Feature: support lifespan state in FastStream – FastAPI integration

[Lancetnik]

Well, we missed ASGI State feature – https://www.starlette.io/lifespan/

The following code should works without errors

from contextlib import asynccontextmanager
from fastapi import FastAPI, Request
from faststream.nats.fastapi import NatsRouter

@asynccontextmanager
async def lifespan(app: FastAPI):
    yield {"data": 1}

app = FastAPI(lifespan=lifespan)
router = NatsRouter()
app.include_router(router)

@router.subscriber("test")
async def handler(request: Request):
    assert request.state.data == 1

@router.after_startup
async def _(app: FastAPI):
    await router.broker.publish("Hi!", "test")

But, it couldn't be implemented in a regular way. Originally, ASGI server stores yielded values and injects it in each HTTP request – https://asgi.readthedocs.io/en/latest/specs/lifespan.html#lifespan-state

But, there is ni HTTP request and ASGI server on router.subscriber call, so we should inject this state manually.

We should pass this maybe_state – https://github.com/airtai/faststream/blob/main/faststream/broker/fastapi/router.py#L315

To request object – somewhere here https://github.com/airtai/faststream/blob/main/faststream/broker/fastapi/route.py#L210

[RenameMe1]

Can i work on this issue?

[Lancetnik]

Can i work on this issue?

For sure, thank you!

[Lancetnik]

Well, seems like it's not so easy. We can't get FastAPI.lifespan_context inside our router.lifespan method. We should figure it out before implement this feature