net: support no-reload option for unix go resolver

It adds support for no-reload option, as specified in resolv.conf(5):
 no-reload (since glibc 2.26)
                     Sets RES_NORELOAD in _res.options.  This option
                     disables automatic reloading of a changed
                     configuration file.

Change-Id: I11182c5829434503f719ed162014f2301e3ba8d4
GitHub-Last-Rev: 7ae44be2d5d5e3242dc39e733f154a64724dbedd
GitHub-Pull-Request: golang/go#56489
Reviewed-on: https://go-review.googlesource.com/c/go/+/446555
Reviewed-by: Damien Neil <dneil@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Run-TryBot: Ian Lance Taylor <iant@google.com>

diff --git a/src/net/dnsclient_unix.go b/src/net/dnsclient_unix.go
index 74029d2311b785f7ef19265bc4ad6e62b5ee7ebb..b958db52b0d11483ffd767f0c73e505d6d93c78c 100644 (file)
--- a/src/net/dnsclient_unix.go
+++ b/src/net/dnsclient_unix.go
@@ -369,6 +369,10 @@ func (conf *resolverConfig) init() {
 func (conf *resolverConfig) tryUpdate(name string) {
        conf.initOnce.Do(conf.init)
 
+       if conf.dnsConfig.noReload {
+               return
+       }
+
        // Ensure only one update at a time checks resolv.conf.
        if !conf.tryAcquireSema() {
                return

diff --git a/src/net/dnsclient_unix_test.go b/src/net/dnsclient_unix_test.go
index 553b220cbe295c537581fa6d54772a01fef40f74..20ee8bd062a2ee01633e873a7e12cf49eb0ebe9f 100644 (file)
--- a/src/net/dnsclient_unix_test.go
+++ b/src/net/dnsclient_unix_test.go
@@ -247,7 +247,7 @@ func newResolvConfTest() (*resolvConfTest, error) {
        return conf, nil
 }
 
-func (conf *resolvConfTest) writeAndUpdate(lines []string) error {
+func (conf *resolvConfTest) write(lines []string) error {
        f, err := os.OpenFile(conf.path, os.O_CREATE|os.O_TRUNC|os.O_WRONLY, 0600)
        if err != nil {
                return err
@@ -257,10 +257,18 @@ func (conf *resolvConfTest) writeAndUpdate(lines []string) error {
                return err
        }
        f.Close()
-       if err := conf.forceUpdate(conf.path, time.Now().Add(time.Hour)); err != nil {
+       return nil
+}
+
+func (conf *resolvConfTest) writeAndUpdate(lines []string) error {
+       return conf.writeAndUpdateWithLastCheckedTime(lines, time.Now().Add(time.Hour))
+}
+
+func (conf *resolvConfTest) writeAndUpdateWithLastCheckedTime(lines []string, lastChecked time.Time) error {
+       if err := conf.write(lines); err != nil {
                return err
        }
-       return nil
+       return conf.forceUpdate(conf.path, lastChecked)
 }
 
 func (conf *resolvConfTest) forceUpdate(name string, lastChecked time.Time) error {
@@ -2409,3 +2417,36 @@ func TestDNSTrustAD(t *testing.T) {
                t.Errorf("lookup failed: %v", err)
        }
 }
+
+func TestDNSConfigNoReload(t *testing.T) {
+       r := &Resolver{PreferGo: true, Dial: func(ctx context.Context, network, address string) (Conn, error) {
+               if address != "192.0.2.1:53" {
+                       return nil, errors.New("configuration unexpectedly changed")
+               }
+               return fakeDNSServerSuccessful.DialContext(ctx, network, address)
+       }}
+
+       conf, err := newResolvConfTest()
+       if err != nil {
+               t.Fatal(err)
+       }
+       defer conf.teardown()
+
+       err = conf.writeAndUpdateWithLastCheckedTime([]string{"nameserver 192.0.2.1", "options no-reload"}, time.Now().Add(-time.Hour))
+       if err != nil {
+               t.Fatal(err)
+       }
+
+       if _, err = r.LookupHost(context.Background(), "go.dev"); err != nil {
+               t.Fatal(err)
+       }
+
+       err = conf.write([]string{"nameserver 192.0.2.200"})
+       if err != nil {
+               t.Fatal(err)
+       }
+
+       if _, err = r.LookupHost(context.Background(), "go.dev"); err != nil {
+               t.Fatal(err)
+       }
+}

diff --git a/src/net/dnsconfig.go b/src/net/dnsconfig.go
index 37252b5a0b5855e206d53dfc7ee65bad48296195..c86a70be5afd57aaab851f7b2c354460a350bd84 100644 (file)
--- a/src/net/dnsconfig.go
+++ b/src/net/dnsconfig.go
@@ -30,6 +30,7 @@ type dnsConfig struct {
        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

diff --git a/src/net/dnsconfig_unix.go b/src/net/dnsconfig_unix.go
index 962314b4b609192c1e9d8eb64cb84dbe75939bae..8f6ae34c1b31eea018e2a3e2d5f45bc285179826 100644 (file)
--- a/src/net/dnsconfig_unix.go
+++ b/src/net/dnsconfig_unix.go
@@ -118,6 +118,8 @@ func dnsReadConfig(filename string) *dnsConfig {
                                case s == "edns0":
                                        // We use EDNS by default.
                                        // Ignore this option.
+                               case s == "no-reload":
+                                       conf.noReload = true
                                default:
                                        conf.unknownOpt = true
                                }