feat: add exponential histogram in otlp metrics exporter (#1851)

Author: xuan-cao-swi

exporter/otlp-metrics/lib/opentelemetry/exporter/otlp/metrics/metrics_exporter.rb

@@ -246,29 +246,50 @@ def as_otlp_metrics(metrics)
               )
 
             when :histogram
+              histogram_data_point(metrics)
+
+            end
+          end
+
+          def as_otlp_aggregation_temporality(type)
+            case type
+            when :delta then Opentelemetry::Proto::Metrics::V1::AggregationTemporality::AGGREGATION_TEMPORALITY_DELTA
+            when :cumulative then Opentelemetry::Proto::Metrics::V1::AggregationTemporality::AGGREGATION_TEMPORALITY_CUMULATIVE
+            else Opentelemetry::Proto::Metrics::V1::AggregationTemporality::AGGREGATION_TEMPORALITY_UNSPECIFIED
+            end
+          end
+
+          def histogram_data_point(metrics)
+            return if metrics.data_points.empty?
+
+            if metrics.data_points.first.instance_of?(OpenTelemetry::SDK::Metrics::Aggregation::ExponentialHistogramDataPoint)
+              Opentelemetry::Proto::Metrics::V1::Metric.new(
+                name: metrics.name,
+                description: metrics.description,
+                unit: metrics.unit,
+                exponential_histogram: Opentelemetry::Proto::Metrics::V1::ExponentialHistogram.new(
+                  aggregation_temporality: as_otlp_aggregation_temporality(metrics.aggregation_temporality),
+                  data_points: metrics.data_points.map do |ehdp|
+                    exponential_histogram_data_point(ehdp)
+                  end
+                )
+              )
+            elsif metrics.data_points.first.instance_of?(OpenTelemetry::SDK::Metrics::Aggregation::HistogramDataPoint)
               Opentelemetry::Proto::Metrics::V1::Metric.new(
                 name: metrics.name,
                 description: metrics.description,
                 unit: metrics.unit,
                 histogram: Opentelemetry::Proto::Metrics::V1::Histogram.new(
                   aggregation_temporality: as_otlp_aggregation_temporality(metrics.aggregation_temporality),
                   data_points: metrics.data_points.map do |hdp|
-                    histogram_data_point(hdp)
+                    explicit_histogram_data_point(hdp)
                   end
                 )
               )
             end
           end
 
-          def as_otlp_aggregation_temporality(type)
-            case type
-            when :delta then Opentelemetry::Proto::Metrics::V1::AggregationTemporality::AGGREGATION_TEMPORALITY_DELTA
-            when :cumulative then Opentelemetry::Proto::Metrics::V1::AggregationTemporality::AGGREGATION_TEMPORALITY_CUMULATIVE
-            else Opentelemetry::Proto::Metrics::V1::AggregationTemporality::AGGREGATION_TEMPORALITY_UNSPECIFIED
-            end
-          end
-
-          def histogram_data_point(hdp)
+          def explicit_histogram_data_point(hdp)
             Opentelemetry::Proto::Metrics::V1::HistogramDataPoint.new(
               attributes: hdp.attributes.map { |k, v| as_otlp_key_value(k, v) },
               start_time_unix_nano: hdp.start_time_unix_nano,
@@ -283,6 +304,31 @@ def histogram_data_point(hdp)
             )
           end
 
+          def exponential_histogram_data_point(ehdp)
+            Opentelemetry::Proto::Metrics::V1::ExponentialHistogramDataPoint.new(
+              attributes: ehdp.attributes.map { |k, v| as_otlp_key_value(k, v) },
+              start_time_unix_nano: ehdp.start_time_unix_nano,
+              time_unix_nano: ehdp.time_unix_nano,
+              count: ehdp.count,
+              sum: ehdp.sum,
+              scale: ehdp.scale,
+              zero_count: ehdp.zero_count,
+              positive: Opentelemetry::Proto::Metrics::V1::ExponentialHistogramDataPoint::Buckets.new(
+                offset: ehdp.positive.offset,
+                bucket_counts: ehdp.positive.counts
+              ),
+              negative: Opentelemetry::Proto::Metrics::V1::ExponentialHistogramDataPoint::Buckets.new(
+                offset: ehdp.negative.offset,
+                bucket_counts: ehdp.negative.counts
+              ),
+              flags: ehdp.flags,
+              exemplars: ehdp.exemplars,
+              min: ehdp.min,
+              max: ehdp.max,
+              zero_threshold: ehdp.zero_threshold
+            )
+          end
+
           def number_data_point(ndp)
             args = {
               attributes: ndp.attributes.map { |k, v| as_otlp_key_value(k, v) },

exporter/otlp-metrics/test/opentelemetry/exporter/otlp/metrics/metrics_exporter_test.rb

@@ -609,6 +609,11 @@
       gauge = meter.create_gauge('test_gauge', unit: 'smidgen', description: 'a small amount of something')
       gauge.record(15, attributes: { 'baz' => 'qux' })
 
+      meter_provider.add_view('*exponential*', aggregation: OpenTelemetry::SDK::Metrics::Aggregation::ExponentialBucketHistogram.new(max_scale: 20), type: :histogram, unit: 'smidgen')
+
+      exponential_histogram = meter.create_histogram('test_exponential_histogram', unit: 'smidgen', description: 'a small amount of something')
+      exponential_histogram.record(20, attributes: { 'lox' => 'xol' })
+
       exporter.pull
       meter_provider.shutdown
 
@@ -711,6 +716,40 @@
                           )
                         ]
                       )
+                    ),
+                    Opentelemetry::Proto::Metrics::V1::Metric.new(
+                      name: 'test_exponential_histogram',
+                      description: 'a small amount of something',
+                      unit: 'smidgen',
+                      exponential_histogram: Opentelemetry::Proto::Metrics::V1::ExponentialHistogram.new(
+                        data_points: [
+                          Opentelemetry::Proto::Metrics::V1::ExponentialHistogramDataPoint.new(
+                            attributes: [
+                              Opentelemetry::Proto::Common::V1::KeyValue.new(key: 'lox', value: Opentelemetry::Proto::Common::V1::AnyValue.new(string_value: 'xol'))
+                            ],
+                            start_time_unix_nano: 1_699_593_427_329_946_585,
+                            time_unix_nano: 1_699_593_427_329_946_586,
+                            count: 1,
+                            sum: 20,
+                            scale: 20,
+                            zero_count: 0,
+                            positive: Opentelemetry::Proto::Metrics::V1::ExponentialHistogramDataPoint::Buckets.new(
+                              offset: 4_531_870,
+                              bucket_counts: [1]
+                            ),
+                            negative: Opentelemetry::Proto::Metrics::V1::ExponentialHistogramDataPoint::Buckets.new(
+                              offset: 0,
+                              bucket_counts: [0]
+                            ),
+                            flags: 0,
+                            exemplars: nil,
+                            min: 20,
+                            max: 20,
+                            zero_threshold: 0
+                          )
+                        ],
+                        aggregation_temporality: Opentelemetry::Proto::Metrics::V1::AggregationTemporality::AGGREGATION_TEMPORALITY_DELTA
+                      )
                     )
                   ]
                 )

exporter/otlp-metrics/test/test_helper.rb

@@ -27,6 +27,7 @@ def collect(start_time, end_time, data_points)
 OpenTelemetry::SDK::Metrics::Aggregation::Sum.prepend(MockSum)
 OpenTelemetry::SDK::Metrics::Aggregation::ExplicitBucketHistogram.prepend(MockSum)
 OpenTelemetry::SDK::Metrics::Aggregation::LastValue.prepend(MockSum)
+OpenTelemetry::SDK::Metrics::Aggregation::ExponentialBucketHistogram.prepend(MockSum)
 
 def create_metrics_data(name: '', description: '', unit: '', instrument_kind: :counter, resource: nil,
                         instrumentation_scope: OpenTelemetry::SDK::InstrumentationScope.new('', 'v0.0.1'),