lifespan context is not stored in state, it actually replaces it

[SirDroun]

Using the lifespan pattern with a context manager and am quite happy with its existence. There is still something that bothers me with with it though. The context that the context manager creates needs to be None, because anything else is regarded as the full state: State() of the the app. It is possible to set this manually in the state, but that does not fit well with a context created by some other object.

Example:

class MyState:
  def __init__(self, application):
    self.some_connecion = connect()

  @asynccontextmanager
  @classmethod
  async def lifespan(cls, application):
    yield cls(application)

app = Starlette(..., lifespan=MyState.lifespan)

def some_endpoint(...):
    request.app.state.lifespan.some_connection.do_stuff()

This will fail today, application.state becoming MyState() and this is not what is expected by a number of other functions.
You would need to do:

 async def lifespan(cls, application):
   my_state = MyState(application)
   application.state.lifespan = my_state
   yield

Which i find counter intuitive for a context manager.

I would suggest changing in routing.Router.lifespan() to check if the returned context is a State() instance (to keep current behavior) and if not, add the context as a lifespan part of the state, or add it as a separate local_state or similar on the application level.

[Kludex]

You need to use request.state in the endpoint, not app.state.

[SirDroun]

Sorry, but I don't think that is the issue. Yes, my example was wrong, but the fact it is that the lifespan code is not handling this. In https://github.com/encode/starlette/blob/master/starlette/routing.py#L725 you have

            async with self.lifespan_context(app) as maybe_state:
                if maybe_state is not None:
                    if "state" not in scope:
                        raise RuntimeError(
                            'The server does not support "state" in the lifespan scope.'
                        )
                    scope["state"].update(maybe_state)

And if I'm not mistaken the scope["state"].update(maybe_state) will replace whatever is in "state", i.e removing everything else that that has previously been assigned to the state. That is also the symptom I see when trying to return other than None from the lifespan ctx manager.

[Kludex]

There was nothing assigned to it at that point. Just an empty dict.