Handle additional error cases in the manifest schema 1 implementation

image/docker/schema1.py

@@ -377,7 +377,11 @@ class DockerSchema1Manifest(ManifestInterface):
 
       metadata_string = history_obj[DOCKER_SCHEMA1_V1_COMPAT_KEY]
 
-      v1_metadata = json.loads(metadata_string)
+      try:
+        v1_metadata = json.loads(metadata_string)
+      except (ValueError, TypeError):
+        raise MalformedSchema1Manifest('Could not parse metadata string: %s' % metadata_string)
+
       command_list = v1_metadata.get('container_config', {}).get('Cmd', None)
       command = to_canonical_json(command_list) if command_list else None
 
@@ -536,7 +540,7 @@ class DockerSchema1ManifestBuilder(object):
       DOCKER_SCHEMA1_BLOB_SUM_KEY: layer_digest,
     })
     self._history.append({
-      DOCKER_SCHEMA1_V1_COMPAT_KEY: v1_json_metadata,
+      DOCKER_SCHEMA1_V1_COMPAT_KEY: v1_json_metadata or '{}',
     })
     return self
 

image/docker/test/test_schema1.py

@@ -197,3 +197,19 @@ def test_validate_manifest_with_emoji(with_key):
   # Ensure the manifest can be reloaded.
   built_bytes = built.bytes.as_encoded_str()
   DockerSchema1Manifest(Bytes.for_string_or_unicode(built_bytes))
+
+
+@pytest.mark.parametrize('with_key', [
+  None,
+  docker_v2_signing_key,
+])
+def test_validate_manifest_with_none_metadata_layer(with_key):
+  builder = DockerSchema1ManifestBuilder('somenamespace', 'somerepo', 'sometag')
+  builder.add_layer('sha256:abcde', None)
+
+  built = builder.build(with_key, ensure_ascii=False)
+  built._validate()
+
+  # Ensure the manifest can be reloaded.
+  built_bytes = built.bytes.as_encoded_str()
+  DockerSchema1Manifest(Bytes.for_string_or_unicode(built_bytes))