dns: simplify resolving code

cmd/dnsd/dnsd.go

@@ -28,7 +28,7 @@ var (
 	dnsListeners  = multilisten.NewPool()
 )
 
-func updateListeners() error {
+func updateListeners(mux *miekgdns.ServeMux) error {
 	hosts, err := gokrazy.PrivateInterfaceAddrs()
 	if err != nil {
 		return err
@@ -39,7 +39,11 @@ func updateListeners() error {
 	})
 
 	dnsListeners.ListenAndServe(hosts, func(host string) multilisten.Listener {
-		return &listenerAdapter{&miekgdns.Server{Addr: net.JoinHostPort(host, "53"), Net: "udp"}}
+		return &listenerAdapter{&miekgdns.Server{
+			Addr:    net.JoinHostPort(host, "53"),
+			Net:     "udp",
+			Handler: mux,
+		}}
 	})
 	return nil
 }
@@ -73,11 +77,11 @@ func logic() error {
 		log.Printf("cannot resolve DHCP hostnames: %v", err)
 	}
 	http.Handle("/metrics", srv.PrometheusHandler())
-	updateListeners()
+	updateListeners(srv.Mux)
 	ch := make(chan os.Signal, 1)
 	signal.Notify(ch, syscall.SIGUSR1)
 	for range ch {
-		if err := updateListeners(); err != nil {
+		if err := updateListeners(srv.Mux); err != nil {
 			log.Printf("updateListeners: %v", err)
 		}
 		if err := readLeases(); err != nil {

integration/dns/dns_test.go

@@ -13,8 +13,8 @@ import (
 )
 
 func TestDNS(t *testing.T) {
-	dns.NewServer("localhost:4453", "lan")
+	srv := dns.NewServer("localhost:4453", "lan")
-	s := &miekgdns.Server{Addr: "localhost:4453", Net: "udp"}
+	s := &miekgdns.Server{Addr: "localhost:4453", Net: "udp", Handler: srv.Mux}
 	go s.ListenAndServe()
 	const port = 4453
 	dig := exec.Command("dig", "-p", strconv.Itoa(port), "+timeout=1", "+short", "-x", "8.8.8.8", "@127.0.0.1")

internal/dns/dns.go

@@ -19,6 +19,8 @@ import (
 )
 
 type Server struct {
+	Mux *dns.ServeMux
+
 	client    *dns.Client
 	domain    string
 	upstream  string
@@ -40,6 +42,7 @@ func NewServer(addr, domain string) *Server {
 	hostname, _ := os.Hostname()
 	ip, _, _ := net.SplitHostPort(addr)
 	server := &Server{
+		Mux:       dns.NewServeMux(),
 		client:    &dns.Client{},
 		domain:    domain,
 		upstream:  "8.8.8.8:53",
@@ -73,7 +76,9 @@ func NewServer(addr, domain string) *Server {
 
 	server.prom.registry.MustRegister(prometheus.NewGoCollector())
 	server.initHostsLocked()
-	dns.HandleFunc(".", server.handleRequest)
+	server.Mux.HandleFunc(".", server.handleRequest)
+	server.Mux.HandleFunc("lan.", server.handleInternal)
+	server.Mux.HandleFunc("localhost.", server.handleInternal)
 	return server
 }
 
@@ -167,83 +172,48 @@ func isLocalInAddrArpa(q string) bool {
 	return local
 }
 
-// TODO: require search domains to be present, then use HandleFunc("lan.", internalName)
+func (s *Server) resolve(q dns.Question) (dns.RR, error) {
-// TODO: add test for non-A records on internal names, they should not go upstream
+	if q.Qclass != dns.ClassINET {
-func (s *Server) handleRequest(w dns.ResponseWriter, r *dns.Msg) {
+		return nil, nil
-	s.prom.queries.Inc()
+	}
-	s.prom.questions.Observe(float64(len(r.Question)))
-	if len(r.Question) == 1 { // TODO: answer all questions we can answer
-		q := r.Question[0]
-		if q.Qtype == dns.TypeAAAA && q.Qclass == dns.ClassINET {
 	if q.Name == "localhost." {
-				s.prom.upstream.WithLabelValues("local").Inc()
+		if q.Qtype == dns.TypeAAAA {
-				rr, err := dns.NewRR(q.Name + " 3600 IN AAAA ::1")
+			return dns.NewRR(q.Name + " 3600 IN AAAA ::1")
-				if err != nil {
-					log.Fatal(err)
 		}
-				m := new(dns.Msg)
+		if q.Qtype == dns.TypeA {
-				m.SetReply(r)
+			return dns.NewRR(q.Name + " 3600 IN A 127.0.0.1")
-				m.Answer = append(m.Answer, rr)
-				w.WriteMsg(m)
-				return
 		}
 	}
-		if q.Qtype == dns.TypeA && q.Qclass == dns.ClassINET {
+	if q.Qtype == dns.TypeA {
 		name := strings.TrimSuffix(q.Name, ".")
 		name = strings.TrimSuffix(name, "."+s.domain)
-
-			if q.Name == "localhost." {
-				s.prom.upstream.WithLabelValues("local").Inc()
-				rr, err := dns.NewRR(q.Name + " 3600 IN A 127.0.0.1")
-				if err != nil {
-					log.Fatal(err)
-				}
-				m := new(dns.Msg)
-				m.SetReply(r)
-				m.Answer = append(m.Answer, rr)
-				w.WriteMsg(m)
-				return
-			}
-			if !strings.Contains(name, ".") {
-				s.prom.upstream.WithLabelValues("local").Inc()
 		if host, ok := s.hostByName(name); ok {
-					rr, err := dns.NewRR(q.Name + " 3600 IN A " + host)
+			return dns.NewRR(q.Name + " 3600 IN A " + host)
-					if err != nil {
-						log.Fatal(err)
-					}
-					m := new(dns.Msg)
-					m.SetReply(r)
-					m.Answer = append(m.Answer, rr)
-					w.WriteMsg(m)
-					return
-				}
-				// Send an authoritative NXDOMAIN for local names:
-				m := new(dns.Msg)
-				m.SetReply(r)
-				m.SetRcode(r, dns.RcodeNameError)
-				w.WriteMsg(m)
-				return
 		}
 	}
-		if q.Qtype == dns.TypePTR && q.Qclass == dns.ClassINET {
+	if q.Qtype == dns.TypePTR {
-			if isLocalInAddrArpa(q.Name) {
-				s.prom.upstream.WithLabelValues("local").Inc()
 		if host, ok := s.hostByIP(q.Name); ok {
-					rr, err := dns.NewRR(q.Name + " 3600 IN PTR " + host + "." + s.domain)
+			return dns.NewRR(q.Name + " 3600 IN PTR " + host + "." + s.domain)
-					if err != nil {
-						log.Fatal(err)
-					}
-					m := new(dns.Msg)
-					m.SetReply(r)
-					m.Answer = append(m.Answer, rr)
-					w.WriteMsg(m)
-					return
 		}
 		if strings.HasSuffix(q.Name, "127.in-addr.arpa.") {
-					rr, err := dns.NewRR(q.Name + " 3600 IN PTR localhost.")
+			return dns.NewRR(q.Name + " 3600 IN PTR localhost.")
+		}
+	}
+	return nil, nil
+}
+
+func (s *Server) handleInternal(w dns.ResponseWriter, r *dns.Msg) {
+	s.prom.queries.Inc()
+	s.prom.questions.Observe(float64(len(r.Question)))
+	s.prom.upstream.WithLabelValues("local").Inc()
+	if len(r.Question) != 1 { // TODO: answer all questions we can answer
+		return
+	}
+	rr, err := s.resolve(r.Question[0])
 	if err != nil {
 		log.Fatal(err)
 	}
+	if rr != nil {
 		m := new(dns.Msg)
 		m.SetReply(r)
 		m.Answer = append(m.Answer, rr)
@@ -255,10 +225,20 @@ func (s *Server) handleRequest(w dns.ResponseWriter, r *dns.Msg) {
 	m.SetReply(r)
 	m.SetRcode(r, dns.RcodeNameError)
 	w.WriteMsg(m)
+}
+
+func (s *Server) handleRequest(w dns.ResponseWriter, r *dns.Msg) {
+	if len(r.Question) == 1 { // TODO: answer all questions we can answer
+		q := r.Question[0]
+		if q.Qtype == dns.TypePTR && q.Qclass == dns.ClassINET && isLocalInAddrArpa(q.Name) {
+			s.handleInternal(w, r)
 			return
 		}
 	}
-	}
+
+	s.prom.queries.Inc()
+	s.prom.questions.Observe(float64(len(r.Question)))
+	s.prom.upstream.WithLabelValues("DNS").Inc()
 
 	in, _, err := s.client.Exchange(r, s.upstream)
 	if err != nil {
@@ -268,5 +248,4 @@ func (s *Server) handleRequest(w dns.ResponseWriter, r *dns.Msg) {
 		return // DNS has no reply for resolving errors
 	}
 	w.WriteMsg(in)
-	s.prom.upstream.WithLabelValues("DNS").Inc()
 }

internal/dns/dns_test.go

@@ -33,7 +33,7 @@ func TestNXDOMAIN(t *testing.T) {
 	s := NewServer("localhost:0", "lan")
 	m := new(dns.Msg)
 	m.SetQuestion("foo.invalid.", dns.TypeA)
-	s.handleRequest(r, m)
+	s.Mux.ServeDNS(r, m)
 	if got, want := r.response.MsgHdr.Rcode, dns.RcodeNameError; got != want {
 		t.Fatalf("unexpected rcode: got %v, want %v", got, want)
 	}
@@ -45,7 +45,7 @@ func TestResolveError(t *testing.T) {
 	s.upstream = "266.266.266.266:53"
 	m := new(dns.Msg)
 	m.SetQuestion("foo.invalid.", dns.TypeA)
-	s.handleRequest(r, m)
+	s.Mux.ServeDNS(r, m)
 	if r.response != nil {
 		t.Fatalf("r.response unexpectedly not nil: %v", r.response)
 	}
@@ -64,7 +64,7 @@ func TestDHCP(t *testing.T) {
 	t.Run("xps.lan.", func(t *testing.T) {
 		m := new(dns.Msg)
 		m.SetQuestion("xps.lan.", dns.TypeA)
-		s.handleRequest(r, m)
+		s.Mux.ServeDNS(r, m)
 		if got, want := len(r.response.Answer), 1; got != want {
 			t.Fatalf("unexpected number of answers: got %d, want %d", got, want)
 		}
@@ -80,7 +80,7 @@ func TestDHCP(t *testing.T) {
 	t.Run("notfound.lan.", func(t *testing.T) {
 		m := new(dns.Msg)
 		m.SetQuestion("notfound.lan.", dns.TypeA)
-		s.handleRequest(r, m)
+		s.Mux.ServeDNS(r, m)
 		if got, want := r.response.Rcode, dns.RcodeNameError; got != want {
 			t.Fatalf("unexpected rcode: got %v, want %v", got, want)
 		}
@@ -99,7 +99,7 @@ func TestHostname(t *testing.T) {
 	t.Run("A", func(t *testing.T) {
 		m := new(dns.Msg)
 		m.SetQuestion(hostname+".lan.", dns.TypeA)
-		s.handleRequest(r, m)
+		s.Mux.ServeDNS(r, m)
 		if got, want := len(r.response.Answer), 1; got != want {
 			t.Fatalf("unexpected number of answers for %v: got %d, want %d", m.Question, got, want)
 		}
@@ -115,7 +115,7 @@ func TestHostname(t *testing.T) {
 	t.Run("PTR", func(t *testing.T) {
 		m := new(dns.Msg)
 		m.SetQuestion("2.0.0.127.in-addr.arpa.", dns.TypePTR)
-		s.handleRequest(r, m)
+		s.Mux.ServeDNS(r, m)
 		if got, want := len(r.response.Answer), 1; got != want {
 			t.Fatalf("unexpected number of answers: got %d, want %d", got, want)
 		}
@@ -136,7 +136,7 @@ func TestLocalhost(t *testing.T) {
 	t.Run("A", func(t *testing.T) {
 		m := new(dns.Msg)
 		m.SetQuestion("localhost.", dns.TypeA)
-		s.handleRequest(r, m)
+		s.Mux.ServeDNS(r, m)
 		if got, want := len(r.response.Answer), 1; got != want {
 			t.Fatalf("unexpected number of answers for %v: got %d, want %d", m.Question, got, want)
 		}
@@ -152,7 +152,7 @@ func TestLocalhost(t *testing.T) {
 	t.Run("AAAA", func(t *testing.T) {
 		m := new(dns.Msg)
 		m.SetQuestion("localhost.", dns.TypeAAAA)
-		s.handleRequest(r, m)
+		s.Mux.ServeDNS(r, m)
 		if got, want := len(r.response.Answer), 1; got != want {
 			t.Fatalf("unexpected number of answers for %v: got %d, want %d", m.Question, got, want)
 		}
@@ -168,7 +168,7 @@ func TestLocalhost(t *testing.T) {
 	t.Run("PTR", func(t *testing.T) {
 		m := new(dns.Msg)
 		m.SetQuestion("1.0.0.127.in-addr.arpa.", dns.TypePTR)
-		s.handleRequest(r, m)
+		s.Mux.ServeDNS(r, m)
 		if got, want := len(r.response.Answer), 1; got != want {
 			t.Fatalf("unexpected number of answers: got %d, want %d", got, want)
 		}
@@ -218,7 +218,7 @@ func TestDHCPReverse(t *testing.T) {
 			})
 			m := new(dns.Msg)
 			m.SetQuestion(test.question, dns.TypePTR)
-			s.handleRequest(r, m)
+			s.Mux.ServeDNS(r, m)
 			if got, want := len(r.response.Answer), 1; got != want {
 				t.Fatalf("unexpected number of answers: got %d, want %d", got, want)
 			}
@@ -237,7 +237,7 @@ func TestDHCPReverse(t *testing.T) {
 		s := NewServer("localhost:0", "lan")
 		m := new(dns.Msg)
 		m.SetQuestion("254.255.31.172.in-addr.arpa.", dns.TypePTR)
-		s.handleRequest(r, m)
+		s.Mux.ServeDNS(r, m)
 		if got, want := r.response.Rcode, dns.RcodeNameError; got != want {
 			t.Fatalf("unexpected rcode: got %v, want %v", got, want)
 		}