Is there any documentation or mapping of OWIN middleware properties/functions and Core?

I had to make some middleware to work for both and started with Core because its easier and I never worked with Owin, now I need to do own and there are methods like HttpRequest.EnableRewind() that I don't know the owin version of or the property HttpRequest.ContentLength doesn't seem to have a counterpart in OwinRequest.

I know its strange as I am sure most people are going from Owin to Core middleware, but even that documentation should be interchangeable and would help.