Bug: APIGatewayHttpResolver with validation enabled returns HTTP 422 when using single value query parameters about powertools-lambda-python HOT 15 OPEN

@DariusKunce Confirmed! We'll add this into the next sprint to fix

def test_weird_issue():
    # GIVEN a Http API V2 proxy type event
    app = APIGatewayRestResolver(enable_validation=True)

    class FunkyTown(BaseModel):
        parameter: str

    @app.get("/my/path")
    def my_path(
        parameter: Annotated[str | None, Query(alias="parameter1")] = None,
    ) -> Response[FunkyTown]:
        assert isinstance(app.current_event, APIGatewayProxyEvent)

        assert parameter == "value"
        return Response(200, content_types.APPLICATION_JSON, FunkyTown(parameter=parameter))

    result = app(load_event("apiGatewayProxyEvent.json"), {})

    print(result)
    assert result["statusCode"] == 200

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The issue isn't related to the alias but the fact that the openapi_validation.py handles all query strings with _normalize_multi_query_string_with_param and takes the first value of the item.

With "queryStringParameters": { "productType": "Category1" } it's normalize to: "productType": "C"

With "multiValueQueryStringParameters": { "productType": ["Category1"] } it's normalize correctly to: "productType": "Category1"

I was able to find this as I was trying to validate the min length of a query string parameter (def get_hello(fname: Annotated[Optional[str], Query(min_length=4)] = None) -> HelloWorld: and fname was always too short... as it was always truncated to 1 character.

The line truncating the value is here

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Thanks for opening your first issue here! We'll come back to you as soon as we can.
In the meantime, check out the #python channel on our Powertools for AWS Lambda Discord: Invite link

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Hi @DariusKunce this is on my list for verification tomorrow, thanks for submitting it!

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@DariusKunce we're aiming to make a release tomorrow with this fix ahead of schedule -- let us know if you're blocked by this and we can make it today.

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Thanks a lot for the timely comment @jpoissant.

@rubenfonseca i think we had mixed messaging and this wasn't fixed -- if you can't look into it tomorrow morning before release, let me know pretty plz

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Thank you so much @jpoissant I'm looking at this right now

from powertools-lambda-python.

The issue isn't related to the alias but the fact that the openapi_validation.py handles all query strings with _normalize_multi_query_string_with_param and takes the first value of the item.

With "queryStringParameters": { "productType": "Category1" } it's normalize to: "productType": "C"

With "multiValueQueryStringParameters": { "productType": ["Category1"] } it's normalize correctly to: "productType": "Category1"

@jpoissant I need to understand the problem a little bit better, since I'm unable to reproduce the problem. Can you please confirm which event handler are you using? Is it the APIGatewayRestResolver ?

Reason I'm asking is that the REST API Gateway will always send multiValueQueryStringParameters, so the existing code already works correctly.

So I need to understand what scenario do you have where you only have queryStringParameters. Can you please clarify?

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@rubenfonseca I am using the APIGatewayHttpResolver resolver. I just tried with the APIGatewayRestResolver and it work. So the bug is only related to the API Gateway v2 proxy payload format

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@rubenfonseca would it be better to open a new bug for the APIGatewayHttpResolver resolver?

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