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interfaces.py
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"""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')