feat: Add plugin support to Client SDK by abelonogov-ld · Pull Request #229 · launchdarkly/dotnet-core

abelonogov-ld · 2026-02-25T19:38:40Z

Summary

This PR adds plugin architecture and hook-based flag evaluation lifecycle support to the LaunchDarkly Client SDK for .NET, ported from the Server SDK implementation.

Plugin System

Introduced a Plugin base class (Plugins/Plugin.cs) that provides a GetHooks() method, allowing plugins to register hooks with the SDK
Added PluginConfiguration and PluginConfigurationBuilder to configure plugins via ConfigurationBuilder.Plugins()
Updated LdClient to initialize plugins during startup, collect their hooks, and dispose of them properly during shutdown
Refactored LdClient cleanup logic to ensure proper disposal order of resources

Hook Framework

Hook base class with virtual BeforeEvaluation, AfterEvaluation, BeforeIdentify, and AfterIdentify stage methods, plus IDisposable support
EvaluationSeriesContext - captures flag key, context, default value, method, and environment ID for evaluation hooks
IdentifySeriesContext / IdentifySeriesResult - context and result types for identify hooks
Method constants mapping to SDK variation methods (e.g. LdClient.BoolVariation)
SeriesDataBuilder - fluent API for building immutable series data passed between hook stages

Hook Execution Engine

Executor / NoopExecutor implementing IHookExecutor - manages hook lifecycle with proper forward/reverse ordering
BeforeEvaluation / AfterEvaluation stage executors with error isolation - exceptions in one hook do not prevent other hooks from executing
Integrated hook execution into LdClient.EvaluateInternal(), wrapping flag evaluations with BeforeEvaluation and AfterEvaluation calls
Added GetMethodName<T>() to resolve the correct Method constant based on variation type and detail mode
Fixed prerequisite evaluation to use EvaluateInternal directly, avoiding recursive hook invocations

Test Plan

EvaluationSeriesTest - hooks execute in LIFO order (forward before, reverse after)
EvaluationSeriesTest - exceptions in hook stages don't prevent other hooks from running
EvaluationSeriesTest - stage failures log expected error messages with flag key and hook name
EvaluationSeriesTest - disposing executor disposes all registered hooks
PluginConfigurationBuilderTest - plugin configuration builder tests pass
LdClientPluginTests - end-to-end plugin/hook integration tests pass
All 7 evaluation series tests pass (dotnet test --filter EvaluationSeriesTest)

Note

Medium Risk
Touches core LdClient evaluation flow by wrapping all Variation* calls with hook execution and adds plugin registration at startup, so regressions could affect flag evaluation behavior/performance despite safeguards like noop execution when unconfigured.

Overview
Adds client-side plugin support by introducing PluginConfigurationBuilder/PluginConfiguration and wiring a new Plugins(...) option through Components, ConfigurationBuilder, and Configuration.

Integrates plugin lifecycle into LdClient initialization: builds plugin config, creates EnvironmentMetadata, collects plugin-provided Hooks, instantiates a hook Executor (or NoopExecutor when none), then registers plugins; hook execution is disposed with the client and logs under a new LogNames.HooksSubLog.

Introduces a hook API and execution pipeline for evaluations (Hook, EvaluationSeriesContext, stage executors) and wraps VariationInternal so hooks run before/after evaluations; prerequisite evaluations are refactored to call EvaluateInternal directly to avoid triggering hooks. Adds unit tests covering hook ordering/error isolation/disposal and plugin builder/registration behavior.

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pkgs/sdk/client/src/LdClient.cs

…sources

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pkgs/sdk/client/src/LdClient.cs

…ailable before registration

tanderson-ld · 2026-02-27T15:33:17Z

pkgs/sdk/client/src/Plugins/Plugin.cs

Do you need onPluginsReady in the base plugin? I think this was added to solve the "two plugins need each other" interaction back when Agustine was working on Replay and Observability being separate plugins but needing to wait until both registered. Spec requirement

My impression is it makes sense to add while you're working on this story.

I needed that logic but I did workaround in Obs-SDK, I count number of getHooks calls and number of register calls. When they are equal it means everything is ready

tanderson-ld · 2026-02-27T15:39:39Z

pkgs/sdk/client/src/LdClient.cs

+
+            var applicationMetadata = new ApplicationMetadata(
+                applicationInfo.ApplicationId,
+                applicationInfo.ApplicationVersion


There is also Name and VersionName params that should be carried over.

tanderson-ld · 2026-02-27T15:41:23Z

pkgs/sdk/client/src/Plugins/Plugin.cs

Do you need to add optional fields id and version in PluginMetadata? https://github.com/launchdarkly/sdk-specs/tree/main/specs/PLUGIN-sdk-plugin-support#requirement-113

Also related to the same sort of problem Agustine was solving.

tanderson-ld · 2026-02-27T15:43:34Z

pkgs/sdk/client/src/LdClient.cs

+            }
+
+            _hookExecutor = _pluginHooks.Any()
+                ? (IHookExecutor)new Executor(_log.SubLogger(LogNames.HooksSubLog), _pluginHooks)


_pluginHooks is only used here. Does it need to be a private member on LDClient? Could it just be local in this function that populates it.

tanderson-ld · 2026-02-27T15:48:25Z

pkgs/sdk/client/src/LdClient.cs


+            PluginConfiguration pluginConfig = null;
+            EnvironmentMetadata environmentMetadata = null;
+            if (_config.Plugins != null)


The nullity, null checks, assignment, and usage of nullables in these next 20 lines of code seems fragile. Consider structuring differently so that their interaction is easier to discern.

tanderson-ld · 2026-02-27T15:51:42Z

pkgs/sdk/client/src/LdClient.cs


+            PluginConfiguration pluginConfig = null;
+            EnvironmentMetadata environmentMetadata = null;
+            if (_config.Plugins != null)


I think the server SDK uses Components.Plugins() if no config is provided. This may be an option to deal with the missing config in an elegant way.

tanderson-ld · 2026-02-27T16:06:43Z

pkgs/sdk/client/src/Hooks/Hook.cs

+        /// <param name="context">parameters associated with this identify operation</param>
+        /// <param name="data">user-configurable data, currently empty</param>
+        /// <returns>user-configurable data, which will be forwarded to <see cref="AfterIdentify"/></returns>
+        public virtual SeriesData BeforeIdentify(IdentifySeriesContext context, SeriesData data) =>


I don't see BeforeIdentify and AfterIdentify being invoked anywhere. Is that in scope of this PR? Seems like it must be if the Hook is now available. Also need tests for this case.

It will be another PR

Ryan said that Evaluation flag is must to be PR mergable

tanderson-ld · 2026-02-27T16:12:45Z

pkgs/sdk/client/src/LdClient.cs

            bool checkType, EventFactory eventFactory)
+        {
+            var evalSeriesContext = new EvaluationSeriesContext(featureKey, Context, defaultJson,
+                GetMethodName<T>(eventFactory));


Is environment id ever passed in to evaluation series context? I can't recall if Dotnet Client got support for this from the data source (ultimately from the headers on the responses from the server).

abelonogov-ld added 2 commits February 25, 2026 10:44

Plugin support for CliendSDK

da37078

Plugin tests

7aee7be

abelonogov-ld requested a review from a team as a code owner February 25, 2026 19:38

abelonogov-ld changed the title ~~feat: Plugin support for CliendSDK~~ feat: Add plugin support to Client SDK Feb 25, 2026

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abelonogov-ld added 2 commits February 25, 2026 13:18

Refactor LdClient cleanup logic to ensure proper disposal order of re…

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Merge branch 'main' into andrey/clientsdk-plugins-and-hooks

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tanderson-ld self-requested a review February 26, 2026 17:10

Flag Evaluations hook

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abelonogov-ld changed the title ~~feat: Add plugin support to Client SDK~~ WIP feat: Add plugin support to Client SDK Feb 26, 2026

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abelonogov-ld added 2 commits February 26, 2026 13:25

Refactor plugin registration logic in LdClient to ensure hooks are av…

5c8ddd4

…ailable before registration

remove unnecessary parameter

e5d9dc0

abelonogov-ld changed the title ~~WIP feat: Add plugin support to Client SDK~~ feat: Add plugin support to Client SDK Feb 26, 2026

tanderson-ld requested changes Feb 27, 2026

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Summary

Plugin System

Hook Framework

Hook Execution Engine

Test Plan

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abelonogov-ld Feb 27, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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abelonogov-ld commented Feb 25, 2026 •

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abelonogov-ld Feb 27, 2026 •

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