CasperSecurity
"""JOSE interfaces."""
import abc
import json
from typing import Any
from josepy import errors
from collections.abc import Sequence, Mapping
# pylint: disable=no-self-argument,no-method-argument,no-init,inherit-non-class
# pylint: disable=too-few-public-methods
class JSONDeSerializable(object, metaclass=abc.ABCMeta):
# pylint: disable=too-few-public-methods
"""Interface for (de)serializable JSON objects.
Please recall, that standard Python library implements
:class:`json.JSONEncoder` and :class:`json.JSONDecoder` that perform
translations based on respective :ref:`conversion tables
<conversion-table>` that look pretty much like the one below (for
complete tables see relevant Python documentation):
.. _conversion-table:
====== ======
JSON Python
====== ======
object dict
... ...
====== ======
While the above **conversion table** is about translation of JSON
documents to/from the basic Python types only,
:class:`JSONDeSerializable` introduces the following two concepts:
serialization
Turning an arbitrary Python object into Python object that can
be encoded into a JSON document. **Full serialization** produces
a Python object composed of only basic types as required by the
:ref:`conversion table <conversion-table>`. **Partial
serialization** (accomplished by :meth:`to_partial_json`)
produces a Python object that might also be built from other
:class:`JSONDeSerializable` objects.
deserialization
Turning a decoded Python object (necessarily one of the basic
types as required by the :ref:`conversion table
<conversion-table>`) into an arbitrary Python object.
Serialization produces **serialized object** ("partially serialized
object" or "fully serialized object" for partial and full
serialization respectively) and deserialization produces
**deserialized object**, both usually denoted in the source code as
``jobj``.
Wording in the official Python documentation might be confusing
after reading the above, but in the light of those definitions, one
can view :meth:`json.JSONDecoder.decode` as decoder and
deserializer of basic types, :meth:`json.JSONEncoder.default` as
serializer of basic types, :meth:`json.JSONEncoder.encode` as
serializer and encoder of basic types.
One could extend :mod:`json` to support arbitrary object
(de)serialization either by:
- overriding :meth:`json.JSONDecoder.decode` and
:meth:`json.JSONEncoder.default` in subclasses
- or passing ``object_hook`` argument (or ``object_hook_pairs``)
to :func:`json.load`/:func:`json.loads` or ``default`` argument
for :func:`json.dump`/:func:`json.dumps`.
Interestingly, ``default`` is required to perform only partial
serialization, as :func:`json.dumps` applies ``default``
recursively. This is the idea behind making :meth:`to_partial_json`
produce only partial serialization, while providing custom
:meth:`json_dumps` that dumps with ``default`` set to
:meth:`json_dump_default`.
To make further documentation a bit more concrete, please, consider
the following imaginatory implementation example::
class Foo(JSONDeSerializable):
def to_partial_json(self):
return 'foo'
@classmethod
def from_json(cls, jobj):
return Foo()
class Bar(JSONDeSerializable):
def to_partial_json(self):
return [Foo(), Foo()]
@classmethod
def from_json(cls, jobj):
return Bar()
"""
@abc.abstractmethod
def to_partial_json(self) -> Any: # pragma: no cover
"""Partially serialize.
Following the example, **partial serialization** means the following::
assert isinstance(Bar().to_partial_json()[0], Foo)
assert isinstance(Bar().to_partial_json()[1], Foo)
# in particular...
assert Bar().to_partial_json() != ['foo', 'foo']
:raises josepy.errors.SerializationError:
in case of any serialization error.
:returns: Partially serializable object.
"""
raise NotImplementedError()
def to_json(self) -> Any:
"""Fully serialize.
Again, following the example from before, **full serialization**
means the following::
assert Bar().to_json() == ['foo', 'foo']
:raises josepy.errors.SerializationError:
in case of any serialization error.
:returns: Fully serialized object.
"""
def _serialize(obj: Any) -> Any:
if isinstance(obj, JSONDeSerializable):
return _serialize(obj.to_partial_json())
if isinstance(obj, str): # strings are Sequence
return obj
elif isinstance(obj, list):
return [_serialize(subobj) for subobj in obj]
elif isinstance(obj, Sequence):
# default to tuple, otherwise Mapping could get
# unhashable list
return tuple(_serialize(subobj) for subobj in obj)
elif isinstance(obj, Mapping):
return {_serialize(key): _serialize(value)
for key, value in obj.items()}
else:
return obj
return _serialize(self)
@classmethod
@abc.abstractmethod
def from_json(cls, jobj: Any) -> 'JSONDeSerializable':
"""Deserialize a decoded JSON document.
:param jobj: Python object, composed of only other basic data
types, as decoded from JSON document. Not necessarily
:class:`dict` (as decoded from "JSON object" document).
:raises josepy.errors.DeserializationError:
if decoding was unsuccessful, e.g. in case of unparseable
X509 certificate, or wrong padding in JOSE base64 encoded
string, etc.
"""
# TypeError: Can't instantiate abstract class <cls> with
# abstract methods from_json, to_partial_json
return cls() # pylint: disable=abstract-class-instantiated
@classmethod
def json_loads(cls, json_string: str) -> 'JSONDeSerializable':
"""Deserialize from JSON document string."""
try:
loads = json.loads(json_string)
except ValueError as error:
raise errors.DeserializationError(error)
return cls.from_json(loads)
def json_dumps(self, **kwargs: Any) -> str:
"""Dump to JSON string using proper serializer.
:returns: JSON document string.
:rtype: str
"""
return json.dumps(self, default=self.json_dump_default, **kwargs)
def json_dumps_pretty(self) -> str:
"""Dump the object to pretty JSON document string.
:rtype: str
"""
return self.json_dumps(sort_keys=True, indent=4, separators=(',', ': '))
@classmethod
def json_dump_default(cls, python_object: 'JSONDeSerializable') -> Any:
"""Serialize Python object.
This function is meant to be passed as ``default`` to
:func:`json.dump` or :func:`json.dumps`. They call
``default(python_object)`` only for non-basic Python types, so
this function necessarily raises :class:`TypeError` if
``python_object`` is not an instance of
:class:`IJSONSerializable`.
Please read the class docstring for more information.
"""
if isinstance(python_object, JSONDeSerializable):
return python_object.to_partial_json()
else: # this branch is necessary, cannot just "return"
raise TypeError(repr(python_object) + ' is not JSON serializable')