Fix logic to disable DNS periodic update

internal/params/dns.go

@@ -137,5 +137,9 @@ func (p *reader) GetDNSOverTLSIPv6() (ipv6 bool, err error) {
 // GetDNSUpdatePeriod obtains the period to use to update the block lists and cryptographic files
 // and restart Unbound from the environment variable DNS_UPDATE_PERIOD
 func (p *reader) GetDNSUpdatePeriod() (period time.Duration, err error) {
-	return p.envParams.GetDuration("DNS_UPDATE_PERIOD", libparams.Default("24h"))
+	s, err := p.envParams.GetEnv("DNS_UPDATE_PERIOD", libparams.Default("24h"))
+	if err != nil {
+		return period, err
+	}
+	return time.ParseDuration(s)
 }

internal/settings/dns.go

@@ -55,6 +55,10 @@ func (d *DNS) String() string {
 	for i := range d.Providers {
 		providersStr[i] = string(d.Providers[i])
 	}
+	update := "deactivated"
+	if d.UpdatePeriod > 0 {
+		update = fmt.Sprintf("every %s", d.UpdatePeriod)
+	}
 	settingsList := []string{
 		"DNS over TLS settings:",
 		"DNS over TLS provider:\n  |--" + strings.Join(providersStr, "\n  |--"),
@@ -68,7 +72,7 @@ func (d *DNS) String() string {
 		"Verbosity details level: " + fmt.Sprintf("%d/4", d.VerbosityDetailsLevel),
 		"Validation log level: " + fmt.Sprintf("%d/2", d.ValidationLogLevel),
 		"IPv6 resolution: " + ipv6,
-		"Update period: " + d.UpdatePeriod.String(),
+		"Update: " + update,
 	}
 	return strings.Join(settingsList, "\n |--")
 }