[messaging] Message order in group chat (attempt at summary)

[Moxie Marlinspike]

On 04/26/2014 06:52 AM, Ximin Luo wrote:
> There are some nice properties to aim for when one is developing an
> algorithm that turns a partial order (things don't get
> misinterpreted) into a linear order (nicer for users):
> 
> - static order (you don't need to redraw the UI later) - globally
> consistent (the same order appears for everyone)
> 
> Unfortunately, achieving both seems infeasible (without awkward
> strategies like holding back messages even though they are perfectly
> OK to display).

One compromise I was considering for the TextSecure UI was:

1) We're sending the last-message-seen hash as a "reply to" field.

2) We display messages linearly, and never re-order.

3) Each message is displayed with a small icon or color which indicates
that you've seen the message it is responding to.

4) If you long-click the message, it'll display "In reply to..."

That way when Alice says "I do!" in reply to what she thought was "who
wants ice cream?", but it shows up below "Who wants to kill the
President?" for everyone else, everyone else will immediately see that
"I do!" is in response to a message they have not seen.

If "Who wants ice cream?" later shows up in their stream, they can still
think "Wait, does Alice really want to kill the President?" and
long-click to see that, in fact, she just wants to get ice cream.

- moxie

-- 
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