feat: Add logging about export status to Metrics SDK (#1947)

* Adds some debug log output for successfully exporting metrics, and additional error logging.  Implementation is borrowed from the Batch Log Record Processor.

Does not include a count.  Eventually that can be handled with the `otel.sdk.exporter.metric_data_point.exported` internal metric.  See https://opentelemetry.io/docs/specs/semconv/otel/sdk-metrics/

Fixes: #1888

* Add a test

* remove rubocop disable

* use endless syntax

* remove unused RaisingExporter copied from BLRP test

* don't set export interval or timeout

* use let statements

* Use public force_flush instead of internal export method

* Remove skip for Windows platform

* remove puts stmt from debugging

Author: wsmoak

metrics_sdk/lib/opentelemetry/sdk/metrics/export/periodic_metric_reader.rb

@@ -123,7 +123,18 @@ def start
           def export(timeout: nil)
             @export_mutex.synchronize do
               collected_metrics = collect
-              @exporter.export(collected_metrics, timeout: timeout || @export_timeout) unless collected_metrics.empty?
+              result_code = @exporter.export(collected_metrics, timeout: timeout || @export_timeout) unless collected_metrics.empty?
+              report_result(result_code)
+              result_code
+            end
+          end
+
+          def report_result(result_code)
+            if result_code == Export::SUCCESS
+              OpenTelemetry.logger.debug 'Successfully exported metrics'
+            else
+              OpenTelemetry.handle_error(exception: ExportError.new('Unable to export metrics'))
+              OpenTelemetry.logger.error("Result code: #{result_code}")
             end
           end
 

metrics_sdk/test/opentelemetry/sdk/metrics/export/periodic_metric_reader_test.rb

@@ -0,0 +1,78 @@
+# frozen_string_literal: true
+
+# Copyright The OpenTelemetry Authors
+#
+# SPDX-License-Identifier: Apache-2.0
+
+require 'test_helper'
+
+describe OpenTelemetry::SDK::Metrics::Export::PeriodicMetricReader do
+  PeriodicMetricReader = OpenTelemetry::SDK::Metrics::Export::PeriodicMetricReader
+  SUCCESS = OpenTelemetry::SDK::Metrics::Export::SUCCESS
+  FAILURE = OpenTelemetry::SDK::Metrics::Export::FAILURE
+  TIMEOUT = OpenTelemetry::SDK::Metrics::Export::TIMEOUT
+
+  class TestExporter
+    def initialize(status_codes: nil)
+      @status_codes = status_codes || []
+      @exported_metrics = []
+    end
+
+    attr_reader :exported_metrics
+
+    def export(metrics, timeout: nil)
+      s = @status_codes.shift
+      if s.nil? || s == SUCCESS
+        @exported_metrics.concat(metrics)
+        SUCCESS
+      else
+        s
+      end
+    end
+
+    def shutdown(timeout: nil) = SUCCESS
+
+    def force_flush(timeout: nil) = SUCCESS
+  end
+
+  describe 'exporter with failure' do
+    let(:exporter) { TestExporter.new(status_codes: [FAILURE]) }
+    let(:reader) { PeriodicMetricReader.new(exporter: exporter) }
+
+    it 'logs export failure as error' do
+      mock_logger = Minitest::Mock.new
+      mock_logger.expect(:error, nil, [/Unable to export metrics/])
+      mock_logger.expect(:error, nil, [/Result code: 1/])
+
+      # Stub collect to return a non-empty array so export is actually called
+      reader.stub(:collect, ['mock_metric']) do
+        OpenTelemetry.stub(:logger, mock_logger) do
+          reader.force_flush
+        end
+      end
+
+      reader.shutdown
+      mock_logger.verify
+    end
+  end
+
+  describe 'succesful exporter' do
+    let(:exporter) { TestExporter.new(status_codes: [SUCCESS]) }
+    let(:reader) { PeriodicMetricReader.new(exporter: exporter) }
+
+    it 'logs successful export as debug' do
+      mock_logger = Minitest::Mock.new
+      mock_logger.expect(:debug, nil, ['Successfully exported metrics'])
+
+      # Stub collect to return a non-empty array so export is actually called
+      reader.stub(:collect, ['mock_metric']) do
+        OpenTelemetry.stub(:logger, mock_logger) do
+          reader.force_flush
+        end
+      end
+
+      reader.shutdown
+      mock_logger.verify
+    end
+  end
+end