Metadata API: add timestamp meta validation

Signed-off-by: Martin Vrachev <[email protected]>

Author: MVrachev

tests/test_metadata_serialization.py

@@ -205,6 +205,21 @@ def test_metafile_serialization(self, test_case_data: str):
         metafile = MetaFile.from_dict(copy.copy(case_dict))
         self.assertDictEqual(case_dict, metafile.to_dict())
 
+    invalid_timestamp: DataSet = {
+        "no meta": '{ "_type": "timestamp", "spec_version": "1.0.0", "version": 1, "expires": "2030-01-01T00:00:00Z"}',
+        "empty meta":
+            '{ "_type": "timestamp", "spec_version": "1.0.0", "version": 1, "expires": "2030-01-01T00:00:00Z", "meta": {}}',
+        "meta with wrong key":
+            '{ "_type": "timestamp", "spec_version": "1.0.0", "version": 1, "expires": "2030-01-01T00:00:00Z", \
+            "meta": {"f.title": {"hashes": {"sha256" : "abc"}, "version": 1}}}'
+    }
+
+    @run_sub_tests_with_dataset(invalid_timestamp)
+    def test_invalid_timestamp_serialization(self, test_case_data: Dict[str, str]):
+        case_dict = json.loads(test_case_data)
+        with self.assertRaises(KeyError):
+            Timestamp.from_dict(copy.deepcopy(case_dict))
+
 
     valid_timestamps: DataSet = {
         "all": '{ "_type": "timestamp", "spec_version": "1.0.0", "version": 1, "expires": "2030-01-01T00:00:00Z", \

tuf/api/metadata.py

@@ -855,6 +855,23 @@ class Timestamp(Signed):
 
     _signed_type = "timestamp"
 
+    @property
+    def meta(self):
+        return self._meta
+
+    @meta.setter
+    def meta(self, new_meta: Dict[str, MetaFile]):
+        if len(new_meta) != 1 or new_meta.get("snapshot.json") is None:
+            raise ValueError(
+                f"meta should contain information only about snapshot.json, "
+                f"instead got {new_meta}"
+            )
+        if not isinstance(new_meta["snapshot.json"], MetaFile):
+            raise TypeError(
+                'meta["snapshot.json"] should be from type MetaFile!'
+            )
+        self._meta = new_meta
+
     @property
     def snapshot_meta(self):
         return self.meta["snapshot.json"]