When copying extended run image layers, use the original number of la…

…yers

in addition to the original top layer digest
to determine what is an extension layer and what is an original layer.
Relying on the original top layer digest (only) introduced errors
if the original run image had a duplicated top layer.

Fixes #1300

Signed-off-by: Natalie Arellano <narellano@vmware.com>

phase/extender.go

@@ -140,7 +140,7 @@ func (e *Extender) extendRun(logger log.Logger) error {
 		return fmt.Errorf("getting run image to extend: %w", err)
 	}
 
-	origTopLayer, err := topLayerDigest(origBaseImage, logger)
+	origTopLayer, origNumLayers, err := topLayerDigest(origBaseImage, logger)
 	if err != nil {
 		return fmt.Errorf("getting original run image top layer: %w", err)
 	}
@@ -151,35 +151,35 @@ func (e *Extender) extendRun(logger log.Logger) error {
 		return fmt.Errorf("extending run image: %w", err)
 	}
 
-	if err = e.saveSparse(extendedImage, origTopLayer, logger); err != nil {
+	if err = e.saveSparse(extendedImage, origTopLayer, origNumLayers, logger); err != nil {
 		return fmt.Errorf("failed to copy extended image to output directory: %w", err)
 	}
 	return e.DockerfileApplier.Cleanup()
 }
 
-func topLayerDigest(image v1.Image, logger log.Logger) (string, error) {
+func topLayerDigest(image v1.Image, logger log.Logger) (string, int, error) {
 	imageHash, err := image.Digest()
 	if err != nil {
-		return "", err
+		return "", -1, err
 	}
 
 	manifest, err := image.Manifest()
 	if err != nil {
-		return "", fmt.Errorf("getting image manifest: %w", err)
+		return "", -1, fmt.Errorf("getting image manifest: %w", err)
 	}
 
 	allLayers := manifest.Layers
 	logger.Debugf("Found %d layers in original image with digest: %s", len(allLayers), imageHash)
 
 	if len(allLayers) == 0 {
-		return "", nil
+		return "", 0, nil
 	}
 
 	layer := allLayers[len(allLayers)-1]
-	return layer.Digest.String(), nil
+	return layer.Digest.String(), len(allLayers), nil
 }
 
-func (e *Extender) saveSparse(image v1.Image, origTopLayerHash string, logger log.Logger) error {
+func (e *Extender) saveSparse(image v1.Image, origTopLayerHash string, origNumLayers int, logger log.Logger) error {
 	// save sparse image (manifest and config)
 	imageHash, err := image.Digest()
 	if err != nil {
@@ -209,7 +209,7 @@ func (e *Extender) saveSparse(image v1.Image, origTopLayerHash string, logger lo
 		needsCopying = true
 	}
 	group, _ := errgroup.WithContext(context.TODO())
-	for _, currentLayer := range allLayers {
+	for idx, currentLayer := range allLayers {
 		currentHash, err = currentLayer.Digest()
 		if err != nil {
 			return fmt.Errorf("getting layer hash: %w", err)
@@ -221,10 +221,13 @@ func (e *Extender) saveSparse(image v1.Image, origTopLayerHash string, logger lo
 			group.Go(func() error {
 				return copyLayer(currentLayer, toPath)
 			})
-		case currentHash.String() == origTopLayerHash:
+		case currentHash.String() == origTopLayerHash && idx+1 == origNumLayers:
 			logger.Debugf("Found original top layer with digest: %s", currentHash)
 			needsCopying = true
 			continue
+		case currentHash.String() == origTopLayerHash:
+			logger.Warnf("Original run image has duplicated top layer with digest: %s", currentHash)
+			continue
 		default:
 			logger.Debugf("Skipping base layer with digest: %s", currentHash)
 			continue