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soypat
136 lines
3.4 KiB
Go
136 lines
3.4 KiB
Go
package dhcp
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import (
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"encoding/binary"
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"errors"
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)
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const (
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sizeSName = 64 // Server name, part of BOOTP too.
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sizeBootFile = 128 // Boot file name, Legacy.
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sizeHeader = 44
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// Magic Cookie offset measured from the start of the UDP payload.
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magicCookieOffset = sizeHeader + sizeSName + sizeBootFile
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// Expected Magic Cookie value.
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MagicCookie uint32 = 0x63825363
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// DHCP Options offset measured from the start of the UDP payload.
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optionsOffset = magicCookieOffset + 4
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DefaultClientPort = 68
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DefaultServerPort = 67
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)
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func NewFrameV4(buf []byte) (FrameV4, error) {
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if len(buf) < sizeHeader {
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return FrameV4{}, errors.New("DHCP short frame")
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}
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return FrameV4{buf: buf}, nil
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}
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// Frame encapsulates the raw data of a DHCP packet
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// and provides methods for manipulating, validating and
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// retrieving fields and payload data. See [RFC2131].
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//
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// [RFC2131]: https://tools.ietf.org/html/rfc2131
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type FrameV4 struct {
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buf []byte
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}
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func (frm FrameV4) Op() Op {
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return Op(frm.buf[0])
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}
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func (frm FrameV4) Hardware() (Type, Len, Ops uint8) {
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return frm.buf[1], frm.buf[2], frm.buf[3]
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}
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func (frm FrameV4) SetHardware(Type, Len, Ops uint8) {
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frm.buf[1], frm.buf[2], frm.buf[3] = Type, Len, Ops
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}
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func (frm FrameV4) XID() uint32 {
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return binary.BigEndian.Uint32(frm.buf[4:8])
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}
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func (frm FrameV4) Secs() uint16 {
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return binary.BigEndian.Uint16(frm.buf[8:10])
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}
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func (frm FrameV4) Flags() uint16 {
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return binary.BigEndian.Uint16(frm.buf[10:12])
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}
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// CIAddr is the client IP address. If the client has not obtained an IP
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// address yet, this field is set to 0.
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func (frm FrameV4) CIAddr() *[4]byte {
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return (*[4]byte)(frm.buf[12:16])
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}
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// YIAddr is the IP address offered by the server to the client.
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func (frm FrameV4) YIAddr() *[4]byte {
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return (*[4]byte)(frm.buf[16:20])
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}
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// SIAddr is the IP address of the next server to use in bootstrap. This
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// field is used in DHCPOFFER and DHCPACK messages.
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func (frm FrameV4) SIAddr() *[4]byte {
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return (*[4]byte)(frm.buf[20:24])
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}
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// GIAddr is the gateway IP address.
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func (frm FrameV4) GIAddr() *[4]byte {
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return (*[4]byte)(frm.buf[24:28])
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}
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// CHAddrAs6 returns [FrameV4.CHAddr] but limited to first 6 bytes.
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func (frm FrameV4) CHAddrAs6() *[6]byte {
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return (*[6]byte)(frm.buf[28 : 28+6])
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}
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// CHAddr is the client hardware address. Can be up to 16 bytes in length but
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// is usually 6 bytes for Ethernet.
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func (frm FrameV4) CHAddr() *[16]byte {
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return (*[16]byte)(frm.buf[28:44])
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}
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func (frm FrameV4) MagicCookie() uint32 {
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return binary.BigEndian.Uint32(frm.buf[magicCookieOffset:])
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}
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// ClearHeader zeros out the header contents.
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func (frm FrameV4) ClearHeader() {
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for i := range frm.buf[:sizeHeader] {
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frm.buf[i] = 0
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}
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}
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func (frm FrameV4) ForEachOption(fn func(opt Option) error) error {
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if fn == nil {
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return errors.New("nil function to parse DHCP")
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}
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// Parse DHCP options.
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ptr := optionsOffset
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if ptr >= len(frm.buf) {
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return errors.New("short payload to parse DHCP options")
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}
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for ptr+1 < len(frm.buf) {
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if int(frm.buf[ptr+1]) >= len(frm.buf) {
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return errors.New("DHCP option length exceeds payload")
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}
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optnum := OptNum(frm.buf[ptr])
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if optnum == 0xff {
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break
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} else if optnum == OptWordAligned {
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ptr++
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continue
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}
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optlen := frm.buf[ptr+1]
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optionData := frm.buf[ptr+2 : ptr+2+int(optlen)]
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if err := fn(Option{optnum, optionData}); err != nil {
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return err
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}
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ptr += int(optlen) + 2
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}
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return nil
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}
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