WebSocket send and receive data asynchronously (using NuGet websocket-client)

Question

I am struggling with the observer pattern with NuGet package websocket-client ( https://github.com/Marfusios/websocket-client )

The connection to the WebSocket server is stable and running.

Every request has a request ID inside the payload. The client sends it to the server and the server responds with the ID and the real data.

On the client side I need to assign every response to the corresponding request.

I thought I can do it like so:

public Task<Data> GetDataAsync()
{
    var webSocket = new WebsocketClient(Uri);
    await webSocket.Start();

    var requestId = Guid.NewGuid();

    var tcs = new TaskCompletionSource<Data>();

    var disposable = webSocket
    .MessageReceived
    .Where(message => message.Text.Contains(requestId))
    .Subscribe(message=>
    {
        var data = ParseData(message.Text);
        tcs.SetResult(data);
    });

    return tcs.Task;
}

But it actually never jumps into the subscribe method. Am I using it wrong?

Answer 1

I think

public Task<Data> GetDataAsync(string request)
{
    var requestId = Guid.NewGuid().ToString();

    var responseTask = WebSocket
    .MessageReceived
    .Timeout(TimeSpan.FromSeconds(5))
    .FirstOrDefaultAsync(message => message.Text.Contains(requestId));

    WebSocket.Send(request);

    var responseMessage = await responseTask;

    return ParseMessage(responseMessage);
}

is the way to go. I would even prefer SingleOrDefaultAsync instead of FirstOrDefaultAsync because there will be only one message with that request id. But that doesn't work. It always runs in the timeout.

Answer 2

You've made your code far more complicated than it needs to me. Rx let's await an observable to get the last value produced. You can write your code like this:

public async Task<Data> GetDataAsync() =>
    await
        Observable
            .Using(
                () => new WebsocketClient(Uri),
                ws =>
                    from x in Observable.FromAsync(() => ws.Start())
                    let requestId = Guid.NewGuid()
                    from m in ws.MessageReceived
                    where m.Text.Contains(requestId)
                    select ParseData(m.Text))
            .Take(1)
            .Timeout(TimeSpan.FromSeconds(5.0));