Uvicorn: Option to disable lifespan protocol

[joshua-s]

Since the lifespan protocol is new, some ASGI frameworks have not implemented it. It would be nice to have a configuration option to disable lifespan so that no errors are thrown.

[simonw]

The example in the README doesn't work any more - if I try to run it I get this error:

$ uvicorn app:App --port 8005
INFO: Started server process [31803]
INFO: Waiting for application startup.
ERROR: Exception in 'lifespan' protocol
Traceback (most recent call last):
  File "/Users/simonw/.local/share/virtualenvs/datasette-oJRYYJuA/lib/python3.7/site-packages/uvicorn/lifespan.py", line 29, in run
    await self.asgi(self.receive, self.send)
  File "./app2.py", line 10, in __call__
    [b'content-type', b'text/plain'],
  File "/Users/simonw/.local/share/virtualenvs/datasette-oJRYYJuA/lib/python3.7/site-packages/uvicorn/lifespan.py", line 50, in send
    raise RuntimeError(error % message['type'])
RuntimeError: Got invalid message type on lifespan protocol "http.response.start"
ERROR: Application startup failed. Exiting.

[elmcrest]

I could work around the issue the README has with uvicorn==0.3.22.

[tomchristie]

@simonw Thanks yup. I've updated that now.

(It should raise an error on anything except HTTP messsges, which will cause the lifespan protocol to be ignored.)

[tomchristie]

Agree that we should have an option for this. #262 gets most of the way there, except that it's important that we default to having it on.

[tomchristie]

Now available as --disable-lifespan