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 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 } 196
