Add CreateCallbackAsync and WaitForCallbackAsync (DOTNET-8660) by GarrettBeatty · Pull Request #2373 · aws/aws-lambda-dotnet

GarrettBeatty · 2026-05-14T21:41:42Z

Fixes DOTNET-8660. Stacked on top of #2372 (Wave 0 cross-cutting types).

What

Adds callback support to Amazon.Lambda.DurableExecution. A workflow can now hand a service-allocated CallbackId to an external system (a queue consumer, a human-approval UI, a long-running job runner) and suspend until that system reports back via the durable execution service. Two entry points: a low-level handle (CreateCallbackAsync) and the common "submit + wait" composition (WaitForCallbackAsync).

Public API:

Type	Purpose
`IDurableContext.CreateCallbackAsync<T>(...)`	Allocate a callback; returns an `ICallback<T>` handle. Errors are deferred to `GetResultAsync` so user code between create and await runs deterministically across replays.
`IDurableContext.WaitForCallbackAsync<T>(...)`	Composite: `CreateCallback` + submitter step + `GetResultAsync` inside a child context. Common path for "submit job, wait for completion".
`ICallback<T>`	Handle exposing `CallbackId` (give to the external system) and `GetResultAsync` (suspends until completion).
`IWaitForCallbackContext`	Logger-only context passed to the submitter delegate. Distinct from `IStepContext` so the submitter API can evolve independently.
`CallbackConfig`	`Timeout` + `HeartbeatTimeout`. Sub-second positive values are rejected (service timer granularity is 1s); `TimeSpan.Zero` disables.
`WaitForCallbackConfig : CallbackConfig`	Adds `RetryStrategy` for the submitter step.
`CallbackException` (base) + `CallbackFailedException`, `CallbackTimeoutException`, `CallbackSubmitterException`	Subclass tree so `catch` clauses can pattern-match the failure mode. Carries `CallbackId`, `ErrorType`, `ErrorData`, `OriginalStackTrace`.

Both APIs read the ILambdaSerializer from ILambdaContext.Serializer (typically registered via LambdaBootstrapBuilder.Create(handler, serializer)) and throw InvalidOperationException if no serializer is registered. AOT and reflection-based scenarios share a single overload — the AOT story is determined entirely by the registered serializer (e.g., SourceGeneratorLambdaJsonSerializer<TContext> for AOT).

How

Internal/CallbackOperation<T> mirrors the Step/Wait pattern from #2360 and the child-context pattern from #2370:

Fresh execution. Synchronously flushes a CALLBACK START checkpoint. The service stamps a freshly-allocated CallbackId onto the response; LambdaDurableServiceClient gains an onNewOperations hook so that ID flows back into ExecutionState during the START flush, where the operation can read it. The handle is returned immediately — CreateCallbackAsync always succeeds.
GetResultAsync suspends. On the invocation that first reaches the await, the workflow hits Termination.SuspendAndAwait and Lambda exits. When the external system delivers a result, the service re-invokes; replay observes the terminal checkpoint and returns (or throws) immediately.
Replay. SUCCEEDED returns the cached value (deserialized via the registered ILambdaSerializer). FAILED throws CallbackFailedException. TIMED_OUT throws CallbackTimeoutException. STARTED / PENDING re-suspend (external system hasn't responded yet). Any other status throws NonDeterministicExecutionException.
Deferred error propagation. Terminal status observed during Start/Replay is stashed on _terminalReplay and only resolved inside GetResultAsync. This keeps CreateCallbackAsync deterministically successful, so user code between create and await sees the same control flow on fresh execution and replay.
WaitForCallbackAsync composes RunInChildContextAsync (from Add RunInChildContextAsync #2370) + CreateCallbackAsync + a submitter StepAsync + GetResultAsync. The child-context wrapper gives a clean observability boundary (SubType = WaitForCallback) and a single error-mapping site: submitter step failures surface as CallbackSubmitterException; callback failures/timeouts preserve their subclass through child-context replay (a CallbackTimeoutException thrown inside the child remains a CallbackTimeoutException after the parent CONTEXT-FAILED replay).

Testing

42 new unit tests across CallbackOperationTests, WaitForCallbackTests, DurableFunctionTests, and ExceptionsTests:

Fresh execution + sync-flush of CALLBACK START (CallbackId stamped onto state).
Suspend on first GetResultAsync; replay returns cached value without re-running.
Terminal-state replay: SUCCEEDED deserializes, FAILED throws CallbackFailedException, TIMED_OUT throws CallbackTimeoutException.
STARTED/PENDING replay re-suspends; unknown status throws NonDeterministicExecutionException.
CreateCallbackAsync is always successful even for terminal-state replays (deferred error propagation).
CallbackConfig.Timeout / HeartbeatTimeout validation: rejects negative and sub-second positive values, accepts TimeSpan.Zero.
WaitForCallbackAsync: submitter receives the CallbackId; submitter failure (after retries exhausted) surfaces as CallbackSubmitterException; callback failure/timeout subclass survives parent CONTEXT-FAILED replay; happy-path returns the deserialized result.
Exception type hierarchy + property serialization round-trip.

5 new integration tests (require AWS credentials to run):
CreateCallbackHappyPath, CallbackTimeout, CallbackFailed, WaitForCallbackHappyPath, WaitForCallbackSubmitterFails. Each ships a deployable test function + Dockerfile under IntegrationTests/TestFunctions/.

203/203 unit tests pass on net8.0 and net10.0 (161 base + 42 new). Production build clean: 0 warnings, TreatWarningsAsErrors enforced.

Out of scope (follow-up PRs)

InvokeAsync / MapAsync / ParallelAsync / WaitForConditionAsync
DefaultJsonCheckpointSerializer
DurableLogger replay-suppression (currently NullLogger)
Annotations source-generator integration / [DurableExecution] attribute
DurableTestRunner / Amazon.Lambda.DurableExecution.Testing package
dotnet new lambda.DurableFunction blueprint

+
+COPY bin/publish/ ${LAMBDA_TASK_ROOT}
+
+ENTRYPOINT ["/var/task/bootstrap"]


+
+COPY bin/publish/ ${LAMBDA_TASK_ROOT}
+
+ENTRYPOINT ["/var/task/bootstrap"]


+
+COPY bin/publish/ ${LAMBDA_TASK_ROOT}
+
+ENTRYPOINT ["/var/task/bootstrap"]


+
+COPY bin/publish/ ${LAMBDA_TASK_ROOT}
+
+ENTRYPOINT ["/var/task/bootstrap"]


+
+COPY bin/publish/ ${LAMBDA_TASK_ROOT}
+
+ENTRYPOINT ["/var/task/bootstrap"]


stack-info: PR: #2363, branch: GarrettBeatty/stack/3

Adds child-context support to the .NET Durable Execution SDK. A child context is a logical sub-workflow with its own deterministic operation-ID space, persisted as a CONTEXT operation so subsequent invocations replay the cached value without re-executing the function. Public surface: - IDurableContext.RunInChildContextAsync<T> (reflection + AOT-safe ICheckpointSerializer<T> overloads, plus a void overload). - ChildContextConfig with SubType (observability label) and ErrorMapping (transform exceptions before they surface to the caller). - ChildContextException for failure surfacing. Used as a building block for upcoming WaitForCallbackAsync. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

+
+COPY bin/publish/ ${LAMBDA_TASK_ROOT}
+
+ENTRYPOINT ["/var/task/bootstrap"]


Adds callback support to the .NET Durable Execution SDK. CreateCallbackAsync returns an ICallback<T> handle (CallbackId + GetResultAsync) that suspends the workflow until an external system delivers a result via the durable execution service. WaitForCallbackAsync composes CreateCallback + a submitter step + GetResultAsync inside a child context for the common "submit and wait" pattern. Public surface: - IDurableContext.CreateCallbackAsync<T> (single overload) - IDurableContext.WaitForCallbackAsync<T> (single overload) - ICallback<T> with CallbackId and GetResultAsync - IWaitForCallbackContext (Logger only) for submitter functions - CallbackConfig (Timeout + HeartbeatTimeout, validates sub-second values) - WaitForCallbackConfig : CallbackConfig adds RetryStrategy - Exception subclass tree: CallbackException base + CallbackFailedException, CallbackTimeoutException, CallbackSubmitterException Both APIs read the ILambdaSerializer from ILambdaContext.Serializer (typically registered via LambdaBootstrapBuilder.Create(handler, serializer)) and throw InvalidOperationException if no serializer is registered. AOT and reflection-based scenarios share a single overload — the AOT story is determined by the registered serializer. Internal: - CallbackOperation<T> handles fresh execution sync-flush of START with service-allocated CallbackId, deferred error propagation, and replay for SUCCEEDED/FAILED/TIMED_OUT/STARTED/PENDING. Unknown statuses throw NonDeterministicExecutionException. - LambdaDurableServiceClient gains an onNewOperations callback so the freshly-allocated CallbackId from NewExecutionState flows back into ExecutionState during the START flush. - WaitForCallback's error mapping preserves subclass fidelity on parent-CONTEXT-FAILED replay (CallbackTimeoutException remains CallbackTimeoutException, etc.). Adds unit tests + integration tests covering happy path, timeout, failure, submitter failure, replay determinism, and replay of each exception subtype. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

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Pull request overview

Adds first-class callback support to the Amazon.Lambda.DurableExecution .NET SDK, enabling workflows to pause until an external system completes a callback, and providing a convenience “submit + wait” composite API.

Changes:

Introduces CreateCallbackAsync<T> / ICallback<T> for durable callback handles and result retrieval.
Adds WaitForCallbackAsync<T> with WaitForCallbackConfig + IWaitForCallbackContext, including retry wiring and error remapping.
Extends checkpoint plumbing to merge service-returned NewExecutionState.Operations into in-memory ExecutionState, plus broad unit/integration test coverage and design-doc updates.

Reviewed changes

Copilot reviewed 43 out of 43 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
Libraries/test/Amazon.Lambda.DurableExecution.Tests/WaitForCallbackTests.cs	New unit tests covering `WaitForCallbackAsync` behavior, naming, determinism, and exception mapping.
Libraries/test/Amazon.Lambda.DurableExecution.Tests/RecordingBatcher.cs	Adds a flush hook used by tests to simulate service-side state updates (e.g., CallbackId allocation).
Libraries/test/Amazon.Lambda.DurableExecution.Tests/MockLambdaClient.cs	Adds a customizable checkpoint response handler for tests modeling `NewExecutionState` behavior.
Libraries/test/Amazon.Lambda.DurableExecution.Tests/ExceptionsTests.cs	Adds ctor/property tests for new callback exception types.
Libraries/test/Amazon.Lambda.DurableExecution.Tests/DurableFunctionTests.cs	Adds end-to-end unit tests through `DurableFunction.WrapAsync` for callback allocation/replay determinism.
Libraries/test/Amazon.Lambda.DurableExecution.Tests/CallbackOperationTests.cs	New unit tests covering callback operation start/replay/result/error behavior and serializer requirements.
Libraries/test/Amazon.Lambda.DurableExecution.IntegrationTests/WaitForCallbackSubmitterFailsTest.cs	New integration test validating submitter failure surfaces as `CallbackSubmitterException`.
Libraries/test/Amazon.Lambda.DurableExecution.IntegrationTests/WaitForCallbackHappyPathTest.cs	New integration test validating two-Lambda “external system” happy path for `WaitForCallbackAsync`.
Libraries/test/Amazon.Lambda.DurableExecution.IntegrationTests/TestFunctions/WaitForCallbackSubmitterFailsFunction/WaitForCallbackSubmitterFailsFunction.csproj	New test function project used by integration tests.
Libraries/test/Amazon.Lambda.DurableExecution.IntegrationTests/TestFunctions/WaitForCallbackSubmitterFailsFunction/Function.cs	Workflow test function that intentionally fails the submitter.
Libraries/test/Amazon.Lambda.DurableExecution.IntegrationTests/TestFunctions/WaitForCallbackSubmitterFailsFunction/Dockerfile	Container packaging for the submitter-failure integration test function.
Libraries/test/Amazon.Lambda.DurableExecution.IntegrationTests/TestFunctions/WaitForCallbackHappyPathFunction/WaitForCallbackHappyPathFunction.csproj	New test function project for happy-path WaitForCallback integration.
Libraries/test/Amazon.Lambda.DurableExecution.IntegrationTests/TestFunctions/WaitForCallbackHappyPathFunction/Function.cs	Workflow test function that invokes an external approver Lambda and waits for callback completion.
Libraries/test/Amazon.Lambda.DurableExecution.IntegrationTests/TestFunctions/WaitForCallbackHappyPathFunction/Dockerfile	Container packaging for the happy-path workflow function.
Libraries/test/Amazon.Lambda.DurableExecution.IntegrationTests/TestFunctions/CreateCallbackHappyPathFunction/Function.cs	Workflow test function that uses `CreateCallbackAsync` and suspends on `GetResultAsync`.
Libraries/test/Amazon.Lambda.DurableExecution.IntegrationTests/TestFunctions/CreateCallbackHappyPathFunction/Dockerfile	Container packaging for CreateCallback happy-path integration test function.
Libraries/test/Amazon.Lambda.DurableExecution.IntegrationTests/TestFunctions/CreateCallbackHappyPathFunction/CreateCallbackHappyPathFunction.csproj	New CreateCallback integration test function project.
Libraries/test/Amazon.Lambda.DurableExecution.IntegrationTests/TestFunctions/CallbackTimeoutFunction/Function.cs	Workflow test function validating callback timeouts via `CallbackConfig.Timeout`.
Libraries/test/Amazon.Lambda.DurableExecution.IntegrationTests/TestFunctions/CallbackTimeoutFunction/Dockerfile	Container packaging for callback-timeout integration test function.
Libraries/test/Amazon.Lambda.DurableExecution.IntegrationTests/TestFunctions/CallbackTimeoutFunction/CallbackTimeoutFunction.csproj	New callback-timeout integration test function project.
Libraries/test/Amazon.Lambda.DurableExecution.IntegrationTests/TestFunctions/CallbackFailedFunction/Function.cs	Workflow test function validating callback failure delivery via `SendDurableExecutionCallbackFailure`.
Libraries/test/Amazon.Lambda.DurableExecution.IntegrationTests/TestFunctions/CallbackFailedFunction/Dockerfile	Container packaging for callback-failure integration test function.
Libraries/test/Amazon.Lambda.DurableExecution.IntegrationTests/TestFunctions/CallbackFailedFunction/CallbackFailedFunction.csproj	New callback-failure integration test function project.
Libraries/test/Amazon.Lambda.DurableExecution.IntegrationTests/TestFunctions/ApproverFunction/Function.cs	External “approver” Lambda that completes callbacks via `SendDurableExecutionCallbackSuccess`.
Libraries/test/Amazon.Lambda.DurableExecution.IntegrationTests/TestFunctions/ApproverFunction/Dockerfile	Container packaging for external approver function.
Libraries/test/Amazon.Lambda.DurableExecution.IntegrationTests/TestFunctions/ApproverFunction/ApproverFunction.csproj	New external approver function project (includes AWSSDK.Lambda).
Libraries/test/Amazon.Lambda.DurableExecution.IntegrationTests/DurableFunctionDeployment.cs	Enhances deployment helper to optionally deploy a paired external Lambda; adds cross-process build locking.
Libraries/test/Amazon.Lambda.DurableExecution.IntegrationTests/CreateCallbackHappyPathTest.cs	New integration test for CreateCallback success delivery.
Libraries/test/Amazon.Lambda.DurableExecution.IntegrationTests/CallbackTimeoutTest.cs	New integration test for callback timeout surface/type recording.
Libraries/test/Amazon.Lambda.DurableExecution.IntegrationTests/CallbackFailedTest.cs	New integration test for callback failure surface/type recording.
Libraries/src/Amazon.Lambda.DurableExecution/WaitForCallbackConfig.cs	Adds configuration type for WaitForCallback (inherits callback timeouts + submitter retry strategy).
Libraries/src/Amazon.Lambda.DurableExecution/Services/LambdaDurableServiceClient.cs	Adds `onNewOperations` callback to checkpointing and maps callback ops from `NewExecutionState`.
Libraries/src/Amazon.Lambda.DurableExecution/Operation.cs	Adds `WaitForCallback` subtype constant and `TIMED_OUT` status constant.
Libraries/src/Amazon.Lambda.DurableExecution/IWaitForCallbackContext.cs	New submitter-context interface (logger-only) for `WaitForCallbackAsync`.
Libraries/src/Amazon.Lambda.DurableExecution/Internal/LambdaSerializerHelper.cs	Centralizes “serializer required” enforcement and message.
Libraries/src/Amazon.Lambda.DurableExecution/Internal/CallbackOperation.cs	Implements durable callback operation semantics and `ICallback<T>` handle behavior.
Libraries/src/Amazon.Lambda.DurableExecution/IDurableContext.cs	Adds public API surface for `CreateCallbackAsync<T>` and `WaitForCallbackAsync<T>`.
Libraries/src/Amazon.Lambda.DurableExecution/ICallback.cs	Introduces public callback handle interface (`CallbackId` + `GetResultAsync`).
Libraries/src/Amazon.Lambda.DurableExecution/DurableFunction.cs	Wires serializer helper and merges `NewExecutionState` operations into `ExecutionState` during checkpointing.
Libraries/src/Amazon.Lambda.DurableExecution/DurableContext.cs	Implements `CreateCallbackAsync` and `WaitForCallbackAsync` composition + error mapping.
Libraries/src/Amazon.Lambda.DurableExecution/CallbackException.cs	Adds callback exception hierarchy (`CallbackException` + Failed/Timeout/Submitter).
Libraries/src/Amazon.Lambda.DurableExecution/CallbackConfig.cs	Adds timeout + heartbeat timeout config with sub-second validation.
Docs/durable-execution-design.md	Updates design doc to reflect callback APIs, contexts, and exception hierarchy.

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+                Error = sdkOp.CallbackDetails.Error != null ? new ErrorObject
+                {
+                    ErrorType = sdkOp.CallbackDetails.Error.ErrorType,
+                    ErrorMessage = sdkOp.CallbackDetails.Error.ErrorMessage


+    public async Task<T> GetResultAsync(CancellationToken cancellationToken = default)
+    {
+        cancellationToken.ThrowIfCancellationRequested();
+
+        // Terminal-state checkpoint already observed by Start/Replay — return
+        // (or throw) immediately without suspending.
+        if (_terminalReplay != null)
+        {
+            return ResolveTerminal(_terminalReplay);
+        }
+
+        // No terminal state yet. Suspend the workflow; the service re-invokes
+        // when the external system delivers a result.
+        return await Termination.SuspendAndAwait<T>(
+            TerminationReason.CallbackPending,
+            $"callback:{Name ?? OperationId}");
+    }


+    private SdkCallbackOptions? BuildCallbackOptions()
+    {
+        if (_config == null) return null;
+        if (_config.Timeout == TimeSpan.Zero && _config.HeartbeatTimeout == TimeSpan.Zero) return null;
+
+        var options = new SdkCallbackOptions();
+        if (_config.Timeout > TimeSpan.Zero)
+            options.TimeoutSeconds = (int)Math.Max(1, Math.Ceiling(_config.Timeout.TotalSeconds));
+        if (_config.HeartbeatTimeout > TimeSpan.Zero)
+            options.HeartbeatTimeoutSeconds = (int)Math.Max(1, Math.Ceiling(_config.HeartbeatTimeout.TotalSeconds));
+        return options;


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GarrettBeatty force-pushed the gcbeatty/durable-wave0 branch from 464c591 to d308c3b Compare May 14, 2026 21:49

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GarrettBeatty force-pushed the gcbeatty/durable-wave0 branch from d308c3b to be4c3ad Compare May 18, 2026 15:23

GarrettBeatty force-pushed the gcbeatty/durable-callbacks branch from 1c88461 to 5cc9a04 Compare May 18, 2026 15:46

GarrettBeatty and others added 2 commits May 20, 2026 11:37

Retry

097e5a1

stack-info: PR: #2363, branch: GarrettBeatty/stack/3

GarrettBeatty force-pushed the gcbeatty/durable-wave0 branch 3 times, most recently from ad4d208 to 3acbed5 Compare May 20, 2026 17:46

update docs (#2372)

646b841

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Base automatically changed from gcbeatty/durable-wave0 to gcbeatty/durable-child-context May 20, 2026 17:46

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Comment thread ...st/Amazon.Lambda.DurableExecution.IntegrationTests/TestFunctions/ApproverFunction/Dockerfile

COPY bin/publish/ ${LAMBDA_TASK_ROOT}

ENTRYPOINT ["/var/task/bootstrap"]

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Add CreateCallbackAsync and WaitForCallbackAsync (DOTNET-8660)#2373

Add CreateCallbackAsync and WaitForCallbackAsync (DOTNET-8660)#2373
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		COPY bin/publish/ ${LAMBDA_TASK_ROOT}

		ENTRYPOINT ["/var/task/bootstrap"]

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