open-swe/agent/middleware/sanitize_tool_inputs.py
langsmith-forge[bot] 48965a82a6
fix: coerce malformed integer strings in read_file offset/limit params (#1216)
- Root cause: LLM occasionally generates strings like '1, 80' or '170, "limit": 60'
  for integer fields, causing a Pydantic ValidationError and wasting an LLM turn
- Change: add SanitizeToolInputsMiddleware in agent/middleware/sanitize_tool_inputs.py
  that extracts the leading integer from any string value in offset/limit before
  the call reaches Pydantic validation; registered before ToolErrorMiddleware in server.py
- Verified: 14 unit tests covering all three production trace patterns pass

Co-authored-by: LangSmith Forge <forge-agent@langsmith.ai>
Co-authored-by: Johannes du Plessis <johannes@langchain.dev>
2026-05-01 14:29:48 -07:00

88 lines
3.1 KiB
Python

"""Sanitize tool input middleware.
Coerces malformed integer fields in read_file calls before they reach Pydantic
validation. The LLM occasionally generates strings like ``'1, 80'`` or
``'170, "limit": 60'`` for integer parameters; we extract the leading digit
sequence so the call succeeds instead of burning an LLM turn on a retry.
"""
from __future__ import annotations
import logging
import re
from collections.abc import Awaitable, Callable
from langchain.agents.middleware.types import AgentMiddleware, AgentState
from langchain_core.messages import ToolMessage
from langgraph.prebuilt.tool_node import ToolCallRequest
from langgraph.types import Command
logger = logging.getLogger(__name__)
_READ_FILE_INT_FIELDS = ("offset", "limit")
def _coerce_int(value: object) -> int | None:
"""Extract the first integer from *value* if it is a non-integer string.
Returns the parsed integer, or ``None`` if no leading digits are found.
If *value* is already an ``int`` (or ``None``), returns it unchanged.
"""
if value is None or isinstance(value, int):
return value
if isinstance(value, str):
match = re.match(r"\s*(\d+)", value)
if match:
return int(match.group(1))
return None
return None
def _sanitize_read_file_args(args: dict) -> dict:
"""Return a copy of *args* with integer fields coerced where needed."""
sanitized = dict(args)
for field in _READ_FILE_INT_FIELDS:
if field in sanitized:
original = sanitized[field]
coerced = _coerce_int(original)
if coerced is not None and coerced != original:
logger.warning("Coercing read_file.%s from %r to %d", field, original, coerced)
sanitized[field] = coerced
return sanitized
class SanitizeToolInputsMiddleware(AgentMiddleware):
"""Intercept read_file calls and coerce malformed integer parameters.
When the LLM produces a string value for an integer field (e.g.
``offset='1, 80'``), this middleware extracts the leading integer so that
Pydantic validation passes rather than raising a ``ValidationError`` and
forcing an unnecessary retry.
"""
state_schema = AgentState
def _sanitize_request(self, request: ToolCallRequest) -> ToolCallRequest:
tool_call = request.tool_call
if not isinstance(tool_call, dict) or tool_call.get("name") != "read_file":
return request
args = tool_call.get("args", {})
sanitized_args = _sanitize_read_file_args(args)
if sanitized_args is args:
return request
new_tool_call = {**tool_call, "args": sanitized_args}
return request.override(tool_call=new_tool_call)
def wrap_tool_call(
self,
request: ToolCallRequest,
handler: Callable[[ToolCallRequest], ToolMessage | Command],
) -> ToolMessage | Command:
return handler(self._sanitize_request(request))
async def awrap_tool_call(
self,
request: ToolCallRequest,
handler: Callable[[ToolCallRequest], Awaitable[ToolMessage | Command]],
) -> ToolMessage | Command:
return await handler(self._sanitize_request(request))