khenaidoo | 5fc5cea | 2021-08-11 17:39:16 -0400 | [diff] [blame^] | 1 | /* |
| 2 | * |
| 3 | * Copyright 2018 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 dns implements a dns resolver to be installed as the default resolver |
| 20 | // in grpc. |
| 21 | package dns |
| 22 | |
| 23 | import ( |
| 24 | "context" |
| 25 | "encoding/json" |
| 26 | "errors" |
| 27 | "fmt" |
| 28 | "net" |
| 29 | "os" |
| 30 | "strconv" |
| 31 | "strings" |
| 32 | "sync" |
| 33 | "time" |
| 34 | |
| 35 | grpclbstate "google.golang.org/grpc/balancer/grpclb/state" |
| 36 | "google.golang.org/grpc/grpclog" |
| 37 | "google.golang.org/grpc/internal/backoff" |
| 38 | "google.golang.org/grpc/internal/envconfig" |
| 39 | "google.golang.org/grpc/internal/grpcrand" |
| 40 | "google.golang.org/grpc/resolver" |
| 41 | "google.golang.org/grpc/serviceconfig" |
| 42 | ) |
| 43 | |
| 44 | // EnableSRVLookups controls whether the DNS resolver attempts to fetch gRPCLB |
| 45 | // addresses from SRV records. Must not be changed after init time. |
| 46 | var EnableSRVLookups = false |
| 47 | |
| 48 | var logger = grpclog.Component("dns") |
| 49 | |
| 50 | // Globals to stub out in tests. TODO: Perhaps these two can be combined into a |
| 51 | // single variable for testing the resolver? |
| 52 | var ( |
| 53 | newTimer = time.NewTimer |
| 54 | newTimerDNSResRate = time.NewTimer |
| 55 | ) |
| 56 | |
| 57 | func init() { |
| 58 | resolver.Register(NewBuilder()) |
| 59 | } |
| 60 | |
| 61 | const ( |
| 62 | defaultPort = "443" |
| 63 | defaultDNSSvrPort = "53" |
| 64 | golang = "GO" |
| 65 | // txtPrefix is the prefix string to be prepended to the host name for txt record lookup. |
| 66 | txtPrefix = "_grpc_config." |
| 67 | // In DNS, service config is encoded in a TXT record via the mechanism |
| 68 | // described in RFC-1464 using the attribute name grpc_config. |
| 69 | txtAttribute = "grpc_config=" |
| 70 | ) |
| 71 | |
| 72 | var ( |
| 73 | errMissingAddr = errors.New("dns resolver: missing address") |
| 74 | |
| 75 | // Addresses ending with a colon that is supposed to be the separator |
| 76 | // between host and port is not allowed. E.g. "::" is a valid address as |
| 77 | // it is an IPv6 address (host only) and "[::]:" is invalid as it ends with |
| 78 | // a colon as the host and port separator |
| 79 | errEndsWithColon = errors.New("dns resolver: missing port after port-separator colon") |
| 80 | ) |
| 81 | |
| 82 | var ( |
| 83 | defaultResolver netResolver = net.DefaultResolver |
| 84 | // To prevent excessive re-resolution, we enforce a rate limit on DNS |
| 85 | // resolution requests. |
| 86 | minDNSResRate = 30 * time.Second |
| 87 | ) |
| 88 | |
| 89 | var customAuthorityDialler = func(authority string) func(ctx context.Context, network, address string) (net.Conn, error) { |
| 90 | return func(ctx context.Context, network, address string) (net.Conn, error) { |
| 91 | var dialer net.Dialer |
| 92 | return dialer.DialContext(ctx, network, authority) |
| 93 | } |
| 94 | } |
| 95 | |
| 96 | var customAuthorityResolver = func(authority string) (netResolver, error) { |
| 97 | host, port, err := parseTarget(authority, defaultDNSSvrPort) |
| 98 | if err != nil { |
| 99 | return nil, err |
| 100 | } |
| 101 | |
| 102 | authorityWithPort := net.JoinHostPort(host, port) |
| 103 | |
| 104 | return &net.Resolver{ |
| 105 | PreferGo: true, |
| 106 | Dial: customAuthorityDialler(authorityWithPort), |
| 107 | }, nil |
| 108 | } |
| 109 | |
| 110 | // NewBuilder creates a dnsBuilder which is used to factory DNS resolvers. |
| 111 | func NewBuilder() resolver.Builder { |
| 112 | return &dnsBuilder{} |
| 113 | } |
| 114 | |
| 115 | type dnsBuilder struct{} |
| 116 | |
| 117 | // Build creates and starts a DNS resolver that watches the name resolution of the target. |
| 118 | func (b *dnsBuilder) Build(target resolver.Target, cc resolver.ClientConn, opts resolver.BuildOptions) (resolver.Resolver, error) { |
| 119 | host, port, err := parseTarget(target.Endpoint, defaultPort) |
| 120 | if err != nil { |
| 121 | return nil, err |
| 122 | } |
| 123 | |
| 124 | // IP address. |
| 125 | if ipAddr, ok := formatIP(host); ok { |
| 126 | addr := []resolver.Address{{Addr: ipAddr + ":" + port}} |
| 127 | cc.UpdateState(resolver.State{Addresses: addr}) |
| 128 | return deadResolver{}, nil |
| 129 | } |
| 130 | |
| 131 | // DNS address (non-IP). |
| 132 | ctx, cancel := context.WithCancel(context.Background()) |
| 133 | d := &dnsResolver{ |
| 134 | host: host, |
| 135 | port: port, |
| 136 | ctx: ctx, |
| 137 | cancel: cancel, |
| 138 | cc: cc, |
| 139 | rn: make(chan struct{}, 1), |
| 140 | disableServiceConfig: opts.DisableServiceConfig, |
| 141 | } |
| 142 | |
| 143 | if target.Authority == "" { |
| 144 | d.resolver = defaultResolver |
| 145 | } else { |
| 146 | d.resolver, err = customAuthorityResolver(target.Authority) |
| 147 | if err != nil { |
| 148 | return nil, err |
| 149 | } |
| 150 | } |
| 151 | |
| 152 | d.wg.Add(1) |
| 153 | go d.watcher() |
| 154 | return d, nil |
| 155 | } |
| 156 | |
| 157 | // Scheme returns the naming scheme of this resolver builder, which is "dns". |
| 158 | func (b *dnsBuilder) Scheme() string { |
| 159 | return "dns" |
| 160 | } |
| 161 | |
| 162 | type netResolver interface { |
| 163 | LookupHost(ctx context.Context, host string) (addrs []string, err error) |
| 164 | LookupSRV(ctx context.Context, service, proto, name string) (cname string, addrs []*net.SRV, err error) |
| 165 | LookupTXT(ctx context.Context, name string) (txts []string, err error) |
| 166 | } |
| 167 | |
| 168 | // deadResolver is a resolver that does nothing. |
| 169 | type deadResolver struct{} |
| 170 | |
| 171 | func (deadResolver) ResolveNow(resolver.ResolveNowOptions) {} |
| 172 | |
| 173 | func (deadResolver) Close() {} |
| 174 | |
| 175 | // dnsResolver watches for the name resolution update for a non-IP target. |
| 176 | type dnsResolver struct { |
| 177 | host string |
| 178 | port string |
| 179 | resolver netResolver |
| 180 | ctx context.Context |
| 181 | cancel context.CancelFunc |
| 182 | cc resolver.ClientConn |
| 183 | // rn channel is used by ResolveNow() to force an immediate resolution of the target. |
| 184 | rn chan struct{} |
| 185 | // wg is used to enforce Close() to return after the watcher() goroutine has finished. |
| 186 | // Otherwise, data race will be possible. [Race Example] in dns_resolver_test we |
| 187 | // replace the real lookup functions with mocked ones to facilitate testing. |
| 188 | // If Close() doesn't wait for watcher() goroutine finishes, race detector sometimes |
| 189 | // will warns lookup (READ the lookup function pointers) inside watcher() goroutine |
| 190 | // has data race with replaceNetFunc (WRITE the lookup function pointers). |
| 191 | wg sync.WaitGroup |
| 192 | disableServiceConfig bool |
| 193 | } |
| 194 | |
| 195 | // ResolveNow invoke an immediate resolution of the target that this dnsResolver watches. |
| 196 | func (d *dnsResolver) ResolveNow(resolver.ResolveNowOptions) { |
| 197 | select { |
| 198 | case d.rn <- struct{}{}: |
| 199 | default: |
| 200 | } |
| 201 | } |
| 202 | |
| 203 | // Close closes the dnsResolver. |
| 204 | func (d *dnsResolver) Close() { |
| 205 | d.cancel() |
| 206 | d.wg.Wait() |
| 207 | } |
| 208 | |
| 209 | func (d *dnsResolver) watcher() { |
| 210 | defer d.wg.Done() |
| 211 | backoffIndex := 1 |
| 212 | for { |
| 213 | state, err := d.lookup() |
| 214 | if err != nil { |
| 215 | // Report error to the underlying grpc.ClientConn. |
| 216 | d.cc.ReportError(err) |
| 217 | } else { |
| 218 | err = d.cc.UpdateState(*state) |
| 219 | } |
| 220 | |
| 221 | var timer *time.Timer |
| 222 | if err == nil { |
| 223 | // Success resolving, wait for the next ResolveNow. However, also wait 30 seconds at the very least |
| 224 | // to prevent constantly re-resolving. |
| 225 | backoffIndex = 1 |
| 226 | timer = newTimerDNSResRate(minDNSResRate) |
| 227 | select { |
| 228 | case <-d.ctx.Done(): |
| 229 | timer.Stop() |
| 230 | return |
| 231 | case <-d.rn: |
| 232 | } |
| 233 | } else { |
| 234 | // Poll on an error found in DNS Resolver or an error received from ClientConn. |
| 235 | timer = newTimer(backoff.DefaultExponential.Backoff(backoffIndex)) |
| 236 | backoffIndex++ |
| 237 | } |
| 238 | select { |
| 239 | case <-d.ctx.Done(): |
| 240 | timer.Stop() |
| 241 | return |
| 242 | case <-timer.C: |
| 243 | } |
| 244 | } |
| 245 | } |
| 246 | |
| 247 | func (d *dnsResolver) lookupSRV() ([]resolver.Address, error) { |
| 248 | if !EnableSRVLookups { |
| 249 | return nil, nil |
| 250 | } |
| 251 | var newAddrs []resolver.Address |
| 252 | _, srvs, err := d.resolver.LookupSRV(d.ctx, "grpclb", "tcp", d.host) |
| 253 | if err != nil { |
| 254 | err = handleDNSError(err, "SRV") // may become nil |
| 255 | return nil, err |
| 256 | } |
| 257 | for _, s := range srvs { |
| 258 | lbAddrs, err := d.resolver.LookupHost(d.ctx, s.Target) |
| 259 | if err != nil { |
| 260 | err = handleDNSError(err, "A") // may become nil |
| 261 | if err == nil { |
| 262 | // If there are other SRV records, look them up and ignore this |
| 263 | // one that does not exist. |
| 264 | continue |
| 265 | } |
| 266 | return nil, err |
| 267 | } |
| 268 | for _, a := range lbAddrs { |
| 269 | ip, ok := formatIP(a) |
| 270 | if !ok { |
| 271 | return nil, fmt.Errorf("dns: error parsing A record IP address %v", a) |
| 272 | } |
| 273 | addr := ip + ":" + strconv.Itoa(int(s.Port)) |
| 274 | newAddrs = append(newAddrs, resolver.Address{Addr: addr, ServerName: s.Target}) |
| 275 | } |
| 276 | } |
| 277 | return newAddrs, nil |
| 278 | } |
| 279 | |
| 280 | func handleDNSError(err error, lookupType string) error { |
| 281 | if dnsErr, ok := err.(*net.DNSError); ok && !dnsErr.IsTimeout && !dnsErr.IsTemporary { |
| 282 | // Timeouts and temporary errors should be communicated to gRPC to |
| 283 | // attempt another DNS query (with backoff). Other errors should be |
| 284 | // suppressed (they may represent the absence of a TXT record). |
| 285 | return nil |
| 286 | } |
| 287 | if err != nil { |
| 288 | err = fmt.Errorf("dns: %v record lookup error: %v", lookupType, err) |
| 289 | logger.Info(err) |
| 290 | } |
| 291 | return err |
| 292 | } |
| 293 | |
| 294 | func (d *dnsResolver) lookupTXT() *serviceconfig.ParseResult { |
| 295 | ss, err := d.resolver.LookupTXT(d.ctx, txtPrefix+d.host) |
| 296 | if err != nil { |
| 297 | if envconfig.TXTErrIgnore { |
| 298 | return nil |
| 299 | } |
| 300 | if err = handleDNSError(err, "TXT"); err != nil { |
| 301 | return &serviceconfig.ParseResult{Err: err} |
| 302 | } |
| 303 | return nil |
| 304 | } |
| 305 | var res string |
| 306 | for _, s := range ss { |
| 307 | res += s |
| 308 | } |
| 309 | |
| 310 | // TXT record must have "grpc_config=" attribute in order to be used as service config. |
| 311 | if !strings.HasPrefix(res, txtAttribute) { |
| 312 | logger.Warningf("dns: TXT record %v missing %v attribute", res, txtAttribute) |
| 313 | // This is not an error; it is the equivalent of not having a service config. |
| 314 | return nil |
| 315 | } |
| 316 | sc := canaryingSC(strings.TrimPrefix(res, txtAttribute)) |
| 317 | return d.cc.ParseServiceConfig(sc) |
| 318 | } |
| 319 | |
| 320 | func (d *dnsResolver) lookupHost() ([]resolver.Address, error) { |
| 321 | addrs, err := d.resolver.LookupHost(d.ctx, d.host) |
| 322 | if err != nil { |
| 323 | err = handleDNSError(err, "A") |
| 324 | return nil, err |
| 325 | } |
| 326 | newAddrs := make([]resolver.Address, 0, len(addrs)) |
| 327 | for _, a := range addrs { |
| 328 | ip, ok := formatIP(a) |
| 329 | if !ok { |
| 330 | return nil, fmt.Errorf("dns: error parsing A record IP address %v", a) |
| 331 | } |
| 332 | addr := ip + ":" + d.port |
| 333 | newAddrs = append(newAddrs, resolver.Address{Addr: addr}) |
| 334 | } |
| 335 | return newAddrs, nil |
| 336 | } |
| 337 | |
| 338 | func (d *dnsResolver) lookup() (*resolver.State, error) { |
| 339 | srv, srvErr := d.lookupSRV() |
| 340 | addrs, hostErr := d.lookupHost() |
| 341 | if hostErr != nil && (srvErr != nil || len(srv) == 0) { |
| 342 | return nil, hostErr |
| 343 | } |
| 344 | |
| 345 | state := resolver.State{Addresses: addrs} |
| 346 | if len(srv) > 0 { |
| 347 | state = grpclbstate.Set(state, &grpclbstate.State{BalancerAddresses: srv}) |
| 348 | } |
| 349 | if !d.disableServiceConfig { |
| 350 | state.ServiceConfig = d.lookupTXT() |
| 351 | } |
| 352 | return &state, nil |
| 353 | } |
| 354 | |
| 355 | // formatIP returns ok = false if addr is not a valid textual representation of an IP address. |
| 356 | // If addr is an IPv4 address, return the addr and ok = true. |
| 357 | // If addr is an IPv6 address, return the addr enclosed in square brackets and ok = true. |
| 358 | func formatIP(addr string) (addrIP string, ok bool) { |
| 359 | ip := net.ParseIP(addr) |
| 360 | if ip == nil { |
| 361 | return "", false |
| 362 | } |
| 363 | if ip.To4() != nil { |
| 364 | return addr, true |
| 365 | } |
| 366 | return "[" + addr + "]", true |
| 367 | } |
| 368 | |
| 369 | // parseTarget takes the user input target string and default port, returns formatted host and port info. |
| 370 | // If target doesn't specify a port, set the port to be the defaultPort. |
| 371 | // If target is in IPv6 format and host-name is enclosed in square brackets, brackets |
| 372 | // are stripped when setting the host. |
| 373 | // examples: |
| 374 | // target: "www.google.com" defaultPort: "443" returns host: "www.google.com", port: "443" |
| 375 | // target: "ipv4-host:80" defaultPort: "443" returns host: "ipv4-host", port: "80" |
| 376 | // target: "[ipv6-host]" defaultPort: "443" returns host: "ipv6-host", port: "443" |
| 377 | // target: ":80" defaultPort: "443" returns host: "localhost", port: "80" |
| 378 | func parseTarget(target, defaultPort string) (host, port string, err error) { |
| 379 | if target == "" { |
| 380 | return "", "", errMissingAddr |
| 381 | } |
| 382 | if ip := net.ParseIP(target); ip != nil { |
| 383 | // target is an IPv4 or IPv6(without brackets) address |
| 384 | return target, defaultPort, nil |
| 385 | } |
| 386 | if host, port, err = net.SplitHostPort(target); err == nil { |
| 387 | if port == "" { |
| 388 | // If the port field is empty (target ends with colon), e.g. "[::1]:", this is an error. |
| 389 | return "", "", errEndsWithColon |
| 390 | } |
| 391 | // target has port, i.e ipv4-host:port, [ipv6-host]:port, host-name:port |
| 392 | if host == "" { |
| 393 | // Keep consistent with net.Dial(): If the host is empty, as in ":80", the local system is assumed. |
| 394 | host = "localhost" |
| 395 | } |
| 396 | return host, port, nil |
| 397 | } |
| 398 | if host, port, err = net.SplitHostPort(target + ":" + defaultPort); err == nil { |
| 399 | // target doesn't have port |
| 400 | return host, port, nil |
| 401 | } |
| 402 | return "", "", fmt.Errorf("invalid target address %v, error info: %v", target, err) |
| 403 | } |
| 404 | |
| 405 | type rawChoice struct { |
| 406 | ClientLanguage *[]string `json:"clientLanguage,omitempty"` |
| 407 | Percentage *int `json:"percentage,omitempty"` |
| 408 | ClientHostName *[]string `json:"clientHostName,omitempty"` |
| 409 | ServiceConfig *json.RawMessage `json:"serviceConfig,omitempty"` |
| 410 | } |
| 411 | |
| 412 | func containsString(a *[]string, b string) bool { |
| 413 | if a == nil { |
| 414 | return true |
| 415 | } |
| 416 | for _, c := range *a { |
| 417 | if c == b { |
| 418 | return true |
| 419 | } |
| 420 | } |
| 421 | return false |
| 422 | } |
| 423 | |
| 424 | func chosenByPercentage(a *int) bool { |
| 425 | if a == nil { |
| 426 | return true |
| 427 | } |
| 428 | return grpcrand.Intn(100)+1 <= *a |
| 429 | } |
| 430 | |
| 431 | func canaryingSC(js string) string { |
| 432 | if js == "" { |
| 433 | return "" |
| 434 | } |
| 435 | var rcs []rawChoice |
| 436 | err := json.Unmarshal([]byte(js), &rcs) |
| 437 | if err != nil { |
| 438 | logger.Warningf("dns: error parsing service config json: %v", err) |
| 439 | return "" |
| 440 | } |
| 441 | cliHostname, err := os.Hostname() |
| 442 | if err != nil { |
| 443 | logger.Warningf("dns: error getting client hostname: %v", err) |
| 444 | return "" |
| 445 | } |
| 446 | var sc string |
| 447 | for _, c := range rcs { |
| 448 | if !containsString(c.ClientLanguage, golang) || |
| 449 | !chosenByPercentage(c.Percentage) || |
| 450 | !containsString(c.ClientHostName, cliHostname) || |
| 451 | c.ServiceConfig == nil { |
| 452 | continue |
| 453 | } |
| 454 | sc = string(*c.ServiceConfig) |
| 455 | break |
| 456 | } |
| 457 | return sc |
| 458 | } |