Implement in-memory metric exporter

Fixes #1405

exporters/memory/BUILD

@@ -3,6 +3,37 @@
 
 package(default_visibility = ["//visibility:public"])
 
+cc_library(
+    name = "in_memory_metric_exporter",
+    srcs = [
+        "src/in_memory_metric_exporter.cc",
+    ],
+    hdrs = [
+        "include/opentelemetry/exporters/memory/in_memory_metric_exporter.h",
+    ],
+    strip_include_prefix = "include",
+    tags = [
+        "memory",
+        "test",
+    ],
+    deps = [
+        "//sdk/src/metrics",
+    ],
+)
+
+cc_test(
+    name = "in_memory_metric_exporter_test",
+    srcs = ["test/in_memory_metric_exporter_test.cc"],
+    tags = [
+        "memory",
+        "test",
+    ],
+    deps = [
+        ":in_memory_metric_exporter",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
 cc_library(
     name = "in_memory_span_data",
     hdrs = [

exporters/memory/CMakeLists.txt

@@ -16,9 +16,24 @@ set_target_version(opentelemetry_exporter_in_memory)
 target_link_libraries(opentelemetry_exporter_in_memory
                       PUBLIC opentelemetry_trace)
 
+add_library(opentelemetry_exporter_in_memory_metric
+            src/in_memory_metric_exporter.cc)
+
+target_include_directories(
+  opentelemetry_exporter_in_memory_metric
+  PUBLIC "$<BUILD_INTERFACE:${CMAKE_CURRENT_LIST_DIR}/include>"
+         "$<INSTALL_INTERFACE:include>")
+
+set_target_properties(opentelemetry_exporter_in_memory_metric
+                      PROPERTIES EXPORT_NAME in_memory_metric_exporter)
+set_target_version(opentelemetry_exporter_in_memory_metric)
+
+target_link_libraries(opentelemetry_exporter_in_memory
+                      PUBLIC opentelemetry_metrics)
+
 if(OPENTELEMETRY_INSTALL)
   install(
-    TARGETS opentelemetry_exporter_in_memory
+    TARGETS opentelemetry_exporter_in_memory opentelemetry_exporter_in_memory_metric
     EXPORT "${PROJECT_NAME}-target"
     RUNTIME DESTINATION ${CMAKE_INSTALL_BINDIR}
     LIBRARY DESTINATION ${CMAKE_INSTALL_LIBDIR}
@@ -35,6 +50,8 @@ if(BUILD_TESTING)
   add_executable(in_memory_span_data_test test/in_memory_span_data_test.cc)
   add_executable(in_memory_span_exporter_test
                  test/in_memory_span_exporter_test.cc)
+  add_executable(in_memory_metric_exporter_test
+                 test/in_memory_metric_exporter_test.cc)
 
   target_link_libraries(
     in_memory_span_data_test ${GTEST_BOTH_LIBRARIES} ${CMAKE_THREAD_LIBS_INIT}
@@ -45,6 +62,11 @@ if(BUILD_TESTING)
     ${CMAKE_THREAD_LIBS_INIT} opentelemetry_exporter_in_memory
     opentelemetry_resources)
 
+  target_link_libraries(
+    in_memory_metric_exporter_test ${GTEST_BOTH_LIBRARIES}
+    ${CMAKE_THREAD_LIBS_INIT} opentelemetry_exporter_in_memory_metric
+    opentelemetry_resources)
+
   gtest_add_tests(
     TARGET in_memory_span_data_test
     TEST_PREFIX exporter.
@@ -53,4 +75,8 @@ if(BUILD_TESTING)
     TARGET in_memory_span_exporter_test
     TEST_PREFIX exporter.
     TEST_LIST in_memory_span_exporter_test)
+  gtest_add_tests(
+    TARGET in_memory_metric_exporter_test
+    TEST_PREFIX exporter.
+    TEST_LIST in_memory_metric_exporter_test)
 endif()

exporters/memory/include/opentelemetry/exporters/memory/in_memory_metric_exporter.h

@@ -0,0 +1,51 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+#pragma once
+
+#include <atomic>
+#include <vector>
+
+#include "opentelemetry/sdk/metrics/export/metric_producer.h"
+#include "opentelemetry/sdk/metrics/push_metric_exporter.h"
+#include "opentelemetry/version.h"
+
+OPENTELEMETRY_BEGIN_NAMESPACE
+namespace exporter
+{
+namespace memory
+{
+
+class InMemoryMetricExporter final : public sdk::metrics::PushMetricExporter
+{
+  using AggregationTemporalityMap =
+      std::map<sdk::metrics::InstrumentType, sdk::metrics::AggregationTemporality>;
+
+public:
+  InMemoryMetricExporter(const AggregationTemporalityMap &temporality = {})
+      : temporality_(temporality)
+  {}
+  InMemoryMetricExporter(const InMemoryMetricExporter &)  = delete;
+  InMemoryMetricExporter(const InMemoryMetricExporter &&) = delete;
+  void operator=(const InMemoryMetricExporter &)          = delete;
+  void operator=(const InMemoryMetricExporter &&)         = delete;
+  ~InMemoryMetricExporter() override                      = default;
+
+  sdk::common::ExportResult Export(const sdk::metrics::ResourceMetrics &data) noexcept override;
+  sdk::metrics::AggregationTemporality GetAggregationTemporality(
+      sdk::metrics::InstrumentType instrument_type) const noexcept override;
+  bool ForceFlush(
+      std::chrono::microseconds timeout = (std::chrono::microseconds::max)()) noexcept override;
+  bool Shutdown(std::chrono::microseconds timeout = std::chrono::microseconds(0)) noexcept override;
+
+  const std::vector<sdk::metrics::ResourceMetrics> &GetData() const;
+
+private:
+  std::vector<sdk::metrics::ResourceMetrics> data_{};
+  std::atomic<bool> is_shutdown_{false};
+  AggregationTemporalityMap temporality_;
+};
+
+}  // namespace memory
+}  // namespace exporter
+OPENTELEMETRY_END_NAMESPACE

exporters/memory/src/in_memory_metric_exporter.cc

@@ -0,0 +1,56 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+#include "opentelemetry/exporters/memory/in_memory_metric_exporter.h"
+#include "opentelemetry/sdk/common/global_log_handler.h"
+
+OPENTELEMETRY_BEGIN_NAMESPACE
+namespace exporter
+{
+namespace memory
+{
+
+using sdk::common::ExportResult;
+using sdk::metrics::AggregationTemporality;
+using sdk::metrics::InstrumentType;
+using sdk::metrics::ResourceMetrics;
+
+ExportResult InMemoryMetricExporter::Export(const ResourceMetrics &data) noexcept
+{
+  if (is_shutdown_)
+  {
+    OTEL_INTERNAL_LOG_ERROR("[In Memory Metric Exporter] Exporting failed, exporter is shutdown");
+    return ExportResult::kFailure;
+  }
+  data_.push_back(data);
+  return ExportResult::kSuccess;
+}
+
+AggregationTemporality InMemoryMetricExporter::GetAggregationTemporality(
+    InstrumentType instrument_type) const noexcept
+{
+  auto result = temporality_.find(instrument_type);
+  return result == std::end(temporality_)  //
+             ? AggregationTemporality::kCumulative
+             : result->second;
+}
+
+bool InMemoryMetricExporter::ForceFlush(std::chrono::microseconds /* timeout */) noexcept
+{
+  return true;
+}
+
+bool InMemoryMetricExporter::Shutdown(std::chrono::microseconds /* timeout */) noexcept
+{
+  is_shutdown_ = true;
+  return true;
+}
+
+const std::vector<ResourceMetrics> &InMemoryMetricExporter::GetData() const
+{
+  return data_;
+}
+
+}  // namespace memory
+}  // namespace exporter
+OPENTELEMETRY_END_NAMESPACE

exporters/memory/test/in_memory_metric_exporter_test.cc

@@ -0,0 +1,13 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+#include "opentelemetry/exporters/memory/in_memory_metric_exporter.h"
+
+#include <gtest/gtest.h>
+
+using opentelemetry::exporter::memory::InMemoryMetricExporter;
+
+TEST(InMemoryMetricExporter, Instantiate)
+{
+  InMemoryMetricExporter exporter;
+}