Add links and callbacks support for standalone activity by fretz12 · Pull Request #759 · temporalio/api

fretz12 · 2026-04-07T16:05:10Z

What changed?

Added completion_callbacks and links fields to StartActivityExecutionRequest.
Added link field to StartActivityExecutionResponse.
Added callbacks field to DescribeActivityExecutionResponse.
Added links field to ActivityExecutionInfo.
Added new Link.Activity variant to the Link message type.
Added new CallbackInfo base message
Updated OpenAPI v2/v3 specs to reflect the above changes.

Why?
To support links and callbacks for standalone activity executions (SAA), bringing feature parity with workflow-based activity scheduling.

temporal/api/workflowservice/v1/request_response.proto

temporal/api/activity/v1/message.proto

temporal/api/workflowservice/v1/request_response.proto

dandavison

Looks great but I think that we need to make CallbackInfo handle Activity before merging.

dandavison · 2026-04-09T12:14:49Z

temporal/api/workflowservice/v1/request_response.proto

    bytes long_poll_token = 5;
+
+    // Callbacks attached to this activity execution and their current state.
+    repeated temporal.api.workflow.v1.CallbackInfo callbacks = 6;


This CallbackInfo is currently workflow-specific:

// CallbackInfo contains the state of an attached workflow callback. message CallbackInfo { // Trigger for when the workflow is closed. message WorkflowClosed {} message Trigger { oneof variant { WorkflowClosed workflow_closed = 1; } }

We either need to make it more general, or add an activity-specific CallbackInfo. I'm thinking we'd want the former -- add an ActivityClosed or ExecutionClosed trigger. We're going to want to straighten this out, and it would be a breaking API change to do it later.

Ah I totally missed this, this callback info struct is only for workflows. You'll need to create a callback info struct for activities instead.

Good call, added an activity specific cb

dandavison · 2026-04-09T12:24:55Z

temporal/api/workflowservice/v1/request_response.proto

+    repeated temporal.api.common.v1.Callback completion_callbacks = 19;
+    // Links to be associated with the activity. Callbacks may also have associated links;
+    // links already included with a callback should not be duplicated here.
+    repeated temporal.api.common.v1.Link links = 20;


The SAA PR only uses links on the callback. Is it necessary/appropriate to add these top-level links in addition to the callback links? If so, could the Nexus team give a refresher on what the respective roles are of the two links (I had it in my head that top-level were deprecated).

Not deprecated, I commented on this before. It's possible to link without attaching callbacks.

For reference: #759 (comment)

dandavison · 2026-04-09T12:38:47Z

temporal/api/activity/v1/message.proto

    // Set if activity cancelation was requested.
    string canceled_reason = 32;
+
+    // Links associated with the activity.


A reader is going to think initially these are links that in some way refer to this activity. However, they're not -- they're links pointing to other entities associated with the activity; typically the entity that started the activity. Let's clarify this for the reader, here and in the workflow counterpart HistoryEvent.links. As an author of a Nexus SDK I found this confusing at first, so there's not much doubt that other users will benefit from some help here.

Suggested change

// Links associated with the activity.

// Links to entities associated with this activity, for example

// to the entity that started this activity.

Gotcha, changed here and at HistoryEvent

Added links/callbacks to describe and start responses Update openapi

Co-authored-by: Quinn Klassen <klassenq@gmail.com>

Co-authored-by: Spencer Judge <spencer@temporal.io>

dandavison · 2026-04-10T13:58:35Z

temporal/api/activity/v1/message.proto

+
+    // If the state is BLOCKED, blocked reason provides additional information.
+    string blocked_reason = 9;
+}


I think this is the right design; just describing it to make it explicit. So each CHASM component will have its own CallbackInfo, the role of which is to describe a callback's state and triggering condition. Since different CHASM components will have their own component-specific sets of possible triggering conditions, we define component-specific CallbackInfo types. In practice the only field that differs for now is that trigger oneof; they'll share identical callback state fields.

Agree, we should ideally have a single type for callback info since it will be used across multiple archetypes. The trigger is the only archetype specific information.

I'm going to walk back what I wrote yesterday and ask you to create a temporal.api.callback.v1.CallbackInfo which has all of the common fields and put only Trigger and temporal.api.callback.v1.CallbackInfo in this message.

I refactored the common fields to temporal.api.callback.v1.CallbackInfo. Left workflow callback info as is to avoid breaking changes

dandavison · 2026-04-10T18:59:03Z

temporal/api/activity/v1/message.proto

+    // Trigger for this callback.
+    Trigger trigger = 1;
+    // Common callback info.
+    temporal.api.callback.v1.CallbackInfo callback_info = 2;


We're thinking let's call this info.

Renamed to info

dandavison

LGTM

fretz12 requested review from a team April 7, 2026 16:05

Quinn-With-Two-Ns reviewed Apr 7, 2026

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bergundy reviewed Apr 7, 2026

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fretz12 changed the title ~~Add links, callbacks, and start delay support for standalone activity~~ Add links and callbacks support for standalone activity Apr 7, 2026

fretz12 requested review from Quinn-With-Two-Ns, Sushisource and bergundy April 7, 2026 17:52

bergundy approved these changes Apr 7, 2026

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Sushisource approved these changes Apr 8, 2026

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dandavison reviewed Apr 9, 2026

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fretz12 and others added 8 commits April 9, 2026 20:06

Add start delay, callbacks, and links to StartActivityExecutionRequest

42e3e05

Added links/callbacks to describe and start responses Update openapi

Fix proto numbering

507bf79

Update temporal/api/workflowservice/v1/request_response.proto

2f05ad9

Co-authored-by: Quinn Klassen <klassenq@gmail.com>

Update temporal/api/activity/v1/message.proto

de1c70f

Co-authored-by: Spencer Judge <spencer@temporal.io>

Update openapi

bb77190

Address PR comments

f0deaf5

Address PR comments

05c3da9

Update openapi

2bc9df1

fretz12 force-pushed the fredtzeng/saa-api-features branch from 8f2ca2c to 2bc9df1 Compare April 10, 2026 03:12

fretz12 requested a review from dandavison April 10, 2026 03:16

dandavison approved these changes Apr 10, 2026

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Refactored callback info to a shared message

c11d581

fretz12 requested review from bergundy and dandavison April 10, 2026 18:41

bergundy approved these changes Apr 10, 2026

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dandavison reviewed Apr 10, 2026

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Changed callback info field name

4f01fa3

dandavison approved these changes Apr 10, 2026

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fretz12 merged commit 6f298e7 into master Apr 10, 2026
4 checks passed

fretz12 deleted the fredtzeng/saa-api-features branch April 10, 2026 21:35

	// Links associated with the activity.
	// Links to entities associated with this activity, for example
	// to the entity that started this activity.

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fretz12 commented Apr 7, 2026 •

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dandavison Apr 9, 2026 •

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