ASGI Lifespan Not Supported in restate-sdk-python

[objecthuman]

The current implementation of the restate Python SDK as of version 0.7.3 does not support the lifespan event.
Current Behavior In the file restate/sdk-python/python/restate/server.py, the following code is present:

async def app(scope: Scope, receive: Receive, send: Send):
    try:
        if scope['type'] == 'lifespan':
            raise LifeSpanNotImplemented()

lifespan event is necessary for applications that open long-running connections (such as database connections or websockets) and require a clean shutdown or restart mechanism. Currently, there's no workaround for this either. For example, I tried this for connection pool shutdown with the atexit library, but it didn't work.

Request: Please consider implementing ASGI lifespan support in a future release of the restate Python SDK.

Also, I didn't find any contributing.md, so I do not know how I can proceed with raising a PR and fixing the issue myself.

[objecthuman]

An update here, I wrote this wrapper workaround to support lifespan events:

import typing

from restate import VirtualObject, app
from restate.server_types import Receive, Scope, Send
from restate.service import Service
from restate.workflow import Workflow


class CustomScope(Scope):
    type: typing.Literal[
        "http", "lifespan", "lifespan.startup", "lifespan.shutdown"
    ]


class CustomAsgiHandler:
    def __init__(
        self,
        services: typing.Iterable[
            typing.Union[Service, VirtualObject, Workflow]
        ],
        protocol: typing.Optional[
            typing.Literal["bidi", "request_response"]
        ] = None,
        identity_keys: typing.Optional[typing.List[str]] = None,
        lifespan_func: typing.Optional[
            typing.Callable[[], typing.AsyncContextManager[typing.Any]]
        ] = None,
    ) -> None:
        self._restate_app = app(services, protocol, identity_keys)
        self._lifespan_func = lifespan_func

    async def __call__(
        self, scope: CustomScope, receive: Receive, send: Send
    ) -> None:
        if scope["type"] == "lifespan":
            await receive()
            if self._lifespan_func is not None:
                async with self._lifespan_func():
                    await send({"type": "lifespan.startup.complete"})
                    await receive()
            return

        return await self._restate_app(scope, receive, send)

[igalshilman]

Hey, yes indeed we did not implement it because restate itself does not manage any resources.

What is it that you are trying to do exactly. Can you show a usage example of the lifespan function you’ve provided.

The implementation you’ve provided looks reasonable, if you want to contribute that, feel free to open a PR, and tag me as a reviewer.
One thing I’d encourage you is to take a look at FastAPI and Starlette, and make sure that with this change app can be still mounted on these frameworks.

[objecthuman]

Hey, yes indeed we did not implement it because restate itself does not manage any resources.

What is it that you are trying to do exactly. Can you show a usage example of the lifespan function you’ve provided.

The implementation you’ve provided looks reasonable, if you want to contribute that, feel free to open a PR, and tag me as a reviewer. One thing I’d encourage you is to take a look at FastAPI and Starlette, and make sure that with this change app can be still mounted on these frameworks.

@igalshilman An example would be something like this:

@asynccontextmanager
async def lifespan():
    await ConnectionPool.start()
    yield
    await ConnectionPool.shutdown()

app = CustomAsgiHandler(
    services=[
        blinkit_brand_scraper,
        swiggy_brand_scraper,
        zepto_brand_scraper,
        token_bucket_limiter,
    ],
    lifespan_func=lifespan,
)

Sure, I will raise a PR & tag you.

[igalshilman]

Hey @objecthuman, just checking in, if you want to proceed with that? other wise I'll assign (possibly myself)

[objecthuman]

@igalshilman I am out for the weekend. I already have the PR ready, but I was waiting for a release to happen and then raise the PR. As soon as I am back, I will raise the PR.