Streaming.cs

public class Configuration(IAppBuilder app)
{
    // TaskCompletionSource
    app.Map("/streaming-api1", map =>
    {
        // Streaming API using SignalR
        var connectionContext = GlobalHost.ConnectionManager.GetConnectionContext<RawConnection>();

        map.Run(async context =>
        {
            var tcs = new TaskCompletionSource<object>();

            // Whenever a message is sent to this connection we're going to write it to the response
            IDisposable disposable = connectionContext.Connection.Receive(async message =>
            {
                await context.Response.WriteAsync(message.ToString());
                await context.Response.Body.FlushAsync();
            });

            context.Request.CallCancelled.Register(() => tcs.TrySetResult(null));

            await tcs.Task;

            disposable.Dispose();
        });
    });
    
    // Awaitable cancelltion tokens
    app.Map("/streaming-api2", map =>
    {
        // Streaming API using SignalR
        var connectionContext = GlobalHost.ConnectionManager.GetConnectionContext<RawConnection>();

        map.Run(async context =>
        {
            // Whenever a message is sent to this connection we're going to write it to the response
            IDisposable disposable = connectionContext.Connection.Receive(async message =>
            {
                await context.Response.WriteAsync(message.ToString());
                await context.Response.Body.FlushAsync();
            });

            await context.Request.CallCancelled;

            disposable.Dispose();
        });
    });

}

// Impl
public static class CancellationTokenExtensions
{
    public static CancellationTokenAwaiter GetAwaiter(this CancellationToken cancellationToken)
    {
        return new CancellationTokenAwaiter(cancellationToken);
    }

    public class CancellationTokenAwaiter : INotifyCompletion
    {
        private readonly CancellationToken _cancellationToken;

        public CancellationTokenAwaiter(CancellationToken cancellationToken)
        {
            _cancellationToken = cancellationToken;
        }

        public void GetResult()
        {
        }

        public bool IsCompleted
        {
            get
            {
                return _cancellationToken.IsCancellationRequested;
            }
        }

        public void OnCompleted(Action action)
        {
            _cancellationToken.Register(action);
        }
    }
}