Understand any codebase.

88        try:
89            result = super().unsign(signed_value)
90            sig_error = None
91        except BadSignature as e:
92            sig_error = e
93            result = e.payload or b""
94​
95        sep = want_bytes(self.sep)
96​
97        # If there is no timestamp in the result there is something
98        # seriously wrong. In case there was a signature error, we raise
99        # that one directly, otherwise we have a weird situation in
100        # which we shouldn't have come except someone uses a time-based
101        # serializer on non-timestamp data, so catch that.
102        if sep not in result:
103            if sig_error:
104                raise sig_error
105​
106            raise BadTimeSignature("timestamp missing", payload=result)
107​
108        value, ts_bytes = result.rsplit(sep, 1)
109        ts_int: int | None = None
110        ts_dt: datetime | None = None
111​
112        try:
113            ts_int = bytes_to_int(base64_decode(ts_bytes))
114        except Exception:
115            pass
116​
117        # Signature is *not* okay. Raise a proper error now that we have
118        # split the value and the timestamp.
119        if sig_error is not None:
120            if ts_int is not None:
121                try:
122                    ts_dt = self.timestamp_to_datetime(ts_int)
123                except (ValueError, OSError, OverflowError) as exc:
124                    # Windows raises OSError
125                    # 32-bit raises OverflowError
126                    raise BadTimeSignature(
127                        "Malformed timestamp", payload=value
128                    ) from exc
129​
130            raise BadTimeSignature(str(sig_error), payload=value, date_signed=ts_dt)
131​
132        # Signature was okay but the timestamp is actually not there or
133        # malformed. Should not happen, but we handle it anyway.
134        if ts_int is None:
135            raise BadTimeSignature("Malformed timestamp", payload=value)
136​
137        # Check timestamp is not older than max_age
138        if max_age is not None:
139            age = self.get_timestamp() - ts_int
140​
141            if age > max_age:
142                raise SignatureExpired(
143                    f"Signature age {age} > {max_age} seconds",
144                    payload=value,
145                    date_signed=self.timestamp_to_datetime(ts_int),
146                )
147​
148            if age < 0:
149                raise SignatureExpired(
150                    f"Signature age {age} < 0 seconds",
151                    payload=value,
152                    date_signed=self.timestamp_to_datetime(ts_int),
153                )