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AI-assisted engineering/Reviewing AI code

Fix the sliding window in a client rate limiter

Review the AI's codeEasy10 minStripe style

Your task

An AI agent added a rate limiter to your Go API gateway that "allows up to N requests per sliding minute per client". Its only test sent N requests and checked that the next one was blocked. You are pinning down what the limiter must do for one client, including what happens after the client has been blocked.

An assistant wrote sliding_window_allow(request_times, limit, window_ms). It is in the editor. It has a bug. Find it and fix it.

Input and output:

  • request_times: one client's request times in milliseconds, never decreasing.
  • limit: how many requests may be allowed within one window.
  • window_ms: the window length in milliseconds.
  • Return one boolean per request: true if it is allowed.

Rules the tests check:

  • Keep a list of the times of allowed requests. It starts empty.
  • For a request at time t, first drop every kept time that is at or before t minus window_ms. A time exactly window_ms old has left the window.
  • Then allow the request when limit is greater than 0 and fewer than limit times remain.
  • Add t to the list only when the request is allowed. A denied request is not recorded.

Examples

sliding_window_allow(request_times: list[int], limit: int, window_ms: int) -> list[bool]
Example 1
Inputsliding_window_allow([0, 100, 200, 300], 2, 1000)
Output[True, True, False, False]
Example 2
Inputsliding_window_allow([0, 100, 200, 1050], 2, 1000)
Output[True, True, False, True]