How can I implement a proxy that handles both TCP

问题:

I was looking into proxy implementations (I am interested in using Java as programming language).
I was wondering, is a proxy supposed to work on all protocols? E.g. TCP and UDP
A single protocol, e.g. TCP only?
Are proxies usually application level e.g. HTTP?
Is it possible to implement a proxy that can proxy TCP and UDP connections?
If I need to build a proxy that reshapes traffic e.g. blocks/drops packets or making some connections slower than others should I be working on IP level? Higher levels?

回答1:

a proxy supposed to work on all protocols? E.g. TCP and UDP. A single protocol, e.g. TCP only?

It depends on whether it's a TCP proxy, a UDP proxy, both, or an application proxy.

Are proxies usually application level e.g. HTTP?

Yes, and application proxies always are.

If I need to build a proxy that reshapes traffic e.g. blocks/drops packets or making some connections slower than others should I be working on IP level? Higher levels?

IP level. I wouldn't even call it a proxy, more of a filter.