Show error messages on login screen

src/python/backend.py

@@ -46,17 +46,22 @@ class Backend:
     # Clients management
 
     async def login_client(self,
-                           user:       str,
-                           password:   str,
-                           device_id:  Optional[str] = None,
-                           homeserver: str = "https://matrix.org") -> str:
+        user:       str,
+        password:   str,
+        device_id:  Optional[str] = None,
+        homeserver: str = "https://matrix.org",
+    ) -> Tuple[bool, str]:
         client = MatrixClient(
             self, user=user, homeserver=homeserver, device_id=device_id,
         )
-        await client.login(password)
+        try:
+            await client.login(password)
+        except RuntimeError as err:
+            return (False, err.args[0].message)
+
         self.clients[client.user_id]         = client
         self.models[Account][client.user_id] = Account(client.user_id)
-        return client.user_id
+        return (True, client.user_id)
 
 
     async def resume_client(self,

src/python/matrix_client.py

@@ -112,7 +112,7 @@ class MatrixClient(nio.AsyncClient):
         )
 
         if isinstance(response, nio.LoginError):
-            log.error(response)
+            raise RuntimeError(response)
         else:
             await self.start()
 
@@ -497,7 +497,7 @@ class MatrixClient(nio.AsyncClient):
 
 
     async def onErrorResponse(self, resp: nio.ErrorResponse) -> None:
-        # TODO: show something in the client
+        # TODO: show something in the client, must be seen on login screen too
         try:
             log.warning("%s - %s", resp, json.dumps(resp.__dict__, indent=4))
         except Exception: