Elia Battiston | be9edc1 | 2022-03-09 11:35:58 +0100 | [diff] [blame^] | 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 | "context" |
| 23 | "errors" |
| 24 | "fmt" |
| 25 | "net" |
| 26 | "strconv" |
| 27 | "time" |
| 28 | |
| 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 | 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. |
| 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 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" |
| 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 |
| 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. |
| 155 | type 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. |
| 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 |
| 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) |
| 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 | |
| 214 | func (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 | |
| 241 | func (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 | |
| 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 | } |