Fix case-sensitive session ID handling in ServiceBusOrchestrationService

[Samir Solanki (solankisamir)]

Summary

Service Bus can change the casing of session IDs during upgrades or failovers. The DurableTask framework used ordinal (case-sensitive) ConcurrentDictionary keys for orchestrationSessions and orchestrationMessages, causing a lowercased session ID to create a ghost session with empty state instead of finding the existing session.

Problem

This broke eternal orchestrations (ContinueAsNew timer bridge) because:

1. Timer message sent with PascalCase session ID (e.g., System_MoveBillingEvents_a3c79b00)
2. Service Bus delivered to lowercased session ID after upgrade (system_movebillingevents_a3c79b00)
3. Framework created a new empty session (ghost) instead of finding the existing one
4. Real session orphaned permanently - no pending messages, stuck forever

Impact

• Eternal orchestration were getting stuck forever

Changes

1. Case-insensitive dictionary (core fix)

Changed both ConcurrentDictionary instances in ServiceBusOrchestrationService.StartAsync() to use StringComparer.OrdinalIgnoreCase:

\\csharp
// Before
this.orchestrationSessions = new ConcurrentDictionary<string, ServiceBusOrchestrationSession>();

// After
this.orchestrationSessions = new ConcurrentDictionary<string, ServiceBusOrchestrationSession>(StringComparer.OrdinalIgnoreCase);
\\

2. Diagnostic logging (3 new log points)

• TrySetSessionState-DeletingState (Warning) - Logs the reason when session state is set to null (previously silent)
• GetSessionState-EmptyState (Warning) - Warns when a session has null/empty state (possible ghost session)
• SentMessageLog enhancement - Now includes ScheduledEnqueueTimeUtc and target SessionId for timer messages

3. Unit tests (5 new tests)

• Case-insensitive dictionary lookup with mixed casing
• Ghost session prevention (duplicate add with different casing fails)
• Exact reproduction of the IcM scenario
• Multiple casing variants treated as same key
• Structural verification of the field type

Testing

All 5 new unit tests pass. Existing build succeeds with 0 warnings, 0 errors.

[Copilot]

Pull request overview

Fixes a reliability issue in the Service Bus backend where session IDs can be delivered with different casing (e.g., after upgrades/failovers), which previously caused “ghost sessions” and could stall long-running/eternal orchestrations.

Changes:

• Initialize orchestrationSessions (and currently also orchestrationMessages) with a case-insensitive ConcurrentDictionary comparer.
• Add diagnostic logging around empty session state reads and state deletion.
• Add new unit tests intended to validate case-insensitive behavior and reproduce the incident scenario.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 6 comments.

File	Description
src/DurableTask.ServiceBus/ServiceBusOrchestrationService.cs	Switches dictionaries to OrdinalIgnoreCase and adds new warning logs + enhanced sent-message logging.
Test/DurableTask.ServiceBus.Tests/SessionIdCaseInsensitiveTests.cs	Adds new MSTest tests for case-insensitive dictionary behavior and incident reproduction (but currently placed outside the solution’s active test/ test project tree).

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[Chris Gillum (cgillum)]

/azp run

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[Samir Solanki (solankisamir)]

/azp run

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Commenter does not have sufficient privileges for PR 1334 in repo Azure/durabletask

[Samir Solanki (solankisamir)]

#1318

[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

Comments suppressed due to low confidence (1)

src/DurableTask.ServiceBus/ServiceBusOrchestrationService.cs:1612

• GetSessionStateAsync logs when the session state is null/empty, but it still constructs a MemoryStream when state.Length == 0. An empty stream will deserialize as an empty string and will throw in RuntimeStateStreamConverter.DeserializeToRuntimeStateWithFallback. Consider treating empty state the same as null when creating rawSessionStream (e.g., only create the stream when state?.Length > 0).

 byte[] state = await session.GetStateAsync();
if (state == null || state.Length == 0)
{
TraceHelper.TraceSession(
TraceEventType.Information,
"ServiceBusOrchestrationService-GetSessionState-EmptyState",
session.SessionId,
$"Session '{session.SessionId}' has null or empty state ({state?.Length ?? 0} bytes).");
}
using (Stream rawSessionStream = state != null ? new MemoryStream(state) : null)
{
this.ServiceStats.OrchestrationDispatcherStats.SessionGets.Increment();
return await RuntimeStateStreamConverter.RawStreamToRuntimeState(rawSessionStream, session.SessionId, orchestrationServiceBlobStore, JsonDataConverter.Default);
}

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[Chris Gillum (cgillum)]

/azp run

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