Avahi optimisations

[Morgan Collett]

Michael Stone wrote:
>>    * Minimize size of announced services (i.e. drop unnecessary data from TXT)
>>      - The biggest item in the TXT of contacts is the key (which is BIG). But
>>        this key is a requirement of bitfrost, so we can't get rid of it.
> 
> So far as I have been informed, the Bitfrost protections that would
> require key transmission have not even been planned, let alone
> implemented. Given that we think reducing mDNS bandwidth usage is a good
> idea, does anyone see a real problem with dropping these keys until that
> basic design work has been completed?

That's right - we have a meeting planned with Ivan and Jonathan Herzog
to look at the *requirements* for crypto, so everything we have now is
subject to change, and we are not using the keys *for crypto*.

However, Sugar's UI code currently tracks buddy objects by key, so the
key is required to be unique. I have a patch in #4656 to fix this, as it
prevented more than one key-less buddy from being displayed (e.g. a
regular XMPP client). This patch was considered too invasive for
Update.1 and has bit-rotted and needs to be redone. We also identify
friends in ~/.sugar/default/friends by key so that needs to change.
Since then we applied the patch in #6142 which actually *requires* all
buddies to have a key, due to a problem discovered by using hyperactivity.

Removing the keys from the TXT records without fixing these issues will
break mesh view so it's not something you can quickly have up and running.

Regards
Morgan