feat: simplify creation of SendReply in message_bus (#178)

src/dbus_fast/message_bus.pxd

@@ -11,6 +11,11 @@ cdef object ServiceInterface
 cdef object MESSAGE_TYPE_CALL
 cdef object MESSAGE_TYPE_SIGNAL
 
+cdef class SendReply:
+
+    cdef object _bus
+    cdef object _msg
+
 cdef class BaseMessageBus:
 
     cdef public object unique_name

src/dbus_fast/message_bus.py

@@ -29,6 +29,60 @@ MESSAGE_TYPE_CALL = MessageType.METHOD_CALL
 MESSAGE_TYPE_SIGNAL = MessageType.SIGNAL
 
 
+class SendReply:
+    """A context manager to send a reply to a message."""
+
+    __slots__ = ("_bus", "_msg")
+
+    def __init__(self, bus: "BaseMessageBus", msg: Message) -> None:
+        """Create a new reply context manager."""
+        self._bus = bus
+        self._msg = msg
+
+    def __enter__(self):
+        return self
+
+    def __call__(self, reply: Message) -> None:
+        if self._msg.flags & MessageFlag.NO_REPLY_EXPECTED:
+            return
+
+        self._bus.send(reply)
+
+    def _exit(
+        self,
+        exc_type: Optional[Type[Exception]],
+        exc_value: Optional[Exception],
+        tb: Optional[TracebackType],
+    ) -> bool:
+        if exc_type is None:
+            return False
+
+        if issubclass(exc_type, DBusError):
+            self(exc_value._as_message(self._msg))  # type: ignore[union-attr]
+            return True
+
+        if issubclass(exc_type, Exception):
+            self(
+                Message.new_error(
+                    self._msg,
+                    ErrorType.SERVICE_ERROR,
+                    f"The service interface raised an error: {exc_value}.\n{traceback.format_tb(tb)}",
+                )
+            )
+            return True
+
+    def __exit__(
+        self,
+        exc_type: Optional[Type[Exception]],
+        exc_value: Optional[Exception],
+        tb: Optional[TracebackType],
+    ) -> bool:
+        return self._exit(exc_type, exc_value, tb)
+
+    def send_error(self, exc: Exception) -> None:
+        self._exit(exc.__class__, exc, exc.__traceback__)
+
+
 class BaseMessageBus:
     """An abstract class to manage a connection to a DBus message bus.
 
@@ -747,55 +801,6 @@ class BaseMessageBus:
                 ErrorType.INTERNAL_ERROR, "invalid message type for method call", msg
             )
 
-    def _send_reply(self, msg: Message):
-        bus = self
-
-        class SendReply:
-            def __enter__(self) -> "SendReply":
-                return self
-
-            def __call__(self, reply: Message) -> None:
-                if msg.flags & MessageFlag.NO_REPLY_EXPECTED:
-                    return
-
-                bus.send(reply)
-
-            def _exit(
-                self,
-                exc_type: Optional[Type[Exception]],
-                exc_value: Optional[Exception],
-                tb: Optional[TracebackType],
-            ) -> bool:
-                if exc_type is None:
-                    return False
-
-                if issubclass(exc_type, DBusError):
-                    self(exc_value._as_message(msg))  # type: ignore[union-attr]
-                    return True
-
-                if issubclass(exc_type, Exception):
-                    self(
-                        Message.new_error(
-                            msg,
-                            ErrorType.SERVICE_ERROR,
-                            f"The service interface raised an error: {exc_value}.\n{traceback.format_tb(tb)}",
-                        )
-                    )
-                    return True
-
-            def __exit__(
-                self,
-                exc_type: Optional[Type[Exception]],
-                exc_value: Optional[Exception],
-                tb: Optional[TracebackType],
-            ) -> bool:
-                return self._exit(exc_type, exc_value, tb)
-
-            def send_error(self, exc: Exception) -> None:
-                self._exit(exc.__class__, exc, exc.__traceback__)
-
-        return SendReply()
-
     def _process_message(self, msg) -> None:
         handled = False
         for user_handler in self._user_message_handlers:
@@ -848,7 +853,7 @@ class BaseMessageBus:
             if not handled:
                 handler = self._find_message_handler(msg)
 
-                send_reply = self._send_reply(msg)
+                send_reply = SendReply(self, msg)
 
                 with send_reply:
                     if handler: