From: Mateusz Poliwczak <mpoliwczak34@gmail.com>
Date: Sat, 7 Feb 2026 10:03:17 +0000 (+0100)
Subject: net: always set the servers field to defaultNS
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=30d5c1b0572f7d021def277097df6a21f300995e;p=gostls13.git

net: always set the servers field to defaultNS

When the field is parsed from a file, it would never
have len(servers) == 0, lets enforce that and update
test cases where we had it wrong.

Change-Id: I7fa6ebcf63b9fe20fbbf791113ca948d6a6a6964
Reviewed-on: https://go-review.googlesource.com/c/go/+/743020
Auto-Submit: Michael Pratt <mpratt@google.com>
Reviewed-by: Junyang Shao <shaojunyang@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Damien Neil <dneil@google.com>
Reviewed-by: Sean Liao <sean@liao.dev>
---

diff --git a/src/net/conf_test.go b/src/net/conf_test.go
index 075253cbc1..e3dbb37f19 100644
--- a/src/net/conf_test.go
+++ b/src/net/conf_test.go
@@ -142,7 +142,7 @@ func TestConfHostLookupOrder(t *testing.T) {
 			c: &conf{
 				goos: "openbsd",
 			},
-			resolv: &dnsConfig{lookup: []string{"bind", "file"}},
+			resolv: &dnsConfig{servers: defaultNS, lookup: []string{"bind", "file"}},
 			hostTests: []nssHostTest{
 				{"google.com", "myhostname", hostLookupDNSFiles},
 				{"foo.local", "myhostname", hostLookupDNSFiles},
@@ -153,7 +153,7 @@ func TestConfHostLookupOrder(t *testing.T) {
 			c: &conf{
 				goos: "openbsd",
 			},
-			resolv:    &dnsConfig{lookup: []string{"file", "bind"}},
+			resolv:    &dnsConfig{servers: defaultNS, lookup: []string{"file", "bind"}},
 			hostTests: []nssHostTest{{"google.com", "myhostname", hostLookupFilesDNS}},
 		},
 		{
@@ -161,7 +161,7 @@ func TestConfHostLookupOrder(t *testing.T) {
 			c: &conf{
 				goos: "openbsd",
 			},
-			resolv:    &dnsConfig{lookup: []string{"bind"}},
+			resolv:    &dnsConfig{servers: defaultNS, lookup: []string{"bind"}},
 			hostTests: []nssHostTest{{"google.com", "myhostname", hostLookupDNS}},
 		},
 		{
@@ -169,7 +169,7 @@ func TestConfHostLookupOrder(t *testing.T) {
 			c: &conf{
 				goos: "openbsd",
 			},
-			resolv:    &dnsConfig{lookup: []string{"file"}},
+			resolv:    &dnsConfig{servers: defaultNS, lookup: []string{"file"}},
 			hostTests: []nssHostTest{{"google.com", "myhostname", hostLookupFiles}},
 		},
 		{
@@ -177,7 +177,7 @@ func TestConfHostLookupOrder(t *testing.T) {
 			c: &conf{
 				goos: "openbsd",
 			},
-			resolv:    &dnsConfig{lookup: []string{"file", "bind", "yp"}},
+			resolv:    &dnsConfig{servers: defaultNS, lookup: []string{"file", "bind", "yp"}},
 			hostTests: []nssHostTest{{"google.com", "myhostname", hostLookupCgo}},
 		},
 		{
@@ -185,7 +185,7 @@ func TestConfHostLookupOrder(t *testing.T) {
 			c: &conf{
 				goos: "openbsd",
 			},
-			resolv:    &dnsConfig{lookup: []string{"file", "foo"}},
+			resolv:    &dnsConfig{servers: defaultNS, lookup: []string{"file", "foo"}},
 			hostTests: []nssHostTest{{"google.com", "myhostname", hostLookupCgo}},
 		},
 		{
@@ -193,7 +193,7 @@ func TestConfHostLookupOrder(t *testing.T) {
 			c: &conf{
 				goos: "openbsd",
 			},
-			resolv:    &dnsConfig{lookup: nil},
+			resolv:    &dnsConfig{servers: defaultNS, lookup: nil},
 			hostTests: []nssHostTest{{"google.com", "myhostname", hostLookupDNSFiles}},
 		},
 		{
diff --git a/src/net/dnsclient_unix.go b/src/net/dnsclient_unix.go
index 4d7b2fb5ea..fc671053f5 100644
--- a/src/net/dnsclient_unix.go
+++ b/src/net/dnsclient_unix.go
@@ -393,6 +393,16 @@ func (conf *resolverConfig) tryUpdate(name string) {
 	conf.initOnce.Do(conf.init)
 
 	dc := conf.dnsConfig.Load()
+
+	// Currently we should never have a config that does not have any
+	// available servers to query, since in such cases the servers field
+	// is set to [defaultNS], see dnsReadConfig.
+	// This assertion main purpose is for testing, such that we never set
+	// the mocked dnsConfig in such way.
+	if len(dc.servers) == 0 {
+		panic("unreachable")
+	}
+
 	if dc.noReload {
 		return
 	}