Add a TTL model

This unifies the logic for handling the dnscontrol-default TTL, and
frees up the TTL value 0 for use by providers (e.g. Linode, which uses
it as its sentinel for its default TTL).

Closes StackExchange#2444.

commands/getZones.go

@@ -227,12 +227,12 @@ func GetZone(args GetZoneArgs) error {
 	for i, recs := range zoneRecs {
 		zoneName := zones[i]
 
-		z := prettyzone.PrettySort(recs, zoneName, 0, nil)
+		z := prettyzone.PrettySort(recs, zoneName, models.EmptyTTL(), nil)
 		switch args.OutputFormat {
 
 		case "zone":
 			fmt.Fprintf(w, "$ORIGIN %s.\n", zoneName)
-			prettyzone.WriteZoneFileRC(w, z.Records, zoneName, uint32(args.DefaultTTL), nil)
+			prettyzone.WriteZoneFileRC(w, z.Records, zoneName, models.NewTTL(uint32(args.DefaultTTL)), nil)
 			fmt.Fprintln(w)
 
 		case "js", "djs":
@@ -243,12 +243,15 @@ func GetZone(args GetZoneArgs) error {
 			fmt.Fprintf(w, `D("%s", REG_CHANGEME%s`, zoneName, sep)
 			var o []string
 			o = append(o, fmt.Sprintf("DnsProvider(%s)", dspVariableName))
-			defaultTTL := uint32(args.DefaultTTL)
-			if defaultTTL == 0 {
+			defaultTTL := models.EmptyTTL()
+			if args.DefaultTTL != 0 {
+				defaultTTL = models.NewTTL(uint32(args.DefaultTTL))
+			}
+			if !defaultTTL.IsSet() {
 				defaultTTL = prettyzone.MostCommonTTL(recs)
 			}
-			if defaultTTL != models.DefaultTTL && defaultTTL != 0 {
-				o = append(o, fmt.Sprintf("DefaultTTL(%d)", defaultTTL))
+			if defaultTTL.IsSet() {
+				o = append(o, fmt.Sprintf("DefaultTTL(%d)", defaultTTL.Value()))
 			}
 			for _, rec := range recs {
 				if (rec.Type == "CNAME") && (rec.Name == "@") {
@@ -287,7 +290,7 @@ func GetZone(args GetZoneArgs) error {
 				}
 
 				fmt.Fprintf(w, "%s\t%s\t%d\tIN\t%s\t%s%s\n",
-					rec.NameFQDN, rec.Name, rec.TTL, rec.Type, rec.GetTargetCombined(), cfproxy)
+					rec.NameFQDN, rec.Name, rec.TTL.Value(), rec.Type, rec.GetTargetCombined(), cfproxy)
 			}
 
 		default:
@@ -307,15 +310,15 @@ func jsonQuoted(i string) string {
 	return string(b)
 }
 
-func formatDsl(zonename string, rec *models.RecordConfig, defaultTTL uint32) string {
+func formatDsl(zonename string, rec *models.RecordConfig, defaultTTL models.TTL) string {
 
 	target := rec.GetTargetCombined()
 
-	ttl := uint32(0)
+	ttl := models.EmptyTTL()
 	ttlop := ""
-	if rec.TTL != defaultTTL && rec.TTL != 0 {
+	if rec.TTL != defaultTTL && rec.TTL.IsSet() {
 		ttl = rec.TTL
-		ttlop = fmt.Sprintf(", TTL(%d)", ttl)
+		ttlop = fmt.Sprintf(", TTL(%d)", ttl.Value())
 	}
 
 	cfproxy := ""
@@ -386,7 +389,7 @@ func makeCaa(rec *models.RecordConfig, ttlop string) string {
 	// TODO(tlim): Generate a CAA_BUILDER() instead?
 }
 
-func makeR53alias(rec *models.RecordConfig, ttl uint32) string {
+func makeR53alias(rec *models.RecordConfig, ttl models.TTL) string {
 	items := []string{
 		"'" + rec.Name + "'",
 		"'" + rec.R53Alias["type"] + "'",
@@ -395,8 +398,8 @@ func makeR53alias(rec *models.RecordConfig, ttl uint32) string {
 	if z, ok := rec.R53Alias["zone_id"]; ok {
 		items = append(items, "R53_ZONE('"+z+"')")
 	}
-	if ttl != 0 {
-		items = append(items, fmt.Sprintf("TTL(%d)", ttl))
+	if ttl.IsSet() {
+		items = append(items, fmt.Sprintf("TTL(%d)", ttl.Value()))
 	}
 	return rec.Type + "(" + strings.Join(items, ", ") + ")"
 }

commands/r53_test.go

@@ -17,7 +17,7 @@ func TestR53Test_1(t *testing.T) {
 	rec.R53Alias = make(map[string]string)
 	rec.R53Alias["type"] = "A"
 	w := `R53_ALIAS('foo', 'A', 'bar')`
-	if g := makeR53alias(&rec, 0); g != w {
+	if g := makeR53alias(&rec, models.EmptyTTL()); g != w {
 		t.Errorf("makeR53alias failure: got `%s` want `%s`", g, w)
 	}
 }
@@ -32,7 +32,7 @@ func TestR53Test_1ttl(t *testing.T) {
 	rec.R53Alias = make(map[string]string)
 	rec.R53Alias["type"] = "A"
 	w := `R53_ALIAS('foo', 'A', 'bar', TTL(321))`
-	if g := makeR53alias(&rec, 321); g != w {
+	if g := makeR53alias(&rec, models.NewTTL(321)); g != w {
 		t.Errorf("makeR53alias failure: got `%s` want `%s`", g, w)
 	}
 }
@@ -48,7 +48,7 @@ func TestR53Test_2(t *testing.T) {
 	rec.R53Alias["type"] = "A"
 	rec.R53Alias["zone_id"] = "blarg"
 	w := `R53_ALIAS('foo', 'A', 'bar', R53_ZONE('blarg'))`
-	if g := makeR53alias(&rec, 0); g != w {
+	if g := makeR53alias(&rec, models.EmptyTTL()); g != w {
 		t.Errorf("makeR53alias failure: got `%s` want `%s`", g, w)
 	}
 }
@@ -64,7 +64,7 @@ func TestR53Test_2ttl(t *testing.T) {
 	rec.R53Alias["type"] = "A"
 	rec.R53Alias["zone_id"] = "blarg"
 	w := `R53_ALIAS('foo', 'A', 'bar', R53_ZONE('blarg'), TTL(123))`
-	if g := makeR53alias(&rec, 123); g != w {
+	if g := makeR53alias(&rec, models.NewTTL(123)); g != w {
 		t.Errorf("makeR53alias failure: got `%s` want `%s`", g, w)
 	}
 }

integrationTest/integration_test.go

@@ -579,7 +579,7 @@ func loc(name string, d1 uint8, m1 uint8, s1 float32, ns string,
 func makeRec(name, target, typ string) *models.RecordConfig {
 	r := &models.RecordConfig{
 		Type: typ,
-		TTL:  300,
+		TTL:  models.NewTTL(300),
 	}
 	SetLabel(r, name, "**current-domain**")
 	r.SetTarget(target)
@@ -734,7 +734,7 @@ func txt(name, target string) *models.RecordConfig {
 
 // func (r *models.RecordConfig) ttl(t uint32) *models.RecordConfig {
 func ttl(r *models.RecordConfig, t uint32) *models.RecordConfig {
-	r.TTL = t
+	r.TTL = models.NewTTL(t)
 	return r
 }
 

models/dns.go

@@ -9,6 +9,48 @@ import (
 // DefaultTTL is applied to any DNS record without an explicit TTL.
 const DefaultTTL = uint32(300)
 
+// TTL implements an optional TTL field, with a default of DefaultTTL.
+type TTL struct {
+	value *uint32
+}
+
+func NewTTL(ttl uint32) TTL {
+	value := new(uint32)
+	*value = ttl
+	return TTL{
+		value,
+	}
+}
+
+// EmptyTTL returns a new TTL without an explicit value.
+func EmptyTTL() TTL {
+	return TTL{
+		value: nil,
+	}
+}
+
+func (ttl TTL) IsSet() bool {
+	return ttl.value != nil
+}
+
+func (ttl TTL) Value() uint32 {
+	if ttl.IsSet() {
+		return *ttl.value
+	} else {
+		return DefaultTTL
+	}
+}
+
+func (ttl *TTL) ValueRef() *uint32 {
+	if ttl.IsSet() {
+		return ttl.value
+	} else {
+		defaultTTL := new(uint32)
+		*defaultTTL = DefaultTTL
+		return defaultTTL
+	}
+}
+
 // DNSConfig describes the desired DNS configuration, usually loaded from dnsconfig.js.
 type DNSConfig struct {
 	Registrars         []*RegistrarConfig            `json:"registrars"`

models/dns_test.go

@@ -1,14 +1,16 @@
 package models
 
-import "testing"
+import (
+	"testing"
+)
 
 func TestRR(t *testing.T) {
 	experiment := RecordConfig{
 		Type:         "A",
 		Name:         "foo",
 		NameFQDN:     "foo.example.com",
 		target:       "1.2.3.4",
-		TTL:          0,
+		TTL:          EmptyTTL(),
 		MxPreference: 0,
 	}
 	expected := "foo.example.com.\t300\tIN\tA\t1.2.3.4"
@@ -22,7 +24,7 @@ func TestRR(t *testing.T) {
 		Name:     "@",
 		NameFQDN: "example.com",
 		target:   "mailto:[email protected]",
-		TTL:      300,
+		TTL:      NewTTL(300),
 		CaaTag:   "iodef",
 		CaaFlag:  1,
 	}
@@ -37,7 +39,7 @@ func TestRR(t *testing.T) {
 		Name:             "@",
 		NameFQDN:         "_443._tcp.example.com",
 		target:           "abcdef0123456789",
-		TTL:              300,
+		TTL:              NewTTL(300),
 		TlsaUsage:        0,
 		TlsaSelector:     0,
 		TlsaMatchingType: 1,

models/dnsrr.go

@@ -61,7 +61,7 @@ func RRtoRC(rr dns.RR, origin string) (RecordConfig, error) {
 	header := rr.Header()
 	rc := new(RecordConfig)
 	rc.Type = dns.TypeToString[header.Rrtype]
-	rc.TTL = header.Ttl
+	rc.TTL = NewTTL(header.Ttl)
 	rc.Original = rr
 	rc.SetLabelFromFQDN(strings.TrimSuffix(header.Name, "."), origin)
 	var err error

models/record.go

@@ -89,7 +89,7 @@ type RecordConfig struct {
 	SubDomain string            `json:"subdomain,omitempty"`
 	NameFQDN  string            `json:"-"` // Must end with ".$origin". See above.
 	target    string            // If a name, must end with "."
-	TTL       uint32            `json:"ttl,omitempty"`
+	TTL       TTL               `json:"ttl,omitempty"`
 	Metadata  map[string]string `json:"meta,omitempty"`
 	Original  interface{}       `json:"-"` // Store pointer to provider-specific record object. Used in diffing.
 
@@ -321,10 +321,10 @@ func (rc *RecordConfig) ToDiffable(extraMaps ...map[string]string) string {
 	var content string
 	switch rc.Type {
 	case "SOA":
-		content = fmt.Sprintf("%s %v %d %d %d %d ttl=%d", rc.target, rc.SoaMbox, rc.SoaRefresh, rc.SoaRetry, rc.SoaExpire, rc.SoaMinttl, rc.TTL)
+		content = fmt.Sprintf("%s %v %d %d %d %d ttl=%d", rc.target, rc.SoaMbox, rc.SoaRefresh, rc.SoaRetry, rc.SoaExpire, rc.SoaMinttl, rc.TTL.Value())
 		// SoaSerial is not used in comparison
 	default:
-		content = fmt.Sprintf("%v ttl=%d", rc.GetTargetCombined(), rc.TTL)
+		content = fmt.Sprintf("%v ttl=%d", rc.GetTargetCombined(), rc.TTL.Value())
 	}
 	for _, valueMap := range extraMaps {
 		// sort the extra values map keys to perform a deterministic
@@ -373,10 +373,7 @@ func (rc *RecordConfig) ToRR() dns.RR {
 	rr.Header().Name = rc.NameFQDN + "."
 	rr.Header().Rrtype = rdtype
 	rr.Header().Class = dns.ClassINET
-	rr.Header().Ttl = rc.TTL
-	if rc.TTL == 0 {
-		rr.Header().Ttl = DefaultTTL
-	}
+	rr.Header().Ttl = rc.TTL.Value()
 
 	// Fill in the data.
 	switch rdtype { // #rtype_variations

models/record_test.go

@@ -146,7 +146,7 @@ func TestRecordConfig_Copy(t *testing.T) {
 				SubDomain:        "sub",
 				NameFQDN:         "namef",
 				target:           "targette",
-				TTL:              12345,
+				TTL:              NewTTL(12345),
 				Metadata:         map[string]string{"me": "ah", "da": "ta"},
 				MxPreference:     123,
 				SrvPriority:      223,
@@ -189,7 +189,7 @@ func TestRecordConfig_Copy(t *testing.T) {
 				SubDomain:        tt.fields.SubDomain,
 				NameFQDN:         tt.fields.NameFQDN,
 				target:           tt.fields.target,
-				TTL:              tt.fields.TTL,
+				TTL:              NewTTL(tt.fields.TTL),
 				Metadata:         tt.fields.Metadata,
 				MxPreference:     tt.fields.MxPreference,
 				SrvPriority:      tt.fields.SrvPriority,

models/target.go

@@ -99,7 +99,7 @@ func (rc *RecordConfig) GetTargetSortable() string {
 
 // GetTargetDebug returns a string with the various fields spelled out.
 func (rc *RecordConfig) GetTargetDebug() string {
-	content := fmt.Sprintf("%s %s %s %d", rc.Type, rc.NameFQDN, rc.target, rc.TTL)
+	content := fmt.Sprintf("%s %s %s %d", rc.Type, rc.NameFQDN, rc.target, rc.TTL.Value())
 	switch rc.Type { // #rtype_variations
 	case "A", "AAAA", "CNAME", "NS", "PTR", "TXT", "AKAMAICDN":
 		// Nothing special.

pkg/diff/diff_test.go

@@ -14,7 +14,7 @@ func myRecord(s string) *models.RecordConfig {
 	ttl, _ := strconv.ParseUint(parts[2], 10, 32)
 	r := &models.RecordConfig{
 		Type:     parts[1],
-		TTL:      uint32(ttl),
+		TTL:      models.NewTTL(uint32(ttl)),
 		Metadata: map[string]string{},
 	}
 	r.SetLabel(parts[0], "example.com")
@@ -72,7 +72,7 @@ func TestUnchangedWithAddition(t *testing.T) {
 
 // s stringifies a RecordConfig for testing purposes.
 func s(rc *models.RecordConfig) string {
-	return fmt.Sprintf("%s %s %d %s", rc.GetLabel(), rc.Type, rc.TTL, rc.GetTargetCombined())
+	return fmt.Sprintf("%s %s %d %s", rc.GetLabel(), rc.Type, rc.TTL.Value(), rc.GetTargetCombined())
 }
 
 func TestOutOfOrderRecords(t *testing.T) {

pkg/diff2/analyze.go

@@ -231,7 +231,7 @@ func humanDiff(a, b targetConfig) string {
 	}
 
 	// Just the TTLs are different:
-	return fmt.Sprintf("%s ttl=(%d->%d)", a.comparableNoTTL, a.rec.TTL, b.rec.TTL)
+	return fmt.Sprintf("%s ttl=(%d->%d)", a.comparableNoTTL, a.rec.TTL.Value(), b.rec.TTL.Value())
 }
 
 func diffTargets(existing, desired []targetConfig) ChangeList {

pkg/diff2/analyze_test.go

@@ -18,22 +18,22 @@ func init() {
 	color.NoColor = true
 }
 
-var testDataAA1234 = makeRec("laba", "A", "1.2.3.4")               //      [0]
-var testDataAA5678 = makeRec("laba", "A", "5.6.7.8")               //
-var testDataAA1234ttl700 = makeRecTTL("laba", "A", "1.2.3.4", 700) //
-var testDataAA5678ttl700 = makeRecTTL("laba", "A", "5.6.7.8", 700) //
-var testDataAMX10a = makeRec("laba", "MX", "10 laba")              //     [1]
-var testDataCCa = makeRec("labc", "CNAME", "laba")                 //     [2]
-var testDataEA15 = makeRec("labe", "A", "10.10.10.15")             //  [3]
-var e4 = makeRec("labe", "A", "10.10.10.16")                       //  [4]
-var e5 = makeRec("labe", "A", "10.10.10.17")                       //  [5]
-var e6 = makeRec("labe", "A", "10.10.10.18")                       //  [6]
-var e7 = makeRec("labg", "NS", "10.10.10.15")                      // [7]
-var e8 = makeRec("labg", "NS", "10.10.10.16")                      // [8]
-var e9 = makeRec("labg", "NS", "10.10.10.17")                      // [9]
-var e10 = makeRec("labg", "NS", "10.10.10.18")                     // [10]
-var e11mx = makeRec("labh", "MX", "22 ttt")                        //     [11]
-var e11 = makeRec("labh", "CNAME", "labd")                         //     [11]
+var testDataAA1234 = makeRec("laba", "A", "1.2.3.4")                              //      [0]
+var testDataAA5678 = makeRec("laba", "A", "5.6.7.8")                              //
+var testDataAA1234ttl700 = makeRecTTL("laba", "A", "1.2.3.4", models.NewTTL(700)) //
+var testDataAA5678ttl700 = makeRecTTL("laba", "A", "5.6.7.8", models.NewTTL(700)) //
+var testDataAMX10a = makeRec("laba", "MX", "10 laba")                             //     [1]
+var testDataCCa = makeRec("labc", "CNAME", "laba")                                //     [2]
+var testDataEA15 = makeRec("labe", "A", "10.10.10.15")                            //  [3]
+var e4 = makeRec("labe", "A", "10.10.10.16")                                      //  [4]
+var e5 = makeRec("labe", "A", "10.10.10.17")                                      //  [5]
+var e6 = makeRec("labe", "A", "10.10.10.18")                                      //  [6]
+var e7 = makeRec("labg", "NS", "10.10.10.15")                                     // [7]
+var e8 = makeRec("labg", "NS", "10.10.10.16")                                     // [8]
+var e9 = makeRec("labg", "NS", "10.10.10.17")                                     // [9]
+var e10 = makeRec("labg", "NS", "10.10.10.18")                                    // [10]
+var e11mx = makeRec("labh", "MX", "22 ttt")                                       //     [11]
+var e11 = makeRec("labh", "CNAME", "labd")                                        //     [11]
 var testDataApexMX1aaa = makeRec("", "MX", "1 aaa")
 
 var testDataAA1234clone = makeRec("laba", "A", "1.2.3.4") //      [0']

pkg/diff2/compareconfig.go

@@ -216,7 +216,7 @@ func mkCompareBlobs(rc *models.RecordConfig, f func(*models.RecordConfig) string
 	}
 
 	lenWithoutTTL := len(comp)
-	compFull := comp + fmt.Sprintf(" ttl=%d", rc.TTL)
+	compFull := comp + fmt.Sprintf(" ttl=%d", rc.TTL.Value())
 
 	return compFull[:lenWithoutTTL], compFull
 }
@@ -230,7 +230,7 @@ func (cc *CompareConfig) addRecords(recs models.Records, storeInExisting bool) {
 	// of the same label+rtype are grouped. We use PrettySort because it works,
 	// has been extensively tested, and assures that the ChangeList will
 	// be in an order that is pretty to look at.
-	z := prettyzone.PrettySort(recs, cc.origin, 0, nil)
+	z := prettyzone.PrettySort(recs, cc.origin, models.EmptyTTL(), nil)
 
 	for _, rec := range z.Records {
 

pkg/diff2/groupsort.go

@@ -19,7 +19,7 @@ func groupbyRSet(recs models.Records, origin string) []recset {
 	// Sort the NameFQDN to a consistent order. The actual sort methodology
 	// doesn't matter as long as equal values are adjacent.
 	// Use the PrettySort ordering so that the records are extra pretty.
-	pretty := prettyzone.PrettySort(recs, origin, 0, nil)
+	pretty := prettyzone.PrettySort(recs, origin, models.EmptyTTL(), nil)
 	recs = pretty.Records
 
 	var result []recset