A stream is vacant when it has no subscribers and occupied when it has at least
one subscriber.
We have a slightly odd model where stream creation is conflated with
subscription creation. Streams are created by attempting to subscribe to a
stream that doesn't exist. We also hide streams with no subscribers from users
to make it seem like they've gone away. However, we can't actually remove those
streams because we want to preserve history.
This commit moves us towards a separation of these two concepts. By sending
events for stream creation, occupation, vacancy, and deletion, we allow clients
to directly observe the global state of streams rather than indirectly observing
subscription information. A more complete solution would involve adding a view
for explicitly creating streams without subscribing to them.
This commit does not handle the intricacies of invite-only streams. We
currently simply do not send these events for invite-only streams.
(imported from commit 5430e5a5eecefafcdba4f5d4f9aa665556fcc559)
Zev Benjamin
Jessica McKellar
Steve Howell