一些搜索和反复试验后，我制定了以下。这似乎正好符合要求。它应该是很容易适应PHP或任何其他服务器端软件，因为它主要涉及到修改的标题。

After some searching and trial and error, I developed the following. It seems to fit the bill exactly. It should be very easily adaptable to PHP or any other server-side software since it mostly involves modifying headers.

protected void streamToResponse()
{
    Response.Clear();
    Response.AddHeader("content-disposition", "attachment; filename=testfile.csv");
    Response.AddHeader("content-type", "text/csv");

    using(StreamWriter writer = new StreamWriter(Response.OutputStream))
    {
        writer.WriteLine("col1,col2,col3");
        writer.WriteLine("1,2,3");
    }
    Response.End();
}