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/schema2/config.py

@@ -99,6 +99,8 @@ from collections import namedtuple
 from jsonschema import validate as validate_schema, ValidationError
 from dateutil.parser import parse as parse_date
 
+from digest import digest_tools
+
 DOCKER_SCHEMA2_CONFIG_HISTORY_KEY = "history"
 DOCKER_SCHEMA2_CONFIG_ROOTFS_KEY = "rootfs"
 DOCKER_SCHEMA2_CONFIG_CREATED_KEY = "created"
@@ -167,6 +169,8 @@ class DockerSchema2Config(object):
   }
 
   def __init__(self, config_bytes):
+    self._config_bytes = config_bytes
+    
     try:
       self._parsed = json.loads(config_bytes)
     except ValueError as ve:
@@ -177,6 +181,21 @@ class DockerSchema2Config(object):
     except ValidationError as ve:
       raise MalformedSchema2Config('config data does not match schema: %s' % ve)
 
+  @property
+  def digest(self):
+    """ Returns the digest of this config object. """
+    return digest_tools.sha256_digest(self._config_bytes)
+
+  @property
+  def size(self):
+    """ Returns the size of this config object. """
+    return len(self._config_bytes)
+
+  @property
+  def labels(self):
+    """ Returns a dictionary of all the labels defined in this configuration. """
+    return self._parsed.get('config', {}).get('Labels', {}) or {}
+
   @property
   def history(self):
     """ Returns the history of the image, started at the base layer. """