fix(plex): a restart that fails to start still deletes the session it moved aside

backend/tests/test_plex_stream.py

@@ -1058,3 +1058,63 @@ class TestSessionsPerViewer:
             self._start(monkeypatch, user_id=uid)
         assert len(stream._sessions) == 3 and (1, "12345") not in stream._sessions
         assert oldest.proc.killed and not oldest.transcode
+
+
+class TestTeardownFinishes:
+    """A session taken down by a cap or replaced by its own viewer is only renamed aside under the
+    lock; it is deleted after. The rename alone already moves the directory and `terminate()` alone
+    already marks the proc killed — so what is pinned here is the tomb: a whole segmented copy of the
+    film that only a restart's sweep would otherwise reclaim."""
+
+    capturing_env = TestTranscodeStartSession.capturing_env
+
+    @staticmethod
+    def _left_behind(root):
+        return sorted(p.name for p in root.iterdir() if stream._TOMB in p.name) + sorted(
+            str(p) for p in stream._dying
+        )
+
+    def test_a_culled_session_is_deleted_not_only_moved_aside(self, capturing_env, monkeypatch):
+        monkeypatch.setattr(stream, "_dying", {})
+        first = TestSessionsPerViewer._start(monkeypatch, user_id=1, rating_key="1")
+        first.last_access -= 60
+        TestSessionsPerViewer._start(monkeypatch, user_id=1, rating_key="2")
+        TestSessionsPerViewer._start(monkeypatch, user_id=1, rating_key="3")
+        assert first.proc.killed and not first.dir.exists()
+        assert self._left_behind(capturing_env) == []
+
+    def test_a_viewers_restart_deletes_the_session_it_replaces(self, capturing_env, monkeypatch):
+        monkeypatch.setattr(stream, "_dying", {})
+        monkeypatch.setattr(
+            stream, "_select_encode", lambda db, item, transcode, src: (False, False)
+        )
+        monkeypatch.setattr(
+            stream, "_probe_first_pts", lambda seg: None
+        )  # no real segment to probe
+        old = stream.start_session(db=None, user_id=1, item=_FakeItem(), start_s=0.0)
+        new = stream.start_session(db=None, user_id=1, item=_FakeItem(), start_s=600.0)
+        assert old.proc.killed and new.dir.exists() and not old.dir.exists()
+        assert self._left_behind(capturing_env) == []
+
+    def test_a_restart_that_fails_to_start_still_deletes_what_it_replaced(
+        self, capturing_env, monkeypatch
+    ):
+        # The new ffmpeg cannot start (a full disk, no ffmpeg, no memory): the old session is already
+        # moved aside, and nothing else in this process would ever delete it.
+        monkeypatch.setattr(stream, "_dying", {})
+        monkeypatch.setattr(
+            stream, "_select_encode", lambda db, item, transcode, src: (False, False)
+        )
+        monkeypatch.setattr(
+            stream, "_probe_first_pts", lambda seg: None
+        )  # no real segment to probe
+        old = stream.start_session(db=None, user_id=1, item=_FakeItem(), start_s=0.0)
+
+        def no_ffmpeg(*args, **kwargs):
+            raise OSError(28, "No space left on device")
+
+        monkeypatch.setattr(stream.subprocess, "Popen", no_ffmpeg)
+        with pytest.raises(OSError):
+            stream.start_session(db=None, user_id=1, item=_FakeItem(), start_s=600.0)
+        assert old.proc.killed and not old.dir.exists()
+        assert self._left_behind(capturing_env) == []