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[Bugfix][Tool Parser] Fix HYV4 guided prefix loss, nested marker splitting, and O(N^2) arg scanning in HYV3/HYV4 - #62502
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…tting, and O(N^2) arg scanning in HYV3/HYV4 Fix streaming correctness and performance issues in `HYV4ToolExtractor` (`vllm/tool_parsers/hy_v4_tool_parser.py`) and `HYV3ToolParser` (`vllm/tool_parsers/hy_v3_tool_parser.py`): 1. In `HYV4ToolExtractor.extract_tool_calls_streaming` (`guided=True`), when a trailing partial overlap with `<tool_calls...>` is held back at the end of `previous_text`, slice the next content delta from `prev_safe_end = len(previous_text) - partial_tag_overlap(previous_text, marker)` instead of `len(previous_text)`, and avoid re-slicing content once `marker` was already present in `previous_text`. Previously, any held-back partial prefix (such as `<` in `"Result: x <"` followed by `" 10"`) was permanently dropped from streamed assistant content. 2. In both `HYV4ToolExtractor.extract_tool_calls_streaming` (`guided=False`) and `HYV3ToolParser.extract_tool_calls_streaming`, only split `delta_text` on `self.tool_calls_start_token` (with `maxsplit=1`) on the transition delta where `self.tool_calls_start_token_id not in previous_token_ids`. Previously, a literal `<tool_calls>` inside a tool argument value was split on subsequent deltas, leaking the argument prefix as assistant `content` and corrupting the JSON argument stream. 3. In `_extract_streaming_incremental` (both HYV3 and HYV4), replace the duplicate full-buffer `findall(args_text)` + `finditer(args_text)` passes with a single incremental `finditer(args_text, self._scanned_args_len)` pass, and use `json.dumps(partial_value, ensure_ascii=False)[1:-1]` in HYV3 to properly escape all JSON control characters. Signed-off-by: Parth Vadera <parthvadera@gmail.com> Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> Signed-off-by: Parth Vadera <parthvadera@gmail.com>
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Purpose
Fixes three streaming correctness and complexity bugs in
HYV4ToolExtractor(vllm/tool_parsers/hy_v4_tool_parser.py) andHYV3ToolParser(vllm/tool_parsers/hy_v3_tool_parser.py):Guided streaming drops held-back partial prefixes (
HYV4ToolExtractor.extract_tool_calls_streaming,guided=True):<tool_calls...>is not yet present incurrent_text, the parser holds backpartial_tag_overlap(current_text, marker)characters at the tail ofcurrent_text(safe_end = len(current_text) - partial_tag_overlap(current_text, marker)).current_text[len(previous_text) : safe_end](andcurrent_text[len(previous_text) : content_end]when the marker arrived) instead of starting from the previously emitted offsetprev_safe_end = len(previous_text) - partial_tag_overlap(previous_text, marker).<tool_calls>(even a single<at the end of a delta such as"Result: x <"followed by" 10", or"Compare a <"followed by"<tool_calls>...") was permanently lost from streamed assistantcontent.Unguided streaming splits literal
<tool_calls>inside tool arguments (HYV4ToolExtractor&HYV3ToolParser):HYV4ToolExtractor.extract_tool_calls_streaming(guided=False) andHYV3ToolParser.extract_tool_calls_streaming,if self.tool_calls_start_token in delta_text:ran on every delta even afterself.tool_calls_start_token_idhad already been seen inprevious_token_ids(and called.split(self.tool_calls_start_token)withoutmaxsplit=1)."<tool_calls>", the parser split the argument delta, leaked the argument text preceding"<tool_calls>"as assistantcontent, stripped"<tool_calls>", and corrupted the streamed JSON arguments.Duplicate$O(N^2)$ regex rescanning and control-character escaping in
_extract_streaming_incremental(HYV3ToolParser&HYV4ToolExtractor):self.func_args_regex.findall(args_text)from index0and immediately ranself.func_args_regex.finditer(args_text)from index0again on every token delta. Trackingself._scanned_args_lenallows a singlefinditer(args_text, self._scanned_args_len)pass over only newly arrived argument text.HYV3ToolParser's partial string escaping withHYV4ToolExtractor(json.dumps(partial_value, ensure_ascii=False)[1:-1]) so control characters (\b,\f,\u0000–\u001f) do not produce invalid JSON or prefix mismatches on close.Test Plan
Test Result
19 passedintests/tool_parsers/test_hy_v3_tool_parser.py.Credits & Acknowledgments
HYV3ToolParser(@stevenkuang-tencent [Model] Support Hy3 preview #40681, [Model] Support Hy3 token suffix and JSON Schema array types #47192; @taneem-ibrahim [Bugfix] Preserve parallel HY-V3 calls delivered in one streaming delta #53965) andHYV4ToolExtractor(@thisjiang [Hy4] support Hy4-preview model #54160; @wtdcode [Frontend] Add--tool-strict-levelfor server-side control for structural tag activation #56268) streaming tool-parser implementations andpartial_tag_overlaphelpers invllm/tool_parsers/.