fix: Preserve original metric names in OM2 output

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

@@ -0,0 +1,118 @@
+package io.prometheus.metrics.core.metrics;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import io.prometheus.metrics.config.EscapingScheme;
+import io.prometheus.metrics.config.OpenMetrics2Properties;
+import io.prometheus.metrics.expositionformats.ExpositionFormatWriter;
+import io.prometheus.metrics.expositionformats.OpenMetrics2TextFormatWriter;
+import io.prometheus.metrics.expositionformats.OpenMetricsTextFormatWriter;
+import io.prometheus.metrics.model.snapshots.MetricSnapshots;
+import io.prometheus.metrics.model.snapshots.Unit;
+import java.io.ByteArrayOutputStream;
+import java.io.IOException;
+import java.nio.charset.StandardCharsets;
+import org.junit.jupiter.api.Test;
+
+class OpenMetrics2TextFormatWriterTest {
+
+  @Test
+  void counterPreservesOriginalNameWhenUnitIsConfigured() throws IOException {
+    Counter counter =
+        Counter.builder()
+            .name("my_counter")
+            .unit(Unit.SECONDS)
+            .help("Test counter")
+            .labelNames("method")
+            .build();
+    counter.labelValues("GET").inc(42.0);
+    MetricSnapshots snapshots = MetricSnapshots.of(counter.collect());
+
+    String om1Output = writeWithOM1(snapshots);
+    String om2Output = writeWithOM2(snapshots);
+
+    assertThat(om1Output).contains("my_counter_seconds_total{method=\"GET\"} 42.0");
+    assertThat(om2Output)
+        .contains("# TYPE my_counter counter\n")
+        .contains("# UNIT my_counter seconds\n")
+        .contains("# HELP my_counter Test counter\n")
+        .containsPattern("(?m)^my_counter\\{method=\"GET\"} 42\\.0 st@\\d+\\.\\d{3}$")
+        .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 =
+        Histogram.builder()
+            .name("my.request.duration")
+            .unit(Unit.SECONDS)
+            .help("Request duration in seconds")
+            .labelNames("http.path")
+            .nativeOnly()
+            .build();
+    histogram.labelValues("/hello").observe(3.2);
+    MetricSnapshots snapshots = MetricSnapshots.of(histogram.collect());
+
+    String om2Output = writeWithNativeHistograms(snapshots);
+
+    assertThat(om2Output)
+        .contains("# TYPE \"my.request.duration\" histogram\n")
+        .contains("# UNIT \"my.request.duration\" seconds\n")
+        .contains("# HELP \"my.request.duration\" Request duration in seconds\n")
+        .contains("{\"my.request.duration\",\"http.path\"=\"/hello\"} {count:1,sum:3.2,")
+        .doesNotContain("my.request.duration_seconds");
+  }
+
+  private String writeWithOM1(MetricSnapshots snapshots) throws IOException {
+    return write(snapshots, OpenMetricsTextFormatWriter.create());
+  }
+
+  private String writeWithOM2(MetricSnapshots snapshots) throws IOException {
+    return write(snapshots, OpenMetrics2TextFormatWriter.create());
+  }
+
+  private String writeWithNativeHistograms(MetricSnapshots snapshots) throws IOException {
+    OpenMetrics2TextFormatWriter writer =
+        OpenMetrics2TextFormatWriter.builder()
+            .setOpenMetrics2Properties(
+                OpenMetrics2Properties.builder().nativeHistograms(true).build())
+            .build();
+    return write(snapshots, writer);
+  }
+
+  private String write(MetricSnapshots snapshots, ExpositionFormatWriter writer)
+      throws IOException {
+    ByteArrayOutputStream out = new ByteArrayOutputStream();
+    writer.write(out, snapshots, EscapingScheme.ALLOW_UTF8);
+    return out.toString(StandardCharsets.UTF_8.name());
+  }
+}

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

@@ -6,7 +6,7 @@
 import static io.prometheus.metrics.expositionformats.TextFormatUtil.writeLong;
 import static io.prometheus.metrics.expositionformats.TextFormatUtil.writeName;
 import static io.prometheus.metrics.expositionformats.TextFormatUtil.writeOpenMetricsTimestamp;
-import static io.prometheus.metrics.model.snapshots.SnapshotEscaper.getExpositionBaseMetadataName;
+import static io.prometheus.metrics.model.snapshots.SnapshotEscaper.getOriginalMetadataName;
 import static io.prometheus.metrics.model.snapshots.SnapshotEscaper.getSnapshotLabelName;
 
 import io.prometheus.metrics.config.EscapingScheme;
@@ -40,8 +40,8 @@
 
 /**
  * Write the OpenMetrics 2.0 text format. Unlike the OM1 writer, this writer outputs metric names as
- * provided by the user — no {@code _total} or unit suffix appending. The {@code _info} suffix is
- * enforced per the OM2 spec (MUST). This is experimental and subject to change as the <a
+ * provided by the user, without appending {@code _total} or unit suffixes. The {@code _info} suffix
+ * is enforced per the OM2 spec (MUST). This is experimental and subject to change as the <a
  * href="https://github.com/prometheus/docs/blob/main/docs/specs/om/open_metrics_spec_2_0.md">OpenMetrics
  * 2.0 specification</a> evolves.
  */
@@ -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);
@@ -170,8 +172,8 @@ public void write(OutputStream out, MetricSnapshots metricSnapshots, EscapingSch
   private void writeCounter(Writer writer, CounterSnapshot snapshot, EscapingScheme scheme)
       throws IOException {
     MetricMetadata metadata = snapshot.getMetadata();
-    // OM2: use the name as provided by the user, no _total appending
-    String counterName = getExpositionBaseMetadataName(metadata, scheme);
+    // OM2: use the original name, no _total or unit suffix appending.
+    String counterName = getOriginalMetadataName(metadata, scheme);
     writeMetadataWithName(writer, counterName, "counter", metadata);
     for (CounterSnapshot.CounterDataPointSnapshot data : snapshot.getDataPoints()) {
       writeNameAndLabels(writer, counterName, null, data.getLabels(), scheme);
@@ -192,7 +194,7 @@ private void writeCounter(Writer writer, CounterSnapshot snapshot, EscapingSchem
   private void writeGauge(Writer writer, GaugeSnapshot snapshot, EscapingScheme scheme)
       throws IOException {
     MetricMetadata metadata = snapshot.getMetadata();
-    String name = getExpositionBaseMetadataName(metadata, scheme);
+    String name = getOriginalMetadataName(metadata, scheme);
     writeMetadataWithName(writer, name, "gauge", metadata);
     for (GaugeSnapshot.GaugeDataPointSnapshot data : snapshot.getDataPoints()) {
       writeNameAndLabels(writer, name, null, data.getLabels(), scheme);
@@ -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 = getExpositionBaseMetadataName(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,
@@ -398,7 +482,7 @@ private void writeSummary(Writer writer, SummarySnapshot snapshot, EscapingSchem
     }
     boolean metadataWritten = false;
     MetricMetadata metadata = snapshot.getMetadata();
-    String name = getExpositionBaseMetadataName(metadata, scheme);
+    String name = getOriginalMetadataName(metadata, scheme);
     for (SummarySnapshot.SummaryDataPointSnapshot data : snapshot.getDataPoints()) {
       if (data.getQuantiles().size() == 0 && !data.hasCount() && !data.hasSum()) {
         continue;
@@ -465,7 +549,7 @@ private void writeInfo(Writer writer, InfoSnapshot snapshot, EscapingScheme sche
     MetricMetadata metadata = snapshot.getMetadata();
     // OM2 spec: Info MetricFamily name MUST end in _info.
     // In OM2, TYPE/HELP use the same name as the data lines.
-    String infoName = ensureSuffix(getExpositionBaseMetadataName(metadata, scheme), "_info");
+    String infoName = ensureSuffix(getOriginalMetadataName(metadata, scheme), "_info");
     writeMetadataWithName(writer, infoName, "info", metadata);
     for (InfoSnapshot.InfoDataPointSnapshot data : snapshot.getDataPoints()) {
       writeNameAndLabels(writer, infoName, null, data.getLabels(), scheme);
@@ -477,7 +561,7 @@ private void writeInfo(Writer writer, InfoSnapshot snapshot, EscapingScheme sche
   private void writeStateSet(Writer writer, StateSetSnapshot snapshot, EscapingScheme scheme)
       throws IOException {
     MetricMetadata metadata = snapshot.getMetadata();
-    String name = getExpositionBaseMetadataName(metadata, scheme);
+    String name = getOriginalMetadataName(metadata, scheme);
     writeMetadataWithName(writer, name, "stateset", metadata);
     for (StateSetSnapshot.StateSetDataPointSnapshot data : snapshot.getDataPoints()) {
       for (int i = 0; i < data.size(); i++) {
@@ -513,7 +597,7 @@ private void writeStateSet(Writer writer, StateSetSnapshot snapshot, EscapingSch
   private void writeUnknown(Writer writer, UnknownSnapshot snapshot, EscapingScheme scheme)
       throws IOException {
     MetricMetadata metadata = snapshot.getMetadata();
-    String name = getExpositionBaseMetadataName(metadata, scheme);
+    String name = getOriginalMetadataName(metadata, scheme);
     writeMetadataWithName(writer, name, "unknown", metadata);
     for (UnknownSnapshot.UnknownDataPointSnapshot data : snapshot.getDataPoints()) {
       writeNameAndLabels(writer, name, null, data.getLabels(), scheme);