package server

import (
	"net"
	"syscall"
)

func BindInterface(ip net.IP, port int, dev string) (net.PacketConn, error) {
	if port == 0 {
		port = 67
	}

	udpAddr := &net.UDPAddr{
		IP:   ip,
		Port: port,
	}

	conn, err := net.ListenUDP("udp4", udpAddr)
	if err != nil {
		return nil, err
	}

	sysconn, err := conn.SyscallConn()
	if err != nil {
		conn.Close()
		return nil, err
	}

	sysconn.Control(func(fd uintptr) {
		err = syscall.BindToDevice(int(fd), dev)
	})

	if err != nil {
		conn.Close()
		return nil, err
	}

	return conn, nil
}