[BUG] Sliding-window counts stale entries before cleanup, causing spurious rejection

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Assessment

Difficulty
2/5
Estimated time
1-3 hours
Newbie friendliness
75/100
Issue type
Bug
Clarity
Clearly specified
Activity status
Quiet
Tech stack
lua
Domain
api, backend

Research direction

Start with shenyu-plugin/shenyu-plugin-fault-tolerance/shenyu-plugin-ratelimiter/src/main/resources/META-INF/scripts/sliding_window_request_rate_limiter.lua, especially lines 34-52, and trace the order of cleanup, counting, and the allow decision. Done means entries outside the window are removed before counting, preventing a spurious 429 at the window boundary.

Written by the indexing model from the issue text.

Description

priority: medium type: bug
  • severity: Medium
  • files: shenyu-plugin/shenyu-plugin-fault-tolerance/shenyu-plugin-ratelimiter/src/main/resources/META-INF/scripts/sliding_window_request_rate_limiter.lua:34-52
  • description: The script computes last_requested = zcard(tokens_key) (line 37) and the allow decision (line 43) BEFORE calling zremrangebyscore(tokens_key, 0, now - window_size) (line 51). Entries whose score is already outside the window are still counted, then removed afterward.
  • impact: Intermittent false-negative (429) on the request that crosses the window boundary.
  • suggested_fix: Move zremrangebyscore before the zcard count.
  • confidence: Medium-High
  • related_existing: none

Identified during the 2026-08-02 deep re-scan; full list in docs/scan2-2026-08-02/06-medium-tiers.md.

Dominant language
Java
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