126 lines
2.8 KiB
Go
126 lines
2.8 KiB
Go
/*
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* Copyright (C) 2020-2022, IrineSistiana
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*
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* This file is part of mosdns.
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*
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* mosdns is free software: you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation, either version 3 of the License, or
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* (at your option) any later version.
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*
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* mosdns is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program. If not, see <https://www.gnu.org/licenses/>.
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*/
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package dnsutils
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import (
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"errors"
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"fmt"
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"net/netip"
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"strconv"
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"strings"
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)
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var errNotPTRDomain = errors.New("domain does not has a ptr suffix")
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const (
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IP4arpa = ".in-addr.arpa."
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IP6arpa = ".ip6.arpa."
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)
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// ParsePTRQName returns the ip that a PTR query name contains.
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func ParsePTRQName(fqdn string) (netip.Addr, error) {
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switch {
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case strings.HasSuffix(fqdn, IP4arpa):
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return reverse4(fqdn[:len(fqdn)-len(IP4arpa)])
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case strings.HasSuffix(fqdn, IP6arpa):
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return reverse6(fqdn[:len(fqdn)-len(IP6arpa)])
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default:
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return netip.Addr{}, errNotPTRDomain
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}
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}
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func reverse4(s string) (netip.Addr, error) {
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var buf [4]byte
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l := 0
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for offset := len(s); offset > 0 && l < len(buf); l++ {
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var label string
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label, offset = prevLabel(s, offset)
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n, err := strconv.ParseUint(label, 10, 8)
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if err != nil {
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return netip.Addr{}, fmt.Errorf("invaild bit, %w", err)
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}
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buf[l] = byte(n)
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}
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if l < len(buf) {
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return netip.Addr{}, fmt.Errorf("expact at least 3 labels, got %d", l)
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}
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return netip.AddrFrom4(buf), nil
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}
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func reverse6(s string) (netip.Addr, error) {
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var buf [16]byte
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var val byte
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var tail bool
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var l int
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for offset := len(s); offset > 0 && l < len(buf); {
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var label string
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label, offset = prevLabel(s, offset)
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if len(label) != 1 {
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return netip.Addr{}, fmt.Errorf("invalid label %s", label)
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}
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b := label[0]
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n, ok := hex2byte(b)
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if !ok {
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return netip.Addr{}, fmt.Errorf("invaild bit %d", b)
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}
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if tail {
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buf[l] = val<<4 + n
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l++
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tail = false
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} else {
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val = n
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tail = true
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}
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}
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if l < len(buf) {
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return netip.Addr{}, fmt.Errorf("expact at least 16 bytes, got %d", l)
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}
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return netip.AddrFrom16(buf), nil
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}
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func hex2byte(c byte) (byte, bool) {
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lower := func(c byte) byte {
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return c | ('x' - 'X')
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}
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var b byte
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switch {
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case '0' <= c && c <= '9':
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b = c - '0'
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case 'a' <= lower(c) && lower(c) <= 'z':
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b = lower(c) - 'a' + 10
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default:
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return 0, false
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}
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return b, true
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}
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func prevLabel(s string, offset int) (string, int) {
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for {
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s = s[:offset]
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n := strings.LastIndexByte(s, '.')
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label := s[n+1 : offset]
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if n != -1 && len(label) == 0 {
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offset = n
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continue
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}
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return label, n
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}
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}
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