From 78546e9242f4eefb72cbc85f023da885c29d1441 Mon Sep 17 00:00:00 2001
From: Sharvil Saxena <97365286+sharziki@users.noreply.github.com>
Date: Sun, 26 Apr 2026 15:13:20 -0400
Subject: [PATCH] fix(core): validate batch_size in _batch and _abatch to
 prevent infinite loop (#36663)

---
 libs/core/langchain_core/indexing/api.py      |  6 ++++++
 .../unit_tests/indexing/test_indexing.py      | 21 +++++++++++++++++++
 2 files changed, 27 insertions(+)

diff --git a/libs/core/langchain_core/indexing/api.py b/libs/core/langchain_core/indexing/api.py
index da3c54fd63f..b4af08b8b54 100644
--- a/libs/core/langchain_core/indexing/api.py
+++ b/libs/core/langchain_core/indexing/api.py
@@ -90,6 +90,9 @@ def _hash_nested_dict(
 
 def _batch(size: int, iterable: Iterable[T]) -> Iterator[list[T]]:
     """Utility batching function."""
+    if size <= 0:
+        msg = f"Batch size must be a positive integer, got {size}."
+        raise ValueError(msg)
     it = iter(iterable)
     while True:
         chunk = list(islice(it, size))
@@ -100,6 +103,9 @@ def _batch(size: int, iterable: Iterable[T]) -> Iterator[list[T]]:
 
 async def _abatch(size: int, iterable: AsyncIterable[T]) -> AsyncIterator[list[T]]:
     """Utility batching function."""
+    if size <= 0:
+        msg = f"Batch size must be a positive integer, got {size}."
+        raise ValueError(msg)
     batch: list[T] = []
     async for element in iterable:
         if len(batch) < size:
diff --git a/libs/core/tests/unit_tests/indexing/test_indexing.py b/libs/core/tests/unit_tests/indexing/test_indexing.py
index f598048a98f..f89786e17d7 100644
--- a/libs/core/tests/unit_tests/indexing/test_indexing.py
+++ b/libs/core/tests/unit_tests/indexing/test_indexing.py
@@ -16,6 +16,7 @@ from langchain_core.indexing import InMemoryRecordManager, aindex, index
 from langchain_core.indexing.api import (
     IndexingException,
     _abatch,
+    _batch,
     _get_document_with_hash,
 )
 from langchain_core.indexing.in_memory import InMemoryDocumentIndex
@@ -2433,6 +2434,26 @@ async def test_abatch() -> None:
     assert [batch async for batch in batches] == [[0, 1], [2, 3], [4]]
 
 
+def test_batch_validation() -> None:
+    """Test that _batch raises ValueError for non-positive batch sizes."""
+    with pytest.raises(ValueError, match="Batch size must be a positive integer"):
+        list(_batch(0, [1, 2, 3]))
+
+    with pytest.raises(ValueError, match="Batch size must be a positive integer"):
+        list(_batch(-1, [1, 2, 3]))
+
+
+async def test_abatch_validation() -> None:
+    """Test that _abatch raises ValueError for non-positive batch sizes."""
+    with pytest.raises(ValueError, match="Batch size must be a positive integer"):
+        async for _ in _abatch(0, _to_async_iter([1, 2, 3])):
+            pass
+
+    with pytest.raises(ValueError, match="Batch size must be a positive integer"):
+        async for _ in _abatch(-1, _to_async_iter([1, 2, 3])):
+            pass
+
+
 def test_indexing_force_update(
     record_manager: InMemoryRecordManager, upserting_vector_store: VectorStore
 ) -> None: