[sohumt123]

Purpose

Fixes #48020.

The DeepSeek V3 and V3.1 streaming tool parsers
(extract_tool_calls_streaming) infer their state by comparing the number of
tool-call begin/end tokens between previous_token_ids and
current_token_ids. Every count-based branch assumes a tool call spends at
least one delta in a "started but not yet closed" state
(start_count > end_count) before its end tag is observed.

That assumption breaks when a whole tool call — begin tag, name, arguments, and
end tag — arrives in a single delta. On the first pass start_count == end_count, so the parser skips the "starting a new tool" branch
(current_tool_id stays -1) and falls into the "closing" branch, finds
prev_tool_call_arr empty, logs attempting to close tool call, but no tool call, and returns None. The call is silently dropped, even though the
non-streaming extract_tool_calls parses the same text correctly. A single
delta carrying a complete call is common in practice: short names/arguments,
--stream-interval > 1, speculative decoding (DeepSeek MTP), or plain scheduler
batching under load.

This is the same failure mode already fixed for DeepSeek-V3.2 in #36056.

Fix

Add one early branch to each parser, immediately before the existing count-based
if/elif chain, that detects the "one or more complete tool calls in this
delta" case:

if (
    cur_tool_start_count == cur_tool_end_count
    and cur_tool_start_count > prev_tool_start_count
    and prev_tool_start_count == prev_tool_end_count
):
    ...

When it fires, it re-uses the parser's own non-streaming tool_call_regex to
parse every complete block from current_text and emits the calls that have not
been streamed yet (sliced by emission state, current_tool_id + 1, not by token
counts). Reusing the non-streaming regex gives streaming/non-streaming parity by
construction. It also updates streamed_args_for_tool and prev_tool_call_arr
so the base-class finalize path (get_remaining_unstreamed_args) stays
consistent and does not double-emit.

The extra guard prev_tool_start_count == prev_tool_end_count restricts the new
branch to the "no call currently open" case, so the existing incremental logic
is left entirely untouched. Token-by-token streaming behaves exactly as before
(the new branch never fires mid-call, when counts are unbalanced).

Per-parser difference: V3's regex yields (type, name, arguments) 3-tuples
(arguments come from inside the ```json fence); V3.1's yields
(name, arguments) 2-tuples with no fence. Both emit type="function",
matching each parser's non-streaming path.

Scope is deliberately limited to the two DeepSeek V3/V3.1 parsers named in the
issue title. The same symptom class was raised in the issue thread for
functiongemma and internlm2; those are separate code paths and are left for
follow-up so this diff stays reviewable. The pre-existing unrelated V3.1 bug at
the stream_tool_call_name_regex branch (tool_name assigned a .groups()
tuple) is also intentionally left alone.

Test Plan

pytest tests/tool_parsers/test_deepseekv3_tool_parser.py \
       tests/tool_parsers/test_deepseekv31_tool_parser.py

New regression tests (added to the two existing parser test files, which already
download the real DeepSeek-V3 / V3.1 tokenizers):

• test_streaming_whole_tool_call_in_one_delta — feeds a full tool call as a
  single streaming delta and asserts the reconstructed name/arguments equal the
  non-streaming result.
• test_streaming_parallel_tool_calls_in_one_delta — feeds two complete tool
  calls in one delta and asserts both survive with correct indices/arguments
  (uses assert_one_tool_per_delta=False, since one delta legitimately carries
  two calls).

Test Result

Before the fix, feeding a complete tool call as a single delta streams nothing;
after the fix it matches the non-streaming result exactly. Verified with the
real parser modules and real DeepSeek tokenizers:

# before
V3   streamed(1 delta): None
V3   parallel streamed: None
V3.1 streamed(1 delta): None

# after
V3   non-streaming    : [('get_weather', '{"city": "Tokyo", "unit": "celsius"}')]
V3   streamed(1 delta): [('get_weather', '{"city": "Tokyo", "unit": "celsius"}')]
V3   parallel streamed: [('get_weather', '{"city": "Tokyo", "unit": "celsius"}'),
                         ('search_hotels', '{"location": "Tokyo", "check_in": "2025-01-15"}')]
V3.1 non-streaming    : [('foo', '{"x":1}')]
V3.1 streamed(1 delta): [('foo', '{"x":1}')]

Token-by-token streaming reconstruction is unchanged before and after the fix
(the new branch does not fire mid-call), confirming no regression on the
incremental path.

Note on the environment: this validation was run as isolated parser logic on
macOS (a full vLLM build is not possible there), exercising the real parser
modules and real DeepSeek tokenizers directly. The added pytest regression
tests are intended to run in Linux CI.

ruff check, ruff format, and the typos/check-spdx-header/
check-forbidden-imports pre-commit hooks pass on the four changed files.

---

Disclosure (AI Assisted Contributions): this change was developed with AI
assistance (Claude). I reviewed every line, reproduced the bug, validated the
fix and its tests locally as described above, and I stand by the change. The
commit carries a Co-authored-by: Claude trailer alongside my
Signed-off-by, per the contributing guidelines.

[claude]

Claude Code Review

This pull request is from a fork — automated review is disabled. A repository maintainer can comment @claude review to run a one-time review.

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🚀

[ErenAta16]

I filed #48020, so not a neutral reviewer. This fixes the case I reported and the shape of the fix is right. One adjacent case still drops calls, and I think it is worth deciding on before this lands rather than after.

What the fix gets right. The guard is three conditions and the third one is the load-bearing one:

if (
    cur_tool_start_count == cur_tool_end_count
    and cur_tool_start_count > prev_tool_start_count
    and prev_tool_start_count == prev_tool_end_count
):

prev_start == prev_end is what stops this branch from hijacking a call that was already open from an earlier delta. Without it, a normal two-delta call would land here on its closing pass and get re-emitted from the regex. Worth a comment saying that explicitly, because it reads like a redundant third clause.

Walking the branch selection confirms nothing else moved:

scenario                                    prev    cur    branch
1 complete call in one delta (the bug)      0/0     1/1    NEW BRANCH
2 complete calls in one delta               0/0     2/2    NEW BRANCH
normal open (delta 1)                       0/0     1/0    starting a new tool call
normal close (delta 2)                      1/0     1/1    closing branch

+185/-0 with no existing branch touched is the right risk profile for a streaming state machine, and both V3 and V3.1 got the identical block, which matters since the original report named both.

The gap: one complete call plus the start of the next, in the same delta.

MIXED: 1 complete + 1 just opened           0/0     2/1    starting a new tool call

cur_start != cur_end, so the new branch does not fire and it falls into "starting a new tool call". That branch does current_tool_id += 1 once and treats the delta as opening a single tool, so the call that was already complete in this delta is never emitted and the parser realigns onto the second one.

The next delta cannot recover it either:

MIXED: the 2nd call then closes             2/1     2/2    closing branch

the new branch needs prev_start == prev_end, and 2 != 1, so it is skipped and the closing branch closes one tool. Net result is the same symptom as #48020, one step out: a silently dropped call, no error.

I do not think this is hypothetical given the PR's own rationale. If chunk boundaries can batch a whole tool call under speculative decoding or scheduler batching, they can equally land a few tokens into the next one. Parallel tool calls are exactly where this shows up, and the PR already adds a parallel-calls test for the 2/2 case.

Two ways out, and I am not arguing for either:

• Relax to cur_start > prev_start and prev_start == prev_end, emit the complete blocks the regex finds, and let the count bookkeeping handle whatever is still open. That covers 2/1 with the same machinery.
• Or leave it and say so in the comment, so the next person hitting 2/1 finds a known boundary rather than rediscovering #48020.

One scope note on the tests, which are otherwise the right design. Using the non-streaming result as the expected value is exactly right for this fix, since the property being restored is "streaming agrees with non-streaming":

_, tools_non = run_tool_extraction(tool_parser, ..., streaming=False)
...
assert reconstructor.tool_calls[0].function.arguments == tools_non[0].function.arguments

The thing to keep in mind is that both sides now go through self.tool_call_regex, so the test pins agreement between the two paths but cannot detect a flaw in the parse itself. The regex is compiled without re.DOTALL and leans on greedy .*, so multi-line arguments and two calls on one line would fail identically on both sides and the assertion would still pass. Pre-existing, not this PR's job, just worth not reading the test as validation of the parse.

Thanks for picking this up, and for covering V3.1 rather than only the parser named in the traceback.

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