guard against empty

Author: hughsimpson

reporters/kamon-opentelemetry/src/main/scala/kamon/otel/MetricsConverter.scala

@@ -65,17 +65,21 @@ class WithResourceMetricsConverter(resource: Resource, kamonVersion: String, fro
       s.value.buckets.map(JLong valueOf _.frequency).asJava
     )
 
-  def toHistogramData(any: Seq[Snapshot[Distribution]]): HistogramData =
-    ImmutableHistogramData.create(AggregationTemporality.CUMULATIVE, any.map(toHistogramDatum).asJava)
-
-  def convertHistogram(histogram: MetricSnapshot.Distributions): MetricData =
-    ImmutableMetricData.createDoubleHistogram(
-      resource,
-      instrumentationScopeInfo(histogram),
-      histogram.name,
-      histogram.description,
-      toString(histogram.settings.unit),
-      toHistogramData(histogram.instruments))
+  def toHistogramData(distributions: Seq[Snapshot[Distribution]]): Option[HistogramData] =
+    distributions.filter(_.value.buckets.nonEmpty) match {
+      case Nil => None
+      case nonEmpty => Some(ImmutableHistogramData.create(AggregationTemporality.CUMULATIVE, nonEmpty.map(toHistogramDatum).asJava))
+    }
+
+  def convertHistogram(histogram: MetricSnapshot.Distributions): Option[MetricData] =
+    toHistogramData(histogram.instruments).map(d =>
+      ImmutableMetricData.createDoubleHistogram(
+        resource,
+        instrumentationScopeInfo(histogram),
+        histogram.name,
+        histogram.description,
+        toString(histogram.settings.unit),
+        d))
 
   def toCounterDatum(g: Snapshot[Long]): LongPointData =
     ImmutableLongPointData.create(fromNs, toNs, SpanConverter.toAttributes(g.tags), g.value)
@@ -100,9 +104,9 @@ class WithResourceMetricsConverter(resource: Resource, kamonVersion: String, fro
 private[otel] object MetricsConverter {
   def convert(resource: Resource, kamonVersion: String)(metrics: PeriodSnapshot): JCollection[MetricData] = {
     val converter = new WithResourceMetricsConverter(resource, kamonVersion, metrics.from, metrics.to)
-    val gauges = metrics.gauges.map(converter.convertGauge)
-    val histograms = (metrics.histograms ++ metrics.timers ++ metrics.rangeSamplers).map(converter.convertHistogram)
-    val counters = metrics.counters.map(converter.convertCounter)
+    val gauges = metrics.gauges.filter(_.instruments.nonEmpty).map(converter.convertGauge)
+    val histograms = (metrics.histograms ++ metrics.timers ++ metrics.rangeSamplers).filter(_.instruments.nonEmpty).flatMap(converter.convertHistogram)
+    val counters = metrics.counters.filter(_.instruments.nonEmpty).map(converter.convertCounter)
 
     (gauges ++ histograms ++ counters).asJava
   }

reporters/kamon-opentelemetry/src/main/scala/kamon/otel/Services.scala

@@ -122,19 +122,21 @@ private[otel] class OtlpMetricsService(c: OpenTelemetryConfiguration) extends Me
       builder.build()
   }
 
-  override def exportMetrics(metrics: JCollection[MetricData]): Future[Unit] = {
-    val result = Promise[Unit]
-    val completableResultCode = delegate.`export`(metrics)
-    val runnable: Runnable = new Runnable {
-      override def run(): Unit =
-        if (completableResultCode.isSuccess) result.success(())
-        else result.failure(MetricStatusRuntimeException)
+  override def exportMetrics(metrics: JCollection[MetricData]): Future[Unit] =
+    if (metrics.isEmpty) Future.successful(())
+    else {
+      val result = Promise[Unit]
+      val completableResultCode = delegate.`export`(metrics)
+      val runnable: Runnable = new Runnable {
+        override def run(): Unit =
+          if (completableResultCode.isSuccess) result.success(())
+          else result.failure(MetricStatusRuntimeException)
+      }
+      completableResultCode.whenComplete {
+        runnable
+      }
+      result.future
     }
-    completableResultCode.whenComplete {
-      runnable
-    }
-    result.future
-  }
 
   override def close(): Unit = delegate.close()
 }