fix(multipart): return HTTP 413 for size limit violations

litestar/_multipart.py

@@ -12,11 +12,16 @@
 )
 
 from litestar.datastructures.upload_file import UploadFile
-from litestar.exceptions import ClientException
+from litestar.exceptions import ClientException, HTTPException, RequestEntityTooLarge
+from starlette.status import HTTP_413_REQUEST_ENTITY_TOO_LARGE
+from litestar.utils.compat import async_next
 
-__all__ = ("parse_content_header", "parse_multipart_form")
+raise HTTPException(
+    status_code=HTTP_413_REQUEST_ENTITY_TOO_LARGE,
+    detail="multipart request exceeds size limits",
+)
 
-from litestar.utils.compat import async_next
+__all__ = ("parse_content_header", "parse_multipart_form")
 
 if TYPE_CHECKING:
     from collections.abc import AsyncGenerator
@@ -133,8 +138,8 @@ async def parse_multipart_form(  # noqa: C901
             await data.close()
         await _close_upload_files(fields)
 
-        # FIXME (3.0): This should raise a '413 - Request Entity Too Large', but for
-        # backwards compatibility, we keep it as a 400 for now
-        raise ClientException("Request Entity Too Large") from None
+        # FIXED (3.0):Raises '413 - Request Entity Too Large' when upload exceeds the configured limit
+        # Note: Previously returned 400 for backward compatibility; now correctly raises 413
+        raise RequestEntityTooLarge("Request Entity Too Large") from None
 
     return {k: v if len(v) > 1 else v[0] for k, v in fields.items()}

tests/unit/test_multipart_413.py

@@ -0,0 +1,19 @@
+import pytest
+from litestar import Litestar, post
+from starlette.status import HTTP_413_REQUEST_ENTITY_TOO_LARGE
+from litestar.testing import create_test_client
+
+@post("/upload")
+async def upload_handler(data):
+    return {"success": True}
+
+@pytest.mark.anyio
+async def test_oversized_file_returns_413():
+    app = Litestar(
+        route_handlers=[upload_handler],
+        multipart_form_part_limit=10,  # small limit to trigger the error
+    )
+
+    async with create_test_client(app) as client:
+        response = await client.post("/upload", data={"file": "x" * 100})
+        assert response.status_code == HTTP_413_REQUEST_ENTITY_TOO_LARGE