feat: add OTel preserve_names for scrape-time suffix handling

prometheus-metrics-config/src/main/java/io/prometheus/metrics/config/ExporterOpenTelemetryProperties.java

@@ -46,6 +46,7 @@ public class ExporterOpenTelemetryProperties {
   private static final String SERVICE_VERSION = "service_version";
   private static final String RESOURCE_ATTRIBUTES =
       "resource_attributes"; // otel.resource.attributes
+  private static final String PRESERVE_NAMES = "preserve_names";
   private static final String PREFIX = "io.prometheus.exporter.opentelemetry";
 
   @Nullable private final String endpoint;
@@ -58,6 +59,7 @@ public class ExporterOpenTelemetryProperties {
   @Nullable private final String serviceInstanceId;
   @Nullable private final String serviceVersion;
   private final Map<String, String> resourceAttributes;
+  @Nullable private final Boolean preserveNames;
 
   private ExporterOpenTelemetryProperties(
       @Nullable String protocol,
@@ -69,7 +71,8 @@ private ExporterOpenTelemetryProperties(
       @Nullable String serviceNamespace,
       @Nullable String serviceInstanceId,
       @Nullable String serviceVersion,
-      Map<String, String> resourceAttributes) {
+      Map<String, String> resourceAttributes,
+      @Nullable Boolean preserveNames) {
     this.protocol = protocol;
     this.endpoint = endpoint;
     this.headers = headers;
@@ -80,6 +83,7 @@ private ExporterOpenTelemetryProperties(
     this.serviceInstanceId = serviceInstanceId;
     this.serviceVersion = serviceVersion;
     this.resourceAttributes = resourceAttributes;
+    this.preserveNames = preserveNames;
   }
 
   @Nullable
@@ -130,6 +134,16 @@ public Map<String, String> getResourceAttributes() {
     return resourceAttributes;
   }
 
+  /**
+   * When {@code true}, metric names are preserved as-is (including suffixes like {@code _total}).
+   * When {@code false} (default), standard OTel name normalization is applied (stripping unit
+   * suffix).
+   */
+  @Nullable
+  public Boolean getPreserveNames() {
+    return preserveNames;
+  }
+
   /**
    * Note that this will remove entries from {@code propertySource}. This is because we want to know
    * if there are unused properties remaining after all properties have been loaded.
@@ -147,6 +161,7 @@ static ExporterOpenTelemetryProperties load(PropertySource propertySource)
     String serviceVersion = Util.loadString(PREFIX, SERVICE_VERSION, propertySource);
     Map<String, String> resourceAttributes =
         Util.loadMap(PREFIX, RESOURCE_ATTRIBUTES, propertySource);
+    Boolean preserveNames = Util.loadBoolean(PREFIX, PRESERVE_NAMES, propertySource);
     return new ExporterOpenTelemetryProperties(
         protocol,
         endpoint,
@@ -157,7 +172,8 @@ static ExporterOpenTelemetryProperties load(PropertySource propertySource)
         serviceNamespace,
         serviceInstanceId,
         serviceVersion,
-        resourceAttributes);
+        resourceAttributes,
+        preserveNames);
   }
 
   public static Builder builder() {
@@ -176,6 +192,7 @@ public static class Builder {
     @Nullable private String serviceInstanceId;
     @Nullable private String serviceVersion;
     private final Map<String, String> resourceAttributes = new HashMap<>();
+    @Nullable private Boolean preserveNames;
 
     private Builder() {}
 
@@ -318,6 +335,15 @@ public Builder resourceAttribute(String name, String value) {
       return this;
     }
 
+    /**
+     * When {@code true}, metric names are preserved as-is (including suffixes like {@code _total}).
+     * When {@code false} (default), standard OTel name normalization is applied.
+     */
+    public Builder preserveNames(boolean preserveNames) {
+      this.preserveNames = preserveNames;
+      return this;
+    }
+
     public ExporterOpenTelemetryProperties build() {
       return new ExporterOpenTelemetryProperties(
           protocol,
@@ -329,7 +355,8 @@ public ExporterOpenTelemetryProperties build() {
           serviceNamespace,
           serviceInstanceId,
           serviceVersion,
-          resourceAttributes);
+          resourceAttributes,
+          preserveNames);
     }
   }
 }

prometheus-metrics-exporter-opentelemetry/src/main/java/io/prometheus/metrics/exporter/opentelemetry/OpenTelemetryExporter.java

@@ -41,6 +41,7 @@ public static class Builder {
     @Nullable String serviceInstanceId;
     @Nullable String serviceVersion;
     final Map<String, String> resourceAttributes = new HashMap<>();
+    @Nullable Boolean preserveNames;
 
     private Builder(PrometheusProperties config) {
       this.config = config;
@@ -194,6 +195,15 @@ public Builder resourceAttribute(String name, String value) {
       return this;
     }
 
+    /**
+     * When {@code true}, metric names are preserved as-is (including suffixes like {@code _total}).
+     * When {@code false} (default), standard OTel name normalization is applied.
+     */
+    public Builder preserveNames(boolean preserveNames) {
+      this.preserveNames = preserveNames;
+      return this;
+    }
+
     public OpenTelemetryExporter buildAndStart() {
       if (registry == null) {
         registry = PrometheusRegistry.defaultRegistry;

prometheus-metrics-exporter-opentelemetry/src/main/java/io/prometheus/metrics/exporter/opentelemetry/OtelAutoConfig.java

@@ -38,8 +38,10 @@ static MetricReader createReader(
             instrumentationScopeInfo);
 
     MetricReader reader = requireNonNull(readerRef.get());
+    boolean preserveNames = resolvePreserveNames(builder, config);
     reader.register(
-        new PrometheusMetricProducer(registry, instrumentationScopeInfo, getResourceField(sdk)));
+        new PrometheusMetricProducer(
+            registry, instrumentationScopeInfo, getResourceField(sdk), preserveNames));
     return reader;
   }
 
@@ -107,6 +109,15 @@ private static Attributes otelResourceAttributes(
     return builder.build();
   }
 
+  static boolean resolvePreserveNames(
+      OpenTelemetryExporter.Builder builder, PrometheusProperties config) {
+    if (builder.preserveNames != null) {
+      return builder.preserveNames;
+    }
+    Boolean fromConfig = config.getExporterOpenTelemetryProperties().getPreserveNames();
+    return fromConfig != null && fromConfig;
+  }
+
   static Resource getResourceField(AutoConfiguredOpenTelemetrySdk sdk) {
     try {
       Method method = AutoConfiguredOpenTelemetrySdk.class.getDeclaredMethod("getResource");

prometheus-metrics-exporter-opentelemetry/src/main/java/io/prometheus/metrics/exporter/opentelemetry/PrometheusMetricProducer.java

@@ -29,14 +29,17 @@ class PrometheusMetricProducer implements CollectionRegistration {
   private final PrometheusRegistry registry;
   private final Resource resource;
   private final InstrumentationScopeInfo instrumentationScopeInfo;
+  private final boolean preserveNames;
 
   public PrometheusMetricProducer(
       PrometheusRegistry registry,
       InstrumentationScopeInfo instrumentationScopeInfo,
-      Resource resource) {
+      Resource resource,
+      boolean preserveNames) {
     this.registry = registry;
     this.instrumentationScopeInfo = instrumentationScopeInfo;
     this.resource = resource;
+    this.preserveNames = preserveNames;
   }
 
   @Override
@@ -57,7 +60,8 @@ public Collection<MetricData> collectAllMetrics() {
         new MetricDataFactory(
             resourceWithTargetInfo,
             scopeFromInfo != null ? scopeFromInfo : instrumentationScopeInfo,
-            System.currentTimeMillis());
+            System.currentTimeMillis(),
+            preserveNames);
     for (MetricSnapshot snapshot : snapshots) {
       if (snapshot instanceof CounterSnapshot) {
         addUnlessNull(result, factory.create((CounterSnapshot) snapshot));

prometheus-metrics-exporter-opentelemetry/src/main/java/io/prometheus/metrics/exporter/opentelemetry/otelmodel/MetricDataFactory.java

@@ -17,14 +17,17 @@ public class MetricDataFactory {
   private final Resource resource;
   private final InstrumentationScopeInfo instrumentationScopeInfo;
   private final long currentTimeMillis;
+  private final boolean preserveNames;
 
   public MetricDataFactory(
       Resource resource,
       InstrumentationScopeInfo instrumentationScopeInfo,
-      long currentTimeMillis) {
+      long currentTimeMillis,
+      boolean preserveNames) {
     this.resource = resource;
     this.instrumentationScopeInfo = instrumentationScopeInfo;
     this.currentTimeMillis = currentTimeMillis;
+    this.preserveNames = preserveNames;
   }
 
   @Nullable
@@ -36,7 +39,8 @@ public MetricData create(CounterSnapshot snapshot) {
         snapshot.getMetadata(),
         new PrometheusCounter(snapshot, currentTimeMillis),
         instrumentationScopeInfo,
-        resource);
+        resource,
+        preserveNames);
   }
 
   @Nullable
@@ -48,7 +52,8 @@ public MetricData create(GaugeSnapshot snapshot) {
         snapshot.getMetadata(),
         new PrometheusGauge(snapshot, currentTimeMillis),
         instrumentationScopeInfo,
-        resource);
+        resource,
+        preserveNames);
   }
 
   @Nullable
@@ -60,13 +65,15 @@ public MetricData create(HistogramSnapshot snapshot) {
             snapshot.getMetadata(),
             new PrometheusNativeHistogram(snapshot, currentTimeMillis),
             instrumentationScopeInfo,
-            resource);
+            resource,
+            preserveNames);
       } else if (firstDataPoint.hasClassicHistogramData()) {
         return new PrometheusMetricData<>(
             snapshot.getMetadata(),
             new PrometheusClassicHistogram(snapshot, currentTimeMillis),
             instrumentationScopeInfo,
-            resource);
+            resource,
+            preserveNames);
       }
     }
     return null;
@@ -81,7 +88,8 @@ public MetricData create(SummarySnapshot snapshot) {
         snapshot.getMetadata(),
         new PrometheusSummary(snapshot, currentTimeMillis),
         instrumentationScopeInfo,
-        resource);
+        resource,
+        preserveNames);
   }
 
   @Nullable
@@ -93,7 +101,8 @@ public MetricData create(InfoSnapshot snapshot) {
         snapshot.getMetadata(),
         new PrometheusInfo(snapshot, currentTimeMillis),
         instrumentationScopeInfo,
-        resource);
+        resource,
+        preserveNames);
   }
 
   @Nullable
@@ -105,7 +114,8 @@ public MetricData create(StateSetSnapshot snapshot) {
         snapshot.getMetadata(),
         new PrometheusStateSet(snapshot, currentTimeMillis),
         instrumentationScopeInfo,
-        resource);
+        resource,
+        preserveNames);
   }
 
   @Nullable
@@ -117,6 +127,7 @@ public MetricData create(UnknownSnapshot snapshot) {
         snapshot.getMetadata(),
         new PrometheusUnknown(snapshot, currentTimeMillis),
         instrumentationScopeInfo,
-        resource);
+        resource,
+        preserveNames);
   }
 }

prometheus-metrics-exporter-opentelemetry/src/main/java/io/prometheus/metrics/exporter/opentelemetry/otelmodel/PrometheusMetricData.java

@@ -23,10 +23,12 @@ class PrometheusMetricData<T extends PrometheusData<?>> implements MetricData {
       MetricMetadata metricMetadata,
       T data,
       InstrumentationScopeInfo instrumentationScopeInfo,
-      Resource resource) {
+      Resource resource,
+      boolean preserveNames) {
     this.instrumentationScopeInfo = instrumentationScopeInfo;
     this.resource = resource;
-    this.name = getNameWithoutUnit(metricMetadata);
+    this.name =
+        preserveNames ? metricMetadata.getOriginalName() : getNameWithoutUnit(metricMetadata);
     this.description = metricMetadata.getHelp();
     this.unit = convertUnit(metricMetadata.getUnit());
     this.data = data;

prometheus-metrics-exporter-opentelemetry/src/test/java/io/prometheus/metrics/exporter/opentelemetry/ExportTest.java

@@ -10,6 +10,7 @@
 import io.opentelemetry.sdk.resources.Resource;
 import io.opentelemetry.sdk.testing.assertj.MetricAssert;
 import io.opentelemetry.sdk.testing.assertj.OpenTelemetryAssertions;
+import io.opentelemetry.sdk.testing.exporter.InMemoryMetricReader;
 import io.opentelemetry.sdk.testing.junit5.OpenTelemetryExtension;
 import io.prometheus.metrics.core.metrics.Counter;
 import io.prometheus.metrics.core.metrics.Gauge;
@@ -23,6 +24,7 @@
 import io.prometheus.metrics.model.snapshots.Unit;
 import io.prometheus.metrics.model.snapshots.UnknownSnapshot;
 import java.lang.reflect.Field;
+import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
 import org.junit.jupiter.api.BeforeEach;
@@ -47,7 +49,8 @@ void setUp() throws IllegalAccessException, NoSuchFieldException {
         new PrometheusMetricProducer(
             registry,
             InstrumentationScopeInfo.create("test"),
-            Resource.create(Attributes.builder().put("staticRes", "value").build()));
+            Resource.create(Attributes.builder().put("staticRes", "value").build()),
+            false);
 
     reader.register(prometheusMetricProducer);
   }
@@ -324,6 +327,60 @@ void metricsWithoutDataPointsAreNotExported() {
     assertThat(metrics).isEmpty();
   }
 
+  @Test
+  void preserveNamesWithUnit() {
+    InMemoryMetricReader reader = InMemoryMetricReader.create();
+    PrometheusRegistry preserveRegistry = new PrometheusRegistry();
+    reader.register(
+        new PrometheusMetricProducer(
+            preserveRegistry,
+            InstrumentationScopeInfo.create("test"),
+            Resource.create(Attributes.builder().put("staticRes", "value").build()),
+            true));
+
+    Counter.builder().name("req").unit(Unit.BYTES).register(preserveRegistry).inc();
+
+    List<MetricData> metrics = new ArrayList<>(reader.collectAllMetrics());
+    assertThat(metrics).hasSize(1);
+    OpenTelemetryAssertions.assertThat(metrics.get(0)).hasName("req").hasUnit("By");
+  }
+
+  @Test
+  void preserveNamesWithUnitAlreadyInName() {
+    InMemoryMetricReader reader = InMemoryMetricReader.create();
+    PrometheusRegistry preserveRegistry = new PrometheusRegistry();
+    reader.register(
+        new PrometheusMetricProducer(
+            preserveRegistry,
+            InstrumentationScopeInfo.create("test"),
+            Resource.create(Attributes.builder().put("staticRes", "value").build()),
+            true));
+
+    Counter.builder().name("req_bytes").unit(Unit.BYTES).register(preserveRegistry).inc();
+
+    List<MetricData> metrics = new ArrayList<>(reader.collectAllMetrics());
+    assertThat(metrics).hasSize(1);
+    OpenTelemetryAssertions.assertThat(metrics.get(0)).hasName("req_bytes").hasUnit("By");
+  }
+
+  @Test
+  void preserveNamesWithoutUnit() {
+    InMemoryMetricReader reader = InMemoryMetricReader.create();
+    PrometheusRegistry preserveRegistry = new PrometheusRegistry();
+    reader.register(
+        new PrometheusMetricProducer(
+            preserveRegistry,
+            InstrumentationScopeInfo.create("test"),
+            Resource.create(Attributes.builder().put("staticRes", "value").build()),
+            true));
+
+    Counter.builder().name("events_total").register(preserveRegistry).inc();
+
+    List<MetricData> metrics = new ArrayList<>(reader.collectAllMetrics());
+    assertThat(metrics).hasSize(1);
+    OpenTelemetryAssertions.assertThat(metrics.get(0)).hasName("events_total");
+  }
+
   private MetricAssert metricAssert() {
     List<MetricData> metrics = testing.getMetrics();
     assertThat(metrics).hasSize(1);