Prometheus label conversion refactored to align with spec

onurkybsi · onurkybsi · commit 43980d9def5f · 2025-04-22T08:00:14.000+02:00
diff --git a/api/all/src/main/java/io/opentelemetry/api/common/AttributeType.java b/api/all/src/main/java/io/opentelemetry/api/common/AttributeType.java
@@ -17,5 +17,32 @@ public enum AttributeType {
   STRING_ARRAY,
   BOOLEAN_ARRAY,
   LONG_ARRAY,
-  DOUBLE_ARRAY
+  DOUBLE_ARRAY;
+
+  /**
+   * Returns whether {@code this} is a primitive type or not.
+   *
+   * @return {@code true} if primitive, otherwise {@code false}
+   */
+  public boolean isPrimitive() {
+    if (AttributeType.STRING.equals(this)) {
+      return true;
+    } else if (AttributeType.BOOLEAN.equals(this)) {
+      return true;
+    } else if (AttributeType.LONG.equals(this)) {
+      return true;
+    } else if (AttributeType.DOUBLE.equals(this)) {
+      return true;
+    } else if (AttributeType.STRING_ARRAY.equals(this)) {
+      return false;
+    } else if (AttributeType.BOOLEAN_ARRAY.equals(this)) {
+      return false;
+    } else if (AttributeType.LONG_ARRAY.equals(this)) {
+      return false;
+    } else if (AttributeType.DOUBLE_ARRAY.equals(this)) {
+      return false;
+    } else {
+      throw new IllegalStateException(("Unrecognized attribute type: " + this));
+    }
+  }
 }
diff --git a/api/all/src/test/java/io/opentelemetry/api/common/AttributeTypeTest.java b/api/all/src/test/java/io/opentelemetry/api/common/AttributeTypeTest.java
@@ -0,0 +1,39 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package io.opentelemetry.api.common;
+
+import static org.assertj.core.api.AssertionsForClassTypes.assertThat;
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
+
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.CsvSource;
+import org.junit.jupiter.params.provider.EnumSource;
+
+final class AttributeTypeTest {
+
+  @ParameterizedTest
+  @CsvSource(
+      value = {
+        "STRING, true",
+        "BOOLEAN, true",
+        "LONG, true",
+        "DOUBLE, true",
+        "STRING_ARRAY, false",
+        "BOOLEAN_ARRAY, false",
+        "LONG_ARRAY, false",
+        "DOUBLE_ARRAY, false",
+      },
+      delimiterString = ",")
+  void isPrimitive(AttributeType type, boolean expected) {
+    assertThat(type.isPrimitive()).isEqualTo(expected);
+  }
+
+  @ParameterizedTest
+  @EnumSource(AttributeType.class)
+  void isPrimitive_CoversAllValues(AttributeType type) {
+    assertDoesNotThrow(type::isPrimitive);
+  }
+}
diff --git a/docs/apidiffs/current_vs_latest/opentelemetry-api.txt b/docs/apidiffs/current_vs_latest/opentelemetry-api.txt
@@ -1,4 +1,7 @@
 Comparing source compatibility of opentelemetry-api-1.50.0-SNAPSHOT.jar against opentelemetry-api-1.49.0.jar
+***  MODIFIED ENUM: PUBLIC FINAL io.opentelemetry.api.common.AttributeType  (compatible)
+	===  CLASS FILE FORMAT VERSION: 52.0 <- 52.0
+	+++  NEW METHOD: PUBLIC(+) boolean isPrimitive()
 ***  MODIFIED INTERFACE: PUBLIC ABSTRACT io.opentelemetry.api.logs.LogRecordBuilder  (not serializable)
 	===  CLASS FILE FORMAT VERSION: 52.0 <- 52.0
 	+++  NEW METHOD: PUBLIC(+) io.opentelemetry.api.logs.LogRecordBuilder setEventName(java.lang.String)
diff --git a/exporters/prometheus/build.gradle.kts b/exporters/prometheus/build.gradle.kts
@@ -13,6 +13,7 @@ dependencies {
   implementation(project(":exporters:common"))
   implementation(project(":sdk-extensions:autoconfigure-spi"))
   implementation("io.prometheus:prometheus-metrics-exporter-httpserver")
+  implementation("com.fasterxml.jackson.core:jackson-databind")
 
   compileOnly("com.google.auto.value:auto-value-annotations")
 
diff --git a/exporters/prometheus/src/main/java/io/opentelemetry/exporter/prometheus/Otel2PrometheusConverter.java b/exporters/prometheus/src/main/java/io/opentelemetry/exporter/prometheus/Otel2PrometheusConverter.java
@@ -9,7 +9,10 @@
 import static io.prometheus.metrics.model.snapshots.PrometheusNaming.sanitizeMetricName;
 import static java.util.Objects.requireNonNull;
 
+import com.fasterxml.jackson.core.JsonProcessingException;
+import com.fasterxml.jackson.databind.ObjectMapper;
 import io.opentelemetry.api.common.AttributeKey;
+import io.opentelemetry.api.common.AttributeType;
 import io.opentelemetry.api.common.Attributes;
 import io.opentelemetry.api.trace.SpanContext;
 import io.opentelemetry.sdk.common.InstrumentationScopeInfo;
@@ -76,6 +79,7 @@ final class Otel2PrometheusConverter {
   private static final String OTEL_SCOPE_NAME = "otel_scope_name";
   private static final String OTEL_SCOPE_VERSION = "otel_scope_version";
   private static final long NANOS_PER_MILLISECOND = TimeUnit.MILLISECONDS.toNanos(1);
+  private static final ObjectMapper OBJECT_MAPPER = new ObjectMapper();
   static final int MAX_CACHE_SIZE = 10;
 
   private final boolean otelScopeEnabled;
@@ -472,7 +476,9 @@ private Labels convertAttributes(
 
     Map<String, String> labelNameToValue = new HashMap<>();
     attributes.forEach(
-        (key, value) -> labelNameToValue.put(sanitizeLabelName(key.getKey()), value.toString()));
+        (key, value) ->
+            labelNameToValue.put(
+                sanitizeLabelName(key.getKey()), toLabelValue(key.getType(), value)));
 
     for (int i = 0; i < additionalAttributes.length; i += 2) {
       labelNameToValue.putIfAbsent(
@@ -642,4 +648,24 @@ private static String typeString(MetricSnapshot snapshot) {
     // Simple helper for a log message.
     return snapshot.getClass().getSimpleName().replace("Snapshot", "").toLowerCase(Locale.ENGLISH);
   }
+
+  private static String toLabelValue(AttributeType type, Object attributeValue) {
+    if (type.isPrimitive()) {
+      return attributeValue.toString();
+    } else {
+      return maybeToJson(attributeValue);
+    }
+  }
+
+  private static String maybeToJson(Object attributeValue) {
+    try {
+      return OBJECT_MAPPER.writeValueAsString(attributeValue);
+    } catch (JsonProcessingException e) {
+      LOGGER.log(
+          Level.WARNING,
+          "Label value couldn't be serialized, toString() is being used as fallback value...",
+          e);
+      return attributeValue.toString();
+    }
+  }
 }
diff --git a/exporters/prometheus/src/module/java/module-info.java b/exporters/prometheus/src/module/java/module-info.java
@@ -5,4 +5,5 @@
   requires transitive io.opentelemetry.sdk.metrics;
   requires jdk.httpserver;
   requires java.logging;
+  requires com.fasterxml.jackson.databind;
 }
diff --git a/exporters/prometheus/src/test/java/io/opentelemetry/exporter/prometheus/Otel2PrometheusConverterTest.java b/exporters/prometheus/src/test/java/io/opentelemetry/exporter/prometheus/Otel2PrometheusConverterTest.java
@@ -9,6 +9,7 @@
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.assertThatCode;
 
+import io.opentelemetry.api.common.AttributeKey;
 import io.opentelemetry.api.common.Attributes;
 import io.opentelemetry.sdk.common.InstrumentationScopeInfo;
 import io.opentelemetry.sdk.metrics.data.AggregationTemporality;
@@ -137,6 +138,56 @@ void prometheusNameCollisionTest_Issue6277() {
     assertThatCode(() -> converter.convert(metricData)).doesNotThrowAnyException();
   }
 
+  @Test
+  void labelValueSerialization_Primitives() {
+    Attributes attributes =
+        Attributes.builder()
+            .put(AttributeKey.stringKey("stringKey"), "stringValue")
+            .put(AttributeKey.booleanKey("booleanKey"), true)
+            .put(AttributeKey.longKey("longKey"), Long.MAX_VALUE)
+            .put(AttributeKey.doubleKey("doubleKey"), 0.12345)
+            .build();
+    MetricData metricData =
+        createSampleMetricData("sample", "1", MetricDataType.LONG_SUM, attributes, null);
+
+    MetricSnapshots snapshots = converter.convert(Collections.singletonList(metricData));
+
+    assertThat(snapshots.get(0).getDataPoints().get(0).getLabels().get("stringKey"))
+        .isEqualTo("stringValue");
+    assertThat(snapshots.get(0).getDataPoints().get(0).getLabels().get("booleanKey"))
+        .isEqualTo("true");
+    assertThat(snapshots.get(0).getDataPoints().get(0).getLabels().get("longKey"))
+        .isEqualTo("9223372036854775807");
+    assertThat(snapshots.get(0).getDataPoints().get(0).getLabels().get("doubleKey"))
+        .isEqualTo("0.12345");
+  }
+
+  @Test
+  void labelValueSerialization_NonPrimitives() {
+    Attributes attributes =
+        Attributes.builder()
+            .put(
+                AttributeKey.stringArrayKey("stringKey"),
+                Arrays.asList("stringValue1", "stringValue2"))
+            .put(AttributeKey.booleanArrayKey("booleanKey"), Arrays.asList(true, false))
+            .put(AttributeKey.longArrayKey("longKey"), Arrays.asList(12345L, 6789L))
+            .put(AttributeKey.doubleArrayKey("doubleKey"), Arrays.asList(0.12345, 0.6789))
+            .build();
+    MetricData metricData =
+        createSampleMetricData("sample", "1", MetricDataType.LONG_SUM, attributes, null);
+
+    MetricSnapshots snapshots = converter.convert(Collections.singletonList(metricData));
+
+    assertThat(snapshots.get(0).getDataPoints().get(0).getLabels().get("stringKey"))
+        .isEqualTo("[\"stringValue1\",\"stringValue2\"]");
+    assertThat(snapshots.get(0).getDataPoints().get(0).getLabels().get("booleanKey"))
+        .isEqualTo("[true,false]");
+    assertThat(snapshots.get(0).getDataPoints().get(0).getLabels().get("longKey"))
+        .isEqualTo("[12345,6789]");
+    assertThat(snapshots.get(0).getDataPoints().get(0).getLabels().get("doubleKey"))
+        .isEqualTo("[0.12345,0.6789]");
+  }
+
   private static Stream<Arguments> resourceAttributesAdditionArgs() {
     List<Arguments> arguments = new ArrayList<>();
 

Original file line number	Diff line number	Diff line change
`@@ -5,4 +5,5 @@`
`5`	`5`	`requires transitive io.opentelemetry.sdk.metrics;`
`6`	`6`	`requires jdk.httpserver;`
`7`	`7`	`requires java.logging;`
	`8`	`+ requires com.fasterxml.jackson.databind;`
`8`	`9`	`}`