Enhancements for Docker schema implementations in preparing for supporting schema 2 in the OCI model

This adds additional required properties and methods to the Docker schema interface to allow us to treat both schema1 and schema2 manifests and lists logically equivalent from the OCI mode perspective

image/docker/interfaces.py

@@ -1,4 +1,4 @@
-from abc import ABCMeta, abstractproperty
+from abc import ABCMeta, abstractproperty, abstractmethod
 from six import add_metaclass
 
 @add_metaclass(ABCMeta)
@@ -26,7 +26,7 @@ class ManifestInterface(object):
 
   @abstractproperty
   def layers(self):
-    """ Returns the layers of this manifest, from base to leaf. """
+    """ Returns the layers of this manifest, from base to leaf or None if none. """
     pass
 
   @abstractproperty
@@ -43,5 +43,34 @@ class ManifestInterface(object):
   @abstractproperty
   def blob_digests(self):
     """ Returns an iterator over all the blob digests referenced by this manifest,
-        from base to leaf. The blob digests are strings with prefixes.
+        from base to leaf. The blob digests are strings with prefixes. For manifests that reference
+        config as a blob, the blob will be included here.
+    """
+
+  @abstractmethod
+  def child_manifests(self, lookup_manifest_fn):
+    """ Returns an iterator of all manifests that live under this manifest, if any or None if none.
+        The lookup_manifest_fn is a function that, when given a blob content SHA, returns the
+        contents of that blob in storage if any or None if none.
+    """
+
+  @abstractmethod
+  def get_manifest_labels(self, lookup_config_fn):
+    """ Returns a dictionary of all the labels defined inside this manifest or None if none. """
+    pass
+
+  @abstractmethod
+  def unsigned(self):
+    """ Returns an unsigned version of this manifest. """
+
+  @abstractmethod
+  def generate_legacy_layers(self, images_map, lookup_config_fn):
+    """
+    Rewrites Docker v1 image IDs and returns a generator of DockerV1Metadata.
+
+    If Docker gives us a layer with a v1 image ID that already points to existing
+    content, but the checksums don't match, then we need to rewrite the image ID
+    to something new in order to ensure consistency.
+
+    Returns None if there are no legacy images associated with the manifest.
     """