aiohttp cors breaks with new aiohttp 3.0 release

[idwaker]

aiohttp cors setup breaks with

 File "/home/idwaker/Code/webapp/app/api/common/utils/loaders.py", line 43, in init_cors
    cors = aiohttp_cors.setup(app, defaults=CORS_DEFAULTS)
  File "/home/idwaker/.local/share/virtualenvs/webapp-69lhAx_Z/lib/python3.6/site-packages/aiohttp_cors/__init__.py", line 65, in setup
    cors = CorsConfig(app, defaults=defaults)
  File "/home/idwaker/.local/share/virtualenvs/webapp-69lhAx_Z/lib/python3.6/site-packages/aiohttp_cors/cors_config.py", line 247, in __init__
    self._resources_router_adapter)
  File "/home/idwaker/.local/share/virtualenvs/webapp-69lhAx_Z/lib/python3.6/site-packages/aiohttp_cors/cors_config.py", line 117, in __init__
    self._app.on_response_prepare.append(self._on_response_prepare)
  File "aiohttp/_frozenlist.pyx", line 97, in aiohttp._frozenlist.FrozenList.append
  File "aiohttp/_frozenlist.pyx", line 19, in aiohttp._frozenlist.FrozenList._check_frozen
RuntimeError: Cannot modify frozen list.

on latest 3.0 release of aiohttp

my init_cors is something like this

async def init_cors(app: web.Application):
    logger = get_logger(app['name'])
    cors = aiohttp_cors.setup(app, defaults=CORS_DEFAULTS)

    # add resources to cors
    for resource in list(app.router.resources()):
        if isinstance(resource, web.Resource):
            cors.add(resource)
    logger.info("Initialized CORS for {}".format(app['name']))

and i am loading init_cors on app.on_startup

The issue seems to occur when i defer cors setup to on_startup signal like

app.on_startup.append(init_cors)

But it works normally if i put the cors init code on app setup like

 # register routes here
    register_routes(app)

    cors = aiohttp_cors.setup(app, defaults=CORS_DEFAULTS)

    # add resources to cors
    for resource in list(app.router.resources()):
        if isinstance(resource, web.Resource):
            cors.add(resource)

[idwaker]

I don't think the appending cors setup to startup signal was good idea anyway, so i removed that with simple function call for setup which works as desired.

[asvetlov]

@idwaker you are right