feat: add hook data support #1620

alexandraoberaigner · 2025-09-19T12:24:57Z

This PR

this re-adds hook data support avoiding breaking changes in the binary (we introduced with v1.18.0)

Related Issues

#1472

###Notes

With v1.18.1 we reverted the hook data feature:

revert hook data to resolve bytecode incompatibility (#1613) (9845601)

gemini-code-assist · 2025-09-19T12:25:22Z

Summary of Changes

Hello @alexandraoberaigner, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request reintroduces and refines the support for HookData within the OpenFeature SDK, allowing individual hooks to maintain state across their lifecycle stages during a flag evaluation. This feature was previously removed in v1.18.0 and is now brought back without introducing breaking changes to the binary. The implementation ensures that each hook instance receives its own isolated data store, enabling more complex and stateful hook logic.

Highlights

Reintroduction of Hook Data Support: The pull request re-enables the ability for hooks to store and retrieve data across their various execution stages during a flag evaluation, a feature previously removed in v1.18.0.
New HookData Interface and Implementation: A new HookData interface is introduced, along with a DefaultHookData implementation, providing a mechanism for hooks to maintain state isolated to a single flag evaluation.
Enhanced HookContext: The HookContext class is updated to include a HookData field, allowing hooks to access their specific data store throughout the evaluation process.
Updated Hook Lifecycle Management: The HookSupport class is refactored to manage HookData instances, ensuring they are created per hook and passed correctly through the before, after, error, and finallyAfter stages.
Comprehensive Testing: New unit tests for HookData and HookContextWithData are added, and existing HookSupport tests are extended to validate the correct isolation and persistence of hook data across stages.

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Code Review

This pull request re-introduces hook data support, which is a great addition for allowing hooks to maintain state across execution stages. The implementation is solid, with good test coverage for the new functionality. I've identified a few areas for improvement, mainly concerning code clarity, consistency, and a potential thread-safety issue in the HookData implementation. My detailed comments and suggestions are provided below.

src/main/java/dev/openfeature/sdk/HookData.java

src/main/java/dev/openfeature/sdk/HookSupport.java

src/main/java/dev/openfeature/sdk/OpenFeatureClient.java

src/main/java/dev/openfeature/sdk/Pair.java

src/main/java/dev/openfeature/sdk/HookContextWithData.java

src/main/java/dev/openfeature/sdk/HookContext.java

src/test/java/dev/openfeature/sdk/benchmark/AllocationBenchmark.java

Signed-off-by: Alexandra Oberaigner <[email protected]>

Signed-off-by: Guido Breitenhuber <[email protected]>

src/main/java/dev/openfeature/sdk/HookContext.java

aepfli

I do like the object based approach, but i have a hard time supporting the changes how hooksupport/hookexecutor is created for each execution. We are bound now for testing, and have no easy way to replace this implementation with a different one.

src/main/java/dev/openfeature/sdk/HookExecutor.java

src/main/java/dev/openfeature/sdk/DefaultHookData.java

aepfli · 2025-09-23T19:19:30Z

src/main/java/dev/openfeature/sdk/OpenFeatureClient.java

+                    new SharedHookContext(key, type, this.getMetadata(), provider.getMetadata(), defaultValue);
+
+            var evalContext = mergeEvaluationContext(ctx);
+            hookExecutor = HookExecutor.create(mergedHooks, sharedHookContext, evalContext, hints);


[issue] Static constructors for object regularly used adds a lot of complexity for testing, we are now heavily bound during the testing of the OpenFeatureClient to the hookExecutor, mocking is only possible with advanced tooling manipulating the bytecode heavily. Although i like the idea of creating one executor per evaluation, i think this adds more complexity to the code now, and maintainability is decreased. Especially our hotpath should be easy to test without dependencies. Hence for clarity i am oppose introducing static creator methods for logic related objects.

Pls let me know if the current changes are going into the direction you had in mind :)

it is going into the direction, but does not solve the issue, that our logic is still tightly coupled. We should keep the initialization within the constructor of our openFeatureClient, and split logic and data into two separate objects.

pls rereview

src/test/java/dev/openfeature/sdk/DefaultHookDataTest.java

…tic factory method to ctor Signed-off-by: Alexandra Oberaigner <[email protected]>

Signed-off-by: Alexandra Oberaigner <[email protected]>

src/main/java/dev/openfeature/sdk/HookSupport.java

chrfwow · 2025-09-25T07:06:06Z

src/main/java/dev/openfeature/sdk/HookSupport.java

+                    Optional.ofNullable(hook.before(hookContext, hints)).orElse(Optional.empty());
+            if (returnedEvalContext.isPresent()) {
+                // update shared evaluation context for all hooks
+                setEvaluationContext(evaluationContext.merge(returnedEvalContext.get()));


I wonder if we should collect all hook contexts in a list and merge them only after the loop. This would mean that the context changes of a hook cannot be read by another hook. Not sure if this would be spec compliant though

I couldn't find something in the spec right away, but with merging it right away we will be at least consistent with what is implemented in dotnet

chrfwow · 2025-09-25T07:08:50Z

src/main/java/dev/openfeature/sdk/OpenFeatureClient.java

            details.setErrorMessage(e.getMessage());
            enrichDetailsWithErrorDefaults(defaultValue, details);
-            hookSupport.errorHooks(type, afterHookContext, e, mergedHooks, hints);
+            hookSupport.executeErrorHooks(e);


add non null check to hookSupport

does this still apply? & if so, can you elaborate how/why you would add the null check?

chrfwow · 2025-09-25T11:39:32Z

src/main/java/dev/openfeature/sdk/HookContext.java

+        return sharedContext.getProviderMetadata();
+    }
+
+    @SuppressFBWarnings(value = "EI_EXPOSE_REP", justification = "Intentional exposure of hookData")


I wonder why this is needed. HookData is already public

spotbugs complained... 🤔

chrfwow · 2025-09-25T11:52:26Z

src/main/java/dev/openfeature/sdk/HookSupportData.java

+ * Encapsulates data for hook execution per flag evaluation
+ */
+@Getter
+class HookSupportData {


I don't see the value of separating HookSupport and HookSupportData. We need to create a new object for every flag evaluation anyway

This was my solution to @aepfli's comment here. It should simplify testing

src/main/java/dev/openfeature/sdk/OpenFeatureClient.java

Signed-off-by: Alexandra Oberaigner <[email protected]>

codecov · 2025-09-25T15:41:22Z

Codecov Report

❌ Patch coverage is 84.32836% with 21 lines in your changes missing coverage. Please review.
✅ Project coverage is 92.37%. Comparing base (3ef41f5) to head (ab2a549).
⚠️ Report is 11 commits behind head on main.

Files with missing lines	Patch %	Lines
...in/java/dev/openfeature/sdk/SharedHookContext.java	50.00%	8 Missing ⚠️
...main/java/dev/openfeature/sdk/DefaultHookData.java	73.68%	5 Missing ⚠️
src/main/java/dev/openfeature/sdk/HookContext.java	81.81%	0 Missing and 4 partials ⚠️
...in/java/dev/openfeature/sdk/OpenFeatureClient.java	90.00%	0 Missing and 2 partials ⚠️
src/main/java/dev/openfeature/sdk/ObjectHook.java	0.00%	1 Missing ⚠️
src/main/java/dev/openfeature/sdk/Pair.java	87.50%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #1620      +/-   ##
============================================
+ Coverage     92.06%   92.37%   +0.31%     
- Complexity      488      519      +31     
============================================
  Files            46       51       +5     
  Lines          1184     1272      +88     
  Branches        105      114       +9     
============================================
+ Hits           1090     1175      +85     
- Misses           62       63       +1     
- Partials         32       34       +2

Flag	Coverage Δ
unittests	`92.37% <84.32%> (+0.31%)`	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
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Signed-off-by: Alexandra Oberaigner <[email protected]>

sonarqubecloud · 2025-09-25T16:28:07Z

Quality Gate passed

Issues
42 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

alexandraoberaigner requested review from a team as code owners September 19, 2025 12:24

gemini-code-assist bot reviewed Sep 19, 2025

View reviewed changes

alexandraoberaigner changed the title ~~feat: add hook data support~~ [DRAFT] feat: add hook data support Sep 19, 2025

aepfli reviewed Sep 19, 2025

View reviewed changes

src/main/java/dev/openfeature/sdk/HookContextWithData.java Outdated Show resolved Hide resolved

chrfwow reviewed Sep 22, 2025

View reviewed changes

src/main/java/dev/openfeature/sdk/HookContext.java Outdated Show resolved Hide resolved

src/test/java/dev/openfeature/sdk/benchmark/AllocationBenchmark.java Outdated Show resolved Hide resolved

alexandraoberaigner force-pushed the feat/hook-data-support branch 2 times, most recently from 9d41b69 to 0761dd1 Compare September 22, 2025 11:08

alexandraoberaigner changed the title ~~[DRAFT] feat: add hook data support~~ feat: add hook data support Sep 22, 2025

alexandraoberaigner force-pushed the feat/hook-data-support branch from 0761dd1 to 84124f8 Compare September 23, 2025 05:22

feat: add hook data support

269dfe4

Signed-off-by: Alexandra Oberaigner <[email protected]>

alexandraoberaigner force-pushed the feat/hook-data-support branch from 84124f8 to 269dfe4 Compare September 23, 2025 05:26

feat: gemini suggestions

3b113c1

Signed-off-by: Alexandra Oberaigner <[email protected]>

alexandraoberaigner force-pushed the feat/hook-data-support branch from a4f18c3 to 3b113c1 Compare September 23, 2025 06:33

alexandraoberaigner and others added 5 commits September 23, 2025 14:25

feat: hook executor impl (WIP)

5fb278b

Signed-off-by: Alexandra Oberaigner <[email protected]>

Use shared hook context

ceedffd

Signed-off-by: Guido Breitenhuber <[email protected]>

Split HookData interface and implementation

2843298

Signed-off-by: Guido Breitenhuber <[email protected]>

Atopted tests

235abba

Signed-off-by: Guido Breitenhuber <[email protected]>

Remove obsolete test

e0935f3

Signed-off-by: Guido Breitenhuber <[email protected]>

aepfli reviewed Sep 23, 2025

View reviewed changes

src/main/java/dev/openfeature/sdk/HookContext.java Outdated Show resolved Hide resolved

aepfli requested changes Sep 23, 2025

View reviewed changes

alexandraoberaigner added 3 commits September 24, 2025 16:45

HookSupport improvements: rename back to old name, move code from sta…

dbfcab6

…tic factory method to ctor Signed-off-by: Alexandra Oberaigner <[email protected]>

PR suggestion: use concrete hooks

a3ed93e

Signed-off-by: Alexandra Oberaigner <[email protected]>

PR suggestions: DefaultHookData access modifier, no star imports

3ea9894

Signed-off-by: Alexandra Oberaigner <[email protected]>

chrfwow reviewed Sep 25, 2025

View reviewed changes

feat: separate hook support data from logic, PR suggestions

27f3e2a

Signed-off-by: Alexandra Oberaigner <[email protected]>

alexandraoberaigner force-pushed the feat/hook-data-support branch from 011a6e4 to 21d8b12 Compare September 25, 2025 12:27

Update DefaultHookDataTest.java spotless

4ab14bf

Signed-off-by: Alexandra Oberaigner <[email protected]>

alexandraoberaigner force-pushed the feat/hook-data-support branch from 21d8b12 to 4ab14bf Compare September 25, 2025 12:33

fix tests, spotless apply

1d8f758

Signed-off-by: Alexandra Oberaigner <[email protected]>

exclude lombok generated functions from codecov

ab2a549

Signed-off-by: Alexandra Oberaigner <[email protected]>

feat: add hook data support #1620

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feat: add hook data support #1620

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