Don't export whiteouts for single layers (#1629)

pkg/crane/export.go

@@ -30,16 +30,23 @@ func Export(img v1.Image, w io.Writer) error {
 		return err
 	}
 	if len(layers) == 1 {
-		// If it's a single layer, we don't have to flatten the filesystem.
-		// An added perk of skipping mutate.Extract here is that this works
-		// for non-tarball layers.
+		// If it's a single layer...
 		l := layers[0]
-		rc, err := l.Uncompressed()
+		mt, err := l.MediaType()
 		if err != nil {
 			return err
 		}
-		_, err = io.Copy(w, rc)
-		return err
+
+		if !mt.IsLayer() {
+			// ...and isn't an OCI mediaType, we don't have to flatten it.
+			// This lets export work for single layer, non-tarball images.
+			rc, err := l.Uncompressed()
+			if err != nil {
+				return err
+			}
+			_, err = io.Copy(w, rc)
+			return err
+		}
 	}
 	fs := mutate.Extract(img)
 	_, err = io.Copy(w, fs)

pkg/v1/types/types.go

@@ -88,3 +88,11 @@ func (m MediaType) IsSchema1() bool {
 	}
 	return false
 }
+
+func (m MediaType) IsLayer() bool {
+	switch m {
+	case DockerLayer, DockerUncompressedLayer, OCILayer, OCILayerZStd, OCIUncompressedLayer, DockerForeignLayer, OCIRestrictedLayer, OCIUncompressedRestrictedLayer:
+		return true
+	}
+	return false
+}