It is symmetrical, but there are nuances. If A closes or errors out, the proxy should first push out any pending data and only then close B. The same goes for

It is symmetrical, but there are nuances. If A closes or errors out, the proxy should first push out any pending data and only then close B. The same goes for when A sends a FIN - it should flush any data queued at application level before calling shutdown() on B's socket. If A becomes unwritable, it should stop reading from B.