// ReplyPacket creates a reply packet that a Server would send to a client.
// It uses the req Packet param to copy across common/necessary fields to
// associate the reply with the request.
func informReplyPacket(req dhcp4.Packet, mt dhcp4.MessageType, serverID net.IP, options []dhcp4.Option) dhcp4.Packet {
p := dhcp4.NewPacket(dhcp4.BootReply)
p.SetXId(req.XId())
p.SetHType(req.HType())
p[2] = req.HLen() // dhcp4 library does not provide a setter
p.SetFlags(req.Flags())
p.SetCIAddr(req.CIAddr())
p.SetCHAddr(req.CHAddr())
p.AddOption(dhcp4.OptionDHCPMessageType, []byte{byte(mt)})
p.AddOption(dhcp4.OptionServerIdentifier, []byte(serverID))
for _, o := range options {
p.AddOption(o.Code, o.Value)
}
p.PadToMinSize()
return p
}
func main() {
if len(os.Args) != 3 {
panic("not enough args")
}
intf, err := net.InterfaceByName(os.Args[1])
if err != nil {
panic(err)
}
containerID := os.Args[2]
log.Infof("Requesting for container ID %q on interface %q", containerID, intf.Name)
contPid := getContainerInfo(containerID)
log.Infof("Container has PID %s", contPid)
runtime.LockOSThread()
f, err := os.Open(fmt.Sprintf("/proc/%s/ns/net", contPid))
if err != nil {
panic(err)
}
if _, _, err := unix.RawSyscall(unix.SYS_SETNS, f.Fd(), syscall.CLONE_NEWNET, 0); err != 0 {
panic(err)
}
link, err := netlink.LinkByName("eth0")
if err != nil {
panic(err)
}
chaddr := link.Attrs().HardwareAddr
p := dhcp.RequestPacket(dhcp.Discover, chaddr, nil, []byte{1, 2, 3, 4}, true, []dhcp.Option{})
conn, err := net.ListenPacket("udp", ":68")
if err != nil {
panic(err)
}
ipc := ipv4.NewPacketConn(conn)
ipc.SetControlMessage(ipv4.FlagInterface, true)
to := &net.UDPAddr{
IP: net.IPv4(255, 255, 255, 255),
Port: 67,
}
eth0, err := net.InterfaceByName("eth0")
if err != nil {
panic(err)
}
if _, err := ipc.WriteTo(p, &ipv4.ControlMessage{IfIndex: eth0.Index}, to); err != nil {
panic(err)
}
newPacket := dhcp.NewPacket(dhcp.BootReply)
for {
_, cm, _, err := ipc.ReadFrom(newPacket)
if err != nil {
panic(err)
}
if cm != nil && cm.IfIndex == eth0.Index {
log.Infof("Received reply: %q", newPacket.YIAddr().String())
break
}
}
addr, err := netlink.ParseAddr(newPacket.YIAddr().String() + "/16")
if err != nil {
panic(err)
}
log.Infof("Setting interface eth0...")
if err := netlink.AddrAdd(link, addr); err != nil {
panic(err)
}
}