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fix(postgres): coerce LIMIT before SQL interpolation #2625

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fix(postgres): coerce LIMIT before SQL interpolation #2625

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fix(postgres): coerce LIMIT before SQL interpolation
Bartok9 Jul 30, 2026
f0eb3c9
test(postgres): stub psycopg before coerce_limit unit import
Bartok9 Jul 30, 2026
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15 changes: 15 additions & 0 deletions core/wren/src/wren/connector/postgres.py
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Original file line number Diff line number Diff line change
Expand Up @@ -220,6 +220,20 @@ def _coerce_decimal(value: PyDecimal | None, target_type: pa.DataType):
return pa.array(values, type=arrow_type, from_pandas=True)


def _coerce_limit(limit: int | None) -> int | None:
"""Validate and coerce a user-supplied ``limit`` to a non-negative ``int``.

``int(limit)`` rejects strings like ``"5 OR 1=1"`` so the value can be
safely interpolated into SQL. Negative limits are also rejected.
"""
if limit is None:
return None
coerced = int(limit)
if coerced < 0:
raise ValueError(f"limit must be non-negative, got {coerced}")
return coerced
Comment on lines +223 to +234

@coderabbitai coderabbitai Bot Jul 30, 2026

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🎯 Functional Correctness | 🟡 Minor | ⚡ Quick win

Validate negativity before integer truncation.

int(-0.5) produces 0, so the current check allows a negative runtime value and emits LIMIT 0. Check the original numeric value before coercion, or reject non-integral limits explicitly; add a regression test for limit=-0.5.

🤖 Prompt for AI Agents 
Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@core/wren/src/wren/connector/postgres.py` around lines 223 - 234, Update
_coerce_limit so negative numeric inputs are rejected before int() truncates
them; alternatively reject non-integral limits explicitly while preserving safe
coercion for valid values. Add a regression test verifying limit=-0.5 raises
ValueError rather than producing LIMIT 0.



class PostgresConnector(ConnectorABC):
"""Native psycopg3 implementation of the Wren postgres connector."""

Expand Down Expand Up @@ -251,6 +265,7 @@ def __init__(self, connection_info):
def query(self, sql: str, limit: int | None = None) -> pa.Table:
# Strip terminating ``;`` even when no LIMIT wrapper is applied so
# client-pasted statements match dry_run / limited composition rules.
limit = _coerce_limit(limit)
sql = strip_trailing_semicolon(sql)
if limit is not None:
sql = f"SELECT * FROM ({sql}) AS _sub LIMIT {limit}"
Expand Down
42 changes: 42 additions & 0 deletions core/wren/tests/unit/test_postgres_coerce_limit.py
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Original file line number Diff line number Diff line change
@@ -0,0 +1,42 @@
"""Postgres query must coerce LIMIT before SQL interpolation."""

from __future__ import annotations

from unittest.mock import MagicMock, patch

import pytest

from wren.connector import postgres as pg_mod


def _connector():
c = object.__new__(pg_mod.PostgresConnector)
c.connection = MagicMock()
c._closed = False
return c


def test_reject_negative_limit():
c = _connector()
with pytest.raises(ValueError, match="non-negative"):
c.query("SELECT 1", limit=-1)


def test_reject_injection_string():
c = _connector()
with pytest.raises(ValueError):
c.query("SELECT 1", limit="1; DROP TABLE t")


def test_numeric_string_limit_interpolated():
c = _connector()
cursor = MagicMock()
cursor.__enter__ = MagicMock(return_value=cursor)
cursor.__exit__ = MagicMock(return_value=False)
c.connection.cursor.return_value = cursor
with patch.object(pg_mod, "_build_pg_arrow_table", return_value="tbl"):
out = c.query("SELECT 1", limit="3")
assert out == "tbl"
executed = cursor.execute.call_args[0][0]
assert "LIMIT 3" in executed
assert "DROP" not in executed
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