// Copyright 2011 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.
// +build aix darwin dragonfly freebsd linux netbsd openbsd solaris
package net
import (
"context"
"internal/bytealg"
"sync"
"syscall"
"internal/x/net/dns/dnsmessage"
)
var onceReadProtocols sync.Once
// readProtocols loads contents of /etc/protocols into protocols map
// for quick access.
func readProtocols() {
file, err := open("/etc/protocols")
if err != nil {
return
}
defer file.close()
for line, ok := file.readLine(); ok; line, ok = file.readLine() {
// tcp 6 TCP # transmission control protocol
if i := bytealg.IndexByteString(line, '#'); i >= 0 {
line = line[0:i]
}
f := getFields(line)
if len(f) < 2 {
continue
}
if proto, _, ok := dtoi(f[1]); ok {
if _, ok := protocols[f[0]]; !ok {
protocols[f[0]] = proto
}
for _, alias := range f[2:] {
if _, ok := protocols[alias]; !ok {
protocols[alias] = proto
}
}
}
}
}
// lookupProtocol looks up IP protocol name in /etc/protocols and
// returns correspondent protocol number.
func lookupProtocol(_ context.Context, name string) (int, error) {
onceReadProtocols.Do(readProtocols)
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 {
if addrs, err, ok := cgoLookupHost(ctx, host); ok {
return addrs, err
}
// cgo not available (or netgo); fall back to Go's DNS resolver
order = hostLookupFilesDNS
}
return r.goLookupHostOrder(ctx, host, order)
}
func (r *Resolver) lookupIP(ctx context.Context, network, host string) (addrs []IPAddr, err error) {
if r.preferGo() {
return r.goLookupIP(ctx, host)
}
order := systemConf().hostLookupOrder(r, host)
if order == hostLookupCgo {
if addrs, err, ok := cgoLookupIP(ctx, network, host); ok {
return addrs, err
}
// cgo not available (or netgo); fall back to Go's DNS resolver
order = hostLookupFilesDNS
}
ips, _, err := r.goLookupIPCNAMEOrder(ctx, host, order)
return ips, err
}
func (r *Resolver) lookupPort(ctx context.Context, network, service string) (int, error) {
if !r.preferGo() && systemConf().canUseCgo() {
if port, err, ok := cgoLookupPort(ctx, network, service); ok {
if err != nil {
// Issue 18213: if cgo fails, first check to see whether we
// have the answer baked-in to the net package.
if port, err := goLookupPort(network, service); err == nil {
return port, nil
}
}
return port, err
}
}
return goLookupPort(network, service)
}
func (r *Resolver) lookupCNAME(ctx context.Context, name string) (string, error) {
if !r.preferGo() && systemConf().canUseCgo() {
if cname, err, ok := cgoLookupCNAME(ctx, name); ok {
return cname, err
}
}
return r.goLookupCNAME(ctx, name)
}
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
}
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
}
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
}
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
}
func (r *Resolver) lookupAddr(ctx context.Context, addr string) ([]string, error) {
if !r.preferGo() && systemConf().canUseCgo() {
if ptrs, err, ok := cgoLookupPTR(ctx, addr); ok {
return ptrs, err
}
}
return r.goLookupPTR(ctx, addr)
}
// concurrentThreadsLimit returns the number of threads we permit to
// run concurrently doing DNS lookups via cgo. A DNS lookup may use a
// file descriptor so we limit this to less than the number of
// permitted open files. On some systems, notably Darwin, if
// getaddrinfo is unable to open a file descriptor it simply returns
// EAI_NONAME rather than a useful error. Limiting the number of
// concurrent getaddrinfo calls to less than the permitted number of
// file descriptors makes that error less likely. We don't bother to
// apply the same limit to DNS lookups run directly from Go, because
// there we will return a meaningful "too many open files" error.
func concurrentThreadsLimit() int {
var rlim syscall.Rlimit
if err := syscall.Getrlimit(syscall.RLIMIT_NOFILE, &rlim); err != nil {
return 500
}
r := int(rlim.Cur)
if r > 500 {
r = 500
} else if r > 30 {
r -= 30
}
return r
}