Add ETag support for local evaluation polling#66
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The crates.io trusted publishing config expects release.yml, not release.yaml. The earlier rename was backwards.
Add HTTP ETag/If-None-Match conditional request support to both FlagPoller (sync) and AsyncFlagPoller (async) polling loops. When flag definitions haven't changed, the server returns 304 Not Modified, saving bandwidth and processing. Changes: - Track last_etag in the polling loop (not on struct, since it's only relevant to the background polling) - Send If-None-Match header when etag is available - Handle 304 Not Modified response by skipping cache update - Extract and store ETag from 200 responses (only after successful JSON parse to avoid partial state) Tests verify: - If-None-Match header is sent after receiving an ETag - 304 response preserves the existing cache - Normal operation when server returns no ETag
haacked
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Feb 5, 2026
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Nice! Happy to see this.
Some non-blocking suggestions.
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| #[cfg(feature = "async-client")] | ||
| #[tokio::test] |
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Tests only cover AsyncFlagPoller. Consider adding equivalent tests for the sync FlagPoller to ensure parity - both implementations have the same ETag logic but only one is tested.
tests/test_local_evaluation.rs
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| .path("/api/feature_flag/local_evaluation/") | ||
| .query_param("send_cohorts", "") | ||
| .matches(|req| { | ||
| // Match only if If-None-Match header exists |
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The mock only verifies that the If-None-Match header exists, but doesn't verify its value is correct. Consider checking that the header value matches the ETag returned by the server:
.matches(|req| {
req.headers.as_ref().is_some_and(|headers| {
headers.iter().any(|(name, value)| {
name.to_lowercase() == "if-none-match"
&& value.as_str() == "\"abc123\""
})
})
})
src/local_evaluation.rs
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| } else if response.status().is_success() { | ||
| // Extract ETag before consuming the response body | ||
| let new_etag = response | ||
| .headers() |
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Minor suggestion: Consider extracting ETag extraction into a shared helper function to reduce duplication with the async version:
fn extract_etag(headers: &HeaderMap) -> Option<String> {
headers.get(ETAG)
.and_then(|v| v.to_str().ok())
.filter(|s| !s.is_empty())
.map(|s| s.to_string())
}- Extract ETag extraction into shared helper function to reduce duplication - Update async tests to verify ETag value matches (not just header existence) - Add equivalent sync FlagPoller tests for ETag behavior parity Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
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Summary
Adds HTTP ETag/If-None-Match conditional request support to both
FlagPoller(sync) andAsyncFlagPoller(async) polling loops. When flag definitions haven't changed, the server returns 304 Not Modified, saving bandwidth and processing.Changes:
last_etagin the polling loop (local to the background thread/task)If-None-Matchheader when an ETag is available from a previous responseDesign notes:
load_flags()methods remain unconditional — they're for initial loads and manual refreshesTest plan
test_etag_sent_on_second_poll— verifiesIf-None-Matchheader is sent after receiving an ETagtest_304_preserves_cache— verifies 304 response preserves the existing cachetest_no_etag_from_server— verifies normal operation when server doesn't return ETags