Metadata API: snapshot_meta property in Timestamp

In Timestamp, the only valid "meta" value is the dictionary representing
meta information for the snapshot file.
That's why we want to provide an access to it without changing the
timestamp representation through the Timestamp class.

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

Author: MVrachev

tests/test_api.py

@@ -326,11 +326,11 @@ def test_metadata_timestamp(self):
         fileinfo = MetaFile(2, 520, hashes)
 
         self.assertNotEqual(
-            timestamp.signed.meta['snapshot.json'].to_dict(), fileinfo.to_dict()
+            timestamp.signed.snapshot_meta.to_dict(), fileinfo.to_dict()
         )
         timestamp.signed.update(fileinfo)
         self.assertEqual(
-            timestamp.signed.meta['snapshot.json'].to_dict(), fileinfo.to_dict()
+            timestamp.signed.snapshot_meta.to_dict(), fileinfo.to_dict()
         )
 
 

tuf/api/metadata.py

@@ -855,6 +855,14 @@ class Timestamp(Signed):
 
     _signed_type = "timestamp"
 
+    @property
+    def snapshot_meta(self):
+        return self.meta["snapshot.json"]
+
+    @snapshot_meta.setter
+    def snapshot_meta(self, value):
+        self.meta["snapshot.json"] = value
+
     def __init__(
         self,
         version: int,
@@ -878,15 +886,13 @@ def from_dict(cls, signed_dict: Dict[str, Any]) -> "Timestamp":
     def to_dict(self) -> Dict[str, Any]:
         """Returns the dict representation of self."""
         res_dict = self._common_fields_to_dict()
-        res_dict["meta"] = {
-            "snapshot.json": self.meta["snapshot.json"].to_dict()
-        }
+        res_dict["meta"] = {"snapshot.json": self.snapshot_meta.to_dict()}
         return res_dict
 
     # Modification.
     def update(self, snapshot_meta: MetaFile) -> None:
         """Assigns passed info about snapshot metadata to meta dict."""
-        self.meta["snapshot.json"] = snapshot_meta
+        self.snapshot_meta = snapshot_meta
 
 
 class Snapshot(Signed):