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[Bugfix] Validate JSON in kimi_k2 tool call arguments #43280

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[Bugfix] Validate JSON in kimi_k2 tool call arguments #43280

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10 changes: 5 additions & 5 deletions tests/tool_parsers/test_kimi_k2_tool_parser.py
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Original file line number Diff line number Diff line change
Expand Up @@ -148,8 +148,8 @@ def test_extract_tool_calls(
# id format: "something:digit"
assert tc.id.split(":")[-1].isdigit()

def test_invalid_json_still_extracted(self, parser):
"""Tool calls with invalid JSON are still returned (arguments as-is)."""
def test_invalid_json_skipped(self, parser):
"""Tool calls with invalid JSON are skipped; valid ones kept."""
model_output = (
"Help. "
+ SECTION_BEGIN
Expand All @@ -158,9 +158,9 @@ def test_invalid_json_still_extracted(self, parser):
+ SECTION_END
)
content, tool_calls = run_tool_extraction(parser, model_output, streaming=False)
assert len(tool_calls) == 2
assert tool_calls[0].function.name == "bad"
assert tool_calls[1].function.name == "good"
assert len(tool_calls) == 1
assert tool_calls[0].function.name == "good"
assert json.loads(tool_calls[0].function.arguments) == {"city": "Shanghai"}

def test_invalid_funcall_id_skipped(self, parser):
"""Tool calls with malformed id (no colon+digit) are skipped."""
Expand Down
10 changes: 10 additions & 0 deletions vllm/tool_parsers/kimi_k2_tool_parser.py
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Original file line number Diff line number Diff line change
@@ -1,6 +1,7 @@
# SPDX-License-Identifier: Apache-2.0
# SPDX-FileCopyrightText: Copyright contributors to the vLLM project

import json
from collections.abc import Sequence

import regex as re
Expand Down Expand Up @@ -96,6 +97,15 @@ def extract_tool_calls(
function_id, function_args = match
# function_id: functions.get_weather:0 or get_weather:0
function_name = function_id.split(":")[0].split(".")[-1]
try:
json.loads(function_args)
except (json.JSONDecodeError, TypeError):
logger.warning(
"Skipping tool call '%s' with invalid JSON: %s",
function_name,
function_args,
)
continue
Comment on lines +100 to +108

@gemini-code-assist gemini-code-assist Bot May 21, 2026

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high

While validating that the arguments are valid JSON is a good first step, tool call arguments are strictly expected to be a JSON object (dictionary) according to the OpenAI-compatible protocol. If the model generates a valid JSON primitive (like a string, number, or null) instead of an object, downstream clients expecting a dictionary will likely crash when attempting to access parameters. Consider adding a check to ensure the parsed JSON is a dictionary.

                    try:
                        if not isinstance(json.loads(function_args), dict):
                            raise ValueError("Tool call arguments must be a JSON object")
                    except (json.JSONDecodeError, TypeError, ValueError):
                        logger.warning(
                            "Skipping tool call '%s' with invalid JSON: %s",
                            function_name,
                            function_args,
                        )
                        continue

tool_calls.append(
ToolCall(
id=function_id,
Expand Down
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