Fix OM2 classic histogram names

Signed-off-by: Gregor Zeitlinger <gregor.zeitlinger@grafana.com>

Author: zeitlinger

prometheus-metrics-core/src/test/java/io/prometheus/metrics/core/metrics/OpenMetrics2TextFormatWriterTest.java

@@ -40,6 +40,35 @@ void counterPreservesOriginalNameWhenUnitIsConfigured() throws IOException {
         .doesNotContain("my_counter_seconds");
   }
 
+  @Test
+  void classicHistogramPreservesOriginalNameWhenUnitIsConfigured() throws IOException {
+    Histogram histogram =
+        Histogram.builder()
+            .name("request_duration")
+            .unit(Unit.SECONDS)
+            .help("Request duration in seconds")
+            .labelNames("path")
+            .classicOnly()
+            .classicUpperBounds(10.0)
+            .build();
+    histogram.labelValues("/hello").observe(3.2);
+    MetricSnapshots snapshots = MetricSnapshots.of(histogram.collect());
+
+    String om1Output = writeWithOM1(snapshots);
+    String om2Output = writeWithOM2(snapshots);
+
+    assertThat(om1Output).contains("request_duration_seconds_bucket");
+    assertThat(om2Output)
+        .contains("# TYPE request_duration histogram\n")
+        .contains("# UNIT request_duration seconds\n")
+        .contains("# HELP request_duration Request duration in seconds\n")
+        .contains("request_duration_bucket{path=\"/hello\",le=\"10.0\"} 1\n")
+        .contains("request_duration_bucket{path=\"/hello\",le=\"+Inf\"} 1\n")
+        .contains("request_duration_count{path=\"/hello\"} 1\n")
+        .contains("request_duration_sum{path=\"/hello\"} 3.2\n")
+        .doesNotContain("request_duration_seconds");
+  }
+
   @Test
   void nativeHistogramPreservesOriginalNameWhenUnitIsConfigured() throws IOException {
     Histogram histogram =

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

@@ -89,6 +89,7 @@ public OpenMetrics2TextFormatWriter build() {
   public static final String CONTENT_TYPE =
       "application/openmetrics-text; version=2.0.0; charset=utf-8";
   private final OpenMetrics2Properties openMetrics2Properties;
+  private final boolean createdTimestampsEnabled;
   private final boolean exemplarsOnAllMetricTypesEnabled;
   private final OpenMetricsTextFormatWriter om1Writer;
 
@@ -102,6 +103,7 @@ public OpenMetrics2TextFormatWriter(
       boolean createdTimestampsEnabled,
       boolean exemplarsOnAllMetricTypesEnabled) {
     this.openMetrics2Properties = openMetrics2Properties;
+    this.createdTimestampsEnabled = createdTimestampsEnabled;
     this.exemplarsOnAllMetricTypesEnabled = exemplarsOnAllMetricTypesEnabled;
     this.om1Writer =
         new OpenMetricsTextFormatWriter(createdTimestampsEnabled, exemplarsOnAllMetricTypesEnabled);
@@ -209,12 +211,12 @@ private void writeHistogram(Writer writer, HistogramSnapshot snapshot, EscapingS
       throws IOException {
     boolean compositeHistogram =
         openMetrics2Properties.getCompositeValues() || openMetrics2Properties.getNativeHistograms();
+    MetricMetadata metadata = snapshot.getMetadata();
+    String name = getOriginalMetadataName(metadata, scheme);
     if (!compositeHistogram && !openMetrics2Properties.getExemplarCompliance()) {
-      om1Writer.writeHistogram(writer, snapshot, scheme);
+      writeClassicHistogram(writer, name, snapshot, scheme);
       return;
     }
-    MetricMetadata metadata = snapshot.getMetadata();
-    String name = getOriginalMetadataName(metadata, scheme);
     if (snapshot.isGaugeHistogram()) {
       writeMetadataWithName(writer, name, "gaugehistogram", metadata);
       for (HistogramSnapshot.HistogramDataPointSnapshot data : snapshot.getDataPoints()) {
@@ -236,6 +238,88 @@ private void writeHistogram(Writer writer, HistogramSnapshot snapshot, EscapingS
     }
   }
 
+  private void writeClassicHistogram(
+      Writer writer, String name, HistogramSnapshot snapshot, EscapingScheme scheme)
+      throws IOException {
+    if (snapshot.isGaugeHistogram()) {
+      writeMetadataWithName(writer, name, "gaugehistogram", snapshot.getMetadata());
+      writeClassicHistogramDataPoints(writer, name, "_gcount", "_gsum", snapshot, scheme);
+    } else {
+      writeMetadataWithName(writer, name, "histogram", snapshot.getMetadata());
+      writeClassicHistogramDataPoints(writer, name, "_count", "_sum", snapshot, scheme);
+    }
+  }
+
+  private void writeClassicHistogramDataPoints(
+      Writer writer,
+      String name,
+      String countSuffix,
+      String sumSuffix,
+      HistogramSnapshot snapshot,
+      EscapingScheme scheme)
+      throws IOException {
+    for (HistogramSnapshot.HistogramDataPointSnapshot data : snapshot.getDataPoints()) {
+      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);
+      }
+      if (data.hasCount() && data.hasSum()) {
+        writeClassicCountAndSum(writer, name, data, countSuffix, sumSuffix, exemplars, scheme);
+      }
+      writeClassicCreated(writer, name, data, scheme);
+    }
+  }
+
+  private void writeClassicCountAndSum(
+      Writer writer,
+      String name,
+      HistogramSnapshot.HistogramDataPointSnapshot data,
+      String countSuffix,
+      String sumSuffix,
+      Exemplars exemplars,
+      EscapingScheme scheme)
+      throws IOException {
+    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);
+    }
+    writeNameAndLabels(writer, name, sumSuffix, data.getLabels(), scheme);
+    writeDouble(writer, data.getSum());
+    writeScrapeTimestampAndExemplar(writer, data, null, scheme);
+  }
+
+  private void writeClassicCreated(
+      Writer writer,
+      String name,
+      HistogramSnapshot.HistogramDataPointSnapshot data,
+      EscapingScheme scheme)
+      throws IOException {
+    if (createdTimestampsEnabled && data.hasCreatedTimestamp()) {
+      writeNameAndLabels(writer, name, "_created", data.getLabels(), scheme);
+      writeOpenMetricsTimestamp(writer, data.getCreatedTimestampMillis());
+      if (data.hasScrapeTimestamp()) {
+        writer.write(' ');
+        writeOpenMetricsTimestamp(writer, data.getScrapeTimestampMillis());
+      }
+      writer.write('\n');
+    }
+  }
+
   private void writeCompositeHistogramDataPoint(
       Writer writer,
       String name,