Santoshkumarpuppala opened a new issue, #13944:
URL: https://github.com/apache/apisix/issues/13944
Raised on #13731 at the maintainers' request, split out from that docs PR.
### Current Behavior
When the set of messages selected for checking is empty, `ai-prompt-guard`
returns `200` from `_M.access` (`apisix/plugins/ai-prompt-guard.lua:162-164`).
`plugin.lua:1406-1419` hands any non-nil code to `core.response.exit`, and
`core/response.lua:126-134` calls `ngx_exit(code)` for any code — the `>= 400`
branch only adds tracing. The client gets an empty 200 and the upstream is
never called.
Two ordinary requests reach it:
- `match_all_roles` left at its default `false`
(`ai-prompt-guard.lua:38-41`) and no `user` message in the request, e.g. only a
`system` message. Non-user messages are filtered out (`:152-154`), the list is
empty, and the request is answered with an empty 200. No non-default
configuration is needed to reach this.
- Embeddings with `input` as an array of strings.
`ai-protocols/openai-embeddings.lua:109-117` only collects a string `input`, so
an array yields `{}`.
The repo already uses both meanings of the return value: `cors.lua:338-339`
returns `200` deliberately to end an OPTIONS preflight, and
`ai-lakera-guard.lua:104-105` uses a bare `return` for the same "no messages"
condition and lets the request continue.
Nothing is logged: the warn at `plugin.lua:1408-1409` only fires for codes
`>= 400`.
### Expected Behavior
Nothing to check should mean pass through to the upstream, as
`ai-lakera-guard` does. The fix is `return` instead of `return 200`.
The tests don't catch this. `t/plugin/ai-prompt-guard.t` TEST 9 (line 243,
"send request with bad word and it will pass for non user") is exactly the
first case — its route, from TEST 8, sets only `allow_patterns` and leaves
`match_all_roles` at the default — and it asserts neither `--- response_body`
nor `--- error_code`, so it passes whether the request was proxied or cut off.
TESTs 3, 6, 14, 20, 23 and 26 have the same gap. Adding `--- response_body` /
`hello world` (`t/lib/server.lua:74-79`) would make them discriminate,
following `t/plugin/ai-lakera-guard.t`, which already asserts `--- error_code:
200` with `--- response_body_like` on its allow paths.
### Error Logs
None — see the note on logging above.
### Steps to Reproduce
1. Use the route from TEST 8 in `t/plugin/ai-prompt-guard.t` (only
`allow_patterns` set; `match_all_roles` at its default).
2. Add `--- response_body` with `hello world` to TEST 9.
3. Run `prove t/plugin/ai-prompt-guard.t` — TEST 9 should fail on current
`master`, and pass once `return 200` becomes `return`.
### Environment
`master` at `d13105e17` (2026-09-14). Traced from source, not run — I don't
have an APISIX test environment set up, so treat the reproduction above as the
expected result rather than an observed one.
Happy to open the PR with the one-line fix and the test assertions.
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