libgo/go/net/lookup_unix.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 // +build aix darwin dragonfly freebsd linux netbsd openbsd solaris
   6
   7 package net
   8
   9 import (
  10         "context"
  11         "sync"
  12 )
  13
  14 var onceReadProtocols sync.Once
  15
  16 // readProtocols loads contents of /etc/protocols into protocols map
  17 // for quick access.
  18 func readProtocols() {
  19         file, err := open("/etc/protocols")
  20         if err != nil {
  21                 return
  22         }
  23         defer file.close()
  24
  25         for line, ok := file.readLine(); ok; line, ok = file.readLine() {
  26                 // tcp    6   TCP    # transmission control protocol
  27                 if i := byteIndex(line, '#'); i >= 0 {
  28                         line = line[0:i]
  29                 }
  30                 f := getFields(line)
  31                 if len(f) < 2 {
  32                         continue
  33                 }
  34                 if proto, _, ok := dtoi(f[1]); ok {
  35                         if _, ok := protocols[f[0]]; !ok {
  36                                 protocols[f[0]] = proto
  37                         }
  38                         for _, alias := range f[2:] {
  39                                 if _, ok := protocols[alias]; !ok {
  40                                         protocols[alias] = proto
  41                                 }
  42                         }
  43                 }
  44         }
  45 }
  46
  47 // lookupProtocol looks up IP protocol name in /etc/protocols and
  48 // returns correspondent protocol number.
  49 func lookupProtocol(_ context.Context, name string) (int, error) {
  50         onceReadProtocols.Do(readProtocols)
  51         return lookupProtocolMap(name)
  52 }
  53
  54 func (r *Resolver) dial(ctx context.Context, network, server string) (dnsConn, error) {
  55         // Calling Dial here is scary -- we have to be sure not to
  56         // dial a name that will require a DNS lookup, or Dial will
  57         // call back here to translate it. The DNS config parser has
  58         // already checked that all the cfg.servers are IP
  59         // addresses, which Dial will use without a DNS lookup.
  60         var c Conn
  61         var err error
  62         if r.Dial != nil {
  63                 c, err = r.Dial(ctx, network, server)
  64         } else {
  65                 var d Dialer
  66                 c, err = d.DialContext(ctx, network, server)
  67         }
  68         if err != nil {
  69                 return nil, mapErr(err)
  70         }
  71         if _, ok := c.(PacketConn); ok {
  72                 return &dnsPacketConn{c}, nil
  73         }
  74         return &dnsStreamConn{c}, nil
  75 }
  76
  77 func (r *Resolver) lookupHost(ctx context.Context, host string) (addrs []string, err error) {
  78         order := systemConf().hostLookupOrder(host)
  79         if !r.PreferGo && order == hostLookupCgo {
  80                 if addrs, err, ok := cgoLookupHost(ctx, host); ok {
  81                         return addrs, err
  82                 }
  83                 // cgo not available (or netgo); fall back to Go's DNS resolver
  84                 order = hostLookupFilesDNS
  85         }
  86         return r.goLookupHostOrder(ctx, host, order)
  87 }
  88
  89 func (r *Resolver) lookupIP(ctx context.Context, host string) (addrs []IPAddr, err error) {
  90         if r.PreferGo {
  91                 return r.goLookupIP(ctx, host)
  92         }
  93         order := systemConf().hostLookupOrder(host)
  94         if order == hostLookupCgo {
  95                 if addrs, err, ok := cgoLookupIP(ctx, host); ok {
  96                         return addrs, err
  97                 }
  98                 // cgo not available (or netgo); fall back to Go's DNS resolver
  99                 order = hostLookupFilesDNS
 100         }
 101         addrs, _, err = r.goLookupIPCNAMEOrder(ctx, host, order)
 102         return
 103 }
 104
 105 func (r *Resolver) lookupPort(ctx context.Context, network, service string) (int, error) {
 106         if !r.PreferGo && systemConf().canUseCgo() {
 107                 if port, err, ok := cgoLookupPort(ctx, network, service); ok {
 108                         if err != nil {
 109                                 // Issue 18213: if cgo fails, first check to see whether we
 110                                 // have the answer baked-in to the net package.
 111                                 if port, err := goLookupPort(network, service); err == nil {
 112                                         return port, nil
 113                                 }
 114                         }
 115                         return port, err
 116                 }
 117         }
 118         return goLookupPort(network, service)
 119 }
 120
 121 func (r *Resolver) lookupCNAME(ctx context.Context, name string) (string, error) {
 122         if !r.PreferGo && systemConf().canUseCgo() {
 123                 if cname, err, ok := cgoLookupCNAME(ctx, name); ok {
 124                         return cname, err
 125                 }
 126         }
 127         return r.goLookupCNAME(ctx, name)
 128 }
 129
 130 func (r *Resolver) lookupSRV(ctx context.Context, service, proto, name string) (string, []*SRV, error) {
 131         var target string
 132         if service == "" && proto == "" {
 133                 target = name
 134         } else {
 135                 target = "_" + service + "._" + proto + "." + name
 136         }
 137         cname, rrs, err := r.lookup(ctx, target, dnsTypeSRV)
 138         if err != nil {
 139                 return "", nil, err
 140         }
 141         srvs := make([]*SRV, len(rrs))
 142         for i, rr := range rrs {
 143                 rr := rr.(*dnsRR_SRV)
 144                 srvs[i] = &SRV{Target: rr.Target, Port: rr.Port, Priority: rr.Priority, Weight: rr.Weight}
 145         }
 146         byPriorityWeight(srvs).sort()
 147         return cname, srvs, nil
 148 }
 149
 150 func (r *Resolver) lookupMX(ctx context.Context, name string) ([]*MX, error) {
 151         _, rrs, err := r.lookup(ctx, name, dnsTypeMX)
 152         if err != nil {
 153                 return nil, err
 154         }
 155         mxs := make([]*MX, len(rrs))
 156         for i, rr := range rrs {
 157                 rr := rr.(*dnsRR_MX)
 158                 mxs[i] = &MX{Host: rr.Mx, Pref: rr.Pref}
 159         }
 160         byPref(mxs).sort()
 161         return mxs, nil
 162 }
 163
 164 func (r *Resolver) lookupNS(ctx context.Context, name string) ([]*NS, error) {
 165         _, rrs, err := r.lookup(ctx, name, dnsTypeNS)
 166         if err != nil {
 167                 return nil, err
 168         }
 169         nss := make([]*NS, len(rrs))
 170         for i, rr := range rrs {
 171                 nss[i] = &NS{Host: rr.(*dnsRR_NS).Ns}
 172         }
 173         return nss, nil
 174 }
 175
 176 func (r *Resolver) lookupTXT(ctx context.Context, name string) ([]string, error) {
 177         _, rrs, err := r.lookup(ctx, name, dnsTypeTXT)
 178         if err != nil {
 179                 return nil, err
 180         }
 181         txts := make([]string, len(rrs))
 182         for i, rr := range rrs {
 183                 txts[i] = rr.(*dnsRR_TXT).Txt
 184         }
 185         return txts, nil
 186 }
 187
 188 func (r *Resolver) lookupAddr(ctx context.Context, addr string) ([]string, error) {
 189         if !r.PreferGo && systemConf().canUseCgo() {
 190                 if ptrs, err, ok := cgoLookupPTR(ctx, addr); ok {
 191                         return ptrs, err
 192                 }
 193         }
 194         return r.goLookupPTR(ctx, addr)
 195 }