src/net/dnsconfig_windows.go

   1 // Copyright 2022 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         "internal/syscall/windows"
   9         "syscall"
  10         "time"
  11 )
  12
  13 func dnsReadConfig(ignoredFilename string) (conf *dnsConfig) {
  14         conf = &dnsConfig{
  15                 ndots:    1,
  16                 timeout:  5 * time.Second,
  17                 attempts: 2,
  18         }
  19         defer func() {
  20                 if len(conf.servers) == 0 {
  21                         conf.servers = defaultNS
  22                 }
  23         }()
  24         aas, err := adapterAddresses()
  25         if err != nil {
  26                 return
  27         }
  28         // TODO(bradfitz): this just collects all the DNS servers on all
  29         // the interfaces in some random order. It should order it by
  30         // default route, or only use the default route(s) instead.
  31         // In practice, however, it mostly works.
  32         for _, aa := range aas {
  33                 for dns := aa.FirstDnsServerAddress; dns != nil; dns = dns.Next {
  34                         // Only take interfaces whose OperStatus is IfOperStatusUp(0x01) into DNS configs.
  35                         if aa.OperStatus != windows.IfOperStatusUp {
  36                                 continue
  37                         }
  38                         sa, err := dns.Address.Sockaddr.Sockaddr()
  39                         if err != nil {
  40                                 continue
  41                         }
  42                         var ip IP
  43                         switch sa := sa.(type) {
  44                         case *syscall.SockaddrInet4:
  45                                 ip = IPv4(sa.Addr[0], sa.Addr[1], sa.Addr[2], sa.Addr[3])
  46                         case *syscall.SockaddrInet6:
  47                                 ip = make(IP, IPv6len)
  48                                 copy(ip, sa.Addr[:])
  49                                 if ip[0] == 0xfe && ip[1] == 0xc0 {
  50                                         // Ignore these fec0/10 ones. Windows seems to
  51                                         // populate them as defaults on its misc rando
  52                                         // interfaces.
  53                                         continue
  54                                 }
  55                         default:
  56                                 // Unexpected type.
  57                                 continue
  58                         }
  59                         conf.servers = append(conf.servers, JoinHostPort(ip.String(), "53"))
  60                 }
  61         }
  62         return conf
  63 }