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

Browse source 
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
Download patch file Download diff file Expand all files Collapse all files

41
src/net/dnsclient_unix_test.go
View file

@ -171,23 +171,26 @@ func TestReloadResolvConfFail(t *testing.T) {
r := newResolvConfTest(t)
defer r.Close()
// resolv.conf.tmp does not exist yet
r.Start()
if _, err := goLookupIP("golang.org"); err == nil {
t.Fatal("goLookupIP(missing) succeeded")
}
r.SetConf("nameserver 8.8.8.8")
if _, err := goLookupIP("golang.org"); err != nil {
t.Fatalf("goLookupIP(missing; good) failed: %v", err)
}
// Using a bad resolv.conf while we had a good
// one before should not update the config
// Using an empty resolv.conf should use localhost as servers
r.SetConf("")
if _, err := goLookupIP("golang.org"); err != nil {
t.Fatalf("goLookupIP(missing; good; bad) failed: %v", err)
if len(cfg.dnsConfig.servers) != len(defaultNS) {
t.Fatalf("goLookupIP(missing; good; bad) failed: servers=%v, want: %v", cfg.dnsConfig.servers, defaultNS)
}
for i := range cfg.dnsConfig.servers {
if cfg.dnsConfig.servers[i] != defaultNS[i] {
t.Fatalf("goLookupIP(missing; good; bad) failed: servers=%v, want: %v", cfg.dnsConfig.servers, defaultNS)
}
}
}
func TestReloadResolvConfChange(t *testing.T) {
@ -198,19 +201,25 @@ func TestReloadResolvConfChange(t *testing.T) {
r := newResolvConfTest(t)
defer r.Close()
r.SetConf("nameserver 8.8.8.8")
r.Start()
r.SetConf("nameserver 8.8.8.8")
if _, err := goLookupIP("golang.org"); err != nil {
t.Fatalf("goLookupIP(good) failed: %v", err)
}
r.WantServers([]string{"8.8.8.8"})
// Using a bad resolv.conf when we had a good one
// before should not update the config
// Using an empty resolv.conf should use localhost as servers
r.SetConf("")
if _, err := goLookupIP("golang.org"); err != nil {
t.Fatalf("goLookupIP(good; bad) failed: %v", err)
if len(cfg.dnsConfig.servers) != len(defaultNS) {
t.Fatalf("goLookupIP(missing; good; bad) failed: servers=%v, want: %v", cfg.dnsConfig.servers, defaultNS)
}
for i := range cfg.dnsConfig.servers {
if cfg.dnsConfig.servers[i] != defaultNS[i] {
t.Fatalf("goLookupIP(missing; good; bad) failed: servers=%v, want: %v", cfg.dnsConfig.servers, defaultNS)
}
}
// A new good config should get picked up
@ -238,9 +247,7 @@ func BenchmarkGoLookupIPWithBrokenNameServer(b *testing.B) {
testHookUninstaller.Do(func() { uninstallTestHooks() })
onceLoadConfig.Do(loadDefaultConfig)
if cfg.dnserr != nil || cfg.dnsConfig == nil {
b.Fatalf("loadConfig failed: %v", cfg.dnserr)
}
// This looks ugly but it's safe as long as benchmarks are run
// sequentially in package testing.
orig := cfg.dnsConfig