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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 (
"os"
"sync/atomic"
"time"
_ "unsafe"
)
// defaultNS is the default name servers to use in the absence of DNS configuration.
//
// defaultNS should be an internal detail,
// but widely used packages access it using linkname.
// Notable members of the hall of shame include:
// - github.com/pojntfx/hydrapp/hydrapp
// - github.com/mtibben/androiddnsfix
// - github.com/metacubex/mihomo
//
// Do not remove or change the type signature.
// See go.dev/issue/67401.
//
//go:linkname defaultNS
var defaultNS = []string{"127.0.0.1:53", "[::1]:53"}
var 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
trustAD bool // add AD flag to queries
noReload bool // do not check for config file updates
}
// 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
}
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