Thank you! :)

Later I benchmarked several TCP proxies, written in C, C++, Golang, Java, Python and compared to this HTTP Tunnel (I added the TCP mode to it later). The Java solution was not Netty, but it was implemented using java.nio and the same Async I/O model as Netty uses (the link to the source code is in the article below).

You can see the results here: https://medium.com/star-gazers/benchmarking-low-level-i-o-c-c-rust-golang-java-python-9a0d505f85f7