InvalidCastException: Unable to cast object of type 'Sentry.Internal.UnsampledTransaction' to type 'Sentry.TransactionTracer'

[danports]

Package

Sentry.Extensions.Logging
Sentry.OpenTelemetry

.NET Flavor

.NET Core

.NET Version

9.0.5

OS

Any (not platform specific)

OS Version

No response

Development Environment

Visual Studio v17.x

SDK Version

5.9.0

Self-Hosted Sentry Version

No response

Workload Versions

N/A

UseSentry or SentrySdk.Init call

logging.AddSentry(options =>
{
    options.UseOpenTelemetry();
    options.DisableUnobservedTaskExceptionCapture();
});

Steps to Reproduce

After upgrading the Sentry SDK from 5.8.0 to 5.9.0, this exception started appearing - seems like a regression in this release.

Expected Result

No exception thrown.

Actual Result

System.InvalidCastException: Unable to cast object of type 'Sentry.Internal.UnsampledTransaction' to type 'Sentry.TransactionTracer'.
  ?, in void SentrySpanProcessor.CreateRootSpan(Activity data)
  ?, in void SentrySpanProcessor.OnStart(Activity data)
  ?, in TracerProviderSdk(IServiceProvider serviceProvider, bool ownsServiceProvider)+(Activity activity) => { }
  ?, in Activity Activity.Start()

[Flash0ver]

Thanks @danports for updating to the latest version of Sentry and for the Bug report!
Our learning is to re-evaluate existing type assumptions when changing implementation details of return types / out types.

Introduced via #4212.

Reproducible via Samples Sentry.Samples.OpenTelemetry.Console and Sentry.Samples.OpenTelemetry.AspNetCore by decrementing SentryOptions.TracesSampleRate.

Cause:

sentry-dotnet/src/Sentry.OpenTelemetry/SentrySpanProcessor.cs

Lines 164 to 166 in 0e11682

	var transaction = (TransactionTracer)_hub.StartTransaction(
	transactionContext, new Dictionary<string, object?>(), dynamicSamplingContext
	);

which may now return an instance of Sentry.Internal.UnsampledTransaction, rather than Sentry.TransactionTracer, when not sampled.

[Flash0ver]

Some other usages that may require re-evaluation if still correct:

2 other usages in Sentry.OpenTelemetry

sentry-dotnet/src/Sentry.OpenTelemetry/SentrySpanProcessor.cs

Lines 202 to 213 in 2e1fff1

	if (_map.TryRemove(data.SpanId, out var removed))
	{
	if (removed is SpanTracer spanTracerToRemove)
	{
	spanTracerToRemove.IsSentryRequest = true;
	}
	if (removed is TransactionTracer transactionTracer)
	{
	transactionTracer.IsSentryRequest = true;
	}
	}

sentry-dotnet/src/Sentry.OpenTelemetry/SentrySpanProcessor.cs

Lines 228 to 248 in 0e11682

	if (span is TransactionTracer transaction)
	{
	transaction.Name = description;
	transaction.NameSource = source;
	// Use the end timestamp from the activity data.
	transaction.EndTimestamp = data.StartTimeUtc + data.Duration;
	// Transactions set otel attributes (and resource attributes) as context.
	transaction.Contexts["otel"] = GetOtelContext(attributes);
	}
	else
	{
	// Use the end timestamp from the activity data.
	((SpanTracer)span).EndTimestamp = data.StartTimeUtc + data.Duration;
	// Spans set otel attributes in extras (passed to Sentry as "data" on the span).
	// Resource attributes do not need to be set, as they would be identical as those set on the transaction.
	span.SetExtras(attributes);
	span.SetExtra("otel.kind", data.Kind);
	}

more usages in /src/

sentry-dotnet/src/Sentry/SentryTransaction.cs

Lines 272 to 282 in 0e11682

	// Some items are not on the interface, but we only ever pass in a TransactionTracer anyway.
	if (tracer is TransactionTracer transactionTracer)
	{
	SampleRate = transactionTracer.SampleRate;
	DynamicSamplingContext = transactionTracer.DynamicSamplingContext;
	TransactionProfiler = transactionTracer.TransactionProfiler;
	if (transactionTracer.HasMetrics)
	{
	_metricsSummary = new MetricsSummary(transactionTracer.MetricsSummary);
	}
	}

sentry-dotnet/src/Sentry/ISpan.cs

Line 73 in 0e11682

var transaction = span.GetTransaction() as TransactionTracer;

sentry-dotnet/src/Sentry/Internal/OriginHelper.cs

Lines 28 to 39 in 0e11682

	public static void SetOrigin(this ISpan span, string origin)
	{
	switch (span)
	{
	case SpanTracer spanTracer:
	spanTracer.Origin = origin;
	break;
	case TransactionTracer transactionTracer:
	transactionTracer.Contexts.Trace.Origin = origin;
	break;
	}
	}

[Flash0ver]

Question / Potential Fix:

• Shall we type-check via an "is Pattern Expression" instead?
• Check specifically if of type UnsampledTransaction or NoOpTransaction and then early out?
• ...?

For the current logic we need the cast to TransactionTracer, because the DateTimeOffset StartTimestamp property is readonly on the interface ISpanData, and has an internal set on the class TransactionTracer.

---

Also ... are there other usages of TransactionTracer in the context of type-checks mentioned in the previous comment that need to be updated?

[jamescrosswell]

Regarding the other places to check...

sentry-dotnet/src/Sentry.OpenTelemetry/SentrySpanProcessor.cs

Lines 209 to 211 in 2e1fff1

	if (removed is TransactionTracer transactionTracer)
	{
	transactionTracer.IsSentryRequest = true;

This one isn't a concern. That property is used to determine whether the transaction gets sent to Sentry or not... UnsampledTransactions never get sent though (so there's no need to have or set that property for these).

sentry-dotnet/src/Sentry.OpenTelemetry/SentrySpanProcessor.cs

Line 242 in 0e11682

((SpanTracer)span).EndTimestamp = data.StartTimeUtc + data.Duration;

Fixed as part of 5b59f01

sentry-dotnet/src/Sentry/SentryTransaction.cs

Lines 272 to 273 in 4169cb7

	// Some items are not on the interface, but we only ever pass in a TransactionTracer anyway.
	if (tracer is TransactionTracer transactionTracer)

We never try to capture/serialise an UnsampledTransaction.

sentry-dotnet/src/Sentry/ISpan.cs

Line 73 in 0e11682

var transaction = span.GetTransaction() as TransactionTracer;

Fixed as part of 5b59f01

sentry-dotnet/src/Sentry/Internal/OriginHelper.cs

Line 28 in 0e11682

public static void SetOrigin(this ISpan span, string origin)

We never capture UnsampledTransactions or send these to Sentry, so there's no reason to track the origin on these. I think the current logic is fine (it's basically a no-op on anything except the concrete tracer classes).

[Flash0ver]

Thanks @jamescrosswell for the quick fix PR and reviewing the other usages.