From: Brad Fitzpatrick <bradfitz@golang.org>
Date: Tue, 27 Jan 2026 17:05:48 +0000 (-0800)
Subject: net: don't wait 5 seconds to re-read /etc/resolv.conf
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=6de7a19fea07bf8a9a54b7d9d3dc839fe2ea9d33;p=gostls13.git

net: don't wait 5 seconds to re-read /etc/resolv.conf

If a Go process starts up, finds /etc/resolv.conf empty, then the DHCP
client writes /etc/resolv.conf, the Go program would find itself
broken for up to 5 seconds.

We noticed this during integration tests in ephemeral VMs using
gokrazy that boot into our application.

Change-Id: Ia64c2b5c698a4ee3efc15d8a8f1850c47e531b84
Reviewed-on: https://go-review.googlesource.com/c/go/+/739620
Reviewed-by: Damien Neil <dneil@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
---

diff --git a/src/net/conf_test.go b/src/net/conf_test.go
index 6ebd6be635..075253cbc1 100644
--- a/src/net/conf_test.go
+++ b/src/net/conf_test.go
@@ -396,7 +396,7 @@ func TestConfHostLookupOrder(t *testing.T) {
 	defer conf.teardown()
 
 	for _, tt := range tests {
-		if !conf.forceUpdateConf(tt.resolv, time.Now().Add(time.Hour)) {
+		if !conf.forceUpdateConf(tt.resolv, distantFuture) {
 			t.Errorf("%s: failed to change resolv config", tt.name)
 		}
 		for _, ht := range tt.hostTests {
diff --git a/src/net/dnsclient_unix.go b/src/net/dnsclient_unix.go
index bf0456ba26..4d7b2fb5ea 100644
--- a/src/net/dnsclient_unix.go
+++ b/src/net/dnsclient_unix.go
@@ -382,13 +382,18 @@ func (conf *resolverConfig) init() {
 	conf.ch = make(chan struct{}, 1)
 }
 
+// distantFuture is a sentinel time used for tests to signal that
+// resolv.conf should not be rechecked.
+var distantFuture = time.Date(3000, 1, 2, 3, 4, 5, 6, time.UTC)
+
 // tryUpdate tries to update conf with the named resolv.conf file.
 // The name variable only exists for testing. It is otherwise always
 // "/etc/resolv.conf".
 func (conf *resolverConfig) tryUpdate(name string) {
 	conf.initOnce.Do(conf.init)
 
-	if conf.dnsConfig.Load().noReload {
+	dc := conf.dnsConfig.Load()
+	if dc.noReload {
 		return
 	}
 
@@ -399,7 +404,8 @@ func (conf *resolverConfig) tryUpdate(name string) {
 	defer conf.releaseSema()
 
 	now := time.Now()
-	if conf.lastChecked.After(now.Add(-5 * time.Second)) {
+	if (len(dc.servers) > 0 && conf.lastChecked.After(now.Add(-5*time.Second))) ||
+		conf.lastChecked == distantFuture {
 		return
 	}
 	conf.lastChecked = now