Add RFC4034 domain comparison + NSEC Cover

Author: monoidic

labels.go

@@ -1,5 +1,9 @@
 package dns
 
+import (
+	"strings"
+)
+
 // Holds a bunch of helper functions for dealing with labels.
 
 // SplitDomainName splits a name string into it's labels.
@@ -186,6 +190,46 @@ func PrevLabel(s string, n int) (i int, start bool) {
 	return 0, n > 1
 }
 
+// compares domains according to the canonical ordering specified in RFC4034
+// returns an integer value similar to strcmp
+// names have to have equal casing!
+// (0 for equal values, -1 if s1 < s2, 1 if s1 > s2)
+func Compare(s1, s2 string) int {
+	s1b := []byte(s1)
+	s2b := []byte(s2)
+
+	doDDD(s1b)
+	doDDD(s2b)
+
+	s1lend := len(s1)
+	s2lend := len(s2)
+
+	for i := 0; ; i++ {
+		s1lstart, end1 := PrevLabel(s1, i)
+		s2lstart, end2 := PrevLabel(s2, i)
+
+		if end1 && end2 {
+			return 0
+		}
+
+		s1l := string(s1b[s1lstart:s1lend])
+		s2l := string(s2b[s2lstart:s2lend])
+
+		if !equal(s1l, s2l) {
+			return strings.Compare(strings.ToLower(s1l), strings.ToLower(s2l))
+		}
+
+		s1lend = s1lstart - 1
+		s2lend = s2lstart - 1
+		if s1lend == -1 {
+			s1lend = 0
+		}
+		if s2lend == -1 {
+			s2lend = 0
+		}
+	}
+}
+
 // equal compares a and b while ignoring case. It returns true when equal otherwise false.
 func equal(a, b string) bool {
 	// might be lifted into API function.
@@ -210,3 +254,16 @@ func equal(a, b string) bool {
 	}
 	return true
 }
+
+func doDDD(b []byte) {
+	lb := len(b)
+	for i := 0; i < lb; i++ {
+		if i+3 < lb && b[i] == '\\' && isDigit(b[i+1]) && isDigit(b[i+2]) && isDigit(b[i+3]) {
+			b[i] = dddToByte(b[i+1 : i+4])
+			for j := i + 1; j < lb-3; j++ {
+				b[j] = b[j+3]
+			}
+			lb -= 3
+		}
+	}
+}

labels_test.go

@@ -334,3 +334,40 @@ func BenchmarkPrevLabelMixed(b *testing.B) {
 		PrevLabel(`www\\\.example.com`, 10)
 	}
 }
+
+func TestCompare(t *testing.T) {
+	domains := []string{ // based on an exanple from RFC 4034
+		"example.",
+		"a.example.",
+		"yljkjljk.a.example.",
+		"Z.a.example.",
+		"zABC.a.EXAMPLE.",
+		"a-.example.",
+		"z.example.",
+		"\001.z.example.",
+		"*.z.example.",
+		"\200.z.example.",
+	}
+
+	len_domains := len(domains)
+
+	for i, domain := range domains {
+		if i != 0 {
+			prev_domain := domains[i-1]
+			if !(Compare(prev_domain, domain) == -1 && Compare(domain, prev_domain) == 1) {
+				t.Fatalf("prev comparison failure between %s and %s", prev_domain, domain)
+			}
+		}
+
+		if Compare(domain, domain) != 0 {
+			t.Fatalf("self comparison failure for %s", domain)
+		}
+
+		if i != len_domains-1 {
+			next_domain := domains[i+1]
+			if !(Compare(domain, next_domain) == -1 && Compare(next_domain, domain) == 1) {
+				t.Fatalf("next comparison failure between %s and %s, %d and %d", domain, next_domain, Compare(domain, next_domain), Compare(next_domain, domain))
+			}
+		}
+	}
+}

nsecx.go

@@ -93,3 +93,8 @@ func (rr *NSEC3) Match(name string) bool {
 	}
 	return false
 }
+
+// Match returns true if the given name is covered by the NSEC record
+func (rr *NSEC) Cover(name string) bool {
+	return Compare(rr.Hdr.Name, name) <= 0 && Compare(name, rr.NextDomain) == -1
+}

nsecx_test.go

@@ -168,3 +168,23 @@ func BenchmarkHashName(b *testing.B) {
 		})
 	}
 }
+
+func TestNsecCover(t *testing.T) {
+	nsec := testRR("aaa.ee.	3600	IN	NSEC	aac.ee. NS RRSIG NSEC").(*NSEC)
+
+	if !nsec.Cover("aaaa.ee.") {
+		t.Fatal("nsec cover not covering in-range name")
+	}
+
+	if !nsec.Cover("aaa.ee.") {
+		t.Fatal("nsec cover not covering start of range")
+	}
+
+	if nsec.Cover("aac.ee.") {
+		t.Fatal("nsec cover range end failure")
+	}
+
+	if nsec.Cover("aad.ee.") {
+		t.Fatal("nsec cover covering out-of-range name")
+	}
+}