refactor: delegate non-composite histogram/summary to OM1 writer

When compositeValues=false, OM2 histogram and summary output is
identical to OM1 format. Delegate to om1Writer instead of duplicating
writeClassicHistogramBuckets, writeNonCompositeSummaryDataPoint, and
writeCountAndSum.

Author: zeitlinger

prometheus-metrics-exposition-textformats/src/main/java/io/prometheus/metrics/expositionformats/OpenMetrics2TextFormatWriter.java

@@ -14,9 +14,7 @@
 import io.prometheus.metrics.model.snapshots.ClassicHistogramBuckets;
 import io.prometheus.metrics.model.snapshots.CounterSnapshot;
 import io.prometheus.metrics.model.snapshots.DataPointSnapshot;
-import io.prometheus.metrics.model.snapshots.DistributionDataPointSnapshot;
 import io.prometheus.metrics.model.snapshots.Exemplar;
-import io.prometheus.metrics.model.snapshots.Exemplars;
 import io.prometheus.metrics.model.snapshots.GaugeSnapshot;
 import io.prometheus.metrics.model.snapshots.HistogramSnapshot;
 import io.prometheus.metrics.model.snapshots.InfoSnapshot;
@@ -36,7 +34,6 @@
 import java.io.OutputStreamWriter;
 import java.io.Writer;
 import java.nio.charset.StandardCharsets;
-import java.util.List;
 import javax.annotation.Nullable;
 
 /**
@@ -92,6 +89,7 @@ public OpenMetrics2TextFormatWriter build() {
   private final OpenMetrics2Properties openMetrics2Properties;
   private final boolean createdTimestampsEnabled;
   private final boolean exemplarsOnAllMetricTypesEnabled;
+  private final OpenMetricsTextFormatWriter om1Writer;
 
   /**
    * @param openMetrics2Properties OpenMetrics 2.0 feature flags
@@ -106,6 +104,8 @@ public OpenMetrics2TextFormatWriter(
     this.openMetrics2Properties = openMetrics2Properties;
     this.createdTimestampsEnabled = createdTimestampsEnabled;
     this.exemplarsOnAllMetricTypesEnabled = exemplarsOnAllMetricTypesEnabled;
+    this.om1Writer =
+        new OpenMetricsTextFormatWriter(createdTimestampsEnabled, exemplarsOnAllMetricTypesEnabled);
   }
 
   public static Builder builder() {
@@ -200,27 +200,21 @@ private void writeGauge(Writer writer, GaugeSnapshot snapshot, EscapingScheme sc
 
   private void writeHistogram(Writer writer, HistogramSnapshot snapshot, EscapingScheme scheme)
       throws IOException {
+    if (!openMetrics2Properties.getCompositeValues()) {
+      om1Writer.writeHistogram(writer, snapshot, scheme);
+      return;
+    }
     MetricMetadata metadata = snapshot.getMetadata();
     String name = getExpositionBaseMetadataName(metadata, scheme);
     if (snapshot.isGaugeHistogram()) {
       writeMetadataWithName(writer, name, "gaugehistogram", metadata);
-      if (openMetrics2Properties.getCompositeValues()) {
-        for (HistogramSnapshot.HistogramDataPointSnapshot data : snapshot.getDataPoints()) {
-          writeCompositeHistogramDataPoint(writer, name, "gcount", "gsum", data, scheme);
-        }
-      } else {
-        writeClassicHistogramBuckets(
-            writer, name, "_gcount", "_gsum", snapshot.getDataPoints(), scheme);
+      for (HistogramSnapshot.HistogramDataPointSnapshot data : snapshot.getDataPoints()) {
+        writeCompositeHistogramDataPoint(writer, name, "gcount", "gsum", data, scheme);
       }
     } else {
       writeMetadataWithName(writer, name, "histogram", metadata);
-      if (openMetrics2Properties.getCompositeValues()) {
-        for (HistogramSnapshot.HistogramDataPointSnapshot data : snapshot.getDataPoints()) {
-          writeCompositeHistogramDataPoint(writer, name, "count", "sum", data, scheme);
-        }
-      } else {
-        writeClassicHistogramBuckets(
-            writer, name, "_count", "_sum", snapshot.getDataPoints(), scheme);
+      for (HistogramSnapshot.HistogramDataPointSnapshot data : snapshot.getDataPoints()) {
+        writeCompositeHistogramDataPoint(writer, name, "count", "sum", data, scheme);
       }
     }
   }
@@ -267,39 +261,6 @@ private void writeCompositeHistogramDataPoint(
     writer.write('\n');
   }
 
-  private void writeClassicHistogramBuckets(
-      Writer writer,
-      String name,
-      String countSuffix,
-      String sumSuffix,
-      List<HistogramSnapshot.HistogramDataPointSnapshot> dataList,
-      EscapingScheme scheme)
-      throws IOException {
-    for (HistogramSnapshot.HistogramDataPointSnapshot data : dataList) {
-      ClassicHistogramBuckets buckets = getClassicBuckets(data);
-      Exemplars exemplars = data.getExemplars();
-      long cumulativeCount = 0;
-      for (int i = 0; i < buckets.size(); i++) {
-        cumulativeCount += buckets.getCount(i);
-        writeNameAndLabels(
-            writer, name, "_bucket", data.getLabels(), scheme, "le", buckets.getUpperBound(i));
-        writeLong(writer, cumulativeCount);
-        Exemplar exemplar;
-        if (i == 0) {
-          exemplar = exemplars.get(Double.NEGATIVE_INFINITY, buckets.getUpperBound(i));
-        } else {
-          exemplar = exemplars.get(buckets.getUpperBound(i - 1), buckets.getUpperBound(i));
-        }
-        writeScrapeTimestampAndExemplar(writer, data, exemplar, scheme);
-      }
-      // In OpenMetrics format, histogram _count and _sum are either both present or both absent.
-      if (data.hasCount() && data.hasSum()) {
-        writeCountAndSum(writer, name, data, countSuffix, sumSuffix, exemplars, scheme);
-      }
-      writeCreated(writer, name, data, scheme);
-    }
-  }
-
   private ClassicHistogramBuckets getClassicBuckets(
       HistogramSnapshot.HistogramDataPointSnapshot data) {
     if (data.getClassicBuckets().isEmpty()) {
@@ -312,6 +273,10 @@ private ClassicHistogramBuckets getClassicBuckets(
 
   private void writeSummary(Writer writer, SummarySnapshot snapshot, EscapingScheme scheme)
       throws IOException {
+    if (!openMetrics2Properties.getCompositeValues()) {
+      om1Writer.writeSummary(writer, snapshot, scheme);
+      return;
+    }
     boolean metadataWritten = false;
     MetricMetadata metadata = snapshot.getMetadata();
     String name = getExpositionBaseMetadataName(metadata, scheme);
@@ -323,11 +288,7 @@ private void writeSummary(Writer writer, SummarySnapshot snapshot, EscapingSchem
         writeMetadataWithName(writer, name, "summary", metadata);
         metadataWritten = true;
       }
-      if (openMetrics2Properties.getCompositeValues()) {
-        writeCompositeSummaryDataPoint(writer, name, data, scheme);
-      } else {
-        writeNonCompositeSummaryDataPoint(writer, name, data, scheme);
-      }
+      writeCompositeSummaryDataPoint(writer, name, data, scheme);
     }
   }
 
@@ -382,33 +343,6 @@ private void writeCompositeSummaryDataPoint(
     writer.write('\n');
   }
 
-  private void writeNonCompositeSummaryDataPoint(
-      Writer writer,
-      String name,
-      SummarySnapshot.SummaryDataPointSnapshot data,
-      EscapingScheme scheme)
-      throws IOException {
-    Exemplars exemplars = data.getExemplars();
-    // Exemplars for summaries are new, and there's no best practice yet which Exemplars to choose
-    // for which time series. We select exemplars[0] for _count, exemplars[1] for _sum, and
-    // exemplars[2...] for the quantiles, all indexes modulo exemplars.length.
-    int exemplarIndex = 1;
-    for (Quantile quantile : data.getQuantiles()) {
-      writeNameAndLabels(
-          writer, name, null, data.getLabels(), scheme, "quantile", quantile.getQuantile());
-      writeDouble(writer, quantile.getValue());
-      if (exemplars.size() > 0 && exemplarsOnAllMetricTypesEnabled) {
-        exemplarIndex = (exemplarIndex + 1) % exemplars.size();
-        writeScrapeTimestampAndExemplar(writer, data, exemplars.get(exemplarIndex), scheme);
-      } else {
-        writeScrapeTimestampAndExemplar(writer, data, null, scheme);
-      }
-    }
-    // Unlike histograms, summaries can have only a count or only a sum according to OpenMetrics.
-    writeCountAndSum(writer, name, data, "_count", "_sum", exemplars, scheme);
-    writeCreated(writer, name, data, scheme);
-  }
-
   private void writeInfo(Writer writer, InfoSnapshot snapshot, EscapingScheme scheme)
       throws IOException {
     MetricMetadata metadata = snapshot.getMetadata();
@@ -475,31 +409,6 @@ private void writeUnknown(Writer writer, UnknownSnapshot snapshot, EscapingSchem
     }
   }
 
-  private void writeCountAndSum(
-      Writer writer,
-      String name,
-      DistributionDataPointSnapshot data,
-      String countSuffix,
-      String sumSuffix,
-      Exemplars exemplars,
-      EscapingScheme scheme)
-      throws IOException {
-    if (data.hasCount()) {
-      writeNameAndLabels(writer, name, countSuffix, data.getLabels(), scheme);
-      writeLong(writer, data.getCount());
-      if (exemplarsOnAllMetricTypesEnabled) {
-        writeScrapeTimestampAndExemplar(writer, data, exemplars.getLatest(), scheme);
-      } else {
-        writeScrapeTimestampAndExemplar(writer, data, null, scheme);
-      }
-    }
-    if (data.hasSum()) {
-      writeNameAndLabels(writer, name, sumSuffix, data.getLabels(), scheme);
-      writeDouble(writer, data.getSum());
-      writeScrapeTimestampAndExemplar(writer, data, null, scheme);
-    }
-  }
-
   private void writeCreated(
       Writer writer, String name, DataPointSnapshot data, EscapingScheme scheme)
       throws IOException {

prometheus-metrics-exposition-textformats/src/main/java/io/prometheus/metrics/expositionformats/OpenMetricsTextFormatWriter.java

@@ -168,7 +168,7 @@ private void writeGauge(Writer writer, GaugeSnapshot snapshot, EscapingScheme sc
     }
   }
 
-  private void writeHistogram(Writer writer, HistogramSnapshot snapshot, EscapingScheme scheme)
+  void writeHistogram(Writer writer, HistogramSnapshot snapshot, EscapingScheme scheme)
       throws IOException {
     MetricMetadata metadata = snapshot.getMetadata();
     if (snapshot.isGaugeHistogram()) {
@@ -231,7 +231,7 @@ private ClassicHistogramBuckets getClassicBuckets(
     }
   }
 
-  private void writeSummary(Writer writer, SummarySnapshot snapshot, EscapingScheme scheme)
+  void writeSummary(Writer writer, SummarySnapshot snapshot, EscapingScheme scheme)
       throws IOException {
     boolean metadataWritten = false;
     MetricMetadata metadata = snapshot.getMetadata();