Injecting instances with a __call__ method on the class

[bejoygm]

One of the use case is to Inject an instance of HttpBearer in FastAPI routes

since the instance will have a different type than the class definition itself, this doesn't inject the instance as a dependency. Is there a workaround? Thanks

[meadsteve]

@bejoygm Have you got a short code snippet that doesn't work correctly so I can get my head around this?

[meadsteve]

My instinct is that with HttpBearer it makes more sense to make your code depend on thing it needs HTTPAuthorizationCredentials and then have something like:

container[HTTPAuthorizationCredentials] = lambda c: c[HttpBearer](c[Request])

[bejoygm]

@meadsteve here's one of the ways

from fastapi import Depends
from fastapi.security import HTTPBearer

@router.get("")
async def get_something(
    auth_token=Depends(HTTPBearer()),  # noqa
):
    pass

you can find similar examples here

[meadsteve]

So if I understood correctly the following might be what you want. I've not tested it but the way I would write something like that with lagom would be:

container = Container()
deps = FastApiIntegration(container)

container[HTTPAuthorizationCredentials] = lambda: HTTPBearer()() # I think - I'm not really sure here what's going on

@router.get("")
async def get_something(
    auth_token= deps.depends(HTTPAuthorizationCredentials)
):
    pass

One of the goals of lagom was to make code work well with type checking so that deps.depends(X) will always return an instance of X.

So it really depends what type you want auth_token to have.

[bejoygm]

container[HTTPAuthorizationCredentials] = lambda: HTTPBearer()()

☝️ This would have worked I guess but the HTTPBearer object's __call__ takes a request parameter. Pasting the code here for ref.

async def __call__(self, request: Request) -> Optional[HTTPAuthorizationCredentials]:
        authorization: str = request.headers.get("Authorization")
        scheme, credentials = get_authorization_scheme_param(authorization)
        if not (authorization and scheme and credentials):
            if self.auto_error:
                raise HTTPException(status_code=HTTP_403_FORBIDDEN, detail="Not authenticated")
            else:
                return None
...

I tried passing the request parameter explicitly, but the injected object is not correct (in this case, a coroutine object)

container[HTTPBearer] = lambda: HTTPBearer()
container[HTTPAuthorizationCredentials] = lambda c: c[HttpBearer](c[Request])

[meadsteve]

ah I missed that it took a request objection as an argument. I believe what you reference here:

container[HTTPBearer] = lambda: HTTPBearer()
container[HTTPAuthorizationCredentials] = lambda c: c[HttpBearer](c[Request])

should have worked. Let me take a deeper look at what's happening.

[meadsteve]

🤦 I totally missed that HTTPBearer is an async __call__ I'll need to rework my suggestion

[meadsteve]

So the "simple" solution is to tweak the above to:

container[HTTPBearer] = Singleton(lambda: HTTPBearer())
container[Awaitable[HTTPAuthorizationCredentials]] = lambda c: c[HTTPBearer](c[Request])

@router.get("")
async def get_something(
    auth_token= deps.depends(Awaitable[HTTPAuthorizationCredentials])
):
    await auth_token

but I'm a bit hesitant to suggest this as if auth_token is not awaited then the auth logic is skipped.

[bejoygm]

with the explicit await, the generated docs will not have the token documented properly. Anyways, I think it is not a big issue. I can always use fastAPI Depends for this stuff. We have started using lagom at other places for dep injection and it is a joy to work with. Thanks for the library! 🙌

[meadsteve]

@bejoygm thank you that's really nice to hear. And using the fastapi one sounds like the best approach here 👍 especially for anything related to security/auth.