[xianlubird]

Summary

Fix native SGLang /generate requests with stream=false and return_flat_raw_output_top_logprobs=true. Dynamo previously forced the engine request to stream, causing SGLang to reject an otherwise valid unary request.

• Preserve the client stream mode in the Rust worker envelope. Reject output-flat plus client streaming before dispatch.
• Keep ordinary Python-worker and native HTTP sidecar requests incremental, but use SGLang unary generation for output-flat responses.
• Accept bounded JSON responses in the sidecar alongside existing SSE responses, preserving the opaque native payload.
• On unary cancellation, send abort without waiting for the final response, retain the generation connection, and retry abort to cover registration races. Keep the existing streaming decode first-token drain and overall drain deadline.
• Keep prefill streaming for the KV handoff: remove its output-flat flag, retain prompt-flat/Base64 options when requested, and obtain output-flat data from decode.

Closes #16868.

Before / after

For example, with top-logprobs explicitly enabled on the Python SGLang worker (DYN_SGL_ALLOW_TOP_LOGPROBS=1):

{
  "input_ids": [1, 2],
  "stream": false,
  "return_logprob": true,
  "top_logprobs_num": 2,
  "return_flat_raw_output_top_logprobs": true
}

Before: both the frontend envelope and backend request reconstruction replace stream=false with true. SGLang rejects the request with return_flat_raw_output_top_logprobs ... does not support stream=True.

After: the generation worker receives stream=false and can return the native meta_info.output_top_logprobs_val_flat, output_top_logprobs_idx_flat, and shape metadata in the final JSON response. Ordinary requests still use internal streaming. A client explicitly requesting output-flat with stream=true receives a validation error.

The request above illustrates the API contract; the validation below does not claim a real-model GPU reproduction.

Validation

The unary cancellation regression failed on the original implementation (abort waited for the final response/drain deadline) and passed with the fix. The HTTP fixture simulates both registered requests and an initial successful abort that is ignored before registration.

• cargo test --locked -p dynamo-llm --no-default-features --lib protocols::sglang: 16 passed, including response aggregation/property tests.
• cargo test --locked -p dynamo-sglang-sidecar --lib native_http::tests: 23 passed, including localhost HTTP JSON/SSE, response-size limits, prefill handoff, streaming cancellation drain, unary cancellation before response headers, and an ignored first abort before registration.
• cargo test --locked -p dynamo-llm --no-default-features --lib http::service::sglang_generate::tests: 8 passed.
• cargo clippy --locked -p dynamo-sglang-sidecar --lib --tests --no-deps -- -D warnings: passed.
• File-scoped pre-commit checks, cargo fmt --all -- --check, and git diff --check.
• A source-isolated CPU replay of the modified Python request builder against SGLang main's _validate_inputs confirms ordinary internal streaming, accepted unary output-flat requests, and rejection of output-flat streaming. The schema adapter is substituted in this replay; it is not an engine integration test.
• Added Python regressions call the installed SGLang request normalizer, but could not collect locally because SGLang is not installed (ModuleNotFoundError: sglang). No real SGLang inference or GPU/P-D run was performed.

Upstream contract checked against SGLang 8683f8ad4ade22b33eb15414f61602c91850360a, GenerateReqInput._validate_inputs.

Summary by CodeRabbit

• New Features
  • Added support for both streaming and non-streaming SGLang generation responses.
  • Added handling for flat top-logprob output in compatible non-streaming requests.
  • Prefill requests now preserve supported prompt log-probability settings while automatically applying compatible response options.
• Bug Fixes
  • Prevented unsupported combinations of streaming and flat top-logprob output.
  • Improved response handling for large non-streaming results while respecting configured size limits.
• Tests
  • Added coverage for streaming modes, log-probability output, prefill behavior, and oversized responses.

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[dynamo-ops]

/ok to test d2edd7b

[coderabbitai]

Walkthrough

The SGLang request path now preserves unary mode for output-flat logprobs. Prefill requests remove incompatible completion-logprob options. The native HTTP transport supports both SSE and unary JSON responses.

Changes

SGLang request modes

Layer / File(s)	Summary
Unary request mode contract lib/llm/src/protocols/sglang/generate.rs, components/src/dynamo/sglang/tests/test_sglang_decode_handler.py	Validation rejects streaming requests with output-flat logprobs. Worker envelopes preserve the requested stream value. Tests cover unary and streaming request modes.
Prefill request normalization components/src/dynamo/sglang/engine_generate.py, components/src/dynamo/sglang/request_handlers/llm/prefill_handler.py, lib/sidecar/sglang/src/native_http.rs, components/src/dynamo/sglang/tests/test_sglang_decode_handler.py	Request construction marks prefill operations and removes incompatible output-flat completion-logprob options. Prefill requests retain streaming and compatible prompt-logprob settings.
Unary HTTP response handling lib/sidecar/sglang/src/native_http.rs	The HTTP client selects an Accept header by request mode. Bounded JSON response bodies are adapted into the existing decoder. Tests cover response size limits and response data preservation.

Priority: ➖ Normal

Estimated code review effort: 3 (Moderate) | ~20 minutes

Severity of issue fixed: Medium

Merge Risk: 🟡 Moderate · up to d2edd

Non-streaming SGLang requests with output-flat logprobs now work as intended. However, when a client cancels such a decode request, the backend may continue generating for up to five minutes before it is aborted. Under cancellation-heavy load, this wastes GPU capacity. A cancellation path that does not wait for the full unary response should be added before merging.

Pre-merge checks: 4 · 1

Failed checks: 1 warning

Check name	Status	Explanation	Resolution
Docstring Coverage		Docstring coverage is 54.17% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 24 functions across 5 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

Passed checks: 4 passed

Check name	Status	Explanation
Title check		The title clearly identifies the primary change: preserving unary output-flat logprob requests for SGLang.
Linked Issues check		Issue #16868 requires preserving client stream mode for native SGLang requests, allowing output-flat logprobs for unary requests, rejecting output-flat plus client streaming, and retaining normal incr…
Out of Scope Changes check		The changed Python builder, prefill handler, Rust protocol, native HTTP transport, and related tests directly implement or verify Issue #16868. JSON response adaptation, response-size enforcement, and…
Description check		The description is complete and relevant. It explains the problem, implementation, behavior before and after, validation results, limitations, and links the required issue with "Closes #16868." It doe…

Full details: Linked Issues check

Explanation

Issue #16868 requires preserving client stream mode for native SGLang requests, allowing output-flat logprobs for unary requests, rejecting output-flat plus client streaming, and retaining normal incremental generation. The Rust envelope now uses self.stream and validates the incompatible combination. The Python builder and native HTTP sidecar keep unary mode for output-flat responses and force streaming for other requests. Prefill removes output-flat fields before the streaming KV handoff. Added Rust, Python, and sidecar tests cover these behaviors, including bounded JSON response handling.

Full details: Out of Scope Changes check

Explanation

The changed Python builder, prefill handler, Rust protocol, native HTTP transport, and related tests directly implement or verify Issue #16868. JSON response adaptation, response-size enforcement, and prefill normalization support the required unary response and KV handoff paths. No unrelated change is demonstrated.

Full details: Description check

Explanation

The description is complete and relevant. It explains the problem, implementation, behavior before and after, validation results, limitations, and links the required issue with "Closes #16868." It does not use the template headings exactly and does not explicitly identify where reviewers should start, but it provides sufficient equivalent detail.

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[coderabbitai]

Actionable comments posted: 1

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• 🪄 Fix comments: Fix CodeRabbit comments on this PR

🤖 Prompt to fix review comments

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Inline comments:
Review comments at @lib/sidecar/sglang/src/native_http.rs:
- Around line 80-81: Update the unary output-flat decode path around the
return_flat_raw_output_top_logprobs condition so cancellation can invoke
/abort_request without waiting for unary /generate to complete. Preserve the
existing KV-transfer safety behavior for streaming requests, while ensuring
AbortGuard handles cancellation before the first unary response and still
respects DECODE_DRAIN_TIMEOUT where required.

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ℹ️ Review info

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📥 Commits

Reviewing files that changed from the base of the PR and between cc02d8b and d2edd7b.

📒 Files selected for processing: 5

• components/src/dynamo/sglang/engine_generate.py
• components/src/dynamo/sglang/request_handlers/llm/prefill_handler.py
• components/src/dynamo/sglang/tests/test_sglang_decode_handler.py
• lib/llm/src/protocols/sglang/generate.rs
• lib/sidecar/sglang/src/native_http.rs

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[dynamo-ops]

/ok to test 90a766b

[dynamo-ops]

/ok to test 4e4d559

[devin-ai-integration]

✅ Dynamo PR CI passed — run 39377458185 (attempt 1) on 2d41dde6bf

Gate checks: ✅ backend-status-check · ✅ deploy-status-check · ✅ dynamo-status-check

_{Posted automatically by Devin for run 39377458185. Updated on every full-CI run of this PR.}

[dynamo-ops]

/ok to test 2d41dde

[devin-ai-integration]

External PR triage

Blocker: review has been requested but is idle for more than 72h. Full CI passed on head 2d41dde6bf, and a current /ok to test approval exists for it. Reviews were requested from the code owners on 2026-10-20, and no human has reviewed the PR since then. The author already addressed the earlier thread.

Next action: @ai-dynamo/dynamo-frontend-codeowners @ai-dynamo/dynamo-backend-sglang-codeowners @ai-dynamo/dynamo-ops-codeowners: review and approve (or request changes). One approval from any owning team satisfies the gate for its files.

_{Automated triage of stuck external contributions. This comment is edited in place when the blocker changes. Devin does not post /ok to test or approve PRs. Written by Devin}

[furionw]

discussed offline. integrated this into #16983

https://ai-dynamo.slack.com/archives/C0BEYK8K3Q9/p1793005100230419?thread_ts=1792467961.967379&cid=C0BEYK8K3Q9

[furionw]

Thank you, @xianlubird .