if err != nil {
return nil, err
}
return ioutils.NewReadCloserWrapper(archive, func() error {
err := archive.Close()
os.RemoveAll(tempFolder)
return err
}), nil
}
var r hcsshim.LayerReader
r, err := hcsshim.NewLayerReader(d.info, id, parentLayerPaths)
if err != nil {
return nil, err
}
archive, w := io.Pipe()
go func() {
err := writeTarFromLayer(r, w)
cerr := r.Close()
if err == nil {
err = cerr
}
w.CloseWithError(err)
}()
return archive, nil
}
// exportLayer generates an archive from a layer based on the given ID.
func (d *Driver) exportLayer(id string, parentLayerPaths []string) (archive.Archive, error) {
var r hcsshim.LayerReader
r, err := hcsshim.NewLayerReader(d.info, id, parentLayerPaths)
if err != nil {
return nil, err
}
archive, w := io.Pipe()
go func() {
err := writeTarFromLayer(r, w)
cerr := r.Close()
if err == nil {
err = cerr
}
w.CloseWithError(err)
}()
return archive, nil
}