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234 lines
8.5 KiB
Python
234 lines
8.5 KiB
Python
5 years ago
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import hashlib
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from ._compat import text_type
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from ._json import json
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from .encoding import want_bytes
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from .exc import BadPayload
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from .exc import BadSignature
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from .signer import Signer
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def is_text_serializer(serializer):
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"""Checks whether a serializer generates text or binary."""
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return isinstance(serializer.dumps({}), text_type)
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class Serializer(object):
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"""This class provides a serialization interface on top of the
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signer. It provides a similar API to json/pickle and other modules
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but is structured differently internally. If you want to change the
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underlying implementation for parsing and loading you have to
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override the :meth:`load_payload` and :meth:`dump_payload`
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functions.
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This implementation uses simplejson if available for dumping and
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loading and will fall back to the standard library's json module if
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it's not available.
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You do not need to subclass this class in order to switch out or
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customize the :class:`.Signer`. You can instead pass a different
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class to the constructor as well as keyword arguments as a dict that
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should be forwarded.
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.. code-block:: python
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s = Serializer(signer_kwargs={'key_derivation': 'hmac'})
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You may want to upgrade the signing parameters without invalidating
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existing signatures that are in use. Fallback signatures can be
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given that will be tried if unsigning with the current signer fails.
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Fallback signers can be defined by providing a list of
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``fallback_signers``. Each item can be one of the following: a
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signer class (which is instantiated with ``signer_kwargs``,
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``salt``, and ``secret_key``), a tuple
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``(signer_class, signer_kwargs)``, or a dict of ``signer_kwargs``.
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For example, this is a serializer that signs using SHA-512, but will
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unsign using either SHA-512 or SHA1:
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.. code-block:: python
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s = Serializer(
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signer_kwargs={"digest_method": hashlib.sha512},
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fallback_signers=[{"digest_method": hashlib.sha1}]
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)
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.. versionchanged:: 0.14:
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The ``signer`` and ``signer_kwargs`` parameters were added to
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the constructor.
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.. versionchanged:: 1.1.0:
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Added support for ``fallback_signers`` and configured a default
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SHA-512 fallback. This fallback is for users who used the yanked
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1.0.0 release which defaulted to SHA-512.
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"""
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#: If a serializer module or class is not passed to the constructor
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#: this one is picked up. This currently defaults to :mod:`json`.
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default_serializer = json
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#: The default :class:`Signer` class that is being used by this
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#: serializer.
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#:
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#: .. versionadded:: 0.14
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default_signer = Signer
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#: The default fallback signers.
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default_fallback_signers = [{"digest_method": hashlib.sha512}]
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def __init__(
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self,
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secret_key,
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salt=b"itsdangerous",
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serializer=None,
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serializer_kwargs=None,
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signer=None,
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signer_kwargs=None,
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fallback_signers=None,
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):
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self.secret_key = want_bytes(secret_key)
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self.salt = want_bytes(salt)
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if serializer is None:
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serializer = self.default_serializer
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self.serializer = serializer
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self.is_text_serializer = is_text_serializer(serializer)
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if signer is None:
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signer = self.default_signer
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self.signer = signer
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self.signer_kwargs = signer_kwargs or {}
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if fallback_signers is None:
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fallback_signers = list(self.default_fallback_signers or ())
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self.fallback_signers = fallback_signers
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self.serializer_kwargs = serializer_kwargs or {}
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def load_payload(self, payload, serializer=None):
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"""Loads the encoded object. This function raises
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:class:`.BadPayload` if the payload is not valid. The
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``serializer`` parameter can be used to override the serializer
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stored on the class. The encoded ``payload`` should always be
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bytes.
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"""
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if serializer is None:
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serializer = self.serializer
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is_text = self.is_text_serializer
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else:
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is_text = is_text_serializer(serializer)
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try:
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if is_text:
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payload = payload.decode("utf-8")
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return serializer.loads(payload)
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except Exception as e:
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raise BadPayload(
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"Could not load the payload because an exception"
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" occurred on unserializing the data.",
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original_error=e,
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)
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def dump_payload(self, obj):
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"""Dumps the encoded object. The return value is always bytes.
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If the internal serializer returns text, the value will be
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encoded as UTF-8.
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"""
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return want_bytes(self.serializer.dumps(obj, **self.serializer_kwargs))
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def make_signer(self, salt=None):
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"""Creates a new instance of the signer to be used. The default
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implementation uses the :class:`.Signer` base class.
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"""
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if salt is None:
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salt = self.salt
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return self.signer(self.secret_key, salt=salt, **self.signer_kwargs)
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def iter_unsigners(self, salt=None):
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"""Iterates over all signers to be tried for unsigning. Starts
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with the configured signer, then constructs each signer
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specified in ``fallback_signers``.
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"""
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if salt is None:
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salt = self.salt
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yield self.make_signer(salt)
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for fallback in self.fallback_signers:
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if type(fallback) is dict:
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kwargs = fallback
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fallback = self.signer
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elif type(fallback) is tuple:
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fallback, kwargs = fallback
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else:
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kwargs = self.signer_kwargs
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yield fallback(self.secret_key, salt=salt, **kwargs)
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def dumps(self, obj, salt=None):
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"""Returns a signed string serialized with the internal
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serializer. The return value can be either a byte or unicode
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string depending on the format of the internal serializer.
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"""
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payload = want_bytes(self.dump_payload(obj))
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rv = self.make_signer(salt).sign(payload)
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if self.is_text_serializer:
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rv = rv.decode("utf-8")
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return rv
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def dump(self, obj, f, salt=None):
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"""Like :meth:`dumps` but dumps into a file. The file handle has
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to be compatible with what the internal serializer expects.
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"""
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f.write(self.dumps(obj, salt))
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def loads(self, s, salt=None):
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"""Reverse of :meth:`dumps`. Raises :exc:`.BadSignature` if the
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signature validation fails.
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"""
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s = want_bytes(s)
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last_exception = None
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for signer in self.iter_unsigners(salt):
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try:
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return self.load_payload(signer.unsign(s))
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except BadSignature as err:
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last_exception = err
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raise last_exception
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def load(self, f, salt=None):
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"""Like :meth:`loads` but loads from a file."""
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return self.loads(f.read(), salt)
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def loads_unsafe(self, s, salt=None):
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"""Like :meth:`loads` but without verifying the signature. This
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is potentially very dangerous to use depending on how your
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serializer works. The return value is ``(signature_valid,
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payload)`` instead of just the payload. The first item will be a
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boolean that indicates if the signature is valid. This function
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never fails.
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Use it for debugging only and if you know that your serializer
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module is not exploitable (for example, do not use it with a
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pickle serializer).
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.. versionadded:: 0.15
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"""
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return self._loads_unsafe_impl(s, salt)
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def _loads_unsafe_impl(self, s, salt, load_kwargs=None, load_payload_kwargs=None):
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"""Low level helper function to implement :meth:`loads_unsafe`
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in serializer subclasses.
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"""
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try:
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return True, self.loads(s, salt=salt, **(load_kwargs or {}))
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except BadSignature as e:
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if e.payload is None:
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return False, None
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try:
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return (
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False,
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self.load_payload(e.payload, **(load_payload_kwargs or {})),
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)
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except BadPayload:
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return False, None
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def load_unsafe(self, f, *args, **kwargs):
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"""Like :meth:`loads_unsafe` but loads from a file.
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.. versionadded:: 0.15
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"""
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return self.loads_unsafe(f.read(), *args, **kwargs)
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