// 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 ( "os" "sync/atomic" "time" ) var ( defaultNS = []string{"127.0.0.1:53", "[::1]:53"} getHostname = os.Hostname // variable for testing ) type dnsConfig struct { servers []string // server addresses (in host:port form) to use search []string // rooted suffixes to append to local name ndots int // number of dots in name to trigger absolute lookup timeout time.Duration // wait before giving up on a query, including retries attempts int // lost packets before giving up on server rotate bool // round robin among servers unknownOpt bool // anything unknown was encountered lookup []string // OpenBSD top-level database "lookup" order err error // any error that occurs during open of resolv.conf mtime time.Time // time of resolv.conf modification soffset uint32 // used by serverOffset singleRequest bool // use sequential A and AAAA queries instead of parallel queries useTCP bool // force usage of TCP for DNS resolutions } // serverOffset returns an offset that can be used to determine // indices of servers in c.servers when making queries. // When the rotate option is enabled, this offset increases. // Otherwise it is always 0. func (c *dnsConfig) serverOffset() uint32 { if c.rotate { return atomic.AddUint32(&c.soffset, 1) - 1 // return 0 to start } return 0 }