libgo/go/net/dnsclient.go

   1 // Copyright 2009 The Go Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style
   3 // license that can be found in the LICENSE file.
   4
   5 package net
   6
   7 import (
   8         "math/rand"
   9         "sort"
  10
  11         "golang.org/x/net/dns/dnsmessage"
  12 )
  13
  14 // reverseaddr returns the in-addr.arpa. or ip6.arpa. hostname of the IP
  15 // address addr suitable for rDNS (PTR) record lookup or an error if it fails
  16 // to parse the IP address.
  17 func reverseaddr(addr string) (arpa string, err error) {
  18         ip := ParseIP(addr)
  19         if ip == nil {
  20                 return "", &DNSError{Err: "unrecognized address", Name: addr}
  21         }
  22         if ip.To4() != nil {
  23                 return uitoa(uint(ip[15])) + "." + uitoa(uint(ip[14])) + "." + uitoa(uint(ip[13])) + "." + uitoa(uint(ip[12])) + ".in-addr.arpa.", nil
  24         }
  25         // Must be IPv6
  26         buf := make([]byte, 0, len(ip)*4+len("ip6.arpa."))
  27         // Add it, in reverse, to the buffer
  28         for i := len(ip) - 1; i >= 0; i-- {
  29                 v := ip[i]
  30                 buf = append(buf, hexDigit[v&0xF],
  31                         '.',
  32                         hexDigit[v>>4],
  33                         '.')
  34         }
  35         // Append "ip6.arpa." and return (buf already has the final .)
  36         buf = append(buf, "ip6.arpa."...)
  37         return string(buf), nil
  38 }
  39
  40 func equalASCIIName(x, y dnsmessage.Name) bool {
  41         if x.Length != y.Length {
  42                 return false
  43         }
  44         for i := 0; i < int(x.Length); i++ {
  45                 a := x.Data[i]
  46                 b := y.Data[i]
  47                 if 'A' <= a && a <= 'Z' {
  48                         a += 0x20
  49                 }
  50                 if 'A' <= b && b <= 'Z' {
  51                         b += 0x20
  52                 }
  53                 if a != b {
  54                         return false
  55                 }
  56         }
  57         return true
  58 }
  59
  60 // isDomainName checks if a string is a presentation-format domain name
  61 // (currently restricted to hostname-compatible "preferred name" LDH labels and
  62 // SRV-like "underscore labels"; see golang.org/issue/12421).
  63 func isDomainName(s string) bool {
  64         // See RFC 1035, RFC 3696.
  65         // Presentation format has dots before every label except the first, and the
  66         // terminal empty label is optional here because we assume fully-qualified
  67         // (absolute) input. We must therefore reserve space for the first and last
  68         // labels' length octets in wire format, where they are necessary and the
  69         // maximum total length is 255.
  70         // So our _effective_ maximum is 253, but 254 is not rejected if the last
  71         // character is a dot.
  72         l := len(s)
  73         if l == 0 || l > 254 || l == 254 && s[l-1] != '.' {
  74                 return false
  75         }
  76
  77         last := byte('.')
  78         nonNumeric := false // true once we've seen a letter or hyphen
  79         partlen := 0
  80         for i := 0; i < len(s); i++ {
  81                 c := s[i]
  82                 switch {
  83                 default:
  84                         return false
  85                 case 'a' <= c && c <= 'z' || 'A' <= c && c <= 'Z' || c == '_':
  86                         nonNumeric = true
  87                         partlen++
  88                 case '0' <= c && c <= '9':
  89                         // fine
  90                         partlen++
  91                 case c == '-':
  92                         // Byte before dash cannot be dot.
  93                         if last == '.' {
  94                                 return false
  95                         }
  96                         partlen++
  97                         nonNumeric = true
  98                 case c == '.':
  99                         // Byte before dot cannot be dot, dash.
 100                         if last == '.' || last == '-' {
 101                                 return false
 102                         }
 103                         if partlen > 63 || partlen == 0 {
 104                                 return false
 105                         }
 106                         partlen = 0
 107                 }
 108                 last = c
 109         }
 110         if last == '-' || partlen > 63 {
 111                 return false
 112         }
 113
 114         return nonNumeric
 115 }
 116
 117 // absDomainName returns an absolute domain name which ends with a
 118 // trailing dot to match pure Go reverse resolver and all other lookup
 119 // routines.
 120 // See golang.org/issue/12189.
 121 // But we don't want to add dots for local names from /etc/hosts.
 122 // It's hard to tell so we settle on the heuristic that names without dots
 123 // (like "localhost" or "myhost") do not get trailing dots, but any other
 124 // names do.
 125 func absDomainName(b []byte) string {
 126         hasDots := false
 127         for _, x := range b {
 128                 if x == '.' {
 129                         hasDots = true
 130                         break
 131                 }
 132         }
 133         if hasDots && b[len(b)-1] != '.' {
 134                 b = append(b, '.')
 135         }
 136         return string(b)
 137 }
 138
 139 // An SRV represents a single DNS SRV record.
 140 type SRV struct {
 141         Target   string
 142         Port     uint16
 143         Priority uint16
 144         Weight   uint16
 145 }
 146
 147 // byPriorityWeight sorts SRV records by ascending priority and weight.
 148 type byPriorityWeight []*SRV
 149
 150 func (s byPriorityWeight) Len() int { return len(s) }
 151 func (s byPriorityWeight) Less(i, j int) bool {
 152         return s[i].Priority < s[j].Priority || (s[i].Priority == s[j].Priority && s[i].Weight < s[j].Weight)
 153 }
 154 func (s byPriorityWeight) Swap(i, j int) { s[i], s[j] = s[j], s[i] }
 155
 156 // shuffleByWeight shuffles SRV records by weight using the algorithm
 157 // described in RFC 2782.
 158 func (addrs byPriorityWeight) shuffleByWeight() {
 159         sum := 0
 160         for _, addr := range addrs {
 161                 sum += int(addr.Weight)
 162         }
 163         for sum > 0 && len(addrs) > 1 {
 164                 s := 0
 165                 n := rand.Intn(sum)
 166                 for i := range addrs {
 167                         s += int(addrs[i].Weight)
 168                         if s > n {
 169                                 if i > 0 {
 170                                         addrs[0], addrs[i] = addrs[i], addrs[0]
 171                                 }
 172                                 break
 173                         }
 174                 }
 175                 sum -= int(addrs[0].Weight)
 176                 addrs = addrs[1:]
 177         }
 178 }
 179
 180 // sort reorders SRV records as specified in RFC 2782.
 181 func (addrs byPriorityWeight) sort() {
 182         sort.Sort(addrs)
 183         i := 0
 184         for j := 1; j < len(addrs); j++ {
 185                 if addrs[i].Priority != addrs[j].Priority {
 186                         addrs[i:j].shuffleByWeight()
 187                         i = j
 188                 }
 189         }
 190         addrs[i:].shuffleByWeight()
 191 }
 192
 193 // An MX represents a single DNS MX record.
 194 type MX struct {
 195         Host string
 196         Pref uint16
 197 }
 198
 199 // byPref implements sort.Interface to sort MX records by preference
 200 type byPref []*MX
 201
 202 func (s byPref) Len() int           { return len(s) }
 203 func (s byPref) Less(i, j int) bool { return s[i].Pref < s[j].Pref }
 204 func (s byPref) Swap(i, j int)      { s[i], s[j] = s[j], s[i] }
 205
 206 // sort reorders MX records as specified in RFC 5321.
 207 func (s byPref) sort() {
 208         for i := range s {
 209                 j := rand.Intn(i + 1)
 210                 s[i], s[j] = s[j], s[i]
 211         }
 212         sort.Sort(s)
 213 }
 214
 215 // An NS represents a single DNS NS record.
 216 type NS struct {
 217         Host string
 218 }