decode rfc1035 header

rfc1035header.go

type Header struct {
  raw [6*2]byte
  Opcode, Rcode, Z byte
  ID, QD, NS, AN, AR []byte // 2 bytes each
  QR, AA, TC, RD, RA bool
}

func decodeHeader(r io.Reader) *Header, os.Error {
  h := &Header{}
  n, err := r.Read(h.raw[:])
  if n != len(h.raw) || err != nil {
    if err == nil {
      err = os.NewError("too few bytes for header")
    }
    return nil, err
  }
  h.ID = h.raw[:2]
  h.QD = h.raw[4:6]
  h.AN = h.raw[6:8]
  h.NS = h.raw[8:10]
  h.AR = h.raw[10:12]
  h.Opcode = (h.raw[2]>>3) & 0xF
  h.Rcode = h.raw[3] & 0xF
  h.Z = (h.raw[3]>>4) & 0x7
  h.QR = h.raw[2] & (1<<7) != 0
  h.AA = h.raw[2] & (1<<2) != 0
  h.TC = h.raw[2] & (1<<1) != 0
  h.RD = h.raw[2] & (1<<0) != 0
  h.RA = h.raw[3] & (1<<7) != 0
  return h, nil
}