More attention to closing Persistence

Avoid ResourceWarning from unclosed SQLite connection.

Author: mvollrath

ohmqtt/persistence/base.py

@@ -1,4 +1,5 @@
 from abc import ABCMeta, abstractmethod
+import sys
 from typing import ClassVar, NamedTuple, Sequence
 
 from ..handles import PublishHandle
@@ -13,6 +14,11 @@
 from ..property import MQTTPublishProps
 from ..topic_alias import AliasPolicy
 
+if sys.version_info >= (3, 11):
+    from typing import Self
+else:
+    from typing_extensions import Self
+
 
 class LostMessageError(Exception):
     """Raised when a message is lost from the persistence store and can not be acknowledged."""
@@ -28,6 +34,12 @@ class Persistence(metaclass=ABCMeta):
     """Abstract base class for message persistence."""
     __slots__: ClassVar[Sequence[str]] = tuple()
 
+    def __enter__(self) -> Self:
+        return self
+
+    def __exit__(self, exc_type: type | None, exc_value: BaseException | None, traceback: object | None) -> None:
+        self.close()
+
     @abstractmethod
     def __len__(self) -> int:
         """Return the number of outgoing messages in the persistence store."""
@@ -90,3 +102,9 @@ def open(self, client_id: str, clear: bool = False) -> None:
 
         This may clear the persistence store if the client_id is different from the persisted,
         or if clear is True."""
+
+    @abstractmethod
+    def close(self) -> None:
+        """Finalize and close the persistence store.
+
+        The store must not be used after this call."""

ohmqtt/persistence/in_memory.py

@@ -177,3 +177,6 @@ def open(self, client_id: str, clear: bool = False) -> None:
             self._client_id = client_id
         else:
             self._reset_inflight()
+
+    def close(self) -> None:
+        self.clear()

ohmqtt/persistence/sqlite.py

@@ -54,11 +54,7 @@ def __init__(self, db_path: str, *, db_fast: bool = False) -> None:
         self._create_tables()
 
     def __del__(self) -> None:
-        # Ignore "already closed" errors while closing resources.
-        with suppress(sqlite3.ProgrammingError):
-            self._cursor.close()
-        with suppress(sqlite3.ProgrammingError):
-            self._conn.close()
+        self.close()
 
     def __len__(self) -> int:
         with self._cond:
@@ -333,3 +329,10 @@ def open(self, client_id: str, clear: bool = False) -> None:
                 self.clear()
             else:
                 self._reset_inflight()
+
+    def close(self) -> None:
+        # Ignore "already closed" errors while closing resources.
+        with suppress(sqlite3.ProgrammingError):
+            self._cursor.close()
+        with suppress(sqlite3.ProgrammingError):
+            self._conn.close()