dhcp4

package main

import (
	"log"
	"net"
	"syscall"
	"time"

	"github.com/google/gopacket/layers"
	"github.com/mdlayher/raw"
	"github.com/rtr7/dhcp4"
)

func main() {
	iface, err := net.InterfaceByName("uplink0")
	if err != nil {
		log.Fatal(err)
	}
	xidGen := dhcp4.XIDGenerator(iface.HardwareAddr)
	conn, err := raw.ListenPacket(iface, syscall.ETH_P_IP, &raw.Config{LinuxSockDGRAM: true})
	if err != nil {
		log.Fatal(err)
	}
	discover := &layers.DHCPv4{
		Operation:    layers.DHCPOpRequest,
		HardwareType: layers.LinkTypeEthernet,
		HardwareLen:  uint8(len(layers.EthernetBroadcast)),
		Xid:          xidGen(),
		ClientHWAddr: iface.HardwareAddr,
		Options: []layers.DHCPOption{
			dhcp4.MessageTypeOpt(layers.DHCPMsgTypeDiscover),
			dhcp4.HostnameOpt("dhcpprobe"),
			dhcp4.ClientIDOpt(layers.LinkTypeEthernet, iface.HardwareAddr),
		},
	}
	if err := dhcp4.Write(conn, discover); err != nil {
		log.Fatal(err)
	}

	// Display all DHCPOFFER packets received within 5s:
	conn.SetDeadline(time.Now().Add(5 * time.Second))
	for {
		offer, err := dhcp4.Read(conn)
		if err != nil {
			log.Fatal(err)
		}
		if offer == nil {
			continue // not a DHCPv4 packet
		}
		if offer.Xid != discover.Xid {
			continue // broadcast reply for different DHCP transaction
		}
		if !dhcp4.HasMessageType(offer.Options, layers.DHCPMsgTypeOffer) {
			continue
		}
		log.Printf("DHCPOFFER: %+v", offer)
	}
}