inviteToRoom works but fails to parse JSON response and raises exception

[schoettl]

I use this client to create a room and then invite another user.

It works so far, it does create the room and invite the user. But then, I get an exception:

user error (Error in $: parsing () failed, expected Array, but encountered Object)

It seems to be a Aeson parse exception on the response returned by the matrix server. I could only handle that exception with a try/catch but it seems like a bug in this package to me.

I'm using version 0.1.4.3 (latest on hackage).

---

This is my code:

createPrivateMatrixRoom :: ClientSession -> Text -> Text -> Text -> [UserID] -> IO ()
createPrivateMatrixRoom sess alias name description users = do
  roomResult <- createRoom sess $ RoomCreateRequest PrivateChat alias name description
  case roomResult of
    Right roomId -> do
      inviteResults <- mapM (flip (inviteToRoom sess roomId) Nothing) users
      case lefts inviteResults of
        [] -> return ()
        err -> error $ "error: could not invite some users. details: " ++ show err
    Left err -> error $ "error: could not create matrix room, maybe due to existing canonical alias. details: " ++ show err

[schoettl]

It looks like inviteToRoom calls doRequest and implicitly specifies the return type to be MatrixIO (). That causes doRequest to parse the JSON response to ().

I'll try if I can provide a fix.

[schoettl]

With traceShowId:

"{\"room_id\":\"!cFEKmHKNNDNsWDRGUv:matrix.org\"}"    -- room create work
"{}"  -- invite user also worked, empty JSON object as response
14/Mar/2023:11:42:15 +0100 [Error#yesod-core] user error (Error in $: parsing () failed, expected Array, but encountered Object)

[schoettl]

Oh, this kind of bug was already fixed for other functions of type MatrixIO ().

It was fixed in many different ways:

• fmap (() <$) $ doRequest' @Value manager req
• fmap ensureEmptyObject <$> doRequest session (request {HTTP.method = "POST"})
• void <$> (doRequest session $ request { ... })

I was close to publishing another possible fix :D

[TristanCacqueray]

Thank you for the bug report and for improving the error handling. It seems like this depends on the server implementation, in #35 I'm adding an invite test that works against conduit.rs.

In the future, we might want to remove the exception throwing by using the existing MatrixError data to return such decoding error.