148 lines
5.5 KiB
Python
148 lines
5.5 KiB
Python
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import time
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from datetime import datetime
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from ._compat import text_type
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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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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):
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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):
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"""Used to convert the timestamp from :meth:`get_timestamp` into
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a datetime object.
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"""
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return datetime.utcfromtimestamp(ts)
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def sign(self, value):
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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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def unsign(self, value, max_age=None, return_timestamp=False):
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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 a naive
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:class:`datetime.datetime` object in UTC.
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"""
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try:
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result = Signer.unsign(self, 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, timestamp = result.rsplit(sep, 1)
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try:
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timestamp = bytes_to_int(base64_decode(timestamp))
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except Exception:
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timestamp = None
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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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raise BadTimeSignature(
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text_type(sig_error), payload=value, date_signed=timestamp
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)
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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 timestamp 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() - timestamp
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if age > max_age:
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raise SignatureExpired(
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"Signature age %s > %s seconds" % (age, max_age),
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payload=value,
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date_signed=self.timestamp_to_datetime(timestamp),
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)
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if return_timestamp:
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return value, self.timestamp_to_datetime(timestamp)
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return value
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def validate(self, signed_value, max_age=None):
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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 = TimestampSigner
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def loads(self, s, max_age=None, return_timestamp=False, salt=None):
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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(s, max_age, return_timestamp=True)
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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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# If we get a signature expired it means we could read the
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# signature but it's invalid. In that case we do not want to
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# try the next signer.
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except SignatureExpired:
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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 last_exception
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def loads_unsafe(self, s, max_age=None, salt=None):
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load_kwargs = {"max_age": max_age}
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load_payload_kwargs = {}
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return self._loads_unsafe_impl(s, salt, load_kwargs, load_payload_kwargs)
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