Add NSEC3 helper function back in

I'm going to use this in 'q', but it may came in handy for other
developers too. This is the first ramp up to a full blown Go only
recursive resolver.

nsecx.go

@@ -11,6 +11,13 @@ import (
 	"strings"
 )
 
+type Denialer interface {
+	// Cover will check if the (unhashed) name is being covered by this NSEC or NSEC3.
+	Cover(name string) bool
+	// Match will check if the ownername matches the (unhashed) name for this NSEC3 or NSEC3.
+	Match(name string) bool
+}
+
 type saltWireFmt struct {
 	Salt string `dns:"size-hex"`
 }
@@ -52,3 +59,52 @@ func HashName(label string, ha uint8, iter uint16, salt string) string {
 	}
 	return unpackBase32(nsec3)
 }
+
+// Cover implements the Denialer interface.
+func (rr *NSEC) Cover(name string) bool {
+
+	return true
+}
+
+// Cover implements the Denialer interface. 
+func (rr *NSEC3) Cover(name string) bool {
+	// FIXME(miek): check if the zones match
+	// FIXME(miek): check if we're not dealing with parent nsec3
+	hname := HashName(name, rr.Hash, rr.Iterations, rr.Salt)
+	labels := Split(rr.Hdr.Name)
+	if len(labels) < 2 {
+		return false
+	}
+	hash := strings.ToUpper(rr.Hdr.Name[labels[0] : labels[1]-1]) // -1 to remove the .
+	if hash == rr.NextDomain { // empty interval
+		return false
+	}
+	if hash > rr.NextDomain { // last name, points to apex
+		// hname > hash
+		// hname > rr.NextDomain
+		// TODO(miek)
+	}
+
+	if hname <= hash {
+		return false
+	}
+	if hname >= rr.NextDomain {
+		return false
+	}
+	return true
+}
+
+// Match implements the Denialer interface.   
+func (rr *NSEC3) Match(name string) bool {
+	// FIXME(miek): Check if we are in the same zone
+	hname := HashName(name, rr.Hash, rr.Iterations, rr.Salt)
+	labels := Split(rr.Hdr.Name)
+	if len(labels) < 2 {
+		return false
+	}
+	hash := strings.ToUpper(rr.Hdr.Name[labels[0] : labels[1]-1]) // -1 to remove the .
+	if hash == hname {
+		return true
+	}
+	return false
+}

nsecx_test.go

@@ -21,3 +21,17 @@ func TestPackNsec3(t *testing.T) {
 		t.Fail()
 	}
 }
+
+func TestNsec3(t *testing.T) {
+	// examples taken from .nl
+	nsec3, _ := NewRR("39p91242oslggest5e6a7cci4iaeqvnk.nl. IN NSEC3 1 1 5 F10E9F7EA83FC8F3 39P99DCGG0MDLARTCRMCF6OFLLUL7PR6 NS DS RRSIG")
+	if !nsec3.(*NSEC3).Cover("snasajsksasasa.nl.") { // 39p94jrinub66hnpem8qdpstrec86pg3
+		t.Logf("39p94jrinub66hnpem8qdpstrec86pg3. should be covered by 39p91242oslggest5e6a7cci4iaeqvnk.nl. - 39P99DCGG0MDLARTCRMCF6OFLLUL7PR6")
+		t.Fail()
+	}
+	nsec3, _ = NewRR("sk4e8fj94u78smusb40o1n0oltbblu2r.nl. IN NSEC3 1 1 5 F10E9F7EA83FC8F3 SK4F38CQ0ATIEI8MH3RGD0P5I4II6QAN NS SOA TXT RRSIG DNSKEY NSEC3PARAM")
+	if !nsec3.(*NSEC3).Match("nl.") { // sk4e8fj94u78smusb40o1n0oltbblu2r.nl.
+		t.Logf("sk4e8fj94u78smusb40o1n0oltbblu2r.nl. should match sk4e8fj94u78smusb40o1n0oltbblu2r.nl.")
+		t.Fail()
+	}
+}