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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 ( | |
107c1cdb | 22 | "context" |
15c0b25d AP |
23 | "errors" |
24 | "fmt" | |
25 | "net" | |
26 | "strconv" | |
27 | "time" | |
28 | ||
15c0b25d AP |
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") | |
107c1cdb ND |
40 | |
41 | lookupHost = net.DefaultResolver.LookupHost | |
42 | lookupSRV = net.DefaultResolver.LookupSRV | |
15c0b25d AP |
43 | ) |
44 | ||
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 | |
49 | } | |
50 | ||
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) | |
55 | } | |
56 | ||
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. | |
60 | freq time.Duration | |
61 | } | |
62 | ||
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) | |
68 | if ip == nil { | |
69 | return "", false | |
70 | } | |
71 | if ip.To4() != nil { | |
72 | return addr, true | |
73 | } | |
74 | return "[" + addr + "]", true | |
75 | } | |
76 | ||
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. | |
81 | // examples: | |
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) { | |
88 | if target == "" { | |
89 | return "", "", errMissingAddr | |
90 | } | |
91 | ||
92 | if ip := net.ParseIP(target); ip != nil { | |
93 | // target is an IPv4 or IPv6(without brackets) address | |
94 | return target, defaultPort, nil | |
95 | } | |
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 | |
98 | if host == "" { | |
99 | // Keep consistent with net.Dial(): If the host is empty, as in ":80", the local system is assumed. | |
100 | host = "localhost" | |
101 | } | |
102 | if port == "" { | |
103 | // If the port field is empty(target ends with colon), e.g. "[::1]:", defaultPort is used. | |
104 | port = defaultPort | |
105 | } | |
106 | return host, port, nil | |
107 | } | |
108 | if host, port, err := net.SplitHostPort(target + ":" + defaultPort); err == nil { | |
109 | // target doesn't have port | |
110 | return host, port, nil | |
111 | } | |
112 | return "", "", fmt.Errorf("invalid target address %v", target) | |
113 | } | |
114 | ||
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) | |
118 | if err != nil { | |
119 | return nil, err | |
120 | } | |
121 | ||
122 | if net.ParseIP(host) != nil { | |
123 | ipWatcher := &ipWatcher{ | |
124 | updateChan: make(chan *Update, 1), | |
125 | } | |
126 | host, _ = formatIP(host) | |
127 | ipWatcher.updateChan <- &Update{Op: Add, Addr: host + ":" + port} | |
128 | return ipWatcher, nil | |
129 | } | |
130 | ||
131 | ctx, cancel := context.WithCancel(context.Background()) | |
132 | return &dnsWatcher{ | |
133 | r: r, | |
134 | host: host, | |
135 | port: port, | |
136 | ctx: ctx, | |
137 | cancel: cancel, | |
138 | t: time.NewTimer(0), | |
139 | }, nil | |
140 | } | |
141 | ||
142 | // dnsWatcher watches for the name resolution update for a specific target | |
143 | type dnsWatcher struct { | |
144 | r *dnsResolver | |
145 | host string | |
146 | port string | |
107c1cdb ND |
147 | // The latest resolved address set |
148 | curAddrs map[string]*Update | |
15c0b25d AP |
149 | ctx context.Context |
150 | cancel context.CancelFunc | |
151 | t *time.Timer | |
152 | } | |
153 | ||
154 | // ipWatcher watches for the name resolution update for an IP address. | |
155 | type ipWatcher struct { | |
156 | updateChan chan *Update | |
157 | } | |
158 | ||
107c1cdb ND |
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, | |
15c0b25d | 161 | // Next() will return an Update the first time it is called, and will be blocked |
107c1cdb | 162 | // for all following calls as no Update exists until watcher is closed. |
15c0b25d AP |
163 | func (i *ipWatcher) Next() ([]*Update, error) { |
164 | u, ok := <-i.updateChan | |
165 | if !ok { | |
166 | return nil, errWatcherClose | |
167 | } | |
168 | return []*Update{u}, nil | |
169 | } | |
170 | ||
171 | // Close closes the ipWatcher. | |
172 | func (i *ipWatcher) Close() { | |
173 | close(i.updateChan) | |
174 | } | |
175 | ||
176 | // AddressType indicates the address type returned by name resolution. | |
177 | type AddressType uint8 | |
178 | ||
179 | const ( | |
180 | // Backend indicates the server is a backend server. | |
181 | Backend AddressType = iota | |
182 | // GRPCLB indicates the server is a grpclb load balancer. | |
183 | GRPCLB | |
184 | ) | |
185 | ||
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). | |
191 | AddrType AddressType | |
192 | // ServerName is the name of the grpc load balancer. Used for authentication. | |
193 | ServerName string | |
194 | } | |
195 | ||
196 | // compileUpdate compares the old resolved addresses and newly resolved addresses, | |
197 | // and generates an update list | |
107c1cdb ND |
198 | func (w *dnsWatcher) compileUpdate(newAddrs map[string]*Update) []*Update { |
199 | var res []*Update | |
200 | for a, u := range w.curAddrs { | |
201 | if _, ok := newAddrs[a]; !ok { | |
202 | u.Op = Delete | |
203 | res = append(res, u) | |
15c0b25d | 204 | } |
15c0b25d | 205 | } |
107c1cdb ND |
206 | for a, u := range newAddrs { |
207 | if _, ok := w.curAddrs[a]; !ok { | |
208 | res = append(res, u) | |
209 | } | |
15c0b25d AP |
210 | } |
211 | return res | |
212 | } | |
213 | ||
107c1cdb ND |
214 | func (w *dnsWatcher) lookupSRV() map[string]*Update { |
215 | newAddrs := make(map[string]*Update) | |
15c0b25d AP |
216 | _, srvs, err := lookupSRV(w.ctx, "grpclb", "tcp", w.host) |
217 | if err != nil { | |
218 | grpclog.Infof("grpc: failed dns SRV record lookup due to %v.\n", err) | |
219 | return nil | |
220 | } | |
221 | for _, s := range srvs { | |
222 | lbAddrs, err := lookupHost(w.ctx, s.Target) | |
223 | if err != nil { | |
224 | grpclog.Warningf("grpc: failed load banlacer address dns lookup due to %v.\n", err) | |
225 | continue | |
226 | } | |
227 | for _, a := range lbAddrs { | |
228 | a, ok := formatIP(a) | |
229 | if !ok { | |
230 | grpclog.Errorf("grpc: failed IP parsing due to %v.\n", err) | |
231 | continue | |
232 | } | |
107c1cdb ND |
233 | addr := a + ":" + strconv.Itoa(int(s.Port)) |
234 | newAddrs[addr] = &Update{Addr: addr, | |
235 | Metadata: AddrMetadataGRPCLB{AddrType: GRPCLB, ServerName: s.Target}} | |
15c0b25d AP |
236 | } |
237 | } | |
238 | return newAddrs | |
239 | } | |
240 | ||
107c1cdb ND |
241 | func (w *dnsWatcher) lookupHost() map[string]*Update { |
242 | newAddrs := make(map[string]*Update) | |
15c0b25d AP |
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 | } | |
107c1cdb ND |
254 | addr := a + ":" + w.port |
255 | newAddrs[addr] = &Update{Addr: addr} | |
15c0b25d AP |
256 | } |
257 | return newAddrs | |
258 | } | |
259 | ||
260 | func (w *dnsWatcher) lookup() []*Update { | |
261 | newAddrs := w.lookupSRV() | |
262 | if newAddrs == nil { | |
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() | |
267 | } | |
268 | result := w.compileUpdate(newAddrs) | |
269 | w.curAddrs = newAddrs | |
270 | return result | |
271 | } | |
272 | ||
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) { | |
276 | for { | |
277 | select { | |
278 | case <-w.ctx.Done(): | |
279 | return nil, errWatcherClose | |
280 | case <-w.t.C: | |
281 | } | |
282 | result := w.lookup() | |
283 | // Next lookup should happen after an interval defined by w.r.freq. | |
284 | w.t.Reset(w.r.freq) | |
285 | if len(result) > 0 { | |
286 | return result, nil | |
287 | } | |
288 | } | |
289 | } | |
290 | ||
291 | func (w *dnsWatcher) Close() { | |
292 | w.cancel() | |
293 | } |