As someone who has also written a TCP proxy (along with many others...), after thoroughly reading the page I'm still unsure of how exactly this is "high performance". It is also curious that, despite the fact that it uses a separate library for networking, the source is already quite a bit longer than some other proxies which don't. I found the explanation overly complex.

Around half the code in this implementation could probably be removed by the realisation that, after a connection is established, both ends are completely symmetric: all it needs to do is try to read from A and write to B, then try to read from B and write to A. If A closes, close B. If B closes, close A.