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package dns
import (
"strings"
)
type packer struct {
buf []byte
names map[string]int
}
func newPacker() *packer {
return &packer{
names: make(map[string]int),
}
}
func (p *packer) writeUint16(v uint16) {
p.buf = append(p.buf, byte(v>>8), byte(v))
}
func (p *packer) writeUint32(v uint32) {
p.buf = append(p.buf, byte(v>>24), byte(v>>16), byte(v>>8), byte(v))
}
func (p *packer) writeName(n Name) error {
labels := SplitDomainName(n.String())
for i := 0; i < len(labels); i++ {
suffix := Fqdn(joinLabels(labels[i:]))
if off, ok := p.names[suffix]; ok {
for _, label := range labels[:i] {
p.buf = append(p.buf, byte(len(label)))
p.buf = append(p.buf, label...)
}
p.writeUint16(uint16(off) | 0xC000)
return nil
}
}
off := len(p.buf)
p.buf = append(p.buf, n.Data...)
for i := 0; i < len(labels); i++ {
suffix := Fqdn(joinLabels(labels[i:]))
suffixOff := off
for j := 0; j < i; j++ {
suffixOff += 1 + len(labels[j])
}
if _, exists := p.names[suffix]; !exists {
p.names[suffix] = suffixOff
}
}
return nil
}
func joinLabels(labels []string) string {
if len(labels) == 0 {
return "."
}
return strings.Join(labels, ".") + "."
}
func Pack(m *Msg) ([]byte, error) {
p := newPacker()
headerOff := len(p.buf)
p.buf = append(p.buf, make([]byte, 12)...)
for _, q := range m.Question {
if err := q.pack(p); err != nil {
return nil, err
}
}
for _, rr := range m.Answer {
if err := rr.pack(p); err != nil {
return nil, err
}
}
for _, rr := range m.Ns {
if err := rr.pack(p); err != nil {
return nil, err
}
}
for _, rr := range m.Extra {
if err := rr.pack(p); err != nil {
return nil, err
}
}
putUint16(p.buf[headerOff:], m.Header.ID)
putUint16(p.buf[headerOff+2:], m.Header.Flags)
putUint16(p.buf[headerOff+4:], uint16(len(m.Question)))
putUint16(p.buf[headerOff+6:], uint16(len(m.Answer)))
putUint16(p.buf[headerOff+8:], uint16(len(m.Ns)))
putUint16(p.buf[headerOff+10:], uint16(len(m.Extra)))
return p.buf, nil
}
func putUint16(b []byte, v uint16) {
b[0] = byte(v >> 8)
b[1] = byte(v)
}
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