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[Bugfix][Tool Parser] Anchor Jamba streamed tool arguments to what was sent - #55669
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…s sent The delta that sends the function name also records whatever argument keys partial_json_parser could complete at that point, without streaming them. Later deltas then diffed against that recorded completion, so text the client never received was treated as already sent and the arguments arrived starting mid-JSON. Anchor both argument-diff paths to streamed_args_for_tool, the approach llama_tool_parser already uses. Co-authored-by: Claude <noreply@anthropic.com> Signed-off-by: Zhiqi Zhang <zhiqizhangg@gmail.com>
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WalkthroughThe Jamba tool parser now computes streaming argument fragments from emitted prefixes and common prefixes. A regression test verifies that arguments beginning in the function-name delta reconstruct valid JSON. ChangesJamba streaming parser
Estimated code review effort: 3 (Moderate) | ~20 minutes Merge Risk: ⚪ Minimal · up to Jamba streamed tool calls now retain arguments that arrive with the function name, preventing truncated JSON arguments for clients. The targeted regression coverage confirms the triggering sequence, with no current merge-blocking risk identified. Suggested reviewers: 🚥 Pre-merge checks | ✅ 4 | ❌ 1❌ Failed checks (1 warning)
✅ Passed checks (4 passed)
✨ Finishing Touches 💡 1🛠️ Fix failing CI checks 💡
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🟢 Approval recommended
The fix aligns Jamba’s streaming behavior with established prefix-anchored patterns and is covered by a targeted regression test that fails pre-fix and passes post-fix.
Pull request overview
Fixes a streaming-mode corruption in JambaToolParser where early argument text can be lost when the delta that first carries the tool name also contains the beginning of arguments, causing clients to accumulate invalid JSON.
Changes:
- Anchor streamed argument diffs to
streamed_args_for_tool(and common-prefix logic) rather than diffing against the previous parsed completion, preventing prefix loss. - Flush unsent arguments on tool transitions by slicing from the already-streamed prefix length (with a single-replace fallback) instead of unbounded
str.replace. - Add a regression test covering “arguments begin in the name delta” streaming.
File summaries
| File | Description |
|---|---|
| vllm/tool_parsers/jamba_tool_parser.py | Reworks streaming argument delta computation/flush to preserve prefix correctness across deltas. |
| tests/tool_parsers/test_jamba_tool_parser.py | Adds regression test for partial arguments arriving in the same delta as the tool name. |
Review details
- Files reviewed: 2/2 changed files
- Comments generated: 0
- Review effort level: Lite
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Our regression case for this (Jamba arguments streamed across several deltas, expected the full JSON) fails on main with a JSONDecodeError and passes with this PR, in case you want to add it as a test. |
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/ci run |
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✅ @shoutoutuoadi325, CI is now available for this PR.
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✅ Triggered Buildkite CI #97399 for commit |
…s sent (vllm-project#55669) Signed-off-by: Zhiqi Zhang <zhiqizhangg@gmail.com> Co-authored-by: Flora Feng <4florafeng@gmail.com> Signed-off-by: Christopher Mackenzie <christopher.mackenzie.software@gmail.com>
…s sent (vllm-project#55669) Signed-off-by: Zhiqi Zhang <zhiqizhangg@gmail.com> Co-authored-by: Flora Feng <4florafeng@gmail.com> Signed-off-by: Christopher Mackenzie <christopher.mackenzie.software@gmail.com>
Purpose
Streaming tool calls with the
jambaparser lose the start of the arguments when the delta that delivers the function name also carries a complete argument pair.The name-sending delta updates
prev_tool_call_arrwith everythingpartial_json_parsercould complete at that point — including argument keys that were never streamed. The next delta takes thecur_arguments and prev_argumentsbranch and diffs withextract_intermediate_diff(cur, prev), which yields only the new tail (say', "state": "TX'). The{"city": "Dallasprefix never goes out, so the arguments the client accumulates are not valid JSON, and the end-of-stream rescue inget_remaining_unstreamed_args()cannot recover it because the streamed text is no longer a prefix of the expected JSON. Non-streaming requests return the full arguments.Multi-token deltas of this shape are routine since incremental detokenization buffers output — it is how the single-delta regression fixed in #48852 came about. That fix covers arguments arriving complete in one delta after the name; arguments that begin inside the name delta itself were still broken.
Both argument-diff paths now anchor to
streamed_args_for_tool, the approachllama_tool_parser.pyalready uses:cur_args_jsonfrom the streamed length, with a full flush once the JSON completes, instead of diffing against the previous completionstr.replaceNot a duplicate
cur_args_json.startswith(streamed + argument_diff)fails and nothing is sent. I applied its patch on top of main and the new test fails the same way.count=1to thestr.replace()scan on the tool-transition flush. This PR replaces that path with length-based slicing (keeping a guarded replace as fallback), which resolves the same corruption; its regression scenario passes with this change.No open issue describes the name-delta prefix loss; happy to file one if it helps tracking.
Test Plan
The new test feeds the triggering sequence (name and the first complete pair in one delta, completion in a later delta) and asserts the accumulated arguments parse back to the original dict. Before the fix it fails with
JSONDecodeErroron', "state": "TX'.I also compared the patched and unpatched parser across ~2800 random splittings of single- and parallel-tool outputs (strings, numbers, booleans, null, nested objects, unicode): the patched version produces complete arguments everywhere the unpatched one did, plus ~1700 splittings the unpatched one mangles. The remaining failures are the pre-existing single-blob limitation tracked by #48294.
Test Result
Run against the v0.28.0 wheel with this parser file applied (main and v0.28 differ in this file only by an import-path move):
This change was written with AI assistance; I reviewed every line and ran the tests above myself.