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 []byte) (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 29 for _, aa := range aas {
30 // Only take interfaces whose OperStatus is IfOperStatusUp(0x01) into DNS configs.
31 if aa.OperStatus != windows.IfOperStatusUp {
32 continue
33 }
34 35 // Only take interfaces which have at least one gateway
36 if aa.FirstGatewayAddress == nil {
37 continue
38 }
39 40 for dns := aa.FirstDnsServerAddress; dns != nil; dns = dns.Next {
41 sa, err := dns.Address.Sockaddr.Sockaddr()
42 if err != nil {
43 continue
44 }
45 var ip IP
46 switch sa := sa.(type) {
47 case *syscall.SockaddrInet4:
48 ip = IPv4(sa.Addr[0], sa.Addr[1], sa.Addr[2], sa.Addr[3])
49 case *syscall.SockaddrInet6:
50 ip = make(IP, IPv6len)
51 copy(ip, sa.Addr[:])
52 if ip[0] == 0xfe && ip[1] == 0xc0 {
53 // fec0/10 IPv6 addresses are site local anycast DNS
54 // addresses Microsoft sets by default if no other
55 // IPv6 DNS address is set. Site local anycast is
56 // deprecated since 2004, see
57 // https://datatracker.ietf.org/doc/html/rfc3879
58 continue
59 }
60 default:
61 // Unexpected type.
62 continue
63 }
64 conf.servers = append(conf.servers, JoinHostPort(ip.String(), "53"))
65 }
66 }
67 return conf
68 }
69