This commit changes the format of the encryption id to be based off 3
things:
1) The group id
2) The timestamp
3) The actual key
Previously this was solely based on the timestamp and the group id, but
this might lead to conflicts. Moreover the format of the key was an
uint32 and so it would wrap periodically.
The migration is a bit tricky, so first we cleared the cache of keys,
that's easier than migrating, and second we set the new field hash_id to
the concatenation of group_id / key_id.
This might lead on some duplication in case keys are re-received, but it
should not have an impact on the correctness of the code.
I have added 2 tests covering compatibility between old/new clients, as
this should not be a breaking change.
It also adds a new message to rekey in a single go, instead of having to
send multiple messages
We only write up migrations, down migrations are not always possible in sqlite or
too complex/too expensive. For example to remove a column you would have to duplicate
the table, copy over the data, delete and recreated.
This can be very expensive for some tables (user_messages for example), so should not be attempted.
Notes
One issue we faced multiple times is that updates to user_messages can be very
expensive, leading to slow upgrade times and interrupted migrations. So avoid
writes if not necessary.
23f71c1125