Allow empty session name for APIs that take it

Summary:
Makes the session name returning and accepting APIs symmetric by allowing empty session names.

Today `torchx.runner.Runner()` takes an empty string as `session_name` and returns an `app_handle` with an empty session name (e.g. `local:///app-id`) when the `run()` or `schedule()` methods are called (see the newly added unittest in `torchx/runner/test/api_test.py#test_empty_session_id()`)

However runner APIs that accept `app_handle` (e.g. `runner.cancel()`) will error when the session name is empty.  This makes the APIs non-symmetric since the `app_handle` returned by `run/schedule` APIs cannot be used.

This PR fixes this.

Differential Revision: D73799333

Author: kiukchung

torchx/runner/test/api_test.py

@@ -25,6 +25,7 @@
     AppDef,
     AppHandle,
     AppState,
+    parse_app_handle,
     Resource,
     Role,
     UnknownAppException,
@@ -132,6 +133,32 @@ def test_session_id(self, record_mock: MagicMock) -> None:
                 event = record_mock.call_args_list[i].args[0]
                 self.assertEqual(event.session, CURRENT_SESSION_ID)
 
+    def test_empty_session_id(self, _: MagicMock) -> None:
+        empty_session_name = ""
+        with Runner(
+            empty_session_name,
+            {"local": cast(SchedulerFactory, create_scheduler)},
+        ) as runner:
+            app = AppDef(
+                "__unused_for_test__",
+                roles=[
+                    Role(
+                        name="echo",
+                        image=str(self.tmpdir),
+                        resource=resource.SMALL,
+                        entrypoint="echo",
+                        args=["__unused_for_test__"],
+                    )
+                ],
+            )
+
+            app_handle = runner.run(app, "local", self.cfg)
+
+            scheduler, session_name, app_id = parse_app_handle(app_handle)
+            self.assertEqual(scheduler, "local")
+            self.assertEqual(empty_session_name, session_name)
+            self.assertEqual(app_handle, f"local:///{app_id}")
+
     def test_run(self, record_mock: MagicMock) -> None:
         test_file = self.tmpdir / "test_file"
 

torchx/specs/api.py

@@ -1122,7 +1122,7 @@ def parse_app_handle(app_handle: AppHandle) -> ParsedAppHandle:
     # define allowed characters nor length for session name and app_id
     import re
 
-    pattern = r"(?P<scheduler_backend>.+)://(?P<session_name>.+)/(?P<app_id>.+)"
+    pattern = r"(?P<scheduler_backend>.+)://(?P<session_name>.*)/(?P<app_id>.+)"
     match = re.match(pattern, app_handle)
     if not match:
         raise MalformedAppHandleException(app_handle)

torchx/specs/test/api_test.py

@@ -377,6 +377,15 @@ def test_parse_malformed_app_handles(self) -> None:
                 with self.assertRaises(MalformedAppHandleException):
                     parse_app_handle(handle)
 
+    def test_parse_app_handle_empty_session_name(self) -> None:
+        # missing session name is not OK but an empty one is
+        app_handle = "local:///my_application_id"
+        handle = parse_app_handle(app_handle)
+
+        self.assertEqual(handle.app_id, "my_application_id")
+        self.assertEqual("local", handle.scheduler_backend)
+        self.assertEqual("", handle.session_name)
+
     def test_parse(self) -> None:
         (scheduler_backend, session_name, app_id) = parse_app_handle(
             "local://my_session/my_app_id_1234"