Add support for pushing and pulling schema 2 manifests with remote layers

This is required for windows image support

image/docker/schema2/manifest.py

@@ -136,6 +136,10 @@ class DockerSchema2Manifest(ManifestInterface):
     except ValidationError as ve:
       raise MalformedSchema2Manifest('manifest data does not match schema: %s' % ve)
 
+    for layer in self.layers:
+      if layer.is_remote and not layer.urls:
+        raise MalformedSchema2Manifest('missing `urls` for remote layer')
+
   @property
   def schema_version(self):
     return 2
@@ -169,18 +173,39 @@ class DockerSchema2Manifest(ManifestInterface):
   def leaf_layer(self):
     return self.layers[-1]
 
+  @property
+  def has_remote_layer(self):
+    for layer in self.layers:
+      if layer.is_remote:
+        return True
+
+    return False
+
   @property
   def leaf_layer_v1_image_id(self):
+    # NOTE: If there exists a layer with remote content, then we consider this manifest
+    # to not support legacy images.
+    if self.has_remote_layer:
+      return None
+
     return list(self.layers_with_v1_ids)[-1].v1_id
 
   @property
   def legacy_image_ids(self):
+    if self.has_remote_layer:
+      return None
+
     return [l.v1_id for l in self.layers_with_v1_ids]
 
   @property
   def blob_digests(self):
     return [str(layer.digest) for layer in self.layers] + [str(self.config.digest)]
 
+  @property
+  def local_blob_digests(self):
+    return ([str(layer.digest) for layer in self.layers if not layer.urls] +
+            [str(self.config.digest)])
+
   def get_manifest_labels(self, lookup_config_fn):
     return self._get_built_config(lookup_config_fn).labels
 
@@ -218,6 +243,7 @@ class DockerSchema2Manifest(ManifestInterface):
 
   @property
   def layers_with_v1_ids(self):
+    assert not self.has_remote_layer
     digest_history = hashlib.sha256()
     v1_layer_parent_id = None
     v1_layer_id = None
@@ -240,6 +266,7 @@ class DockerSchema2Manifest(ManifestInterface):
         this schema. The `lookup_config_fn` is a function that, when given the config
         digest SHA, returns the associated configuration JSON bytes for this schema.
     """
+    assert not self.has_remote_layer
     schema2_config = self._get_built_config(lookup_config_fn)
 
     # Build the V1 IDs for the layers.
@@ -253,6 +280,8 @@ class DockerSchema2Manifest(ManifestInterface):
     return v1_builder
 
   def generate_legacy_layers(self, images_map, lookup_config_fn):
+    assert not self.has_remote_layer
+
     # NOTE: We use the DockerSchema1ManifestBuilder here because it already contains
     # the logic for generating the DockerV1Metadata. All of this will go away once we get
     # rid of legacy images in the database, so this is a temporary solution.
@@ -261,6 +290,9 @@ class DockerSchema2Manifest(ManifestInterface):
     return v1_builder.build().generate_legacy_layers(images_map, lookup_config_fn)
 
   def get_v1_compatible_manifest(self, namespace_name, repo_name, tag_name, lookup_fn):
+    if self.has_remote_layer:
+      return None
+
     v1_builder = DockerSchema1ManifestBuilder(namespace_name, repo_name, tag_name)
     self.populate_schema1_builder(v1_builder, lookup_fn)
     return v1_builder.build()