using (var reader = new CancellableStreamReader(stream))
{
    while (true)
    {
        cancellationToken.ThrowIfCancellationRequested();

        // create timeout cancellation token source
        using (var timeoutTokenSource = new CancellationTokenSource(readTimeout))
        using (var compositeTokenSource = CancellationTokenSource.CreateLinkedTokenSource(
            cancellationToken, timeoutTokenSource.Token))
        {
            // execute read line
            var line = await reader.ReadLineAsync(compositeTokenSource.Token).ConfigureAwait(false);
            if (String.IsNullOrEmpty(line))
            {
                System.Diagnostics.Debug.WriteLine("#USERSTREAM# CONNECTION CLOSED.");
                break;
            }

            // read operation completed successfully
            Task.Run(() => DispatchStreamingElements(DynamicJson.Parse(line), handler),
                cancellationToken).ConfigureAwait(false);
        }
    }

    // more performant?
    using (var timeoutTokenSource = new CancellationTokenSource())
    using (var compositeTokenSource = CancellationTokenSource.CreateLinkedTokenSource(
        cancellationToken, timeoutTokenSource.Token))
    {
        while (true)
        {
            cancellationToken.ThrowIfCancellationRequested();

            // create timeout cancellation token source
            // execute read line
            var readTask = reader.ReadLineAsync(compositeTokenSource.Token);
            if (await Task.WhenAny(readTask, Task.Delay(readTimeout, compositeTokenSource.Token))
                          .ConfigureAwait(false) == readTask)
            {
                var line = readTask.Result;
                // read operation completed successfully
                Task.Run(() => DispatchStreamingElements(DynamicJson.Parse(line), handler),
                    cancellationToken).ConfigureAwait(false);
            }
            else
            {
                timeoutTokenSource.Cancel();
                System.Diagnostics.Debug.WriteLine("#USERSTREAM# CONNECTION CLOSED.");
                break;
            }
        }
    }
}