I suspect the n-by-k array part is a typo, an one-dimensional array of closures is all you need. I also don't think the closure approach is bad for code reuse.

I suspect the n-by-k array part is a typo, an one-dimensional array of closures is all you need. I also don't think the closure approach is bad for code reuse. The closures serve just to bind the environment to the TCP-handler and UDP-handler functions. The closures themselves are probably trivial and not worth sharing, and the protocol handler functions (or closures) can be shared like any other library function.