353 lines
8.8 KiB
Go
353 lines
8.8 KiB
Go
// Copyright 2011 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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//go:build aix || darwin || dragonfly || freebsd || hurd || linux || netbsd || openbsd || solaris
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package net
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import (
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"context"
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"internal/bytealg"
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"sync"
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"syscall"
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"golang.org/x/net/dns/dnsmessage"
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)
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var onceReadProtocols sync.Once
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// readProtocols loads contents of /etc/protocols into protocols map
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// for quick access.
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func readProtocols() {
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file, err := open("/etc/protocols")
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if err != nil {
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return
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}
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defer file.close()
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for line, ok := file.readLine(); ok; line, ok = file.readLine() {
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// tcp 6 TCP # transmission control protocol
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if i := bytealg.IndexByteString(line, '#'); i >= 0 {
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line = line[0:i]
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}
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f := getFields(line)
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if len(f) < 2 {
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continue
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}
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if proto, _, ok := dtoi(f[1]); ok {
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if _, ok := protocols[f[0]]; !ok {
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protocols[f[0]] = proto
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}
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for _, alias := range f[2:] {
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if _, ok := protocols[alias]; !ok {
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protocols[alias] = proto
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}
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}
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}
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}
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}
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// lookupProtocol looks up IP protocol name in /etc/protocols and
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// returns correspondent protocol number.
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func lookupProtocol(_ context.Context, name string) (int, error) {
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onceReadProtocols.Do(readProtocols)
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return lookupProtocolMap(name)
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}
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func (r *Resolver) dial(ctx context.Context, network, server string) (Conn, error) {
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// Calling Dial here is scary -- we have to be sure not to
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// dial a name that will require a DNS lookup, or Dial will
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// call back here to translate it. The DNS config parser has
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// already checked that all the cfg.servers are IP
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// addresses, which Dial will use without a DNS lookup.
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var c Conn
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var err error
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if r != nil && r.Dial != nil {
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c, err = r.Dial(ctx, network, server)
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} else {
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var d Dialer
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c, err = d.DialContext(ctx, network, server)
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}
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if err != nil {
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return nil, mapErr(err)
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}
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return c, nil
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}
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func (r *Resolver) lookupHost(ctx context.Context, host string) (addrs []string, err error) {
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order := systemConf().hostLookupOrder(r, host)
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if !r.preferGo() && order == hostLookupCgo {
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if addrs, err, ok := cgoLookupHost(ctx, host); ok {
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return addrs, err
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}
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// cgo not available (or netgo); fall back to Go's DNS resolver
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order = hostLookupFilesDNS
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}
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return r.goLookupHostOrder(ctx, host, order)
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}
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func (r *Resolver) lookupIP(ctx context.Context, network, host string) (addrs []IPAddr, err error) {
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if r.preferGo() {
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return r.goLookupIP(ctx, network, host)
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}
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order := systemConf().hostLookupOrder(r, host)
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if order == hostLookupCgo {
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if addrs, err, ok := cgoLookupIP(ctx, network, host); ok {
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return addrs, err
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}
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// cgo not available (or netgo); fall back to Go's DNS resolver
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order = hostLookupFilesDNS
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}
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ips, _, err := r.goLookupIPCNAMEOrder(ctx, network, host, order)
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return ips, err
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}
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func (r *Resolver) lookupPort(ctx context.Context, network, service string) (int, error) {
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if !r.preferGo() && systemConf().canUseCgo() {
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if port, err, ok := cgoLookupPort(ctx, network, service); ok {
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if err != nil {
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// Issue 18213: if cgo fails, first check to see whether we
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// have the answer baked-in to the net package.
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if port, err := goLookupPort(network, service); err == nil {
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return port, nil
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}
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}
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return port, err
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}
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}
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return goLookupPort(network, service)
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}
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func (r *Resolver) lookupCNAME(ctx context.Context, name string) (string, error) {
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if !r.preferGo() && systemConf().canUseCgo() {
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if cname, err, ok := cgoLookupCNAME(ctx, name); ok {
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return cname, err
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}
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}
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return r.goLookupCNAME(ctx, name)
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}
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func (r *Resolver) lookupSRV(ctx context.Context, service, proto, name string) (string, []*SRV, error) {
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var target string
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if service == "" && proto == "" {
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target = name
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} else {
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target = "_" + service + "._" + proto + "." + name
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}
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p, server, err := r.lookup(ctx, target, dnsmessage.TypeSRV)
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if err != nil {
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return "", nil, err
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}
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var srvs []*SRV
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var cname dnsmessage.Name
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for {
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h, err := p.AnswerHeader()
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if err == dnsmessage.ErrSectionDone {
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break
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}
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if err != nil {
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return "", nil, &DNSError{
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Err: "cannot unmarshal DNS message",
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Name: name,
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Server: server,
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}
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}
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if h.Type != dnsmessage.TypeSRV {
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if err := p.SkipAnswer(); err != nil {
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return "", nil, &DNSError{
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Err: "cannot unmarshal DNS message",
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Name: name,
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Server: server,
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}
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}
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continue
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}
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if cname.Length == 0 && h.Name.Length != 0 {
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cname = h.Name
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}
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srv, err := p.SRVResource()
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if err != nil {
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return "", nil, &DNSError{
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Err: "cannot unmarshal DNS message",
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Name: name,
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Server: server,
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}
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}
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srvs = append(srvs, &SRV{Target: srv.Target.String(), Port: srv.Port, Priority: srv.Priority, Weight: srv.Weight})
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}
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byPriorityWeight(srvs).sort()
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return cname.String(), srvs, nil
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}
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func (r *Resolver) lookupMX(ctx context.Context, name string) ([]*MX, error) {
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p, server, err := r.lookup(ctx, name, dnsmessage.TypeMX)
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if err != nil {
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return nil, err
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}
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var mxs []*MX
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for {
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h, err := p.AnswerHeader()
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if err == dnsmessage.ErrSectionDone {
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break
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}
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if err != nil {
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return nil, &DNSError{
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Err: "cannot unmarshal DNS message",
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Name: name,
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Server: server,
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}
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}
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if h.Type != dnsmessage.TypeMX {
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if err := p.SkipAnswer(); err != nil {
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return nil, &DNSError{
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Err: "cannot unmarshal DNS message",
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Name: name,
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Server: server,
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}
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}
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continue
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}
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mx, err := p.MXResource()
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if err != nil {
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return nil, &DNSError{
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Err: "cannot unmarshal DNS message",
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Name: name,
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Server: server,
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}
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}
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mxs = append(mxs, &MX{Host: mx.MX.String(), Pref: mx.Pref})
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}
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byPref(mxs).sort()
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return mxs, nil
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}
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func (r *Resolver) lookupNS(ctx context.Context, name string) ([]*NS, error) {
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p, server, err := r.lookup(ctx, name, dnsmessage.TypeNS)
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if err != nil {
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return nil, err
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}
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var nss []*NS
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for {
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h, err := p.AnswerHeader()
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if err == dnsmessage.ErrSectionDone {
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break
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}
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if err != nil {
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return nil, &DNSError{
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Err: "cannot unmarshal DNS message",
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Name: name,
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Server: server,
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}
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}
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if h.Type != dnsmessage.TypeNS {
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if err := p.SkipAnswer(); err != nil {
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return nil, &DNSError{
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Err: "cannot unmarshal DNS message",
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Name: name,
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Server: server,
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}
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}
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continue
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}
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ns, err := p.NSResource()
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if err != nil {
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return nil, &DNSError{
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Err: "cannot unmarshal DNS message",
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Name: name,
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Server: server,
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}
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}
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nss = append(nss, &NS{Host: ns.NS.String()})
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}
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return nss, nil
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}
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func (r *Resolver) lookupTXT(ctx context.Context, name string) ([]string, error) {
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p, server, err := r.lookup(ctx, name, dnsmessage.TypeTXT)
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if err != nil {
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return nil, err
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}
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var txts []string
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for {
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h, err := p.AnswerHeader()
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if err == dnsmessage.ErrSectionDone {
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break
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}
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if err != nil {
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return nil, &DNSError{
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Err: "cannot unmarshal DNS message",
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Name: name,
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Server: server,
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}
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}
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if h.Type != dnsmessage.TypeTXT {
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if err := p.SkipAnswer(); err != nil {
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return nil, &DNSError{
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Err: "cannot unmarshal DNS message",
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Name: name,
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Server: server,
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}
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}
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continue
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}
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txt, err := p.TXTResource()
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if err != nil {
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return nil, &DNSError{
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Err: "cannot unmarshal DNS message",
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Name: name,
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Server: server,
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}
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}
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// Multiple strings in one TXT record need to be
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// concatenated without separator to be consistent
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// with previous Go resolver.
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n := 0
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for _, s := range txt.TXT {
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n += len(s)
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}
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txtJoin := make([]byte, 0, n)
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for _, s := range txt.TXT {
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txtJoin = append(txtJoin, s...)
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}
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if len(txts) == 0 {
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txts = make([]string, 0, 1)
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}
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txts = append(txts, string(txtJoin))
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}
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return txts, nil
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}
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func (r *Resolver) lookupAddr(ctx context.Context, addr string) ([]string, error) {
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if !r.preferGo() && systemConf().canUseCgo() {
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if ptrs, err, ok := cgoLookupPTR(ctx, addr); ok {
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return ptrs, err
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}
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}
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return r.goLookupPTR(ctx, addr)
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}
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// concurrentThreadsLimit returns the number of threads we permit to
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// run concurrently doing DNS lookups via cgo. A DNS lookup may use a
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// file descriptor so we limit this to less than the number of
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// permitted open files. On some systems, notably Darwin, if
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// getaddrinfo is unable to open a file descriptor it simply returns
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// EAI_NONAME rather than a useful error. Limiting the number of
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// concurrent getaddrinfo calls to less than the permitted number of
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// file descriptors makes that error less likely. We don't bother to
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// apply the same limit to DNS lookups run directly from Go, because
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// there we will return a meaningful "too many open files" error.
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func concurrentThreadsLimit() int {
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var rlim syscall.Rlimit
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if err := syscall.Getrlimit(syscall.RLIMIT_NOFILE, &rlim); err != nil {
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return 500
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}
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r := int(rlim.Cur)
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if r > 500 {
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r = 500
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} else if r > 30 {
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r -= 30
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}
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return r
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}
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