haza/pkt.go

package haza

import "errors"
import "fmt"
import "io"
import "net"

type Dhcp4Op = uint8
type Dhcp4Htype = uint8

const (
	_ Dhcp4Op = iota
	DHCP4_OP_BOOTREQUEST = 1
	DHCP4_OP_BOOTREPLY = 2
)

const (
	_ Dhcp4Htype = iota
	DHCP4_HTYPE_ETHER = 1
	DHCP4_HTYPE_IEEE802 = 6
	DHCP4_HTYPE_ARCNET = 7
	DHCP4_HTYPE_APPLETALK = 8
	DHCP4_HTYPE_HDLC = 17
	DHCP4_HTYPE_ATM = 19
	DHCP4_HTYPE_ARPSEC = 30
	DHCP4_HTYPE_IPSEC = 31
	DHCP4_HTYPE_INFINIBAND = 32
	DHCP4_HTYPE_PUREIP = 35
)

type Dhcp4Pkt struct {
	Op    Dhcp4Op
	Htype Dhcp4Htype
	Hlen uint8 // length of Chaddr

	Hops uint8
	Xid uint32
	Secs uint16
	Flags uint16

	Ciaddr net.IP // uint32
	Yiaddr net.IP // uint32
	Siaddr net.IP // uint32
	Gwaddr net.IP // uint32
	Chaddr [16]byte

	Sname  [64]byte // server host name
	File   [128]byte // boot file name

	// options are placed after the header.
	// the first four bytes of the options compose a magic cookie
	// 0x63 0x82 0x53 0x63

	Options map[Dhcp4OptCode][]byte

	// internal fields
	msg_type Dhcp4MsgType
}

var dhcp4_magic_cookie [4]byte = [4]byte{ 0x63, 0x82, 0x53, 0x63 }

func NewDhcp4Pkt(msg_type Dhcp4MsgType) *Dhcp4Pkt {
	var pkt *Dhcp4Pkt
	var opt Dhcp4Opt

	pkt = &Dhcp4Pkt{
		Op:  DHCP4_OP_BOOTREQUEST, // TODO: choose between request and reply based on the msg type..
		Htype: DHCP4_HTYPE_ETHER,
		Hlen: 6,
		Xid: 0, // TODO: generate it?

		Ciaddr: net.IPv4zero,
		Yiaddr: net.IPv4zero,
		Siaddr: net.IPv4zero,
		Gwaddr: net.IPv4zero,

		//Chaddr:
		//Sname:
		//File:


		// fill the internal fields
		msg_type: msg_type,
	}

	// add the message type option
	opt = Dhcp4OptMsgType(msg_type)
	pkt.Options[opt.Code()] = opt.Bytes()

	return pkt
}

func (pkt *Dhcp4Pkt) AddOption(opt Dhcp4Opt) {
	pkt.Options[opt.Code()] = opt.Bytes();
}

func (pkt *Dhcp4Pkt) Decode(b []byte) error {
	// fill the packet with data from the bytes
	var nbr *NetByteReader
	var u8 byte
	var p Dhcp4Pkt
	var cookie [4]byte
	var ov []byte
	var ok bool
	var err error

	nbr = NewNetByteReader(b)

	u8, err = nbr.ReadByte()
	if err != nil { return err }
	p.Op = Dhcp4Op(u8)

	u8, err = nbr.ReadByte()
	if err != nil { return err }
	p.Htype = Dhcp4Htype(u8)

	p.Hlen, err = nbr.ReadByte()
	if err != nil { return err }
	if p.Hlen > 16 { return fmt.Errorf("invalid hlen %d", p.Hlen) }

	p.Hops, err = nbr.ReadByte()
	if err != nil { return err }

	p.Xid, err = nbr.ReadUint32()
	if err != nil { return err }

	p.Secs, err = nbr.ReadUint16()
	if err != nil { return err }

	p.Flags, err = nbr.ReadUint16()
	if err != nil { return err }

	p.Ciaddr, err = nbr.ReadIp4()
	if err != nil { return err }

	p.Yiaddr, err = nbr.ReadIp4()
	if err != nil { return err }

	p.Siaddr, err = nbr.ReadIp4()
	if err != nil { return err }

	p.Gwaddr, err = nbr.ReadIp4()
	if err != nil { return err }

	err = nbr.ReadBytesFull(p.Chaddr[:])
	if err != nil { return err }

	err = nbr.ReadBytesFull(p.Sname[:])
	if err != nil { return err }

	err = nbr.ReadBytesFull(p.File[:])
	if err != nil { return err }

	err = nbr.ReadBytesFull(cookie[:])
	if err != nil {
		if errors.Is(err, io.EOF) {
			// TODO: no options
		}
		return err
	}
	if cookie != dhcp4_magic_cookie {
		return fmt.Errorf("invalid magic cookie %v", cookie)
	}

	// load options
	p.Options = make(map[Dhcp4OptCode][]byte)
	for {
		var oc uint8
		var ol uint8
		var optval [255]byte

		oc, err = nbr.ReadByte() // option code
		if err != nil {
			if errors.Is(err, io.EOF) { break }
			return err
		}

		if oc == DHCP4_OPT_PADDING { continue }
		if oc == DHCP4_OPT_END { break }

		ol, err = nbr.ReadByte() // option length
		if err != nil { return err }

		err = nbr.ReadBytesAtLeast(optval[:], int(ol))
		if err != nil { return err }

		// RFC 3396 mandates that when multiple occurrences of a concatenation-requiring
		// option appear in a DHCPv4 packet, their data MUST be concatenated prior to
		// processing. For non-concatenation-requiring (e.g. fixed-length) options, concatenation
		// is not defined. but let's not make an exception and let the processor check
		// validity.
		p.Options[oc] = append(p.Options[oc], optval[:ol]...)
	}

	//for oc, ov = range p.Optons {
	//	ot = oc_to_type(oc)
	//	switch (ot) {
	//		case OT_UINT8:
	//		case OT_UINT16:
	//		case OT_UINT18:
	//		case OT_UINT32:
	//		case OT_IP4ADDR:
	//		case OT_IP46DDR:
	//		case OT_STRING:
	//		default:
	//			leave it as is
	//	}
	//
	//}

	ov, ok = p.Options[DHCP4_OPT_MSG_TYPE]
	if !ok { return fmt.Errorf("no message type") }
	if len(ov) != 1 { return fmt.Errorf("invalid message type option") }
	p.msg_type = ov[0]

	*pkt = p
	return nil
}

func (pkt *Dhcp4Pkt) Encode() []byte {
	return nil
}

func (pkt *Dhcp4Pkt) MsgType() Dhcp4MsgType {
	return pkt.msg_type
}