Start Langium as standalone server

[theogiraudet]

Hi!
I want to use my DSL in others IDEs using Monaco, how can I run the Langium server as a standalone program?
I tried to launch the main in these two ways:

node .\out\language-server\main.js --node-ipc
node .\out\language-server\main.js --stdio

But it doesn't seem to work.

Thanks!

[msujew]

Hi @theogiraudet,

That's weird, I just tried to use node .\out\language-server\main.js --stdio, which seems to work fine for me. What issues are you experiencing with that approach? Any errors or something similar in the console?

[theogiraudet]

Thanks for the details about stdio!
I think the two solutions work (usually), if I check the source code:

But in these two cases, no process runs on the port 2000.

[msujew]

Hm, true, that's weird. Doesn't work for me either...

I digged a bit more into it, and it seems like the --socket option works a bit ... let's say unexpected. See this explanation by the devs. Instead of using the language server as the actual server (i.e. listening to the specified port), the language server expects the client to act as the server, to which it will try to connect to.

I assume that since no client provides the specified port on your machine, the language server simply ends the process, as there's no one to connect to.

[theogiraudet]

Thanks for the link and for the response!
For the moment, even with the code I can't do it, I'm still looking.
Perhaps it would be a good idea to propose with Langium a way to create sockets more easily or do you think it's out of the goal of the project?

[spoenemann]

I think that is out of scope for Langium. You can use Node.js to create a socket server and connect the language server to it using the vscode-languageserver API. It would be nice to have an example for that, but so far I'm not aware of any.

[theogiraudet]

Hi,
Thanks you for your answer. I built a bridge opening a Websocket and connecting to Langium via stdout and it's work perfectly.
I don't really know if it's a perfect solution but it's enough for my use case !

[spoenemann]

You can connect Langium directly to a WebSocket with a custom message reader / writer. The following snippet is based on the ws package:

class WebSocketMessageWriter extends AbstractMessageWriter {
    private readonly ws: WebSocket;

    constructor(ws: WebSocket) {
        super();
        this.ws = ws;
    }

    write(msg: Message): Promise<void> {
        return new Promise((resolve, reject) => {
            const content = JSON.stringify(msg);
            this.ws.send(content, err => {
                if (err) {
                    reject(err);
                } else {
                    resolve();
                }
            });
        });
    }

    end(): void {}
}

class WebSocketMessageReader extends AbstractMessageReader {
    private readonly ws: WebSocket;

    constructor(ws: WebSocket) {
        super();
        this.ws = ws;
    }

    listen(callback: DataCallback): Disposable {
        const messageListener = (rawMessage: Message) => {
            const message = JSON.parse(rawMessage.toString()) as Message;
            callback(message);
        };
        const closeListener = () => this.fireClose()

        this.ws.on('message', messageListener);
        this.ws.on('close', closeListener);

        return {
            dispose: () => {
                this.ws.removeListener('message', messageListener);
                this.ws.removeListener('close', closeListener);
            }
        };
    }
}

const wsServer = new WebSocket.Server(/* options */);
wsServer.on('connection', (ws, request) => {
    const reader = new WebSocketMessageReader(ws);
    const writer = new WebSocketMessageWriter(ws);
    const connection = createConnection(reader, writer);

    const services = createMyLanguageServices({ connection });
    startLanguageServer(services.shared);
});

[theogiraudet]

I have replaced my bridge with your implementations and it works perfectly, thanks!