Carter: Unable to respond with a Stream

I’m unable to work out how to reply with a streamed response using Botwin. Reading up on ASP.NET Core it looks liked I’d be able to do the following:

[HttpGet]
public FileStreamResult GetTest()
{
  var stream = new MemoryStream(Encoding.ASCII.GetBytes("Hello World"));
  return new FileStreamResult(stream, new MediaTypeHeaderValue("text/plain"))
  {
    FileDownloadName = "test.txt"
  };
}

(https://stackoverflow.com/questions/42771409/how-to-stream-with-asp-net-core#42772150)

However, I can’t work out how I can do this using the HttpResponse I have from the BotwinModule handler?

Here’s a snippet of my module, but it doesn’t return any data:

var models = this.journalReader.Read(start, end, type, ct);

var fileStream =
    new FileStreamResult(CreateExportStream(models, requestLog, ct), "application/csv")
        {
            FileDownloadName
                = $"journal-{type}.csv"
        };

res.Body = fileStream.FileStream;