src/core/ext/filters/client_channel/resolving_lb_policy.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 #include "src/core/ext/filters/client_channel/resolving_lb_policy.h"
  22
  23 #include <inttypes.h>
  24 #include <limits.h>
  25 #include <stdbool.h>
  26 #include <stdio.h>
  27 #include <string.h>
  28
  29 #include <grpc/support/alloc.h>
  30 #include <grpc/support/log.h>
  31 #include <grpc/support/string_util.h>
  32 #include <grpc/support/sync.h>
  33
  34 #include "src/core/ext/filters/client_channel/backup_poller.h"
  35 #include "src/core/ext/filters/client_channel/http_connect_handshaker.h"
  36 #include "src/core/ext/filters/client_channel/lb_policy/child_policy_handler.h"
  37 #include "src/core/ext/filters/client_channel/lb_policy_registry.h"
  38 #include "src/core/ext/filters/client_channel/proxy_mapper_registry.h"
  39 #include "src/core/ext/filters/client_channel/resolver_registry.h"
  40 #include "src/core/ext/filters/client_channel/retry_throttle.h"
  41 #include "src/core/ext/filters/client_channel/server_address.h"
  42 #include "src/core/ext/filters/client_channel/service_config.h"
  43 #include "src/core/ext/filters/client_channel/subchannel.h"
  44 #include "src/core/ext/filters/deadline/deadline_filter.h"
  45 #include "src/core/lib/backoff/backoff.h"
  46 #include "src/core/lib/channel/channel_args.h"
  47 #include "src/core/lib/channel/connected_channel.h"
  48 #include "src/core/lib/channel/status_util.h"
  49 #include "src/core/lib/gpr/string.h"
  50 #include "src/core/lib/gprpp/inlined_vector.h"
  51 #include "src/core/lib/gprpp/manual_constructor.h"
  52 #include "src/core/lib/gprpp/sync.h"
  53 #include "src/core/lib/iomgr/combiner.h"
  54 #include "src/core/lib/iomgr/iomgr.h"
  55 #include "src/core/lib/iomgr/polling_entity.h"
  56 #include "src/core/lib/profiling/timers.h"
  57 #include "src/core/lib/slice/slice_internal.h"
  58 #include "src/core/lib/slice/slice_string_helpers.h"
  59 #include "src/core/lib/surface/channel.h"
  60 #include "src/core/lib/transport/connectivity_state.h"
  61 #include "src/core/lib/transport/error_utils.h"
  62 #include "src/core/lib/transport/metadata.h"
  63 #include "src/core/lib/transport/metadata_batch.h"
  64 #include "src/core/lib/transport/static_metadata.h"
  65 #include "src/core/lib/transport/status_metadata.h"
  66
  67 namespace grpc_core {
  68
  69 //
  70 // ResolvingLoadBalancingPolicy::ResolverResultHandler
  71 //
  72
  73 class ResolvingLoadBalancingPolicy::ResolverResultHandler
  74     : public Resolver::ResultHandler {
  75  public:
  76   explicit ResolverResultHandler(
  77       RefCountedPtr<ResolvingLoadBalancingPolicy> parent)
  78       : parent_(std::move(parent)) {}
  79
  80   ~ResolverResultHandler() {
  81     if (GRPC_TRACE_FLAG_ENABLED(*(parent_->tracer_))) {
  82       gpr_log(GPR_INFO, "resolving_lb=%p: resolver shutdown complete",
  83               parent_.get());
  84     }
  85   }
  86
  87   void ReturnResult(Resolver::Result result) override {
  88     parent_->OnResolverResultChangedLocked(std::move(result));
  89   }
  90
  91   void ReturnError(grpc_error* error) override {
  92     parent_->OnResolverError(error);
  93   }
  94
  95  private:
  96   RefCountedPtr<ResolvingLoadBalancingPolicy> parent_;
  97 };
  98
  99 //
 100 // ResolvingLoadBalancingPolicy::ResolvingControlHelper
 101 //
 102
 103 class ResolvingLoadBalancingPolicy::ResolvingControlHelper
 104     : public LoadBalancingPolicy::ChannelControlHelper {
 105  public:
 106   explicit ResolvingControlHelper(
 107       RefCountedPtr<ResolvingLoadBalancingPolicy> parent)
 108       : parent_(std::move(parent)) {}
 109
 110   RefCountedPtr<SubchannelInterface> CreateSubchannel(
 111       const grpc_channel_args& args) override {
 112     if (parent_->resolver_ == nullptr) return nullptr;  // Shutting down.
 113     return parent_->channel_control_helper()->CreateSubchannel(args);
 114   }
 115
 116   void UpdateState(grpc_connectivity_state state,
 117                    std::unique_ptr<SubchannelPicker> picker) override {
 118     if (parent_->resolver_ == nullptr) return;  // Shutting down.
 119     parent_->channel_control_helper()->UpdateState(state, std::move(picker));
 120   }
 121
 122   void RequestReresolution() override {
 123     if (parent_->resolver_ == nullptr) return;  // Shutting down.
 124     if (GRPC_TRACE_FLAG_ENABLED(*(parent_->tracer_))) {
 125       gpr_log(GPR_INFO, "resolving_lb=%p: started name re-resolving",
 126               parent_.get());
 127     }
 128     parent_->resolver_->RequestReresolutionLocked();
 129   }
 130
 131   void AddTraceEvent(TraceSeverity severity, StringView message) override {
 132     if (parent_->resolver_ == nullptr) return;  // Shutting down.
 133     parent_->channel_control_helper()->AddTraceEvent(severity, message);
 134   }
 135
 136  private:
 137   RefCountedPtr<ResolvingLoadBalancingPolicy> parent_;
 138 };
 139
 140 //
 141 // ResolvingLoadBalancingPolicy
 142 //
 143
 144 ResolvingLoadBalancingPolicy::ResolvingLoadBalancingPolicy(
 145     Args args, TraceFlag* tracer, grpc_core::UniquePtr<char> target_uri,
 146     ProcessResolverResultCallback process_resolver_result,
 147     void* process_resolver_result_user_data)
 148     : LoadBalancingPolicy(std::move(args)),
 149       tracer_(tracer),
 150       target_uri_(std::move(target_uri)),
 151       process_resolver_result_(process_resolver_result),
 152       process_resolver_result_user_data_(process_resolver_result_user_data) {
 153   GPR_ASSERT(process_resolver_result != nullptr);
 154   resolver_ = ResolverRegistry::CreateResolver(
 155       target_uri_.get(), args.args, interested_parties(), combiner(),
 156       absl::make_unique<ResolverResultHandler>(Ref()));
 157   // Since the validity of args has been checked when create the channel,
 158   // CreateResolver() must return a non-null result.
 159   GPR_ASSERT(resolver_ != nullptr);
 160   if (GRPC_TRACE_FLAG_ENABLED(*tracer_)) {
 161     gpr_log(GPR_INFO, "resolving_lb=%p: starting name resolution", this);
 162   }
 163   channel_control_helper()->UpdateState(GRPC_CHANNEL_CONNECTING,
 164                                         absl::make_unique<QueuePicker>(Ref()));
 165   resolver_->StartLocked();
 166 }
 167
 168 ResolvingLoadBalancingPolicy::~ResolvingLoadBalancingPolicy() {
 169   GPR_ASSERT(resolver_ == nullptr);
 170   GPR_ASSERT(lb_policy_ == nullptr);
 171 }
 172
 173 void ResolvingLoadBalancingPolicy::ShutdownLocked() {
 174   if (resolver_ != nullptr) {
 175     resolver_.reset();
 176     if (lb_policy_ != nullptr) {
 177       if (GRPC_TRACE_FLAG_ENABLED(*tracer_)) {
 178         gpr_log(GPR_INFO, "resolving_lb=%p: shutting down lb_policy=%p", this,
 179                 lb_policy_.get());
 180       }
 181       grpc_pollset_set_del_pollset_set(lb_policy_->interested_parties(),
 182                                        interested_parties());
 183       lb_policy_.reset();
 184     }
 185   }
 186 }
 187
 188 void ResolvingLoadBalancingPolicy::ExitIdleLocked() {
 189   if (lb_policy_ != nullptr) lb_policy_->ExitIdleLocked();
 190 }
 191
 192 void ResolvingLoadBalancingPolicy::ResetBackoffLocked() {
 193   if (resolver_ != nullptr) {
 194     resolver_->ResetBackoffLocked();
 195     resolver_->RequestReresolutionLocked();
 196   }
 197   if (lb_policy_ != nullptr) lb_policy_->ResetBackoffLocked();
 198 }
 199
 200 void ResolvingLoadBalancingPolicy::OnResolverError(grpc_error* error) {
 201   if (resolver_ == nullptr) {
 202     GRPC_ERROR_UNREF(error);
 203     return;
 204   }
 205   if (GRPC_TRACE_FLAG_ENABLED(*tracer_)) {
 206     gpr_log(GPR_INFO, "resolving_lb=%p: resolver transient failure: %s", this,
 207             grpc_error_string(error));
 208   }
 209   // If we already have an LB policy from a previous resolution
 210   // result, then we continue to let it set the connectivity state.
 211   // Otherwise, we go into TRANSIENT_FAILURE.
 212   if (lb_policy_ == nullptr) {
 213     grpc_error* state_error = GRPC_ERROR_CREATE_REFERENCING_FROM_STATIC_STRING(
 214         "Resolver transient failure", &error, 1);
 215     channel_control_helper()->UpdateState(
 216         GRPC_CHANNEL_TRANSIENT_FAILURE,
 217         absl::make_unique<TransientFailurePicker>(state_error));
 218   }
 219   GRPC_ERROR_UNREF(error);
 220 }
 221
 222 void ResolvingLoadBalancingPolicy::CreateOrUpdateLbPolicyLocked(
 223     RefCountedPtr<LoadBalancingPolicy::Config> lb_policy_config,
 224     Resolver::Result result) {
 225   // Construct update.
 226   UpdateArgs update_args;
 227   update_args.addresses = std::move(result.addresses);
 228   update_args.config = std::move(lb_policy_config);
 229   // TODO(roth): Once channel args is converted to C++, use std::move() here.
 230   update_args.args = result.args;
 231   result.args = nullptr;
 232   // Create policy if needed.
 233   if (lb_policy_ == nullptr) {
 234     lb_policy_ = CreateLbPolicyLocked(*update_args.args);
 235   }
 236   // Update the policy.
 237   if (GRPC_TRACE_FLAG_ENABLED(*tracer_)) {
 238     gpr_log(GPR_INFO, "resolving_lb=%p: Updating child policy %p", this,
 239             lb_policy_.get());
 240   }
 241   lb_policy_->UpdateLocked(std::move(update_args));
 242 }
 243
 244 // Creates a new LB policy.
 245 // Updates trace_strings to indicate what was done.
 246 OrphanablePtr<LoadBalancingPolicy>
 247 ResolvingLoadBalancingPolicy::CreateLbPolicyLocked(
 248     const grpc_channel_args& args) {
 249   LoadBalancingPolicy::Args lb_policy_args;
 250   lb_policy_args.combiner = combiner();
 251   lb_policy_args.channel_control_helper =
 252       absl::make_unique<ResolvingControlHelper>(Ref());
 253   lb_policy_args.args = &args;
 254   OrphanablePtr<LoadBalancingPolicy> lb_policy =
 255       MakeOrphanable<ChildPolicyHandler>(std::move(lb_policy_args), tracer_);
 256   if (GRPC_TRACE_FLAG_ENABLED(*tracer_)) {
 257     gpr_log(GPR_INFO, "resolving_lb=%p: created new LB policy %p", this,
 258             lb_policy.get());
 259   }
 260   grpc_pollset_set_add_pollset_set(lb_policy->interested_parties(),
 261                                    interested_parties());
 262   return lb_policy;
 263 }
 264
 265 void ResolvingLoadBalancingPolicy::MaybeAddTraceMessagesForAddressChangesLocked(
 266     bool resolution_contains_addresses, TraceStringVector* trace_strings) {
 267   if (!resolution_contains_addresses &&
 268       previous_resolution_contained_addresses_) {
 269     trace_strings->push_back(gpr_strdup("Address list became empty"));
 270   } else if (resolution_contains_addresses &&
 271              !previous_resolution_contained_addresses_) {
 272     trace_strings->push_back(gpr_strdup("Address list became non-empty"));
 273   }
 274   previous_resolution_contained_addresses_ = resolution_contains_addresses;
 275 }
 276
 277 void ResolvingLoadBalancingPolicy::ConcatenateAndAddChannelTraceLocked(
 278     TraceStringVector* trace_strings) const {
 279   if (!trace_strings->empty()) {
 280     gpr_strvec v;
 281     gpr_strvec_init(&v);
 282     gpr_strvec_add(&v, gpr_strdup("Resolution event: "));
 283     bool is_first = 1;
 284     for (size_t i = 0; i < trace_strings->size(); ++i) {
 285       if (!is_first) gpr_strvec_add(&v, gpr_strdup(", "));
 286       is_first = false;
 287       gpr_strvec_add(&v, (*trace_strings)[i]);
 288     }
 289     size_t len = 0;
 290     grpc_core::UniquePtr<char> message(gpr_strvec_flatten(&v, &len));
 291     channel_control_helper()->AddTraceEvent(ChannelControlHelper::TRACE_INFO,
 292                                             StringView(message.get()));
 293     gpr_strvec_destroy(&v);
 294   }
 295 }
 296
 297 void ResolvingLoadBalancingPolicy::OnResolverResultChangedLocked(
 298     Resolver::Result result) {
 299   // Handle race conditions.
 300   if (resolver_ == nullptr) return;
 301   if (GRPC_TRACE_FLAG_ENABLED(*tracer_)) {
 302     gpr_log(GPR_INFO, "resolving_lb=%p: got resolver result", this);
 303   }
 304   // We only want to trace the address resolution in the follow cases:
 305   // (a) Address resolution resulted in service config change.
 306   // (b) Address resolution that causes number of backends to go from
 307   //     zero to non-zero.
 308   // (c) Address resolution that causes number of backends to go from
 309   //     non-zero to zero.
 310   // (d) Address resolution that causes a new LB policy to be created.
 311   //
 312   // We track a list of strings to eventually be concatenated and traced.
 313   TraceStringVector trace_strings;
 314   const bool resolution_contains_addresses = result.addresses.size() > 0;
 315   // Process the resolver result.
 316   RefCountedPtr<LoadBalancingPolicy::Config> lb_policy_config;
 317   bool service_config_changed = false;
 318   char* service_config_error_string = nullptr;
 319   if (process_resolver_result_ != nullptr) {
 320     grpc_error* service_config_error = GRPC_ERROR_NONE;
 321     bool no_valid_service_config = false;
 322     service_config_changed = process_resolver_result_(
 323         process_resolver_result_user_data_, result, &lb_policy_config,
 324         &service_config_error, &no_valid_service_config);
 325     if (service_config_error != GRPC_ERROR_NONE) {
 326       service_config_error_string =
 327           gpr_strdup(grpc_error_string(service_config_error));
 328       if (no_valid_service_config) {
 329         // We received an invalid service config and we don't have a
 330         // fallback service config.
 331         OnResolverError(service_config_error);
 332       } else {
 333         GRPC_ERROR_UNREF(service_config_error);
 334       }
 335     }
 336   } else {
 337     lb_policy_config = child_lb_config_;
 338   }
 339   if (lb_policy_config != nullptr) {
 340     // Create or update LB policy, as needed.
 341     CreateOrUpdateLbPolicyLocked(std::move(lb_policy_config),
 342                                  std::move(result));
 343   }
 344   // Add channel trace event.
 345   if (service_config_changed) {
 346     // TODO(ncteisen): might be worth somehow including a snippet of the
 347     // config in the trace, at the risk of bloating the trace logs.
 348     trace_strings.push_back(gpr_strdup("Service config changed"));
 349   }
 350   if (service_config_error_string != nullptr) {
 351     trace_strings.push_back(service_config_error_string);
 352     service_config_error_string = nullptr;
 353   }
 354   MaybeAddTraceMessagesForAddressChangesLocked(resolution_contains_addresses,
 355                                                &trace_strings);
 356   ConcatenateAndAddChannelTraceLocked(&trace_strings);
 357 }
 358
 359 }  // namespace grpc_core