export: add --skip-non-distributable

The flag skips adding non-distributable blobs such as Windows layers to archive.

Signed-off-by: Akihiro Suda <akihiro.suda.cz@hco.ntt.co.jp>

images/mediatypes.go

@@ -102,6 +102,12 @@ func parseMediaTypes(mt string) (string, []string) {
 	return s[0], ext
 }
 
+// IsNonDistributable returns true if the media type is non-distributable.
+func IsNonDistributable(mt string) bool {
+	return strings.HasPrefix(mt, "application/vnd.oci.image.layer.nondistributable.") ||
+		strings.HasPrefix(mt, "application/vnd.docker.image.rootfs.foreign.")
+}
+
 // IsLayerTypes returns true if the media type is a layer
 func IsLayerType(mt string) bool {
 	if strings.HasPrefix(mt, "application/vnd.oci.image.layer.") {