e.g. inside of lua-http, I've also needed:
- socket buffering (including flushing and :unget; which needs to be
able to be optionally fed back to through TLS)
- a coroutine scheduler
- that supports locking
- a TLS library
- that supports mid-stream TLS upgrades
- that supports ALPN
- slightly advanced tcp flags such as NOPUSH
- shutdown(2)
I see cqueues as a particular good solution, as it doesn't tie you
into a particular event library.