chore: Support flag change listeners in contract tests#349
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I don't see any issues, but probably makes sense to get @keelerm84 review.
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Add command constants, parameter structs, and the ListenerNotification payload type to support the three new flag change listener commands: registerFlagChangeListener, registerFlagValueChangeListener, and unregisterListener. Also adds the CapabilityFlagChangeListeners constant to service_params.go. No runtime behavior is introduced in this commit; these are pure type definitions that subsequent commits will build on.
Add flag_change_listener.go with a listenerRegistry that manages goroutine-based subscriptions to the SDK's FlagTracker channels. Each registered listener spawns a goroutine that consumes SDK events and POSTs a ListenerNotification JSON payload to the provided callback URI. General flag change listeners support optional key filtering; value change listeners include old and new values in the payload. Wire the three new commands into SDKClientEntity.DoCommand: registerFlagChangeListener, registerFlagValueChangeListener, and unregisterListener. Also calls closeAll() in Close() to cancel all listener goroutines before the SDK client shuts down. The flag-change-listeners capability is not yet advertised, so no test harness tests are run yet.
Add CapabilityFlagChangeListeners to the test service capabilities list. All 8 flag change listener tests pass against the sdk-test-harness.
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This pull request is part of a larger set of PRs that implement Flag Change Listener tests for server SDKs. Here's the list of pull requests that I currently have open:
Summary
Implements test service support for the new flag change listener contract tests defined in sdk-test-harness#317. No changes to the SDK itself — only the test service (
testservice/) is modified.For context on how the test harness drives these tests and what the full test matrix covers, see the sdk-test-harness PR description.
What this PR does
Adds type definitions (
testservice/servicedef/) for the three new commands and theListenerNotificationcallback payload, plus theflag-change-listenerscapability constant.Implements a
listenerRegistry(testservice/flag_change_listener.go) that manages all active listener subscriptions for an SDK client entity. Each registration spawns a goroutine that consumes events from the Go SDK'sFlagTrackerchannel and POSTs aListenerNotificationJSON payload to the callback URI provided by the test harness. The registry handles:FlagTracker.AddFlagChangeListener(), with optional key filtering when the test registers for a specific flagFlagTracker.AddFlagValueChangeListener(), which handles context-specific evaluation and old/new value tracking internallycloseAll()is called when the SDK client entity shuts down, ensuring no orphaned goroutinesAdvertises the capability by adding
flag-change-listenersto the test service's capabilities list. All 8 contract tests pass.Requirements
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Note
Medium Risk
Adds new goroutine-based listener registrations that POST callbacks on flag updates; main risk is concurrency/lifecycle management causing leaks or flaky test behavior if listeners aren’t cleaned up correctly.
Overview
Adds contract-test support for flag change listeners in the Go
testserviceby introducing new service commands to register/unregister listeners and a callback payload (ListenerNotification).Implements a per-client
listenerRegistrythat subscribes to the SDKFlagTrackerfor either any flag config change or value changes for a specific flag+context, forwards events to the harness via HTTP POST, and ensures listeners are cancelled onunregisterand when the client entity closes. The service now advertisesflag-change-listenersandflag-value-change-listenerscapabilities.Written by Cursor Bugbot for commit cbb3c53. This will update automatically on new commits. Configure here.