src/net/lookup_unix.go - go - Git at Google

 // 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 darwin dragonfly freebsd linux netbsd openbsd solaris

 package net

 import (
 	"context"
 	"internal/bytealg"
 	"sync"
 	"syscall"

 	"golang_org/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, 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, 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,
 			}
 		}
 		if len(txts) == 0 {
 			txts = txt.TXT
 		} else {
 			txts = append(txts, txt.TXT...)
 		}
 	}
 	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
 }
	// 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 darwin dragonfly freebsd linux netbsd openbsd solaris

	package net

	import (
	"context"
	"internal/bytealg"
	"sync"
	"syscall"

	"golang_org/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, 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, 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,
	}
	}
	if len(txts) == 0 {
	txts = txt.TXT
	} else {
	txts = append(txts, txt.TXT...)
	}
	}
	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
	}