BIND Provider: Pick default TTL automatically for zonefiles (#109)

* BIND Provider: Pick default TTL automatically for zonefiles

misc/convertzone/main.go

@@ -70,7 +70,7 @@ func pretty(zonename string, filename string, r io.Reader, defaultTTL uint32) {
 			l = append(l, x.RR)
 		}
 	}
-	bind.WriteZoneFile(os.Stdout, l, zonename, defaultTTL)
+	bind.WriteZoneFile(os.Stdout, l, zonename)
 }
 
 // rrFormat outputs the zonefile in either DSL or TSV format.

providers/bind/bindProvider.go

@@ -238,7 +238,7 @@ func (c *Bind) GetDomainCorrections(dc *models.DomainConfig) ([]*models.Correcti
 					for _, r := range dc.Records {
 						zonefilerecords = append(zonefilerecords, r.RR())
 					}
-					err = WriteZoneFile(zf, zonefilerecords, dc.Name, models.DefaultTTL)
+					err = WriteZoneFile(zf, zonefilerecords, dc.Name)
 
 					if err != nil {
 						log.Fatalf("WriteZoneFile error: %v\n", err)

providers/bind/prettyzone.go

@@ -57,8 +57,38 @@ func (z *zoneGenData) Less(i, j int) bool {
 	return a.String() < b.String()
 }
 
+// mostCommonTtl returns the most common TTL in a set of records. If there is
+// a tie, the highest TTL is selected. This makes the results consistent.
+// NS records are not included in the analysis because Tom said so.
+func mostCommonTtl(records []dns.RR) uint32 {
+	// Index the TTLs in use:
+	d := make(map[uint32]int)
+	for _, r := range records {
+		if r.Header().Rrtype != dns.TypeNS {
+			d[r.Header().Ttl]++
+		}
+	}
+	// Find the largest count:
+	var mc int
+	for _, value := range d {
+		if value > mc {
+			mc = value
+		}
+	}
+	// Find the largest key with that count:
+	var mk uint32
+	for key, value := range d {
+		if value == mc {
+			if key > mk {
+				mk = key
+			}
+		}
+	}
+	return mk
+}
+
 // WriteZoneFile writes a beautifully formatted zone file.
-func WriteZoneFile(w io.Writer, records []dns.RR, origin string, defaultTtl uint32) error {
+func WriteZoneFile(w io.Writer, records []dns.RR, origin string) error {
 	// This function prioritizes beauty over efficiency.
 	// * The zone records are sorted by label, grouped by subzones to
 	//   be easy to read and pleasant to the eye.
@@ -66,9 +96,11 @@ func WriteZoneFile(w io.Writer, records []dns.RR, origin string, defaultTtl uint
 	// * MX records are sorted numericly by preference value.
 	// * A records are sorted by IP address, not lexicographically.
 	// * Repeated labels are removed.
-	// * $TTL is used to eliminate clutter.
+	// * $TTL is used to eliminate clutter. The most common TTL value is used.
 	// * "@" is used instead of the apex domain name.
 
+	defaultTtl := mostCommonTtl(records)
+
 	z := &zoneGenData{
 		Origin:     origin,
 		DefaultTtl: defaultTtl,

providers/bind/prettyzone_test.go

@@ -27,7 +27,7 @@ func parseAndRegen(t *testing.T, buf *bytes.Buffer, expected string) {
 	}
 	// Generate it back:
 	buf2 := &bytes.Buffer{}
-	WriteZoneFile(buf2, parsed, "bosun.org.", 300)
+	WriteZoneFile(buf2, parsed, "bosun.org.")
 
 	// Compare:
 	if buf2.String() != expected {
@@ -35,6 +35,49 @@ func parseAndRegen(t *testing.T, buf *bytes.Buffer, expected string) {
 	}
 }
 
+func TestMostCommonTtl(t *testing.T) {
+	var records []dns.RR
+	var g, e uint32
+	r1, _ := dns.NewRR("bosun.org. 100 IN A 1.1.1.1")
+	r2, _ := dns.NewRR("bosun.org. 200 IN A 1.1.1.1")
+	r3, _ := dns.NewRR("bosun.org. 300 IN A 1.1.1.1")
+	r4, _ := dns.NewRR("bosun.org. 400 IN NS foo.bosun.org.")
+	r5, _ := dns.NewRR("bosun.org. 400 IN NS bar.bosun.org.")
+
+	// All records are TTL=100
+	records = nil
+	records, e = append(records, r1, r1, r1), 100
+	g = mostCommonTtl(records)
+	if e != g {
+		t.Fatalf("expected %d; got %d\n", e, g)
+	}
+
+	// Mixture of TTLs with an obvious winner.
+	records = nil
+	records, e = append(records, r1, r2, r2), 200
+	g = mostCommonTtl(records)
+	if e != g {
+		t.Fatalf("expected %d; got %d\n", e, g)
+	}
+
+	// 3-way tie. Largest TTL should be used.
+	records = nil
+	records, e = append(records, r1, r2, r3), 300
+	g = mostCommonTtl(records)
+	if e != g {
+		t.Fatalf("expected %d; got %d\n", e, g)
+	}
+
+	// NS records are ignored.
+	records = nil
+	records, e = append(records, r1, r4, r5), 100
+	g = mostCommonTtl(records)
+	if e != g {
+		t.Fatalf("expected %d; got %d\n", e, g)
+	}
+
+}
+
 // func WriteZoneFile
 
 func TestWriteZoneFileSimple(t *testing.T) {
@@ -42,7 +85,7 @@ func TestWriteZoneFileSimple(t *testing.T) {
 	r2, _ := dns.NewRR("bosun.org. 300 IN A 192.30.252.154")
 	r3, _ := dns.NewRR("www.bosun.org. 300 IN CNAME bosun.org.")
 	buf := &bytes.Buffer{}
-	WriteZoneFile(buf, []dns.RR{r1, r2, r3}, "bosun.org.", 300)
+	WriteZoneFile(buf, []dns.RR{r1, r2, r3}, "bosun.org.")
 	expected := `$TTL 300
 @                IN A     192.30.252.153
                  IN A     192.30.252.154
@@ -57,6 +100,28 @@ www              IN CNAME bosun.org.
 	parseAndRegen(t, buf, expected)
 }
 
+func TestWriteZoneFileSimpleTtl(t *testing.T) {
+	r1, _ := dns.NewRR("bosun.org. 100 IN A 192.30.252.153")
+	r2, _ := dns.NewRR("bosun.org. 100 IN A 192.30.252.154")
+	r3, _ := dns.NewRR("bosun.org. 100 IN A 192.30.252.155")
+	r4, _ := dns.NewRR("www.bosun.org. 300 IN CNAME bosun.org.")
+	buf := &bytes.Buffer{}
+	WriteZoneFile(buf, []dns.RR{r1, r2, r3, r4}, "bosun.org.")
+	expected := `$TTL 100
+@                IN A     192.30.252.153
+                 IN A     192.30.252.154
+                 IN A     192.30.252.155
+www        300   IN CNAME bosun.org.
+`
+	if buf.String() != expected {
+		t.Log(buf.String())
+		t.Log(expected)
+		t.Fatalf("Zone file does not match.")
+	}
+
+	parseAndRegen(t, buf, expected)
+}
+
 func TestWriteZoneFileMx(t *testing.T) {
 	//exhibits explicit ttls and long name
 	r1, _ := dns.NewRR(`bosun.org. 300 IN TXT "aaa"`)
@@ -70,7 +135,7 @@ func TestWriteZoneFileMx(t *testing.T) {
 	r8, _ := dns.NewRR(`_domainkey.bosun.org. 300 IN TXT "vvvv"`)
 	r9, _ := dns.NewRR(`google._domainkey.bosun.org. 300 IN TXT "\"foo\""`)
 	buf := &bytes.Buffer{}
-	WriteZoneFile(buf, []dns.RR{r1, r2, r3, r4, r5, r6, r7, r8, r9}, "bosun.org", 300)
+	WriteZoneFile(buf, []dns.RR{r1, r2, r3, r4, r5, r6, r7, r8, r9}, "bosun.org")
 	if buf.String() != testdataZFMX {
 		t.Log(buf.String())
 		t.Log(testdataZFMX)
@@ -117,7 +182,7 @@ func TestWriteZoneFileOrder(t *testing.T) {
 	}
 
 	buf := &bytes.Buffer{}
-	WriteZoneFile(buf, records, "stackoverflow.com.", 300)
+	WriteZoneFile(buf, records, "stackoverflow.com.")
 	// Compare
 	if buf.String() != testdataOrder {
 		t.Log("Found:")
@@ -138,7 +203,7 @@ func TestWriteZoneFileOrder(t *testing.T) {
 		}
 		// Generate
 		buf := &bytes.Buffer{}
-		WriteZoneFile(buf, records, "stackoverflow.com.", 300)
+		WriteZoneFile(buf, records, "stackoverflow.com.")
 		// Compare
 		if buf.String() != testdataOrder {
 			t.Log(buf.String())