TODO

-) server, client support usage stat, like received packets, bytes, current connections

-) the capability of sending raw packet

-) implement unix domain socket only under Unix

-) socket can accept or connect on specific interface according to its name

-) client connect to server via specific port, it's an advance tool

-) client use specific port and address, if host have multiple NICs, but want use specific NIC

-) timeout when user connect in but no send any data

-) allow udp connect to a fixed address

-) if udp is connected to a address, then send and recv only allow this address's packets

-) report error if udp already connect to a fixed addr but still send to another address

-) allow multicast and broadcast on socket

-) deadline is not same as timeout, add deadline support for socket

-) support set max connections limit in tcp, udp server socket

-) add sendfile, TransmitFile, use method name: transmit

-) async dns resolve

-) detect file changes using reactor

-) reactor accept base class ref instead of fd

-) librector only provide io, timer, signal and so on, sockets move to another library

-) Windows support AF_UNIX https://blogs.msdn.microsoft.com/commandline/2017/12/19/af_unix-comes-to-windows/

-) support socketpair

-）support signal, file