Nexus support #517

cretz · 2025-08-29T20:33:27Z

What was changed

Added Nexus support. Notes:

Nexus PR that must be merged/published first at Initial Nexus implementation nexus-rpc/sdk-dotnet#4
💥 Slight compatibility break when manually instantiating a worker tuner where we require a 4th parameter to constructor now for Nexus
Issue opened to do samples at Sample request: Nexus simple samples-dotnet#104
Issue opened for cancellation types at [Feature Request] Nexus cancellation type support #514
Issue opened for OTel support at [Feature Request] Nexus OpenTelemetry support #515
Issue opened for Core to dedupe headers at [Feature Request] Nexus should deduplicate and lowercase inbound headers sdk-core#993
Issue that will encompass Nexus slot supplier tests at [Feature Request] Ensure tests exist to confirm custom slot supplier slot info has proper fields #519

Checklist

Closes [Feature Request] Initial Nexus implementation #426

# Conflicts: # src/Temporalio/Bridge/Interop/Interop.cs # src/Temporalio/Bridge/OptionsExtensions.cs # src/Temporalio/Bridge/include/temporal-sdk-bridge.h # src/Temporalio/Bridge/src/worker.rs # src/Temporalio/Temporalio.csproj # src/Temporalio/Worker/TemporalWorker.cs

cretz · 2025-08-29T20:34:44Z

src/Temporalio/Temporalio.csproj

    <PackageReference Include="Microsoft.Extensions.Logging.Abstractions" Version="2.2.0" />
-    <PackageReference Include="Microsoft.SourceLink.GitHub" Version="1.1.1" PrivateAssets="All" />
+    <PackageReference Include="Microsoft.SourceLink.GitHub" Version="8.0.0" PrivateAssets="All" />
+    <ProjectReference Include="..\..\..\nexus-sdk-dotnet\src\NexusRpc\NexusRpc.csproj" />


Won't pass CI until nexus-rpc/sdk-dotnet#4 merged/published

Quinn-With-Two-Ns · 2025-09-08T16:07:16Z

src/Temporalio/Nexus/NexusOperationInfo.cs

+    /// <param name="Namespace">Current namespace.</param>
+    /// <param name="TaskQueue">Current task queue.</param>
+    /// <remarks>WARNING: Nexus support is experimental.</remarks>
+    public record NexusOperationInfo(


Is this exposed to users? I am not sure we exposed anything similar in Go or Java? Not saying we shouldn't just if we do we should open issue in Go and Java for parity.

This info was exposed in Python by @dandavison. We can make this one and that one internal only or we can open Go/Java/TypeScript issues. Do you have a preference/vote?

I am fine with adding it, might be worth having a way for a user to detect they are in a Nexus operation context like we have for activities

Ok, setting reminder to open issues in Go, Java, and TypeScript to ensure it is included there too

I have opened temporalio/features#674 to track it in general

src/Temporalio/Testing/WorkflowEnvironment.cs

src/Temporalio/Worker/WorkflowInstance.cs

Quinn-With-Two-Ns · 2025-09-08T16:23:32Z

src/Temporalio/Worker/WorkflowInstance.cs

+                    OperationName: operationName,
+                    Arg: arg,
+                    Options: options ?? new(),
+                    Headers: null));


Is there a reason you pass null headers vs an empty map? If that is what we did in other places in the dotnet SDK not suggesting we change, just curious.

Yes, it is what we did in other places. .NET devs are self-conscious about unnessesarily creating new objects if they don't have to and they aren't used often. For headers, to create an empty mutable dictionary would be extra unnecessary object creation in most cases (and immutable dictionary w/ copy-on-write semantics is not a common .NET approach here). Granted .NET has good short-lived-object GC like Java these days so it's not a big deal, but it's more proper to allow nullable here (which can be expressed via the type system so users are not surprised).

tests/Temporalio.Tests/Worker/NexusWorkerTests.cs

Quinn-With-Two-Ns · 2025-09-08T18:11:29Z

src/Temporalio/Worker/NexusWorker.cs

+                    appExc,
+                    HandlerErrorRetryBehavior.NonRetryable);
+            }
+            else if (exc is WorkflowAlreadyStartedException)


Is there any test for this behaviour? Would be good to have some tests for the general RPC exception to handler translation, but IMO this is the more important error to translate since most async nexus operations are just starting workflows

👍 No, will add test. The tests I had done so far on dupe checking were more about checking conflict policy. I will add a test that confirms regular start will fail as non-retryable.

Actually, just realized we do have a test that confirms this, it is part of the ExecuteNexusOperationAsync_SimpleWorkflow_ConflictPolicy test (the test confirms already-started behavior before it confirms conflict-policy-use-existing behavior)

Quinn-With-Two-Ns

other then my previous comments LGTM

# Conflicts: # src/Temporalio/Bridge/Interop/Interop.cs

Quinn-With-Two-Ns · 2025-09-22T15:08:17Z

src/Temporalio/Worker/WorkflowInstance.cs

+                    Endpoint = input.ClientOptions.Endpoint,
+                    Service = input.Service,
+                    Operation = input.OperationName,
+                    Input = input.Arg == null ? null : instance.PayloadConverter.ToPayload(input.Arg),


to confirm this PayloadConverter does not have the workflow context attached correct?

It does as do all workflow calls. Based on off-PR discussions ,I have opened a separate issue at #523 to solve this generally (it is not a Nexus-specific concern).

I think we should fix this for Nexus to not make the problem worse

We can't just fix in Nexus, we have to fix everywhere. It is a general fix, not a Nexus specific fix. I do not think we should hold up experimental Nexus support for a general fix to this problem.

Quinn-With-Two-Ns · 2025-09-22T15:12:49Z

src/Temporalio/Worker/WorkflowInstance.cs

+                var token = input.Options.CancellationToken ?? instance.CancellationToken;
+                // We do not even want to schedule if the cancellation token is already cancelled.
+                // We choose to use cancelled failure instead of wrapping in Nexus failure which is
+                // similar to what Java and TypeScript do, with the accepted tradeoff that it makes


Suggested change

// similar to what Java and TypeScript do, with the accepted tradeoff that it makes

// similar to what TypeScript do, with the accepted tradeoff that it makes

Java does wrap the cancelled failure in a Nexus failure. What does dotnet do in other immediate cancellation scenarios ?

To clarify, this is copied from the child workflow comment. I was under the impression for child/nexus cancel-before-start, that Java and TypeScript just throw (i.e. set promise result to) a CanceledFailure, not a wrapped cancel failure as would happen if the cancel happened after schedule/start.

I was under the impression for child/nexus cancel-before-start, that Java and TypeScript just throw (i.e. set promise result to) a CanceledFailure

That is not true for Java, cancel-before-start throws the same error chain as cancel happened after schedule/start.

cretz added 3 commits August 20, 2025 08:24

Nexus work

7591efc

More Nexus work

1613cf0

cretz requested a review from a team as a code owner August 29, 2025 20:33

cretz commented Aug 29, 2025

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cretz mentioned this pull request Aug 29, 2025

Initial Nexus implementation nexus-rpc/sdk-dotnet#4

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Quinn-With-Two-Ns reviewed Sep 8, 2025

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Minor PR suggested updates

26566db

cretz mentioned this pull request Sep 12, 2025

Nexus context propagation sample temporalio/samples-dotnet#108

Merged

maciejdudko mentioned this pull request Sep 18, 2025

Added retry policy to activity info #511

Merged

cretz added 3 commits September 22, 2025 08:33

Update Nexus version and require Nexus slot supplier

93e3ad7

Merge remote-tracking branch 'remotes/origin/main' into nexus-initial

e410149

# Conflicts: # src/Temporalio/Bridge/Interop/Interop.cs

Update Core

46db4d3

cretz mentioned this pull request Sep 22, 2025

[Feature Request] Consider updating tests to use .NET 10 #522

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Quinn-With-Two-Ns reviewed Sep 22, 2025

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CI fix

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Quinn-With-Two-Ns approved these changes Sep 22, 2025

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cretz merged commit da7202a into temporalio:main Sep 22, 2025
10 checks passed

cretz deleted the nexus-initial branch September 22, 2025 17:18

mjameswh mentioned this pull request Nov 14, 2025

Initial Nexus implementation temporalio/features#609

Open

9 tasks

	// similar to what Java and TypeScript do, with the accepted tradeoff that it makes
	// similar to what TypeScript do, with the accepted tradeoff that it makes

Nexus support #517

Nexus support #517

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