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

backend/app/plex/stream.py

@@ -820,6 +820,9 @@ def start_session(
         # platform without fork (the API always runs in a Linux container in prod) it's simply omitted.
         preexec = _sw_child_preexec if (transcode and not hw and os.name == "posix") else None
         doomed: list[tuple[HlsSession, Path | None]] = []
+        # Finished even when the new session fails to start (no space, no ffmpeg, a DB error): what
+        # was moved aside under the lock is otherwise left for a restart's sweep.
+        try:
             with _lock:
                 if replace_only is not None and _sessions.get(reg) is not replace_only:
                     return None  # superseded/culled while we waited out of lock — don't clobber the newer one
@@ -887,6 +890,7 @@ def start_session(
                     max(1, sysconfig.get_int(db, "plex_max_transcodes")),
                     max(1, sysconfig.get_int(db, "plex_max_sessions")),
                 )
+        finally:
             _finish(doomed)
         return s
 

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) == []