fix(quota): run input guardrails before the rate-limit reservation (#542)

[moonming]

What

A guardrail-blocked request burned an RPM/RPD/RPS/RPH slot. /v1/messages, /v1/responses, /v1/embeddings ran check_input after crate::quota::enforce, and Reservation::drop only releases the concurrency permit — it never refunds the request counter. So a content-policy refusal counted against the caller's quota. /v1/chat/completions already runs guardrails before the reservation precisely to avoid this (its own code comment says so).

How

Hoist the resolve-chain + check_input block above quota::enforce on all three surfaces. (messages was pre-existing; responses + embeddings inherited the ordering from #541/#544.) The budget pre-check ordering is unchanged. Deliberately not fixed via a Reservation::drop refund — that would also refund slots on upstream 5xx/timeouts, a separate policy decision affecting every surface.

Test plan

blocked_request_does_not_consume_rate_limit_slot: API key capped at RPM=1, a blocking guardrail; a blocked request (422) followed by a benign one — the benign request still returns 200 (pre-fix it got 429 because the block burned the only slot). The existing per-surface input-block tests still pass (the guardrail blocks correctly in its new position). fmt + clippy clean; 408 aisix-proxy lib tests pass.

Surfaced by the independent pre-fix audit of the #719 follow-up batch. Refs #542, #719.

Summary by CodeRabbit

• Improvements

  • Requests blocked by input guardrails and content policies are now evaluated before rate-limit reservation. This prevents blocked requests from consuming your quota, allowing a higher proportion of your rate limit to serve legitimate requests.

• Tests

  • Added test to verify that content-blocked requests do not consume rate limit slots.

[coderabbitai]

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Free

Run ID: 38d6f1dd-47fe-4149-a3d3-c67e718af39b

📥 Commits

Reviewing files that changed from the base of the PR and between 963068f and f48ce10.

📒 Files selected for processing (3)

• crates/aisix-proxy/src/embeddings.rs
• crates/aisix-proxy/src/messages.rs
• crates/aisix-proxy/src/responses.rs

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📝 Walkthrough

Walkthrough

Three request handlers reorder quota enforcement to occur after input guardrail checks, preventing content-policy blocks from consuming rate-limit slots. A test verifies blocked requests preserve the quota reservation.

Changes

Guardrail-before-quota reordering

Layer / File(s)	Summary
Guardrail-before-quota reordering across handlers crates/aisix-proxy/src/embeddings.rs, crates/aisix-proxy/src/messages.rs, crates/aisix-proxy/src/responses.rs	Embeddings, messages, and responses handlers relocate ModelRateLimit construction and crate::quota::enforce() calls to occur after input guardrail checks resolve, preventing blocked requests from consuming RPM slots. Documentation updates explain the ordering requirement and issue references (#542, #719).
Rate-limit slot preservation test crates/aisix-proxy/src/responses.rs	New test blocked_request_does_not_consume_rate_limit_slot verifies that with rpm=1, a guardrail-blocked /v1/responses request returns 422 and does not consume the quota slot, allowing a subsequent benign request to succeed with 200.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~12 minutes

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Note

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