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While streaming DeepSeek V4 tool calls, an in-progress parameter value can
be followed by the beginning of its closing tag (`</｜DSML｜parameter>`),
because a chunk boundary may land anywhere inside that tag. The partial
matcher used a greedy `(.*)$`, so the truncated tag fragment was captured
into the argument value, e.g. `{"location": "Paris</｜DSML｜parameter"}`.
Fix by trimming any trailing fragment of the partial value that is a prefix
of a DSML tag (the parameter closing tag or the next `<｜DSML｜...`
opening), at the earliest offset where such a fragment starts. Checking
prefixes instead of matching the full marker handles truncation at every
position inside the tag; plain angle brackets in values are unaffected.
Fixes vllm-project#53227
Signed-off-by: fei <204683769+feiiiiii5@users.noreply.github.com>
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Thanks for the note! Understood on the CI policy — the change is localized to the streaming tool-argument parser (with a regression test covering the split-tag case). Could a reviewer trigger /ci run when convenient? Happy to address any lint or test feedback that surfaces. |
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This pull request has merge conflicts that must be resolved before it can be |
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Closing: the underlying issue #53227 has been closed (marked completed), this PR has had no maintainer traction (vLLM needs a maintainer to add the ready/verified labels and trigger CI), and it now carries merge conflicts. The fix (stop the partial-parameter matcher |
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Purpose
While streaming DeepSeek V4 tool calls (
stream: true+tool_choice: required), an in-progress parameter value can be followed by the beginning of its closing tag</｜DSML｜parameter>, because a chunk boundary may land anywhere inside that tag. The partial matcher in_dsml_arg_converterused a greedy(.*)$, so the truncated tag fragment was captured into the argument value:This corrupts streamed tool arguments for every agent harness consuming them.
Changes
_TAG_PREFIXES, the set of all non-empty prefixes of</｜DSML｜parameter>and of<｜DSML._strip_partial_dsml_tag(): trim the partial value at the earliest offset where the remainder is one of those prefixes. Applied only in the partial branch; the complete-parameter path is untouched.TestArgConverter, including truncation in the middle of the closing tag.Why prefix trimming instead of a tempered regex
A tempered pattern such as
(?:(?!</?｜DSML｜).)*only stops when it can see the full｜DSML｜sequence. Streaming truncation can land earlier than that — e.g. a value ending iny</｜DSMstill leaks under that approach (verified experimentally). Checking whether any suffix of the value is a prefix of a DSML tag handles every truncation point exactly, and leaves ordinary angle brackets in values (a<b) untouched.Test Plan
>(the issue's repro), closing tag truncated midway (y</｜DSM), invalid in-progress JSON plus close remnant stays omitted.TestArgConverterclass passes against the patched converter (20/20), and plain<values keep working via the existing angle-bracket tests.Fixes #53227