Add and test IsSubDomain function

defaults.go

@@ -262,16 +262,16 @@ func IsDomainName(s string) (uint8, uint8, bool) { // copied from net package.
 	return labels, uint8(l - longer), ok
 }
 
-// IsSubDomain checks if child is indeed a child of parent.
-// In the DNS this is called in bailiwick.
+// IsSubDomain checks if child is indeed a child of the parent.
+// In the DNS this is called "the subdomain is in bailiwick".
 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(plabs) < len(clabs) {
-                // parent is smaller than child
+        if len(clabs) < len(plabs) {
+                // child is smaller than parent, reversed arguments?
                 return false
         }
         // Copied from CompareLabels to prevent another SplitLabels

dns_test.go

@@ -78,3 +78,26 @@ func TestEDNS_RR(t *testing.T) {
 	edns.Option[0].Data = "lalalala"
 	//t..Logf("%v\n", edns)
 }
+
+func TestBailiwick(t *testing.T) {
+        yes := map[string]string{
+                "miek.nl": "ns.miek.nl",
+                ".": "miek.nl",
+        }
+        for parent, child := range yes {
+                if !IsSubDomain(parent, child) {
+                        t.Logf("%s should be child of %s\n", child, parent)
+                        t.Fail()
+                }
+        }
+        no := map[string]string{
+                "www.miek.nl": "ns.miek.nl",
+                "miek.nl": ".",
+        }
+        for parent, child := range no {
+                if IsSubDomain(parent, child) {
+                        t.Logf("%s should not be child of %s\n", child, parent)
+                        t.Fail()
+                }
+        }
+}