| // 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 | |
| // | |
| // 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 | |
| } | |