net/dns/resolver: unexport Packet, only use it internally.

Signed-off-by: David Anderson <danderson@tailscale.com>

net/dns/resolver/forwarder.go

@@ -105,7 +105,7 @@ type forwarder struct {
 	logf logger.Logf
 
 	// responses is a channel by which responses are returned.
-	responses chan Packet
+	responses chan packet
 	// closed signals all goroutines to stop.
 	closed chan struct{}
 	// wg signals when all goroutines have stopped.
@@ -126,7 +126,7 @@ func init() {
 	rand.Seed(time.Now().UnixNano())
 }
 
-func newForwarder(logf logger.Logf, responses chan Packet) *forwarder {
+func newForwarder(logf logger.Logf, responses chan packet) *forwarder {
 	return &forwarder{
 		logf:      logger.WithPrefix(logf, "forward: "),
 		responses: responses,
@@ -218,14 +218,11 @@ func (f *forwarder) recv(conn *fwdConn) {
 
 		f.mu.Unlock()
 
-		packet := Packet{
-			Payload: out,
-			Addr:    record.src,
-		}
+		pkt := packet{out, record.src}
 		select {
 		case <-f.closed:
 			return
-		case f.responses <- packet:
+		case f.responses <- pkt:
 			// continue
 		}
 	}
@@ -258,8 +255,8 @@ func (f *forwarder) cleanMap() {
 }
 
 // forward forwards the query to all upstream nameservers and returns the first response.
-func (f *forwarder) forward(query Packet) error {
-	txid := getTxID(query.Payload)
+func (f *forwarder) forward(query packet) error {
+	txid := getTxID(query.bs)
 
 	f.mu.Lock()
 
@@ -269,14 +266,14 @@ func (f *forwarder) forward(query Packet) error {
 		return errNoUpstreams
 	}
 	f.txMap[txid] = forwardingRecord{
-		src:       query.Addr,
+		src:       query.addr,
 		createdAt: time.Now(),
 	}
 
 	f.mu.Unlock()
 
 	for _, upstream := range upstreams {
-		f.send(query.Payload, upstream)
+		f.send(query.bs, upstream)
 	}
 
 	return nil

net/dns/resolver/tsdns.go

@@ -44,14 +44,9 @@ var (
 	errNotOurName     = errors.New("not a Tailscale DNS name")
 )
 
-// Packet represents a DNS payload together with the address of its origin.
-type Packet struct {
-	// Payload is the application layer DNS payload.
-	// Resolver assumes ownership of the request payload when it is enqueued
-	// and cedes ownership of the response payload when it is returned from NextResponse.
-	Payload []byte
-	// Addr is the source address for a request and the destination address for a response.
-	Addr netaddr.IPPort
+type packet struct {
+	bs   []byte
+	addr netaddr.IPPort // src for a request, dst for a response
 }
 
 // Resolver is a DNS resolver for nodes on the Tailscale network,
@@ -66,9 +61,9 @@ type Resolver struct {
 	forwarder *forwarder
 
 	// queue is a buffered channel holding DNS requests queued for resolution.
-	queue chan Packet
+	queue chan packet
 	// responses is an unbuffered channel to which responses are returned.
-	responses chan Packet
+	responses chan packet
 	// errors is an unbuffered channel to which errors are returned.
 	errors chan error
 	// closed signals all goroutines to stop.
@@ -88,8 +83,8 @@ func New(logf logger.Logf, linkMon *monitor.Mon) (*Resolver, error) {
 	r := &Resolver{
 		logf:      logger.WithPrefix(logf, "dns: "),
 		linkMon:   linkMon,
-		queue:     make(chan Packet, queueSize),
-		responses: make(chan Packet),
+		queue:     make(chan packet, queueSize),
+		responses: make(chan packet),
 		errors:    make(chan error),
 		closed:    make(chan struct{}),
 	}
@@ -153,11 +148,11 @@ func (r *Resolver) SetUpstreams(upstreams []net.Addr) {
 // EnqueueRequest places the given DNS request in the resolver's queue.
 // It takes ownership of the payload and does not block.
 // If the queue is full, the request will be dropped and an error will be returned.
-func (r *Resolver) EnqueueRequest(request Packet) error {
+func (r *Resolver) EnqueueRequest(bs []byte, from netaddr.IPPort) error {
 	select {
 	case <-r.closed:
 		return ErrClosed
-	case r.queue <- request:
+	case r.queue <- packet{bs, from}:
 		return nil
 	default:
 		return errFullQueue
@@ -166,14 +161,14 @@ func (r *Resolver) EnqueueRequest(request Packet) error {
 
 // NextResponse returns a DNS response to a previously enqueued request.
 // It blocks until a response is available and gives up ownership of the response payload.
-func (r *Resolver) NextResponse() (Packet, error) {
+func (r *Resolver) NextResponse() (packet []byte, to netaddr.IPPort, err error) {
 	select {
 	case <-r.closed:
-		return Packet{}, ErrClosed
+		return nil, netaddr.IPPort{}, ErrClosed
 	case resp := <-r.responses:
-		return resp, nil
+		return resp.bs, resp.addr, nil
 	case err := <-r.errors:
-		return Packet{}, err
+		return nil, netaddr.IPPort{}, err
 	}
 }
 
@@ -266,19 +261,19 @@ func (r *Resolver) ResolveReverse(ip netaddr.IP) (string, dns.RCode, error) {
 func (r *Resolver) poll() {
 	defer r.wg.Done()
 
-	var packet Packet
+	var pkt packet
 	for {
 		select {
 		case <-r.closed:
 			return
-		case packet = <-r.queue:
+		case pkt = <-r.queue:
 			// continue
 		}
 
-		out, err := r.respond(packet.Payload)
+		out, err := r.respond(pkt.bs)
 
 		if err == errNotOurName {
-			err = r.forwarder.forward(packet)
+			err = r.forwarder.forward(pkt)
 			if err == nil {
 				// forward will send response into r.responses, nothing to do.
 				continue
@@ -293,11 +288,11 @@ func (r *Resolver) poll() {
 				// continue
 			}
 		} else {
-			packet.Payload = out
+			pkt.bs = out
 			select {
 			case <-r.closed:
 				return
-			case r.responses <- packet:
+			case r.responses <- pkt:
 				// continue
 			}
 		}

net/dns/resolver/tsdns_test.go

@@ -109,10 +109,9 @@ func unpackResponse(payload []byte) (dnsResponse, error) {
 }
 
 func syncRespond(r *Resolver, query []byte) ([]byte, error) {
-	request := Packet{Payload: query}
-	r.EnqueueRequest(request)
-	resp, err := r.NextResponse()
-	return resp.Payload, err
+	r.EnqueueRequest(query, netaddr.IPPort{})
+	payload, _, err := r.NextResponse()
+	return payload, err
 }
 
 func mustIP(str string) netaddr.IP {
@@ -418,21 +417,20 @@ func TestDelegateCollision(t *testing.T) {
 	// packets will have the same dns txid.
 	for _, p := range packets {
 		payload := dnspacket(p.qname, p.qtype)
-		req := Packet{Payload: payload, Addr: p.addr}
-		err := r.EnqueueRequest(req)
+		err := r.EnqueueRequest(payload, p.addr)
 		if err != nil {
 			t.Error(err)
 		}
 	}
 
 	// Despite the txid collision, the answer(s) should still match the query.
-	resp, err := r.NextResponse()
+	resp, addr, err := r.NextResponse()
 	if err != nil {
 		t.Error(err)
 	}
 
 	var p dns.Parser
-	_, err = p.Start(resp.Payload)
+	_, err = p.Start(resp)
 	if err != nil {
 		t.Error(err)
 	}
@@ -456,8 +454,8 @@ func TestDelegateCollision(t *testing.T) {
 	}
 
 	for _, p := range packets {
-		if p.qtype == wantType && p.addr != resp.Addr {
-			t.Errorf("addr = %v; want %v", resp.Addr, p.addr)
+		if p.qtype == wantType && p.addr != addr {
+			t.Errorf("addr = %v; want %v", addr, p.addr)
 		}
 	}
 }

wgengine/userspace.go

@@ -433,11 +433,7 @@ func (e *userspaceEngine) handleLocalPackets(p *packet.Parsed, t *tstun.Wrapper)
 // handleDNS is an outbound pre-filter resolving Tailscale domains.
 func (e *userspaceEngine) handleDNS(p *packet.Parsed, t *tstun.Wrapper) filter.Response {
 	if p.Dst.IP == magicDNSIP && p.Dst.Port == magicDNSPort && p.IPProto == ipproto.UDP {
-		request := resolver.Packet{
-			Payload: append([]byte(nil), p.Payload()...),
-			Addr:    netaddr.IPPort{IP: p.Src.IP, Port: p.Src.Port},
-		}
-		err := e.resolver.EnqueueRequest(request)
+		err := e.resolver.EnqueueRequest(append([]byte(nil), p.Payload()...), p.Src)
 		if err != nil {
 			e.logf("dns: enqueue: %v", err)
 		}
@@ -449,7 +445,7 @@ func (e *userspaceEngine) handleDNS(p *packet.Parsed, t *tstun.Wrapper) filter.R
 // pollResolver reads responses from the DNS resolver and injects them inbound.
 func (e *userspaceEngine) pollResolver() {
 	for {
-		resp, err := e.resolver.NextResponse()
+		bs, to, err := e.resolver.NextResponse()
 		if err == resolver.ErrClosed {
 			return
 		}
@@ -461,17 +457,17 @@ func (e *userspaceEngine) pollResolver() {
 		h := packet.UDP4Header{
 			IP4Header: packet.IP4Header{
 				Src: magicDNSIP,
-				Dst: resp.Addr.IP,
+				Dst: to.IP,
 			},
 			SrcPort: magicDNSPort,
-			DstPort: resp.Addr.Port,
+			DstPort: to.Port,
 		}
 		hlen := h.Len()
 
 		// TODO(dmytro): avoid this allocation without importing tstun quirks into dns.
 		const offset = tstun.PacketStartOffset
-		buf := make([]byte, offset+hlen+len(resp.Payload))
-		copy(buf[offset+hlen:], resp.Payload)
+		buf := make([]byte, offset+hlen+len(bs))
+		copy(buf[offset+hlen:], bs)
 		h.Marshal(buf[offset:])
 
 		e.tundev.InjectInboundDirect(buf, offset)