Improve span details percentage calculation

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

@@ -140,8 +140,8 @@ static SpanWaterfallViewModel CreateViewModel(OtlpSpan span, int depth, bool hid
             var relativeStart = span.StartTime - traceStart;
             var rootDuration = span.Trace.Duration.TotalMilliseconds;
 
-            var leftOffset = relativeStart.TotalMilliseconds / rootDuration * 100;
-            var width = span.Duration.TotalMilliseconds / rootDuration * 100;
+            var leftOffset = CalculatePercent(relativeStart.TotalMilliseconds, rootDuration);
+            var width = CalculatePercent(span.Duration.TotalMilliseconds, rootDuration);
 
             // Figure out if the label is displayed to the left or right of the span.
             // If the label position is based on whether more than half of the span is on the left or right side of the trace.
@@ -163,7 +163,7 @@ static SpanWaterfallViewModel CreateViewModel(OtlpSpan span, int depth, bool hid
                     {
                         Index = currentSpanLogIndex++,
                         LogEntry = log,
-                        LeftOffset = logRelativeStart.TotalMilliseconds / rootDuration * 100
+                        LeftOffset = CalculatePercent(logRelativeStart.TotalMilliseconds, rootDuration)
                     });
                 }
             }
@@ -192,6 +192,15 @@ static SpanWaterfallViewModel CreateViewModel(OtlpSpan span, int depth, bool hid
 
             return viewModel;
         }
+
+        static double CalculatePercent(double value, double total)
+        {
+            if (total == 0)
+            {
+                return 0;
+            }
+            return value / total * 100;
+        }
     }
 
     private static string? ResolveUninstrumentedPeerName(OtlpSpan span, IOutgoingPeerResolver[] outgoingPeerResolvers)

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

@@ -5,7 +5,9 @@
 using Aspire.Dashboard.Model.Otlp;
 using Aspire.Dashboard.Otlp.Model;
 using Aspire.Tests.Shared.Telemetry;
+using Google.Protobuf.Collections;
 using Microsoft.Extensions.Logging.Abstractions;
+using OpenTelemetry.Proto.Common.V1;
 using Xunit;
 
 namespace Aspire.Dashboard.Tests.Model;
@@ -42,6 +44,36 @@ public void Create_HasChildren_ChildrenPopulated()
             });
     }
 
+    [Fact]
+    public void Create_RootSpanZeroDuration_ZeroPercentage()
+    {
+        // Arrange
+        var context = new OtlpContext { Logger = NullLogger.Instance, Options = new() };
+        var app1 = new OtlpApplication("app1", "instance", uninstrumentedPeer: false, context);
+        var app1View = new OtlpApplicationView(app1, new RepeatedField<KeyValue>());
+
+        var date = new DateTime(2001, 1, 1, 1, 1, 2, DateTimeKind.Utc);
+        var trace = new OtlpTrace(new byte[] { 1, 2, 3 });
+        var scope = TelemetryTestHelpers.CreateOtlpScope(context);
+        trace.AddSpan(TelemetryTestHelpers.CreateOtlpSpan(app1, trace, scope, spanId: "31", parentSpanId: null, startDate: date, endDate: date));
+        var log = new OtlpLogEntry(TelemetryTestHelpers.CreateLogRecord(traceId: trace.TraceId, spanId: "1"), app1View, scope, context);
+
+        // Act
+        var vm = SpanWaterfallViewModel.Create(trace, [log], new SpanWaterfallViewModel.TraceDetailState([], []));
+
+        // Assert
+        Assert.Collection(vm,
+            e =>
+            {
+                Assert.Equal("31", e.Span.SpanId);
+                Assert.Equal(0, e.LeftOffset);
+                Assert.Equal(0, e.Width);
+
+                var spanLog = Assert.Single(e.SpanLogs);
+                Assert.Equal(0, spanLog.LeftOffset);
+            });
+    }
+
     [Fact]
     public void Create_OutgoingPeers_BrowserLink()
     {

tests/Shared/Telemetry/TelemetryTestHelpers.cs

@@ -184,15 +184,16 @@ public static Span CreateSpan(string traceId, string spanId, DateTime startTime,
         return span;
     }
 
-    public static LogRecord CreateLogRecord(DateTime? time = null, DateTime? observedTime = null, string? message = null, SeverityNumber? severity = null, IEnumerable<KeyValuePair<string, string>>? attributes = null, bool? skipBody = null)
+    public static LogRecord CreateLogRecord(DateTime? time = null, DateTime? observedTime = null, string? message = null, SeverityNumber? severity = null, IEnumerable<KeyValuePair<string, string>>? attributes = null,
+        bool? skipBody = null, string? traceId = null, string? spanId = null)
     {
         attributes ??= [new KeyValuePair<string, string>("{OriginalFormat}", "Test {Log}"), new KeyValuePair<string, string>("Log", "Value!")];
 
         var logRecord = new LogRecord
         {
             Body = (skipBody ?? false) ? null : new AnyValue { StringValue = message ?? "Test Value!" },
-            TraceId = ByteString.CopyFrom(Convert.FromHexString("5465737454726163654964")),
-            SpanId = ByteString.CopyFrom(Convert.FromHexString("546573745370616e4964")),
+            TraceId = (traceId != null) ? ByteString.CopyFrom(Encoding.UTF8.GetBytes(traceId)) : ByteString.CopyFrom(Convert.FromHexString("5465737454726163654964")),
+            SpanId = (spanId != null) ? ByteString.CopyFrom(Encoding.UTF8.GetBytes(spanId)) : ByteString.CopyFrom(Convert.FromHexString("546573745370616e4964")),
             TimeUnixNano = time != null ? DateTimeToUnixNanoseconds(time.Value) : 1000,
             ObservedTimeUnixNano = observedTime != null ? DateTimeToUnixNanoseconds(observedTime.Value) : 1000,
             SeverityNumber = severity ?? SeverityNumber.Info
@@ -303,13 +304,13 @@ public static OtlpContext CreateContext(TelemetryLimitOptions? options = null, I
 
     public static OtlpSpan CreateOtlpSpan(OtlpApplication app, OtlpTrace trace, OtlpScope scope, string spanId, string? parentSpanId, DateTime startDate,
         KeyValuePair<string, string>[]? attributes = null, OtlpSpanStatusCode? statusCode = null, string? statusMessage = null, OtlpSpanKind kind = OtlpSpanKind.Unspecified,
-        OtlpApplication? uninstrumentedPeer = null)
+        OtlpApplication? uninstrumentedPeer = null, DateTime? endDate = null)
     {
         return new OtlpSpan(app.GetView([]), trace, scope)
         {
             Attributes = attributes ?? [],
             BackLinks = [],
-            EndTime = DateTime.MaxValue,
+            EndTime = endDate ?? DateTime.MaxValue,
             Events = [],
             Kind = kind,
             Links = [],