Prometheus label conversion refactored to align with spec

exporters/prometheus/src/main/java/io/opentelemetry/exporter/prometheus/Otel2PrometheusConverter.java

@@ -10,6 +10,7 @@
 import static java.util.Objects.requireNonNull;
 
 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;
@@ -472,7 +473,9 @@
 
     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 +645,78 @@
     // Simple helper for a log message.
     return snapshot.getClass().getSimpleName().replace("Snapshot", "").toLowerCase(Locale.ENGLISH);
   }
+
+  private static String toLabelValue(AttributeType type, Object attributeValue) {
+    if (AttributeType.STRING.equals(type)) {
+      return attributeValue.toString();
+    } else if (AttributeType.BOOLEAN.equals(type)) {
+      return attributeValue.toString();
+    } else if (AttributeType.LONG.equals(type)) {
+      return attributeValue.toString();
+    } else if (AttributeType.DOUBLE.equals(type)) {
+      return attributeValue.toString();
+    } else if (AttributeType.STRING_ARRAY.equals(type)) {
+      if (attributeValue instanceof List) {
+        return ((List<?>) attributeValue)
+            .stream()
+                .map(String.class::cast)
+                .map(Otel2PrometheusConverter::toJsonValidStr)
+                .collect(Collectors.toList())
+                .toString();
+      } else {
+        LOGGER.log(
+            Level.WARNING,
+            "Unexpected label value for AttributeType.STRING_ARRAY, toString() is being used as fallback value...");
+        return attributeValue.toString();
+      }
+    } else if (AttributeType.BOOLEAN_ARRAY.equals(type)) {
+      return attributeValue.toString();
+    } else if (AttributeType.LONG_ARRAY.equals(type)) {
+      return attributeValue.toString();
+    } else if (AttributeType.DOUBLE_ARRAY.equals(type)) {
+      return attributeValue.toString();
+    } else {
+      throw new IllegalStateException(("Unrecognized AttributeType: " + type));
+    }
+  }
+
+  public static String toJsonValidStr(String str) {
+    StringBuilder sb = new StringBuilder();
+    sb.append('"');
+    for (int i = 0; i < str.length(); i++) {
+      char c = str.charAt(i);
+
+      switch (c) {
+        case '"':
+          sb.append("\\\"");
+          break;
+        case '\\':
+          sb.append("\\\\");
+          break;
+        case '\b':
+          sb.append("\\b");
+          break;
+        case '\f':
+          sb.append("\\f");
+          break;
+        case '\n':
+          sb.append("\\n");
+          break;
+        case '\r':
+          sb.append("\\r");
+          break;
+        case '\t':
+          sb.append("\\t");
+          break;
+        default:
+          if (c <= 0x1F) {
+            sb.append(String.format(Locale.ROOT, "\\u%04X", (int) c));
+          } else {
+            sb.append(c);
+          }
+      }
+    }
+    sb.append('"');
+    return sb.toString();
+  }
 }

exporters/prometheus/src/test/java/io/opentelemetry/exporter/prometheus/Otel2PrometheusConverterTest.java

@@ -9,6 +9,8 @@
 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.AttributeType;
 import io.opentelemetry.api.common.Attributes;
 import io.opentelemetry.sdk.common.InstrumentationScopeInfo;
 import io.opentelemetry.sdk.metrics.data.AggregationTemporality;
@@ -137,6 +139,71 @@ 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", "\\\\\\+\b+\f+\n+\r+\t+" + (char) 0))
+            .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\", \"\\\\\\\\\\\\+\\b+\\f+\\n+\\r+\\t+\\u0000\"]");
+    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]");
+  }
+
+  @Test
+  void labelValueSerialization_Should_Handle_All_AttributeTypes() {
+    assertThat(Stream.of(AttributeType.values()).map(Enum::name))
+        .isEqualTo(
+            Arrays.asList(
+                "STRING",
+                "BOOLEAN",
+                "LONG",
+                "DOUBLE",
+                "STRING_ARRAY",
+                "BOOLEAN_ARRAY",
+                "LONG_ARRAY",
+                "DOUBLE_ARRAY"));
+  }
+
   private static Stream<Arguments> resourceAttributesAdditionArgs() {
     List<Arguments> arguments = new ArrayList<>();