Fix an NPE when trying to pull a manifest without a legacy image via V1

data/registry_model/interface.py

@@ -12,6 +12,12 @@ class RegistryDataInterface(object):
     """ Returns whether the implementation of the data interface supports schema 2 format
         manifests. """
 
+  @abstractmethod
+  def get_tag_legacy_image_id(self, repository_ref, tag_name, storage):
+    """ Returns the legacy image ID for the tag with a legacy images in
+        the repository. Returns None if None.
+    """
+
   @abstractmethod
   def get_legacy_tags_map(self, repository_ref, storage):
     """ Returns a map from tag name to its legacy image ID, for all tags with legacy images in

data/registry_model/registry_oci_model.py

@@ -30,6 +30,25 @@ class OCIModel(SharedModel, RegistryDataInterface):
         manifests. """
     return True
 
+  def get_tag_legacy_image_id(self, repository_ref, tag_name, storage):
+    """ Returns the legacy image ID for the tag with a legacy images in
+        the repository. Returns None if None.
+    """
+    tag = self.get_repo_tag(repository_ref, tag_name, include_legacy_image=True)
+    if tag is None:
+      return None
+
+    if tag.legacy_image_if_present is not None:
+      return tag.legacy_image_if_present.docker_image_id
+
+    if tag.manifest.media_type == DOCKER_SCHEMA2_MANIFESTLIST_CONTENT_TYPE:
+      # See if we can lookup a schema1 legacy image.
+      v1_compatible = self.get_schema1_parsed_manifest(tag.manifest, '', '', '', storage)
+      if v1_compatible is not None:
+        return v1_compatible.leaf_layer_v1_image_id
+
+    return None
+
   def get_legacy_tags_map(self, repository_ref, storage):
     """ Returns a map from tag name to its legacy image ID, for all tags with legacy images in
         the repository. Note that this can be a *very* heavy operation.
@@ -52,7 +71,6 @@ class OCIModel(SharedModel, RegistryDataInterface):
             if v1_id is not None:
               tags_map[tag.name] = v1_id
 
-
     return tags_map
 
   def _get_legacy_compatible_image_for_manifest(self, manifest, storage):

data/registry_model/registry_pre_oci_model.py

@@ -33,6 +33,16 @@ class PreOCIModel(SharedModel, RegistryDataInterface):
         manifests. """
     return False
 
+  def get_tag_legacy_image_id(self, repository_ref, tag_name, storage):
+    """ Returns the legacy image ID for the tag with a legacy images in
+        the repository. Returns None if None.
+    """
+    tag = self.get_repo_tag(repository_ref, tag_name, include_legacy_image=True)
+    if tag is None:
+      return None
+
+    return tag.legacy_image.docker_image_id
+
   def get_legacy_tags_map(self, repository_ref, storage):
     """ Returns a map from tag name to its legacy image, for all tags with legacy images in
         the repository.