[Bugfix][Tool Parser] Implement streaming for phi4_mini_json parser#49028
[Bugfix][Tool Parser] Implement streaming for phi4_mini_json parser#49028Yigtwxx wants to merge 1 commit into
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Phi4MiniJsonToolParser.extract_tool_calls_streaming() was a stub that always returned None. The serving layer forwards that value directly, so streaming requests using this parser received neither tool calls nor plain-text content. Implement it following the Llama3JsonToolParser pattern, reusing partial_json_loads and find_common_prefix. Terminated objects are decoded with raw_decode so the array's closing bracket never reaches the partial JSON parser, which raises IndexError on an unmatched bracket. The eight streaming tests in the shared parser suite were marked xfail(strict=True) for this parser and now pass, so the markers are removed. Signed-off-by: Yigtwxx <yigiterdogan023@gmail.com> Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>
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Purpose
Phi4MiniJsonToolParser.extract_tool_calls_streaming()is a stub that unconditionally returnsNone.ParserManager.extract_tool_calls_streaming()forwards that return value straight to the serving layer, so with--tool-call-parser phi4_mini_jsonand"stream": trueevery delta is discarded: the client receives neither tool calls nor the assistant's plain-text content. Only the non-streaming path works today.This was reported in #18257 (Phi-4 function calling with streaming) and closed as stale without a fix.
The Rust frontend already implements streaming for this parser (
rust/src/parser/src/tool/json/phi4mini.rs, covered byphi4mini_streaming_emits_argument_deltasandphi4mini_streaming_handles_split_markers), so this is a Python/Rust parity gap.VLLM_USE_RUST_FRONTENDdefaults to0, which means the broken Python path is the default one.Modification
extract_tool_calls_streaming()is implemented following the existingLlama3JsonToolParserpattern, which handles the same "JSON array of{name, arguments}objects behind a marker" shape, reusingpartial_json_loadsandfind_common_prefixfromvllm/tool_parsers/utils.py:functoolsmarker is streamed as content. The marker is not a special token, so it arrives split across several ordinary tokens; trailing text that is still a prefix of the marker is held back so it never leaks intocontent.[...]array is decoded incrementally. Terminated objects go throughJSONDecoder.raw_decode, which also keeps the array's closing bracket away from the partial JSON parser (it raisesIndexErroron an unmatched closing bracket). Objects still being generated fall back topartial_json_loads.find_common_prefixso premature closing quotes and braces are not sent. The name and the first arguments chunk are emitted together when the object is already terminated, which keeps the output correct regardless of how the text is chunked.argumentsandparameterskey variants are handled, matching the non-streaming path and the Rust implementation.The non-streaming
extract_tool_calls()is deliberately left untouched: the nested-array truncation there is being fixed separately in #48795, so these two changes do not overlap.Test Plan
tests/tool_parsers/common_tests.pyalready contains full streaming coverage for this parser, but all eight streaming tests were markedxfail(strict=True)with the reason "Phi4 Mini streaming not implemented". Those markers are removed, so the shared suite itself becomes the regression test. Three phi-4-specific tests are added for cases the shared suite does not exercise: the marker split across deltas, theparameterskey variant, and content preceding the marker.Test Result
Before (this branch's tests against the unmodified parser), 11 failures:
After:
The two remaining xfails are the pre-existing non-streaming ones, which are out of scope here.
Full parser suite:
The 15 errors are all in
test_llama3_json_tool_parser.pyand are environmental: the fixture downloads the gatedmeta-llama/Llama-3.2-1B-Instructrepo and gets HTTP 401 without HF credentials. They reproduce identically on an unmodified checkout.Lint and types:
No end-to-end serving run: the available GPU (8 GB) cannot hold Phi-4-mini alongside the KV cache. The change is confined to parser logic, which the unit suite covers in both streaming and non-streaming modes.
Duplicate-work check: no open PR addresses phi-4-mini streaming.
gh pr list --repo vllm-project/vllm --state open --search "phi4mini"returns only #48795, which is scoped to the non-streaming regex in the same file. #18257 is closed and unfixed.AI assistance was used in preparing this change; all code and test results were reviewed by the submitter.