feat: Add environment ID support for hooks. by kinyoklion · Pull Request #594 · launchdarkly/cpp-sdks

kinyoklion · 2026-08-12T18:34:19Z

Summary

Server SDK: the X-LD-EnvID response header now reaches EvaluationSeriesContext / TrackSeriesContext, for both FDv1 and FDv2 data systems.

The environment ID travels with the data rather than through a side channel, mirroring dotnet-core#81 (InitWithMetadata → store metadata → client reads it back):

IDestination gains SetEnvironmentId(std::string); MemoryStore retains it and only reports it once initialized, so hooks never see an ID before a payload has been applied.
FDv2 sources report it on the result they already return (FDv2SourceResult::environment_id), and FDv2DataSystem writes it to the store alongside the changeset.
The FDv1 fallback adapter stamps it onto the FDv2 results it synthesizes, so fallback keeps working.
IDataSystem::EnvironmentId() is what ClientImpl passes into the hook contexts (std::nullopt for offline/lazy load).

Only successful responses count: errors, missing headers, and empty values leave the value untouched.

// FDv1 polling/streaming
sink_->SetEnvironmentId(header_value);

// FDv2
result.environment_id = ReadEnvironmentId(res.Headers());
...
change_notifier_.SetEnvironmentId(*result.environment_id);

Verified with harness hooks/evaluation/provides the environment ID (default + polling) against both v2.39.0 (FDv1) and v3.2.0-alpha.6 (FDv2), plus the server unit suite.

Link to Devin session: https://app.devin.ai/sessions/bfe54128e2804a96bb100e6120e9a3ef
Requested by: @kinyoklion

Co-Authored-By: rlamb@launchdarkly.com <4955475+kinyoklion@users.noreply.github.com>

devin-ai-integration · 2026-08-12T18:34:23Z

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devin-ai-integration · 2026-08-12T18:34:27Z

@cursor review

@kinyoklion

**Requirements** - [x] I have added test coverage for new or changed functionality - [x] I have followed the repository's [pull request submission guidelines](../blob/master/CONTRIBUTING.md#submitting-pull-requests) - [x] I have validated my changes against all supported platform versions **Related issues** Ports #410 (v2) to v3. Companion SDK work: launchdarkly/python-server-sdk#484, launchdarkly/cpp-sdks#594. **Describe the solution you've provided** Same capability and test as #410, adapted to the v3 data system: - the `hook-environment-id` capability, documented in `docs/service_spec.md` - `DataSystemOptionEnvironmentID(...)`, a top-level `SDKDataSystemOption` that makes every mock service of the data system (initializers and synchronizers, in all connection modes) send an `X-LD-EnvID` response header - an evaluation-series test (`hooks/evaluation/provides the environment ID`) asserting `evaluationSeriesContext.environmentId` on `afterEvaluation`, run against the SDK's default data source plus an explicit polling subtest for client-side/`server-side-polling` SDKs Unlike v2, where the option wrapped the single `SDKDataSource` handler, the header is applied in `createEndpoints`, so both FDv2 initializers and synchronizers report it — matching production, where the header is on every flag-delivery response. **Describe alternatives you've considered** Making the option per-connection-mode. Environment ID is a property of the environment, not of a connection mode, so a single top-level option keeps call sites simple and covers every mode. **Additional context** Verified against the FDv2 contract services of python-server-sdk (#484) and cpp-sdks (#594): `hooks/evaluation/provides the environment ID` passes for both, in default (streaming) and polling modes. Track hooks (`trackSeriesContext.environmentId`) are documented but not yet asserted, same as in v2. Link to Devin session: https://app.devin.ai/sessions/bfe54128e2804a96bb100e6120e9a3ef Requested by: @kinyoklion  --- > [!NOTE] > **Overview** > Adds the **`hook-environment-id`** capability so SDKs that read LaunchDarkly’s `X-LD-EnvID` from streaming/polling responses must surface it on hook series contexts (`evaluationSeriesContext.environmentId`, and `trackSeriesContext` when track hooks are supported). The harness documents this in `service_spec.md` and gates a new evaluation hook test on the capability. > > **Mock flag delivery** now supports `DataSystemOptionEnvironmentID(...)`, a top-level data-system option that wraps every initializer and synchronizer endpoint (all connection modes) to emit `X-LD-EnvID`, matching production flag-delivery responses in the v3 data system. > > The test **“provides the environment ID”** evaluates a flag and asserts `environmentId` on the `afterEvaluation` hook payload, under the default data source and an explicit polling subtest for client-side / server-side-polling SDKs. Track-hook `environmentId` is documented but not asserted yet (same as v2). > > <sup>Reviewed by [Cursor Bugbot](https://cursor.com/bugbot) for commit 8331c29. Bugbot is set up for automated code reviews on this repo. Configure [here](https://www.cursor.com/dashboard/bugbot).</sup>  --------- Co-authored-by: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>

Co-Authored-By: rlamb@launchdarkly.com <4955475+kinyoklion@users.noreply.github.com>

devin-ai-integration · 2026-08-12T22:47:15Z

@cursor review

Co-Authored-By: rlamb@launchdarkly.com <4955475+kinyoklion@users.noreply.github.com>

kinyoklion · 2026-08-17T18:04:14Z


 void PollingDataSource::HandlePollResult(network::HttpResult const& res) {
+    if (!res.IsError() && (res.Status() == 200 || res.Status() == 304)) {
+        if (auto const it = res.Headers().find("X-LD-EnvID");


We should have a centralized location for this header definition. Also potentially a shared function for getting this header and setting it into a sink.

Done in e2ac563 — new data_systems/environment_id_header.hpp holds kEnvironmentIdHeader, ReadEnvironmentId overloads for HttpResult and Beast headers, and a ReportEnvironmentId(destination, headers) helper. All four sites (FDv1 polling/streaming, FDv2 polling/streaming) use it, and the local copy in fdv2_polling_impl.cpp is gone.

kinyoklion · 2026-08-17T18:04:32Z

+            if (status ==
+                DataSourceEventHandler::MessageStatus::kInvalidMessage) {
                // Invalid data received - restart the connection with backoff
                // to get a fresh stream. The backoff mechanism prevents rapid
                // reconnection attempts.
                LD_LOG(self->logger_, LogLevel::kWarn)
-                    << "Received invalid data from stream, restarting connection";
+                    << "Received invalid data from stream, restarting "
+                       "connection";
                if (self->client_) {


Why were these lines changed?

Co-Authored-By: rlamb@launchdarkly.com <4955475+kinyoklion@users.noreply.github.com>

feat: Propagate environment ID to hooks

6436533

Co-Authored-By: rlamb@launchdarkly.com <4955475+kinyoklion@users.noreply.github.com>

kinyoklion self-assigned this Aug 12, 2026

devin-ai-integration Bot added the devin-pr label Aug 12, 2026

kinyoklion mentioned this pull request Aug 12, 2026

feat: Add hook-environment-id capability and test launchdarkly/sdk-test-harness#412

Merged

3 tasks

devin-ai-integration Bot and others added 2 commits August 12, 2026 21:54

ci: Re-run contract tests against the released test harness

bdbbb0c

Co-Authored-By: rlamb@launchdarkly.com <4955475+kinyoklion@users.noreply.github.com>

ci: Re-run contract tests against the released test harness

9f6f39b

Co-Authored-By: rlamb@launchdarkly.com <4955475+kinyoklion@users.noreply.github.com>

devin-ai-integration Bot changed the title ~~feat: Propagate environment ID to hooks~~ feat: Add environment ID support for hooks. Aug 12, 2026

refactor: Carry the environment ID with data payload metadata

d1cbdd5

Co-Authored-By: rlamb@launchdarkly.com <4955475+kinyoklion@users.noreply.github.com>

devin-ai-integration Bot and others added 2 commits August 12, 2026 23:16

ci: Re-run after a transient dependency fetch failure

1ca4842

Co-Authored-By: rlamb@launchdarkly.com <4955475+kinyoklion@users.noreply.github.com>

ci: Re-run after transient runner failures

abe15ec

Co-Authored-By: rlamb@launchdarkly.com <4955475+kinyoklion@users.noreply.github.com>

This was referenced Aug 13, 2026

feat: Add environment ID support for hooks launchdarkly/ruby-server-sdk#414

Draft

feat: Add environment ID support for hooks launchdarkly/java-core#202

Open

kinyoklion commented Aug 17, 2026

View reviewed changes

refactor: Centralize the environment ID header definition

e2ac563

Co-Authored-By: rlamb@launchdarkly.com <4955475+kinyoklion@users.noreply.github.com>

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