cmd/cli: add config to control DNS watchdog

cmd/cli/prog.go

@@ -40,7 +40,7 @@ const (
 	upstreamPrefix             = "upstream."
 	upstreamOS                 = upstreamPrefix + "os"
 	upstreamPrivate            = upstreamPrefix + "private"
-	dnsWatchdogInterval        = time.Minute
+	dnsWatchdogDefaultInterval = 20 * time.Second
 )
 
 // ControlSocketName returns name for control unix socket.
@@ -532,7 +532,27 @@ func (p *prog) setDNS() {
 			return setDnsIgnoreUnusableInterface(i, nameservers)
 		})
 	}
+	if p.dnsWatchdogEnabled() {
 		go p.dnsWatchdog(netIface, nameservers, allIfaces)
+	}
+}
+
+// dnsWatchdogEnabled reports whether DNS watchdog is enabled.
+func (p *prog) dnsWatchdogEnabled() bool {
+	if ptr := p.cfg.Service.DnsWatchdogEnabled; ptr != nil {
+		return *ptr
+	}
+	return true
+}
+
+// dnsWatchdogDuration returns the time duration between each DNS watchdog loop.
+func (p *prog) dnsWatchdogDuration() time.Duration {
+	if ptr := p.cfg.Service.DnsWatchdogInvterval; ptr != nil {
+		if (*ptr).Seconds() > 0 {
+			return *ptr
+		}
+	}
+	return dnsWatchdogDefaultInterval
 }
 
 // dnsWatchdog watches for DNS changes on Darwin and Windows then re-applying ctrld's settings.
@@ -546,7 +566,7 @@ func (p *prog) dnsWatchdog(iface *net.Interface, nameservers []string, allIfaces
 		mainLog.Load().Debug().Msg("start DNS settings watchdog")
 		ns := nameservers
 		slices.Sort(ns)
-		ticker := time.NewTicker(dnsWatchdogInterval)
+		ticker := time.NewTicker(p.dnsWatchdogDuration())
 		logger := mainLog.Load().With().Str("iface", iface.Name).Logger()
 		for range ticker.C {
 			if dnsChanged(iface, ns) {

cmd/cli/prog_test.go

@@ -0,0 +1,57 @@
+package cli
+
+import (
+	"testing"
+	"time"
+
+	"github.com/Control-D-Inc/ctrld"
+	"github.com/stretchr/testify/assert"
+)
+
+func Test_prog_dnsWatchdogEnabled(t *testing.T) {
+	p := &prog{cfg: &ctrld.Config{}}
+
+	// Default value is true.
+	assert.True(t, p.dnsWatchdogEnabled())
+
+	tests := []struct {
+		name    string
+		enabled bool
+	}{
+		{"enabled", true},
+		{"disabled", false},
+	}
+
+	for _, tc := range tests {
+		tc := tc
+		t.Run(tc.name, func(t *testing.T) {
+			p.cfg.Service.DnsWatchdogEnabled = &tc.enabled
+			assert.Equal(t, tc.enabled, p.dnsWatchdogEnabled())
+		})
+	}
+}
+
+func Test_prog_dnsWatchdogInterval(t *testing.T) {
+	p := &prog{cfg: &ctrld.Config{}}
+
+	// Default value is 20s.
+	assert.Equal(t, dnsWatchdogDefaultInterval, p.dnsWatchdogDuration())
+
+	tests := []struct {
+		name     string
+		duration time.Duration
+		expected time.Duration
+	}{
+		{"valid", time.Minute, time.Minute},
+		{"zero", 0, dnsWatchdogDefaultInterval},
+		{"nagative", time.Duration(-1 * time.Minute), dnsWatchdogDefaultInterval},
+	}
+
+	for _, tc := range tests {
+		tc := tc
+		t.Run(tc.name, func(t *testing.T) {
+			p.cfg.Service.DnsWatchdogInvterval = &tc.duration
+			assert.Equal(t, tc.expected, p.dnsWatchdogDuration())
+		})
+	}
+}

config.go

@@ -207,6 +207,8 @@ type ServiceConfig struct {
 	ClientIDPref            string         `mapstructure:"client_id_preference" toml:"client_id_preference,omitempty" validate:"omitempty,oneof=host mac"`
 	MetricsQueryStats       bool           `mapstructure:"metrics_query_stats" toml:"metrics_query_stats,omitempty"`
 	MetricsListener         string         `mapstructure:"metrics_listener" toml:"metrics_listener,omitempty"`
+	DnsWatchdogEnabled      *bool          `mapstructure:"dns_watchdog_enabled" toml:"dns_watchdog_enabled,omitempty"`
+	DnsWatchdogInvterval    *time.Duration `mapstructure:"dns_watchdog_interval" toml:"dns_watchdog_interval,omitempty"`
 	Daemon                  bool           `mapstructure:"-" toml:"-"`
 	AllocateIP              bool           `mapstructure:"-" toml:"-"`
 }

config_test.go

@@ -5,6 +5,7 @@ import (
 	"os"
 	"strings"
 	"testing"
+	"time"
 
 	"github.com/go-playground/validator/v10"
 	"github.com/spf13/viper"
@@ -22,6 +23,8 @@ func TestLoadConfig(t *testing.T) {
 
 	assert.Equal(t, "info", cfg.Service.LogLevel)
 	assert.Equal(t, "/path/to/log.log", cfg.Service.LogPath)
+	assert.Equal(t, false, *cfg.Service.DnsWatchdogEnabled)
+	assert.Equal(t, time.Duration(20*time.Second), *cfg.Service.DnsWatchdogInvterval)
 
 	assert.Len(t, cfg.Network, 2)
 	assert.Contains(t, cfg.Network, "0")

docs/config.md

@@ -252,6 +252,27 @@ Specifying the `ip` and `port` of the Prometheus metrics server. The Prometheus
 - Required: no
 - Default: ""
 
+### dns_watchdog_enabled
+Checking DNS changes to network interfaces and reverting to ctrld's own settings.
+
+The DNS watchdog process only runs on Windows and MacOS.
+
+- Type: boolean
+- Required: no
+- Default: true
+
+### dns_watchdog_interval
+Time duration between each DNS watchdog iteration.
+
+A duration string is a possibly signed sequence of decimal numbers, each with optional fraction and a unit suffix,
+such as "300ms", "-1.5h" or "2h45m". Valid time units are "ns", "us" (or "µs"), "ms", "s", "m", "h".
+
+If the time duration is non-positive, default value will be used.
+
+- Type: time duration string
+- Required: no
+- Default: 20s
+
 ## Upstream
 The `[upstream]` section specifies the DNS upstream servers that `ctrld` will forward DNS requests to.
 

testhelper/config.go

@@ -27,6 +27,8 @@ var sampleConfigContent = `
 [service]
 log_level = "info"
 log_path = "/path/to/log.log"
+dns_watchdog_enabled = false
+dns_watchdog_interval = "20s"
 
 [network.0]
 name = "Home Wifi"