Make qname filtering case-insensitive

filter.go

@@ -3,6 +3,7 @@ package main
 import (
 	"errors"
 	"github.com/miekg/dns"
+	"strings"
 )
 
 type nameFilter map[string]bool
@@ -12,6 +13,7 @@ func (n *nameFilter) AddString(name string) error {
 		*n = make(map[string]bool)
 	}
 
+	name = strings.ToLower(name)
 	if name[len(name)-1] != '.' {
 		name += "."
 	}
@@ -38,7 +40,7 @@ func (n nameFilter) Lookup(name []byte) bool {
 			break
 		}
 
-		if n[string(name)] {
+		if n[strings.ToLower(string(name))] {
 			return true
 		}
 		name = rest[llen:]
@@ -76,6 +78,14 @@ var errShortMessage = errors.New("DNS Message too short")
 var errTruncMessage = errors.New("DNS Message truncated")
 var errInvalidQname = errors.New("Invalid qname")
 
+func lowerByte(b byte) byte {
+	const lower = byte('a') - byte('A')
+	if b >= byte('A') && b <= byte('Z') {
+		return b + lower
+	}
+	return b
+}
+
 func (n nameFilter) FilterMsgQname(m []byte) (bool, error) {
 	if n == nil {
 		return false, nil
@@ -93,19 +103,31 @@ func (n nameFilter) FilterMsgQname(m []byte) (bool, error) {
 
 	m = m[12:]
 
-	var qnameLen int
+	var name []byte
 	for i := 0; i < len(m); i += int(m[i]) + 1 {
-		if m[i] == 0 {
-			qnameLen = i + 1
+		llen := int(m[i])
+		if llen == 0 {
+			name = append(name, 0)
 			break
 		}
-		if m[i] > 63 {
+		if llen > 63 {
 			return false, errInvalidQname
 		}
+
+		lend := llen + i + 1
+		if lend >= len(m) {
+			return false, errTruncMessage
+		}
+		name = append(name, byte(llen))
+
+		label := m[i+1 : lend]
+		for _, b := range label {
+			name = append(name, lowerByte(b))
+		}
 	}
-	if qnameLen == 0 {
+	if len(name) == 0 {
 		return false, errTruncMessage
 	}
 
-	return n.Lookup(m[:qnameLen]), nil
+	return n.Lookup(name), nil
 }