impl(bigtable): make MetricServiceConnection more shareable

google/cloud/bigtable/internal/data_connection_impl.cc

@@ -31,6 +31,8 @@
 #include "google/cloud/bigtable/result_source_interface.h"
 #include "google/cloud/bigtable/retry_policy.h"
 #include "google/cloud/background_threads.h"
+#include "google/cloud/common_options.h"
+#include "google/cloud/credentials.h"
 #include "google/cloud/grpc_options.h"
 #include "google/cloud/idempotency.h"
 #include "google/cloud/internal/algorithm.h"
@@ -39,6 +41,7 @@
 #include "google/cloud/internal/random.h"
 #include "google/cloud/internal/retry_loop.h"
 #include "google/cloud/internal/streaming_read_rpc.h"
+#include "google/cloud/universe_domain_options.h"
 #include <memory>
 #include <string>
 
@@ -195,6 +198,17 @@ std::string_view InstanceNameFromTableName(std::string_view table_name) {
   return table_name.substr(0, pos);
 }
 
+#ifdef GOOGLE_CLOUD_CPP_BIGTABLE_WITH_OTEL_METRICS
+Options MetricsExporterConnectionOptions(Options options) {
+  // We start with a copy of the client options to preserve credentials and
+  // universe domain, but we must unset Bigtable-specific endpoints/authorities
+  // to allow default Monitoring defaults.
+  options.unset<EndpointOption>();
+  options.unset<AuthorityOption>();
+  return options;
+}
+#endif  // GOOGLE_CLOUD_CPP_BIGTABLE_WITH_OTEL_METRICS
+
 }  // namespace
 
 bigtable::Row TransformReadModifyWriteRowResponse(
@@ -227,23 +241,25 @@ DataConnectionImpl::DataConnectionImpl(
       options_(MergeOptions(std::move(options), DataConnection::options())) {
 #ifdef GOOGLE_CLOUD_CPP_BIGTABLE_WITH_OTEL_METRICS
   if (options_.get<bigtable::EnableMetricsOption>()) {
+    metric_service_connection_ = monitoring_v3::MakeMetricServiceConnection(
+        MetricsExporterConnectionOptions(options_));
     // The client_uid is eventually used in conjunction with other data labels
     // to identify metric data points. This pseudorandom string is used to aid
     // in disambiguation.
     auto gen = internal::MakeDefaultPRNG();
     std::string client_uid =
         internal::Sample(gen, 16, "abcdefghijklmnopqrstuvwxyz0123456789");
     operation_context_factory_ =
-        std::make_unique<MetricsOperationContextFactory>(std::move(client_uid),
-                                                         options_);
+        std::make_unique<MetricsOperationContextFactory>(
+            std::move(client_uid), metric_service_connection_, options_);
   } else {
     operation_context_factory_ =
         std::make_unique<SimpleOperationContextFactory>();
   }
 #else
   operation_context_factory_ =
       std::make_unique<SimpleOperationContextFactory>();
-#endif
+#endif  // GOOGLE_CLOUD_CPP_BIGTABLE_WITH_OTEL_METRICS
 }
 
 DataConnectionImpl::DataConnectionImpl(

google/cloud/bigtable/internal/data_connection_impl.h

@@ -25,6 +25,9 @@
 #include "google/cloud/bigtable/prepared_query.h"
 #include "google/cloud/bigtable/result_source_interface.h"
 #include "google/cloud/background_threads.h"
+#ifdef GOOGLE_CLOUD_CPP_BIGTABLE_WITH_OTEL_METRICS
+#include "google/cloud/monitoring/v3/metric_connection.h"
+#endif  // GOOGLE_CLOUD_CPP_BIGTABLE_WITH_OTEL_METRICS
 #include "google/cloud/options.h"
 #include "google/cloud/status_or.h"
 #include "google/cloud/version.h"
@@ -142,6 +145,10 @@ class DataConnectionImpl : public bigtable::DataConnection {
 
   std::unique_ptr<BackgroundThreads> background_;
   std::unique_ptr<StubManager> stub_manager_;
+#ifdef GOOGLE_CLOUD_CPP_BIGTABLE_WITH_OTEL_METRICS
+  std::shared_ptr<::google::cloud::monitoring_v3::MetricServiceConnection>
+      metric_service_connection_;
+#endif  // GOOGLE_CLOUD_CPP_BIGTABLE_WITH_OTEL_METRICS
   std::unique_ptr<OperationContextFactory> operation_context_factory_;
   std::shared_ptr<MutateRowsLimiter> limiter_;
   Options options_;

google/cloud/bigtable/internal/operation_context_factory.cc

@@ -158,9 +158,11 @@ MetricsOperationContextFactory::MetricsOperationContextFactory(
 }
 
 MetricsOperationContextFactory::MetricsOperationContextFactory(
-    std::string client_uid, Options options)
+    std::string client_uid,
+    std::shared_ptr<monitoring_v3::MetricServiceConnection> conn,
+    Options options)
     : MetricsOperationContextFactory(
-          std::move(client_uid), nullptr,
+          std::move(client_uid), std::move(conn),
           std::make_shared<OperationContext::Clock>(), std::move(options)) {}
 
 MetricsOperationContextFactory::MetricsOperationContextFactory(

google/cloud/bigtable/internal/operation_context_factory.h

@@ -88,16 +88,16 @@ class SimpleOperationContextFactory : public OperationContextFactory {
 
 class MetricsOperationContextFactory : public OperationContextFactory {
  public:
-  explicit MetricsOperationContextFactory(std::string client_uid,
-                                          Options options = {});
+  MetricsOperationContextFactory(
+      std::string client_uid,
+      std::shared_ptr<monitoring_v3::MetricServiceConnection> conn,
+      Options options = {});
 
   // Used for injecting a MockMetricsServiceConnection for testing.
   MetricsOperationContextFactory(
       std::string client_uid,
       std::shared_ptr<monitoring_v3::MetricServiceConnection> conn,
-      std::shared_ptr<OperationContext::Clock> clock =
-          std::make_shared<OperationContext::Clock>(),
-      Options options = {});
+      std::shared_ptr<OperationContext::Clock> clock, Options options = {});
 
   // This constructs an instance only suitable for testing. The provided metric
   // is copied into every RPC metric vector, preventing normal Metric