Overwrite request last id for avoiding infinite loop

[Iftimie]

Summary:

• Get the id of last event in the list of maximum 100 items, and overwrite the request.channel_last_ids[channel] with it
• Add unit test

Explanation: When the frontend sends lastEventId like ReconnectingEventSource('/events/?channel=testchannel', {lastEventId: 'testchannel:0'}) or like this ReconnectingEventSource('/events/?channel=testchannel&lastEventId=testchannel:0')

the backend can get in an infinite loop.

• in eventstream.py, resp.channel_more.add(channel) is executed
• in consumers.py, if len(event_response.channel_more) > 0 is true and the loop continues
• in consumers.py, await self.get_events(event_request) is executed with the same requests which has the same initial last_id

Thus, overwriting the last_id in the same request object solves the problem

[jkarneges]

Thanks for this!

It looks like the two commits aren't quite related. The one that fixes the infinite loop seems legitimate, and I'm willing to merge it. However, I'm skeptical about the one that changes the storage behavior. Can you remove the latter (perhaps put it in a separate PR) so that I can merge this PR to only fix the infinite loop?

[Iftimie]

Hi! Sorry for the second commit. That was a mistake.