implement charybdis' synflood mitigation strategies

[kaniini]

we need to implement charybdis' listen::defer_accept. this will allow the kernel to discard synflood traffic without clogging the ircd or tcp stack resources up.

on Linux, this is a matter of using socket.setsockopt() on the listener, with the socket.TCP_DEFER_ACCEPT constant and the socket.SOL_TCP layer constant.

on FreeBSD, I need to still investigate how to get access to accept filters from Python.

[usrbinsam]

Python's socket module documentation states that the TCP_* constants should all be the same, On FreeBSD, I would think it's just socket.TCP_FILTERACCEPT. Not sure on the layer constant, maybe socket.IPPROTO_TCP?

[kaniini]

you have to attach a struct so_acceptfilter to the setsockopt(2) call.