Fix and test rfc 1982 arithmetic

dns.go

@@ -82,7 +82,7 @@ import (
 )
 
 const (
-	Year68         = 1 << 32 // For RFC1982 (Serial Arithmetic) calculations in 32 bits.
+	Year68         = 1 << 31 // For RFC1982 (Serial Arithmetic) calculations in 32 bits.
 	DefaultMsgSize = 4096    // Standard default for larger than 512 packets.
 	UDPMsgSize     = 512     // Default buffer size for servers receiving UDP packets.
 	MaxMsgSize     = 65536   // Largest possible DNS packet.

parse_test.go

@@ -509,3 +509,47 @@ func TestLineNumberError2(t *testing.T) {
 		//		fmt.Printf("%s\n", err.Error())
 	}
 }
+
+// Test if the calculations are correct
+func TestRfc1982(t *testing.T) {
+	// If the current time and the timestamp are more than 68 years apart
+	// it means the date has wrapped. 0 is 1970
+
+	// fall in the current 68 year span
+	strtests := []string{"20120525134203", "19700101000000", "20380119031408"}
+	for _, v := range strtests {
+		if x, _ := DateToTime(v); v != TimeToDate(x) {
+			t.Logf("1982 arithmetic string failure %s (%s:%d)", v, TimeToDate(x), x)
+			t.Fail()
+		}
+	}
+
+	inttests := map[uint32]string{0: "19700101000000",
+		1 << 31:   "20380119031408",
+		1<<32 - 1: "21060207062815",
+	}
+	for i, v := range inttests {
+		if TimeToDate(i) != v {
+			t.Logf("1982 arithmetic int failure %d:%s (%s)", i, v, TimeToDate(i))
+			t.Fail()
+		}
+	}
+
+	// Future tests, these dates get parsed to a date within the current 136 year span
+	future := map[string]string{"22680119031408": "20631123173144",
+		"19010101121212": "20370206184028",
+		"19210101121212": "20570206184028",
+		"19500101121212": "20860206184028",
+		"19700101000000": "19700101000000",
+		"19690101000000": "21050207062816",
+		"29210101121212": "21040522212236",
+	}
+	for from, to := range future {
+		x, _ := DateToTime(from)
+		y := TimeToDate(x)
+		if y != to {
+			t.Logf("1982 arithmetic future failure %s:%s (%s)", from, to, y)
+			t.Fail()
+		}
+	}
+}

types.go

@@ -1100,23 +1100,27 @@ func (rr *RR_HIP) Len() int {
 // string representation used when printing the record.
 // It takes serial arithmetic (RFC 1982) into account. [TODO]
 func TimeToDate(t uint32) string {
-	//	utc := time.Now().UTC().Unix()
-	//	mod := (int64(t) - utc) / Year68
-	ti := time.Unix(int64(t), 0).UTC()
+	mod := ( (int64(t) - time.Now().Unix()) / Year68 ) - 1
+	if mod < 0 {
+		mod = 0
+	}
+	ti := time.Unix(int64(t) - (mod * Year68), 0).UTC()
 	return ti.Format("20060102150405")
 }
 
 // DateToTime translates the RRSIG's incep. and expir. times from 
 // string values like "20110403154150" to an 32 bit integer.
-// It takes serial arithmetic (RFC 1982) into account. [TODO]
+// It takes serial arithmetic (RFC 1982) into account.
 func DateToTime(s string) (uint32, error) {
 	t, e := time.Parse("20060102150405", s)
 	if e != nil {
 		return 0, e
 	}
-	mod := t.Unix() / Year68
-	ti := uint32(t.Unix() - (mod * Year68))
-	return ti, nil
+	mod := ( t.Unix() / Year68 ) - 1
+	if mod < 0 {
+		mod = 0
+	}
+	return uint32(t.Unix() - (mod * Year68)), nil
 }
 
 // saltString converts a NSECX salt to uppercase and