Middleware - change response html

Does anybody have an example of how to write middleware to change the response html before it gets sent back to the client? I'm trying to remove unnecessary white space with my middleware. I followed the example at the following site http://www.mikesdotnetting.com/article/269/asp-net-5-middleware-or-where-has-my-httpmodule-gone, but it only works when appending to the response body, not changing the response body that has already been written. Thanks!