feat(flags): Add ETag support for feature flag definitions polling #84
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Add ETag-based caching to reduce bandwidth and server load when polling for feature flag definitions. The server can now return 304 Not Modified when flags haven't changed, avoiding unnecessary data transfer. - Store ETag from feature flag definitions responses - Send If-None-Match header on subsequent requests - Handle 304 Not Modified by preserving cached flags - Add helper to mask tokens in URLs for debug logging
Replace plain @flags_etag instance variable with Concurrent::AtomicReference to ensure thread-safe access from background polling thread. This aligns with the existing pattern used for @quota_limited (AtomicBoolean) and other concurrent state in FeatureFlagsPoller.
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Pull request overview
This PR adds HTTP conditional request support using ETags to optimize bandwidth when polling for feature flag definitions. The implementation stores the ETag from successful responses and sends it with subsequent requests via the If-None-Match header. When the server responds with 304 Not Modified, the SDK skips reprocessing and preserves cached flag data.
Key changes:
- Added thread-safe ETag storage using
Concurrent::AtomicReference - Modified the HTTP request/response flow to handle 304 Not Modified responses
- Added token masking utility for secure logging
Reviewed changes
Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.
| File | Description |
|---|---|
| lib/posthog/feature_flags.rb | Added ETag storage (@flags_etag), request/response handling for 304 status codes, If-None-Match header support, and _mask_tokens_in_url helper for secure logging |
| spec/posthog/flags_spec.rb | Updated existing tests to expect etag: nil in responses and added comprehensive test coverage for ETag functionality including storage, 304 handling, ETag updates, and token masking |
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Move ETag update logic inside the successful response block so that error responses (400, 500, etc.) don't clear the cached ETag. This ensures subsequent requests can still use If-None-Match for conditional requests after transient server errors. Address review feedback from PR #84.
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Pull request overview
Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.
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Replace hardcoded "GET" with request_object.method for accuracy.
Add include_etag parameter to _request method to control whether ETag is included in responses. Only the feature flag definitions endpoint needs ETag support for conditional requests, so other endpoints no longer include unnecessary etag: nil in their responses.
Add an example script that demonstrates ETag support for local evaluation polling. The script polls every 5 seconds with debug logging enabled, showing ETag headers and 304 Not Modified responses.
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Pull request overview
Copilot reviewed 4 out of 4 changed files in this pull request and generated no new comments.
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Add support for HTTP conditional requests using ETags to reduce bandwidth when polling for feature flag definitions. When flag definitions haven't changed, the server returns 304 Not Modified and the SDK skips processing.
Based on PostHog/posthog-python#381