fix(api): let only one request probe a half-open circuit - #414
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Ivancheng7 wants to merge 1 commit into
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Ivancheng7 wants to merge 1 commit into
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isAvailable() returned true for every request while the circuit was half-open, so a traffic burst was admitted in full to a bot that had not actually recovered — and the burst finished halfOpenMaxAttempts quickly, closing the circuit without a verified recovery. - Track halfOpenProbeInFlight: the request that transitions open -> half-open takes the probe slot; further requests are rejected until it settles. - recordSuccess()/recordFailure() release the slot; a failed probe re-opens the circuit as before. - New tests/circuit-breaker.test.ts: one probe per window with a burst behind it, successful probe sequence closes, failed probe re-opens and the next window gates again.
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Problem
Once a circuit turns
half-open,isAvailable()returnstruefor every request — the "probe" is not a probe. Under load all requests that arrive while the probe is in flight are admitted to a bot that has not recovered yet, and the burst also driveshalfOpenSuccessestohalfOpenMaxAttempts, closing the circuit without any genuine recovery having been verified.Fix
Track
halfOpenProbeInFlighton the circuit:open → half-opentakes the probe slot;recordSuccess()/recordFailure(), and a failed probe re-opens the circuit exactly as before.Tests
New
tests/circuit-breaker.test.ts:Full local suite: no new failures.