Make sure list_manifest_layers is not callable for manifest lists

data/registry_model/interface.py

@@ -199,7 +199,7 @@ class RegistryDataInterface(object):
     """ Returns an *ordered list* of the layers found in the manifest, starting at the base
         and working towards the leaf, including the associated Blob and its placements
         (if specified). The layer information in `layer_info` will be of type
-        `image.docker.types.ManifestImageLayer`.
+        `image.docker.types.ManifestImageLayer`. Should not be called for a manifest list.
     """
 
   @abstractmethod
@@ -208,7 +208,7 @@ class RegistryDataInterface(object):
     """ Returns an *ordered list* of the layers found in the parsed manifest, starting at the base
         and working towards the leaf, including the associated Blob and its placements
         (if specified). The layer information in `layer_info` will be of type
-        `image.docker.types.ManifestImageLayer`.
+        `image.docker.types.ManifestImageLayer`. Should not be called for a manifest list.
     """
 
   @abstractmethod

data/registry_model/shared.py

@@ -345,6 +345,8 @@ class SharedModel:
         working towards the leaf, including the associated Blob and its placements (if specified).
         Returns None if the manifest could not be parsed and validated.
     """
+    assert not parsed.is_manifest_list
+
     retriever = RepositoryContentRetriever(repo_id, storage)
     requires_empty_blob = parsed.get_requires_empty_layer_blob(retriever)
 

endpoints/api/manifest.py

@@ -58,8 +58,10 @@ def _manifest_dict(manifest):
   if manifest.legacy_image_if_present is not None:
     image = image_dict(manifest.legacy_image, with_history=True)
 
+  layers = None
+  if not manifest.is_manifest_list:
     layers = registry_model.list_manifest_layers(manifest, storage)
-  if layers is None and not manifest.is_manifest_list:
+    if layers is None:
       logger.debug('Missing layers for manifest `%s`', manifest.digest)
       abort(404)