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235 lines
8.0 KiB
Python
235 lines
8.0 KiB
Python
2 years ago
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import time
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import typing
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import typing as _t
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from datetime import datetime
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from datetime import timezone
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from .encoding import base64_decode
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from .encoding import base64_encode
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from .encoding import bytes_to_int
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from .encoding import int_to_bytes
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from .encoding import want_bytes
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from .exc import BadSignature
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from .exc import BadTimeSignature
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from .exc import SignatureExpired
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from .serializer import Serializer
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from .signer import Signer
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_t_str_bytes = _t.Union[str, bytes]
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_t_opt_str_bytes = _t.Optional[_t_str_bytes]
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_t_opt_int = _t.Optional[int]
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if _t.TYPE_CHECKING:
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import typing_extensions as _te
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class TimestampSigner(Signer):
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"""Works like the regular :class:`.Signer` but also records the time
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of the signing and can be used to expire signatures. The
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:meth:`unsign` method can raise :exc:`.SignatureExpired` if the
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unsigning failed because the signature is expired.
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"""
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def get_timestamp(self) -> int:
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"""Returns the current timestamp. The function must return an
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integer.
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"""
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return int(time.time())
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def timestamp_to_datetime(self, ts: int) -> datetime:
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"""Convert the timestamp from :meth:`get_timestamp` into an
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aware :class`datetime.datetime` in UTC.
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.. versionchanged:: 2.0
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The timestamp is returned as a timezone-aware ``datetime``
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in UTC rather than a naive ``datetime`` assumed to be UTC.
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"""
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return datetime.fromtimestamp(ts, tz=timezone.utc)
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def sign(self, value: _t_str_bytes) -> bytes:
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"""Signs the given string and also attaches time information."""
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value = want_bytes(value)
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timestamp = base64_encode(int_to_bytes(self.get_timestamp()))
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sep = want_bytes(self.sep)
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value = value + sep + timestamp
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return value + sep + self.get_signature(value)
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# Ignore overlapping signatures check, return_timestamp is the only
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# parameter that affects the return type.
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@typing.overload
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def unsign( # type: ignore
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self,
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signed_value: _t_str_bytes,
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max_age: _t_opt_int = None,
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return_timestamp: "_te.Literal[False]" = False,
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) -> bytes:
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...
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@typing.overload
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def unsign(
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self,
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signed_value: _t_str_bytes,
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max_age: _t_opt_int = None,
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return_timestamp: "_te.Literal[True]" = True,
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) -> _t.Tuple[bytes, datetime]:
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...
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def unsign(
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self,
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signed_value: _t_str_bytes,
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max_age: _t_opt_int = None,
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return_timestamp: bool = False,
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) -> _t.Union[_t.Tuple[bytes, datetime], bytes]:
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"""Works like the regular :meth:`.Signer.unsign` but can also
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validate the time. See the base docstring of the class for
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the general behavior. If ``return_timestamp`` is ``True`` the
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timestamp of the signature will be returned as an aware
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:class:`datetime.datetime` object in UTC.
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.. versionchanged:: 2.0
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The timestamp is returned as a timezone-aware ``datetime``
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in UTC rather than a naive ``datetime`` assumed to be UTC.
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"""
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try:
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result = super().unsign(signed_value)
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sig_error = None
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except BadSignature as e:
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sig_error = e
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result = e.payload or b""
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sep = want_bytes(self.sep)
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# If there is no timestamp in the result there is something
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# seriously wrong. In case there was a signature error, we raise
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# that one directly, otherwise we have a weird situation in
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# which we shouldn't have come except someone uses a time-based
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# serializer on non-timestamp data, so catch that.
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if sep not in result:
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if sig_error:
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raise sig_error
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raise BadTimeSignature("timestamp missing", payload=result)
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value, ts_bytes = result.rsplit(sep, 1)
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ts_int: _t_opt_int = None
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ts_dt: _t.Optional[datetime] = None
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try:
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ts_int = bytes_to_int(base64_decode(ts_bytes))
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except Exception:
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pass
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# Signature is *not* okay. Raise a proper error now that we have
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# split the value and the timestamp.
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if sig_error is not None:
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if ts_int is not None:
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try:
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ts_dt = self.timestamp_to_datetime(ts_int)
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except (ValueError, OSError, OverflowError) as exc:
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# Windows raises OSError
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# 32-bit raises OverflowError
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raise BadTimeSignature(
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"Malformed timestamp", payload=value
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) from exc
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raise BadTimeSignature(str(sig_error), payload=value, date_signed=ts_dt)
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# Signature was okay but the timestamp is actually not there or
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# malformed. Should not happen, but we handle it anyway.
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if ts_int is None:
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raise BadTimeSignature("Malformed timestamp", payload=value)
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# Check timestamp is not older than max_age
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if max_age is not None:
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age = self.get_timestamp() - ts_int
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if age > max_age:
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raise SignatureExpired(
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f"Signature age {age} > {max_age} seconds",
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payload=value,
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date_signed=self.timestamp_to_datetime(ts_int),
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)
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if age < 0:
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raise SignatureExpired(
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f"Signature age {age} < 0 seconds",
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payload=value,
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date_signed=self.timestamp_to_datetime(ts_int),
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)
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if return_timestamp:
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return value, self.timestamp_to_datetime(ts_int)
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return value
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def validate(self, signed_value: _t_str_bytes, max_age: _t_opt_int = None) -> bool:
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"""Only validates the given signed value. Returns ``True`` if
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the signature exists and is valid."""
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try:
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self.unsign(signed_value, max_age=max_age)
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return True
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except BadSignature:
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return False
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class TimedSerializer(Serializer):
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"""Uses :class:`TimestampSigner` instead of the default
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:class:`.Signer`.
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"""
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default_signer: _t.Type[TimestampSigner] = TimestampSigner
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def iter_unsigners(
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self, salt: _t_opt_str_bytes = None
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) -> _t.Iterator[TimestampSigner]:
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return _t.cast("_t.Iterator[TimestampSigner]", super().iter_unsigners(salt))
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# TODO: Signature is incompatible because parameters were added
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# before salt.
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def loads( # type: ignore
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self,
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s: _t_str_bytes,
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max_age: _t_opt_int = None,
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return_timestamp: bool = False,
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salt: _t_opt_str_bytes = None,
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) -> _t.Any:
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"""Reverse of :meth:`dumps`, raises :exc:`.BadSignature` if the
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signature validation fails. If a ``max_age`` is provided it will
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ensure the signature is not older than that time in seconds. In
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case the signature is outdated, :exc:`.SignatureExpired` is
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raised. All arguments are forwarded to the signer's
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:meth:`~TimestampSigner.unsign` method.
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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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base64d, timestamp = signer.unsign(
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s, max_age=max_age, return_timestamp=True
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)
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payload = self.load_payload(base64d)
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if return_timestamp:
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return payload, timestamp
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return payload
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except SignatureExpired:
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# The signature was unsigned successfully but was
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# expired. Do not try the next signer.
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raise
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except BadSignature as err:
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last_exception = err
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raise _t.cast(BadSignature, last_exception)
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def loads_unsafe( # type: ignore
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self,
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s: _t_str_bytes,
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max_age: _t_opt_int = None,
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salt: _t_opt_str_bytes = None,
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) -> _t.Tuple[bool, _t.Any]:
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return self._loads_unsafe_impl(s, salt, load_kwargs={"max_age": max_age})
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