Create a background server

Question

It is quite simple, this code works, but only once, after the first time it is started no other request is answered, as if after it runs once the Streamsocketlistener stops.

public void Run(IBackgroundTaskInstance taskInstance)
{
    var deferral = taskInstance.GetDeferral();
    var detalhes = taskInstance.TriggerDetails as SocketActivityTriggerDetails;
    if (detalhes.SocketInformation.SocketKind == SocketActivityKind.StreamSocketListener &&
        detalhes.Reason == SocketActivityTriggerReason.ConnectionAccepted)
    {
        var list = detalhes.SocketInformation.StreamSocketListener;
        list.ConnectionReceived += async (sender, args) =>
        {
            using (DataWriter escritor = new DataWriter(args.Socket.OutputStream))
            {
                escritor.WriteString("HTTP/1.1 200 OK\r\nContent-Length: 2\r\nConnection: close\r\n\r\nOK");
                await escritor.StoreAsync();
            }
        };
    }
    deferral.Complete();
}

Background job logging is done with this code:

private void Registrar()
{
    var tasks = BackgroundTaskRegistration.AllTasks;
    int quant = tasks.Values.Count(x => x.Name == "SocketActivityBackgroundTask");
    if (quant == 1)
    {
        task = tasks.Values.Single(x => x.Name == "SocketActivityBackgroundTask");
    }
    else
    {
        var socketTaskBuilder = new BackgroundTaskBuilder();
        socketTaskBuilder.Name = "SocketActivityBackgroundTask";
        socketTaskBuilder.TaskEntryPoint = "SocketActivityBackgroundTask.SocketActivityTask";
        var trigger = new SocketActivityTrigger();
        socketTaskBuilder.SetTrigger(trigger);
        task = socketTaskBuilder.Register();
    }
}

private async Task Iniciar()
{
    var sockets = SocketActivityInformation.AllSockets;
    if (!sockets.Keys.Contains(socketId))
    {
        StreamSocketListener socket = new StreamSocketListener();
        socket.EnableTransferOwnership(task.TaskId, SocketActivityConnectedStandbyAction.DoNotWake);
        await socket.BindServiceNameAsync(serverPort);
        await Task.Delay(500);
        await socket.CancelIOAsync();
        socket.TransferOwnership(socketId);
    }
}

The record works and the task goes to the background, but it only works once, and this is the current problem, because the previous one was solved but this one was created.

Answer 1

It’s not that simple, according to documentation in addition to the use of deferrals when an asynchronous function is performed, it is also recommended: (Re-register your background tasks during app launch.) Deregister` and re-register a task during application startup, among other recommendations.

foreach (var cur in BackgroundTaskRegistration.AllTasks)
{
   if (cur.Value.Name != name) continue;
   cur.Value.Unregister(true);
}

As the process needs to run, apparently the use of the deferral.Complete(); , makes the task stop responding to requests SocketActivityTrigger.

I prepared a functional example with the implementations shown here, the source code is at the end of the answer.

Obviously the code needs to be improved but demonstrates the operation of a simple application UWP cliente/servidor based on communication via sockets

Source Code:
https://github.com/rubgithub/ClientServerSocketUWP

References:

https://docs.microsoft.com/en-us/windows/uwp/launch-resume/guidelines-for-background-tasks https://social.technet.microsoft.com/wiki/contents/articles/36500.uwp-linux-socket-communication-handling-communciation-in-the-backgroundtask.aspx https://github.com/Microsoft/Windows-universal-samples/tree/master/Samples/WebSocket