use EmptyResult instead of custom NoResponse

BTCPayServer/Controllers/InvoiceController.UI.cs

@@ -217,15 +217,7 @@ namespace BTCPayServer.Controllers
                 leases.Dispose();
                 await CloseSocket(webSocket);
             }
-            return new NoResponse();
+            return new EmptyResult();
-        }
-
-        class NoResponse : IActionResult
-        {
-            public Task ExecuteResultAsync(ActionContext context)
-            {
-                return Task.CompletedTask;
-            }
         }
         
         ArraySegment<Byte> DummyBuffer = new ArraySegment<Byte>(new Byte[1]);

BTCPayServer/EventAggregator.cs

@@ -4,6 +4,7 @@ using System.Collections.Generic;
 using System.Linq;
 using System.Threading.Tasks;
 using BTCPayServer.Logging;
+using System.Threading;
 
 namespace BTCPayServer
 {
@@ -26,8 +27,12 @@ namespace BTCPayServer
 
             public Action<Object> Act { get; set; }
 
+            bool _Disposed;
             public void Dispose()
             {
+                if (_Disposed)
+                    return;
+                _Disposed = true;
                 lock (this.aggregator._Subscriptions)
                 {
                     if (this.aggregator._Subscriptions.TryGetValue(t, out Dictionary<Subscription, Action<object>> actions))
@@ -51,6 +56,19 @@ namespace BTCPayServer
                 Dispose();
             }
         }
+        public Task<T> WaitNext<T>(CancellationToken cancellation = default(CancellationToken))
+        {
+            return WaitNext<T>(o => true, cancellation);
+        }
+        public async Task<T> WaitNext<T>(Func<T, bool> predicate, CancellationToken cancellation = default(CancellationToken))
+        {
+            TaskCompletionSource<T> tcs = new TaskCompletionSource<T>();
+            var subscription = Subscribe<T>((a, b) => { if (predicate(b)) { tcs.TrySetResult(b); a.Unsubscribe(); } });
+            using (cancellation.Register(() => { tcs.TrySetCanceled(); subscription.Unsubscribe(); }))
+            {
+                return await tcs.Task.ConfigureAwait(false);
+            }
+        }
 
         public void Publish<T>(T evt) where T : class
         {