func (p *Packet) Unpack(buf *packet.Buffer) error {
buf.ReadN(&p.SrcPort)
buf.ReadN(&p.DstPort)
buf.ReadN(&p.Seq)
buf.ReadN(&p.Ack)
var offns uint8
buf.ReadN(&offns)
p.DataOff = offns >> 4
if offns&0x01 != 0 {
p.Flags |= NS
}
var flags uint8
buf.ReadN(&flags)
if flags&0x01 != 0 {
p.Flags |= Fin
}
if flags&0x02 != 0 {
p.Flags |= Syn
}
if flags&0x04 != 0 {
p.Flags |= Rst
}
if flags&0x08 != 0 {
p.Flags |= PSH
}
if flags&0x10 != 0 {
p.Flags |= Ack
}
if flags&0x20 != 0 {
p.Flags |= Urg
}
if flags&0x40 != 0 {
p.Flags |= ECE
}
if flags&0x80 != 0 {
p.Flags |= Cwr
}
buf.ReadN(&p.WindowSize)
buf.ReadN(&p.Checksum)
buf.ReadN(&p.Urgent)
options:
for buf.LayerLen() < int(p.DataOff)*4 {
var opt_type OptType
buf.ReadN(&opt_type)
switch opt_type {
case End: /* end of options */
break options
case Nop: /* padding */
continue
default:
opt := Option{Type: opt_type}
buf.ReadN(&opt.Len)
opt.Data = buf.Next(int(opt.Len) - 2)
p.Options = append(p.Options, opt)
}
}
/* remove padding */
if buf.LayerLen() < int(p.DataOff)*4 {
buf.Next(int(p.DataOff)*4 - buf.LayerLen())
}
return nil
}
func (p *Packet) Pack(buf *packet.Buffer) error {
buf.WriteN(p.SrcPort)
buf.WriteN(p.DstPort)
buf.WriteN(p.Seq)
buf.WriteN(p.Ack)
flags := uint16(p.DataOff) << 12
if p.Flags&Fin != 0 {
flags |= 0x0001
}
if p.Flags&Syn != 0 {
flags |= 0x0002
}
if p.Flags&Rst != 0 {
flags |= 0x0004
}
if p.Flags&PSH != 0 {
flags |= 0x0008
}
if p.Flags&Ack != 0 {
flags |= 0x0010
}
if p.Flags&Urg != 0 {
flags |= 0x0020
}
if p.Flags&ECE != 0 {
flags |= 0x0040
}
if p.Flags&Cwr != 0 {
flags |= 0x0080
}
if p.Flags&NS != 0 {
flags |= 0x0100
}
buf.WriteN(flags)
buf.WriteN(p.WindowSize)
buf.WriteN(uint16(0x0000))
buf.WriteN(p.Urgent)
for _, opt := range p.Options {
buf.WriteN(opt.Type)
buf.WriteN(opt.Len)
buf.WriteN(opt.Data)
}
if p.csum_seed != 0 {
p.Checksum =
ipv4.CalculateChecksum(buf.LayerBytes(), p.csum_seed)
}
buf.PutUint16N(16, p.Checksum)
/* add padding */
for buf.LayerLen() < int(p.DataOff)*4 {
buf.WriteN(uint8(0x00))
}
return nil
}