This is a very exciting project - thanks for releasing this!

I tried to get it working with my https://datasette.io/ ASGI app and ran into this error:

  File "/Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/multiprocessing/process.py", line 121, in start
    self._popen = self._Popen(self)
                  ^^^^^^^^^^^^^^^^^
  File "/Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/multiprocessing/context.py", line 288, in _Popen
    return Popen(process_obj)
           ^^^^^^^^^^^^^^^^^^
  File "/Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/multiprocessing/popen_spawn_posix.py", line 32, in __init__
    super().__init__(process_obj)
  File "/Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/multiprocessing/popen_fork.py", line 19, in __init__
    self._launch(process_obj)
  File "/Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/multiprocessing/popen_spawn_posix.py", line 47, in _launch
    reduction.dump(process_obj, fp)
  File "/Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/multiprocessing/reduction.py", line 60, in dump
    ForkingPickler(file, protocol).dump(obj)
AttributeError: Can't pickle local object 'asgi_csrf_decorator.<locals>._asgi_csrf_decorator.<locals>.app_wrapped_with_csrf'

Here's the script I wrote to replicate the problem, saved as serve_datasette_with_granian.py:

from granian.server import Granian
from granian.constants import HTTPModes, Interfaces, Loops, ThreadModes
from granian.log import LogLevels
from datasette.app import Datasette


def serve_with_granian():
    ds = Datasette(memory=True)
    app = ds.app()
    Granian(
        app,
        address="127.0.0.1",
        port=8002,
        interface=Interfaces.ASGI,
        workers=1,
        threads=1,
        pthreads=1,
        threading_mode=ThreadModes.workers.value,
        loop=Loops.auto.value,
        http=HTTPModes.auto.value,
        websockets=True,
        backlog=1024,
        log_level=LogLevels.info.value,
        ssl_cert=None,
        ssl_key=None,
    ).serve()


if __name__ == "__main__":
    serve_with_granian()

Run it like this to see the error (run pip install datasette first):

python serve_datasette_with_granian.py

Are there changes I can make to Datasette to get this to work, or is this something that illustrates a bug in Granian?

Relevant Datasette code is here: https://github.com/simonw/datasette/blob/6a352e99ab988dbf8fd22a100049caa6ad33f1ec/datasette/app.py#L1429-L1454

It's applying my asgi-csrf ASGI middleware from https://github.com/simonw/asgi-csrf