Change OCI data model to use a content retriever for the various manifest operations

image/docker/schema2/list.py

@@ -225,8 +225,8 @@ class DockerSchema2ManifestList(ManifestInterface):
 
   @property
   def blob_digests(self):
-    manifests = self._parsed[DOCKER_SCHEMA2_MANIFESTLIST_MANIFESTS_KEY]
-    return [m[DOCKER_SCHEMA2_MANIFESTLIST_DIGEST_KEY] for m in manifests]
+    # Manifest lists have no blob digests, since everything is stored as a manifest.
+    return []
 
   @property
   def local_blob_digests(self):

image/docker/schema2/test/test_list.py

@@ -79,7 +79,7 @@ def test_valid_manifestlist():
   assert manifestlist.media_type == 'application/vnd.docker.distribution.manifest.list.v2+json'
   assert manifestlist.bytes == MANIFESTLIST_BYTES
   assert manifestlist.manifest_dict == json.loads(MANIFESTLIST_BYTES)
-  assert set(manifestlist.blob_digests) == {'sha256:e6', 'sha256:5b'}
+  assert not manifestlist.blob_digests
 
   for index, manifest in enumerate(manifestlist.manifests(retriever)):
     if index == 0: