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