Steve Howell 1498b2ef69 apply_event: Fix broken deepcopy attempt for subs. ...

When we were getting an apply_event call for
a subscription/add event, we were trying not to
mutate the event itself, but this clumsy code
was still mutating the actual event:

    # Avoid letting 'subscribers' entries end up in the list
    for i, sub in enumerate(event['subscriptions']):
        event['subscriptions'][i] = \
            copy.deepcopy(event['subscriptions'][i])
        del event['subscriptions'][i]['subscribers']

This is only a theoretical bug.

The only person who receives a subscription/add
event is the current user.

And it wouldn't have affected the current user,
since the apply_event was correctly updating the
state, and we wouldn't actually deliver the event
to the client (because the whole point of apply_event
is to prevent us from having to piggyback the
super-recent events on to our payload or put
them into the event queue and possibly race).

The new code just cleanly makes a copy of each
sub, if necessary, as we add them to state["subscriptions"].

And I updated the event schemas to reflect that
subscribers is always present in subscription/add
event.

Long term we should probably avoid sending subscribers
on this event when the clients don't set something
like include_subscribers.  That's a fairly complicated
fix that involves passing in flags to ClientDescriptor.
Alternatively, we could just say that our policy is
that we never send subscribers there, but we instead
use peer_add events.  See issue #17089 for more
details.

2021-01-21 15:04:07 -08:00

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