switch net {
	case "tcp":
		laddr = new(TCPAddr)
		raddr = new(TCPAddr)
	case "udp":
		laddr = new(UDPAddr)
		raddr = new(UDPAddr)
	default:
		laddr = unknownAddr{}
		raddr = unknownAddr{}
	}
	return &netFD{
		pfd:   pfd,
		net:   net,
		laddr: laddr,
		raddr: raddr,
	}
}

func (fd *netFD) init() error {
	return fd.pfd.Init(fd.net, true)
}

	h.laddr = c.fd.laddr.(*UDPAddr).IP.To16()
	h.ifcaddr = IPv6zero // ignored (receive only)
	h.rport = uint16(addr.Port)
	h.lport = uint16(c.fd.laddr.(*UDPAddr).Port)

	buf := make([]byte, udpHeaderSize+len(b))
	i := copy(buf, h.Bytes())
	copy(buf[i:], b)
	if _, err := c.fd.Write(buf); err != nil {
		return 0, err
	}
	return len(b), nil
}

		// port to join the same group address.
		if addr.IP != nil && addr.IP.IsMulticast() {
			if err := setDefaultMulticastSockopts(fd.pfd.Sysfd); err != nil {
				return err
			}
			addr := *addr
			switch fd.family {
			case syscall.AF_INET:
				addr.IP = IPv4zero
			case syscall.AF_INET6:
				addr.IP = IPv6unspecified
			}
			laddr = &addr
		}
	}
	var err error
	var lsa syscall.Sockaddr

}

func (sd *sysDialer) dialTCP(ctx context.Context, laddr, raddr *TCPAddr) (*TCPConn, error) {
	if h := sd.testHookDialTCP; h != nil {
		return h(ctx, sd.network, laddr, raddr)
	}
	if h := testHookDialTCP; h != nil {
		return h(ctx, sd.network, laddr, raddr)
	}
	return sd.doDialTCP(ctx, laddr, raddr)
}

func (sd *sysDialer) doDialTCP(ctx context.Context, laddr, raddr *TCPAddr) (*TCPConn, error) {
	switch sd.network {

		}
	} else if err := setKeepAliveIdleAndInterval(c.fd, config.Idle, config.Interval); err != nil {
		return &OpError{Op: "set", Net: c.fd.net, Source: c.fd.laddr, Addr: c.fd.raddr, Err: err}
	}
	if err := setKeepAliveCount(c.fd, config.Count); err != nil {
		return &OpError{Op: "set", Net: c.fd.net, Source: c.fd.laddr, Addr: c.fd.raddr, Err: err}
	}

	return nil

		return &OpError{Op: "set", Net: c.fd.net, Source: c.fd.laddr, Addr: c.fd.raddr, Err: err}
	}
	if err := setKeepAliveIdle(c.fd, config.Idle); err != nil {
		return &OpError{Op: "set", Net: c.fd.net, Source: c.fd.laddr, Addr: c.fd.raddr, Err: err}
	}
	if err := setKeepAliveInterval(c.fd, config.Interval); err != nil {
		return &OpError{Op: "set", Net: c.fd.net, Source: c.fd.laddr, Addr: c.fd.raddr, Err: err}
	}

}

func (sd *sysDialer) dialTCP(ctx context.Context, laddr, raddr *TCPAddr) (*TCPConn, error) {
	if h := sd.testHookDialTCP; h != nil {
		return h(ctx, sd.network, laddr, raddr)
	}
	if h := testHookDialTCP; h != nil {
		return h(ctx, sd.network, laddr, raddr)
	}
	return sd.doDialTCP(ctx, laddr, raddr)
}

func (sd *sysDialer) doDialTCP(ctx context.Context, laddr, raddr *TCPAddr) (*TCPConn, error) {

//
// If laddr is nil, a local address is automatically chosen.
// If the IP field of raddr is nil or an unspecified IP address, the
// local system is assumed.
func DialIP(network string, laddr, raddr *IPAddr) (*IPConn, error) {
	if raddr == nil {
		return nil, &OpError{Op: "dial", Net: network, Source: laddr.opAddr(), Addr: nil, Err: errMissingAddress}
	}

		return nil, &OpError{Op: "dial", Net: network, Source: laddr.opAddr(), Addr: nil, Err: errMissingAddress}
	}
	sd := &sysDialer{network: network, address: raddr.String()}
	c, err := sd.dialUDP(context.Background(), laddr, raddr)
	if err != nil {
		return nil, &OpError{Op: "dial", Net: network, Source: laddr.opAddr(), Addr: raddr.opAddr(), Err: err}
	}
	return c, nil
}

// ListenUDP acts like ListenPacket for UDP networks.

		sotype = syscall.SOCK_SEQPACKET
	default:
		return nil, UnknownNetworkError(net)
	}

	switch mode {
	case "dial":
		if laddr != nil && laddr.isWildcard() {
			laddr = nil
		}
		if raddr != nil && raddr.isWildcard() {
			raddr = nil
		}
		if raddr == nil && (sotype != syscall.SOCK_DGRAM || laddr == nil) {
			return nil, errMissingAddress
		}
	case "listen":
	default:
		return nil, errors.New("unknown mode: " + mode)