Make opencensus Stackdriver exporter respects initial_metadata option

source/common/grpc/google_async_client_impl.cc

@@ -86,7 +86,7 @@ GoogleAsyncClientImpl::GoogleAsyncClientImpl(Event::Dispatcher& dispatcher,
   // smart enough to do connection pooling and reuse with identical channel args, so this should
   // have comparable overhead to what we are doing in Grpc::AsyncClientImpl, i.e. no expensive
   // new connection implied.
-  std::shared_ptr<grpc::Channel> channel = GoogleGrpcUtils::createChannel(config, api);
+  std::shared_ptr<grpc::Channel> channel = GoogleGrpcUtils::createChannel(config, api, false);
   stub_ = stub_factory.createStub(channel);
   // Initialize client stats.
   // TODO(jmarantz): Capture these names in async_client_manager_impl.cc and

source/common/grpc/google_grpc_utils.cc

@@ -44,6 +44,46 @@ getGoogleGrpcChannelCredentials(const envoy::config::core::v3::GrpcService& grpc
   return credentials_factory->getChannelCredentials(grpc_service, api);
 }
 
+// InitialMetadataInterceptor is used to inject the given initial metadata to gRPC channel.
+class InitialMetadataInterceptor : public grpc::experimental::Interceptor {
+public:
+  InitialMetadataInterceptor(
+      const Protobuf::RepeatedPtrField<envoy::config::core::v3::HeaderValue>& initial_metadata)
+      : initial_metadata_(initial_metadata) {}
+
+  void Intercept(grpc::experimental::InterceptorBatchMethods* methods) override {
+    if (methods->QueryInterceptionHookPoint(
+            grpc::experimental::InterceptionHookPoints::PRE_SEND_INITIAL_METADATA)) {
+      auto* metadata_map = methods->GetSendInitialMetadata();
+      if (metadata_map != nullptr) {
+        for (const auto& header_value : initial_metadata_) {
+          metadata_map->insert(std::make_pair(header_value.key(), header_value.value()));
+        }
+      }
+    }
+    methods->Proceed();
+  }
+
+private:
+  const Protobuf::RepeatedPtrField<envoy::config::core::v3::HeaderValue>& initial_metadata_;
+};
+
+class InitialMetadataInterceptorFactory
+    : public grpc::experimental::ClientInterceptorFactoryInterface {
+public:
+  InitialMetadataInterceptorFactory(
+      const Protobuf::RepeatedPtrField<envoy::config::core::v3::HeaderValue>& initial_metadata)
+      : initial_metadata_(initial_metadata) {}
+
+  grpc::experimental::Interceptor*
+  CreateClientInterceptor(grpc::experimental::ClientRpcInfo*) override {
+    return new InitialMetadataInterceptor(initial_metadata_);
+  }
+
+private:
+  const Protobuf::RepeatedPtrField<envoy::config::core::v3::HeaderValue> initial_metadata_;
+};
+
 } // namespace
 
 struct BufferInstanceContainer {
@@ -134,10 +174,23 @@ GoogleGrpcUtils::channelArgsFromConfig(const envoy::config::core::v3::GrpcServic
 }
 
 std::shared_ptr<grpc::Channel>
-GoogleGrpcUtils::createChannel(const envoy::config::core::v3::GrpcService& config, Api::Api& api) {
+GoogleGrpcUtils::createChannel(const envoy::config::core::v3::GrpcService& config, Api::Api& api,
+                               bool enable_initial_metadata_interceptor) {
   std::shared_ptr<grpc::ChannelCredentials> creds = getGoogleGrpcChannelCredentials(config, api);
   const grpc::ChannelArguments args = channelArgsFromConfig(config);
-  return CreateCustomChannel(config.google_grpc().target_uri(), creds, args);
+  if (!enable_initial_metadata_interceptor || config.initial_metadata().empty()) {
+    // Skip adding initial metadata interceptor if it is not enabled, or initial metadata is not
+    // configured.
+    return CreateCustomChannel(config.google_grpc().target_uri(), creds, args);
+  }
+
+  // Create gRPC channel with initial metadata interceptor.
+  std::vector<std::unique_ptr<grpc::experimental::ClientInterceptorFactoryInterface>>
+      interceptor_factories;
+  interceptor_factories.push_back(
+      std::make_unique<InitialMetadataInterceptorFactory>((config.initial_metadata())));
+  return ::grpc::experimental::CreateCustomChannelWithInterceptors(
+      config.google_grpc().target_uri(), creds, args, std::move(interceptor_factories));
 }
 
 } // namespace Grpc

source/common/grpc/google_grpc_utils.h

@@ -43,10 +43,13 @@ class GoogleGrpcUtils {
    * Build gRPC channel based on the given GrpcService configuration.
    * @param config Google gRPC config.
    * @param api reference to the Api object
+   * @param enable_initial_metadata_interceptor enables initial metadata interceptor if it is
+   * configured.
    * @return static std::shared_ptr<grpc::Channel> a gRPC channel.
    */
   static std::shared_ptr<grpc::Channel>
-  createChannel(const envoy::config::core::v3::GrpcService& config, Api::Api& api);
+  createChannel(const envoy::config::core::v3::GrpcService& config, Api::Api& api,
+                bool enable_initial_metadata_interceptor);
 };
 
 } // namespace Grpc

source/extensions/tracers/opencensus/opencensus_tracer_impl.cc

@@ -280,7 +280,7 @@ Driver::Driver(const envoy::config::trace::v3::OpenCensusConfig& oc_config,
         // address will be used.
         stackdriver_service.mutable_google_grpc()->set_target_uri(GoogleStackdriverTraceAddress);
       }
-      auto channel = Envoy::Grpc::GoogleGrpcUtils::createChannel(stackdriver_service, api);
+      auto channel = Envoy::Grpc::GoogleGrpcUtils::createChannel(stackdriver_service, api, true);
       opts.trace_service_stub = ::google::devtools::cloudtrace::v2::TraceService::NewStub(channel);
 #else
       throw EnvoyException("Opencensus tracer: cannot handle stackdriver google grpc service, "
@@ -303,7 +303,7 @@ Driver::Driver(const envoy::config::trace::v3::OpenCensusConfig& oc_config,
 #ifdef ENVOY_GOOGLE_GRPC
       const envoy::config::core::v3::GrpcService& ocagent_service =
           oc_config.ocagent_grpc_service();
-      auto channel = Envoy::Grpc::GoogleGrpcUtils::createChannel(ocagent_service, api);
+      auto channel = Envoy::Grpc::GoogleGrpcUtils::createChannel(ocagent_service, api, true);
       opts.trace_service_stub =
           ::opencensus::proto::agent::trace::v1::TraceService::NewStub(channel);
 #else