Set the recursion available flag

go mod tidy

internal/dns/dns.go

@@ -172,8 +172,6 @@ func (m measurement) String() string {
 }
 
 func (s *Server) probeUpstreamLatency() {
-	if !s.once {
-		s.once = true
 	upstreams := s.upstreams()
 	results := make([]measurement, len(upstreams))
 	var wg sync.WaitGroup
@@ -201,7 +199,7 @@ func (s *Server) probeUpstreamLatency() {
 	sort.Slice(results, func(i, j int) bool {
 		return results[i].rtt < results[j].rtt
 	})
-		log.Printf("probe results: %v %v", s.once, results)
+	log.Printf("probe results: %v", results)
 	for idx, result := range results {
 		upstreams[idx] = result.upstream
 	}
@@ -209,7 +207,6 @@ func (s *Server) probeUpstreamLatency() {
 	defer s.upstreamMu.Unlock()
 	s.upstream = upstreams
 }
-}
 
 func (s *Server) hostByName(n lcHostname) (string, bool) {
 	s.mu.Lock()
@@ -480,6 +477,7 @@ func (s *Server) handleInternal(w dns.ResponseWriter, r *dns.Msg) {
 		if err == errEmpty {
 			m := new(dns.Msg)
 			m.SetReply(r)
+			m.RecursionAvailable = true
 			w.WriteMsg(m)
 			return
 		}
@@ -488,6 +486,7 @@ func (s *Server) handleInternal(w dns.ResponseWriter, r *dns.Msg) {
 	if rr != nil {
 		m := new(dns.Msg)
 		m.SetReply(r)
+		m.RecursionAvailable = true
 		m.Answer = append(m.Answer, rr)
 		w.WriteMsg(m)
 		return
@@ -495,6 +494,7 @@ func (s *Server) handleInternal(w dns.ResponseWriter, r *dns.Msg) {
 	// Send an authoritative NXDOMAIN for local:
 	m := new(dns.Msg)
 	m.SetReply(r)
+	m.RecursionAvailable = true
 	m.SetRcode(r, dns.RcodeNameError)
 	w.WriteMsg(m)
 }
@@ -582,6 +582,7 @@ func (s *Server) subnameHandler(hostname lcHostname) func(w dns.ResponseWriter,
 			if err == errEmpty {
 				m := new(dns.Msg)
 				m.SetReply(r)
+				m.RecursionAvailable = true
 				w.WriteMsg(m)
 				return
 			}
@@ -591,6 +592,7 @@ func (s *Server) subnameHandler(hostname lcHostname) func(w dns.ResponseWriter,
 			s.promInc("local", r)
 			m := new(dns.Msg)
 			m.SetReply(r)
+			m.RecursionAvailable = true
 			m.Answer = append(m.Answer, rr)
 			w.WriteMsg(m)
 			return
@@ -601,6 +603,7 @@ func (s *Server) subnameHandler(hostname lcHostname) func(w dns.ResponseWriter,
 			s.promInc("local", r)
 			m := new(dns.Msg)
 			m.SetReply(r)
+			m.RecursionAvailable = true
 			m.SetRcode(r, dns.RcodeNameError)
 			w.WriteMsg(m)
 			return