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  
    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
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