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         if file, err := open("/etc/protocols"); err == nil {
  20                 for line, ok := file.readLine(); ok; line, ok = file.readLine() {
  21                         // tcp    6   TCP    # transmission control protocol
  22                         if i := byteIndex(line, '#'); i >= 0 {
  23                                 line = line[0:i]
  24                         }
  25                         f := getFields(line)
  26                         if len(f) < 2 {
  27                                 continue
  28                         }
  29                         if proto, _, ok := dtoi(f[1]); ok {
  30                                 if _, ok := protocols[f[0]]; !ok {
  31                                         protocols[f[0]] = proto
  32                                 }
  33                                 for _, alias := range f[2:] {
  34                                         if _, ok := protocols[alias]; !ok {
  35                                                 protocols[alias] = proto
  36                                         }
  37                                 }
  38                         }
  39                 }
  40                 file.close()
  41         }
  42 }
  43
  44 // lookupProtocol looks up IP protocol name in /etc/protocols and
  45 // returns correspondent protocol number.
  46 func lookupProtocol(_ context.Context, name string) (int, error) {
  47         onceReadProtocols.Do(readProtocols)
  48         return lookupProtocolMap(name)
  49 }
  50
  51 func (r *Resolver) lookupHost(ctx context.Context, host string) (addrs []string, err error) {
  52         order := systemConf().hostLookupOrder(host)
  53         if !r.PreferGo && order == hostLookupCgo {
  54                 if addrs, err, ok := cgoLookupHost(ctx, host); ok {
  55                         return addrs, err
  56                 }
  57                 // cgo not available (or netgo); fall back to Go's DNS resolver
  58                 order = hostLookupFilesDNS
  59         }
  60         return goLookupHostOrder(ctx, host, order)
  61 }
  62
  63 func (r *Resolver) lookupIP(ctx context.Context, host string) (addrs []IPAddr, err error) {
  64         if r.PreferGo {
  65                 return goLookupIP(ctx, host)
  66         }
  67         order := systemConf().hostLookupOrder(host)
  68         if order == hostLookupCgo {
  69                 if addrs, err, ok := cgoLookupIP(ctx, host); ok {
  70                         return addrs, err
  71                 }
  72                 // cgo not available (or netgo); fall back to Go's DNS resolver
  73                 order = hostLookupFilesDNS
  74         }
  75         addrs, _, err = goLookupIPCNAMEOrder(ctx, host, order)
  76         return
  77 }
  78
  79 func (r *Resolver) lookupPort(ctx context.Context, network, service string) (int, error) {
  80         if !r.PreferGo && systemConf().canUseCgo() {
  81                 if port, err, ok := cgoLookupPort(ctx, network, service); ok {
  82                         if err != nil {
  83                                 // Issue 18213: if cgo fails, first check to see whether we
  84                                 // have the answer baked-in to the net package.
  85                                 if port, err := goLookupPort(network, service); err == nil {
  86                                         return port, nil
  87                                 }
  88                         }
  89                         return port, err
  90                 }
  91         }
  92         return goLookupPort(network, service)
  93 }
  94
  95 func (r *Resolver) lookupCNAME(ctx context.Context, name string) (string, error) {
  96         if !r.PreferGo && systemConf().canUseCgo() {
  97                 if cname, err, ok := cgoLookupCNAME(ctx, name); ok {
  98                         return cname, err
  99                 }
 100         }
 101         return goLookupCNAME(ctx, name)
 102 }
 103
 104 func (*Resolver) lookupSRV(ctx context.Context, service, proto, name string) (string, []*SRV, error) {
 105         var target string
 106         if service == "" && proto == "" {
 107                 target = name
 108         } else {
 109                 target = "_" + service + "._" + proto + "." + name
 110         }
 111         cname, rrs, err := lookup(ctx, target, dnsTypeSRV)
 112         if err != nil {
 113                 return "", nil, err
 114         }
 115         srvs := make([]*SRV, len(rrs))
 116         for i, rr := range rrs {
 117                 rr := rr.(*dnsRR_SRV)
 118                 srvs[i] = &SRV{Target: rr.Target, Port: rr.Port, Priority: rr.Priority, Weight: rr.Weight}
 119         }
 120         byPriorityWeight(srvs).sort()
 121         return cname, srvs, nil
 122 }
 123
 124 func (*Resolver) lookupMX(ctx context.Context, name string) ([]*MX, error) {
 125         _, rrs, err := lookup(ctx, name, dnsTypeMX)
 126         if err != nil {
 127                 return nil, err
 128         }
 129         mxs := make([]*MX, len(rrs))
 130         for i, rr := range rrs {
 131                 rr := rr.(*dnsRR_MX)
 132                 mxs[i] = &MX{Host: rr.Mx, Pref: rr.Pref}
 133         }
 134         byPref(mxs).sort()
 135         return mxs, nil
 136 }
 137
 138 func (*Resolver) lookupNS(ctx context.Context, name string) ([]*NS, error) {
 139         _, rrs, err := lookup(ctx, name, dnsTypeNS)
 140         if err != nil {
 141                 return nil, err
 142         }
 143         nss := make([]*NS, len(rrs))
 144         for i, rr := range rrs {
 145                 nss[i] = &NS{Host: rr.(*dnsRR_NS).Ns}
 146         }
 147         return nss, nil
 148 }
 149
 150 func (r *Resolver) lookupTXT(ctx context.Context, name string) ([]string, error) {
 151         _, rrs, err := lookup(ctx, name, dnsTypeTXT)
 152         if err != nil {
 153                 return nil, err
 154         }
 155         txts := make([]string, len(rrs))
 156         for i, rr := range rrs {
 157                 txts[i] = rr.(*dnsRR_TXT).Txt
 158         }
 159         return txts, nil
 160 }
 161
 162 func (r *Resolver) lookupAddr(ctx context.Context, addr string) ([]string, error) {
 163         if !r.PreferGo && systemConf().canUseCgo() {
 164                 if ptrs, err, ok := cgoLookupPTR(ctx, addr); ok {
 165                         return ptrs, err
 166                 }
 167         }
 168         return goLookupPTR(ctx, addr)
 169 }