We need to reset things at the UI level when we get a gappy sync, so give the
clients something to listen for.
Also add a bunch of tests for that bit of code.
Removing the last event in an EventTimeline (as we might, for instance, if it
was a local echo in an empty timeline) got us into a state where the baseIndex
would increment when adding events to the end of the timeline, causing much
confusion.
* This should fix the problem where we could end up with two concurrent syncs
due to both retrying /sync and hitting /versions. There is now one and only
one mechanism for connection recovery.
* Hit /versions a little less often as I think every 2 seconds is a little
over-aggressive. Also introduce randomness to minimize possibility of
thundering herds.
* Add a listener for the 'online' event in case any browser is nice enough
to ever fire it.
* Treat a 400 response from /versions as successful since older synapses
will not support it.
In order to resolve the conflict between local and remote read-receipts, try to
give precedence to the read-receipt which refers to the most recent event.
Also fix the read-receipt synthesis in _addLiveEvents so that it actually works
(drop the spurious MatrixEvent wrapper), and remove the synthesis in
recalculate() (which appears to be redundant).
This provides optional support for fetching old events via the /context API,
and paginating backwards and forwards from them, eventually merging into the
live timeline.
To support it, events are now stored in an EventTimeline, rather than directly
in an array in the Room; the old names are maintained as references for
compatibility.
The feature has to be enabled explicitly, otherwise it would be impossible for
existing clients to back-paginate to the old events after a gappy /sync.
Still TODO here:
* An object which provides a window into the timelines to make them possible to
use. This will be a separate PR.
* Rewrite the 'EventContext' used by the searchRoomEvents API in terms of an
EventTimeline - it is essentially a subset.
