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go mod tidy

internal/dns/dns.go

@@ -172,40 +172,43 @@ func (m measurement) String() string {
 }
 
 func (s *Server) probeUpstreamLatency() {
-	upstreams := s.upstreams()
-	results := make([]measurement, len(upstreams))
-	var wg sync.WaitGroup
-	for idx, u := range upstreams {
-		wg.Add(1)
-		go func(idx int, u string) {
-			defer wg.Done()
-			// resolve a most-definitely cached record
-			m := new(dns.Msg)
-			m.SetQuestion("google.ch.", dns.TypeA)
-			start := time.Now()
-			_, _, err := s.client.Exchange(m, u)
-			rtt := time.Since(start)
-			if err != nil {
-				// including unresponsive upstreams in results makes the update
-				// code simpler:
-				results[idx] = measurement{u, time.Duration(math.MaxInt64)}
-				return
-			}
-			results[idx] = measurement{u, rtt}
-		}(idx, u)
+	if !s.once {
+		s.once = true
+		upstreams := s.upstreams()
+		results := make([]measurement, len(upstreams))
+		var wg sync.WaitGroup
+		for idx, u := range upstreams {
+			wg.Add(1)
+			go func(idx int, u string) {
+				defer wg.Done()
+				// resolve a most-definitely cached record
+				m := new(dns.Msg)
+				m.SetQuestion("google.ch.", dns.TypeA)
+				start := time.Now()
+				_, _, err := s.client.Exchange(m, u)
+				rtt := time.Since(start)
+				if err != nil {
+					// including unresponsive upstreams in results makes the update
+					// code simpler:
+					results[idx] = measurement{u, time.Duration(math.MaxInt64)}
+					return
+				}
+				results[idx] = measurement{u, rtt}
+			}(idx, u)
+		}
+		wg.Wait()
+		// Re-order by resolving latency:
+		sort.Slice(results, func(i, j int) bool {
+			return results[i].rtt < results[j].rtt
+		})
+		log.Printf("probe results: %v %v", s.once, results)
+		for idx, result := range results {
+			upstreams[idx] = result.upstream
+		}
+		s.upstreamMu.Lock()
+		defer s.upstreamMu.Unlock()
+		s.upstream = upstreams
 	}
-	wg.Wait()
-	// Re-order by resolving latency:
-	sort.Slice(results, func(i, j int) bool {
-		return results[i].rtt < results[j].rtt
-	})
-	log.Printf("probe results: %v", results)
-	for idx, result := range results {
-		upstreams[idx] = result.upstream
-	}
-	s.upstreamMu.Lock()
-	defer s.upstreamMu.Unlock()
-	s.upstream = upstreams
 }
 
 func (s *Server) hostByName(n lcHostname) (string, bool) {
@@ -477,7 +480,6 @@ 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
 		}
@@ -486,7 +488,6 @@ 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
@@ -494,7 +495,6 @@ 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)
 }
@@ -582,7 +582,6 @@ 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
 			}
@@ -592,7 +591,6 @@ 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
@@ -603,7 +601,6 @@ 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