Histogram Aggregation - Prometheus exporter

exporters/prometheus/src/main/java/io/opentelemetry/exporter/prometheus/MetricAdapter.java

@@ -9,6 +9,7 @@
 
 import io.opentelemetry.api.metrics.common.Labels;
 import io.opentelemetry.sdk.metrics.data.AggregationTemporality;
+import io.opentelemetry.sdk.metrics.data.DoubleHistogramPointData;
 import io.opentelemetry.sdk.metrics.data.DoublePointData;
 import io.opentelemetry.sdk.metrics.data.DoubleSumData;
 import io.opentelemetry.sdk.metrics.data.DoubleSummaryPointData;
@@ -46,7 +47,9 @@ final class MetricAdapter {
 
   static final String SAMPLE_SUFFIX_COUNT = "_count";
   static final String SAMPLE_SUFFIX_SUM = "_sum";
+  static final String SAMPLE_SUFFIX_BUCKET = "_bucket";
   static final String LABEL_NAME_QUANTILE = "quantile";
+  static final String LABEL_NAME_LE = "le";
 
   // Converts a MetricData to a Prometheus MetricFamilySamples.
   static MetricFamilySamples toMetricFamilySamples(MetricData metricData) {
@@ -125,7 +128,8 @@ static List<Sample> toSamples(
               (DoubleSummaryPointData) pointData, name, labelNames, labelValues, samples);
           break;
         case HISTOGRAM:
-          // no-op, will add in the following PRs
+          addHistogramSamples(
+              (DoubleHistogramPointData) pointData, name, labelNames, labelValues, samples);
           break;
       }
     }
@@ -174,6 +178,42 @@ private static void addSummarySamples(
     }
   }
 
+  private static void addHistogramSamples(
+      DoubleHistogramPointData doubleHistogramPointData,
+      String name,
+      List<String> labelNames,
+      List<String> labelValues,
+      List<Sample> samples) {
+    samples.add(
+        new Sample(
+            name + SAMPLE_SUFFIX_COUNT,
+            labelNames,
+            labelValues,
+            doubleHistogramPointData.getCount()));
+    samples.add(
+        new Sample(
+            name + SAMPLE_SUFFIX_SUM, labelNames, labelValues, doubleHistogramPointData.getSum()));
+
+    List<String> labelNamesWithLe = new ArrayList<>(labelNames.size() + 1);
+    labelNamesWithLe.addAll(labelNames);
+    labelNamesWithLe.add(LABEL_NAME_LE);
+
+    long cumulativeCount = 0;
+    List<Double> boundaries = doubleHistogramPointData.getBoundaries();
+    List<Long> counts = doubleHistogramPointData.getCounts();
+    for (int i = 0; i < counts.size(); i++) {
+      List<String> labelValuesWithLe = new ArrayList<>(labelValues.size() + 1);
+      labelValuesWithLe.addAll(labelValues);
+      labelValuesWithLe.add(
+          doubleToGoString(i < boundaries.size() ? boundaries.get(i) : Double.POSITIVE_INFINITY));
+
+      cumulativeCount += counts.get(i);
+      samples.add(
+          new Sample(
+              name + SAMPLE_SUFFIX_BUCKET, labelNamesWithLe, labelValuesWithLe, cumulativeCount));
+    }
+  }
+
   private static int estimateNumSamples(int numPoints, MetricDataType type) {
     if (type == MetricDataType.SUMMARY) {
       // count + sum + estimated 2 percentiles (default MinMaxSumCount aggregator).

exporters/prometheus/src/test/java/io/opentelemetry/exporter/prometheus/MetricAdapterTest.java

@@ -14,6 +14,8 @@
 import io.opentelemetry.sdk.common.InstrumentationLibraryInfo;
 import io.opentelemetry.sdk.metrics.data.AggregationTemporality;
 import io.opentelemetry.sdk.metrics.data.DoubleGaugeData;
+import io.opentelemetry.sdk.metrics.data.DoubleHistogramData;
+import io.opentelemetry.sdk.metrics.data.DoubleHistogramPointData;
 import io.opentelemetry.sdk.metrics.data.DoublePointData;
 import io.opentelemetry.sdk.metrics.data.DoubleSumData;
 import io.opentelemetry.sdk.metrics.data.DoubleSummaryData;
@@ -157,6 +159,23 @@ class MetricAdapterTest {
               Collections.singletonList(
                   DoubleSummaryPointData.create(
                       123, 456, Labels.of("kp", "vp"), 5, 7, Collections.emptyList()))));
+  private static final MetricData HISTOGRAM =
+      MetricData.createDoubleHistogram(
+          Resource.create(Attributes.of(stringKey("kr"), "vr")),
+          InstrumentationLibraryInfo.create("full", "version"),
+          "instrument.name",
+          "description",
+          "1",
+          DoubleHistogramData.create(
+              AggregationTemporality.DELTA,
+              Collections.singletonList(
+                  DoubleHistogramPointData.create(
+                      123,
+                      456,
+                      Labels.of("kp", "vp"),
+                      1.0,
+                      Collections.emptyList(),
+                      Collections.singletonList(2L)))));
 
   @Test
   void toProtoMetricDescriptorType() {
@@ -204,6 +223,10 @@ void toProtoMetricDescriptorType() {
     metricFamilySamples = MetricAdapter.toMetricFamilySamples(LONG_GAUGE);
     assertThat(metricFamilySamples.type).isEqualTo(Collector.Type.GAUGE);
     assertThat(metricFamilySamples.samples).hasSize(1);
+
+    metricFamilySamples = MetricAdapter.toMetricFamilySamples(HISTOGRAM);
+    assertThat(metricFamilySamples.type).isEqualTo(Collector.Type.HISTOGRAM);
+    assertThat(metricFamilySamples.samples).hasSize(3);
   }
 
   @Test
@@ -323,6 +346,36 @@ void toSamples_SummaryPoints() {
                 12.3));
   }
 
+  @Test
+  void toSamples_HistogramPoints() {
+    assertThat(
+            MetricAdapter.toSamples("full_name", MetricDataType.HISTOGRAM, Collections.emptyList()))
+        .isEmpty();
+
+    assertThat(
+            MetricAdapter.toSamples(
+                "full_name",
+                MetricDataType.HISTOGRAM,
+                ImmutableList.of(
+                    DoubleHistogramPointData.create(
+                        321,
+                        654,
+                        Labels.of("kp", "vp"),
+                        18.3,
+                        ImmutableList.of(1.0),
+                        ImmutableList.of(4L, 9L)))))
+        .containsExactly(
+            new Sample("full_name_count", ImmutableList.of("kp"), ImmutableList.of("vp"), 13),
+            new Sample("full_name_sum", ImmutableList.of("kp"), ImmutableList.of("vp"), 18.3),
+            new Sample(
+                "full_name_bucket", ImmutableList.of("kp", "le"), ImmutableList.of("vp", "1.0"), 4),
+            new Sample(
+                "full_name_bucket",
+                ImmutableList.of("kp", "le"),
+                ImmutableList.of("vp", "+Inf"),
+                13));
+  }
+
   @Test
   void toMetricFamilySamples() {
     MetricData metricData = MONOTONIC_CUMULATIVE_DOUBLE_SUM;