One more helper function for compression

label_test.go

@@ -28,3 +28,14 @@ func TestCompareLabels(t *testing.T) {
                 t.Fail()
         }
 }
+
+func TestOffLabelFromRight(t *testing.T) {
+        s1 := "www.miek.nl" // fqdn??
+
+        t.Log(offsetLabelFromRight(s1, 4))
+        t.Log(offsetLabelFromRight(s1, 3))
+        t.Log(offsetLabelFromRight(s1, 2))
+        t.Log(offsetLabelFromRight(s1, 1))
+        t.Log(offsetLabelFromRight(s1, 0))
+        t.Fail()
+}

labels.go

@@ -6,15 +6,15 @@ package dns
 func SplitLabels(s string) []string {
 	last := byte('.')
 	k := 0
-        labels := make([]string, 0)
-        s = Fqdn(s)     // Make fully qualified
+	labels := make([]string, 0)
+	s = Fqdn(s) // Make fully qualified
 	for i := 0; i < len(s); i++ {
 		if s[i] == '.' {
 			if last == '\\' {
 				// do nothing
 				break
 			}
-			labels = append(labels,s[k:i])
+			labels = append(labels, s[k:i])
 			k = i + 1 // + dot
 		}
 		last = s[i]
@@ -32,19 +32,35 @@ func CompareLabels(s1, s2 string) (n int) {
 	l1 := SplitLabels(s1)
 	l2 := SplitLabels(s2)
 
-	x1 := len(l1)-1
-	x2 := len(l2)-1
+	x1 := len(l1) - 1
+	x2 := len(l2) - 1
 	for {
-                if x1 < 0 || x2 < 0 {
-                        break
-                }
-                if l1[x1] == l2[x2] {
-                        n++
-                } else {
-                        break
-                }
-                x1--
-                x2--
+		if x1 < 0 || x2 < 0 {
+			break
+		}
+		if l1[x1] == l2[x2] {
+			n++
+		} else {
+			break
+		}
+		x1--
+		x2--
 	}
-        return
+	return
+}
+
+// This function is needed for easy handling of compression 
+// pointers
+// www.miek.nl, 2, gives that start of miek.nl (which is
+// 2 labels from the right)
+// labeloffset of zero is fishy as is a labeloffset larger
+// than the number of labels... TODO: make it an error?
+func offsetLabelFromRight(s string, labeloffset int) int {
+	l := SplitLabels(s)
+	fromleft := len(l) - labeloffset
+	off := 0
+	for i := 0; i < fromleft; i++ {
+		off += len(l[i]) + 1
+	}
+	return off
 }