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net: permit use of Resolver.PreferGo, netgo on Windows and Plan 9

Browse source 
This reverts commit CL 401754 (440c9312c8) which reverted CL 400654,
thus reapplying CL 400654, re-adding the func init() { netGo = true }
to cgo_stub.go CL 400654 had originally removed (mistakenly during
development?) that had broken the darwin nocgo builder.

Fixes #33097

Change-Id: I90f59746d2ceb6b5d2bd832c9fc90068f8ff7417
Reviewed-on: https://go-review.googlesource.com/c/go/+/409234
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Keith Randall <khr@google.com>
This commit is contained in:
Brad Fitzpatrick 2022-05-28 14:06:43 -07:00
parent a21cf916f4
commit af88fb6502
15 changed files with 835 additions and 290 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

2
src/net/addrselect.go
View file

@ -2,8 +2,6 @@
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
//go:build unix
// Minimal RFC 6724 address selection.
package net

36
src/net/conf.go
View file

@ -2,7 +2,7 @@
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
//go:build unix
//go:build !js
package net
@ -21,7 +21,7 @@ type conf struct {
forceCgoLookupHost bool
netGo bool // go DNS resolution forced
netCgo bool // cgo DNS resolution forced
netCgo bool // non-go DNS resolution forced (cgo, or win32)
// machine has an /etc/mdns.allow file
hasMDNSAllow bool
@ -49,9 +49,23 @@ func initConfVal() {
confVal.dnsDebugLevel = debugLevel
confVal.netGo = netGo || dnsMode == "go"
confVal.netCgo = netCgo || dnsMode == "cgo"
if !confVal.netGo && !confVal.netCgo && (runtime.GOOS == "windows" || runtime.GOOS == "plan9") {
// Neither of these platforms actually use cgo.
//
// The meaning of "cgo" mode in the net package is
// really "the native OS way", which for libc meant
// cgo on the original platforms that motivated
// PreferGo support before Windows and Plan9 got support,
// at which time the GODEBUG=netdns=go and GODEBUG=netdns=cgo
// names were already kinda locked in.
confVal.netCgo = true
}
if confVal.dnsDebugLevel > 0 {
defer func() {
if confVal.dnsDebugLevel > 1 {
println("go package net: confVal.netCgo =", confVal.netCgo, " netGo =", confVal.netGo)
}
switch {
case confVal.netGo:
if netGo {
@ -75,6 +89,10 @@ func initConfVal() {
return
}
if runtime.GOOS == "windows" || runtime.GOOS == "plan9" {
return
}
// If any environment-specified resolver options are specified,
// force cgo. Note that LOCALDOMAIN can change behavior merely
// by being specified with the empty string.
@ -129,7 +147,19 @@ func (c *conf) hostLookupOrder(r *Resolver, hostname string) (ret hostLookupOrde
}
fallbackOrder := hostLookupCgo
if c.netGo || r.preferGo() {
fallbackOrder = hostLookupFilesDNS
switch c.goos {
case "windows":
// TODO(bradfitz): implement files-based
// lookup on Windows too? I guess /etc/hosts
// kinda exists on Windows. But for now, only
// do DNS.
fallbackOrder = hostLookupDNS
default:
fallbackOrder = hostLookupFilesDNS
}
}
if c.goos == "windows" || c.goos == "plan9" {
return fallbackOrder
}
if c.forceCgoLookupHost || c.resolv.unknownOpt || c.goos == "android" {
return fallbackOrder

24
src/net/dnsclient_unix.go
View file

@ -2,7 +2,7 @@
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
//go:build unix
//go:build !js
// DNS client: see RFC 1035.
// Has to be linked into package net for Dial.
@ -20,6 +20,7 @@ import (
"internal/itoa"
"io"
"os"
"runtime"
"sync"
"time"
@ -381,12 +382,21 @@ func (conf *resolverConfig) tryUpdate(name string) {
}
conf.lastChecked = now
var mtime time.Time
if fi, err := os.Stat(name); err == nil {
mtime = fi.ModTime()
}
if mtime.Equal(conf.dnsConfig.mtime) {
return
switch runtime.GOOS {
case "windows":
// There's no file on disk, so don't bother checking
// and failing.
//
// The Windows implementation of dnsReadConfig (called
// below) ignores the name.
default:
var mtime time.Time
if fi, err := os.Stat(name); err == nil {
mtime = fi.ModTime()
}
if mtime.Equal(conf.dnsConfig.mtime) {
return
}
}
dnsConf := dnsReadConfig(name)

43
src/net/dnsconfig.go Normal file
View file

@ -0,0 +1,43 @@
// Copyright 2022 The Go 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 net
import (
"os"
"sync/atomic"
"time"
)
var (
defaultNS = []string{"127.0.0.1:53", "[::1]:53"}
getHostname = os.Hostname // variable for testing
)
type dnsConfig struct {
servers []string // server addresses (in host:port form) to use
search []string // rooted suffixes to append to local name
ndots int // number of dots in name to trigger absolute lookup
timeout time.Duration // wait before giving up on a query, including retries
attempts int // lost packets before giving up on server
rotate bool // round robin among servers
unknownOpt bool // anything unknown was encountered
lookup []string // OpenBSD top-level database "lookup" order
err error // any error that occurs during open of resolv.conf
mtime time.Time // time of resolv.conf modification
soffset uint32 // used by serverOffset
singleRequest bool // use sequential A and AAAA queries instead of parallel queries
useTCP bool // force usage of TCP for DNS resolutions
}
// serverOffset returns an offset that can be used to determine
// indices of servers in c.servers when making queries.
// When the rotate option is enabled, this offset increases.
// Otherwise it is always 0.
func (c *dnsConfig) serverOffset() uint32 {
if c.rotate {
return atomic.AddUint32(&c.soffset, 1) - 1 // return 0 to start
}
return 0
}

36
src/net/dnsconfig_unix.go
View file

@ -2,7 +2,7 @@
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
//go:build unix
//go:build !js && !windows
// Read system DNS config from /etc/resolv.conf
@ -10,32 +10,9 @@ package net
import (
"internal/bytealg"
"os"
"sync/atomic"
"time"
)
var (
defaultNS = []string{"127.0.0.1:53", "[::1]:53"}
getHostname = os.Hostname // variable for testing
)
type dnsConfig struct {
servers []string // server addresses (in host:port form) to use
search []string // rooted suffixes to append to local name
ndots int // number of dots in name to trigger absolute lookup
timeout time.Duration // wait before giving up on a query, including retries
attempts int // lost packets before giving up on server
rotate bool // round robin among servers
unknownOpt bool // anything unknown was encountered
lookup []string // OpenBSD top-level database "lookup" order
err error // any error that occurs during open of resolv.conf
mtime time.Time // time of resolv.conf modification
soffset uint32 // used by serverOffset
singleRequest bool // use sequential A and AAAA queries instead of parallel queries
useTCP bool // force usage of TCP for DNS resolutions
}
// See resolv.conf(5) on a Linux machine.
func dnsReadConfig(filename string) *dnsConfig {
conf := &dnsConfig{
@ -156,17 +133,6 @@ func dnsReadConfig(filename string) *dnsConfig {
return conf
}
// serverOffset returns an offset that can be used to determine
// indices of servers in c.servers when making queries.
// When the rotate option is enabled, this offset increases.
// Otherwise it is always 0.
func (c *dnsConfig) serverOffset() uint32 {
if c.rotate {
return atomic.AddUint32(&c.soffset, 1) - 1 // return 0 to start
}
return 0
}
func dnsDefaultSearch() []string {
hn, err := getHostname()
if err != nil {

58
src/net/dnsconfig_windows.go Normal file
View file

@ -0,0 +1,58 @@
// Copyright 2022 The Go 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 net
import (
"syscall"
"time"
)
func dnsReadConfig(ignoredFilename string) (conf *dnsConfig) {
conf = &dnsConfig{
ndots: 1,
timeout: 5 * time.Second,
attempts: 2,
}
defer func() {
if len(conf.servers) == 0 {
conf.servers = defaultNS
}
}()
aas, err := adapterAddresses()
if err != nil {
return
}
// TODO(bradfitz): this just collects all the DNS servers on all
// the interfaces in some random order. It should order it by
// default route, or only use the default route(s) instead.
// In practice, however, it mostly works.
for _, aa := range aas {
for dns := aa.FirstDnsServerAddress; dns != nil; dns = dns.Next {
sa, err := dns.Address.Sockaddr.Sockaddr()
if err != nil {
continue
}
var ip IP
switch sa := sa.(type) {
case *syscall.SockaddrInet4:
ip = IPv4(sa.Addr[0], sa.Addr[1], sa.Addr[2], sa.Addr[3])
case *syscall.SockaddrInet6:
ip = make(IP, IPv6len)
copy(ip, sa.Addr[:])
if ip[0] == 0xfe && ip[1] == 0xc0 {
// Ignore these fec0/10 ones. Windows seems to
// populate them as defaults on its misc rando
// interfaces.
continue
}
default:
// Unexpected type.
continue
}
conf.servers = append(conf.servers, JoinHostPort(ip.String(), "53"))
}
}
return conf
}

226
src/net/lookup.go
View file

@ -10,6 +10,8 @@ import (
"internal/singleflight"
"net/netip"
"sync"
"golang.org/x/net/dns/dnsmessage"
)
// protocols contains minimal mappings between internet protocol
@ -665,3 +667,227 @@ func (r *Resolver) LookupAddr(ctx context.Context, addr string) ([]string, error
// method receives DNS records which contain invalid DNS names. This may be returned alongside
// results which have had the malformed records filtered out.
var errMalformedDNSRecordsDetail = "DNS response contained records which contain invalid names"
// dial makes a new connection to the provided server (which must be
// an IP address) with the provided network type, using either r.Dial
// (if both r and r.Dial are non-nil) or else Dialer.DialContext.
func (r *Resolver) dial(ctx context.Context, network, server string) (Conn, error) {
// Calling Dial here is scary -- we have to be sure not to
// dial a name that will require a DNS lookup, or Dial will
// call back here to translate it. The DNS config parser has
// already checked that all the cfg.servers are IP
// addresses, which Dial will use without a DNS lookup.
var c Conn
var err error
if r != nil && r.Dial != nil {
c, err = r.Dial(ctx, network, server)
} else {
var d Dialer
c, err = d.DialContext(ctx, network, server)
}
if err != nil {
return nil, mapErr(err)
}
return c, nil
}
// goLookupSRV returns the SRV records for a target name, built either
// from its component service ("sip"), protocol ("tcp"), and name
// ("example.com."), or from name directly (if service and proto are
// both empty).
//
// In either case, the returned target name ("_sip._tcp.example.com.")
// is also returned on success.
//
// The records are sorted by weight.
func (r *Resolver) goLookupSRV(ctx context.Context, service, proto, name string) (target string, srvs []*SRV, err error) {
if service == "" && proto == "" {
target = name
} else {
target = "_" + service + "._" + proto + "." + name
}
p, server, err := r.lookup(ctx, target, dnsmessage.TypeSRV)
if err != nil {
return "", nil, err
}
var cname dnsmessage.Name
for {
h, err := p.AnswerHeader()
if err == dnsmessage.ErrSectionDone {
break
}
if err != nil {
return "", nil, &DNSError{
Err: "cannot unmarshal DNS message",
Name: name,
Server: server,
}
}
if h.Type != dnsmessage.TypeSRV {
if err := p.SkipAnswer(); err != nil {
return "", nil, &DNSError{
Err: "cannot unmarshal DNS message",
Name: name,
Server: server,
}
}
continue
}
if cname.Length == 0 && h.Name.Length != 0 {
cname = h.Name
}
srv, err := p.SRVResource()
if err != nil {
return "", nil, &DNSError{
Err: "cannot unmarshal DNS message",
Name: name,
Server: server,
}
}
srvs = append(srvs, &SRV{Target: srv.Target.String(), Port: srv.Port, Priority: srv.Priority, Weight: srv.Weight})
}
byPriorityWeight(srvs).sort()
return cname.String(), srvs, nil
}
// goLookupMX returns the MX records for name.
func (r *Resolver) goLookupMX(ctx context.Context, name string) ([]*MX, error) {
p, server, err := r.lookup(ctx, name, dnsmessage.TypeMX)
if err != nil {
return nil, err
}
var mxs []*MX
for {
h, err := p.AnswerHeader()
if err == dnsmessage.ErrSectionDone {
break
}
if err != nil {
return nil, &DNSError{
Err: "cannot unmarshal DNS message",
Name: name,
Server: server,
}
}
if h.Type != dnsmessage.TypeMX {
if err := p.SkipAnswer(); err != nil {
return nil, &DNSError{
Err: "cannot unmarshal DNS message",
Name: name,
Server: server,
}
}
continue
}
mx, err := p.MXResource()
if err != nil {
return nil, &DNSError{
Err: "cannot unmarshal DNS message",
Name: name,
Server: server,
}
}
mxs = append(mxs, &MX{Host: mx.MX.String(), Pref: mx.Pref})
}
byPref(mxs).sort()
return mxs, nil
}
// goLookupNS returns the NS records for name.
func (r *Resolver) goLookupNS(ctx context.Context, name string) ([]*NS, error) {
p, server, err := r.lookup(ctx, name, dnsmessage.TypeNS)
if err != nil {
return nil, err
}
var nss []*NS
for {
h, err := p.AnswerHeader()
if err == dnsmessage.ErrSectionDone {
break
}
if err != nil {
return nil, &DNSError{
Err: "cannot unmarshal DNS message",
Name: name,
Server: server,
}
}
if h.Type != dnsmessage.TypeNS {
if err := p.SkipAnswer(); err != nil {
return nil, &DNSError{
Err: "cannot unmarshal DNS message",
Name: name,
Server: server,
}
}
continue
}
ns, err := p.NSResource()
if err != nil {
return nil, &DNSError{
Err: "cannot unmarshal DNS message",
Name: name,
Server: server,
}
}
nss = append(nss, &NS{Host: ns.NS.String()})
}
return nss, nil
}
// goLookupTXT returns the TXT records from name.
func (r *Resolver) goLookupTXT(ctx context.Context, name string) ([]string, error) {
p, server, err := r.lookup(ctx, name, dnsmessage.TypeTXT)
if err != nil {
return nil, err
}
var txts []string
for {
h, err := p.AnswerHeader()
if err == dnsmessage.ErrSectionDone {
break
}
if err != nil {
return nil, &DNSError{
Err: "cannot unmarshal DNS message",
Name: name,
Server: server,
}
}
if h.Type != dnsmessage.TypeTXT {
if err := p.SkipAnswer(); err != nil {
return nil, &DNSError{
Err: "cannot unmarshal DNS message",
Name: name,
Server: server,
}
}
continue
}
txt, err := p.TXTResource()
if err != nil {
return nil, &DNSError{
Err: "cannot unmarshal DNS message",
Name: name,
Server: server,
}
}
// Multiple strings in one TXT record need to be
// concatenated without separator to be consistent
// with previous Go resolver.
n := 0
for _, s := range txt.TXT {
n += len(s)
}
txtJoin := make([]byte, 0, n)
for _, s := range txt.TXT {
txtJoin = append(txtJoin, s...)
}
if len(txts) == 0 {
txts = make([]string, 0, 1)
}
txts = append(txts, string(txtJoin))
}
return txts, nil
}

52
src/net/lookup_plan9.go
View file

@ -179,7 +179,27 @@ loop:
return
}
func (r *Resolver) lookupIP(ctx context.Context, _, host string) (addrs []IPAddr, err error) {
// preferGoOverPlan9 reports whether the resolver should use the
// "PreferGo" implementation rather than asking plan9 services
// for the answers.
func (r *Resolver) preferGoOverPlan9() bool {
conf := systemConf()
order := conf.hostLookupOrder(r, "") // name is unused
// TODO(bradfitz): for now we only permit use of the PreferGo
// implementation when there's a non-nil Resolver with a
// non-nil Dialer. This is a sign that they the code is trying
// to use their DNS-speaking net.Conn (such as an in-memory
// DNS cache) and they don't want to actually hit the network.
// Once we add support for looking the default DNS servers
// from plan9, though, then we can relax this.
return order != hostLookupCgo && r != nil && r.Dial != nil
}
func (r *Resolver) lookupIP(ctx context.Context, network, host string) (addrs []IPAddr, err error) {
if r.preferGoOverPlan9() {
return r.goLookupIP(ctx, network, host)
}
lits, err := r.lookupHost(ctx, host)
if err != nil {
return
@ -223,7 +243,10 @@ func (*Resolver) lookupPort(ctx context.Context, network, service string) (port
return 0, unknownPortError
}
func (*Resolver) lookupCNAME(ctx context.Context, name string) (cname string, err error) {
func (r *Resolver) lookupCNAME(ctx context.Context, name string) (cname string, err error) {
if r.preferGoOverPlan9() {
return r.goLookupCNAME(ctx, name)
}
lines, err := queryDNS(ctx, name, "cname")
if err != nil {
if stringsHasSuffix(err.Error(), "dns failure") || stringsHasSuffix(err.Error(), "resource does not exist; negrcode 0") {
@ -240,7 +263,10 @@ func (*Resolver) lookupCNAME(ctx context.Context, name string) (cname string, er
return "", errors.New("bad response from ndb/dns")
}
func (*Resolver) lookupSRV(ctx context.Context, service, proto, name string) (cname string, addrs []*SRV, err error) {
func (r *Resolver) lookupSRV(ctx context.Context, service, proto, name string) (cname string, addrs []*SRV, err error) {
if r.preferGoOverPlan9() {
return r.goLookupSRV(ctx, service, proto, name)
}
var target string
if service == "" && proto == "" {
target = name
@ -269,7 +295,10 @@ func (*Resolver) lookupSRV(ctx context.Context, service, proto, name string) (cn
return
}
func (*Resolver) lookupMX(ctx context.Context, name string) (mx []*MX, err error) {
func (r *Resolver) lookupMX(ctx context.Context, name string) (mx []*MX, err error) {
if r.preferGoOverPlan9() {
return r.goLookupMX(ctx, name)
}
lines, err := queryDNS(ctx, name, "mx")
if err != nil {
return
@ -287,7 +316,10 @@ func (*Resolver) lookupMX(ctx context.Context, name string) (mx []*MX, err error
return
}
func (*Resolver) lookupNS(ctx context.Context, name string) (ns []*NS, err error) {
func (r *Resolver) lookupNS(ctx context.Context, name string) (ns []*NS, err error) {
if r.preferGoOverPlan9() {
return r.goLookupNS(ctx, name)
}
lines, err := queryDNS(ctx, name, "ns")
if err != nil {
return
@ -302,7 +334,10 @@ func (*Resolver) lookupNS(ctx context.Context, name string) (ns []*NS, err error
return
}
func (*Resolver) lookupTXT(ctx context.Context, name string) (txt []string, err error) {
func (r *Resolver) lookupTXT(ctx context.Context, name string) (txt []string, err error) {
if r.preferGoOverPlan9() {
return r.goLookupTXT(ctx, name)
}
lines, err := queryDNS(ctx, name, "txt")
if err != nil {
return
@ -315,7 +350,10 @@ func (*Resolver) lookupTXT(ctx context.Context, name string) (txt []string, err
return
}
func (*Resolver) lookupAddr(ctx context.Context, addr string) (name []string, err error) {
func (r *Resolver) lookupAddr(ctx context.Context, addr string) (name []string, err error) {
if r.preferGoOverPlan9() {
return r.goLookupPTR(ctx, addr)
}
arpa, err := reverseaddr(addr)
if err != nil {
return

205
src/net/lookup_unix.go
View file

@ -11,8 +11,6 @@ import (
"internal/bytealg"
"sync"
"syscall"
"golang.org/x/net/dns/dnsmessage"
)
var onceReadProtocols sync.Once
@ -55,26 +53,6 @@ func lookupProtocol(_ context.Context, name string) (int, error) {
return lookupProtocolMap(name)
}
func (r *Resolver) dial(ctx context.Context, network, server string) (Conn, error) {
// Calling Dial here is scary -- we have to be sure not to
// dial a name that will require a DNS lookup, or Dial will
// call back here to translate it. The DNS config parser has
// already checked that all the cfg.servers are IP
// addresses, which Dial will use without a DNS lookup.
var c Conn
var err error
if r != nil && r.Dial != nil {
c, err = r.Dial(ctx, network, server)
} else {
var d Dialer
c, err = d.DialContext(ctx, network, server)
}
if err != nil {
return nil, mapErr(err)
}
return c, nil
}
func (r *Resolver) lookupHost(ctx context.Context, host string) (addrs []string, err error) {
order := systemConf().hostLookupOrder(r, host)
if !r.preferGo() && order == hostLookupCgo {
@ -129,194 +107,19 @@ func (r *Resolver) lookupCNAME(ctx context.Context, name string) (string, error)
}
func (r *Resolver) lookupSRV(ctx context.Context, service, proto, name string) (string, []*SRV, error) {
var target string
if service == "" && proto == "" {
target = name
} else {
target = "_" + service + "._" + proto + "." + name
}
p, server, err := r.lookup(ctx, target, dnsmessage.TypeSRV)
if err != nil {
return "", nil, err
}
var srvs []*SRV
var cname dnsmessage.Name
for {
h, err := p.AnswerHeader()
if err == dnsmessage.ErrSectionDone {
break
}
if err != nil {
return "", nil, &DNSError{
Err: "cannot unmarshal DNS message",
Name: name,
Server: server,
}
}
if h.Type != dnsmessage.TypeSRV {
if err := p.SkipAnswer(); err != nil {
return "", nil, &DNSError{
Err: "cannot unmarshal DNS message",
Name: name,
Server: server,
}
}
continue
}
if cname.Length == 0 && h.Name.Length != 0 {
cname = h.Name
}
srv, err := p.SRVResource()
if err != nil {
return "", nil, &DNSError{
Err: "cannot unmarshal DNS message",
Name: name,
Server: server,
}
}
srvs = append(srvs, &SRV{Target: srv.Target.String(), Port: srv.Port, Priority: srv.Priority, Weight: srv.Weight})
}
byPriorityWeight(srvs).sort()
return cname.String(), srvs, nil
return r.goLookupSRV(ctx, service, proto, name)
}
func (r *Resolver) lookupMX(ctx context.Context, name string) ([]*MX, error) {
p, server, err := r.lookup(ctx, name, dnsmessage.TypeMX)
if err != nil {
return nil, err
}
var mxs []*MX
for {
h, err := p.AnswerHeader()
if err == dnsmessage.ErrSectionDone {
break
}
if err != nil {
return nil, &DNSError{
Err: "cannot unmarshal DNS message",
Name: name,
Server: server,
}
}
if h.Type != dnsmessage.TypeMX {
if err := p.SkipAnswer(); err != nil {
return nil, &DNSError{
Err: "cannot unmarshal DNS message",
Name: name,
Server: server,
}
}
continue
}
mx, err := p.MXResource()
if err != nil {
return nil, &DNSError{
Err: "cannot unmarshal DNS message",
Name: name,
Server: server,
}
}
mxs = append(mxs, &MX{Host: mx.MX.String(), Pref: mx.Pref})
}
byPref(mxs).sort()
return mxs, nil
return r.goLookupMX(ctx, name)
}
func (r *Resolver) lookupNS(ctx context.Context, name string) ([]*NS, error) {
p, server, err := r.lookup(ctx, name, dnsmessage.TypeNS)
if err != nil {
return nil, err
}
var nss []*NS
for {
h, err := p.AnswerHeader()
if err == dnsmessage.ErrSectionDone {
break
}
if err != nil {
return nil, &DNSError{
Err: "cannot unmarshal DNS message",
Name: name,
Server: server,
}
}
if h.Type != dnsmessage.TypeNS {
if err := p.SkipAnswer(); err != nil {
return nil, &DNSError{
Err: "cannot unmarshal DNS message",
Name: name,
Server: server,
}
}
continue
}
ns, err := p.NSResource()
if err != nil {
return nil, &DNSError{
Err: "cannot unmarshal DNS message",
Name: name,
Server: server,
}
}
nss = append(nss, &NS{Host: ns.NS.String()})
}
return nss, nil
return r.goLookupNS(ctx, name)
}
func (r *Resolver) lookupTXT(ctx context.Context, name string) ([]string, error) {
p, server, err := r.lookup(ctx, name, dnsmessage.TypeTXT)
if err != nil {
return nil, err
}
var txts []string
for {
h, err := p.AnswerHeader()
if err == dnsmessage.ErrSectionDone {
break
}
if err != nil {
return nil, &DNSError{
Err: "cannot unmarshal DNS message",
Name: name,
Server: server,
}
}
if h.Type != dnsmessage.TypeTXT {
if err := p.SkipAnswer(); err != nil {
return nil, &DNSError{
Err: "cannot unmarshal DNS message",
Name: name,
Server: server,
}
}
continue
}
txt, err := p.TXTResource()
if err != nil {
return nil, &DNSError{
Err: "cannot unmarshal DNS message",
Name: name,
Server: server,
}
}
// Multiple strings in one TXT record need to be
// concatenated without separator to be consistent
// with previous Go resolver.
n := 0
for _, s := range txt.TXT {
n += len(s)
}
txtJoin := make([]byte, 0, n)
for _, s := range txt.TXT {
txtJoin = append(txtJoin, s...)
}
if len(txts) == 0 {
txts = make([]string, 0, 1)
}
txts = append(txts, string(txtJoin))
}
return txts, nil
return r.goLookupTXT(ctx, name)
}
func (r *Resolver) lookupAddr(ctx context.Context, addr string) ([]string, error) {

93
src/net/lookup_windows.go
View file

@ -82,7 +82,19 @@ func (r *Resolver) lookupHost(ctx context.Context, name string) ([]string, error
return addrs, nil
}
// preferGoOverWindows reports whether the resolver should use the
// pure Go implementation rather than making win32 calls to ask the
// kernel for its answer.
func (r *Resolver) preferGoOverWindows() bool {
conf := systemConf()
order := conf.hostLookupOrder(r, "") // name is unused
return order != hostLookupCgo
}
func (r *Resolver) lookupIP(ctx context.Context, network, name string) ([]IPAddr, error) {
if r.preferGoOverWindows() {
return r.goLookupIP(ctx, network, name)
}
// TODO(bradfitz,brainman): use ctx more. See TODO below.
var family int32 = syscall.AF_UNSPEC
@ -169,7 +181,7 @@ func (r *Resolver) lookupIP(ctx context.Context, network, name string) ([]IPAddr
}
func (r *Resolver) lookupPort(ctx context.Context, network, service string) (int, error) {
if r.preferGo() {
if r.preferGoOverWindows() {
return lookupPortMap(network, service)
}
@ -217,12 +229,15 @@ func (r *Resolver) lookupPort(ctx context.Context, network, service string) (int
return 0, &DNSError{Err: syscall.EINVAL.Error(), Name: network + "/" + service}
}
func (*Resolver) lookupCNAME(ctx context.Context, name string) (string, error) {
func (r *Resolver) lookupCNAME(ctx context.Context, name string) (string, error) {
if r.preferGoOverWindows() {
return r.goLookupCNAME(ctx, name)
}
// TODO(bradfitz): finish ctx plumbing. Nothing currently depends on this.
acquireThread()
defer releaseThread()
var r *syscall.DNSRecord
e := syscall.DnsQuery(name, syscall.DNS_TYPE_CNAME, 0, nil, &r, nil)
var rec *syscall.DNSRecord
e := syscall.DnsQuery(name, syscall.DNS_TYPE_CNAME, 0, nil, &rec, nil)
// windows returns DNS_INFO_NO_RECORDS if there are no CNAME-s
if errno, ok := e.(syscall.Errno); ok && errno == syscall.DNS_INFO_NO_RECORDS {
// if there are no aliases, the canonical name is the input name
@ -231,14 +246,17 @@ func (*Resolver) lookupCNAME(ctx context.Context, name string) (string, error) {
if e != nil {
return "", &DNSError{Err: winError("dnsquery", e).Error(), Name: name}
}
defer syscall.DnsRecordListFree(r, 1)
defer syscall.DnsRecordListFree(rec, 1)
resolved := resolveCNAME(syscall.StringToUTF16Ptr(name), r)
resolved := resolveCNAME(syscall.StringToUTF16Ptr(name), rec)
cname := windows.UTF16PtrToString(resolved)
return absDomainName(cname), nil
}
func (*Resolver) lookupSRV(ctx context.Context, service, proto, name string) (string, []*SRV, error) {
func (r *Resolver) lookupSRV(ctx context.Context, service, proto, name string) (string, []*SRV, error) {
if r.preferGoOverWindows() {
return r.goLookupSRV(ctx, service, proto, name)
}
// TODO(bradfitz): finish ctx plumbing. Nothing currently depends on this.
acquireThread()
defer releaseThread()
@ -248,15 +266,15 @@ func (*Resolver) lookupSRV(ctx context.Context, service, proto, name string) (st
} else {
target = "_" + service + "._" + proto + "." + name
}
var r *syscall.DNSRecord
e := syscall.DnsQuery(target, syscall.DNS_TYPE_SRV, 0, nil, &r, nil)
var rec *syscall.DNSRecord
e := syscall.DnsQuery(target, syscall.DNS_TYPE_SRV, 0, nil, &rec, nil)
if e != nil {
return "", nil, &DNSError{Err: winError("dnsquery", e).Error(), Name: target}
}
defer syscall.DnsRecordListFree(r, 1)
defer syscall.DnsRecordListFree(rec, 1)
srvs := make([]*SRV, 0, 10)
for _, p := range validRecs(r, syscall.DNS_TYPE_SRV, target) {
for _, p := range validRecs(rec, syscall.DNS_TYPE_SRV, target) {
v := (*syscall.DNSSRVData)(unsafe.Pointer(&p.Data[0]))
srvs = append(srvs, &SRV{absDomainName(syscall.UTF16ToString((*[256]uint16)(unsafe.Pointer(v.Target))[:])), v.Port, v.Priority, v.Weight})
}
@ -264,19 +282,22 @@ func (*Resolver) lookupSRV(ctx context.Context, service, proto, name string) (st
return absDomainName(target), srvs, nil
}
func (*Resolver) lookupMX(ctx context.Context, name string) ([]*MX, error) {
func (r *Resolver) lookupMX(ctx context.Context, name string) ([]*MX, error) {
if r.preferGoOverWindows() {
return r.goLookupMX(ctx, name)
}
// TODO(bradfitz): finish ctx plumbing. Nothing currently depends on this.
acquireThread()
defer releaseThread()
var r *syscall.DNSRecord
e := syscall.DnsQuery(name, syscall.DNS_TYPE_MX, 0, nil, &r, nil)
var rec *syscall.DNSRecord
e := syscall.DnsQuery(name, syscall.DNS_TYPE_MX, 0, nil, &rec, nil)
if e != nil {
return nil, &DNSError{Err: winError("dnsquery", e).Error(), Name: name}
}
defer syscall.DnsRecordListFree(r, 1)
defer syscall.DnsRecordListFree(rec, 1)
mxs := make([]*MX, 0, 10)
for _, p := range validRecs(r, syscall.DNS_TYPE_MX, name) {
for _, p := range validRecs(rec, syscall.DNS_TYPE_MX, name) {
v := (*syscall.DNSMXData)(unsafe.Pointer(&p.Data[0]))
mxs = append(mxs, &MX{absDomainName(windows.UTF16PtrToString(v.NameExchange)), v.Preference})
}
@ -284,38 +305,44 @@ func (*Resolver) lookupMX(ctx context.Context, name string) ([]*MX, error) {
return mxs, nil
}
func (*Resolver) lookupNS(ctx context.Context, name string) ([]*NS, error) {
func (r *Resolver) lookupNS(ctx context.Context, name string) ([]*NS, error) {
if r.preferGoOverWindows() {
return r.goLookupNS(ctx, name)
}
// TODO(bradfitz): finish ctx plumbing. Nothing currently depends on this.
acquireThread()
defer releaseThread()
var r *syscall.DNSRecord
e := syscall.DnsQuery(name, syscall.DNS_TYPE_NS, 0, nil, &r, nil)
var rec *syscall.DNSRecord
e := syscall.DnsQuery(name, syscall.DNS_TYPE_NS, 0, nil, &rec, nil)
if e != nil {
return nil, &DNSError{Err: winError("dnsquery", e).Error(), Name: name}
}
defer syscall.DnsRecordListFree(r, 1)
defer syscall.DnsRecordListFree(rec, 1)
nss := make([]*NS, 0, 10)
for _, p := range validRecs(r, syscall.DNS_TYPE_NS, name) {
for _, p := range validRecs(rec, syscall.DNS_TYPE_NS, name) {
v := (*syscall.DNSPTRData)(unsafe.Pointer(&p.Data[0]))
nss = append(nss, &NS{absDomainName(syscall.UTF16ToString((*[256]uint16)(unsafe.Pointer(v.Host))[:]))})
}
return nss, nil
}
func (*Resolver) lookupTXT(ctx context.Context, name string) ([]string, error) {
func (r *Resolver) lookupTXT(ctx context.Context, name string) ([]string, error) {
if r.preferGoOverWindows() {
return r.lookupTXT(ctx, name)
}
// TODO(bradfitz): finish ctx plumbing. Nothing currently depends on this.
acquireThread()
defer releaseThread()
var r *syscall.DNSRecord
e := syscall.DnsQuery(name, syscall.DNS_TYPE_TEXT, 0, nil, &r, nil)
var rec *syscall.DNSRecord
e := syscall.DnsQuery(name, syscall.DNS_TYPE_TEXT, 0, nil, &rec, nil)
if e != nil {
return nil, &DNSError{Err: winError("dnsquery", e).Error(), Name: name}
}
defer syscall.DnsRecordListFree(r, 1)
defer syscall.DnsRecordListFree(rec, 1)
txts := make([]string, 0, 10)
for _, p := range validRecs(r, syscall.DNS_TYPE_TEXT, name) {
for _, p := range validRecs(rec, syscall.DNS_TYPE_TEXT, name) {
d := (*syscall.DNSTXTData)(unsafe.Pointer(&p.Data[0]))
s := ""
for _, v := range (*[1 << 10]*uint16)(unsafe.Pointer(&(d.StringArray[0])))[:d.StringCount:d.StringCount] {
@ -326,7 +353,11 @@ func (*Resolver) lookupTXT(ctx context.Context, name string) ([]string, error) {
return txts, nil
}
func (*Resolver) lookupAddr(ctx context.Context, addr string) ([]string, error) {
func (r *Resolver) lookupAddr(ctx context.Context, addr string) ([]string, error) {
if r.preferGoOverWindows() {
return r.goLookupPTR(ctx, addr)
}
// TODO(bradfitz): finish ctx plumbing. Nothing currently depends on this.
acquireThread()
defer releaseThread()
@ -334,15 +365,15 @@ func (*Resolver) lookupAddr(ctx context.Context, addr string) ([]string, error)
if err != nil {
return nil, err
}
var r *syscall.DNSRecord
e := syscall.DnsQuery(arpa, syscall.DNS_TYPE_PTR, 0, nil, &r, nil)
var rec *syscall.DNSRecord
e := syscall.DnsQuery(arpa, syscall.DNS_TYPE_PTR, 0, nil, &rec, nil)
if e != nil {
return nil, &DNSError{Err: winError("dnsquery", e).Error(), Name: addr}
}
defer syscall.DnsRecordListFree(r, 1)
defer syscall.DnsRecordListFree(rec, 1)
ptrs := make([]string, 0, 10)
for _, p := range validRecs(r, syscall.DNS_TYPE_PTR, arpa) {
for _, p := range validRecs(rec, syscall.DNS_TYPE_PTR, arpa) {
v := (*syscall.DNSPTRData)(unsafe.Pointer(&p.Data[0]))
ptrs = append(ptrs, absDomainName(windows.UTF16PtrToString(v.Host)))
}

5
src/net/net.go
View file

@ -61,7 +61,7 @@ The resolver decision can be overridden by setting the netdns value of the
GODEBUG environment variable (see package runtime) to go or cgo, as in:
export GODEBUG=netdns=go # force pure Go resolver
export GODEBUG=netdns=cgo # force cgo resolver
export GODEBUG=netdns=cgo # force native resolver (cgo, win32)
The decision can also be forced while building the Go source tree
by setting the netgo or netcgo build tag.
@ -73,7 +73,8 @@ join the two settings by a plus sign, as in GODEBUG=netdns=go+1.
On Plan 9, the resolver always accesses /net/cs and /net/dns.
On Windows, the resolver always uses C library functions, such as GetAddrInfo and DnsQuery.
On Windows, in Go 1.18.x and earlier, the resolver always used C
library functions, such as GetAddrInfo and DnsQuery.
*/
package net

6
src/net/net_fake.go
View file

@ -16,6 +16,8 @@ import (
"sync"
"syscall"
"time"
"golang.org/x/net/dns/dnsmessage"
)
var listenersMu sync.Mutex
@ -314,3 +316,7 @@ func (fd *netFD) writeMsg(p []byte, oob []byte, sa syscall.Sockaddr) (n int, oob
func (fd *netFD) dup() (f *os.File, err error) {
return nil, syscall.ENOSYS
}
func (r *Resolver) lookup(ctx context.Context, name string, qtype dnsmessage.Type) (dnsmessage.Parser, string, error) {
panic("unreachable")
}

9
src/net/netgo.go Normal file
View file

@ -0,0 +1,9 @@
// Copyright 2022 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
//go:build netgo
package net
func init() { netGo = true }

2
src/net/nss.go
View file

@ -2,8 +2,6 @@
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
//go:build unix
package net
import (

328
src/net/resolverdialfunc_test.go Normal file
View file

@ -0,0 +1,328 @@
// Copyright 2022 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
//go:build !js
// Test that Resolver.Dial can be a func returning an in-memory net.Conn
// speaking DNS.
package net
import (
"bytes"
"context"
"errors"
"fmt"
"reflect"
"sort"
"testing"
"time"
"golang.org/x/net/dns/dnsmessage"
)
func TestResolverDialFunc(t *testing.T) {
r := &Resolver{
PreferGo: true,
Dial: newResolverDialFunc(&resolverDialHandler{
StartDial: func(network, address string) error {
t.Logf("StartDial(%q, %q) ...", network, address)
return nil
},
Question: func(h dnsmessage.Header, q dnsmessage.Question) {
t.Logf("Header: %+v for %q (type=%v, class=%v)", h,
q.Name.String(), q.Type, q.Class)
},
// TODO: add test without HandleA* hooks specified at all, that Go
// doesn't issue retries; map to something terminal.
HandleA: func(w AWriter, name string) error {
w.AddIP([4]byte{1, 2, 3, 4})
w.AddIP([4]byte{5, 6, 7, 8})
return nil
},
HandleAAAA: func(w AAAAWriter, name string) error {
w.AddIP([16]byte{1: 1, 15: 15})
w.AddIP([16]byte{2: 2, 14: 14})
return nil
},
HandleSRV: func(w SRVWriter, name string) error {
w.AddSRV(1, 2, 80, "foo.bar.")
w.AddSRV(2, 3, 81, "bar.baz.")
return nil
},
}),
}
ctx := context.Background()
const fakeDomain = "something-that-is-a-not-a-real-domain.fake-tld."
t.Run("LookupIP", func(t *testing.T) {
ips, err := r.LookupIP(ctx, "ip", fakeDomain)
if err != nil {
t.Fatal(err)
}
if got, want := sortedIPStrings(ips), []string{"0:200::e00", "1.2.3.4", "1::f", "5.6.7.8"}; !reflect.DeepEqual(got, want) {
t.Errorf("LookupIP wrong.\n got: %q\nwant: %q\n", got, want)
}
})
t.Run("LookupSRV", func(t *testing.T) {
_, got, err := r.LookupSRV(ctx, "some-service", "tcp", fakeDomain)
if err != nil {
t.Fatal(err)
}
want := []*SRV{
{
Target: "foo.bar.",
Port: 80,
Priority: 1,
Weight: 2,
},
{
Target: "bar.baz.",
Port: 81,
Priority: 2,
Weight: 3,
},
}
if !reflect.DeepEqual(got, want) {
t.Errorf("wrong result. got:")
for _, r := range got {
t.Logf(" - %+v", r)
}
}
})
}
func sortedIPStrings(ips []IP) []string {
ret := make([]string, len(ips))
for i, ip := range ips {
ret[i] = ip.String()
}
sort.Strings(ret)
return ret
}
func newResolverDialFunc(h *resolverDialHandler) func(ctx context.Context, network, address string) (Conn, error) {
return func(ctx context.Context, network, address string) (Conn, error) {
a := &resolverFuncConn{
h: h,
network: network,
address: address,
ttl: 10, // 10 second default if unset
}
if h.StartDial != nil {
if err := h.StartDial(network, address); err != nil {
return nil, err
}
}
return a, nil
}
}
type resolverDialHandler struct {
// StartDial, if non-nil, is called when Go first calls Resolver.Dial.
// Any error returned aborts the dial and is returned unwrapped.
StartDial func(network, address string) error
Question func(dnsmessage.Header, dnsmessage.Question)
// err may be ErrNotExist or ErrRefused; others map to SERVFAIL (RCode2).
// A nil error means success.
HandleA func(w AWriter, name string) error
HandleAAAA func(w AAAAWriter, name string) error
HandleSRV func(w SRVWriter, name string) error
}
type ResponseWriter struct{ a *resolverFuncConn }
func (w ResponseWriter) header() dnsmessage.ResourceHeader {
q := w.a.q
return dnsmessage.ResourceHeader{
Name: q.Name,
Type: q.Type,
Class: q.Class,
TTL: w.a.ttl,
}
}
// SetTTL sets the TTL for subsequent written resources.
// Once a resource has been written, SetTTL calls are no-ops.
// That is, it can only be called at most once, before anything
// else is written.
func (w ResponseWriter) SetTTL(seconds uint32) {
// ... intention is last one wins and mutates all previously
// written records too, but that's a little annoying.
// But it's also annoying if the requirement is it needs to be set
// last.
// And it's also annoying if it's possible for users to set
// different TTLs per Answer.
if w.a.wrote {
return
}
w.a.ttl = seconds
}
type AWriter struct{ ResponseWriter }
func (w AWriter) AddIP(v4 [4]byte) {
w.a.wrote = true
err := w.a.builder.AResource(w.header(), dnsmessage.AResource{A: v4})
if err != nil {
panic(err)
}
}
type AAAAWriter struct{ ResponseWriter }
func (w AAAAWriter) AddIP(v6 [16]byte) {
w.a.wrote = true
err := w.a.builder.AAAAResource(w.header(), dnsmessage.AAAAResource{AAAA: v6})
if err != nil {
panic(err)
}
}
type SRVWriter struct{ ResponseWriter }
// AddSRV adds a SRV record. The target name must end in a period and
// be 63 bytes or fewer.
func (w SRVWriter) AddSRV(priority, weight, port uint16, target string) error {
targetName, err := dnsmessage.NewName(target)
if err != nil {
return err
}
w.a.wrote = true
err = w.a.builder.SRVResource(w.header(), dnsmessage.SRVResource{
Priority: priority,
Weight: weight,
Port: port,
Target: targetName,
})
if err != nil {
panic(err) // internal fault, not user
}
return nil
}
var (
ErrNotExist = errors.New("name does not exist") // maps to RCode3, NXDOMAIN
ErrRefused = errors.New("refused") // maps to RCode5, REFUSED
)
type resolverFuncConn struct {
h *resolverDialHandler
ctx context.Context
network string
address string
builder *dnsmessage.Builder
q dnsmessage.Question
ttl uint32
wrote bool
rbuf bytes.Buffer
}
func (*resolverFuncConn) Close() error { return nil }
func (*resolverFuncConn) LocalAddr() Addr { return someaddr{} }
func (*resolverFuncConn) RemoteAddr() Addr { return someaddr{} }
func (*resolverFuncConn) SetDeadline(t time.Time) error { return nil }
func (*resolverFuncConn) SetReadDeadline(t time.Time) error { return nil }
func (*resolverFuncConn) SetWriteDeadline(t time.Time) error { return nil }
func (a *resolverFuncConn) Read(p []byte) (n int, err error) {
return a.rbuf.Read(p)
}
func (a *resolverFuncConn) Write(packet []byte) (n int, err error) {
if len(packet) < 2 {
return 0, fmt.Errorf("short write of %d bytes; want 2+", len(packet))
}
reqLen := int(packet[0])<<8 | int(packet[1])
req := packet[2:]
if len(req) != reqLen {
return 0, fmt.Errorf("packet declared length %d doesn't match body length %d", reqLen, len(req))
}
var parser dnsmessage.Parser
h, err := parser.Start(req)
if err != nil {
// TODO: hook
return 0, err
}
q, err := parser.Question()
hadQ := (err == nil)
if err == nil && a.h.Question != nil {
a.h.Question(h, q)
}
if err != nil && err != dnsmessage.ErrSectionDone {
return 0, err
}
resh := h
resh.Response = true
resh.Authoritative = true
if hadQ {
resh.RCode = dnsmessage.RCodeSuccess
} else {
resh.RCode = dnsmessage.RCodeNotImplemented
}
a.rbuf.Grow(514)
a.rbuf.WriteByte('X') // reserved header for beu16 length
a.rbuf.WriteByte('Y') // reserved header for beu16 length
builder := dnsmessage.NewBuilder(a.rbuf.Bytes(), resh)
a.builder = &builder
if hadQ {
a.q = q
a.builder.StartQuestions()
err := a.builder.Question(q)
if err != nil {
return 0, fmt.Errorf("Question: %w", err)
}
a.builder.StartAnswers()
switch q.Type {
case dnsmessage.TypeA:
if a.h.HandleA != nil {
resh.RCode = mapRCode(a.h.HandleA(AWriter{ResponseWriter{a}}, q.Name.String()))
}
case dnsmessage.TypeAAAA:
if a.h.HandleAAAA != nil {
resh.RCode = mapRCode(a.h.HandleAAAA(AAAAWriter{ResponseWriter{a}}, q.Name.String()))
}
case dnsmessage.TypeSRV:
if a.h.HandleSRV != nil {
resh.RCode = mapRCode(a.h.HandleSRV(SRVWriter{ResponseWriter{a}}, q.Name.String()))
}
}
}
tcpRes, err := builder.Finish()
if err != nil {
return 0, fmt.Errorf("Finish: %w", err)
}
n = len(tcpRes) - 2
tcpRes[0] = byte(n >> 8)
tcpRes[1] = byte(n)
a.rbuf.Write(tcpRes[2:])
return len(packet), nil
}
type someaddr struct{}
func (someaddr) Network() string { return "unused" }
func (someaddr) String() string { return "unused-someaddr" }
func mapRCode(err error) dnsmessage.RCode {
switch err {
case nil:
return dnsmessage.RCodeSuccess
case ErrNotExist:
return dnsmessage.RCodeNameError
case ErrRefused:
return dnsmessage.RCodeRefused
default:
return dnsmessage.RCodeServerFailure
}
}