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Matteo Scandoloa6a3aee2019-11-26 13:30:14 -07001/*
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
19package naming
20
21import (
22 "context"
23 "errors"
24 "fmt"
25 "net"
26 "strconv"
27 "time"
28
29 "google.golang.org/grpc/grpclog"
30)
31
32const (
33 defaultPort = "443"
34 defaultFreq = time.Minute * 30
35)
36
37var (
38 errMissingAddr = errors.New("missing address")
39 errWatcherClose = errors.New("watcher has been closed")
40
41 lookupHost = net.DefaultResolver.LookupHost
42 lookupSRV = net.DefaultResolver.LookupSRV
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.
47func 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.
53func NewDNSResolver() (Resolver, error) {
54 return NewDNSResolverWithFreq(defaultFreq)
55}
56
57// dnsResolver handles name resolution for names following the DNS scheme
58type 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.
66func 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 square brackets, brackets
80// are stripped 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"
87func 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.
116func (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
143type dnsWatcher struct {
144 r *dnsResolver
145 host string
146 port string
147 // The latest resolved address set
148 curAddrs map[string]*Update
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.
155type ipWatcher struct {
156 updateChan chan *Update
157}
158
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.
163func (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.
172func (i *ipWatcher) Close() {
173 close(i.updateChan)
174}
175
176// AddressType indicates the address type returned by name resolution.
177type AddressType uint8
178
179const (
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.
189type 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
198func (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)
204 }
205 }
206 for a, u := range newAddrs {
207 if _, ok := w.curAddrs[a]; !ok {
208 res = append(res, u)
209 }
210 }
211 return res
212}
213
214func (w *dnsWatcher) lookupSRV() map[string]*Update {
215 newAddrs := make(map[string]*Update)
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 balancer 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 }
233 addr := a + ":" + strconv.Itoa(int(s.Port))
234 newAddrs[addr] = &Update{Addr: addr,
235 Metadata: AddrMetadataGRPCLB{AddrType: GRPCLB, ServerName: s.Target}}
236 }
237 }
238 return newAddrs
239}
240
241func (w *dnsWatcher) lookupHost() map[string]*Update {
242 newAddrs := make(map[string]*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 addr := a + ":" + w.port
255 newAddrs[addr] = &Update{Addr: addr}
256 }
257 return newAddrs
258}
259
260func (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.
275func (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
291func (w *dnsWatcher) Close() {
292 w.cancel()
293}