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package layer // import "github.com/docker/docker/layer"
import (
"archive/tar"
"bytes"
"fmt"
"io"
)
// DigestSHA256EmptyTar is the canonical sha256 digest of empty tar file -
// (1024 NULL bytes)
const DigestSHA256EmptyTar = DiffID("sha256:5f70bf18a086007016e948b04aed3b82103a36bea41755b6cddfaf10ace3c6ef")
type emptyLayer struct{}
// EmptyLayer is a layer that corresponds to empty tar.
var EmptyLayer = &emptyLayer{}
func (el *emptyLayer) TarStream() (io.ReadCloser, error) {
buf := new(bytes.Buffer)
tarWriter := tar.NewWriter(buf)
tarWriter.Close()
return io.NopCloser(buf), nil
}
func (el *emptyLayer) TarStreamFrom(p ChainID) (io.ReadCloser, error) {
if p == "" {
return el.TarStream()
}
return nil, fmt.Errorf("can't get parent tar stream of an empty layer")
}
func (el *emptyLayer) ChainID() ChainID {
return ChainID(DigestSHA256EmptyTar)
}
func (el *emptyLayer) DiffID() DiffID {
return DigestSHA256EmptyTar
}
func (el *emptyLayer) Parent() Layer {
return nil
}
func (el *emptyLayer) Size() (size int64, err error) {
return 0, nil
}
func (el *emptyLayer) DiffSize() (size int64, err error) {
return 0, nil
}
func (el *emptyLayer) Metadata() (map[string]string, error) {
return make(map[string]string), nil
}
// IsEmpty returns true if the layer is an EmptyLayer
func IsEmpty(diffID DiffID) bool {
return diffID == DigestSHA256EmptyTar
}
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