libgo/go/net/dnsconfig.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 // +build darwin freebsd linux netbsd openbsd
   6
   7 // Read system DNS config from /etc/resolv.conf
   8
   9 package net
  10
  11 type dnsConfig struct {
  12         servers  []string // servers to use
  13         search   []string // suffixes to append to local name
  14         ndots    int      // number of dots in name to trigger absolute lookup
  15         timeout  int      // seconds before giving up on packet
  16         attempts int      // lost packets before giving up on server
  17         rotate   bool     // round robin among servers
  18 }
  19
  20 // See resolv.conf(5) on a Linux machine.
  21 // TODO(rsc): Supposed to call uname() and chop the beginning
  22 // of the host name to get the default search domain.
  23 // We assume it's in resolv.conf anyway.
  24 func dnsReadConfig() (*dnsConfig, error) {
  25         file, err := open("/etc/resolv.conf")
  26         if err != nil {
  27                 return nil, &DNSConfigError{err}
  28         }
  29         conf := new(dnsConfig)
  30         conf.servers = make([]string, 3)[0:0] // small, but the standard limit
  31         conf.search = make([]string, 0)
  32         conf.ndots = 1
  33         conf.timeout = 5
  34         conf.attempts = 2
  35         conf.rotate = false
  36         for line, ok := file.readLine(); ok; line, ok = file.readLine() {
  37                 f := getFields(line)
  38                 if len(f) < 1 {
  39                         continue
  40                 }
  41                 switch f[0] {
  42                 case "nameserver": // add one name server
  43                         a := conf.servers
  44                         n := len(a)
  45                         if len(f) > 1 && n < cap(a) {
  46                                 // One more check: make sure server name is
  47                                 // just an IP address.  Otherwise we need DNS
  48                                 // to look it up.
  49                                 name := f[1]
  50                                 switch len(ParseIP(name)) {
  51                                 case 16:
  52                                         name = "[" + name + "]"
  53                                         fallthrough
  54                                 case 4:
  55                                         a = a[0 : n+1]
  56                                         a[n] = name
  57                                         conf.servers = a
  58                                 }
  59                         }
  60
  61                 case "domain": // set search path to just this domain
  62                         if len(f) > 1 {
  63                                 conf.search = make([]string, 1)
  64                                 conf.search[0] = f[1]
  65                         } else {
  66                                 conf.search = make([]string, 0)
  67                         }
  68
  69                 case "search": // set search path to given servers
  70                         conf.search = make([]string, len(f)-1)
  71                         for i := 0; i < len(conf.search); i++ {
  72                                 conf.search[i] = f[i+1]
  73                         }
  74
  75                 case "options": // magic options
  76                         for i := 1; i < len(f); i++ {
  77                                 s := f[i]
  78                                 switch {
  79                                 case len(s) >= 6 && s[0:6] == "ndots:":
  80                                         n, _, _ := dtoi(s, 6)
  81                                         if n < 1 {
  82                                                 n = 1
  83                                         }
  84                                         conf.ndots = n
  85                                 case len(s) >= 8 && s[0:8] == "timeout:":
  86                                         n, _, _ := dtoi(s, 8)
  87                                         if n < 1 {
  88                                                 n = 1
  89                                         }
  90                                         conf.timeout = n
  91                                 case len(s) >= 8 && s[0:9] == "attempts:":
  92                                         n, _, _ := dtoi(s, 9)
  93                                         if n < 1 {
  94                                                 n = 1
  95                                         }
  96                                         conf.attempts = n
  97                                 case s == "rotate":
  98                                         conf.rotate = true
  99                                 }
 100                         }
 101                 }
 102         }
 103         file.close()
 104
 105         return conf, nil
 106 }