vendor/google.golang.org/grpc/naming/dns_resolver.go

   1 /*
   2  *
   3  * Copyright 2017 gRPC authors.
   4  *
   5  * Licensed under the Apache License, Version 2.0 (the "License");
   6  * you may not use this file except in compliance with the License.
   7  * You may obtain a copy of the License at
   8  *
   9  *     http://www.apache.org/licenses/LICENSE-2.0
  10  *
  11  * Unless required by applicable law or agreed to in writing, software
  12  * distributed under the License is distributed on an "AS IS" BASIS,
  13  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  14  * See the License for the specific language governing permissions and
  15  * limitations under the License.
  16  *
  17  */
  18
  19 package naming
  20
  21 import (
  22         "errors"
  23         "fmt"
  24         "net"
  25         "strconv"
  26         "time"
  27
  28         "golang.org/x/net/context"
  29         "google.golang.org/grpc/grpclog"
  30 )
  31
  32 const (
  33         defaultPort = "443"
  34         defaultFreq = time.Minute * 30
  35 )
  36
  37 var (
  38         errMissingAddr  = errors.New("missing address")
  39         errWatcherClose = errors.New("watcher has been closed")
  40 )
  41
  42 // NewDNSResolverWithFreq creates a DNS Resolver that can resolve DNS names, and
  43 // create watchers that poll the DNS server using the frequency set by freq.
  44 func NewDNSResolverWithFreq(freq time.Duration) (Resolver, error) {
  45         return &dnsResolver{freq: freq}, nil
  46 }
  47
  48 // NewDNSResolver creates a DNS Resolver that can resolve DNS names, and create
  49 // watchers that poll the DNS server using the default frequency defined by defaultFreq.
  50 func NewDNSResolver() (Resolver, error) {
  51         return NewDNSResolverWithFreq(defaultFreq)
  52 }
  53
  54 // dnsResolver handles name resolution for names following the DNS scheme
  55 type dnsResolver struct {
  56         // frequency of polling the DNS server that the watchers created by this resolver will use.
  57         freq time.Duration
  58 }
  59
  60 // formatIP returns ok = false if addr is not a valid textual representation of an IP address.
  61 // If addr is an IPv4 address, return the addr and ok = true.
  62 // If addr is an IPv6 address, return the addr enclosed in square brackets and ok = true.
  63 func formatIP(addr string) (addrIP string, ok bool) {
  64         ip := net.ParseIP(addr)
  65         if ip == nil {
  66                 return "", false
  67         }
  68         if ip.To4() != nil {
  69                 return addr, true
  70         }
  71         return "[" + addr + "]", true
  72 }
  73
  74 // parseTarget takes the user input target string, returns formatted host and port info.
  75 // If target doesn't specify a port, set the port to be the defaultPort.
  76 // If target is in IPv6 format and host-name is enclosed in sqarue brackets, brackets
  77 // are strippd when setting the host.
  78 // examples:
  79 // target: "www.google.com" returns host: "www.google.com", port: "443"
  80 // target: "ipv4-host:80" returns host: "ipv4-host", port: "80"
  81 // target: "[ipv6-host]" returns host: "ipv6-host", port: "443"
  82 // target: ":80" returns host: "localhost", port: "80"
  83 // target: ":" returns host: "localhost", port: "443"
  84 func parseTarget(target string) (host, port string, err error) {
  85         if target == "" {
  86                 return "", "", errMissingAddr
  87         }
  88
  89         if ip := net.ParseIP(target); ip != nil {
  90                 // target is an IPv4 or IPv6(without brackets) address
  91                 return target, defaultPort, nil
  92         }
  93         if host, port, err := net.SplitHostPort(target); err == nil {
  94                 // target has port, i.e ipv4-host:port, [ipv6-host]:port, host-name:port
  95                 if host == "" {
  96                         // Keep consistent with net.Dial(): If the host is empty, as in ":80", the local system is assumed.
  97                         host = "localhost"
  98                 }
  99                 if port == "" {
 100                         // If the port field is empty(target ends with colon), e.g. "[::1]:", defaultPort is used.
 101                         port = defaultPort
 102                 }
 103                 return host, port, nil
 104         }
 105         if host, port, err := net.SplitHostPort(target + ":" + defaultPort); err == nil {
 106                 // target doesn't have port
 107                 return host, port, nil
 108         }
 109         return "", "", fmt.Errorf("invalid target address %v", target)
 110 }
 111
 112 // Resolve creates a watcher that watches the name resolution of the target.
 113 func (r *dnsResolver) Resolve(target string) (Watcher, error) {
 114         host, port, err := parseTarget(target)
 115         if err != nil {
 116                 return nil, err
 117         }
 118
 119         if net.ParseIP(host) != nil {
 120                 ipWatcher := &ipWatcher{
 121                         updateChan: make(chan *Update, 1),
 122                 }
 123                 host, _ = formatIP(host)
 124                 ipWatcher.updateChan <- &Update{Op: Add, Addr: host + ":" + port}
 125                 return ipWatcher, nil
 126         }
 127
 128         ctx, cancel := context.WithCancel(context.Background())
 129         return &dnsWatcher{
 130                 r:      r,
 131                 host:   host,
 132                 port:   port,
 133                 ctx:    ctx,
 134                 cancel: cancel,
 135                 t:      time.NewTimer(0),
 136         }, nil
 137 }
 138
 139 // dnsWatcher watches for the name resolution update for a specific target
 140 type dnsWatcher struct {
 141         r    *dnsResolver
 142         host string
 143         port string
 144         // The latest resolved address list
 145         curAddrs []*Update
 146         ctx      context.Context
 147         cancel   context.CancelFunc
 148         t        *time.Timer
 149 }
 150
 151 // ipWatcher watches for the name resolution update for an IP address.
 152 type ipWatcher struct {
 153         updateChan chan *Update
 154 }
 155
 156 // Next returns the adrress resolution Update for the target. For IP address,
 157 // the resolution is itself, thus polling name server is unncessary. Therefore,
 158 // Next() will return an Update the first time it is called, and will be blocked
 159 // for all following calls as no Update exisits until watcher is closed.
 160 func (i *ipWatcher) Next() ([]*Update, error) {
 161         u, ok := <-i.updateChan
 162         if !ok {
 163                 return nil, errWatcherClose
 164         }
 165         return []*Update{u}, nil
 166 }
 167
 168 // Close closes the ipWatcher.
 169 func (i *ipWatcher) Close() {
 170         close(i.updateChan)
 171 }
 172
 173 // AddressType indicates the address type returned by name resolution.
 174 type AddressType uint8
 175
 176 const (
 177         // Backend indicates the server is a backend server.
 178         Backend AddressType = iota
 179         // GRPCLB indicates the server is a grpclb load balancer.
 180         GRPCLB
 181 )
 182
 183 // AddrMetadataGRPCLB contains the information the name resolver for grpclb should provide. The
 184 // name resolver used by the grpclb balancer is required to provide this type of metadata in
 185 // its address updates.
 186 type AddrMetadataGRPCLB struct {
 187         // AddrType is the type of server (grpc load balancer or backend).
 188         AddrType AddressType
 189         // ServerName is the name of the grpc load balancer. Used for authentication.
 190         ServerName string
 191 }
 192
 193 // compileUpdate compares the old resolved addresses and newly resolved addresses,
 194 // and generates an update list
 195 func (w *dnsWatcher) compileUpdate(newAddrs []*Update) []*Update {
 196         update := make(map[Update]bool)
 197         for _, u := range newAddrs {
 198                 update[*u] = true
 199         }
 200         for _, u := range w.curAddrs {
 201                 if _, ok := update[*u]; ok {
 202                         delete(update, *u)
 203                         continue
 204                 }
 205                 update[Update{Addr: u.Addr, Op: Delete, Metadata: u.Metadata}] = true
 206         }
 207         res := make([]*Update, 0, len(update))
 208         for k := range update {
 209                 tmp := k
 210                 res = append(res, &tmp)
 211         }
 212         return res
 213 }
 214
 215 func (w *dnsWatcher) lookupSRV() []*Update {
 216         var newAddrs []*Update
 217         _, srvs, err := lookupSRV(w.ctx, "grpclb", "tcp", w.host)
 218         if err != nil {
 219                 grpclog.Infof("grpc: failed dns SRV record lookup due to %v.\n", err)
 220                 return nil
 221         }
 222         for _, s := range srvs {
 223                 lbAddrs, err := lookupHost(w.ctx, s.Target)
 224                 if err != nil {
 225                         grpclog.Warningf("grpc: failed load banlacer address dns lookup due to %v.\n", err)
 226                         continue
 227                 }
 228                 for _, a := range lbAddrs {
 229                         a, ok := formatIP(a)
 230                         if !ok {
 231                                 grpclog.Errorf("grpc: failed IP parsing due to %v.\n", err)
 232                                 continue
 233                         }
 234                         newAddrs = append(newAddrs, &Update{Addr: a + ":" + strconv.Itoa(int(s.Port)),
 235                                 Metadata: AddrMetadataGRPCLB{AddrType: GRPCLB, ServerName: s.Target}})
 236                 }
 237         }
 238         return newAddrs
 239 }
 240
 241 func (w *dnsWatcher) lookupHost() []*Update {
 242         var newAddrs []*Update
 243         addrs, err := lookupHost(w.ctx, w.host)
 244         if err != nil {
 245                 grpclog.Warningf("grpc: failed dns A record lookup due to %v.\n", err)
 246                 return nil
 247         }
 248         for _, a := range addrs {
 249                 a, ok := formatIP(a)
 250                 if !ok {
 251                         grpclog.Errorf("grpc: failed IP parsing due to %v.\n", err)
 252                         continue
 253                 }
 254                 newAddrs = append(newAddrs, &Update{Addr: a + ":" + w.port})
 255         }
 256         return newAddrs
 257 }
 258
 259 func (w *dnsWatcher) lookup() []*Update {
 260         newAddrs := w.lookupSRV()
 261         if newAddrs == nil {
 262                 // If failed to get any balancer address (either no corresponding SRV for the
 263                 // target, or caused by failure during resolution/parsing of the balancer target),
 264                 // return any A record info available.
 265                 newAddrs = w.lookupHost()
 266         }
 267         result := w.compileUpdate(newAddrs)
 268         w.curAddrs = newAddrs
 269         return result
 270 }
 271
 272 // Next returns the resolved address update(delta) for the target. If there's no
 273 // change, it will sleep for 30 mins and try to resolve again after that.
 274 func (w *dnsWatcher) Next() ([]*Update, error) {
 275         for {
 276                 select {
 277                 case <-w.ctx.Done():
 278                         return nil, errWatcherClose
 279                 case <-w.t.C:
 280                 }
 281                 result := w.lookup()
 282                 // Next lookup should happen after an interval defined by w.r.freq.
 283                 w.t.Reset(w.r.freq)
 284                 if len(result) > 0 {
 285                         return result, nil
 286                 }
 287         }
 288 }
 289
 290 func (w *dnsWatcher) Close() {
 291         w.cancel()
 292 }