tailscale/ipn/ipnlocal/peerapi_test.go
James Tucker b4b2ec7801 ipn/ipnlocal: fix pretty printing of multi-record peer DNS results
The API on the DNS record parser is slightly subtle and requires
explicit handling of unhandled records. Failure to advance previously
resulted in an infinite loop in the pretty responder for any reply that
contains a record other than A/AAAA/TXT.

Updates tailscale/corp#16928

Signed-off-by: James Tucker <james@tailscale.com>
2024-01-31 15:59:17 -08:00

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// Copyright (c) Tailscale Inc & AUTHORS
// SPDX-License-Identifier: BSD-3-Clause
package ipnlocal
import (
"bytes"
"context"
"encoding/json"
"fmt"
"io"
"io/fs"
"math/rand"
"net/http"
"net/http/httptest"
"net/netip"
"os"
"path/filepath"
"slices"
"strings"
"testing"
"github.com/google/go-cmp/cmp"
"go4.org/netipx"
"golang.org/x/net/dns/dnsmessage"
"tailscale.com/appc"
"tailscale.com/appc/appctest"
"tailscale.com/client/tailscale/apitype"
"tailscale.com/ipn"
"tailscale.com/ipn/store/mem"
"tailscale.com/tailcfg"
"tailscale.com/taildrop"
"tailscale.com/tstest"
"tailscale.com/types/logger"
"tailscale.com/types/netmap"
"tailscale.com/util/must"
"tailscale.com/wgengine"
"tailscale.com/wgengine/filter"
)
type peerAPITestEnv struct {
ph *peerAPIHandler
rr *httptest.ResponseRecorder
logBuf tstest.MemLogger
}
type check func(*testing.T, *peerAPITestEnv)
func checks(vv ...check) []check { return vv }
func httpStatus(wantStatus int) check {
return func(t *testing.T, e *peerAPITestEnv) {
if res := e.rr.Result(); res.StatusCode != wantStatus {
t.Errorf("HTTP response code = %v; want %v", res.Status, wantStatus)
}
}
}
func bodyContains(sub string) check {
return func(t *testing.T, e *peerAPITestEnv) {
if body := e.rr.Body.String(); !strings.Contains(body, sub) {
t.Errorf("HTTP response body does not contain %q; got: %s", sub, body)
}
}
}
func bodyNotContains(sub string) check {
return func(t *testing.T, e *peerAPITestEnv) {
if body := e.rr.Body.String(); strings.Contains(body, sub) {
t.Errorf("HTTP response body unexpectedly contains %q; got: %s", sub, body)
}
}
}
func fileHasSize(name string, size int) check {
return func(t *testing.T, e *peerAPITestEnv) {
root := e.ph.ps.taildrop.Dir()
if root == "" {
t.Errorf("no rootdir; can't check whether %q has size %v", name, size)
return
}
path := filepath.Join(root, name)
if fi, err := os.Stat(path); err != nil {
t.Errorf("fileHasSize(%q, %v): %v", name, size, err)
} else if fi.Size() != int64(size) {
t.Errorf("file %q has size %v; want %v", name, fi.Size(), size)
}
}
}
func fileHasContents(name string, want string) check {
return func(t *testing.T, e *peerAPITestEnv) {
root := e.ph.ps.taildrop.Dir()
if root == "" {
t.Errorf("no rootdir; can't check contents of %q", name)
return
}
path := filepath.Join(root, name)
got, err := os.ReadFile(path)
if err != nil {
t.Errorf("fileHasContents: %v", err)
return
}
if string(got) != want {
t.Errorf("file contents = %q; want %q", got, want)
}
}
}
func hexAll(v string) string {
var sb strings.Builder
for i := 0; i < len(v); i++ {
fmt.Fprintf(&sb, "%%%02x", v[i])
}
return sb.String()
}
func TestHandlePeerAPI(t *testing.T) {
tests := []struct {
name string
isSelf bool // the peer sending the request is owned by us
capSharing bool // self node has file sharing capability
debugCap bool // self node has debug capability
omitRoot bool // don't configure
reqs []*http.Request
checks []check
}{
{
name: "not_peer_api",
isSelf: true,
capSharing: true,
reqs: []*http.Request{httptest.NewRequest("GET", "/", nil)},
checks: checks(
httpStatus(200),
bodyContains("This is my Tailscale device."),
bodyContains("You are the owner of this node."),
),
},
{
name: "not_peer_api_not_owner",
isSelf: false,
capSharing: true,
reqs: []*http.Request{httptest.NewRequest("GET", "/", nil)},
checks: checks(
httpStatus(200),
bodyContains("This is my Tailscale device."),
bodyNotContains("You are the owner of this node."),
),
},
{
name: "goroutines/deny-self-no-cap",
isSelf: true,
debugCap: false,
reqs: []*http.Request{httptest.NewRequest("GET", "/v0/goroutines", nil)},
checks: checks(httpStatus(403)),
},
{
name: "goroutines/deny-nonself",
isSelf: false,
debugCap: true,
reqs: []*http.Request{httptest.NewRequest("GET", "/v0/goroutines", nil)},
checks: checks(httpStatus(403)),
},
{
name: "goroutines/accept-self",
isSelf: true,
debugCap: true,
reqs: []*http.Request{httptest.NewRequest("GET", "/v0/goroutines", nil)},
checks: checks(
httpStatus(200),
bodyContains("ServeHTTP"),
),
},
{
name: "reject_non_owner_put",
isSelf: false,
capSharing: true,
reqs: []*http.Request{httptest.NewRequest("PUT", "/v0/put/foo", nil)},
checks: checks(
httpStatus(http.StatusForbidden),
bodyContains("Taildrop disabled"),
),
},
{
name: "owner_without_cap",
isSelf: true,
capSharing: false,
reqs: []*http.Request{httptest.NewRequest("PUT", "/v0/put/foo", nil)},
checks: checks(
httpStatus(http.StatusForbidden),
bodyContains("Taildrop disabled"),
),
},
{
name: "owner_with_cap_no_rootdir",
omitRoot: true,
isSelf: true,
capSharing: true,
reqs: []*http.Request{httptest.NewRequest("PUT", "/v0/put/foo", nil)},
checks: checks(
httpStatus(http.StatusForbidden),
bodyContains("Taildrop disabled; no storage directory"),
),
},
{
name: "bad_method",
isSelf: true,
capSharing: true,
reqs: []*http.Request{httptest.NewRequest("POST", "/v0/put/foo", nil)},
checks: checks(
httpStatus(405),
bodyContains("expected method GET or PUT"),
),
},
{
name: "put_zero_length",
isSelf: true,
capSharing: true,
reqs: []*http.Request{httptest.NewRequest("PUT", "/v0/put/foo", nil)},
checks: checks(
httpStatus(200),
bodyContains("{}"),
fileHasSize("foo", 0),
fileHasContents("foo", ""),
),
},
{
name: "put_non_zero_length_content_length",
isSelf: true,
capSharing: true,
reqs: []*http.Request{httptest.NewRequest("PUT", "/v0/put/foo", strings.NewReader("contents"))},
checks: checks(
httpStatus(200),
bodyContains("{}"),
fileHasSize("foo", len("contents")),
fileHasContents("foo", "contents"),
),
},
{
name: "put_non_zero_length_chunked",
isSelf: true,
capSharing: true,
reqs: []*http.Request{httptest.NewRequest("PUT", "/v0/put/foo", struct{ io.Reader }{strings.NewReader("contents")})},
checks: checks(
httpStatus(200),
bodyContains("{}"),
fileHasSize("foo", len("contents")),
fileHasContents("foo", "contents"),
),
},
{
name: "bad_filename_partial",
isSelf: true,
capSharing: true,
reqs: []*http.Request{httptest.NewRequest("PUT", "/v0/put/foo.partial", nil)},
checks: checks(
httpStatus(400),
bodyContains("invalid filename"),
),
},
{
name: "bad_filename_deleted",
isSelf: true,
capSharing: true,
reqs: []*http.Request{httptest.NewRequest("PUT", "/v0/put/foo.deleted", nil)},
checks: checks(
httpStatus(400),
bodyContains("invalid filename"),
),
},
{
name: "bad_filename_dot",
isSelf: true,
capSharing: true,
reqs: []*http.Request{httptest.NewRequest("PUT", "/v0/put/.", nil)},
checks: checks(
httpStatus(400),
bodyContains("invalid filename"),
),
},
{
name: "bad_filename_empty",
isSelf: true,
capSharing: true,
reqs: []*http.Request{httptest.NewRequest("PUT", "/v0/put/", nil)},
checks: checks(
httpStatus(400),
bodyContains("invalid filename"),
),
},
{
name: "bad_filename_slash",
isSelf: true,
capSharing: true,
reqs: []*http.Request{httptest.NewRequest("PUT", "/v0/put/foo/bar", nil)},
checks: checks(
httpStatus(400),
bodyContains("invalid filename"),
),
},
{
name: "bad_filename_encoded_dot",
isSelf: true,
capSharing: true,
reqs: []*http.Request{httptest.NewRequest("PUT", "/v0/put/"+hexAll("."), nil)},
checks: checks(
httpStatus(400),
bodyContains("invalid filename"),
),
},
{
name: "bad_filename_encoded_slash",
isSelf: true,
capSharing: true,
reqs: []*http.Request{httptest.NewRequest("PUT", "/v0/put/"+hexAll("/"), nil)},
checks: checks(
httpStatus(400),
bodyContains("invalid filename"),
),
},
{
name: "bad_filename_encoded_backslash",
isSelf: true,
capSharing: true,
reqs: []*http.Request{httptest.NewRequest("PUT", "/v0/put/"+hexAll("\\"), nil)},
checks: checks(
httpStatus(400),
bodyContains("invalid filename"),
),
},
{
name: "bad_filename_encoded_dotdot",
isSelf: true,
capSharing: true,
reqs: []*http.Request{httptest.NewRequest("PUT", "/v0/put/"+hexAll(".."), nil)},
checks: checks(
httpStatus(400),
bodyContains("invalid filename"),
),
},
{
name: "bad_filename_encoded_dotdot_out",
isSelf: true,
capSharing: true,
reqs: []*http.Request{httptest.NewRequest("PUT", "/v0/put/"+hexAll("foo/../../../../../etc/passwd"), nil)},
checks: checks(
httpStatus(400),
bodyContains("invalid filename"),
),
},
{
name: "put_spaces_and_caps",
isSelf: true,
capSharing: true,
reqs: []*http.Request{httptest.NewRequest("PUT", "/v0/put/"+hexAll("Foo Bar.dat"), strings.NewReader("baz"))},
checks: checks(
httpStatus(200),
bodyContains("{}"),
fileHasContents("Foo Bar.dat", "baz"),
),
},
{
name: "put_unicode",
isSelf: true,
capSharing: true,
reqs: []*http.Request{httptest.NewRequest("PUT", "/v0/put/"+hexAll("Томас и его друзья.mp3"), strings.NewReader("главный озорник"))},
checks: checks(
httpStatus(200),
bodyContains("{}"),
fileHasContents("Томас и его друзья.mp3", "главный озорник"),
),
},
{
name: "put_invalid_utf8",
isSelf: true,
capSharing: true,
reqs: []*http.Request{httptest.NewRequest("PUT", "/v0/put/"+(hexAll("😜")[:3]), nil)},
checks: checks(
httpStatus(400),
bodyContains("invalid filename"),
),
},
{
name: "put_invalid_null",
isSelf: true,
capSharing: true,
reqs: []*http.Request{httptest.NewRequest("PUT", "/v0/put/%00", nil)},
checks: checks(
httpStatus(400),
bodyContains("invalid filename"),
),
},
{
name: "put_invalid_non_printable",
isSelf: true,
capSharing: true,
reqs: []*http.Request{httptest.NewRequest("PUT", "/v0/put/%01", nil)},
checks: checks(
httpStatus(400),
bodyContains("invalid filename"),
),
},
{
name: "put_invalid_colon",
isSelf: true,
capSharing: true,
reqs: []*http.Request{httptest.NewRequest("PUT", "/v0/put/"+hexAll("nul:"), nil)},
checks: checks(
httpStatus(400),
bodyContains("invalid filename"),
),
},
{
name: "put_invalid_surrounding_whitespace",
isSelf: true,
capSharing: true,
reqs: []*http.Request{httptest.NewRequest("PUT", "/v0/put/"+hexAll(" foo "), nil)},
checks: checks(
httpStatus(400),
bodyContains("invalid filename"),
),
},
{
name: "host-val/bad-ip",
isSelf: true,
debugCap: true,
reqs: []*http.Request{httptest.NewRequest("GET", "http://12.23.45.66:1234/v0/env", nil)},
checks: checks(
httpStatus(403),
),
},
{
name: "host-val/no-port",
isSelf: true,
debugCap: true,
reqs: []*http.Request{httptest.NewRequest("GET", "http://100.100.100.101/v0/env", nil)},
checks: checks(
httpStatus(403),
),
},
{
name: "host-val/peer",
isSelf: true,
debugCap: true,
reqs: []*http.Request{httptest.NewRequest("GET", "http://peer/v0/env", nil)},
checks: checks(
httpStatus(200),
),
},
{
name: "duplicate_zero_length",
isSelf: true,
capSharing: true,
reqs: []*http.Request{
httptest.NewRequest("PUT", "/v0/put/foo", nil),
httptest.NewRequest("PUT", "/v0/put/foo", nil),
},
checks: checks(
httpStatus(200),
func(t *testing.T, env *peerAPITestEnv) {
got, err := env.ph.ps.taildrop.WaitingFiles()
if err != nil {
t.Fatalf("WaitingFiles error: %v", err)
}
want := []apitype.WaitingFile{{Name: "foo", Size: 0}}
if diff := cmp.Diff(got, want); diff != "" {
t.Fatalf("WaitingFile mismatch (-got +want):\n%s", diff)
}
},
),
},
{
name: "duplicate_non_zero_length_content_length",
isSelf: true,
capSharing: true,
reqs: []*http.Request{
httptest.NewRequest("PUT", "/v0/put/foo", strings.NewReader("contents")),
httptest.NewRequest("PUT", "/v0/put/foo", strings.NewReader("contents")),
},
checks: checks(
httpStatus(200),
func(t *testing.T, env *peerAPITestEnv) {
got, err := env.ph.ps.taildrop.WaitingFiles()
if err != nil {
t.Fatalf("WaitingFiles error: %v", err)
}
want := []apitype.WaitingFile{{Name: "foo", Size: 8}}
if diff := cmp.Diff(got, want); diff != "" {
t.Fatalf("WaitingFile mismatch (-got +want):\n%s", diff)
}
},
),
},
{
name: "duplicate_different_files",
isSelf: true,
capSharing: true,
reqs: []*http.Request{
httptest.NewRequest("PUT", "/v0/put/foo", strings.NewReader("fizz")),
httptest.NewRequest("PUT", "/v0/put/foo", strings.NewReader("buzz")),
},
checks: checks(
httpStatus(200),
func(t *testing.T, env *peerAPITestEnv) {
got, err := env.ph.ps.taildrop.WaitingFiles()
if err != nil {
t.Fatalf("WaitingFiles error: %v", err)
}
want := []apitype.WaitingFile{{Name: "foo", Size: 4}, {Name: "foo (1)", Size: 4}}
if diff := cmp.Diff(got, want); diff != "" {
t.Fatalf("WaitingFile mismatch (-got +want):\n%s", diff)
}
},
),
},
}
for _, tt := range tests {
t.Run(tt.name, func(t *testing.T) {
selfNode := &tailcfg.Node{
Addresses: []netip.Prefix{
netip.MustParsePrefix("100.100.100.101/32"),
},
}
if tt.debugCap {
selfNode.Capabilities = append(selfNode.Capabilities, tailcfg.CapabilityDebug)
}
var e peerAPITestEnv
lb := &LocalBackend{
logf: e.logBuf.Logf,
capFileSharing: tt.capSharing,
netMap: &netmap.NetworkMap{SelfNode: selfNode.View()},
clock: &tstest.Clock{},
}
e.ph = &peerAPIHandler{
isSelf: tt.isSelf,
selfNode: selfNode.View(),
peerNode: (&tailcfg.Node{
ComputedName: "some-peer-name",
}).View(),
ps: &peerAPIServer{
b: lb,
},
}
var rootDir string
if !tt.omitRoot {
rootDir = t.TempDir()
if e.ph.ps.taildrop == nil {
e.ph.ps.taildrop = taildrop.ManagerOptions{
Logf: e.logBuf.Logf,
Dir: rootDir,
}.New()
}
}
for _, req := range tt.reqs {
e.rr = httptest.NewRecorder()
if req.Host == "example.com" {
req.Host = "100.100.100.101:12345"
}
e.ph.ServeHTTP(e.rr, req)
}
for _, f := range tt.checks {
f(t, &e)
}
if t.Failed() && rootDir != "" {
t.Logf("Contents of %s:", rootDir)
des, _ := fs.ReadDir(os.DirFS(rootDir), ".")
for _, de := range des {
fi, err := de.Info()
if err != nil {
t.Log(err)
} else {
t.Logf(" %v %5d %s", fi.Mode(), fi.Size(), de.Name())
}
}
}
})
}
}
// Windows likes to hold on to file descriptors for some indeterminate
// amount of time after you close them and not let you delete them for
// a bit. So test that we work around that sufficiently.
func TestFileDeleteRace(t *testing.T) {
dir := t.TempDir()
ps := &peerAPIServer{
b: &LocalBackend{
logf: t.Logf,
capFileSharing: true,
clock: &tstest.Clock{},
},
taildrop: taildrop.ManagerOptions{
Logf: t.Logf,
Dir: dir,
}.New(),
}
ph := &peerAPIHandler{
isSelf: true,
peerNode: (&tailcfg.Node{
ComputedName: "some-peer-name",
}).View(),
selfNode: (&tailcfg.Node{
Addresses: []netip.Prefix{netip.MustParsePrefix("100.100.100.101/32")},
}).View(),
ps: ps,
}
buf := make([]byte, 2<<20)
for i := 0; i < 30; i++ {
rr := httptest.NewRecorder()
ph.ServeHTTP(rr, httptest.NewRequest("PUT", "http://100.100.100.101:123/v0/put/foo.txt", bytes.NewReader(buf[:rand.Intn(len(buf))])))
if res := rr.Result(); res.StatusCode != 200 {
t.Fatal(res.Status)
}
wfs, err := ps.taildrop.WaitingFiles()
if err != nil {
t.Fatal(err)
}
if len(wfs) != 1 {
t.Fatalf("waiting files = %d; want 1", len(wfs))
}
if err := ps.taildrop.DeleteFile("foo.txt"); err != nil {
t.Fatal(err)
}
wfs, err = ps.taildrop.WaitingFiles()
if err != nil {
t.Fatal(err)
}
if len(wfs) != 0 {
t.Fatalf("waiting files = %d; want 0", len(wfs))
}
}
}
func TestPeerAPIReplyToDNSQueries(t *testing.T) {
var h peerAPIHandler
h.isSelf = true
if !h.replyToDNSQueries() {
t.Errorf("for isSelf = false; want true")
}
h.isSelf = false
h.remoteAddr = netip.MustParseAddrPort("100.150.151.152:12345")
eng, _ := wgengine.NewFakeUserspaceEngine(logger.Discard, 0)
pm := must.Get(newProfileManager(new(mem.Store), t.Logf))
h.ps = &peerAPIServer{
b: &LocalBackend{
e: eng,
pm: pm,
store: pm.Store(),
},
}
if h.ps.b.OfferingExitNode() {
t.Fatal("unexpectedly offering exit node")
}
h.ps.b.pm.SetPrefs((&ipn.Prefs{
AdvertiseRoutes: []netip.Prefix{
netip.MustParsePrefix("0.0.0.0/0"),
netip.MustParsePrefix("::/0"),
},
}).View(), ipn.NetworkProfile{})
if !h.ps.b.OfferingExitNode() {
t.Fatal("unexpectedly not offering exit node")
}
if h.replyToDNSQueries() {
t.Errorf("unexpectedly doing DNS without filter")
}
h.ps.b.setFilter(filter.NewAllowNone(logger.Discard, new(netipx.IPSet)))
if h.replyToDNSQueries() {
t.Errorf("unexpectedly doing DNS without filter")
}
f := filter.NewAllowAllForTest(logger.Discard)
h.ps.b.setFilter(f)
if !h.replyToDNSQueries() {
t.Errorf("unexpectedly deny; wanted to be a DNS server")
}
// Also test IPv6.
h.remoteAddr = netip.MustParseAddrPort("[fe70::1]:12345")
if !h.replyToDNSQueries() {
t.Errorf("unexpectedly IPv6 deny; wanted to be a DNS server")
}
}
func TestPeerAPIPrettyReplyCNAME(t *testing.T) {
var h peerAPIHandler
h.remoteAddr = netip.MustParseAddrPort("100.150.151.152:12345")
eng, _ := wgengine.NewFakeUserspaceEngine(logger.Discard, 0)
pm := must.Get(newProfileManager(new(mem.Store), t.Logf))
h.ps = &peerAPIServer{
b: &LocalBackend{
e: eng,
pm: pm,
store: pm.Store(),
// configure as an app connector just to enable the API.
appConnector: appc.NewAppConnector(t.Logf, &appctest.RouteCollector{}),
},
}
h.ps.resolver = &fakeResolver{build: func(b *dnsmessage.Builder) {
b.CNAMEResource(
dnsmessage.ResourceHeader{
Name: dnsmessage.MustNewName("www.example.com."),
Type: dnsmessage.TypeCNAME,
Class: dnsmessage.ClassINET,
TTL: 0,
},
dnsmessage.CNAMEResource{
CNAME: dnsmessage.MustNewName("example.com."),
},
)
b.AResource(
dnsmessage.ResourceHeader{
Name: dnsmessage.MustNewName("example.com."),
Type: dnsmessage.TypeA,
Class: dnsmessage.ClassINET,
TTL: 0,
},
dnsmessage.AResource{
A: [4]byte{192, 0, 0, 8},
},
)
}}
f := filter.NewAllowAllForTest(logger.Discard)
h.ps.b.setFilter(f)
if !h.replyToDNSQueries() {
t.Errorf("unexpectedly deny; wanted to be a DNS server")
}
w := httptest.NewRecorder()
h.handleDNSQuery(w, httptest.NewRequest("GET", "/dns-query?q=www.example.com.", nil))
if w.Code != http.StatusOK {
t.Errorf("unexpected status code: %v", w.Code)
}
var addrs []string
json.NewDecoder(w.Body).Decode(&addrs)
if len(addrs) == 0 {
t.Fatalf("no addresses returned")
}
for _, addr := range addrs {
netip.MustParseAddr(addr)
}
}
func TestPeerAPIReplyToDNSQueriesAreObserved(t *testing.T) {
ctx := context.Background()
var h peerAPIHandler
h.remoteAddr = netip.MustParseAddrPort("100.150.151.152:12345")
rc := &appctest.RouteCollector{}
eng, _ := wgengine.NewFakeUserspaceEngine(logger.Discard, 0)
pm := must.Get(newProfileManager(new(mem.Store), t.Logf))
h.ps = &peerAPIServer{
b: &LocalBackend{
e: eng,
pm: pm,
store: pm.Store(),
appConnector: appc.NewAppConnector(t.Logf, rc),
},
}
h.ps.b.appConnector.UpdateDomains([]string{"example.com"})
h.ps.b.appConnector.Wait(ctx)
h.ps.resolver = &fakeResolver{build: func(b *dnsmessage.Builder) {
b.AResource(
dnsmessage.ResourceHeader{
Name: dnsmessage.MustNewName("example.com."),
Type: dnsmessage.TypeA,
Class: dnsmessage.ClassINET,
TTL: 0,
},
dnsmessage.AResource{
A: [4]byte{192, 0, 0, 8},
},
)
}}
f := filter.NewAllowAllForTest(logger.Discard)
h.ps.b.setFilter(f)
if !h.ps.b.OfferingAppConnector() {
t.Fatal("expecting to be offering app connector")
}
if !h.replyToDNSQueries() {
t.Errorf("unexpectedly deny; wanted to be a DNS server")
}
w := httptest.NewRecorder()
h.handleDNSQuery(w, httptest.NewRequest("GET", "/dns-query?q=example.com.", nil))
if w.Code != http.StatusOK {
t.Errorf("unexpected status code: %v", w.Code)
}
h.ps.b.appConnector.Wait(ctx)
wantRoutes := []netip.Prefix{netip.MustParsePrefix("192.0.0.8/32")}
if !slices.Equal(rc.Routes(), wantRoutes) {
t.Errorf("got %v; want %v", rc.Routes(), wantRoutes)
}
}
type fakeResolver struct {
build func(*dnsmessage.Builder)
}
func (f *fakeResolver) HandlePeerDNSQuery(ctx context.Context, q []byte, from netip.AddrPort, allowName func(name string) bool) (res []byte, err error) {
b := dnsmessage.NewBuilder(nil, dnsmessage.Header{})
b.EnableCompression()
b.StartAnswers()
f.build(&b)
return b.Finish()
}