3 * Copyright 2017 gRPC authors.
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
9 * http://www.apache.org/licenses/LICENSE-2.0
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.
29 "google.golang.org/grpc/grpclog"
34 defaultFreq = time.Minute * 30
38 errMissingAddr = errors.New("missing address")
39 errWatcherClose = errors.New("watcher has been closed")
41 lookupHost = net.DefaultResolver.LookupHost
42 lookupSRV = net.DefaultResolver.LookupSRV
45 // NewDNSResolverWithFreq creates a DNS Resolver that can resolve DNS names, and
46 // create watchers that poll the DNS server using the frequency set by freq.
47 func NewDNSResolverWithFreq(freq time.Duration) (Resolver, error) {
48 return &dnsResolver{freq: freq}, nil
51 // NewDNSResolver creates a DNS Resolver that can resolve DNS names, and create
52 // watchers that poll the DNS server using the default frequency defined by defaultFreq.
53 func NewDNSResolver() (Resolver, error) {
54 return NewDNSResolverWithFreq(defaultFreq)
57 // dnsResolver handles name resolution for names following the DNS scheme
58 type dnsResolver struct {
59 // frequency of polling the DNS server that the watchers created by this resolver will use.
63 // formatIP returns ok = false if addr is not a valid textual representation of an IP address.
64 // If addr is an IPv4 address, return the addr and ok = true.
65 // If addr is an IPv6 address, return the addr enclosed in square brackets and ok = true.
66 func formatIP(addr string) (addrIP string, ok bool) {
67 ip := net.ParseIP(addr)
74 return "[" + addr + "]", true
77 // parseTarget takes the user input target string, returns formatted host and port info.
78 // If target doesn't specify a port, set the port to be the defaultPort.
79 // If target is in IPv6 format and host-name is enclosed in sqarue brackets, brackets
80 // are strippd when setting the host.
82 // target: "www.google.com" returns host: "www.google.com", port: "443"
83 // target: "ipv4-host:80" returns host: "ipv4-host", port: "80"
84 // target: "[ipv6-host]" returns host: "ipv6-host", port: "443"
85 // target: ":80" returns host: "localhost", port: "80"
86 // target: ":" returns host: "localhost", port: "443"
87 func parseTarget(target string) (host, port string, err error) {
89 return "", "", errMissingAddr
92 if ip := net.ParseIP(target); ip != nil {
93 // target is an IPv4 or IPv6(without brackets) address
94 return target, defaultPort, nil
96 if host, port, err := net.SplitHostPort(target); err == nil {
97 // target has port, i.e ipv4-host:port, [ipv6-host]:port, host-name:port
99 // Keep consistent with net.Dial(): If the host is empty, as in ":80", the local system is assumed.
103 // If the port field is empty(target ends with colon), e.g. "[::1]:", defaultPort is used.
106 return host, port, nil
108 if host, port, err := net.SplitHostPort(target + ":" + defaultPort); err == nil {
109 // target doesn't have port
110 return host, port, nil
112 return "", "", fmt.Errorf("invalid target address %v", target)
115 // Resolve creates a watcher that watches the name resolution of the target.
116 func (r *dnsResolver) Resolve(target string) (Watcher, error) {
117 host, port, err := parseTarget(target)
122 if net.ParseIP(host) != nil {
123 ipWatcher := &ipWatcher{
124 updateChan: make(chan *Update, 1),
126 host, _ = formatIP(host)
127 ipWatcher.updateChan <- &Update{Op: Add, Addr: host + ":" + port}
128 return ipWatcher, nil
131 ctx, cancel := context.WithCancel(context.Background())
142 // dnsWatcher watches for the name resolution update for a specific target
143 type dnsWatcher struct {
147 // The latest resolved address set
148 curAddrs map[string]*Update
150 cancel context.CancelFunc
154 // ipWatcher watches for the name resolution update for an IP address.
155 type ipWatcher struct {
156 updateChan chan *Update
159 // Next returns the address resolution Update for the target. For IP address,
160 // the resolution is itself, thus polling name server is unnecessary. Therefore,
161 // Next() will return an Update the first time it is called, and will be blocked
162 // for all following calls as no Update exists until watcher is closed.
163 func (i *ipWatcher) Next() ([]*Update, error) {
164 u, ok := <-i.updateChan
166 return nil, errWatcherClose
168 return []*Update{u}, nil
171 // Close closes the ipWatcher.
172 func (i *ipWatcher) Close() {
176 // AddressType indicates the address type returned by name resolution.
177 type AddressType uint8
180 // Backend indicates the server is a backend server.
181 Backend AddressType = iota
182 // GRPCLB indicates the server is a grpclb load balancer.
186 // AddrMetadataGRPCLB contains the information the name resolver for grpclb should provide. The
187 // name resolver used by the grpclb balancer is required to provide this type of metadata in
188 // its address updates.
189 type AddrMetadataGRPCLB struct {
190 // AddrType is the type of server (grpc load balancer or backend).
192 // ServerName is the name of the grpc load balancer. Used for authentication.
196 // compileUpdate compares the old resolved addresses and newly resolved addresses,
197 // and generates an update list
198 func (w *dnsWatcher) compileUpdate(newAddrs map[string]*Update) []*Update {
200 for a, u := range w.curAddrs {
201 if _, ok := newAddrs[a]; !ok {
206 for a, u := range newAddrs {
207 if _, ok := w.curAddrs[a]; !ok {
214 func (w *dnsWatcher) lookupSRV() map[string]*Update {
215 newAddrs := make(map[string]*Update)
216 _, srvs, err := lookupSRV(w.ctx, "grpclb", "tcp", w.host)
218 grpclog.Infof("grpc: failed dns SRV record lookup due to %v.\n", err)
221 for _, s := range srvs {
222 lbAddrs, err := lookupHost(w.ctx, s.Target)
224 grpclog.Warningf("grpc: failed load banlacer address dns lookup due to %v.\n", err)
227 for _, a := range lbAddrs {
230 grpclog.Errorf("grpc: failed IP parsing due to %v.\n", err)
233 addr := a + ":" + strconv.Itoa(int(s.Port))
234 newAddrs[addr] = &Update{Addr: addr,
235 Metadata: AddrMetadataGRPCLB{AddrType: GRPCLB, ServerName: s.Target}}
241 func (w *dnsWatcher) lookupHost() map[string]*Update {
242 newAddrs := make(map[string]*Update)
243 addrs, err := lookupHost(w.ctx, w.host)
245 grpclog.Warningf("grpc: failed dns A record lookup due to %v.\n", err)
248 for _, a := range addrs {
251 grpclog.Errorf("grpc: failed IP parsing due to %v.\n", err)
254 addr := a + ":" + w.port
255 newAddrs[addr] = &Update{Addr: addr}
260 func (w *dnsWatcher) lookup() []*Update {
261 newAddrs := w.lookupSRV()
263 // If failed to get any balancer address (either no corresponding SRV for the
264 // target, or caused by failure during resolution/parsing of the balancer target),
265 // return any A record info available.
266 newAddrs = w.lookupHost()
268 result := w.compileUpdate(newAddrs)
269 w.curAddrs = newAddrs
273 // Next returns the resolved address update(delta) for the target. If there's no
274 // change, it will sleep for 30 mins and try to resolve again after that.
275 func (w *dnsWatcher) Next() ([]*Update, error) {
279 return nil, errWatcherClose
283 // Next lookup should happen after an interval defined by w.r.freq.
291 func (w *dnsWatcher) Close() {