impl(bigtable): add and test some metric utility functions (#15299)

Author: scotthart

google/cloud/bigtable/CMakeLists.txt

@@ -454,6 +454,7 @@ if (BUILD_TESTING)
         internal/legacy_bulk_mutator_test.cc
         internal/legacy_row_reader_test.cc
         internal/logging_data_client_test.cc
+        internal/metrics_test.cc
         internal/mutate_rows_limiter_test.cc
         internal/operation_context_test.cc
         internal/prefix_range_end_test.cc

google/cloud/bigtable/bigtable_client_unit_tests.bzl

@@ -59,6 +59,7 @@ bigtable_client_unit_tests = [
     "internal/legacy_bulk_mutator_test.cc",
     "internal/legacy_row_reader_test.cc",
     "internal/logging_data_client_test.cc",
+    "internal/metrics_test.cc",
     "internal/mutate_rows_limiter_test.cc",
     "internal/operation_context_test.cc",
     "internal/prefix_range_end_test.cc",

google/cloud/bigtable/internal/metrics.cc

@@ -22,7 +22,7 @@ namespace cloud {
 namespace bigtable_internal {
 GOOGLE_CLOUD_CPP_INLINE_NAMESPACE_BEGIN
 
-LabelMap IntoMap(ResourceLabels const& r, DataLabels const& d) {
+LabelMap IntoLabelMap(ResourceLabels const& r, DataLabels const& d) {
   return {
       {"project_id", r.project_id},
       {"instance", r.instance},
@@ -38,6 +38,20 @@ LabelMap IntoMap(ResourceLabels const& r, DataLabels const& d) {
   };
 }
 
+absl::optional<google::bigtable::v2::ResponseParams>
+GetResponseParamsFromTrailingMetadata(
+    grpc::ClientContext const& client_context) {
+  auto metadata = client_context.GetServerTrailingMetadata();
+  auto iter = metadata.find("x-goog-ext-425905942-bin");
+  if (iter == metadata.end()) return absl::nullopt;
+  google::bigtable::v2::ResponseParams p;
+  // The value for this key should always be the same in a response, so we
+  // return the first value we find.
+  std::string value{iter->second.data(), iter->second.size()};
+  if (p.ParseFromString(value)) return p;
+  return absl::nullopt;
+}
+
 Metric::~Metric() = default;
 
 GOOGLE_CLOUD_CPP_INLINE_NAMESPACE_END

google/cloud/bigtable/internal/metrics.h

@@ -20,6 +20,7 @@
 #include "google/cloud/bigtable/internal/operation_context.h"
 #include "google/cloud/bigtable/version.h"
 #include "google/cloud/status.h"
+#include <google/bigtable/v2/response_params.pb.h>
 #include <grpcpp/grpcpp.h>
 #include <opentelemetry/context/context.h>
 #include <memory>
@@ -49,7 +50,11 @@ struct DataLabels {
 };
 
 using LabelMap = std::unordered_map<std::string, std::string>;
-LabelMap IntoMap(ResourceLabels const& r, DataLabels const& d);
+LabelMap IntoLabelMap(ResourceLabels const& r, DataLabels const& d);
+
+absl::optional<google::bigtable::v2::ResponseParams>
+GetResponseParamsFromTrailingMetadata(
+    grpc::ClientContext const& client_context);
 
 struct PreCallParams {
   OperationContext::Clock::time_point attempt_start;

google/cloud/bigtable/internal/metrics_test.cc

@@ -0,0 +1,85 @@
+// Copyright 2025 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifdef GOOGLE_CLOUD_CPP_BIGTABLE_WITH_OTEL_METRICS
+
+#include "google/cloud/bigtable/internal/metrics.h"
+#include "google/cloud/bigtable/version.h"
+#include "google/cloud/testing_util/validate_metadata.h"
+#include <gmock/gmock.h>
+
+namespace google {
+namespace cloud {
+namespace bigtable_internal {
+GOOGLE_CLOUD_CPP_INLINE_NAMESPACE_BEGIN
+namespace {
+
+using ::google::cloud::testing_util::SetServerMetadata;
+
+using ::testing::Eq;
+using ::testing::Pair;
+using ::testing::UnorderedElementsAre;
+
+TEST(LabelMap, IntoLabelMap) {
+  ResourceLabels r{"my-project", "my-instance", "my-table", "my-cluster",
+                   "my-zone"};
+  DataLabels d{"my-method",     "my-streaming",   "my-client-name",
+               "my-client-uid", "my-app-profile", "my-status"};
+
+  auto label_map = IntoLabelMap(r, d);
+
+  EXPECT_THAT(
+      label_map,
+      UnorderedElementsAre(
+          Pair("project_id", "my-project"), Pair("instance", "my-instance"),
+          Pair("table", "my-table"), Pair("cluster", "my-cluster"),
+          Pair("zone", "my-zone"), Pair("method", "my-method"),
+          Pair("streaming", "my-streaming"),
+          Pair("client_name", "my-client-name"),
+          Pair("client_uid", "my-client-uid"),
+          Pair("app_profile", "my-app-profile"), Pair("status", "my-status")));
+}
+
+TEST(GetResponseParamsFromMetadata, NonEmptyHeader) {
+  google::bigtable::v2::ResponseParams expected_response_params;
+  expected_response_params.set_cluster_id("my-cluster");
+  expected_response_params.set_zone_id("my-zone");
+  grpc::ClientContext client_context;
+  RpcMetadata server_metadata;
+  server_metadata.trailers.emplace(
+      "x-goog-ext-425905942-bin", expected_response_params.SerializeAsString());
+  SetServerMetadata(client_context, server_metadata);
+
+  auto result = GetResponseParamsFromTrailingMetadata(client_context);
+  ASSERT_TRUE(result);
+  EXPECT_THAT(result->cluster_id(), Eq("my-cluster"));
+  EXPECT_THAT(result->zone_id(), Eq("my-zone"));
+}
+
+TEST(GetResponseParamsFromMetadata, EmptyHeader) {
+  grpc::ClientContext client_context;
+  RpcMetadata server_metadata;
+  SetServerMetadata(client_context, server_metadata);
+
+  auto result = GetResponseParamsFromTrailingMetadata(client_context);
+  EXPECT_FALSE(result);
+}
+
+}  // namespace
+GOOGLE_CLOUD_CPP_INLINE_NAMESPACE_END
+}  // namespace bigtable_internal
+}  // namespace cloud
+}  // namespace google
+
+#endif  // GOOGLE_CLOUD_CPP_BIGTABLE_WITH_OTEL_METRICS