feat: handle kwargs in signal callback

src/dbus_fast/proxy_object.py

@@ -136,13 +136,30 @@ def _message_handler(self, msg):
     def _add_signal(self, intr_signal, interface):
         def on_signal_fn(fn, *, unpack_variants: bool = False):
             fn_signature = inspect.signature(fn)
-            if len(fn_signature.parameters) != len(intr_signal.args) and (
-                inspect.Parameter.VAR_POSITIONAL
-                not in [par.kind for par in fn_signature.parameters.values()]
-                or len(fn_signature.parameters) - 1 > len(intr_signal.args)
+            if 0 < len(
+                [
+                    par
+                    for par in fn_signature.parameters.values()
+                    if par.kind == inspect.Parameter.KEYWORD_ONLY
+                    and par.default == inspect.Parameter.empty
+                ]
             ):
                 raise TypeError(
-                    f"reply_notify must be a function with {len(intr_signal.args)} parameters"
+                    "reply_notify cannot have required keyword only parameters"
+                )
+
+            positional_params = [
+                par.kind
+                for par in fn_signature.parameters.values()
+                if par.kind
+                not in [inspect.Parameter.KEYWORD_ONLY, inspect.Parameter.VAR_KEYWORD]
+            ]
+            if len(positional_params) != len(intr_signal.args) and (
+                inspect.Parameter.VAR_POSITIONAL not in positional_params
+                or len(positional_params) - 1 > len(intr_signal.args)
+            ):
+                raise TypeError(
+                    f"reply_notify must be a function with {len(intr_signal.args)} positional parameters"
                 )
 
             if not self._signal_handlers:

tests/client/test_signals.py

@@ -290,6 +290,75 @@ def varargs_plus_handler(value, *_):
     bus2.disconnect()
 
 
+@pytest.mark.asyncio
+async def test_kwargs_callback():
+    """Test callback for signal with kwargs."""
+    bus1 = await MessageBus().connect()
+    bus2 = await MessageBus().connect()
+
+    await bus1.request_name("test.signals.name")
+    service_interface = ExampleInterface()
+    bus1.export("/test/path", service_interface)
+
+    obj = bus2.get_proxy_object(
+        "test.signals.name", "/test/path", bus1._introspect_export_path("/test/path")
+    )
+    interface = obj.get_interface(service_interface.name)
+
+    async def ping():
+        await bus2.call(
+            Message(
+                destination=bus1.unique_name,
+                interface="org.freedesktop.DBus.Peer",
+                path="/test/path",
+                member="Ping",
+            )
+        )
+
+    kwargs_handler_counter = 0
+    kwargs_handler_err = None
+    kwarg_default_handler_counter = 0
+    kwarg_default_handler_err = None
+
+    def kwargs_handler(value, **_):
+        nonlocal kwargs_handler_counter
+        nonlocal kwargs_handler_err
+        try:
+            assert value == "hello"
+            kwargs_handler_counter += 1
+        except AssertionError as ex:
+            kwargs_handler_err = ex
+
+    def kwarg_default_handler(value, *, _=True):
+        nonlocal kwarg_default_handler_counter
+        nonlocal kwarg_default_handler_err
+        try:
+            assert value == "hello"
+            kwarg_default_handler_counter += 1
+        except AssertionError as ex:
+            kwarg_default_handler_err = ex
+
+    interface.on_some_signal(kwargs_handler)
+    interface.on_some_signal(kwarg_default_handler)
+    await ping()
+
+    service_interface.SomeSignal()
+    await ping()
+    assert kwargs_handler_err is None
+    assert kwargs_handler_counter == 1
+    assert kwarg_default_handler_err is None
+    assert kwarg_default_handler_counter == 1
+
+    def kwarg_bad_handler(value, *, bad_kwarg):
+        pass
+
+    with pytest.raises(TypeError):
+        interface.on_some_signal(kwarg_bad_handler)
+
+    bus1.disconnect()
+    bus2.disconnect()
+
+
 @pytest.mark.asyncio
 async def test_on_signal_type_error():
     """Test on callback raises type errors for invalid callbacks."""