Start-Up / Tear-Down / Configuration

shallot provides a way to register functions, which get called when the webserver has started or when it is about to stop. This functions can be used for setting-up your application. Your on_start - function will be called when the server has started, but before it actually accepts connections. Even more, the asyncio-loop has been set by the server and can now been used by your application for starting background-tasks or initialize other code like database-connections.

To register your on_start - function, create an async-function with the following signature:

async def on_start(context):
    return {"db": db_connnection, "anything_else": ...}

You must provide an async-function, that accepts one parameter. Your on_start- function will be called with the current scope of the lifespan-event (a dict), that is provided by the server. (see asgi-specification). The data you return, will be appended to every request and is accessible under the key config

async def http_handler(request):
    db = request["config"]["db"]
    result = db.query()
    ...

If you want to be notified when the server is going to shut down, then you can provide an on_stop - function with the same signature as on_start:

async def on_stop(context):
    ...
    db_connnection.close()
    # log the server-shutdown

When on_stop is called, then the server has already stopped accepting requests and just waits on you to tear-down your application.

Both functions on_start and on_stop are registered via build_server

server = build_server(handler, on_start=on_start, on_stop=on_stop)