lookup_plan9.go

     1  // Copyright 2011 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package net
     6  
     7  import (
     8  	"context"
     9  	"errors"
    10  	"internal/bytealg"
    11  	"internal/itoa"
    12  	"io"
    13  	"os"
    14  )
    15  
    16  // cgoAvailable set to true to indicate that the cgo resolver
    17  // is available on Plan 9. Note that on Plan 9 the cgo resolver
    18  // does not actually use cgo.
    19  const cgoAvailable = true
    20  
    21  func query(ctx context.Context, filename, query string, bufSize int) (addrs []string, err error) {
    22  	queryAddrs := func() (addrs []string, err error) {
    23  		file, err := os.OpenFile(filename, os.O_RDWR, 0)
    24  		if err != nil {
    25  			return nil, err
    26  		}
    27  		defer file.Close()
    28  
    29  		_, err = file.Seek(0, io.SeekStart)
    30  		if err != nil {
    31  			return nil, err
    32  		}
    33  		_, err = file.WriteString(query)
    34  		if err != nil {
    35  			return nil, err
    36  		}
    37  		_, err = file.Seek(0, io.SeekStart)
    38  		if err != nil {
    39  			return nil, err
    40  		}
    41  		buf := make([]byte, bufSize)
    42  		for {
    43  			n, _ := file.Read(buf)
    44  			if n <= 0 {
    45  				break
    46  			}
    47  			addrs = append(addrs, string(buf[:n]))
    48  		}
    49  		return addrs, nil
    50  	}
    51  
    52  	type ret struct {
    53  		addrs []string
    54  		err   error
    55  	}
    56  
    57  	ch := make(chan ret, 1)
    58  	go func() {
    59  		addrs, err := queryAddrs()
    60  		ch <- ret{addrs: addrs, err: err}
    61  	}()
    62  
    63  	select {
    64  	case r := <-ch:
    65  		return r.addrs, r.err
    66  	case <-ctx.Done():
    67  		return nil, &DNSError{
    68  			Name:      query,
    69  			Err:       ctx.Err().Error(),
    70  			IsTimeout: ctx.Err() == context.DeadlineExceeded,
    71  		}
    72  	}
    73  }
    74  
    75  func queryCS(ctx context.Context, net, host, service string) (res []string, err error) {
    76  	switch net {
    77  	case "tcp4", "tcp6":
    78  		net = "tcp"
    79  	case "udp4", "udp6":
    80  		net = "udp"
    81  	}
    82  	if host == "" {
    83  		host = "*"
    84  	}
    85  	return query(ctx, netdir+"/cs", net+"!"+host+"!"+service, 128)
    86  }
    87  
    88  func queryCS1(ctx context.Context, net string, ip IP, port int) (clone, dest string, err error) {
    89  	ips := "*"
    90  	if len(ip) != 0 && !ip.IsUnspecified() {
    91  		ips = ip.String()
    92  	}
    93  	lines, err := queryCS(ctx, net, ips, itoa.Itoa(port))
    94  	if err != nil {
    95  		return
    96  	}
    97  	f := getFields(lines[0])
    98  	if len(f) < 2 {
    99  		return "", "", errors.New("bad response from ndb/cs")
   100  	}
   101  	clone, dest = f[0], f[1]
   102  	return
   103  }
   104  
   105  func queryDNS(ctx context.Context, addr string, typ string) (res []string, err error) {
   106  	return query(ctx, netdir+"/dns", addr+" "+typ, 1024)
   107  }
   108  
   109  // toLower returns a lower-case version of in. Restricting us to
   110  // ASCII is sufficient to handle the IP protocol names and allow
   111  // us to not depend on the strings and unicode packages.
   112  func toLower(in string) string {
   113  	for _, c := range in {
   114  		if 'A' <= c && c <= 'Z' {
   115  			// Has upper case; need to fix.
   116  			out := []byte(in)
   117  			for i := 0; i < len(in); i++ {
   118  				c := in[i]
   119  				if 'A' <= c && c <= 'Z' {
   120  					c += 'a' - 'A'
   121  				}
   122  				out[i] = c
   123  			}
   124  			return string(out)
   125  		}
   126  	}
   127  	return in
   128  }
   129  
   130  // lookupProtocol looks up IP protocol name and returns
   131  // the corresponding protocol number.
   132  func lookupProtocol(ctx context.Context, name string) (proto int, err error) {
   133  	lines, err := query(ctx, netdir+"/cs", "!protocol="+toLower(name), 128)
   134  	if err != nil {
   135  		return 0, err
   136  	}
   137  	if len(lines) == 0 {
   138  		return 0, UnknownNetworkError(name)
   139  	}
   140  	f := getFields(lines[0])
   141  	if len(f) < 2 {
   142  		return 0, UnknownNetworkError(name)
   143  	}
   144  	s := f[1]
   145  	if n, _, ok := dtoi(s[bytealg.IndexByteString(s, '=')+1:]); ok {
   146  		return n, nil
   147  	}
   148  	return 0, UnknownNetworkError(name)
   149  }
   150  
   151  func (*Resolver) lookupHost(ctx context.Context, host string) (addrs []string, err error) {
   152  	// Use netdir/cs instead of netdir/dns because cs knows about
   153  	// host names in local network (e.g. from /lib/ndb/local)
   154  	lines, err := queryCS(ctx, "net", host, "1")
   155  	if err != nil {
   156  		dnsError := &DNSError{Err: err.Error(), Name: host}
   157  		if stringsHasSuffix(err.Error(), "dns failure") {
   158  			dnsError.Err = errNoSuchHost.Error()
   159  			dnsError.IsNotFound = true
   160  		}
   161  		return nil, dnsError
   162  	}
   163  loop:
   164  	for _, line := range lines {
   165  		f := getFields(line)
   166  		if len(f) < 2 {
   167  			continue
   168  		}
   169  		addr := f[1]
   170  		if i := bytealg.IndexByteString(addr, '!'); i >= 0 {
   171  			addr = addr[:i] // remove port
   172  		}
   173  		if ParseIP(addr) == nil {
   174  			continue
   175  		}
   176  		// only return unique addresses
   177  		for _, a := range addrs {
   178  			if a == addr {
   179  				continue loop
   180  			}
   181  		}
   182  		addrs = append(addrs, addr)
   183  	}
   184  	return
   185  }
   186  
   187  // preferGoOverPlan9 reports whether the resolver should use the
   188  // "PreferGo" implementation rather than asking plan9 services
   189  // for the answers.
   190  func (r *Resolver) preferGoOverPlan9() bool {
   191  	_, _, res := r.preferGoOverPlan9WithOrderAndConf()
   192  	return res
   193  }
   194  
   195  func (r *Resolver) preferGoOverPlan9WithOrderAndConf() (hostLookupOrder, *dnsConfig, bool) {
   196  	order, conf := systemConf().hostLookupOrder(r, "") // name is unused
   197  
   198  	// TODO(bradfitz): for now we only permit use of the PreferGo
   199  	// implementation when there's a non-nil Resolver with a
   200  	// non-nil Dialer. This is a sign that they the code is trying
   201  	// to use their DNS-speaking net.Conn (such as an in-memory
   202  	// DNS cache) and they don't want to actually hit the network.
   203  	// Once we add support for looking the default DNS servers
   204  	// from plan9, though, then we can relax this.
   205  	return order, conf, order != hostLookupCgo && r != nil && r.Dial != nil
   206  }
   207  
   208  func (r *Resolver) lookupIP(ctx context.Context, network, host string) (addrs []IPAddr, err error) {
   209  	if r.preferGoOverPlan9() {
   210  		return r.goLookupIP(ctx, network, host)
   211  	}
   212  	lits, err := r.lookupHost(ctx, host)
   213  	if err != nil {
   214  		return
   215  	}
   216  	for _, lit := range lits {
   217  		host, zone := splitHostZone(lit)
   218  		if ip := ParseIP(host); ip != nil {
   219  			addr := IPAddr{IP: ip, Zone: zone}
   220  			addrs = append(addrs, addr)
   221  		}
   222  	}
   223  	return
   224  }
   225  
   226  func (*Resolver) lookupPort(ctx context.Context, network, service string) (port int, err error) {
   227  	switch network {
   228  	case "tcp4", "tcp6":
   229  		network = "tcp"
   230  	case "udp4", "udp6":
   231  		network = "udp"
   232  	}
   233  	lines, err := queryCS(ctx, network, "127.0.0.1", toLower(service))
   234  	if err != nil {
   235  		return
   236  	}
   237  	unknownPortError := &AddrError{Err: "unknown port", Addr: network + "/" + service}
   238  	if len(lines) == 0 {
   239  		return 0, unknownPortError
   240  	}
   241  	f := getFields(lines[0])
   242  	if len(f) < 2 {
   243  		return 0, unknownPortError
   244  	}
   245  	s := f[1]
   246  	if i := bytealg.IndexByteString(s, '!'); i >= 0 {
   247  		s = s[i+1:] // remove address
   248  	}
   249  	if n, _, ok := dtoi(s); ok {
   250  		return n, nil
   251  	}
   252  	return 0, unknownPortError
   253  }
   254  
   255  func (r *Resolver) lookupCNAME(ctx context.Context, name string) (cname string, err error) {
   256  	if order, conf, preferGo := r.preferGoOverPlan9WithOrderAndConf(); preferGo {
   257  		return r.goLookupCNAME(ctx, name, order, conf)
   258  	}
   259  
   260  	lines, err := queryDNS(ctx, name, "cname")
   261  	if err != nil {
   262  		if stringsHasSuffix(err.Error(), "dns failure") || stringsHasSuffix(err.Error(), "resource does not exist; negrcode 0") {
   263  			cname = name + "."
   264  			err = nil
   265  		}
   266  		return
   267  	}
   268  	if len(lines) > 0 {
   269  		if f := getFields(lines[0]); len(f) >= 3 {
   270  			return f[2] + ".", nil
   271  		}
   272  	}
   273  	return "", errors.New("bad response from ndb/dns")
   274  }
   275  
   276  func (r *Resolver) lookupSRV(ctx context.Context, service, proto, name string) (cname string, addrs []*SRV, err error) {
   277  	if r.preferGoOverPlan9() {
   278  		return r.goLookupSRV(ctx, service, proto, name)
   279  	}
   280  	var target string
   281  	if service == "" && proto == "" {
   282  		target = name
   283  	} else {
   284  		target = "_" + service + "._" + proto + "." + name
   285  	}
   286  	lines, err := queryDNS(ctx, target, "srv")
   287  	if err != nil {
   288  		return
   289  	}
   290  	for _, line := range lines {
   291  		f := getFields(line)
   292  		if len(f) < 6 {
   293  			continue
   294  		}
   295  		port, _, portOk := dtoi(f[4])
   296  		priority, _, priorityOk := dtoi(f[3])
   297  		weight, _, weightOk := dtoi(f[2])
   298  		if !(portOk && priorityOk && weightOk) {
   299  			continue
   300  		}
   301  		addrs = append(addrs, &SRV{absDomainName(f[5]), uint16(port), uint16(priority), uint16(weight)})
   302  		cname = absDomainName(f[0])
   303  	}
   304  	byPriorityWeight(addrs).sort()
   305  	return
   306  }
   307  
   308  func (r *Resolver) lookupMX(ctx context.Context, name string) (mx []*MX, err error) {
   309  	if r.preferGoOverPlan9() {
   310  		return r.goLookupMX(ctx, name)
   311  	}
   312  	lines, err := queryDNS(ctx, name, "mx")
   313  	if err != nil {
   314  		return
   315  	}
   316  	for _, line := range lines {
   317  		f := getFields(line)
   318  		if len(f) < 4 {
   319  			continue
   320  		}
   321  		if pref, _, ok := dtoi(f[2]); ok {
   322  			mx = append(mx, &MX{absDomainName(f[3]), uint16(pref)})
   323  		}
   324  	}
   325  	byPref(mx).sort()
   326  	return
   327  }
   328  
   329  func (r *Resolver) lookupNS(ctx context.Context, name string) (ns []*NS, err error) {
   330  	if r.preferGoOverPlan9() {
   331  		return r.goLookupNS(ctx, name)
   332  	}
   333  	lines, err := queryDNS(ctx, name, "ns")
   334  	if err != nil {
   335  		return
   336  	}
   337  	for _, line := range lines {
   338  		f := getFields(line)
   339  		if len(f) < 3 {
   340  			continue
   341  		}
   342  		ns = append(ns, &NS{absDomainName(f[2])})
   343  	}
   344  	return
   345  }
   346  
   347  func (r *Resolver) lookupTXT(ctx context.Context, name string) (txt []string, err error) {
   348  	if r.preferGoOverPlan9() {
   349  		return r.goLookupTXT(ctx, name)
   350  	}
   351  	lines, err := queryDNS(ctx, name, "txt")
   352  	if err != nil {
   353  		return
   354  	}
   355  	for _, line := range lines {
   356  		if i := bytealg.IndexByteString(line, '\t'); i >= 0 {
   357  			txt = append(txt, line[i+1:])
   358  		}
   359  	}
   360  	return
   361  }
   362  
   363  func (r *Resolver) lookupAddr(ctx context.Context, addr string) (name []string, err error) {
   364  	if order, conf, preferGo := r.preferGoOverPlan9WithOrderAndConf(); preferGo {
   365  		return r.goLookupPTR(ctx, addr, order, conf)
   366  	}
   367  	arpa, err := reverseaddr(addr)
   368  	if err != nil {
   369  		return
   370  	}
   371  	lines, err := queryDNS(ctx, arpa, "ptr")
   372  	if err != nil {
   373  		return
   374  	}
   375  	for _, line := range lines {
   376  		f := getFields(line)
   377  		if len(f) < 3 {
   378  			continue
   379  		}
   380  		name = append(name, absDomainName(f[2]))
   381  	}
   382  	return
   383  }
   384  
   385  // concurrentThreadsLimit returns the number of threads we permit to
   386  // run concurrently doing DNS lookups.
   387  func concurrentThreadsLimit() int {
   388  	return 500
   389  }
   390
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