lookup_plan9.go

Documentation: net

     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  func query(ctx context.Context, filename, query string, bufSize int) (addrs []string, err error) {
    17  	queryAddrs := func() (addrs []string, err error) {
    18  		file, err := os.OpenFile(filename, os.O_RDWR, 0)
    19  		if err != nil {
    20  			return nil, err
    21  		}
    22  		defer file.Close()
    23  
    24  		_, err = file.Seek(0, io.SeekStart)
    25  		if err != nil {
    26  			return nil, err
    27  		}
    28  		_, err = file.WriteString(query)
    29  		if err != nil {
    30  			return nil, err
    31  		}
    32  		_, err = file.Seek(0, io.SeekStart)
    33  		if err != nil {
    34  			return nil, err
    35  		}
    36  		buf := make([]byte, bufSize)
    37  		for {
    38  			n, _ := file.Read(buf)
    39  			if n <= 0 {
    40  				break
    41  			}
    42  			addrs = append(addrs, string(buf[:n]))
    43  		}
    44  		return addrs, nil
    45  	}
    46  
    47  	type ret struct {
    48  		addrs []string
    49  		err   error
    50  	}
    51  
    52  	ch := make(chan ret, 1)
    53  	go func() {
    54  		addrs, err := queryAddrs()
    55  		ch <- ret{addrs: addrs, err: err}
    56  	}()
    57  
    58  	select {
    59  	case r := <-ch:
    60  		return r.addrs, r.err
    61  	case <-ctx.Done():
    62  		return nil, &DNSError{
    63  			Name:      query,
    64  			Err:       ctx.Err().Error(),
    65  			IsTimeout: ctx.Err() == context.DeadlineExceeded,
    66  		}
    67  	}
    68  }
    69  
    70  func queryCS(ctx context.Context, net, host, service string) (res []string, err error) {
    71  	switch net {
    72  	case "tcp4", "tcp6":
    73  		net = "tcp"
    74  	case "udp4", "udp6":
    75  		net = "udp"
    76  	}
    77  	if host == "" {
    78  		host = "*"
    79  	}
    80  	return query(ctx, netdir+"/cs", net+"!"+host+"!"+service, 128)
    81  }
    82  
    83  func queryCS1(ctx context.Context, net string, ip IP, port int) (clone, dest string, err error) {
    84  	ips := "*"
    85  	if len(ip) != 0 && !ip.IsUnspecified() {
    86  		ips = ip.String()
    87  	}
    88  	lines, err := queryCS(ctx, net, ips, itoa.Itoa(port))
    89  	if err != nil {
    90  		return
    91  	}
    92  	f := getFields(lines[0])
    93  	if len(f) < 2 {
    94  		return "", "", errors.New("bad response from ndb/cs")
    95  	}
    96  	clone, dest = f[0], f[1]
    97  	return
    98  }
    99  
   100  func queryDNS(ctx context.Context, addr string, typ string) (res []string, err error) {
   101  	return query(ctx, netdir+"/dns", addr+" "+typ, 1024)
   102  }
   103  
   104  // toLower returns a lower-case version of in. Restricting us to
   105  // ASCII is sufficient to handle the IP protocol names and allow
   106  // us to not depend on the strings and unicode packages.
   107  func toLower(in string) string {
   108  	for _, c := range in {
   109  		if 'A' <= c && c <= 'Z' {
   110  			// Has upper case; need to fix.
   111  			out := []byte(in)
   112  			for i := 0; i < len(in); i++ {
   113  				c := in[i]
   114  				if 'A' <= c && c <= 'Z' {
   115  					c += 'a' - 'A'
   116  				}
   117  				out[i] = c
   118  			}
   119  			return string(out)
   120  		}
   121  	}
   122  	return in
   123  }
   124  
   125  // lookupProtocol looks up IP protocol name and returns
   126  // the corresponding protocol number.
   127  func lookupProtocol(ctx context.Context, name string) (proto int, err error) {
   128  	lines, err := query(ctx, netdir+"/cs", "!protocol="+toLower(name), 128)
   129  	if err != nil {
   130  		return 0, err
   131  	}
   132  	if len(lines) == 0 {
   133  		return 0, UnknownNetworkError(name)
   134  	}
   135  	f := getFields(lines[0])
   136  	if len(f) < 2 {
   137  		return 0, UnknownNetworkError(name)
   138  	}
   139  	s := f[1]
   140  	if n, _, ok := dtoi(s[bytealg.IndexByteString(s, '=')+1:]); ok {
   141  		return n, nil
   142  	}
   143  	return 0, UnknownNetworkError(name)
   144  }
   145  
   146  func (*Resolver) lookupHost(ctx context.Context, host string) (addrs []string, err error) {
   147  	// Use netdir/cs instead of netdir/dns because cs knows about
   148  	// host names in local network (e.g. from /lib/ndb/local)
   149  	lines, err := queryCS(ctx, "net", host, "1")
   150  	if err != nil {
   151  		dnsError := &DNSError{Err: err.Error(), Name: host}
   152  		if stringsHasSuffix(err.Error(), "dns failure") {
   153  			dnsError.Err = errNoSuchHost.Error()
   154  			dnsError.IsNotFound = true
   155  		}
   156  		return nil, dnsError
   157  	}
   158  loop:
   159  	for _, line := range lines {
   160  		f := getFields(line)
   161  		if len(f) < 2 {
   162  			continue
   163  		}
   164  		addr := f[1]
   165  		if i := bytealg.IndexByteString(addr, '!'); i >= 0 {
   166  			addr = addr[:i] // remove port
   167  		}
   168  		if ParseIP(addr) == nil {
   169  			continue
   170  		}
   171  		// only return unique addresses
   172  		for _, a := range addrs {
   173  			if a == addr {
   174  				continue loop
   175  			}
   176  		}
   177  		addrs = append(addrs, addr)
   178  	}
   179  	return
   180  }
   181  
   182  func (r *Resolver) lookupIP(ctx context.Context, _, host string) (addrs []IPAddr, err error) {
   183  	lits, err := r.lookupHost(ctx, host)
   184  	if err != nil {
   185  		return
   186  	}
   187  	for _, lit := range lits {
   188  		host, zone := splitHostZone(lit)
   189  		if ip := ParseIP(host); ip != nil {
   190  			addr := IPAddr{IP: ip, Zone: zone}
   191  			addrs = append(addrs, addr)
   192  		}
   193  	}
   194  	return
   195  }
   196  
   197  func (*Resolver) lookupPort(ctx context.Context, network, service string) (port int, err error) {
   198  	switch network {
   199  	case "tcp4", "tcp6":
   200  		network = "tcp"
   201  	case "udp4", "udp6":
   202  		network = "udp"
   203  	}
   204  	lines, err := queryCS(ctx, network, "127.0.0.1", toLower(service))
   205  	if err != nil {
   206  		return
   207  	}
   208  	unknownPortError := &AddrError{Err: "unknown port", Addr: network + "/" + service}
   209  	if len(lines) == 0 {
   210  		return 0, unknownPortError
   211  	}
   212  	f := getFields(lines[0])
   213  	if len(f) < 2 {
   214  		return 0, unknownPortError
   215  	}
   216  	s := f[1]
   217  	if i := bytealg.IndexByteString(s, '!'); i >= 0 {
   218  		s = s[i+1:] // remove address
   219  	}
   220  	if n, _, ok := dtoi(s); ok {
   221  		return n, nil
   222  	}
   223  	return 0, unknownPortError
   224  }
   225  
   226  func (*Resolver) lookupCNAME(ctx context.Context, name string) (cname string, err error) {
   227  	lines, err := queryDNS(ctx, name, "cname")
   228  	if err != nil {
   229  		if stringsHasSuffix(err.Error(), "dns failure") || stringsHasSuffix(err.Error(), "resource does not exist; negrcode 0") {
   230  			cname = name + "."
   231  			err = nil
   232  		}
   233  		return
   234  	}
   235  	if len(lines) > 0 {
   236  		if f := getFields(lines[0]); len(f) >= 3 {
   237  			return f[2] + ".", nil
   238  		}
   239  	}
   240  	return "", errors.New("bad response from ndb/dns")
   241  }
   242  
   243  func (*Resolver) lookupSRV(ctx context.Context, service, proto, name string) (cname string, addrs []*SRV, err error) {
   244  	var target string
   245  	if service == "" && proto == "" {
   246  		target = name
   247  	} else {
   248  		target = "_" + service + "._" + proto + "." + name
   249  	}
   250  	lines, err := queryDNS(ctx, target, "srv")
   251  	if err != nil {
   252  		return
   253  	}
   254  	for _, line := range lines {
   255  		f := getFields(line)
   256  		if len(f) < 6 {
   257  			continue
   258  		}
   259  		port, _, portOk := dtoi(f[4])
   260  		priority, _, priorityOk := dtoi(f[3])
   261  		weight, _, weightOk := dtoi(f[2])
   262  		if !(portOk && priorityOk && weightOk) {
   263  			continue
   264  		}
   265  		addrs = append(addrs, &SRV{absDomainName([]byte(f[5])), uint16(port), uint16(priority), uint16(weight)})
   266  		cname = absDomainName([]byte(f[0]))
   267  	}
   268  	byPriorityWeight(addrs).sort()
   269  	return
   270  }
   271  
   272  func (*Resolver) lookupMX(ctx context.Context, name string) (mx []*MX, err error) {
   273  	lines, err := queryDNS(ctx, name, "mx")
   274  	if err != nil {
   275  		return
   276  	}
   277  	for _, line := range lines {
   278  		f := getFields(line)
   279  		if len(f) < 4 {
   280  			continue
   281  		}
   282  		if pref, _, ok := dtoi(f[2]); ok {
   283  			mx = append(mx, &MX{absDomainName([]byte(f[3])), uint16(pref)})
   284  		}
   285  	}
   286  	byPref(mx).sort()
   287  	return
   288  }
   289  
   290  func (*Resolver) lookupNS(ctx context.Context, name string) (ns []*NS, err error) {
   291  	lines, err := queryDNS(ctx, name, "ns")
   292  	if err != nil {
   293  		return
   294  	}
   295  	for _, line := range lines {
   296  		f := getFields(line)
   297  		if len(f) < 3 {
   298  			continue
   299  		}
   300  		ns = append(ns, &NS{absDomainName([]byte(f[2]))})
   301  	}
   302  	return
   303  }
   304  
   305  func (*Resolver) lookupTXT(ctx context.Context, name string) (txt []string, err error) {
   306  	lines, err := queryDNS(ctx, name, "txt")
   307  	if err != nil {
   308  		return
   309  	}
   310  	for _, line := range lines {
   311  		if i := bytealg.IndexByteString(line, '\t'); i >= 0 {
   312  			txt = append(txt, line[i+1:])
   313  		}
   314  	}
   315  	return
   316  }
   317  
   318  func (*Resolver) lookupAddr(ctx context.Context, addr string) (name []string, err error) {
   319  	arpa, err := reverseaddr(addr)
   320  	if err != nil {
   321  		return
   322  	}
   323  	lines, err := queryDNS(ctx, arpa, "ptr")
   324  	if err != nil {
   325  		return
   326  	}
   327  	for _, line := range lines {
   328  		f := getFields(line)
   329  		if len(f) < 3 {
   330  			continue
   331  		}
   332  		name = append(name, absDomainName([]byte(f[2])))
   333  	}
   334  	return
   335  }
   336  
   337  // concurrentThreadsLimit returns the number of threads we permit to
   338  // run concurrently doing DNS lookups.
   339  func concurrentThreadsLimit() int {
   340  	return 500
   341  }
   342
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