Bug: Injecting a custom Context field implementing __eq__ does not work

[antoinehumbert]

Describe the bug
Since https://github.com/airtai/faststream/pull/1667/files, when trying to use a custom Context field that implements __eq__ returning NotImplemented in some cases, the dependency is not injected in subscriber.

How to reproduce
Having following User class:

class User:
    def __init__(self, id):
        self.id = id

    def __eq__(self, other):
        if not isinstance(other, User):
            return NotImplemented
        return self.id == other.id

Having a middleware injecting a User object in the context:

from faststream import BaseMiddleware, context


class UserMiddleware(BaseMiddleware):
    async def on_consume(self, msg):
        context.set_local("user", User(1))
        return await super().on_consume(msg)

Having a subscriber with user from context as a dependency:

@broker.subscriber("authenticated-topic")
def handler(msg, user: User = Context("user")):
    ...

The user parameter is not injected leading to a pydantic validation error because field is missing.

The issue arises because this (

faststream/faststream/utils/context/types.py

Line 63 in 689f674

if (

) if statement always evaluates to False.

Here is what happens when doing the comparison with EMPTY:

• User.__eq__ is called, returning NotImplementError
• So, the comparison User(1) != EMPTY evaluates to not(NotImplementedError) which is False, leading to not injecting user in kwargs.

I think that _EmptyPlaceHolder.__eq__ should return False instead of NotImplementedError when compared with an object which is not an _EmptyPlaceHolder object, because this kind of comparison is what would most commonly happen at

faststream/faststream/utils/context/types.py

Line 63 in 689f674

if (

, and the fact is that any object that is not an _EmptyPlaceHolder instance should pass the test.

Additionaly, I think this comparison should be made with EMPTY as the lhs operand (i.e. EMPTY != ...), as this will ensure that _EmptyPlaceHolder.__eq__ is called first and will always return a result (True if the rhs is an _EmptyPlaceHolder object, False otherwise), avoiding potential side effects depending on implementation of __eq__ in the compared object

[Lancetnik]

@antoinehumbert thank you for such detail Issue! Do you want to make a PR (I see you almost have a fix) or let me do it by myself?

[antoinehumbert]

I'll provide a PR soon

[Lancetnik]

Thank you a lot!