fix(frontend): return the busy_threshold error envelope on bad input - #13699
fix(frontend): return the busy_threshold error envelope on bad input#13699ayaangazali wants to merge 2 commits into
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`POST /busy_threshold` documents and returns an `{"error": "..."}` envelope,
and its `json_error_middleware` produces one for a 422. Requests that fail
before reaching the handler did not get it, because the handler used Axum's
`Json` extractor, whose rejections are `text/plain`:
Content-Type: text/plain -> 415 text/plain Expected request with `Content-Type: application/json`
body "{not json" -> 400 text/plain Failed to parse the request body as JSON: ...
schema mismatch -> 422 application/json {"error":"..."} (middleware, already correct)
The middleware only rewrites 422, so the first two fall through. This is the
frontend admin API, so the caller is usually a script or an operator tool that
parses the documented shape.
Read the body explicitly and report unsupported media type, oversized body and
malformed JSON through the same `ErrorResponse`. Content-type parsing reuses
`is_json_content_type` from the openai module rather than reimplementing it,
and the body is now bounded by `get_body_limit()`.
The policy is unchanged, only the envelope: an absent `Content-Type` is still
rejected.
Signed-off-by: ayaangazali <ayaangazali.work@gmail.com>
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| serde_json::from_slice(&bytes).map_err(|err| { | ||
| error( | ||
| StatusCode::BAD_REQUEST, | ||
| format!("Failed to parse the request body as JSON: {err}"), | ||
| ) | ||
| }) |
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🟡 Schema-mismatch requests change from 422 to 400
Well-formed JSON with a schema violation (missing model, wrong field type) is now parsed by serde_json::from_slice, which maps every error to 400. The old Json extractor returned 422 for these, so callers checking for 422 on schema errors now get 400. json_error_middleware becomes dead code, since no path produces a 422.
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Correct, and this one was a real regression in my change rather than a style point. Fixed in fe02f7e.
The detail that makes it specific to this route: json_error_middleware here keeps the 422, it only reshapes the body.
if response.status() == StatusCode::UNPROCESSABLE_ENTITY {
...
(StatusCode::UNPROCESSABLE_ENTITY, Json(...))
}Compare smart_json_error_middleware on the openai and generate routers, and anthropic_error_middleware, which all rewrite 422 to 400 on purpose, with the comment that downstream OpenAI-compatible clients expect 400. So on those routes a schema mismatch already surfaced as a 400 and collapsing the parse errors changes nothing. Here the 422 was reaching callers, and I was silently turning it into a 400 while claiming in the PR description that only the envelope changed. That claim was wrong.
The fix classifies the serde error and preserves the split Axum made:
let code = match err.classify() {
serde_json::error::Category::Data => StatusCode::UNPROCESSABLE_ENTITY,
_ => StatusCode::BAD_REQUEST,
};test_busy_threshold_schema_mismatch_stays_422 pins it, and I confirmed it fails against the previous version of this branch with left: 400, right: 422 rather than just re-running it green.
On json_error_middleware becoming dead: not quite, and I would rather not delete it in this PR. It still catches a 422 from anywhere else on this router, and the GET handler shares it. It is now unreachable from the POST parse path specifically, which is worth a follow-up look, but removing a safety net in the same change that reroutes the errors it was catching is how you find out you were wrong about the reachability. Happy to do it separately if you want it gone.
I checked my three sibling PRs for the same mistake, since the pattern is shared: #13685, #13696 and #13698 all sit behind middleware that rewrites 422 to 400, so none of them changes an observable status. Only this route did.
WalkthroughThe busy-threshold endpoint now validates JSON content types, enforces request body limits, parses request bodies explicitly, and returns structured JSON errors. Integration tests cover unsupported media types and malformed JSON. ChangesBusy threshold validation
Estimated code review effort: 3 (Moderate) | ~20 minutes Merge Risk: 🟡 Moderate · up to The endpoint now normalizes bad-input responses into the documented JSON envelope, but JSON values with invalid field types may incorrectly return 400 instead of 422. That status-code mismatch can break clients relying on the API contract and should be corrected before merge. 🚥 Pre-merge checks | ✅ 5✅ Passed checks (5 passed)
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Inline comments:
In `@lib/llm/src/http/service/busy_threshold.rs`:
- Around line 196-201: Update the serde_json error mapping in the request-body
parsing flow to return StatusCode::UNPROCESSABLE_ENTITY for
serde_json::error::Category::Data, while retaining StatusCode::BAD_REQUEST for
syntax and EOF errors. Add a regression test covering the {"model":1} request
body.
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lib/llm/src/http/service/busy_threshold.rslib/llm/src/http/service/openai.rslib/llm/src/http/service/service_v2.rs
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Reading the body by hand collapsed both parse failures into a 400, which changed the status for a well-formed body that does not match the schema. Axum's `Json` extractor returned 400 for a syntax error and 422 for a data error, and this route's `json_error_middleware` keeps the 422 rather than rewriting it, unlike the openai and anthropic middlewares. So the 422 was reaching callers and this PR was silently turning it into a 400. Classify the serde error and preserve the split. `test_busy_threshold_schema_mismatch_stays_422` fails with `left: 400, right: 422` against the previous version of this branch. Raised by Devin and CodeRabbit on ai-dynamo#13699. Signed-off-by: ayaangazali <ayaangazali.work@gmail.com>
Summary
POST /busy_thresholddocuments and returns an{"error": "..."}envelope, and itsjson_error_middlewarealready produces one for a schema mismatch. Requests that fail before reaching the handler did not get it, because the handler used Axum'sJsonextractor, whose rejections aretext/plain. Measured onmain:Three failure modes, two shapes. The middleware only rewrites 422, so the first two fall through. I checked that rather than assuming the middleware covered them, which is the same check that mattered on #13696 and #13698.
This is the frontend admin API, gated by
DYN_DISABLE_FRONTEND_ADMIN_API, so the caller is usually a script or operator tool parsing the documented shape rather than a person reading the body.The fix reads the body explicitly and reports unsupported media type, oversized body and malformed JSON through the same
ErrorResponse. Content-type parsing reusesis_json_content_typefrom the openai module rather than reimplementing it. The body read is now bounded byget_body_limit()as well; the middleware's own read usedusize::MAX, which is fine there because it is re-reading a response the server produced, but the request path should be bounded.The policy is unchanged, only the envelope: an absent
Content-Typeis still rejected.Where this sits
This completes the class. I swept every route module under
lib/llm/src/http/service/for the same pattern:openai.rsgenerate.rsanthropic.rsbusy_threshold.rssglang_generate.rsResult<Json<T>, JsonRejection>and handles the rejection itselfFour modules, four different envelopes, so none of these is a copy of another.
sglang_generate.rsis worth a look as the pattern the others could have used.Note that #13696 and #13698 make the identical one-line change exposing
is_json_content_typeaspub(super). It is the same edit in all three, so merging them in any order should not conflict; whichever lands first, the others become no-ops on that line.Validation
Measured before and after through
spawn_default_service, which registers this route:Content-Type: text/plain415 text/plain415 application/json{"error":"..."}{not json400 text/plain400 application/json{"error":"..."}422envelopedAdded
test_busy_threshold_bad_content_type_returns_json_errorandtest_busy_threshold_malformed_json_returns_json_error, asserting the responsecontent-typeas well as the body, because the status codes were already correct and only the shape was wrong. Both confirmed red first by restoringbusy_threshold.rsfromupstream/mainand re-running:main's 2041 plus the two added.cargo clippyandcargo fmt --all -- --checkclean.test_oversized_body_returns_json_413, the pre-existing intermittent I reported on fix(frontend): preserve chat_template_args through Responses conversion #13624, unrelated to this change.Not verified here: no GPU. This change only affects how the request body is read and how that read is reported when it fails; the handler logic is untouched.
Summary by CodeRabbit
Bug Fixes
Tests