Failing to parse FastAPI Form using dishka inject

[dimanu-py]

I've been introducing dishka in a personal project that has an API built with FastAPI. Until now, all the endpoints that I've migrated have worked smoothly, but I am facing some issues when working with a basic authentication endpoint that emits a JWT token.

The current router and endpoint looks like this:

@authenticate_account_router.post("/login")
@inject
async def authenticate_account(
    login_form: Annotated[OAuth2PasswordRequestForm, Depends()],
    controller: FromDishka[AuthenticateAccountController],
) -> JSONResponse:
    result = await controller.authenticate(
        identification=login_form.username,
        password=login_form.password,
    )
    return FastAPIResponse.as_json(result)

When I make a request or run an acceptance test I keep getting a 422 status code with the following detail:

{
  "detail": [
    {
      "type": "model_attributes_type",
      "loc": [
        "body"
      ],
      "msg": "Input should be a valid dictionary or object to extract fields from",
      "input": "grant_type=password&username=string&password=********&scope=&client_id=string&client_secret=********"
    }
  ]
}

It looked like the @inject decorator was interfering with how FastAPI solves the Depends. Searching in the documentation, I found the section where it was explained how to integrate dishka with FastAPI Depends. Basically, we need to make a helper function annotated with the @inject too and pass that function to the Depends parameter. So I iterated the solution tryhing to keep it as simple as possible:

@inject
async def get_login_form(username: str = Form(...), password: str = Form(...)) -> OAuth2PasswordRequestForm:
    return OAuth2PasswordRequestForm(username=username, password=password)


@authenticate_account_router.post(
    "/login",
    responses={
        status.HTTP_200_OK: {"model": OkResponse},
        status.HTTP_422_UNPROCESSABLE_CONTENT: {"model": UnprocessableEntityError},
        status.HTTP_401_UNAUTHORIZED: {"model": UnauthorizedError},
    },
)
@inject
async def authenticate_account(
    login_form: Annotated[OAuth2PasswordRequestForm, Depends(get_login_form)],
    controller: FromDishka[AuthenticateAccountController],
) -> JSONResponse:
    result = await controller.authenticate(
        identification=login_form.username,
        password=login_form.password,
    )
    return FastAPIResponse.as_json(result)

But I still get a similar error:

{
  "detail": [
    {
      "type": "model_attributes_type",
      "loc": [
        "body"
      ],
      "msg": "Input should be a valid dictionary or object to extract fields from",
      "input": "username=johndoe&password=superstrongpassword"
    }
  ]
}

Is there a bug working with form requests? Or is it just not supported?

[Tishka17]

I am not sure if dishka is related here. Try removing @inject and controller from your authenticate_account function and check if is starts working without dishka usage (I know, you won't be able to call controller in handler, but we only want to check if it is executed, so no real code required)

[dimanu-py]

Yep… Dishka wasn’t the problem. It’s been a real headache, but the issue turned out to be that my endpoint was being shadowed by another one, causing the request to hit the wrong endpoint instead of the login endpoint.

Thanks for taking the time to reply anyway 🫶