Bug: Open API Validation not validating response serialization when body is Falsy. #5887
Description
Expected Behaviour
When:
- resolver (of type APIGatewayResolver) has
enable_validation=Trueand, - route's function is annotated with a return type
X(e.g. a Pydantic model) and, - route's function return value is not of type X (and cannot be casted)
Expected:
raise a 422 (HTTPStatus.UNPROCESSABLE_ENTITY) as the result of error in response serialization
Current Behaviour
If function's return value is Falsy, the route is resolved to a 200 OK.
Code snippet
from typing import Literal
from aws_lambda_powertools.event_handler.api_gateway import APIGatewayRestResolver
from pydantic import BaseModel
import pytest
app = APIGatewayRestResolver(enable_validation=True)
class Todo(BaseModel):
title: str
status: Literal["Pending", "Done"]
@app.get("/none")
def return_none() -> Todo:
return None
@app.get("/empty_list")
def return_empty_list() -> Todo:
return list()
@app.get("/empty_dict")
def return_empty_dict() -> Todo:
return dict()
@app.get("/empty_string")
def return_empty_string() -> Todo:
return ""
def lambda_handler(event, context):
return app.resolve(event, context)
# --- Tests below ---
@pytest.fixture()
def event_factory():
def _factory(path: str):
return {
"httpMethod": "GET",
"path": path,
}
yield _factory
@pytest.mark.parametrize(
"path, body",
[
("/empty_dict", "{}"),
("/empty_list", "[]"),
("/none", "null"),
("/empty_string", ""),
],
ids=["empty_dict", "empty_list", "none", "empty_string"],
)
def test_unexpected_response_validation(path, body, event_factory):
"""Test to demonstrate cases where a non-OK response is expected from APIGatewayResolver."""
event = event_factory(path)
response = lambda_handler(event, None)
assert response["statusCode"] == 200
assert response["body"] == body
if __name__ == "__main__":
pytest.main(["-v", __file__])Possible Solution
Replace the falsy valuation of the response body in the _handle_response method of the OpenAPIValidationMiddleware class with a more robust class/type comparison.
Steps to Reproduce
- save snippet above to a file
- install the following dependencies
- "aws-lambda-powertools>=3.4.1"
- "pydantic>=2.10.5"
- "pytest>=8.3.4"
- run the file
Powertools for AWS Lambda (Python) version
latest, 3.4.1
AWS Lambda function runtime
3.12
Packaging format used
PyPi