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package rfc1035label
import (
"errors"
"strings"
)
// This implements RFC 1035 labels, including compression.
// https://tools.ietf.org/html/rfc1035#section-4.1.4
// LabelsFromBytes decodes a serialized stream and returns a list of labels
func LabelsFromBytes(buf []byte) ([]string, error) {
var (
pos, oldPos int
labels = make([]string, 0)
label string
handlingPointer bool
)
for {
if pos >= len(buf) {
break
}
length := int(buf[pos])
pos++
var chunk string
if length == 0 {
labels = append(labels, label)
label = ""
if handlingPointer {
pos = oldPos
handlingPointer = false
}
} else if length&0xc0 == 0xc0 {
// compression pointer
if handlingPointer {
return nil, errors.New("rfc1035label: cannot handle nested pointers")
}
handlingPointer = true
if pos+1 > len(buf) {
return nil, errors.New("rfc1035label: pointer buffer too short")
}
off := int(buf[pos-1]&^0xc0)<<8 + int(buf[pos])
oldPos = pos + 1
pos = off
} else {
if pos+length > len(buf) {
return nil, errors.New("rfc1035label: buffer too short")
}
chunk = string(buf[pos : pos+length])
if label != "" {
label += "."
}
label += chunk
pos += length
}
}
return labels, nil
}
// LabelToBytes encodes a label and returns a serialized stream of bytes
func LabelToBytes(label string) []byte {
var encodedLabel []byte
if len(label) == 0 {
return []byte{0}
}
for _, part := range strings.Split(label, ".") {
encodedLabel = append(encodedLabel, byte(len(part)))
encodedLabel = append(encodedLabel, []byte(part)...)
}
return append(encodedLabel, 0)
}
// LabelsToBytes encodes a list of labels and returns a serialized stream of
// bytes
func LabelsToBytes(labels []string) []byte {
var encodedLabels []byte
for _, label := range labels {
encodedLabels = append(encodedLabels, LabelToBytes(label)...)
}
return encodedLabels
}
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