src/core/ext/filters/client_channel/resolver/dns/c_ares/dns_resolver_ares.cc

   1 /*
   2  *
   3  * Copyright 2015 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 #include <grpc/support/port_platform.h>
  20
  21 #if GRPC_ARES == 1
  22
  23 #include <limits.h>
  24 #include <stdio.h>
  25 #include <string.h>
  26
  27 #include <grpc/support/alloc.h>
  28 #include <grpc/support/string_util.h>
  29
  30 #include <address_sorting/address_sorting.h>
  31
  32 #include "src/core/ext/filters/client_channel/http_connect_handshaker.h"
  33 #include "src/core/ext/filters/client_channel/lb_policy_registry.h"
  34 #include "src/core/ext/filters/client_channel/resolver/dns/c_ares/grpc_ares_wrapper.h"
  35 #include "src/core/ext/filters/client_channel/resolver/dns/dns_resolver_selection.h"
  36 #include "src/core/ext/filters/client_channel/resolver_registry.h"
  37 #include "src/core/ext/filters/client_channel/server_address.h"
  38 #include "src/core/ext/filters/client_channel/service_config.h"
  39 #include "src/core/lib/backoff/backoff.h"
  40 #include "src/core/lib/channel/channel_args.h"
  41 #include "src/core/lib/gpr/host_port.h"
  42 #include "src/core/lib/gpr/string.h"
  43 #include "src/core/lib/gprpp/manual_constructor.h"
  44 #include "src/core/lib/iomgr/combiner.h"
  45 #include "src/core/lib/iomgr/gethostname.h"
  46 #include "src/core/lib/iomgr/iomgr_custom.h"
  47 #include "src/core/lib/iomgr/resolve_address.h"
  48 #include "src/core/lib/iomgr/timer.h"
  49 #include "src/core/lib/json/json.h"
  50
  51 #define GRPC_DNS_INITIAL_CONNECT_BACKOFF_SECONDS 1
  52 #define GRPC_DNS_RECONNECT_BACKOFF_MULTIPLIER 1.6
  53 #define GRPC_DNS_RECONNECT_MAX_BACKOFF_SECONDS 120
  54 #define GRPC_DNS_RECONNECT_JITTER 0.2
  55
  56 namespace grpc_core {
  57
  58 namespace {
  59
  60 const char kDefaultPort[] = "https";
  61
  62 class AresDnsResolver : public Resolver {
  63  public:
  64   explicit AresDnsResolver(ResolverArgs args);
  65
  66   void StartLocked() override;
  67
  68   void RequestReresolutionLocked() override;
  69
  70   void ResetBackoffLocked() override;
  71
  72   void ShutdownLocked() override;
  73
  74  private:
  75   virtual ~AresDnsResolver();
  76
  77   void MaybeStartResolvingLocked();
  78   void StartResolvingLocked();
  79
  80   static void OnNextResolutionLocked(void* arg, grpc_error* error);
  81   static void OnResolvedLocked(void* arg, grpc_error* error);
  82
  83   /// DNS server to use (if not system default)
  84   char* dns_server_;
  85   /// name to resolve (usually the same as target_name)
  86   char* name_to_resolve_;
  87   /// channel args
  88   grpc_channel_args* channel_args_;
  89   /// whether to request the service config
  90   bool request_service_config_;
  91   /// pollset_set to drive the name resolution process
  92   grpc_pollset_set* interested_parties_;
  93   /// closures used by the combiner
  94   grpc_closure on_next_resolution_;
  95   grpc_closure on_resolved_;
  96   /// are we currently resolving?
  97   bool resolving_ = false;
  98   /// the pending resolving request
  99   grpc_ares_request* pending_request_ = nullptr;
 100   /// next resolution timer
 101   bool have_next_resolution_timer_ = false;
 102   grpc_timer next_resolution_timer_;
 103   /// min interval between DNS requests
 104   grpc_millis min_time_between_resolutions_;
 105   /// timestamp of last DNS request
 106   grpc_millis last_resolution_timestamp_ = -1;
 107   /// retry backoff state
 108   BackOff backoff_;
 109   /// currently resolving addresses
 110   UniquePtr<ServerAddressList> addresses_;
 111   /// currently resolving service config
 112   char* service_config_json_ = nullptr;
 113   // has shutdown been initiated
 114   bool shutdown_initiated_ = false;
 115   // timeout in milliseconds for active DNS queries
 116   int query_timeout_ms_;
 117   // whether or not to enable SRV DNS queries
 118   bool enable_srv_queries_;
 119 };
 120
 121 AresDnsResolver::AresDnsResolver(ResolverArgs args)
 122     : Resolver(args.combiner, std::move(args.result_handler)),
 123       backoff_(
 124           BackOff::Options()
 125               .set_initial_backoff(GRPC_DNS_INITIAL_CONNECT_BACKOFF_SECONDS *
 126                                    1000)
 127               .set_multiplier(GRPC_DNS_RECONNECT_BACKOFF_MULTIPLIER)
 128               .set_jitter(GRPC_DNS_RECONNECT_JITTER)
 129               .set_max_backoff(GRPC_DNS_RECONNECT_MAX_BACKOFF_SECONDS * 1000)) {
 130   // Get name to resolve from URI path.
 131   const char* path = args.uri->path;
 132   if (path[0] == '/') ++path;
 133   name_to_resolve_ = gpr_strdup(path);
 134   // Get DNS server from URI authority.
 135   dns_server_ = nullptr;
 136   if (0 != strcmp(args.uri->authority, "")) {
 137     dns_server_ = gpr_strdup(args.uri->authority);
 138   }
 139   channel_args_ = grpc_channel_args_copy(args.args);
 140   // Disable service config option
 141   const grpc_arg* arg = grpc_channel_args_find(
 142       channel_args_, GRPC_ARG_SERVICE_CONFIG_DISABLE_RESOLUTION);
 143   request_service_config_ = !grpc_channel_arg_get_bool(arg, true);
 144   // Min time b/t resolutions option
 145   arg = grpc_channel_args_find(channel_args_,
 146                                GRPC_ARG_DNS_MIN_TIME_BETWEEN_RESOLUTIONS_MS);
 147   min_time_between_resolutions_ =
 148       grpc_channel_arg_get_integer(arg, {1000, 0, INT_MAX});
 149   // Enable SRV queries option
 150   arg = grpc_channel_args_find(channel_args_, GRPC_ARG_DNS_ENABLE_SRV_QUERIES);
 151   enable_srv_queries_ = grpc_channel_arg_get_bool(arg, false);
 152   interested_parties_ = grpc_pollset_set_create();
 153   if (args.pollset_set != nullptr) {
 154     grpc_pollset_set_add_pollset_set(interested_parties_, args.pollset_set);
 155   }
 156   GRPC_CLOSURE_INIT(&on_next_resolution_, OnNextResolutionLocked, this,
 157                     grpc_combiner_scheduler(combiner()));
 158   GRPC_CLOSURE_INIT(&on_resolved_, OnResolvedLocked, this,
 159                     grpc_combiner_scheduler(combiner()));
 160   const grpc_arg* query_timeout_ms_arg =
 161       grpc_channel_args_find(channel_args_, GRPC_ARG_DNS_ARES_QUERY_TIMEOUT_MS);
 162   query_timeout_ms_ = grpc_channel_arg_get_integer(
 163       query_timeout_ms_arg,
 164       {GRPC_DNS_ARES_DEFAULT_QUERY_TIMEOUT_MS, 0, INT_MAX});
 165 }
 166
 167 AresDnsResolver::~AresDnsResolver() {
 168   GRPC_CARES_TRACE_LOG("resolver:%p destroying AresDnsResolver", this);
 169   grpc_pollset_set_destroy(interested_parties_);
 170   gpr_free(dns_server_);
 171   gpr_free(name_to_resolve_);
 172   grpc_channel_args_destroy(channel_args_);
 173 }
 174
 175 void AresDnsResolver::StartLocked() {
 176   GRPC_CARES_TRACE_LOG("resolver:%p AresDnsResolver::StartLocked() is called.",
 177                        this);
 178   MaybeStartResolvingLocked();
 179 }
 180
 181 void AresDnsResolver::RequestReresolutionLocked() {
 182   if (!resolving_) {
 183     MaybeStartResolvingLocked();
 184   }
 185 }
 186
 187 void AresDnsResolver::ResetBackoffLocked() {
 188   if (have_next_resolution_timer_) {
 189     grpc_timer_cancel(&next_resolution_timer_);
 190   }
 191   backoff_.Reset();
 192 }
 193
 194 void AresDnsResolver::ShutdownLocked() {
 195   shutdown_initiated_ = true;
 196   if (have_next_resolution_timer_) {
 197     grpc_timer_cancel(&next_resolution_timer_);
 198   }
 199   if (pending_request_ != nullptr) {
 200     grpc_cancel_ares_request_locked(pending_request_);
 201   }
 202 }
 203
 204 void AresDnsResolver::OnNextResolutionLocked(void* arg, grpc_error* error) {
 205   AresDnsResolver* r = static_cast<AresDnsResolver*>(arg);
 206   GRPC_CARES_TRACE_LOG(
 207       "resolver:%p re-resolution timer fired. error: %s. shutdown_initiated_: "
 208       "%d",
 209       r, grpc_error_string(error), r->shutdown_initiated_);
 210   r->have_next_resolution_timer_ = false;
 211   if (error == GRPC_ERROR_NONE && !r->shutdown_initiated_) {
 212     if (!r->resolving_) {
 213       GRPC_CARES_TRACE_LOG(
 214           "resolver:%p start resolving due to re-resolution timer", r);
 215       r->StartResolvingLocked();
 216     }
 217   }
 218   r->Unref(DEBUG_LOCATION, "next_resolution_timer");
 219 }
 220
 221 bool ValueInJsonArray(grpc_json* array, const char* value) {
 222   for (grpc_json* entry = array->child; entry != nullptr; entry = entry->next) {
 223     if (entry->type == GRPC_JSON_STRING && strcmp(entry->value, value) == 0) {
 224       return true;
 225     }
 226   }
 227   return false;
 228 }
 229
 230 char* ChooseServiceConfig(char* service_config_choice_json,
 231                           grpc_error** error) {
 232   grpc_json* choices_json = grpc_json_parse_string(service_config_choice_json);
 233   if (choices_json == nullptr) {
 234     *error = GRPC_ERROR_CREATE_FROM_STATIC_STRING(
 235         "Service Config JSON Parsing, error: could not parse");
 236     return nullptr;
 237   }
 238   if (choices_json->type != GRPC_JSON_ARRAY) {
 239     *error = GRPC_ERROR_CREATE_FROM_STATIC_STRING(
 240         "Service Config Choices, error: should be of type array");
 241     return nullptr;
 242   }
 243   char* service_config = nullptr;
 244   InlinedVector<grpc_error*, 4> error_list;
 245   bool found_choice = false;  // have we found a choice?
 246   for (grpc_json* choice = choices_json->child; choice != nullptr;
 247        choice = choice->next) {
 248     if (choice->type != GRPC_JSON_OBJECT) {
 249       error_list.push_back(GRPC_ERROR_CREATE_FROM_STATIC_STRING(
 250           "Service Config Choice, error: should be of type object"));
 251       continue;
 252     }
 253     grpc_json* service_config_json = nullptr;
 254     bool selected = true;  // has this choice been rejected?
 255     for (grpc_json* field = choice->child; field != nullptr;
 256          field = field->next) {
 257       // Check client language, if specified.
 258       if (strcmp(field->key, "clientLanguage") == 0) {
 259         if (field->type != GRPC_JSON_ARRAY) {
 260           error_list.push_back(GRPC_ERROR_CREATE_FROM_STATIC_STRING(
 261               "field:clientLanguage error:should be of type array"));
 262         } else if (!ValueInJsonArray(field, "c++")) {
 263           selected = false;
 264         }
 265       }
 266       // Check client hostname, if specified.
 267       if (strcmp(field->key, "clientHostname") == 0) {
 268         if (field->type != GRPC_JSON_ARRAY) {
 269           error_list.push_back(GRPC_ERROR_CREATE_FROM_STATIC_STRING(
 270               "field:clientHostname error:should be of type array"));
 271           continue;
 272         }
 273         char* hostname = grpc_gethostname();
 274         if (hostname == nullptr || !ValueInJsonArray(field, hostname)) {
 275           selected = false;
 276         }
 277       }
 278       // Check percentage, if specified.
 279       if (strcmp(field->key, "percentage") == 0) {
 280         if (field->type != GRPC_JSON_NUMBER) {
 281           error_list.push_back(GRPC_ERROR_CREATE_FROM_STATIC_STRING(
 282               "field:percentage error:should be of type number"));
 283           continue;
 284         }
 285         int random_pct = rand() % 100;
 286         int percentage;
 287         if (sscanf(field->value, "%d", &percentage) != 1) {
 288           error_list.push_back(GRPC_ERROR_CREATE_FROM_STATIC_STRING(
 289               "field:percentage error:should be of type integer"));
 290           continue;
 291         }
 292         if (random_pct > percentage || percentage == 0) {
 293           selected = false;
 294         }
 295       }
 296       // Save service config.
 297       if (strcmp(field->key, "serviceConfig") == 0) {
 298         if (field->type == GRPC_JSON_OBJECT) {
 299           service_config_json = field;
 300         } else {
 301           error_list.push_back(GRPC_ERROR_CREATE_FROM_STATIC_STRING(
 302               "field:serviceConfig error:should be of type object"));
 303         }
 304       }
 305     }
 306     if (!found_choice && selected && service_config_json != nullptr) {
 307       service_config = grpc_json_dump_to_string(service_config_json, 0);
 308       found_choice = true;
 309     }
 310   }
 311   grpc_json_destroy(choices_json);
 312   if (!error_list.empty()) {
 313     gpr_free(service_config);
 314     service_config = nullptr;
 315     *error = GRPC_ERROR_CREATE_FROM_VECTOR("Service Config Choices Parser",
 316                                            &error_list);
 317   }
 318   return service_config;
 319 }
 320
 321 void AresDnsResolver::OnResolvedLocked(void* arg, grpc_error* error) {
 322   AresDnsResolver* r = static_cast<AresDnsResolver*>(arg);
 323   GPR_ASSERT(r->resolving_);
 324   r->resolving_ = false;
 325   gpr_free(r->pending_request_);
 326   r->pending_request_ = nullptr;
 327   if (r->shutdown_initiated_) {
 328     r->Unref(DEBUG_LOCATION, "OnResolvedLocked() shutdown");
 329     return;
 330   }
 331   if (r->addresses_ != nullptr) {
 332     Result result;
 333     result.addresses = std::move(*r->addresses_);
 334     if (r->service_config_json_ != nullptr) {
 335       char* service_config_string = ChooseServiceConfig(
 336           r->service_config_json_, &result.service_config_error);
 337       gpr_free(r->service_config_json_);
 338       if (result.service_config_error == GRPC_ERROR_NONE &&
 339           service_config_string != nullptr) {
 340         GRPC_CARES_TRACE_LOG("resolver:%p selected service config choice: %s",
 341                              r, service_config_string);
 342         result.service_config = ServiceConfig::Create(
 343             service_config_string, &result.service_config_error);
 344       }
 345       gpr_free(service_config_string);
 346     }
 347     result.args = grpc_channel_args_copy(r->channel_args_);
 348     r->result_handler()->ReturnResult(std::move(result));
 349     r->addresses_.reset();
 350     // Reset backoff state so that we start from the beginning when the
 351     // next request gets triggered.
 352     r->backoff_.Reset();
 353   } else {
 354     GRPC_CARES_TRACE_LOG("resolver:%p dns resolution failed: %s", r,
 355                          grpc_error_string(error));
 356     r->result_handler()->ReturnError(grpc_error_set_int(
 357         GRPC_ERROR_CREATE_REFERENCING_FROM_STATIC_STRING(
 358             "DNS resolution failed", &error, 1),
 359         GRPC_ERROR_INT_GRPC_STATUS, GRPC_STATUS_UNAVAILABLE));
 360     // Set retry timer.
 361     grpc_millis next_try = r->backoff_.NextAttemptTime();
 362     grpc_millis timeout = next_try - ExecCtx::Get()->Now();
 363     GRPC_CARES_TRACE_LOG("resolver:%p dns resolution failed (will retry): %s",
 364                          r, grpc_error_string(error));
 365     GPR_ASSERT(!r->have_next_resolution_timer_);
 366     r->have_next_resolution_timer_ = true;
 367     // TODO(roth): We currently deal with this ref manually.  Once the
 368     // new closure API is done, find a way to track this ref with the timer
 369     // callback as part of the type system.
 370     r->Ref(DEBUG_LOCATION, "retry-timer").release();
 371     if (timeout > 0) {
 372       GRPC_CARES_TRACE_LOG("resolver:%p retrying in %" PRId64 " milliseconds",
 373                            r, timeout);
 374     } else {
 375       GRPC_CARES_TRACE_LOG("resolver:%p retrying immediately", r);
 376     }
 377     grpc_timer_init(&r->next_resolution_timer_, next_try,
 378                     &r->on_next_resolution_);
 379   }
 380   r->Unref(DEBUG_LOCATION, "dns-resolving");
 381 }
 382
 383 void AresDnsResolver::MaybeStartResolvingLocked() {
 384   // If there is an existing timer, the time it fires is the earliest time we
 385   // can start the next resolution.
 386   if (have_next_resolution_timer_) return;
 387   if (last_resolution_timestamp_ >= 0) {
 388     const grpc_millis earliest_next_resolution =
 389         last_resolution_timestamp_ + min_time_between_resolutions_;
 390     const grpc_millis ms_until_next_resolution =
 391         earliest_next_resolution - grpc_core::ExecCtx::Get()->Now();
 392     if (ms_until_next_resolution > 0) {
 393       const grpc_millis last_resolution_ago =
 394           grpc_core::ExecCtx::Get()->Now() - last_resolution_timestamp_;
 395       GRPC_CARES_TRACE_LOG(
 396           "resolver:%p In cooldown from last resolution (from %" PRId64
 397           " ms ago). Will resolve again in %" PRId64 " ms",
 398           this, last_resolution_ago, ms_until_next_resolution);
 399       have_next_resolution_timer_ = true;
 400       // TODO(roth): We currently deal with this ref manually.  Once the
 401       // new closure API is done, find a way to track this ref with the timer
 402       // callback as part of the type system.
 403       Ref(DEBUG_LOCATION, "next_resolution_timer_cooldown").release();
 404       grpc_timer_init(&next_resolution_timer_, ms_until_next_resolution,
 405                       &on_next_resolution_);
 406       return;
 407     }
 408   }
 409   StartResolvingLocked();
 410 }
 411
 412 void AresDnsResolver::StartResolvingLocked() {
 413   // TODO(roth): We currently deal with this ref manually.  Once the
 414   // new closure API is done, find a way to track this ref with the timer
 415   // callback as part of the type system.
 416   Ref(DEBUG_LOCATION, "dns-resolving").release();
 417   GPR_ASSERT(!resolving_);
 418   resolving_ = true;
 419   service_config_json_ = nullptr;
 420   pending_request_ = grpc_dns_lookup_ares_locked(
 421       dns_server_, name_to_resolve_, kDefaultPort, interested_parties_,
 422       &on_resolved_, &addresses_, enable_srv_queries_ /* check_grpclb */,
 423       request_service_config_ ? &service_config_json_ : nullptr,
 424       query_timeout_ms_, combiner());
 425   last_resolution_timestamp_ = grpc_core::ExecCtx::Get()->Now();
 426   GRPC_CARES_TRACE_LOG("resolver:%p Started resolving. pending_request_:%p",
 427                        this, pending_request_);
 428 }
 429
 430 //
 431 // Factory
 432 //
 433
 434 class AresDnsResolverFactory : public ResolverFactory {
 435  public:
 436   OrphanablePtr<Resolver> CreateResolver(ResolverArgs args) const override {
 437     return OrphanablePtr<Resolver>(New<AresDnsResolver>(std::move(args)));
 438   }
 439
 440   const char* scheme() const override { return "dns"; }
 441 };
 442
 443 }  // namespace
 444
 445 }  // namespace grpc_core
 446
 447 extern grpc_address_resolver_vtable* grpc_resolve_address_impl;
 448 static grpc_address_resolver_vtable* default_resolver;
 449
 450 static grpc_error* blocking_resolve_address_ares(
 451     const char* name, const char* default_port,
 452     grpc_resolved_addresses** addresses) {
 453   return default_resolver->blocking_resolve_address(name, default_port,
 454                                                     addresses);
 455 }
 456
 457 static grpc_address_resolver_vtable ares_resolver = {
 458     grpc_resolve_address_ares, blocking_resolve_address_ares};
 459
 460 #ifdef GRPC_UV
 461 /* TODO(murgatroid99): Remove this when we want the cares resolver to be the
 462  * default when using libuv */
 463 static bool should_use_ares(const char* resolver_env) {
 464   return resolver_env != nullptr && gpr_stricmp(resolver_env, "ares") == 0;
 465 }
 466 #else  /* GRPC_UV */
 467 static bool should_use_ares(const char* resolver_env) {
 468   // TODO(lidiz): Remove the "g_custom_iomgr_enabled" flag once c-ares support
 469   // custom IO managers (e.g. gevent).
 470   return !g_custom_iomgr_enabled &&
 471          (resolver_env == nullptr || strlen(resolver_env) == 0 ||
 472           gpr_stricmp(resolver_env, "ares") == 0);
 473 }
 474 #endif /* GRPC_UV */
 475
 476 void grpc_resolver_dns_ares_init() {
 477   grpc_core::UniquePtr<char> resolver =
 478       GPR_GLOBAL_CONFIG_GET(grpc_dns_resolver);
 479   if (should_use_ares(resolver.get())) {
 480     gpr_log(GPR_DEBUG, "Using ares dns resolver");
 481     address_sorting_init();
 482     grpc_error* error = grpc_ares_init();
 483     if (error != GRPC_ERROR_NONE) {
 484       GRPC_LOG_IF_ERROR("grpc_ares_init() failed", error);
 485       return;
 486     }
 487     if (default_resolver == nullptr) {
 488       default_resolver = grpc_resolve_address_impl;
 489     }
 490     grpc_set_resolver_impl(&ares_resolver);
 491     grpc_core::ResolverRegistry::Builder::RegisterResolverFactory(
 492         grpc_core::UniquePtr<grpc_core::ResolverFactory>(
 493             grpc_core::New<grpc_core::AresDnsResolverFactory>()));
 494   }
 495 }
 496
 497 void grpc_resolver_dns_ares_shutdown() {
 498   grpc_core::UniquePtr<char> resolver =
 499       GPR_GLOBAL_CONFIG_GET(grpc_dns_resolver);
 500   if (should_use_ares(resolver.get())) {
 501     address_sorting_shutdown();
 502     grpc_ares_cleanup();
 503   }
 504 }
 505
 506 #else /* GRPC_ARES == 1 */
 507
 508 void grpc_resolver_dns_ares_init(void) {}
 509
 510 void grpc_resolver_dns_ares_shutdown(void) {}
 511
 512 #endif /* GRPC_ARES == 1 */