Add label functions and tests

Makefile

@@ -15,6 +15,7 @@ GOFILES=\
 	edns.go\
 	keygen.go\
 	kscan.go\
+	labels.go\
 	msg.go\
 	nsec3.go \
 	rawmsg.go \

defaults.go

@@ -268,24 +268,3 @@ func Fqdn(s string) string {
 	}
 	return s + "."
 }
-
-// SplitLabels splits a domainname string into its labels.
-// No syntax checks are performed.
-// TODO: labels functions...
-func SplitLabels(s string) (labels []string) {
-        last := byte('.')
-        k := 0
-        l := 0
-	for i := 0; i < len(s); i++ {
-                if s[i] == '.' {
-                        if last == '\\' {
-                                // do nothing
-                                break
-                        }
-                        labels[l] = s[k:i]
-                        k = i+1 // + dot
-                }
-                last = s[i]
-        }
-        return
-}

label_test.go

@@ -0,0 +1,30 @@
+package dns
+
+import (
+	"testing"
+)
+
+func TestCompareLabels(t *testing.T) {
+        s1 := "www.miek.nl."
+        s2 := "miek.nl."
+        s3 := "www.bla.nl."
+        s4 := "nl.www.bla."
+        s5 := "nl"
+
+        if CompareLabels(s1, s2) != 2 {
+                t.Logf("%s with %s should be %d", s1, s2, 2)
+                t.Fail()
+        }
+        if CompareLabels(s1, s3) != 1 {
+                t.Logf("%s with %s should be %d", s1, s3, 1)
+                t.Fail()
+        }
+        if CompareLabels(s3, s4) != 0 {
+                t.Logf("%s with %s should be %d", s3, s4, 0)
+                t.Fail()
+        }
+        if CompareLabels(s1, s5) != 1 {
+                t.Logf("%s with %s should be %d", s1, s5, 1)
+                t.Fail()
+        }
+}

labels.go

@@ -0,0 +1,50 @@
+package dns
+
+// Holds a bunch of helper functions for dealing with labels.
+
+// SplitLabels splits a domainname string into its labels.
+func SplitLabels(s string) []string {
+	last := byte('.')
+	k := 0
+        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])
+			k = i + 1 // + dot
+		}
+		last = s[i]
+	}
+	return labels
+}
+
+// CompareLabels compares the strings s1 and s2 and
+// returns how many labels they have in common.
+// The compare start with the right most label and stops at
+// the label that is different.
+// www.miek.nl and miek.nl have two labels in common: miek and nl
+// www.miek.nl and www.bla.nl have one label in common: nl
+func CompareLabels(s1, s2 string) (n int) {
+	l1 := SplitLabels(s1)
+	l2 := SplitLabels(s2)
+
+	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--
+	}
+        return
+}