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// Copyright 2022 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package net
import (
"syscall"
"time"
)
func dnsReadConfig(ignoredFilename string) (conf *dnsConfig) {
conf = &dnsConfig{
ndots: 1,
timeout: 5 * time.Second,
attempts: 2,
}
defer func() {
if len(conf.servers) == 0 {
conf.servers = defaultNS
}
}()
aas, err := adapterAddresses()
if err != nil {
return
}
// TODO(bradfitz): this just collects all the DNS servers on all
// the interfaces in some random order. It should order it by
// default route, or only use the default route(s) instead.
// In practice, however, it mostly works.
for _, aa := range aas {
for dns := aa.FirstDnsServerAddress; dns != nil; dns = dns.Next {
sa, err := dns.Address.Sockaddr.Sockaddr()
if err != nil {
continue
}
var ip IP
switch sa := sa.(type) {
case *syscall.SockaddrInet4:
ip = IPv4(sa.Addr[0], sa.Addr[1], sa.Addr[2], sa.Addr[3])
case *syscall.SockaddrInet6:
ip = make(IP, IPv6len)
copy(ip, sa.Addr[:])
if ip[0] == 0xfe && ip[1] == 0xc0 {
// Ignore these fec0/10 ones. Windows seems to
// populate them as defaults on its misc rando
// interfaces.
continue
}
default:
// Unexpected type.
continue
}
conf.servers = append(conf.servers, JoinHostPort(ip.String(), "53"))
}
}
return conf
}
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