src/net/lookup_plan9.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.

 package net

 import (
 	"context"
 	"errors"
 	"internal/bytealg"
 	"internal/itoa"
 	"io"
 	"os"
 )

 func query(ctx context.Context, filename, query string, bufSize int) (addrs []string, err error) {
 	queryAddrs := func() (addrs []string, err error) {
 		file, err := os.OpenFile(filename, os.O_RDWR, 0)
 		if err != nil {
 			return nil, err
 		}
 		defer file.Close()

 		_, err = file.Seek(0, io.SeekStart)
 		if err != nil {
 			return nil, err
 		}
 		_, err = file.WriteString(query)
 		if err != nil {
 			return nil, err
 		}
 		_, err = file.Seek(0, io.SeekStart)
 		if err != nil {
 			return nil, err
 		}
 		buf := make([]byte, bufSize)
 		for {
 			n, _ := file.Read(buf)
 			if n <= 0 {
 				break
 			}
 			addrs = append(addrs, string(buf[:n]))
 		}
 		return addrs, nil
 	}

 	type ret struct {
 		addrs []string
 		err   error
 	}

 	ch := make(chan ret, 1)
 	go func() {
 		addrs, err := queryAddrs()
 		ch <- ret{addrs: addrs, err: err}
 	}()

 	select {
 	case r := <-ch:
 		return r.addrs, r.err
 	case <-ctx.Done():
 		return nil, &DNSError{
 			Name:      query,
 			Err:       ctx.Err().Error(),
 			IsTimeout: ctx.Err() == context.DeadlineExceeded,
 		}
 	}
 }

 func queryCS(ctx context.Context, net, host, service string) (res []string, err error) {
 	switch net {
 	case "tcp4", "tcp6":
 		net = "tcp"
 	case "udp4", "udp6":
 		net = "udp"
 	}
 	if host == "" {
 		host = "*"
 	}
 	return query(ctx, netdir+"/cs", net+"!"+host+"!"+service, 128)
 }

 func queryCS1(ctx context.Context, net string, ip IP, port int) (clone, dest string, err error) {
 	ips := "*"
 	if len(ip) != 0 && !ip.IsUnspecified() {
 		ips = ip.String()
 	}
 	lines, err := queryCS(ctx, net, ips, itoa.Itoa(port))
 	if err != nil {
 		return
 	}
 	f := getFields(lines[0])
 	if len(f) < 2 {
 		return "", "", errors.New("bad response from ndb/cs")
 	}
 	clone, dest = f[0], f[1]
 	return
 }

 func queryDNS(ctx context.Context, addr string, typ string) (res []string, err error) {
 	return query(ctx, netdir+"/dns", addr+" "+typ, 1024)
 }

 // toLower returns a lower-case version of in. Restricting us to
 // ASCII is sufficient to handle the IP protocol names and allow
 // us to not depend on the strings and unicode packages.
 func toLower(in string) string {
 	for _, c := range in {
 		if 'A' <= c && c <= 'Z' {
 			// Has upper case; need to fix.
 			out := []byte(in)
 			for i := 0; i < len(in); i++ {
 				c := in[i]
 				if 'A' <= c && c <= 'Z' {
 					c += 'a' - 'A'
 				}
 				out[i] = c
 			}
 			return string(out)
 		}
 	}
 	return in
 }

 // lookupProtocol looks up IP protocol name and returns
 // the corresponding protocol number.
 func lookupProtocol(ctx context.Context, name string) (proto int, err error) {
 	lines, err := query(ctx, netdir+"/cs", "!protocol="+toLower(name), 128)
 	if err != nil {
 		return 0, err
 	}
 	if len(lines) == 0 {
 		return 0, UnknownNetworkError(name)
 	}
 	f := getFields(lines[0])
 	if len(f) < 2 {
 		return 0, UnknownNetworkError(name)
 	}
 	s := f[1]
 	if n, _, ok := dtoi(s[bytealg.IndexByteString(s, '=')+1:]); ok {
 		return n, nil
 	}
 	return 0, UnknownNetworkError(name)
 }

 func (*Resolver) lookupHost(ctx context.Context, host string) (addrs []string, err error) {
 	// Use netdir/cs instead of netdir/dns because cs knows about
 	// host names in local network (e.g. from /lib/ndb/local)
 	lines, err := queryCS(ctx, "net", host, "1")
 	if err != nil {
 		dnsError := &DNSError{Err: err.Error(), Name: host}
 		if stringsHasSuffix(err.Error(), "dns failure") {
 			dnsError.Err = errNoSuchHost.Error()
 			dnsError.IsNotFound = true
 		}
 		return nil, dnsError
 	}
 loop:
 	for _, line := range lines {
 		f := getFields(line)
 		if len(f) < 2 {
 			continue
 		}
 		addr := f[1]
 		if i := bytealg.IndexByteString(addr, '!'); i >= 0 {
 			addr = addr[:i] // remove port
 		}
 		if ParseIP(addr) == nil {
 			continue
 		}
 		// only return unique addresses
 		for _, a := range addrs {
 			if a == addr {
 				continue loop
 			}
 		}
 		addrs = append(addrs, addr)
 	}
 	return
 }

 // 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
 	}
 	for _, lit := range lits {
 		host, zone := splitHostZone(lit)
 		if ip := ParseIP(host); ip != nil {
 			addr := IPAddr{IP: ip, Zone: zone}
 			addrs = append(addrs, addr)
 		}
 	}
 	return
 }

 func (*Resolver) lookupPort(ctx context.Context, network, service string) (port int, err error) {
 	switch network {
 	case "tcp4", "tcp6":
 		network = "tcp"
 	case "udp4", "udp6":
 		network = "udp"
 	}
 	lines, err := queryCS(ctx, network, "127.0.0.1", toLower(service))
 	if err != nil {
 		return
 	}
 	unknownPortError := &AddrError{Err: "unknown port", Addr: network + "/" + service}
 	if len(lines) == 0 {
 		return 0, unknownPortError
 	}
 	f := getFields(lines[0])
 	if len(f) < 2 {
 		return 0, unknownPortError
 	}
 	s := f[1]
 	if i := bytealg.IndexByteString(s, '!'); i >= 0 {
 		s = s[i+1:] // remove address
 	}
 	if n, _, ok := dtoi(s); ok {
 		return n, nil
 	}
 	return 0, unknownPortError
 }

 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") {
 			cname = name + "."
 			err = nil
 		}
 		return
 	}
 	if len(lines) > 0 {
 		if f := getFields(lines[0]); len(f) >= 3 {
 			return f[2] + ".", nil
 		}
 	}
 	return "", errors.New("bad response from ndb/dns")
 }

 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
 	} else {
 		target = "_" + service + "._" + proto + "." + name
 	}
 	lines, err := queryDNS(ctx, target, "srv")
 	if err != nil {
 		return
 	}
 	for _, line := range lines {
 		f := getFields(line)
 		if len(f) < 6 {
 			continue
 		}
 		port, _, portOk := dtoi(f[4])
 		priority, _, priorityOk := dtoi(f[3])
 		weight, _, weightOk := dtoi(f[2])
 		if !(portOk && priorityOk && weightOk) {
 			continue
 		}
 		addrs = append(addrs, &SRV{absDomainName(f[5]), uint16(port), uint16(priority), uint16(weight)})
 		cname = absDomainName(f[0])
 	}
 	byPriorityWeight(addrs).sort()
 	return
 }

 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
 	}
 	for _, line := range lines {
 		f := getFields(line)
 		if len(f) < 4 {
 			continue
 		}
 		if pref, _, ok := dtoi(f[2]); ok {
 			mx = append(mx, &MX{absDomainName(f[3]), uint16(pref)})
 		}
 	}
 	byPref(mx).sort()
 	return
 }

 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
 	}
 	for _, line := range lines {
 		f := getFields(line)
 		if len(f) < 3 {
 			continue
 		}
 		ns = append(ns, &NS{absDomainName(f[2])})
 	}
 	return
 }

 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
 	}
 	for _, line := range lines {
 		if i := bytealg.IndexByteString(line, '\t'); i >= 0 {
 			txt = append(txt, line[i+1:])
 		}
 	}
 	return
 }

 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
 	}
 	lines, err := queryDNS(ctx, arpa, "ptr")
 	if err != nil {
 		return
 	}
 	for _, line := range lines {
 		f := getFields(line)
 		if len(f) < 3 {
 			continue
 		}
 		name = append(name, absDomainName(f[2]))
 	}
 	return
 }

 // concurrentThreadsLimit returns the number of threads we permit to
 // run concurrently doing DNS lookups.
 func concurrentThreadsLimit() int {
 	return 500
 }
	// 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.

	package net

	import (
	"context"
	"errors"
	"internal/bytealg"
	"internal/itoa"
	"io"
	"os"
	)

	func query(ctx context.Context, filename, query string, bufSize int) (addrs []string, err error) {
	queryAddrs := func() (addrs []string, err error) {
	file, err := os.OpenFile(filename, os.O_RDWR, 0)
	if err != nil {
	return nil, err
	}
	defer file.Close()

	_, err = file.Seek(0, io.SeekStart)
	if err != nil {
	return nil, err
	}
	_, err = file.WriteString(query)
	if err != nil {
	return nil, err
	}
	_, err = file.Seek(0, io.SeekStart)
	if err != nil {
	return nil, err
	}
	buf := make([]byte, bufSize)
	for {
	n, _ := file.Read(buf)
	if n <= 0 {
	break
	}
	addrs = append(addrs, string(buf[:n]))
	}
	return addrs, nil
	}

	type ret struct {
	addrs []string
	err error
	}

	ch := make(chan ret, 1)
	go func() {
	addrs, err := queryAddrs()
	ch <- ret{addrs: addrs, err: err}
	}()

	select {
	case r := <-ch:
	return r.addrs, r.err
	case <-ctx.Done():
	return nil, &DNSError{
	Name: query,
	Err: ctx.Err().Error(),
	IsTimeout: ctx.Err() == context.DeadlineExceeded,
	}
	}
	}

	func queryCS(ctx context.Context, net, host, service string) (res []string, err error) {
	switch net {
	case "tcp4", "tcp6":
	net = "tcp"
	case "udp4", "udp6":
	net = "udp"
	}
	if host == "" {
	host = "*"
	}
	return query(ctx, netdir+"/cs", net+"!"+host+"!"+service, 128)
	}

	func queryCS1(ctx context.Context, net string, ip IP, port int) (clone, dest string, err error) {
	ips := "*"
	if len(ip) != 0 && !ip.IsUnspecified() {
	ips = ip.String()
	}
	lines, err := queryCS(ctx, net, ips, itoa.Itoa(port))
	if err != nil {
	return
	}
	f := getFields(lines[0])
	if len(f) < 2 {
	return "", "", errors.New("bad response from ndb/cs")
	}
	clone, dest = f[0], f[1]
	return
	}

	func queryDNS(ctx context.Context, addr string, typ string) (res []string, err error) {
	return query(ctx, netdir+"/dns", addr+" "+typ, 1024)
	}

	// toLower returns a lower-case version of in. Restricting us to
	// ASCII is sufficient to handle the IP protocol names and allow
	// us to not depend on the strings and unicode packages.
	func toLower(in string) string {
	for _, c := range in {
	if 'A' <= c && c <= 'Z' {
	// Has upper case; need to fix.
	out := []byte(in)
	for i := 0; i < len(in); i++ {
	c := in[i]
	if 'A' <= c && c <= 'Z' {
	c += 'a' - 'A'
	}
	out[i] = c
	}
	return string(out)
	}
	}
	return in
	}

	// lookupProtocol looks up IP protocol name and returns
	// the corresponding protocol number.
	func lookupProtocol(ctx context.Context, name string) (proto int, err error) {
	lines, err := query(ctx, netdir+"/cs", "!protocol="+toLower(name), 128)
	if err != nil {
	return 0, err
	}
	if len(lines) == 0 {
	return 0, UnknownNetworkError(name)
	}
	f := getFields(lines[0])
	if len(f) < 2 {
	return 0, UnknownNetworkError(name)
	}
	s := f[1]
	if n, _, ok := dtoi(s[bytealg.IndexByteString(s, '=')+1:]); ok {
	return n, nil
	}
	return 0, UnknownNetworkError(name)
	}

	func (*Resolver) lookupHost(ctx context.Context, host string) (addrs []string, err error) {
	// Use netdir/cs instead of netdir/dns because cs knows about
	// host names in local network (e.g. from /lib/ndb/local)
	lines, err := queryCS(ctx, "net", host, "1")
	if err != nil {
	dnsError := &DNSError{Err: err.Error(), Name: host}
	if stringsHasSuffix(err.Error(), "dns failure") {
	dnsError.Err = errNoSuchHost.Error()
	dnsError.IsNotFound = true
	}
	return nil, dnsError
	}
	loop:
	for _, line := range lines {
	f := getFields(line)
	if len(f) < 2 {
	continue
	}
	addr := f[1]
	if i := bytealg.IndexByteString(addr, '!'); i >= 0 {
	addr = addr[:i] // remove port
	}
	if ParseIP(addr) == nil {
	continue
	}
	// only return unique addresses
	for _, a := range addrs {
	if a == addr {
	continue loop
	}
	}
	addrs = append(addrs, addr)
	}
	return
	}

	// 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
	}
	for _, lit := range lits {
	host, zone := splitHostZone(lit)
	if ip := ParseIP(host); ip != nil {
	addr := IPAddr{IP: ip, Zone: zone}
	addrs = append(addrs, addr)
	}
	}
	return
	}

	func (*Resolver) lookupPort(ctx context.Context, network, service string) (port int, err error) {
	switch network {
	case "tcp4", "tcp6":
	network = "tcp"
	case "udp4", "udp6":
	network = "udp"
	}
	lines, err := queryCS(ctx, network, "127.0.0.1", toLower(service))
	if err != nil {
	return
	}
	unknownPortError := &AddrError{Err: "unknown port", Addr: network + "/" + service}
	if len(lines) == 0 {
	return 0, unknownPortError
	}
	f := getFields(lines[0])
	if len(f) < 2 {
	return 0, unknownPortError
	}
	s := f[1]
	if i := bytealg.IndexByteString(s, '!'); i >= 0 {
	s = s[i+1:] // remove address
	}
	if n, _, ok := dtoi(s); ok {
	return n, nil
	}
	return 0, unknownPortError
	}

	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") {
	cname = name + "."
	err = nil
	}
	return
	}
	if len(lines) > 0 {
	if f := getFields(lines[0]); len(f) >= 3 {
	return f[2] + ".", nil
	}
	}
	return "", errors.New("bad response from ndb/dns")
	}

	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
	} else {
	target = "_" + service + "._" + proto + "." + name
	}
	lines, err := queryDNS(ctx, target, "srv")
	if err != nil {
	return
	}
	for _, line := range lines {
	f := getFields(line)
	if len(f) < 6 {
	continue
	}
	port, _, portOk := dtoi(f[4])
	priority, _, priorityOk := dtoi(f[3])
	weight, _, weightOk := dtoi(f[2])
	if !(portOk && priorityOk && weightOk) {
	continue
	}
	addrs = append(addrs, &SRV{absDomainName(f[5]), uint16(port), uint16(priority), uint16(weight)})
	cname = absDomainName(f[0])
	}
	byPriorityWeight(addrs).sort()
	return
	}

	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
	}
	for _, line := range lines {
	f := getFields(line)
	if len(f) < 4 {
	continue
	}
	if pref, _, ok := dtoi(f[2]); ok {
	mx = append(mx, &MX{absDomainName(f[3]), uint16(pref)})
	}
	}
	byPref(mx).sort()
	return
	}

	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
	}
	for _, line := range lines {
	f := getFields(line)
	if len(f) < 3 {
	continue
	}
	ns = append(ns, &NS{absDomainName(f[2])})
	}
	return
	}

	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
	}
	for _, line := range lines {
	if i := bytealg.IndexByteString(line, '\t'); i >= 0 {
	txt = append(txt, line[i+1:])
	}
	}
	return
	}

	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
	}
	lines, err := queryDNS(ctx, arpa, "ptr")
	if err != nil {
	return
	}
	for _, line := range lines {
	f := getFields(line)
	if len(f) < 3 {
	continue
	}
	name = append(name, absDomainName(f[2]))
	}
	return
	}

	// concurrentThreadsLimit returns the number of threads we permit to
	// run concurrently doing DNS lookups.
	func concurrentThreadsLimit() int {
	return 500
	}