New metadata API: add MetadataInfo and TargetFile classes

tuf/api/metadata.py

@@ -281,8 +281,6 @@ def __init__(
  self.expires = expires
 
  # TODO: Should we separate data validation from constructor?
- if version < 0:
- raise ValueError(f'version must be < 0, got {version}')
  self.version = version
 
 
@@ -291,22 +289,24 @@ def __init__(
  def from_dict(cls, signed_dict: JsonDict) -> 'Signed':
  """Creates Signed object from its JSON/dict representation. """
 
+ # Create empty object with default or parametrized constructor with
+ # default arguments.
+ obj = cls()
+ obj._type = signed_dict['_type']
+ obj.version = signed_dict['version']
+ obj.spec_version = signed_dict['spec_version']
  # Convert 'expires' TUF metadata string to a datetime object, which is
  # what the constructor expects and what we store. The inverse operation
  # is implemented in 'to_dict'.
- signed_dict['expires'] = tuf.formats.expiry_string_to_datetime(
+ obj.expires = tuf.formats.expiry_string_to_datetime(
  signed_dict['expires'])
- # NOTE: We write the converted 'expires' back into 'signed_dict' above
- # so that we can pass it to the constructor as '**signed_dict' below,
- # along with other fields that belong to Signed subclasses.
- # Any 'from_dict'(-like) conversions of fields that correspond to a
- # subclass should be performed in the 'from_dict' method of that
- # subclass and also be written back into 'signed_dict' before calling
- # super().from_dict.
+ # NOTE: Any 'from_dict'(-like) conversions of fields that correspond
+ # to a subclass should be performed in the 'from_dict' method of that
+ # subclass and assigned to the below returned object.
 
  # NOTE: cls might be a subclass of Signed, if 'from_dict' was called on
  # that subclass (see e.g. Metadata.from_dict).
- return cls(**signed_dict)
+ return obj
 
 
  # Serialization.
@@ -378,16 +378,28 @@ class Root(Signed):
  # default max-args value for pylint is 5
  # pylint: disable=too-many-arguments
  def __init__(
- self, _type: str, version: int, spec_version: str,
- expires: datetime, consistent_snapshot: bool,
- keys: JsonDict, roles: JsonDict) -> None:
+ self, _type: str=None, version: int=None, spec_version: str=None,
+ expires: datetime=None, consistent_snapshot: bool=None,
+ keys: JsonDict=None, roles: JsonDict=None) -> None:
  super().__init__(_type, version, spec_version, expires)
  # TODO: Add classes for keys and roles
  self.consistent_snapshot = consistent_snapshot
  self.keys = keys
  self.roles = roles
 
 
+ @classmethod
+ def from_dict(cls, signed_dict: JsonDict) -> 'Root':
+ """Creates Root object from its JSON/dict representation. """
+
+ # Get a parent object with its attributes already assigned.
+ obj = super().from_dict(signed_dict)
+ obj.consistent_snapshot = signed_dict['consistent_snapshot']
+ obj.keys = signed_dict['keys']
+ obj.roles = signed_dict['roles']
+ return obj
+
+
  # Serialization.
  def to_dict(self) -> JsonDict:
  """Returns the JSON-serializable dictionary representation of self. """
@@ -478,8 +490,9 @@ class Timestamp(Signed):
 
  """
  def __init__(
- self, _type: str, version: int, spec_version: str,
- expires: datetime, meta: Dict[str, MetadataInfo]) -> None:
+ self, _type: str=None, version: int=None, spec_version: str=None,
+ expires: datetime=None, meta: Dict[str, MetadataInfo]=None
+ ) -> None:
  super().__init__(_type, version, spec_version, expires)
  self.meta = meta
 
@@ -500,10 +513,14 @@ def to_dict(self) -> JsonDict:
  def from_dict(cls, signed_dict: JsonDict) -> 'Timestamp':
  """Creates Timestamp object from its JSON/dict representation. """
 
- signed_dict['meta']['snapshot.json'] = MetadataInfo(
- **signed_dict['meta']['snapshot.json'])
+ # Get a parent object with its attributes already assigned.
+ obj = super().from_dict(signed_dict)
+ obj.meta = {}
+ meta = signed_dict['meta']['snapshot.json']
+ obj.meta['snapshot.json'] = MetadataInfo(meta['version'],
+ meta.get('length'), meta.get('hashes'))
 
- return super().from_dict(signed_dict)
+ return obj
 
 
  # Modification.
@@ -529,8 +546,9 @@ class Snapshot(Signed):
 
  """
  def __init__(
- self, _type: str, version: int, spec_version: str,
- expires: datetime, meta: Dict[str, MetadataInfo]) -> None:
+ self, _type: str=None, version: int=None, spec_version: str=None,
+ expires: datetime=None, meta: Dict[str, MetadataInfo]=None
+ ) -> None:
  super().__init__(_type, version, spec_version, expires)
  self.meta = meta
 
@@ -539,11 +557,15 @@ def __init__(
  def from_dict(cls, signed_dict: JsonDict) -> 'Snapshot':
  """Creates Snapshot object from its JSON/dict representation. """
 
+ # Get a parent object with its attributes already assigned.
+ obj = super().from_dict(signed_dict)
+ obj.meta = {}
  for meta_path in signed_dict['meta'].keys():
- signed_dict['meta'][meta_path] = MetadataInfo(
- **signed_dict['meta'][meta_path])
+ meta = signed_dict['meta'][meta_path]
+ obj.meta[meta_path] = MetadataInfo(meta['version'],
+ meta.get('length'), meta.get('hashes'))
 
- return super().from_dict(signed_dict)
+ return obj
 
 
  # Serialization.
@@ -672,9 +694,9 @@ class Targets(Signed):
  # default max-args value for pylint is 5
  # pylint: disable=too-many-arguments
  def __init__(
- self, _type: str, version: int, spec_version: str,
- expires: datetime, targets: Dict[str, TargetInfo],
- delegations: JsonDict) -> None:
+ self, _type: str=None, version: int=None, spec_version: str=None,
+ expires: datetime=None, targets: Dict[str, TargetInfo]=None,
+ delegations: JsonDict=None) -> None:
  super().__init__(_type, version, spec_version, expires)
  self.targets = targets
 
@@ -685,11 +707,17 @@ def __init__(
  @classmethod
  def from_dict(cls, signed_dict: JsonDict) -> 'Targets':
  """Creates Targets object from its JSON/dict representation. """
+
+ # Get a parent object with its attributes already assigned.
+ obj = super().from_dict(signed_dict)
+ obj.targets = {}
  for target_path in signed_dict['targets'].keys():
- signed_dict['targets'][target_path] = TargetInfo(
- **signed_dict['targets'][target_path])
+ info = signed_dict['targets'][target_path]
+ obj.targets[target_path] = TargetInfo(info['length'],
+ info['hashes'], info.get('custom'))
 
- return super().from_dict(signed_dict)
+ obj.delegations = signed_dict['delegations']
+ return obj
 
 
  # Serialization.