Remove miscroseconds from metadata API Signed.expires

This change removes microseconds from expiry in order to fit TUF
specification

Fixes #1678

Signed-off-by: Ivana Atanasova <[email protected]>

Author: ivanayov

tests/test_metadata_serialization.py

@@ -200,6 +200,9 @@ def test_root_serialization(self, test_case_data: str) -> None:
                 "snapshot": {"keyids": ["keyid2"], "threshold": 1}, \
                 "foo": {"keyids": ["keyid2"], "threshold": 1}} \
             }',
+        "invalid expiry with microsecond    s": '{"_type": "root", "spec_version": "1.0.0", "version": 1, \
+            "expires": "2030-01-01T12:00:00.123456Z", "consistent_snapshot": false, \
+            "keys": {}, "roles": {"root": {}, "timestamp": {}, "targets": {}, "snapshot": {}}}',
     }
 
     @utils.run_sub_tests_with_dataset(invalid_roots)

tuf/api/metadata.py

@@ -408,6 +408,14 @@ class Signed(metaclass=abc.ABCMeta):
     def _type(self) -> str:
         return self.type
 
+    @property
+    def expires(self) -> datetime:
+        return self._expires
+
+    @expires.setter
+    def expires(self, value: datetime) -> None:
+        self._expires = value.replace(microsecond=0)
+
     # NOTE: Signed is a stupid name, because this might not be signed yet, but
     # we keep it to match spec terminology (I often refer to this as "payload",
     # or "inner metadata")
@@ -469,6 +477,7 @@ def _common_fields_from_dict(
         # what the constructor expects and what we store. The inverse operation
         # is implemented in '_common_fields_to_dict'.
         expires = datetime.strptime(expires_str, "%Y-%m-%dT%H:%M:%SZ")
+
         return version, spec_version, expires
 
     def _common_fields_to_dict(self) -> Dict[str, Any]: