network_service_matcher/dhcp/dhcp.go

package dhcp

import (
	"bytes"
	"encoding/binary"
	"fmt"
	"net"
	"time"

	"git.loafle.net/commons_go/logging"
)

const (
	MAGIC_COOKIE               uint32 = 0x63825363
	OPT_CODE_SERVER_IDENTIFIER uint8  = 54
	OPT_CODE_SUBNET_MASK       uint8  = 1
	OPT_CODE_ROUTER            uint8  = 3
	OPT_CODE_DNS               uint8  = 6
)

type dhcpDiscover struct {
	MsgType             byte
	HwType              byte
	HwAddrLen           byte
	Hops                byte
	Xid                 uint32
	Secs                uint16
	BootpFlags          uint16
	ClientIp            uint32
	YourIp              uint32
	NextServerIp        uint32
	RelayAgentIp        uint32
	ClientMacAddr       [6]byte
	ClientHwAddrPadding [10]byte
	ServerHostName      [64]byte
	BootFileName        [128]byte
	MagicCookie         uint32
	Mtype               byte
	MtypeLen            byte
	MtypeVal            byte
	Opts                [200]byte
	End                 byte
	Padding             [16]byte
}

func DiscoverDHCP() {
	err := sendDHCPDiscovery()
	if err != nil {
		logging.Logger().Errorf("Discovery: DHCP Matcher %v", err)
		return
	}
	recvDHCPOffer()
}

func sendDHCPDiscovery() error {
	dhcp := dhcpDiscover{
		MsgType:      0x01,
		HwType:       0x01,
		HwAddrLen:    0x06,
		Hops:         0x00,
		Xid:          0x00000000,
		Secs:         0x0000,
		ClientIp:     0x00000000,
		YourIp:       0x00000000,
		NextServerIp: 0x00000000,
		RelayAgentIp: 0x00000000,
		MagicCookie:  MAGIC_COOKIE,
		Mtype:        0x35,
		MtypeLen:     0x01,
		MtypeVal:     0x01,
		End:          0xff,
	}

	var flag uint16 = 0
	dhcp.BootpFlags = ^flag // flag = unicast , ^flag = broadcast

	//TODO : getting mac addr from zone
	//dhcp.ClientMacAddr[0] = 0x50
	//dhcp.ClientMacAddr[1] = 0xe5
	//dhcp.ClientMacAddr[2] = 0x49
	//dhcp.ClientMacAddr[3] = 0x46
	//dhcp.ClientMacAddr[4] = 0x93
	//dhcp.ClientMacAddr[5] = 0x28

	writer := new(bytes.Buffer)
	binary.Write(writer, binary.BigEndian, dhcp)
	conn, err := net.Dial("udp", "255.255.255.255:67")
	if err != nil {
		return err
	}
	conn.Write(writer.Bytes())
	defer conn.Close()

	return nil
}

func recvDHCPOffer() {

	socket, err := net.ListenUDP("udp4", &net.UDPAddr{
		IP:   net.IPv4(255, 255, 255, 255),
		Port: 68,
	})
	if err != nil {
		logging.Logger().Errorf("Discovery: DHCP Matcher %v", err)
		return
	}
	err = socket.SetDeadline(time.Now().Add(3 * time.Second))
	if err != nil {
		logging.Logger().Errorf("Discovery: DHCP Matcher %v", err)
		return
	}

	buf := make([]byte, 4096)
	n, _, err := socket.ReadFromUDP(buf)
	if err != nil {
		logging.Logger().Errorf("Discovery: DHCP Matcher %v", err)
		return
	}
	if n <= 0 {
		logging.Logger().Errorf("Discovery: DHCP Matcher has no DHCP offer.")
		return
	}

	offer := dhcpDiscover{}

	reader := new(bytes.Buffer)
	reader.Write(buf)
	if err := binary.Read(reader, binary.BigEndian, &offer); err != nil {
		logging.Logger().Errorf("Discovery: DHCP Matcher %v", err)
		return
	}
	if offer.MagicCookie != MAGIC_COOKIE {
		logging.Logger().Errorf("Discovery: DHCP Matcher is not a DHCP packet.")
		return
	}

	//option searching
	r := new(bytes.Buffer)
	r.Write(offer.Opts[:])

	for i := 0; i < r.Len(); i++ {
		v := r.Next(1)[0]

		if v == OPT_CODE_SUBNET_MASK && r.Next(1)[0] == 4 {
			ipStr := byteToIpString(r.Next(4))
			logging.Logger().Infof("Discovery: DHCP Matcher SUBNET MASK: %s", ipStr)
		}

		if v == OPT_CODE_ROUTER && r.Next(1)[0] == 4 {
			ipStr := byteToIpString(r.Next(4))
			logging.Logger().Infof("Discovery: DHCP Matcher ROUTER: %s", ipStr)
		}

		if v == OPT_CODE_DNS {
			len := r.Next(1)[0]
			var dns []string = make([]string, 0)
			var ipStr string
			ipStr = byteToIpString(r.Next(4))
			dns = append(dns, ipStr)
			if len == 8 {
				ipStr = byteToIpString(r.Next(4))
				dns = append(dns, ipStr)
			}
			logging.Logger().Infof("Discovery: DHCP Matcher DNS: %s", dns)
		}

		if v == OPT_CODE_SERVER_IDENTIFIER && r.Next(1)[0] == 4 {
			ipStr := byteToIpString(r.Next(4))
			logging.Logger().Infof("Discovery: DHCP Matcher DHCP SERVER: %s", ipStr)
		}
	}
	logging.Logger().Sync()

}

func byteToIpString(b []byte) string {
	var ipStr string
	len := len(b)
	for i := 0; i < len; i++ {
		v := b[i]
		ipStr += fmt.Sprintf("%d", v)
		if i < len-1 {
			ipStr += "."
		}
	}

	return ipStr
}