[OpenTelemetry] Drop non-finite values from histogram aggregations

src/OpenTelemetry/CHANGELOG.md

@@ -20,6 +20,12 @@ Notes](../../RELEASENOTES.md).
   reset does not result in an unnecessary scale reduction.
   ([#7749](https://github.com/open-telemetry/opentelemetry-dotnet/pull/7749))
 
+* Non-finite histogram measurements (`NaN`, `+Inf`, `-Inf`) are now dropped
+  rather than recorded, so they can no longer permanently corrupt the sum,
+  min, and max of a cumulative histogram stream. This aligns the explicit-bucket
+  and exponential histograms with the metrics SDK specification.
+  ([#7726](https://github.com/open-telemetry/opentelemetry-dotnet/pull/7726))
+
 ## 1.18.0
 
 Released 2026-Aug-21

src/OpenTelemetry/Metrics/MetricPoint/MetricPoint.cs

@@ -947,6 +947,13 @@ internal void NullifyMetricPointState()
 
     private void UpdateHistogram(double number, ReadOnlySpan<KeyValuePair<string, object?>> tags = default, bool offerExemplar = false)
     {
+        if (double.IsNaN(number) || double.IsInfinity(number))
+        {
+            // Non-finite values would poison RunningSum for the lifetime of a cumulative stream.
+            this.CompleteUpdateWithoutMeasurement();
+            return;
+        }
+
         var histogramBuckets = this.mpComponents!.HistogramBuckets!;
 
         this.mpComponents.AcquireLock();
@@ -966,6 +973,14 @@ private void UpdateHistogram(double number, ReadOnlySpan<KeyValuePair<string, ob
 
     private void UpdateHistogramWithMinMax(double number, ReadOnlySpan<KeyValuePair<string, object?>> tags = default, bool offerExemplar = false)
     {
+        if (double.IsNaN(number) || double.IsInfinity(number))
+        {
+            // Non-finite values would poison RunningSum/RunningMin/RunningMax for the lifetime of
+            // a cumulative stream.
+            this.CompleteUpdateWithoutMeasurement();
+            return;
+        }
+
         var histogramBuckets = this.mpComponents!.HistogramBuckets!;
 
         this.mpComponents.AcquireLock();
@@ -988,6 +1003,13 @@ private void UpdateHistogramWithMinMax(double number, ReadOnlySpan<KeyValuePair<
 
     private void UpdateHistogramWithBuckets(double number, ReadOnlySpan<KeyValuePair<string, object?>> tags = default, bool offerExemplar = false)
     {
+        if (double.IsNaN(number) || double.IsInfinity(number))
+        {
+            // Non-finite values would poison RunningSum for the lifetime of a cumulative stream.
+            this.CompleteUpdateWithoutMeasurement();
+            return;
+        }
+
         var histogramBuckets = this.mpComponents!.HistogramBuckets!;
 
         var bucketIndex = histogramBuckets.FindBucketIndex(number);
@@ -1010,6 +1032,14 @@ private void UpdateHistogramWithBuckets(double number, ReadOnlySpan<KeyValuePair
 
     private void UpdateHistogramWithBucketsAndMinMax(double number, ReadOnlySpan<KeyValuePair<string, object?>> tags = default, bool offerExemplar = false)
     {
+        if (double.IsNaN(number) || double.IsInfinity(number))
+        {
+            // Non-finite values would poison RunningSum/RunningMin/RunningMax for the lifetime of
+            // a cumulative stream.
+            this.CompleteUpdateWithoutMeasurement();
+            return;
+        }
+
         var histogramBuckets = this.mpComponents!.HistogramBuckets!;
 
         var bucketIndex = histogramBuckets.FindBucketIndex(number);
@@ -1035,8 +1065,10 @@ private void UpdateHistogramWithBucketsAndMinMax(double number, ReadOnlySpan<Key
 
     private void UpdateBase2ExponentialHistogram(double number, ReadOnlySpan<KeyValuePair<string, object?>> tags = default, bool offerExemplar = false)
     {
-        if (number < 0)
+        if (number < 0 || double.IsNaN(number) || double.IsInfinity(number))
         {
+            // Negatives are undefined for exponential histograms; non-finite values would also
+            // poison RunningSum/RunningMin/RunningMax for the lifetime of a cumulative stream.
             this.CompleteUpdateWithoutMeasurement();
             return;
         }
@@ -1061,8 +1093,10 @@ private void UpdateBase2ExponentialHistogram(double number, ReadOnlySpan<KeyValu
 
     private void UpdateBase2ExponentialHistogramWithMinMax(double number, ReadOnlySpan<KeyValuePair<string, object?>> tags = default, bool offerExemplar = false)
     {
-        if (number < 0)
+        if (number < 0 || double.IsNaN(number) || double.IsInfinity(number))
         {
+            // Negatives are undefined for exponential histograms; non-finite values would also
+            // poison RunningSum/RunningMin/RunningMax for the lifetime of a cumulative stream.
             this.CompleteUpdateWithoutMeasurement();
             return;
         }

test/OpenTelemetry.Exporter.Prometheus.HttpListener.Tests/snapshots/PrometheusSerializer.HistogramInfinities.verified.txt

@@ -14,6 +14,6 @@ test_histogram_bucket{otel_scope_name="HistogramInfinities",le="2500"} 1
 test_histogram_bucket{otel_scope_name="HistogramInfinities",le="5000"} 1
 test_histogram_bucket{otel_scope_name="HistogramInfinities",le="7500"} 1
 test_histogram_bucket{otel_scope_name="HistogramInfinities",le="10000"} 1
-test_histogram_bucket{otel_scope_name="HistogramInfinities",le="+Inf"} 3
-test_histogram_sum{otel_scope_name="HistogramInfinities"} +Inf
-test_histogram_count{otel_scope_name="HistogramInfinities"} 3
+test_histogram_bucket{otel_scope_name="HistogramInfinities",le="+Inf"} 1
+test_histogram_sum{otel_scope_name="HistogramInfinities"} 18
+test_histogram_count{otel_scope_name="HistogramInfinities"} 1

test/OpenTelemetry.Exporter.Prometheus.HttpListener.Tests/snapshots/PrometheusSerializer.HistogramNaN.verified.txt

@@ -14,6 +14,6 @@ test_histogram_bucket{otel_scope_name="HistogramNaN",le="2500"} 1
 test_histogram_bucket{otel_scope_name="HistogramNaN",le="5000"} 1
 test_histogram_bucket{otel_scope_name="HistogramNaN",le="7500"} 1
 test_histogram_bucket{otel_scope_name="HistogramNaN",le="10000"} 1
-test_histogram_bucket{otel_scope_name="HistogramNaN",le="+Inf"} 3
-test_histogram_sum{otel_scope_name="HistogramNaN"} NaN
-test_histogram_count{otel_scope_name="HistogramNaN"} 3
+test_histogram_bucket{otel_scope_name="HistogramNaN",le="+Inf"} 1
+test_histogram_sum{otel_scope_name="HistogramNaN"} 18
+test_histogram_count{otel_scope_name="HistogramNaN"} 1

test/OpenTelemetry.Tests/Metrics/AggregatorTests.cs

@@ -21,6 +21,30 @@ public AggregatorTests()
 
     public static TheoryData<HistogramBoundaryTestCase> HistogramInfinityBoundariesTestCases => HistogramBoundaryTestCase.HistogramInfinityBoundariesTestCases();
 
+    [Theory]
+    [InlineData(double.NaN)]
+    [InlineData(double.PositiveInfinity)]
+    [InlineData(double.NegativeInfinity)]
+    public void NonFiniteMeasurementIsIgnoredByCumulativeHistogram(double nonFinite)
+    {
+        var boundaries = new HistogramExplicitBounds(Metric.DefaultHistogramBounds);
+        var histogramPoint = new MetricPoint(this.aggregatorStore, AggregationType.HistogramWithBuckets, null, boundaries, Metric.DefaultExponentialHistogramMaxBuckets, Metric.DefaultExponentialHistogramMaxScale);
+
+        histogramPoint.Update(1);
+        histogramPoint.Update(nonFinite);
+        histogramPoint.Update(2);
+        histogramPoint.Update(3);
+
+        // Cumulative snapshot (outputDelta: false) retains the running values.
+        histogramPoint.TakeSnapshot(false);
+
+        // The non-finite measurement is dropped: only the three finite values are counted...
+        Assert.Equal(3, histogramPoint.GetHistogramCount());
+
+        // ...and the sum is exactly 1 + 2 + 3, not poisoned to NaN/Infinity.
+        Assert.Equal(6, histogramPoint.GetHistogramSum());
+    }
+
     [Fact]
     public void HistogramDistributeToAllBucketsDefault()
     {

test/OpenTelemetry.Tests/Metrics/MetricTestData.cs

@@ -40,8 +40,7 @@ internal static class MetricTestData
     public static TheoryData<double[], HistogramConfiguration, double, double> ValidHistogramMinMax => new()
     {
         { [-10.0, 0.0, 1.0, 9.0, 10.0, 11.0, 19.0], new HistogramConfiguration(), -10.0, 19.0 },
-        { [double.NegativeInfinity], new HistogramConfiguration(), double.NegativeInfinity, double.NegativeInfinity },
-        { [double.NegativeInfinity, 0.0, double.PositiveInfinity], new HistogramConfiguration(), double.NegativeInfinity, double.PositiveInfinity },
+        { [double.NegativeInfinity, 0.0, double.PositiveInfinity], new HistogramConfiguration(), 0.0, 0.0 },
         { [1.0], new HistogramConfiguration(), 1.0, 1.0 },
         { [5.0, 100.0, 4.0, 101.0, -2.0, 97.0], new ExplicitBucketHistogramConfiguration { Boundaries = [10.0, 20.0] }, -2.0, 101.0 },
         { [5.0, 100.0, 4.0, 101.0, -2.0, 97.0], new Base2ExponentialBucketHistogramConfiguration(), 4.0, 101.0 },