Add getter functions for Signed objects

These are equivalent to the edit_X() context managers but for cases
where user is not interested in creating a new version of the metadata.

Signed-off-by: Jussi Kukkonen <jkukkonen@google.com>

examples/repository/_simplerepo.py

@@ -176,15 +176,10 @@ def submit_role(self, role: str, data: bytes) -> bool:
                 if not targetpath.startswith(f"{role}/"):
                     raise ValueError(f"targets allowed under {role}/ only")
 
-            targets_md = self.role_cache["targets"][-1]
+            targets_md = self.open("targets")
             targets_md.verify_delegate(role, md)
-            if role in self.role_cache:
-                current_md = self.role_cache[role][-1]
-                current_ver = current_md.signed.version
-            else:
-                current_ver = 0
 
-            if md.signed.version != current_ver + 1:
+            if md.signed.version != self.targets(role).version + 1:
                 raise ValueError("Invalid version {md.signed.version}")
 
         except (RepositoryError, ValueError) as e:

tuf/repository/_repository.py

@@ -107,7 +107,7 @@ def edit_root(self) -> Generator[Root, None, None]:
         """Context manager for editing root metadata. See edit()"""
         with self.edit(Root.type) as root:
             if not isinstance(root, Root):
-                raise RuntimeError("Unexpected Root type")
+                raise RuntimeError("Unexpected root type")
             yield root
 
     @contextmanager
@@ -115,7 +115,7 @@ def edit_timestamp(self) -> Generator[Timestamp, None, None]:
         """Context manager for editing timestamp metadata. See edit()"""
         with self.edit(Timestamp.type) as timestamp:
             if not isinstance(timestamp, Timestamp):
-                raise RuntimeError("Unexpected Timestamp type")
+                raise RuntimeError("Unexpected timestamp type")
             yield timestamp
 
     @contextmanager
@@ -123,7 +123,7 @@ def edit_snapshot(self) -> Generator[Snapshot, None, None]:
         """Context manager for editing snapshot metadata. See edit()"""
         with self.edit(Snapshot.type) as snapshot:
             if not isinstance(snapshot, Snapshot):
-                raise RuntimeError("Unexpected Snapshot type")
+                raise RuntimeError("Unexpected snapshot type")
             yield snapshot
 
     @contextmanager
@@ -131,9 +131,37 @@ def edit_targets(self, rolename: str) -> Generator[Targets, None, None]:
         """Context manager for editing targets metadata. See edit()"""
         with self.edit(rolename) as targets:
             if not isinstance(targets, Targets):
-                raise RuntimeError(f"Unexpected Targets ({rolename}) type")
+                raise RuntimeError(f"Unexpected targets ({rolename}) type")
             yield targets
 
+    def root(self) -> Root:
+        """Read current root metadata"""
+        root = self.open(Root.type).signed
+        if not isinstance(root, Root):
+            raise RuntimeError("Unexpected root type")
+        return root
+
+    def timestamp(self) -> Timestamp:
+        """Read current timestamp metadata"""
+        timestamp = self.open(Timestamp.type).signed
+        if not isinstance(timestamp, Timestamp):
+            raise RuntimeError("Unexpected timestamp type")
+        return timestamp
+
+    def snapshot(self) -> Snapshot:
+        """Read current snapshot metadata"""
+        snapshot = self.open(Snapshot.type).signed
+        if not isinstance(snapshot, Snapshot):
+            raise RuntimeError("Unexpected snapshot type")
+        return snapshot
+
+    def targets(self, rolename: str) -> Targets:
+        """Read current targets metadata"""
+        targets = self.open(rolename).signed
+        if not isinstance(targets, Targets):
+            raise RuntimeError("Unexpected targets type")
+        return targets
+
     def do_snapshot(
         self, force: bool = False
     ) -> Tuple[bool, Dict[str, MetaFile]]: