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 "os" 9 "sync/atomic" 10 "time" 11 ) 12 13 var ( 14 defaultNS = []string{"127.0.0.1:53", "[::1]:53"} 15 getHostname = os.Hostname // variable for testing 16 ) 17 18 type dnsConfig struct { 19 servers []string // server addresses (in host:port form) to use 20 search []string // rooted suffixes to append to local name 21 ndots int // number of dots in name to trigger absolute lookup 22 timeout time.Duration // wait before giving up on a query, including retries 23 attempts int // lost packets before giving up on server 24 rotate bool // round robin among servers 25 unknownOpt bool // anything unknown was encountered 26 lookup []string // OpenBSD top-level database "lookup" order 27 err error // any error that occurs during open of resolv.conf 28 mtime time.Time // time of resolv.conf modification 29 soffset uint32 // used by serverOffset 30 singleRequest bool // use sequential A and AAAA queries instead of parallel queries 31 useTCP bool // force usage of TCP for DNS resolutions 32 trustAD bool // add AD flag to queries 33 noReload bool // do not check for config file updates 34 } 35 36 // serverOffset returns an offset that can be used to determine 37 // indices of servers in c.servers when making queries. 38 // When the rotate option is enabled, this offset increases. 39 // Otherwise it is always 0. 40 func (c *dnsConfig) serverOffset() uint32 { 41 if c.rotate { 42 return atomic.AddUint32(&c.soffset, 1) - 1 // return 0 to start 43 } 44 return 0 45 } 46