@@ -133,6 +133,7 @@ type v2LayerDescriptor struct {

 	V2MetadataService *metadata.V2MetadataService

 	tmpFile           *os.File

 	verifier          digest.Verifier

+	foreignSrc        *distribution.Descriptor

 }

 func (ld *v2LayerDescriptor) Key() string {

@@ -180,9 +181,8 @@ func (ld *v2LayerDescriptor) Download(ctx context.Context, progressOutput progre

 	}

 	tmpFile := ld.tmpFile

-	blobs := ld.repo.Blobs(ctx)

-	layerDownload, err := blobs.Open(ctx, ld.digest)

+	layerDownload, err := ld.open(ctx)

 	if err != nil {

 		logrus.Errorf("Error initiating layer download: %v", err)

 		if err == distribution.ErrBlobUnknown {

@@ -501,6 +501,29 @@ func (p *v2Puller) pullSchema2(ctx context.Context, ref reference.Named, mfst *s

 		return imageID, manifestDigest, nil

 	}

+	var descriptors []xfer.DownloadDescriptor

+

+	// Note that the order of this loop is in the direction of bottom-most

+	// to top-most, so that the downloads slice gets ordered correctly.

+	for _, d := range mfst.Layers {

+		layerDescriptor := &v2LayerDescriptor{

+			digest:            d.Digest,

+			repo:              p.repo,

+			repoInfo:          p.repoInfo,

+			V2MetadataService: p.V2MetadataService,

+		}

+

+		if d.MediaType == schema2.MediaTypeForeignLayer && len(d.URLs) > 0 {

+			if !layer.ForeignSourceSupported() {

+				return "", "", errors.New("foreign layers are not supported on this OS")

+			}

+

+			layerDescriptor.foreignSrc = &d

+		}

+

+		descriptors = append(descriptors, layerDescriptor)

+	}

+

 	configChan := make(chan []byte, 1)

 	errChan := make(chan error, 1)

 	var cancel func()

@@ -517,21 +540,6 @@ func (p *v2Puller) pullSchema2(ctx context.Context, ref reference.Named, mfst *s

 		configChan <- configJSON

 	}()

-	var descriptors []xfer.DownloadDescriptor

-

-	// Note that the order of this loop is in the direction of bottom-most

-	// to top-most, so that the downloads slice gets ordered correctly.

-	for _, d := range mfst.References() {

-		layerDescriptor := &v2LayerDescriptor{

-			digest:            d.Digest,

-			repo:              p.repo,

-			repoInfo:          p.repoInfo,

-			V2MetadataService: p.V2MetadataService,

-		}

-

-		descriptors = append(descriptors, layerDescriptor)

-	}

-

 	var (

 		configJSON         []byte       // raw serialized image config

 		unmarshalledConfig image.Image  // deserialized image config

@@ -3,6 +3,8 @@

 package distribution

 import (

+	"github.com/docker/distribution"

+	"github.com/docker/distribution/context"

 	"github.com/docker/distribution/manifest/schema1"

 	"github.com/docker/docker/image"

 )

@@ -10,3 +12,8 @@ import (

 func detectBaseLayer(is image.Store, m *schema1.Manifest, rootFS *image.RootFS) error {

 	return nil

 }

+

+func (ld *v2LayerDescriptor) open(ctx context.Context) (distribution.ReadSeekCloser, error) {

+	blobs := ld.repo.Blobs(ctx)

+	return blobs.Open(ctx, ld.digest)

+}

@@ -5,9 +5,15 @@ package distribution

 import (

 	"encoding/json"

 	"fmt"

+	"net/http"

+	"os"

+	"github.com/docker/distribution"

+	"github.com/docker/distribution/context"

 	"github.com/docker/distribution/manifest/schema1"

+	"github.com/docker/distribution/registry/client/transport"

 	"github.com/docker/docker/image"

+	"github.com/docker/docker/layer"

 )

 func detectBaseLayer(is image.Store, m *schema1.Manifest, rootFS *image.RootFS) error {

@@ -28,3 +34,33 @@ func detectBaseLayer(is image.Store, m *schema1.Manifest, rootFS *image.RootFS)

 	}

 	return fmt.Errorf("Invalid base layer %q", v1img.Parent)

 }

+

+var _ layer.ForeignSourcer = &v2LayerDescriptor{}

+

+func (ld *v2LayerDescriptor) ForeignSource() *distribution.Descriptor {

+	return ld.foreignSrc

+}

+

+func (ld *v2LayerDescriptor) open(ctx context.Context) (distribution.ReadSeekCloser, error) {

+	if ld.foreignSrc == nil {

+		blobs := ld.repo.Blobs(ctx)

+		return blobs.Open(ctx, ld.digest)

+	}

+

+	var (

+		err error

+		rsc distribution.ReadSeekCloser

+	)

+

+	// Find the first URL that results in a 200 result code.

+	for _, url := range ld.foreignSrc.URLs {

+		rsc = transport.NewHTTPReadSeeker(http.DefaultClient, url, nil)

+		_, err = rsc.Seek(0, os.SEEK_SET)

+		if err == nil {

+			break

+		}

+		rsc.Close()

+		rsc = nil

+	}

+	return rsc, err

+}

@@ -240,6 +240,13 @@ func (pd *v2PushDescriptor) DiffID() layer.DiffID {

 }

 func (pd *v2PushDescriptor) Upload(ctx context.Context, progressOutput progress.Output) (distribution.Descriptor, error) {

+	if fs, ok := pd.layer.(layer.ForeignSourcer); ok {

+		if d := fs.ForeignSource(); d != nil {

+			progress.Update(progressOutput, pd.ID(), "Skipped foreign layer")

+			return *d, nil

+		}

+	}

+

 	diffID := pd.DiffID()

 	pd.pushState.Lock()

@@ -7,6 +7,7 @@ import (

 	"time"

 	"github.com/Sirupsen/logrus"

+	"github.com/docker/distribution"

 	"github.com/docker/docker/image"

 	"github.com/docker/docker/layer"

 	"github.com/docker/docker/pkg/archive"

@@ -318,7 +319,11 @@ func (ldm *LayerDownloadManager) makeDownloadFunc(descriptor DownloadDescriptor,

 				return

 			}

-			d.layer, err = d.layerStore.Register(inflatedLayerData, parentLayer)

+			var src *distribution.Descriptor

+			if fs, ok := descriptor.(layer.ForeignSourcer); ok {

+				src = fs.ForeignSource()

+			}

+			d.layer, err = d.layerStore.RegisterForeign(inflatedLayerData, parentLayer, src)

 			if err != nil {

 				select {

 				case <-d.Transfer.Context().Done():

@@ -409,7 +414,11 @@ func (ldm *LayerDownloadManager) makeDownloadFuncFromDownload(descriptor Downloa

 			}

 			defer layerReader.Close()

-			d.layer, err = d.layerStore.Register(layerReader, parentLayer)

+			var src *distribution.Descriptor

+			if fs, ok := l.(layer.ForeignSourcer); ok {

+				src = fs.ForeignSource()

+			}

+			d.layer, err = d.layerStore.RegisterForeign(layerReader, parentLayer, src)

 			if err != nil {

 				d.err = fmt.Errorf("failed to register layer: %v", err)

 				return

@@ -10,6 +10,7 @@ import (

 	"testing"

 	"time"

+	"github.com/docker/distribution"

 	"github.com/docker/distribution/digest"

 	"github.com/docker/docker/image"

 	"github.com/docker/docker/layer"

@@ -71,6 +72,10 @@ func createChainIDFromParent(parent layer.ChainID, dgsts ...layer.DiffID) layer.

 }

 func (ls *mockLayerStore) Register(reader io.Reader, parentID layer.ChainID) (layer.Layer, error) {

+	return ls.RegisterForeign(reader, parentID, nil)

+}

+

+func (ls *mockLayerStore) RegisterForeign(reader io.Reader, parentID layer.ChainID, _ *distribution.Descriptor) (layer.Layer, error) {

 	var (

 		parent layer.Layer

 		err    error

@@ -10,6 +10,7 @@ import (

 	"reflect"

 	"github.com/Sirupsen/logrus"

+	"github.com/docker/distribution"

 	"github.com/docker/docker/image"

 	"github.com/docker/docker/image/v1"

 	"github.com/docker/docker/layer"

@@ -63,6 +64,10 @@ func (l *tarexporter) Load(inTar io.ReadCloser, outStream io.Writer, quiet bool)

 	var parentLinks []parentLink

 	for _, m := range manifest {

+		if m.LayerSources != nil && !layer.ForeignSourceSupported() {

+			return fmt.Errorf("invalid manifest, foreign layers not supported on this operating system")

+		}

+

 		configPath, err := safePath(tmpDir, m.Config)

 		if err != nil {

 			return err

@@ -92,7 +97,7 @@ func (l *tarexporter) Load(inTar io.ReadCloser, outStream io.Writer, quiet bool)

 			r.Append(diffID)

 			newLayer, err := l.ls.Get(r.ChainID())

 			if err != nil {

-				newLayer, err = l.loadLayer(layerPath, rootFS, diffID.String(), progressOutput)

+				newLayer, err = l.loadLayer(layerPath, rootFS, diffID.String(), m.LayerSources[diffID], progressOutput)

 				if err != nil {

 					return err

 				}

@@ -151,7 +156,7 @@ func (l *tarexporter) setParentID(id, parentID image.ID) error {

 	return l.is.SetParent(id, parentID)

 }

-func (l *tarexporter) loadLayer(filename string, rootFS image.RootFS, id string, progressOutput progress.Output) (layer.Layer, error) {

+func (l *tarexporter) loadLayer(filename string, rootFS image.RootFS, id string, foreignSrc *distribution.Descriptor, progressOutput progress.Output) (layer.Layer, error) {

 	rawTar, err := os.Open(filename)

 	if err != nil {

 		logrus.Debugf("Error reading embedded tar: %v", err)

@@ -174,9 +179,9 @@ func (l *tarexporter) loadLayer(filename string, rootFS image.RootFS, id string,

 		progressReader := progress.NewProgressReader(inflatedLayerData, progressOutput, fileInfo.Size(), stringid.TruncateID(id), "Loading layer")

-		return l.ls.Register(progressReader, rootFS.ChainID())

+		return l.ls.RegisterForeign(progressReader, rootFS.ChainID(), foreignSrc)

 	}

-	return l.ls.Register(inflatedLayerData, rootFS.ChainID())

+	return l.ls.RegisterForeign(inflatedLayerData, rootFS.ChainID(), foreignSrc)

 }

 func (l *tarexporter) setLoadedTag(ref reference.NamedTagged, imgID image.ID, outStream io.Writer) error {

@@ -298,7 +303,7 @@ func (l *tarexporter) legacyLoadImage(oldID, sourceDir string, loadedMap map[str

 	if err != nil {

 		return err

 	}

-	newLayer, err := l.loadLayer(layerPath, *rootFS, oldID, progressOutput)

+	newLayer, err := l.loadLayer(layerPath, *rootFS, oldID, nil, progressOutput)

 	if err != nil {

 		return err

 	}

@@ -9,6 +9,7 @@ import (

 	"path/filepath"

 	"time"

+	"github.com/docker/distribution"

 	"github.com/docker/distribution/digest"

 	"github.com/docker/docker/image"

 	"github.com/docker/docker/image/v1"

@@ -131,7 +132,8 @@ func (s *saveSession) save(outStream io.Writer) error {

 	var parentLinks []parentLink

 	for id, imageDescr := range s.images {

-		if err = s.saveImage(id); err != nil {

+		foreignSrcs, err := s.saveImage(id)

+		if err != nil {

 			return err

 		}

@@ -151,9 +153,10 @@ func (s *saveSession) save(outStream io.Writer) error {

 		}

 		manifest = append(manifest, manifestItem{

-			Config:   digest.Digest(id).Hex() + ".json",

-			RepoTags: repoTags,

-			Layers:   layers,

+			Config:       digest.Digest(id).Hex() + ".json",

+			RepoTags:     repoTags,

+			Layers:       layers,

+			LayerSources: foreignSrcs,

 		})

 		parentID, _ := s.is.GetParent(id)

@@ -213,18 +216,19 @@ func (s *saveSession) save(outStream io.Writer) error {

 	return nil

 }

-func (s *saveSession) saveImage(id image.ID) error {

+func (s *saveSession) saveImage(id image.ID) (map[layer.DiffID]*distribution.Descriptor, error) {

 	img, err := s.is.Get(id)

 	if err != nil {

-		return err

+		return nil, err

 	}

 	if len(img.RootFS.DiffIDs) == 0 {

-		return fmt.Errorf("empty export - not implemented")

+		return nil, fmt.Errorf("empty export - not implemented")

 	}

 	var parent digest.Digest

 	var layers []string

+	var foreignSrcs map[layer.DiffID]*distribution.Descriptor

 	for i := range img.RootFS.DiffIDs {

 		v1Img := image.V1Image{}

 		if i == len(img.RootFS.DiffIDs)-1 {

@@ -234,7 +238,7 @@ func (s *saveSession) saveImage(id image.ID) error {

 		rootFS.DiffIDs = rootFS.DiffIDs[:i+1]

 		v1ID, err := v1.CreateID(v1Img, rootFS.ChainID(), parent)

 		if err != nil {

-			return err

+			return nil, err

 		}

 		v1Img.ID = v1ID.Hex()

@@ -242,79 +246,91 @@ func (s *saveSession) saveImage(id image.ID) error {

 			v1Img.Parent = parent.Hex()

 		}

-		if err := s.saveLayer(rootFS.ChainID(), v1Img, img.Created); err != nil {

-			return err

+		src, err := s.saveLayer(rootFS.ChainID(), v1Img, img.Created)

+		if err != nil {

+			return nil, err

 		}

 		layers = append(layers, v1Img.ID)

 		parent = v1ID

+		if src != nil {

+			if foreignSrcs == nil {

+				foreignSrcs = make(map[layer.DiffID]*distribution.Descriptor)

+			}

+			foreignSrcs[img.RootFS.DiffIDs[i]] = src

+		}

 	}

 	configFile := filepath.Join(s.outDir, digest.Digest(id).Hex()+".json")

 	if err := ioutil.WriteFile(configFile, img.RawJSON(), 0644); err != nil {

-		return err

+		return nil, err

 	}

 	if err := system.Chtimes(configFile, img.Created, img.Created); err != nil {

-		return err

+		return nil, err

 	}

 	s.images[id].layers = layers

-	return nil

+	return foreignSrcs, nil

 }

-func (s *saveSession) saveLayer(id layer.ChainID, legacyImg image.V1Image, createdTime time.Time) error {

+func (s *saveSession) saveLayer(id layer.ChainID, legacyImg image.V1Image, createdTime time.Time) (*distribution.Descriptor, error) {

 	if _, exists := s.savedLayers[legacyImg.ID]; exists {

-		return nil

+		return nil, nil

 	}

 	outDir := filepath.Join(s.outDir, legacyImg.ID)

 	if err := os.Mkdir(outDir, 0755); err != nil {

-		return err

+		return nil, err

 	}

 	// todo: why is this version file here?

 	if err := ioutil.WriteFile(filepath.Join(outDir, legacyVersionFileName), []byte("1.0"), 0644); err != nil {

-		return err

+		return nil, err

 	}

 	imageConfig, err := json.Marshal(legacyImg)

 	if err != nil {

-		return err

+		return nil, err

 	}

 	if err := ioutil.WriteFile(filepath.Join(outDir, legacyConfigFileName), imageConfig, 0644); err != nil {

-		return err

+		return nil, err

 	}

 	// serialize filesystem

 	tarFile, err := os.Create(filepath.Join(outDir, legacyLayerFileName))

 	if err != nil {

-		return err

+		return nil, err

 	}

 	defer tarFile.Close()

 	l, err := s.ls.Get(id)

 	if err != nil {

-		return err

+		return nil, err

 	}

 	defer layer.ReleaseAndLog(s.ls, l)

 	arch, err := l.TarStream()

 	if err != nil {

-		return err

+		return nil, err

 	}

 	defer arch.Close()

 	if _, err := io.Copy(tarFile, arch); err != nil {

-		return err

+		return nil, err

 	}

 	for _, fname := range []string{"", legacyVersionFileName, legacyConfigFileName, legacyLayerFileName} {

 		// todo: maybe save layer created timestamp?

 		if err := system.Chtimes(filepath.Join(outDir, fname), createdTime, createdTime); err != nil {

-			return err

+			return nil, err

 		}

 	}

 	s.savedLayers[legacyImg.ID] = struct{}{}

-	return nil

+

+	var src *distribution.Descriptor

+	if fs, ok := l.(layer.ForeignSourcer); ok {

+		src = fs.ForeignSource()

+	}

+	return src, nil

 }

@@ -1,6 +1,7 @@

 package tarexport

 import (

+	"github.com/docker/distribution"

 	"github.com/docker/docker/image"

 	"github.com/docker/docker/layer"

 	"github.com/docker/docker/reference"

@@ -15,10 +16,11 @@ const (

 )

 type manifestItem struct {

-	Config   string

-	RepoTags []string

-	Layers   []string

-	Parent   image.ID `json:",omitempty"`

+	Config       string

+	RepoTags     []string

+	Layers       []string

+	Parent       image.ID                                  `json:",omitempty"`

+	LayerSources map[layer.DiffID]*distribution.Descriptor `json:",omitempty"`

 }

 type tarexporter struct {

@@ -2,6 +2,7 @@ package layer

 import (

 	"compress/gzip"

+	"encoding/json"

 	"errors"

 	"fmt"

 	"io"

@@ -13,6 +14,7 @@ import (

 	"strings"

 	"github.com/Sirupsen/logrus"

+	"github.com/docker/distribution"

 	"github.com/docker/distribution/digest"

 	"github.com/docker/docker/pkg/ioutils"

 )

@@ -24,6 +26,9 @@ var (

 		// digest.SHA384, // Currently not used

 		// digest.SHA512, // Currently not used

 	}

+

+	// ErrNoForeignSource is returned when no foreign source is set for a layer.

+	ErrNoForeignSource = errors.New("layer does not have a foreign source")

 )

 type fileMetadataStore struct {

@@ -98,6 +103,14 @@ func (fm *fileMetadataTransaction) SetCacheID(cacheID string) error {

 	return ioutil.WriteFile(filepath.Join(fm.root, "cache-id"), []byte(cacheID), 0644)

 }

+func (fm *fileMetadataTransaction) SetForeignSource(ref distribution.Descriptor) error {

+	jsonRef, err := json.Marshal(ref)

+	if err != nil {

+		return err

+	}

+	return ioutil.WriteFile(filepath.Join(fm.root, "descriptor.json"), jsonRef, 0644)

+}

+

 func (fm *fileMetadataTransaction) TarSplitWriter(compressInput bool) (io.WriteCloser, error) {

 	f, err := os.OpenFile(filepath.Join(fm.root, "tar-split.json.gz"), os.O_TRUNC|os.O_CREATE|os.O_WRONLY, 0644)

 	if err != nil {

@@ -191,6 +204,23 @@ func (fms *fileMetadataStore) GetCacheID(layer ChainID) (string, error) {

 	return content, nil

 }

+func (fms *fileMetadataStore) GetForeignSource(layer ChainID) (distribution.Descriptor, error) {

+	content, err := ioutil.ReadFile(fms.getLayerFilename(layer, "descriptor.json"))

+	if err != nil {

+		if os.IsNotExist(err) {

+			return distribution.Descriptor{}, ErrNoForeignSource

+		}

+		return distribution.Descriptor{}, err

+	}

+

+	var ref distribution.Descriptor

+	err = json.Unmarshal(content, &ref)

+	if err != nil {

+		return distribution.Descriptor{}, err

+	}

+	return ref, err

+}

+

 func (fms *fileMetadataStore) TarSplitReader(layer ChainID) (io.ReadCloser, error) {

 	fz, err := os.Open(fms.getLayerFilename(layer, "tar-split.json.gz"))

 	if err != nil {

@@ -14,6 +14,7 @@ import (

 	"io"

 	"github.com/Sirupsen/logrus"

+	"github.com/docker/distribution"

 	"github.com/docker/distribution/digest"

 	"github.com/docker/docker/pkg/archive"

 )

@@ -107,6 +108,14 @@ type Layer interface {

 	Metadata() (map[string]string, error)

 }

+// ForeignSourcer is an interface used to describe the source of layers

+// and objects representing layers, when the source is a foreign URL.

+type ForeignSourcer interface {

+	// ForeignSource returns the descriptor for this layer if it is

+	// a foreign layer, or nil for ordinary layers.

+	ForeignSource() *distribution.Descriptor

+}

+

 // RWLayer represents a layer which is

 // read and writable

 type RWLayer interface {

@@ -168,6 +177,7 @@ type MountInit func(root string) error

 // read-only and read-write layers.

 type Store interface {

 	Register(io.Reader, ChainID) (Layer, error)

+	RegisterForeign(io.Reader, ChainID, *distribution.Descriptor) (Layer, error)

 	Get(ChainID) (Layer, error)

 	Release(Layer) ([]Metadata, error)

@@ -189,6 +199,7 @@ type MetadataTransaction interface {

 	SetParent(parent ChainID) error

 	SetDiffID(DiffID) error

 	SetCacheID(string) error

+	SetForeignSource(distribution.Descriptor) error

 	TarSplitWriter(compressInput bool) (io.WriteCloser, error)

 	Commit(ChainID) error

@@ -208,6 +219,7 @@ type MetadataStore interface {

 	GetParent(ChainID) (ChainID, error)

 	GetDiffID(ChainID) (DiffID, error)

 	GetCacheID(ChainID) (string, error)

+	GetForeignSource(ChainID) (distribution.Descriptor, error)

 	TarSplitReader(ChainID) (io.ReadCloser, error)

 	SetMountID(string, string) error

@@ -8,6 +8,7 @@ import (

 	"sync"

 	"github.com/Sirupsen/logrus"

+	"github.com/docker/distribution"

 	"github.com/docker/distribution/digest"

 	"github.com/docker/docker/daemon/graphdriver"

 	"github.com/docker/docker/pkg/archive"

@@ -137,6 +138,13 @@ func (ls *layerStore) loadLayer(layer ChainID) (*roLayer, error) {

 		references: map[Layer]struct{}{},

 	}

+	foreignSrc, err := ls.store.GetForeignSource(layer)

+	if err == nil {

+		cl.foreignSrc = &foreignSrc

+	} else if err != ErrNoForeignSource {

+		return nil, fmt.Errorf("failed to get foreign reference for %s: %s", layer, err)

+	}

+

 	if parent != "" {

 		p, err := ls.loadLayer(parent)

 		if err != nil {

@@ -228,6 +236,10 @@ func (ls *layerStore) applyTar(tx MetadataTransaction, ts io.Reader, parent stri

 }

 func (ls *layerStore) Register(ts io.Reader, parent ChainID) (Layer, error) {

+	return ls.RegisterForeign(ts, parent, nil)

+}

+

+func (ls *layerStore) RegisterForeign(ts io.Reader, parent ChainID, foreignSrc *distribution.Descriptor) (Layer, error) {

 	// err is used to hold the error which will always trigger

 	// cleanup of creates sources but may not be an error returned

 	// to the caller (already exists).

@@ -258,6 +270,7 @@ func (ls *layerStore) Register(ts io.Reader, parent ChainID) (Layer, error) {

 	layer := &roLayer{

 		parent:         p,

 		cacheID:        stringid.GenerateRandomID(),

+		foreignSrc:     foreignSrc,

 		referenceCount: 1,

 		layerStore:     ls,

 		references:     map[Layer]struct{}{},

@@ -7,3 +7,9 @@ import "github.com/docker/docker/pkg/stringid"

 func (ls *layerStore) mountID(name string) string {

 	return stringid.GenerateRandomID()

 }

+

+// ForeignSourceSupported returns whether layers downloaded from foreign sources are

+// supported in this daemon.

+func ForeignSourceSupported() bool {

+	return false

+}

@@ -96,3 +96,9 @@ func (ls *layerStore) mountID(name string) string {

 func (ls *layerStore) GraphDriver() graphdriver.Driver {

 	return ls.driver

 }

+

+// ForeignSourceSupported returns whether layers downloaded from foreign sources are

+// supported in this daemon.

+func ForeignSourceSupported() bool {

+	return true

+}

@@ -4,6 +4,7 @@ import (

 	"fmt"

 	"io"

+	"github.com/docker/distribution"

 	"github.com/docker/distribution/digest"

 )

@@ -14,6 +15,7 @@ type roLayer struct {

 	cacheID    string

 	size       int64

 	layerStore *layerStore

+	foreignSrc *distribution.Descriptor

 	referenceCount int

 	references     map[Layer]struct{}

@@ -123,6 +125,11 @@ func storeLayer(tx MetadataTransaction, layer *roLayer) error {

 			return err

 		}

 	}

+	if layer.foreignSrc != nil {

+		if err := tx.SetForeignSource(*layer.foreignSrc); err != nil {

+			return err

+		}

+	}

 	return nil

 }

new file mode 100644

@@ -0,0 +1,9 @@

+package layer

+

+import "github.com/docker/distribution"

+

+var _ ForeignSourcer = &roLayer{}

+

+func (rl *roLayer) ForeignSource() *distribution.Descriptor {

+	return rl.foreignSrc

+}