Don't swallow asyncio.CancelledError

[Oleg A.]

No library should be swallowing CancelledError exceptions unconditionally like that, it will just break other people's applications.

aiohttp-sse/aiohttp_sse/__init__.py

Lines 138 to 146 in 7fdb432

     async def wait(self) -> None: 
         """EventSourceResponse object is used for streaming data to the client, 
         this method returns future, so we can wait until connection will 
         be closed or other task explicitly call ``stop_streaming`` method. 
         """ 
         if self._ping_task is None: 
             raise RuntimeError("Response is not started") 
         with suppress(asyncio.CancelledError): 
             await self._ping_task 

The problem is that your program won't stop when you explicitly told it to stop.

async def my_task():
    while True:
        ...
        await sse_response.wait()

async def main():
    t = asyncio.create_task(my_task())
    await asyncio.sleep(0.5)
    t.cancel()
    with suppress(asyncio.CancelledError):
        await my_task()

This program will never exit.

Originally posted by @Dreamsorcerer in #456 (comment)

[Oleg A.]

Then we discussed that we need to add something like that:

if asyncio.current_task().cancelling():
            raise asyncio.CancelledError

[Oleg A.]

Workaround for python < 3.11

Use delayed sse.stop_streaming() instead of timeout

loop = asyncio.get_event_loop()
loop.call_later(delay, sse.stop_streaming)
await sse.wait()