Add support for setting up language servers to use websockets

[MangoIV]

Allow the user to set up an lsp server that talks to the user using the websocket protocol instead of standard IO and do enough refactoring to make the setup with websockets possible

[MangoIV]

I have tried to make as few breaking changes as possible (I don't think there are any) except that I changed from BS.ByteString and BSL.ByteString (which are not visible in the haddock) to BS.StrictByteString and BSL.LazyByteString (which are visible in the haddock) Unfortunately these are very recent additions, so let me know if I should revert them for the sake of better backwards compatibility with older bytestring versions.

[michaelpj]

Looks fine to me.

[michaelpj]

Should some of these include extra information beyond the constant string?

[MangoIV]

I just thought about it, but nothing interesting comes to mind - I think this should purely exist to get status information of the websocket, the rest should be logged elsewhere

[derekstavis]

Hello 👋 is there anything I could help with to get this one merged? This is going to be quite useful for a project I'm working on!

[MangoIV]

Not really. I just came back from holidays and gotta finish this :)

[MangoIV]

It’s usable though, you can pin it to this revision

[derekstavis]

I'm testing it here and it doesn't seem to reply to any messages - it does read incoming requests but does not send a reply.

[MangoIV]

You probably need

defaultOptions
{ optTextDocumentSync =
Just
TextDocumentSyncOptions
{ _openClose = Just True
, _willSaveWaitUntil = Just False
, _willSave = Just False
, _save = Just $ InR $ SaveOptions $ Just False
, _change = Just TextDocumentSyncKind_Incremental
}

Do you already have this?

[derekstavis]

Yep. Here's my server definition - confirmed to work with the stdin transport:

serverDefinition state =
  ServerDefinition
    { defaultConfig = defaultLspConfig
    , configSection = "mylang"
    , parseConfig = \_oldConfig newConfigValue -> case fromJSON newConfigValue of
        Success cfg -> Right cfg
        Error err -> Left (T.pack err)
    , onConfigChange = liftIO . atomically . writeTVar (config state)
    , doInitialize = \env _req -> pure $ Right env
    , staticHandlers = const $ lspHandlers state
    , interpretHandler = \env -> Iso (runLspT env) liftIO
    , options =
        S.defaultOptions
          { optTextDocumentSync =
              Just $
                LSP.TextDocumentSyncOptions
                  { _openClose = Just True
                  , _change = Just LSP.TextDocumentSyncKind_Full
                  , _willSave = Just False
                  , _willSaveWaitUntil = Just False
                  , _save = Just $ InR $ LSP.SaveOptions $ Just False
                  }
          }
    }

The web socket message is being sent and received:

Logs:

[Debug] Websocket: New connection established
[Info] Starting server
[Debug] Websocket: Received request

[MangoIV]

Alright, imma look into it tomorrow, thanks for testing.

[MangoIV]

you are right, there must be something gone wrong when copy-pasting the working definition over - I'm investigating.

[MangoIV]

i found the reason - parse takeByteString always returns partial - I somehow need to mark the end of websocket request

[derekstavis]

My understanding is that stdio can be chunked but WebSockets are not, this means that we can just trust that whatever the websockets package gives is the full packet.

I'm not a Haskeller so I asked Claude to start from scratch basing off of this PR's changes and this was the result. Now I get the responses accordingly.

[MangoIV]

this means that we can just trust that whatever the websockets package gives is the full packet.

That is correct. I just want to figure out the best way to do this. I know how to „make it work“ that is not the problem. If you want to use whatever the LLM spat out, then that is not relevant to my PR :)