Handle DNS Rcodes

resolver/namerecord.go

@@ -28,6 +28,7 @@ type NameRecord struct {
 
 	Domain   string
 	Question string
+	RCode    int
 	Answer   []string
 	Ns       []string
 	Extra    []string

resolver/resolve.go

@@ -206,10 +206,10 @@ func checkCache(ctx context.Context, q *Query) *RRCache {
 	// We still return the cache, if it isn't NXDomain, as it will be used if the
 	// new query fails.
 	if rrCache.Expired() {
-		if rrCache.IsNXDomain() {
-			return nil
+		if rrCache.RCode == dns.RcodeSuccess {
+			return rrCache
 		}
-		return rrCache
+		return nil
 	}
 
 	// Check if the cache will expire soon and start an async request.
@@ -377,8 +377,8 @@ resolveLoop:
 				// Defensive: This should normally not happen.
 				continue
 			}
-			// Check if we got NXDomain and whether we should try another resolver.
-			if rrCache.IsNXDomain() && tryAll {
+			// Check if request suceeded and whether we should try another resolver.
+			if rrCache.RCode != dns.RcodeSuccess && tryAll {
 				continue
 			}
 			break resolveLoop
@@ -404,7 +404,7 @@ resolveLoop:
 			// There was an error during resolving, return the old cache entry instead.
 			log.Tracer(ctx).Debugf("resolver: serving backup cache of %s because query failed: %s", q.ID(), err)
 			return oldCache, nil
-		case rrCache.IsNXDomain():
+		case !rrCache.Cacheable():
 			// The new result is NXDomain, return the old cache entry instead.
 			log.Tracer(ctx).Debugf("resolver: serving backup cache of %s because fresh response is NXDomain", q.ID())
 			return oldCache, nil
@@ -417,7 +417,7 @@ resolveLoop:
 	}
 
 	// Save the new entry if cache is enabled.
-	if !q.NoCaching {
+	if !q.NoCaching && rrCache.Cacheable() {
 		rrCache.Clean(minTTL)
 		err = rrCache.Save()
 		if err != nil {

resolver/resolver-env.go

@@ -111,6 +111,7 @@ func (er *envResolverConn) makeRRCache(q *Query, answers []dns.RR) *RRCache {
 	return &RRCache{
 		Domain:      q.FQDN,
 		Question:    q.QType,
+		RCode:       dns.RcodeSuccess,
 		Answer:      answers,
 		Extra:       []dns.RR{internalSpecialUseComment}, // Always add comment about this TLD.
 		Server:      envResolver.Server,

resolver/resolver-mdns.go

@@ -202,6 +202,7 @@ func handleMDNSMessages(ctx context.Context, messages chan *dns.Msg) error {
 					rrCache = &RRCache{
 						Domain:      question.Name,
 						Question:    dns.Type(question.Qtype),
+						RCode:       dns.RcodeSuccess,
 						Server:      mDNSResolver.Server,
 						ServerScope: mDNSResolver.ServerIPScope,
 						ServerInfo:  mDNSResolver.ServerInfo,
@@ -303,6 +304,7 @@ func handleMDNSMessages(ctx context.Context, messages chan *dns.Msg) error {
 				rrCache = &RRCache{
 					Domain:      v.Header().Name,
 					Question:    dns.Type(v.Header().Class),
+					RCode:       dns.RcodeSuccess,
 					Answer:      []dns.RR{v},
 					Server:      mDNSResolver.Server,
 					ServerScope: mDNSResolver.ServerIPScope,
@@ -423,6 +425,7 @@ func queryMulticastDNS(ctx context.Context, q *Query) (*RRCache, error) {
 	return &RRCache{
 		Domain:      q.FQDN,
 		Question:    q.QType,
+		RCode:       dns.RcodeNameError,
 		Server:      mDNSResolver.Server,
 		ServerScope: mDNSResolver.ServerIPScope,
 		ServerInfo:  mDNSResolver.ServerInfo,

resolver/resolver-plain.go

@@ -81,6 +81,7 @@ func (pr *PlainResolver) Query(ctx context.Context, q *Query) (*RRCache, error)
 	newRecord := &RRCache{
 		Domain:      q.FQDN,
 		Question:    q.QType,
+		RCode:       reply.Rcode,
 		Answer:      reply.Answer,
 		Ns:          reply.Ns,
 		Extra:       reply.Extra,

resolver/resolver-tcp.go

@@ -50,6 +50,7 @@ func (ifq *InFlightQuery) MakeCacheRecord(reply *dns.Msg) *RRCache {
 	return &RRCache{
 		Domain:      ifq.Query.FQDN,
 		Question:    ifq.Query.QType,
+		RCode:       reply.Rcode,
 		Answer:      reply.Answer,
 		Ns:          reply.Ns,
 		Extra:       reply.Extra,
@@ -477,6 +478,10 @@ func (mgr *tcpResolverConnMgr) handleQueryResponse(conn *dns.Conn, msg *dns.Msg)
 
 	// persist to database
 	rrCache := inFlight.MakeCacheRecord(msg)
+	if !rrCache.Cacheable() {
+		return
+	}
+
 	rrCache.Clean(minTTL)
 	err := rrCache.Save()
 	if err != nil {

resolver/rrcache.go

@@ -22,6 +22,7 @@ type RRCache struct {
 
 	Domain   string   // constant
 	Question dns.Type // constant
+	RCode    int      // constant
 
 	Answer []dns.RR // constant
 	Ns     []dns.RR // constant
@@ -84,8 +85,8 @@ func (rrCache *RRCache) Clean(minExpires uint32) {
 
 	// shorten caching
 	switch {
-	case rrCache.IsNXDomain():
-		// NXDomain
+	case rrCache.RCode != dns.RcodeSuccess:
+		// Any sort of error.
 		lowestTTL = 10
 	case netenv.IsConnectivityDomain(rrCache.Domain):
 		// Responses from these domains might change very quickly depending on the environment.
@@ -127,6 +128,7 @@ func (rrCache *RRCache) ToNameRecord() *NameRecord {
 	new := &NameRecord{
 		Domain:      rrCache.Domain,
 		Question:    rrCache.Question.String(),
+		RCode:       rrCache.RCode,
 		TTL:         rrCache.TTL,
 		Server:      rrCache.Server,
 		ServerScope: rrCache.ServerScope,
@@ -147,8 +149,27 @@ func (rrCache *RRCache) ToNameRecord() *NameRecord {
 	return new
 }
 
+// rcodeIsCacheable returns whether a record with the given RCode should be cached.
+func rcodeIsCacheable(rCode int) bool {
+	switch rCode {
+	case dns.RcodeSuccess, dns.RcodeNameError, dns.RcodeRefused:
+		return true
+	default:
+		return false
+	}
+}
+
+// Cacheable returns whether the record should be cached.
+func (rrCache *RRCache) Cacheable() bool {
+	return rcodeIsCacheable(rrCache.RCode)
+}
+
 // Save saves the RRCache to the database as a NameRecord.
 func (rrCache *RRCache) Save() error {
+	if !rrCache.Cacheable() {
+		return nil
+	}
+
 	return rrCache.ToNameRecord().Save()
 }
 
@@ -164,6 +185,7 @@ func GetRRCache(domain string, question dns.Type) (*RRCache, error) {
 		return nil, err
 	}
 
+	rrCache.RCode = nameRecord.RCode
 	rrCache.TTL = nameRecord.TTL
 	for _, entry := range nameRecord.Answer {
 		rrCache.Answer = parseRR(rrCache.Answer, entry)
@@ -227,16 +249,12 @@ func (rrCache *RRCache) Flags() string {
 	return ""
 }
 
-// IsNXDomain returnes whether the result is nxdomain.
-func (rrCache *RRCache) IsNXDomain() bool {
-	return len(rrCache.Answer) == 0
-}
-
 // ShallowCopy returns a shallow copy of the cache. slices are not copied, but referenced.
 func (rrCache *RRCache) ShallowCopy() *RRCache {
 	return &RRCache{
 		Domain:   rrCache.Domain,
 		Question: rrCache.Question,
+		RCode:    rrCache.RCode,
 		Answer:   rrCache.Answer,
 		Ns:       rrCache.Ns,
 		Extra:    rrCache.Extra,
@@ -259,14 +277,11 @@ func (rrCache *RRCache) ShallowCopy() *RRCache {
 func (rrCache *RRCache) ReplyWithDNS(ctx context.Context, request *dns.Msg) *dns.Msg {
 	// reply to query
 	reply := new(dns.Msg)
-	reply.SetRcode(request, dns.RcodeSuccess)
+	reply.SetRcode(request, rrCache.RCode)
 	reply.Ns = rrCache.Ns
 	reply.Extra = rrCache.Extra
 
-	if rrCache.IsNXDomain() {
-		// Set NXDomain return code if not the reply has no answers.
-		reply.Rcode = dns.RcodeNameError
-	} else {
+	if len(rrCache.Answer) > 0 {
 		// Copy answers, as we randomize their order a little.
 		reply.Answer = make([]dns.RR, len(rrCache.Answer))
 		copy(reply.Answer, rrCache.Answer)