FA-73615 / Rate limiter algorithms / Member archive

Escalating failure penalty box: failure log survives the ban · case 05

The first failure after a ban immediately triggers another, longer ban.

Member previewVariant 5 · 3 implementations · 7 checks per implementation

Case contract

Input {threshold, window_s, ban_s, events [[t, ok]]} with nondecreasing t. While t < ban end every event is "banned" and ignored. Failures are kept for window_s seconds (f > t - window_s). When the kept failures reach threshold the key is banned until t + ban_s * 2^strikes, strikes increments and the failure log is cleared; the event reports "ban-until-<end>". Otherwise failures report "fail" and successes "ok". Return the per-event results.

Why this case matters

Login and abuse throttles escalate bans after repeated failures; window, escalation and log-reset rules decide whether attackers are slowed and legitimate users recover.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
ban and escalate	`["fail", "fail", "ban-until-12", "banned", "ban-until-32", "banned", "banned", "ban-until-75", "banned"]`	`["fail", "fail", "ban-until-12", "banned", "fail", "fail", "ban-until-34", "fail", "ok"]`	Failed

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