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tsdns.go
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tsdns.go
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// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Package resolver implements a stub DNS resolver that can also serve
// records out of an internal local zone.
package resolver
import (
"bufio"
"bytes"
"context"
"encoding/hex"
"errors"
"fmt"
"io"
"net"
"os"
"runtime"
"sort"
"strings"
"sync"
"sync/atomic"
"time"
"go4.org/mem"
dns "golang.org/x/net/dns/dnsmessage"
"inet.af/netaddr"
"tailscale.com/net/tsaddr"
"tailscale.com/net/tsdial"
"tailscale.com/types/dnstype"
"tailscale.com/types/logger"
"tailscale.com/util/clientmetric"
"tailscale.com/util/dnsname"
"tailscale.com/util/lineread"
"tailscale.com/wgengine/monitor"
)
// maxResponseBytes is the maximum size of a response from a Resolver. The
// actual buffer size will be one larger than this so that we can detect
// truncation in a platform-agnostic way.
const maxResponseBytes = 4095
// maxActiveQueries returns the maximal number of DNS requests that be
// can running.
// If EnqueueRequest is called when this many requests are already pending,
// the request will be dropped to avoid blocking the caller.
func maxActiveQueries() int32 {
if runtime.GOOS == "ios" {
// For memory paranoia reasons on iOS, match the
// historical Tailscale 1.x..1.8 behavior for now
// (just before the 1.10 release).
return 64
}
// But for other platforms, allow more burstiness:
return 256
}
// defaultTTL is the TTL of all responses from Resolver.
const defaultTTL = 600 * time.Second
// ErrClosed indicates that the resolver has been closed and readers should exit.
var ErrClosed = errors.New("closed")
var (
errFullQueue = errors.New("request queue full")
errNotQuery = errors.New("not a DNS query")
errNotOurName = errors.New("not a Tailscale DNS name")
)
type packet struct {
bs []byte
addr netaddr.IPPort // src for a request, dst for a response
}
// Config is a resolver configuration.
// Given a Config, queries are resolved in the following order:
// If the query is an exact match for an entry in LocalHosts, return that.
// Else if the query suffix matches an entry in LocalDomains, return NXDOMAIN.
// Else forward the query to the most specific matching entry in Routes.
// Else return SERVFAIL.
type Config struct {
// Routes is a map of DNS name suffix to the resolvers to use for
// queries within that suffix.
// Queries only match the most specific suffix.
// To register a "default route", add an entry for ".".
Routes map[dnsname.FQDN][]dnstype.Resolver
// LocalHosts is a map of FQDNs to corresponding IPs.
Hosts map[dnsname.FQDN][]netaddr.IP
// LocalDomains is a list of DNS name suffixes that should not be
// routed to upstream resolvers.
LocalDomains []dnsname.FQDN
}
// WriteToBufioWriter write a debug version of c for logs to w, omitting
// spammy stuff like *.arpa entries and replacing it with a total count.
func (c *Config) WriteToBufioWriter(w *bufio.Writer) {
w.WriteString("{Routes:")
WriteRoutes(w, c.Routes)
fmt.Fprintf(w, " Hosts:%v LocalDomains:[", len(c.Hosts))
space := false
arpa := 0
for _, d := range c.LocalDomains {
if strings.HasSuffix(string(d), ".arpa.") {
arpa++
continue
}
if space {
w.WriteByte(' ')
}
w.WriteString(string(d))
space = true
}
w.WriteString("]")
if arpa > 0 {
fmt.Fprintf(w, "+%darpa", arpa)
}
w.WriteString("}")
}
// WriteIPPorts writes vv to w.
func WriteIPPorts(w *bufio.Writer, vv []netaddr.IPPort) {
w.WriteByte('[')
var b []byte
for i, v := range vv {
if i > 0 {
w.WriteByte(' ')
}
b = v.AppendTo(b[:0])
w.Write(b)
}
w.WriteByte(']')
}
// WriteDNSResolver writes r to w.
func WriteDNSResolver(w *bufio.Writer, r dnstype.Resolver) {
io.WriteString(w, r.Addr)
if len(r.BootstrapResolution) > 0 {
w.WriteByte('(')
var b []byte
for _, ip := range r.BootstrapResolution {
ip.AppendTo(b[:0])
w.Write(b)
}
w.WriteByte(')')
}
}
// WriteDNSResolvers writes resolvers to w.
func WriteDNSResolvers(w *bufio.Writer, resolvers []dnstype.Resolver) {
w.WriteByte('[')
for i, r := range resolvers {
if i > 0 {
w.WriteByte(' ')
}
WriteDNSResolver(w, r)
}
w.WriteByte(']')
}
// WriteRoutes writes routes to w, omitting *.arpa routes and instead
// summarizing how many of them there were.
func WriteRoutes(w *bufio.Writer, routes map[dnsname.FQDN][]dnstype.Resolver) {
var kk []dnsname.FQDN
arpa := 0
for k := range routes {
if strings.HasSuffix(string(k), ".arpa.") {
arpa++
continue
}
kk = append(kk, k)
}
sort.Slice(kk, func(i, j int) bool { return kk[i] < kk[j] })
w.WriteByte('{')
for i, k := range kk {
if i > 0 {
w.WriteByte(' ')
}
w.WriteString(string(k))
w.WriteByte(':')
WriteDNSResolvers(w, routes[k])
}
w.WriteByte('}')
if arpa > 0 {
fmt.Fprintf(w, "+%darpa", arpa)
}
}
// Resolver is a DNS resolver for nodes on the Tailscale network,
// associating them with domain names of the form <mynode>.<mydomain>.<root>.
// If it is asked to resolve a domain that is not of that form,
// it delegates to upstream nameservers if any are set.
type Resolver struct {
logf logger.Logf
linkMon *monitor.Mon // or nil
dialer *tsdial.Dialer // non-nil
saveConfigForTests func(cfg Config) // used in tests to capture resolver config
// forwarder forwards requests to upstream nameservers.
forwarder *forwarder
activeQueriesAtomic int32 // number of DNS queries in flight
// responses is an unbuffered channel to which responses are returned.
responses chan packet
// errors is an unbuffered channel to which errors are returned.
errors chan error
// closed signals all goroutines to stop.
closed chan struct{}
// wg signals when all goroutines have stopped.
wg sync.WaitGroup
// mu guards the following fields from being updated while used.
mu sync.Mutex
localDomains []dnsname.FQDN
hostToIP map[dnsname.FQDN][]netaddr.IP
ipToHost map[netaddr.IP]dnsname.FQDN
}
type ForwardLinkSelector interface {
// PickLink returns which network device should be used to query
// the DNS server at the given IP.
// The empty string means to use an unspecified default.
PickLink(netaddr.IP) (linkName string)
}
// New returns a new resolver.
// linkMon optionally specifies a link monitor to use for socket rebinding.
func New(logf logger.Logf, linkMon *monitor.Mon, linkSel ForwardLinkSelector, dialer *tsdial.Dialer) *Resolver {
if dialer == nil {
panic("nil Dialer")
}
r := &Resolver{
logf: logger.WithPrefix(logf, "resolver: "),
linkMon: linkMon,
responses: make(chan packet),
errors: make(chan error),
closed: make(chan struct{}),
hostToIP: map[dnsname.FQDN][]netaddr.IP{},
ipToHost: map[netaddr.IP]dnsname.FQDN{},
dialer: dialer,
}
r.forwarder = newForwarder(r.logf, r.responses, linkMon, linkSel, dialer)
return r
}
func (r *Resolver) TestOnlySetHook(hook func(Config)) { r.saveConfigForTests = hook }
func (r *Resolver) SetConfig(cfg Config) error {
if r.saveConfigForTests != nil {
r.saveConfigForTests(cfg)
}
reverse := make(map[netaddr.IP]dnsname.FQDN, len(cfg.Hosts))
for host, ips := range cfg.Hosts {
for _, ip := range ips {
reverse[ip] = host
}
}
r.forwarder.setRoutes(cfg.Routes)
r.mu.Lock()
defer r.mu.Unlock()
r.localDomains = cfg.LocalDomains
r.hostToIP = cfg.Hosts
r.ipToHost = reverse
return nil
}
// Close shuts down the resolver and ensures poll goroutines have exited.
// The Resolver cannot be used again after Close is called.
func (r *Resolver) Close() {
select {
case <-r.closed:
return
default:
// continue
}
close(r.closed)
r.forwarder.Close()
}
// 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(bs []byte, from netaddr.IPPort) error {
metricDNSQueryLocal.Add(1)
select {
case <-r.closed:
metricDNSQueryErrorClosed.Add(1)
return ErrClosed
default:
}
if n := atomic.AddInt32(&r.activeQueriesAtomic, 1); n > maxActiveQueries() {
atomic.AddInt32(&r.activeQueriesAtomic, -1)
metricDNSQueryErrorQueue.Add(1)
return errFullQueue
}
go r.handleQuery(packet{bs, from})
return nil
}
// 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 []byte, to netaddr.IPPort, err error) {
select {
case <-r.closed:
return nil, netaddr.IPPort{}, ErrClosed
case resp := <-r.responses:
return resp.bs, resp.addr, nil
case err := <-r.errors:
return nil, netaddr.IPPort{}, err
}
}
// parseExitNodeQuery parses a DNS request packet.
// It returns nil if it's malformed or lacking a question.
func parseExitNodeQuery(q []byte) *response {
p := dnsParserPool.Get().(*dnsParser)
defer dnsParserPool.Put(p)
p.zeroParser()
defer p.zeroParser()
if err := p.parseQuery(q); err != nil {
return nil
}
return p.response()
}
// HandleExitNodeDNSQuery handles a DNS query that arrived from a peer
// via the peerapi's DoH server. This is only used when the local
// node is being an exit node.
//
// The provided allowName callback is whether a DNS query for a name
// (as found by parsing q) is allowed.
//
// In most (all?) cases, err will be nil. A bogus DNS query q will
// still result in a response DNS packet (saying there's a failure)
// and a nil error.
// TODO: figure out if we even need an error result.
func (r *Resolver) HandleExitNodeDNSQuery(ctx context.Context, q []byte, from netaddr.IPPort, allowName func(name string) bool) (res []byte, err error) {
metricDNSExitProxyQuery.Add(1)
ch := make(chan packet, 1)
resp := parseExitNodeQuery(q)
if resp == nil {
return nil, errors.New("bad query")
}
name := resp.Question.Name.String()
if !allowName(name) {
metricDNSExitProxyErrorName.Add(1)
resp.Header.RCode = dns.RCodeRefused
return marshalResponse(resp)
}
switch runtime.GOOS {
default:
return nil, errors.New("unsupported exit node OS")
case "windows", "android":
return handleExitNodeDNSQueryWithNetPkg(ctx, nil, resp)
case "darwin":
// /etc/resolv.conf is a lie and only says one upstream DNS
// but for now that's probably good enough. Later we'll
// want to blend in everything from scutil --dns.
fallthrough
case "linux", "freebsd", "openbsd", "illumos":
nameserver, err := stubResolverForOS()
if err != nil {
r.logf("stubResolverForOS: %v", err)
metricDNSExitProxyErrorResolvConf.Add(1)
return nil, err
}
// TODO: more than 1 resolver from /etc/resolv.conf?
var resolvers []resolverAndDelay
if nameserver == tsaddr.TailscaleServiceIP() || nameserver == tsaddr.TailscaleServiceIPv6() {
// If resolv.conf says 100.100.100.100, it's coming right back to us anyway
// so avoid the loop through the kernel and just do what we
// would've done anyway. By not passing any resolvers, the forwarder
// will use its default ones from our DNS config.
} else {
resolvers = []resolverAndDelay{{
name: dnstype.Resolver{Addr: net.JoinHostPort(nameserver.String(), "53")},
}}
}
err = r.forwarder.forwardWithDestChan(ctx, packet{q, from}, ch, resolvers...)
if err != nil {
metricDNSExitProxyErrorForward.Add(1)
return nil, err
}
}
select {
case p, ok := <-ch:
if ok {
return p.bs, nil
}
panic("unexpected close chan")
default:
panic("unexpected unreadable chan")
}
}
// handleExitNodeDNSQueryWithNetPkg takes a DNS query message in q and
// return a reply (for the ExitDNS DoH service) using the net package's
// native APIs. This is only used on Windows for now.
//
// If resolver is nil, the net.Resolver zero value is used.
//
// response contains the pre-serialized response, which notably
// includes the original question and its header.
func handleExitNodeDNSQueryWithNetPkg(ctx context.Context, resolver *net.Resolver, resp *response) (res []byte, err error) {
if resp.Question.Class != dns.ClassINET {
return nil, errors.New("unsupported class")
}
r := resolver
if r == nil {
r = new(net.Resolver)
}
name := resp.Question.Name.String()
handleError := func(err error) (res []byte, _ error) {
if isGoNoSuchHostError(err) {
resp.Header.RCode = dns.RCodeNameError
return marshalResponse(resp)
}
// TODO: map other errors to RCodeServerFailure?
// Or I guess our caller should do that?
return nil, err
}
resp.Header.RCode = dns.RCodeSuccess // unless changed below
switch resp.Question.Type {
case dns.TypeA, dns.TypeAAAA:
network := "ip4"
if resp.Question.Type == dns.TypeAAAA {
network = "ip6"
}
ips, err := r.LookupIP(ctx, network, name)
if err != nil {
return handleError(err)
}
for _, stdIP := range ips {
if ip, ok := netaddr.FromStdIP(stdIP); ok {
resp.IPs = append(resp.IPs, ip)
}
}
case dns.TypeTXT:
strs, err := r.LookupTXT(ctx, name)
if err != nil {
return handleError(err)
}
resp.TXT = strs
case dns.TypePTR:
ipStr, ok := unARPA(name)
if !ok {
// TODO: is this RCodeFormatError?
return nil, errors.New("bogus PTR name")
}
addrs, err := r.LookupAddr(ctx, ipStr)
if err != nil {
return handleError(err)
}
if len(addrs) > 0 {
resp.Name, _ = dnsname.ToFQDN(addrs[0])
}
case dns.TypeCNAME:
cname, err := r.LookupCNAME(ctx, name)
if err != nil {
return handleError(err)
}
resp.CNAME = cname
case dns.TypeSRV:
// Thanks, Go: "To accommodate services publishing SRV
// records under non-standard names, if both service
// and proto are empty strings, LookupSRV looks up
// name directly."
_, srvs, err := r.LookupSRV(ctx, "", "", name)
if err != nil {
return handleError(err)
}
resp.SRVs = srvs
case dns.TypeNS:
nss, err := r.LookupNS(ctx, name)
if err != nil {
return handleError(err)
}
resp.NSs = nss
default:
return nil, fmt.Errorf("unsupported record type %v", resp.Question.Type)
}
return marshalResponse(resp)
}
func isGoNoSuchHostError(err error) bool {
if de, ok := err.(*net.DNSError); ok {
return de.IsNotFound
}
return false
}
type resolvConfCache struct {
mod time.Time
size int64
ip netaddr.IP
// TODO: inode/dev?
}
// resolvConfCacheValue contains the most recent stat metadata and parsed
// version of /etc/resolv.conf.
var resolvConfCacheValue atomic.Value // of resolvConfCache
var errEmptyResolvConf = errors.New("resolv.conf has no nameservers")
// stubResolverForOS returns the IP address of the first nameserver in
// /etc/resolv.conf.
func stubResolverForOS() (ip netaddr.IP, err error) {
fi, err := os.Stat("/etc/resolv.conf")
if err != nil {
return netaddr.IP{}, err
}
cur := resolvConfCache{
mod: fi.ModTime(),
size: fi.Size(),
}
if c, ok := resolvConfCacheValue.Load().(resolvConfCache); ok && c.mod == cur.mod && c.size == cur.size {
return c.ip, nil
}
// TODO(bradfitz): unify this /etc/resolv.conf parsing code with readResolv
// in net/dns, which we can't use due to circular dependency reasons.
// Move it to a leaf, including the OSConfig type (perhaps in its own dnstype
// package?)
err = lineread.File("/etc/resolv.conf", func(line []byte) error {
if !ip.IsZero() {
return nil
}
line = bytes.TrimSpace(line)
if len(line) == 0 || line[0] == '#' {
return nil
}
// Normalize tabs to spaces to simplify parsing code later.
for i, b := range line {
if b == '\t' {
line[i] = ' '
}
}
if mem.HasPrefix(mem.B(line), mem.S("nameserver ")) {
s := strings.TrimSpace(strings.TrimPrefix(string(line), "nameserver "))
ip, err = netaddr.ParseIP(s)
return err
}
return nil
})
if err != nil {
return netaddr.IP{}, err
}
if !ip.IsValid() {
return netaddr.IP{}, errEmptyResolvConf
}
cur.ip = ip
resolvConfCacheValue.Store(cur)
return ip, nil
}
// resolveLocal returns an IP for the given domain, if domain is in
// the local hosts map and has an IP corresponding to the requested
// typ (A, AAAA, ALL).
// Returns dns.RCodeRefused to indicate that the local map is not
// authoritative for domain.
func (r *Resolver) resolveLocal(domain dnsname.FQDN, typ dns.Type) (netaddr.IP, dns.RCode) {
metricDNSResolveLocal.Add(1)
// Reject .onion domains per RFC 7686.
if dnsname.HasSuffix(domain.WithoutTrailingDot(), ".onion") {
metricDNSResolveLocalErrorOnion.Add(1)
return netaddr.IP{}, dns.RCodeNameError
}
r.mu.Lock()
hosts := r.hostToIP
localDomains := r.localDomains
r.mu.Unlock()
addrs, found := hosts[domain]
if !found {
for _, suffix := range localDomains {
if suffix.Contains(domain) {
// We are authoritative for the queried domain.
metricDNSResolveLocalErrorMissing.Add(1)
return netaddr.IP{}, dns.RCodeNameError
}
}
// Not authoritative, signal that forwarding is advisable.
return netaddr.IP{}, dns.RCodeRefused
}
// Refactoring note: this must happen after we check suffixes,
// otherwise we will respond with NOTIMP to requests that should be forwarded.
//
// DNS semantics subtlety: when a DNS name exists, but no records
// are available for the requested record type, we must return
// RCodeSuccess with no data, not NXDOMAIN.
switch typ {
case dns.TypeA:
for _, ip := range addrs {
if ip.Is4() {
metricDNSResolveLocalOKA.Add(1)
return ip, dns.RCodeSuccess
}
}
metricDNSResolveLocalNoA.Add(1)
return netaddr.IP{}, dns.RCodeSuccess
case dns.TypeAAAA:
for _, ip := range addrs {
if ip.Is6() {
metricDNSResolveLocalOKAAAA.Add(1)
return ip, dns.RCodeSuccess
}
}
metricDNSResolveLocalNoAAAA.Add(1)
return netaddr.IP{}, dns.RCodeSuccess
case dns.TypeALL:
// Answer with whatever we've got.
// It could be IPv4, IPv6, or a zero addr.
// TODO: Return all available resolutions (A and AAAA, if we have them).
if len(addrs) == 0 {
metricDNSResolveLocalNoAll.Add(1)
return netaddr.IP{}, dns.RCodeSuccess
}
metricDNSResolveLocalOKAll.Add(1)
return addrs[0], dns.RCodeSuccess
// Leave some some record types explicitly unimplemented.
// These types relate to recursive resolution or special
// DNS semantics and might be implemented in the future.
case dns.TypeNS, dns.TypeSOA, dns.TypeAXFR, dns.TypeHINFO:
metricDNSResolveNotImplType.Add(1)
return netaddr.IP{}, dns.RCodeNotImplemented
// For everything except for the few types above that are explicitly not implemented, return no records.
// This is what other DNS systems do: always return NOERROR
// without any records whenever the requested record type is unknown.
// You can try this with:
// dig -t TYPE9824 example.com
// and note that NOERROR is returned, despite that record type being made up.
default:
metricDNSResolveNoRecordType.Add(1)
// The name exists, but no records exist of the requested type.
return netaddr.IP{}, dns.RCodeSuccess
}
}
// resolveReverse returns the unique domain name that maps to the given address.
func (r *Resolver) resolveLocalReverse(name dnsname.FQDN) (dnsname.FQDN, dns.RCode) {
var ip netaddr.IP
var ok bool
switch {
case strings.HasSuffix(name.WithTrailingDot(), rdnsv4Suffix):
ip, ok = rdnsNameToIPv4(name)
case strings.HasSuffix(name.WithTrailingDot(), rdnsv6Suffix):
ip, ok = rdnsNameToIPv6(name)
}
if !ok {
// This isn't a well-formed in-addr.arpa or ip6.arpa name, but
// who knows what upstreams might do, try kicking it up to
// them. We definitely won't handle it.
return "", dns.RCodeRefused
}
r.mu.Lock()
defer r.mu.Unlock()
ret, ok := r.ipToHost[ip]
if !ok {
for _, suffix := range r.localDomains {
if suffix.Contains(name) {
// We are authoritative for this chunk of IP space.
return "", dns.RCodeNameError
}
}
// Not authoritative, signal that forwarding is advisable.
return "", dns.RCodeRefused
}
return ret, dns.RCodeSuccess
}
func (r *Resolver) handleQuery(pkt packet) {
defer atomic.AddInt32(&r.activeQueriesAtomic, -1)
out, err := r.respond(pkt.bs)
if err == errNotOurName {
err = r.forwarder.forward(pkt)
if err == nil {
// forward will send response into r.responses, nothing to do.
return
}
}
if err != nil {
select {
case <-r.closed:
case r.errors <- err:
}
} else {
select {
case <-r.closed:
case r.responses <- packet{out, pkt.addr}:
}
}
}
type response struct {
Header dns.Header
Question dns.Question
// Name is the response to a PTR query.
Name dnsname.FQDN
// IP and IPs are the responses to an A, AAAA, or ALL query.
// Either/both/neither can be populated.
IP netaddr.IP
IPs []netaddr.IP
// TXT is the response to a TXT query.
// Each one is its own RR with one string.
TXT []string
// CNAME is the response to a CNAME query.
CNAME string
// SRVs are the responses to a SRV query.
SRVs []*net.SRV
// NSs are the responses to an NS query.
NSs []*net.NS
}
var dnsParserPool = &sync.Pool{
New: func() interface{} {
return new(dnsParser)
},
}
// dnsParser parses DNS queries using x/net/dns/dnsmessage.
// These structs are pooled with dnsParserPool.
type dnsParser struct {
Header dns.Header
Question dns.Question
parser dns.Parser
}
func (p *dnsParser) response() *response {
return &response{Header: p.Header, Question: p.Question}
}
// zeroParser clears parser so it doesn't retain its most recently
// parsed DNS query's []byte while it's sitting in a sync.Pool.
// It's not useful to keep anyway: the next Start will do the same.
func (p *dnsParser) zeroParser() { p.parser = dns.Parser{} }
// parseQuery parses the query in given packet into p.Header and
// p.Question.
func (p *dnsParser) parseQuery(query []byte) error {
defer p.zeroParser()
p.zeroParser()
var err error
p.Header, err = p.parser.Start(query)
if err != nil {
return err
}
if p.Header.Response {
return errNotQuery
}
p.Question, err = p.parser.Question()
return err
}
// marshalARecord serializes an A record into an active builder.
// The caller may continue using the builder following the call.
func marshalARecord(name dns.Name, ip netaddr.IP, builder *dns.Builder) error {
var answer dns.AResource
answerHeader := dns.ResourceHeader{
Name: name,
Type: dns.TypeA,
Class: dns.ClassINET,
TTL: uint32(defaultTTL / time.Second),
}
ipbytes := ip.As4()
copy(answer.A[:], ipbytes[:])
return builder.AResource(answerHeader, answer)
}
// marshalAAAARecord serializes an AAAA record into an active builder.
// The caller may continue using the builder following the call.
func marshalAAAARecord(name dns.Name, ip netaddr.IP, builder *dns.Builder) error {
var answer dns.AAAAResource
answerHeader := dns.ResourceHeader{
Name: name,
Type: dns.TypeAAAA,
Class: dns.ClassINET,
TTL: uint32(defaultTTL / time.Second),
}
ipbytes := ip.As16()
copy(answer.AAAA[:], ipbytes[:])
return builder.AAAAResource(answerHeader, answer)
}
func marshalIP(name dns.Name, ip netaddr.IP, builder *dns.Builder) error {
if ip.Is4() {
return marshalARecord(name, ip, builder)
}
if ip.Is6() {
return marshalAAAARecord(name, ip, builder)
}
return nil
}
// marshalPTRRecord serializes a PTR record into an active builder.
// The caller may continue using the builder following the call.
func marshalPTRRecord(queryName dns.Name, name dnsname.FQDN, builder *dns.Builder) error {
var answer dns.PTRResource
var err error
answerHeader := dns.ResourceHeader{
Name: queryName,
Type: dns.TypePTR,
Class: dns.ClassINET,
TTL: uint32(defaultTTL / time.Second),
}
answer.PTR, err = dns.NewName(name.WithTrailingDot())
if err != nil {
return err
}
return builder.PTRResource(answerHeader, answer)
}
func marshalTXT(queryName dns.Name, txts []string, builder *dns.Builder) error {
for _, txt := range txts {
if err := builder.TXTResource(dns.ResourceHeader{
Name: queryName,
Type: dns.TypeTXT,
Class: dns.ClassINET,
TTL: uint32(defaultTTL / time.Second),
}, dns.TXTResource{
TXT: []string{txt},
}); err != nil {
return err
}
}
return nil
}
func marshalCNAME(queryName dns.Name, cname string, builder *dns.Builder) error {
if cname == "" {
return nil
}
name, err := dns.NewName(cname)
if err != nil {
return err
}
return builder.CNAMEResource(dns.ResourceHeader{
Name: queryName,
Type: dns.TypeCNAME,
Class: dns.ClassINET,
TTL: uint32(defaultTTL / time.Second),
}, dns.CNAMEResource{
CNAME: name,
})
}
func marshalNS(queryName dns.Name, nss []*net.NS, builder *dns.Builder) error {
for _, ns := range nss {
name, err := dns.NewName(ns.Host)
if err != nil {
return err
}
err = builder.NSResource(dns.ResourceHeader{
Name: queryName,
Type: dns.TypeNS,
Class: dns.ClassINET,
TTL: uint32(defaultTTL / time.Second),
}, dns.NSResource{NS: name})
if err != nil {
return err
}
}
return nil
}
func marshalSRV(queryName dns.Name, srvs []*net.SRV, builder *dns.Builder) error {
for _, s := range srvs {
srvName, err := dns.NewName(s.Target)
if err != nil {
return err
}
err = builder.SRVResource(dns.ResourceHeader{
Name: queryName,
Type: dns.TypeSRV,
Class: dns.ClassINET,
TTL: uint32(defaultTTL / time.Second),
}, dns.SRVResource{
Target: srvName,
Priority: s.Priority,
Port: s.Port,
Weight: s.Weight,
})
if err != nil {
return err
}
}
return nil
}
// marshalResponse serializes the DNS response into a new buffer.
func marshalResponse(resp *response) ([]byte, error) {
resp.Header.Response = true
resp.Header.Authoritative = true
if resp.Header.RecursionDesired {
resp.Header.RecursionAvailable = true
}
builder := dns.NewBuilder(nil, resp.Header)
// TODO(bradfitz): I'm not sure why this wasn't enabled
// before, but for now (2021-12-09) enable it at least when
// there's more than 1 record (which was never the case
// before), where it really helps.
if len(resp.IPs) > 1 {
builder.EnableCompression()
}
isSuccess := resp.Header.RCode == dns.RCodeSuccess
if resp.Question.Type != 0 || isSuccess {
err := builder.StartQuestions()
if err != nil {
return nil, err
}
err = builder.Question(resp.Question)
if err != nil {
return nil, err
}
}
// Only successful responses contain answers.
if !isSuccess {
return builder.Finish()
}
err := builder.StartAnswers()
if err != nil {
return nil, err
}
switch resp.Question.Type {
case dns.TypeA, dns.TypeAAAA, dns.TypeALL:
if err := marshalIP(resp.Question.Name, resp.IP, &builder); err != nil {
return nil, err
}
for _, ip := range resp.IPs {
if err := marshalIP(resp.Question.Name, ip, &builder); err != nil {
return nil, err
}
}
case dns.TypePTR:
err = marshalPTRRecord(resp.Question.Name, resp.Name, &builder)
case dns.TypeTXT:
err = marshalTXT(resp.Question.Name, resp.TXT, &builder)
case dns.TypeCNAME:
err = marshalCNAME(resp.Question.Name, resp.CNAME, &builder)
case dns.TypeSRV:
err = marshalSRV(resp.Question.Name, resp.SRVs, &builder)
case dns.TypeNS:
err = marshalNS(resp.Question.Name, resp.NSs, &builder)
}
if err != nil {
return nil, err
}
return builder.Finish()
}
const (
rdnsv4Suffix = ".in-addr.arpa."
rdnsv6Suffix = ".ip6.arpa."
)
// hasRDNSBonjourPrefix reports whether name has a Bonjour Service Prefix..
//
// https://tools.ietf.org/html/rfc6763 lists
// "five special RR names" for Bonjour service discovery:
//
// b._dns-sd._udp.<domain>.
// db._dns-sd._udp.<domain>.
// r._dns-sd._udp.<domain>.
// dr._dns-sd._udp.<domain>.