Fix issues around metrics with unit rates

playground/Stress/Stress.ApiService/Program.cs

@@ -20,6 +20,11 @@
 
 app.Lifetime.ApplicationStarted.Register(ConsoleStresser.Stress);
 
+app.Lifetime.ApplicationStarted.Register(() =>
+{
+    _ = app.Services.GetRequiredService<TestMetrics>();
+});
+
 app.MapGet("/", () => "Hello world");
 
 app.MapGet("/write-console", () =>

playground/Stress/Stress.ApiService/TestMetrics.cs

@@ -15,15 +15,42 @@ public class TestMetrics : IDisposable
 
     public TestMetrics()
     {
-        _meter = new Meter(MeterName, "1.0.0", new[]
-        {
+        _meter = new Meter(MeterName, "1.0.0",
+        [
             new KeyValuePair<string, object?>("meter-tag", Guid.NewGuid().ToString())
-        });
+        ]);
 
-        _counter = _meter.CreateCounter<int>("test-counter", unit: null, description: null, tags: new[]
-        {
+        _counter = _meter.CreateCounter<int>("test-counter", unit: null, description: null, tags:
+        [
             new KeyValuePair<string, object?>("instrument-tag", Guid.NewGuid().ToString())
+        ]);
+
+        var uploadSpeed = new List<double>();
+
+        Task.Run(async () =>
+        {
+            while (true)
+            {
+                lock (uploadSpeed)
+                {
+                    uploadSpeed.Add(Random.Shared.Next(5, 10));
+                }
+                await Task.Delay(1000);
+            }
         });
+
+        _meter.CreateObservableGauge<double>("observable-gauge", () =>
+        {
+            lock (uploadSpeed)
+            {
+                var sum = 0d;
+                for (var i = 0; i < uploadSpeed.Count; i++)
+                {
+                    sum += uploadSpeed[i];
+                }
+                return new Measurement<double>(sum / uploadSpeed.Count);
+            }
+        }, unit: "By/s");
     }
 
     public void IncrementCounter(int value, in TagList tags)

src/Aspire.Dashboard/Model/DefaultInstrumentUnitResolver.cs

@@ -15,15 +15,19 @@ public string ResolveDisplayedUnit(OtlpInstrumentSummary instrument, bool titleC
     {
         if (!string.IsNullOrEmpty(instrument.Unit))
         {
-            var unit = OtlpUnits.GetUnit(instrument.Unit.TrimStart('{').TrimEnd('}'));
-            if (pluralize)
+            var (unit, isRateUnit) = OtlpUnits.GetUnit(instrument.Unit.TrimStart('{').TrimEnd('}'));
+
+            // Don't pluralize rate units, e.g. We want "Bytes per second", not "Bytes per seconds".
+            if (pluralize && !isRateUnit)
             {
                 unit = unit.Pluralize();
             }
+
             if (titleCase)
             {
                 unit = unit.Titleize();
             }
+
             return unit;
         }
 

src/Aspire.Dashboard/Otlp/Model/OtlpUnits.cs

@@ -8,17 +8,19 @@ namespace Aspire.Dashboard.Otlp.Model;
 
 public static class OtlpUnits
 {
-    public static string GetUnit(string unit)
+    public static (string Unit, bool IsRateUnit) GetUnit(string unit)
     {
         // Dropping the portions of the Unit within brackets (e.g. {packet}). Brackets MUST NOT be included in the resulting unit. A "count of foo" is considered unitless in Prometheus.
         // https://github.com/open-telemetry/opentelemetry-specification/blob/b2f923fb1650dde1f061507908b834035506a796/specification/compatibility/prometheus_and_openmetrics.md#L238
         var updatedUnit = RemoveAnnotations(unit);
 
+        var isRateUnit = false;
         // Converting "foo/bar" to "foo_per_bar".
         // https://github.com/open-telemetry/opentelemetry-specification/blob/b2f923fb1650dde1f061507908b834035506a796/specification/compatibility/prometheus_and_openmetrics.md#L240C3-L240C41
         if (TryProcessRateUnits(updatedUnit, out var updatedPerUnit))
         {
             updatedUnit = updatedPerUnit;
+            isRateUnit = true;
         }
         else
         {
@@ -27,7 +29,7 @@ public static string GetUnit(string unit)
             updatedUnit = MapUnit(updatedUnit.AsSpan());
         }
 
-        return updatedUnit;
+        return (updatedUnit, isRateUnit);
     }
 
     private static bool TryProcessRateUnits(string updatedUnit, [NotNullWhen(true)] out string? updatedPerUnit)
@@ -44,7 +46,7 @@ private static bool TryProcessRateUnits(string updatedUnit, [NotNullWhen(true)]
                     return false;
                 }
 
-                updatedPerUnit = MapUnit(updatedUnit.AsSpan(0, i)) + " per" + MapPerUnit(updatedUnit.AsSpan(i + 1, updatedUnit.Length - i - 1));
+                updatedPerUnit = MapUnit(updatedUnit.AsSpan(0, i)) + " per " + MapPerUnit(updatedUnit.AsSpan(i + 1, updatedUnit.Length - i - 1));
                 return true;
             }
         }

tests/Aspire.Dashboard.Tests/Model/DefaultInstrumentUnitResolverTests.cs

@@ -0,0 +1,52 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using Aspire.Dashboard.Configuration;
+using Aspire.Dashboard.Model;
+using Aspire.Dashboard.Otlp.Model;
+using Aspire.Dashboard.Resources;
+using Microsoft.Extensions.Localization;
+using OpenTelemetry.Proto.Common.V1;
+using Xunit;
+
+namespace Aspire.Dashboard.Tests.Model;
+
+public sealed class DefaultInstrumentUnitResolverTests
+{
+    [Theory]
+    [InlineData("By/s", "instrument_name", "Bytes Per Second")]
+    [InlineData("connection", "instrument_name", "Connections")]
+    [InlineData("{connection}", "instrument_name", "Connections")]
+    [InlineData("", "instrument_name", "Localized:PlotlyChartValue")]
+    [InlineData("", "instrument_name.count", "Localized:PlotlyChartCount")]
+    [InlineData("", "instrument_name.length", "Localized:PlotlyChartLength")]
+    public void ResolveDisplayedUnit(string unit, string name, string expected)
+    {
+        // Arrange
+        var localizer = new TestStringLocalizer<ControlsStrings>();
+        var resolver = new DefaultInstrumentUnitResolver(localizer);
+
+        var otlpInstrumentSummary = new OtlpInstrumentSummary
+        {
+            Description = "Description!",
+            Name = name,
+            Parent = new OtlpMeter(new InstrumentationScope { Name = "meter_name" }, new TelemetryLimitOptions()),
+            Type = OtlpInstrumentType.Gauge,
+            Unit = unit
+        };
+
+        // Act
+        var result = resolver.ResolveDisplayedUnit(otlpInstrumentSummary, titleCase: true, pluralize: true);
+
+        // Assert
+        Assert.Equal(expected, result);
+    }
+
+    private sealed class TestStringLocalizer<T> : IStringLocalizer<T>
+    {
+        public LocalizedString this[string name] => new LocalizedString(name, $"Localized:{name}");
+        public LocalizedString this[string name, params object[] arguments] => new LocalizedString(name, $"Localized:{name}");
+
+        public IEnumerable<LocalizedString> GetAllStrings(bool includeParentCultures) => [];
+    }
+}