Sending file html ?

[snippsat]

I need to do without using third party framework

Why?

Something here you can look at. here, here.
WSGI middleware is the more correct way,this stuff is not easy do right,that's why we have framework.
Look at how Werkzeug dos it,a even thinner layer above WSGI,Flask has a lot werkzeug stuff in bottom.
Serve Shared Static Files, Github.