fixes

homeassistant/components/websocket_api/connection.py

@@ -221,7 +221,12 @@ class ActiveConnection:
         handler, schema = handler_schema
 
         try:
-            handler(self.hass, self, msg if schema is False else schema(msg))
+            if schema is False:
+                if len(msg) > 2:
+                    raise vol.Invalid("Message has unexpected keys")
+                handler(self.hass, self, msg)
+            else:
+                handler(self.hass, self, schema(msg))
         except Exception as err:  # pylint: disable=broad-except
             self.async_handle_exception(msg, err)
 

tests/components/websocket_api/test_decorators.py

@@ -122,6 +122,23 @@ async def test_async_response_request_context(
     assert msg["error"]["code"] == "invalid_format"
     assert msg["error"]["message"] == "Message incorrectly formatted."
 
+    await websocket_client.send_json(
+        {
+            "id": 10,
+            "type": "test-get-request",
+            "not_valid": "dog",
+        }
+    )
+
+    msg = await websocket_client.receive_json()
+    assert msg["id"] == 10
+    assert not msg["success"]
+    assert msg["error"]["code"] == "invalid_format"
+    assert msg["error"]["message"] == (
+        "Message has unexpected keys. "
+        "Got {'id': 10, 'type': 'test-get-request', 'not_valid': 'dog'}"
+    )
+
 
 async def test_supervisor_only(hass: HomeAssistant, websocket_client) -> None:
     """Test that only the Supervisor can make requests."""