StopAsync resets state on inactive connection (#20083) (#23962)

src/SignalR/clients/csharp/Client.Core/src/HubConnection.cs

@@ -501,6 +501,11 @@ namespace Microsoft.AspNetCore.SignalR.Client
                 {
                     connectionState.Stopping = true;
                 }
+                else
+                {
+                    // Reset StopCts if there isn't an active connection so that the next StartAsync wont immediately fail due to the token being canceled
+                    _state.StopCts = new CancellationTokenSource();
+                }
 
                 if (disposing)
                 {

src/SignalR/clients/csharp/Client/test/UnitTests/HubConnectionTests.ConnectionLifecycle.cs

@@ -334,6 +334,26 @@ namespace Microsoft.AspNetCore.SignalR.Client.Tests
                 });
             }
 
+            [Fact]
+            public async Task StopAsyncOnInactiveConnectionDoesNotAffectNextStartAsync()
+            {
+                // Regression test:
+                // If there wasn't an active underlying connection, StopAsync would leave a CTS canceled which would cause the next StartAsync to fail
+                var testConnection = new TestConnection();
+                await AsyncUsing(CreateHubConnection(testConnection), async connection =>
+                {
+                    Assert.Equal(HubConnectionState.Disconnected, connection.State);
+
+                    await connection.StopAsync().OrTimeout();
+                    Assert.False(testConnection.Disposed.IsCompleted);
+                    Assert.Equal(HubConnectionState.Disconnected, connection.State);
+
+                    await connection.StartAsync().OrTimeout();
+                    Assert.True(testConnection.Started.IsCompleted);
+                    Assert.Equal(HubConnectionState.Connected, connection.State);
+                });
+            }
+
             [Fact]
             public async Task CompletingTheTransportSideMarksConnectionAsClosed()
             {