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net: make go DNS use localhost if resolv.conf is missing or empty

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Per resolv.conf man page, "If this file does not exist, only the name
server on the local machine will be queried."

This behavior also occurs if file is present but unreadable,
or if no nameservers are listed.

Fixes #10566

Change-Id: Id5716da0eae534d5ebfafea111bbc657f302e307
Reviewed-on: https://go-review.googlesource.com/9380
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
This commit is contained in:
Alex A Skinner 2015-04-25 20:50:21 -04:00 • committed by Brad Fitzpatrick
parent 7556948ebf
commit f390135733
8 changed files with 134 additions and 75 deletions
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27
src/net/dnsclient_unix.go
View file

@ -216,10 +216,10 @@ func convertRR_AAAA(records []dnsRR) []IP {
var cfg struct {
ch chan struct{}
mu sync.RWMutex // protects dnsConfig and dnserr
mu sync.RWMutex // protects dnsConfig
dnsConfig *dnsConfig
dnserr error
}
var onceLoadConfig sync.Once
// Assume dns config file is /etc/resolv.conf here
@ -230,12 +230,12 @@ func loadDefaultConfig() {
func loadConfig(resolvConfPath string, reloadTime time.Duration, quit <-chan chan struct{}) {
var mtime time.Time
cfg.ch = make(chan struct{}, 1)
if fi, err := os.Stat(resolvConfPath); err != nil {
cfg.dnserr = err
} else {
if fi, err := os.Stat(resolvConfPath); err == nil {
mtime = fi.ModTime()
cfg.dnsConfig, cfg.dnserr = dnsReadConfig(resolvConfPath)
}
cfg.dnsConfig = dnsReadConfig(resolvConfPath)
go func() {
for {
time.Sleep(reloadTime)
@ -258,14 +258,11 @@ func loadConfig(resolvConfPath string, reloadTime time.Duration, quit <-chan cha
}
mtime = m
// In case of error, we keep the previous config
ncfg, err := dnsReadConfig(resolvConfPath)
if err != nil || len(ncfg.servers) == 0 {
continue
if ncfg := dnsReadConfig(resolvConfPath); ncfg.err == nil {
cfg.mu.Lock()
cfg.dnsConfig = ncfg
cfg.mu.Unlock()
}
cfg.mu.Lock()
cfg.dnsConfig = ncfg
cfg.dnserr = nil
cfg.mu.Unlock()
}
}()
}
@ -284,10 +281,6 @@ func lookup(name string, qtype uint16) (cname string, rrs []dnsRR, err error) {
cfg.mu.RLock()
defer cfg.mu.RUnlock()
if cfg.dnserr != nil || cfg.dnsConfig == nil {
err = cfg.dnserr
return
}
// If name is rooted (trailing dot) or has enough dots,
// try it by itself first.
rooted := len(name) > 0 && name[len(name)-1] == '.'