Fix IsSubDomain

defaults.go

@@ -273,32 +273,8 @@ func IsDomainName(s string) (uint8, uint8, bool) { // copied from net package.
 
 // IsSubDomain checks if child is indeed a child of the parent.
 func IsSubDomain(parent, child string) bool {
-	// If the number of labels both domain name have
-	// in common equals the number of labels of parent,
-	// child is a subdomain of parent.
-	plabs := SplitLabels(parent)
-	clabs := SplitLabels(child)
-	if len(clabs) < len(plabs) {
-		// child is smaller than parent, reversed arguments?
-		return false
-	}
-	// Copied from CompareLabels to prevent another SplitLabels
-	n := 0
-	p := len(plabs) - 1
-	c := len(clabs) - 1
-	for {
-		if p < 0 || c < 0 {
-			break
-		}
-		if plabs[p] == clabs[c] {
-			n++
-		} else {
-			break
-		}
-		p--
-		c--
-	}
-	return n == len(plabs)
+	// Entire child is contained in parent
+	return CompareLabels(child, parent) == LenLabels(child)
 }
 
 // IsFqdn checks if a domain name is fully qualified.

labels.go

@@ -38,9 +38,6 @@ func SplitLabels(s string) []string {
 //
 // 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
-// 
-// Domain s1 is a subdomain of s2 if
-// CompareLabels(s1, s2) == LenLabels(s1)
 func CompareLabels(s1, s2 string) (n int) {
 	l1 := SplitLabels(s1)
 	l2 := SplitLabels(s2)
@@ -62,7 +59,7 @@ func CompareLabels(s1, s2 string) (n int) {
 	return
 }
 
-// LenLabels returns the number of labels in a domain name
+// LenLabels returns the number of labels in a domain name.
 func LenLabels(s string) (labels int) {
 	if s == "." {
 		return