Presence not updated, when client disconencts from telepathy-salut

[ajay_garg]

Corresponding downstream ticket ::
 https://dev.laptop.org.au/issues/1332

[ajay_garg]

This required patching Avahi.

F14-patched rpms available at ::
 http://people.sugarlabs.org/ajay/root/freedesktop_bug_51501/RPMS/

If required, corresponding F17 patches maybe generated easily, via "customize-avahi-default-ttl-values.patch" patch available in the source-rpm at  http://people.sugarlabs.org/ajay/root/freedesktop_bug_51501/SRPM/

Please refer  https://bugs.freedesktop.org/show_bug.cgi?id=51501

History ::
===========

As pointed out by Simon McVittie in  https://bugs.freedesktop.org/show_bug.cgi?id=51501#c4,
 https://tools.ietf.org/html/draft-cheshire-dnsext-multicastdns-15#section-10
suggests that the Time-To-Live (TT) of the mDNS record is likely to be 120 seconds.

However, for all purposes, in whatever testing I came across Avahi, the TTL in effect was
75 minutes , which seemed a bit too late a notification of buddy-going-disconnected.

Fix ::
======
Decrease the Time-To-Live (TTL).

Solution ::
===========

Obviously, the easiest solution is to set the appropriate values in

#define AVAHI_DEFAULT_TTL_HOST_NAME
#define AVAHI_DEFAULT_TTL

However, this has the following caveats ::

(i)
It needs a re-compilation/re-packaging of avahi rpms, for every
change in the values. This is a major deployment headache.

(ii)
Also, there is no ideal "TTL" values.

The lesses the TTL values, more frequent multicast DNS packets will be exchanged
between a pair of peers, thus leading to more traffic.

However, too large a TTL value, would mean that the peer gets too late a notification
of the buddy going disconnected.

Thus, ideal values can only be found out by testing in real-field.
This requires easy configuration of the TTL values, without needing to
re-compile the rpms.

Solution-Implementation ::
==========================

The cutomized TTL values will be read during "avahi-daemon" startup.

1.
AVAHI_DEFAULT_TTL_HOST_NAME will be set to the value, contained in the
file "/etc/avahi/avahi-default-ttl-host-name.conf".

Default value is the same as before, i.e. 120 (seconds).

2.
AVAHI_DEFAULT_TTL will be set to the value, contained in the
file "/etc/avahi/avahi-default-ttl.conf".

Default value is the same as before, i.e. 4500 (seconds), which is equal to
75 minutes.

How to customize ::
===================

a)
"sudo service avahi-daemon stop"

b)
Change the values in the corresponding conf files.

c)
"sudo service avahi-daemon start"

AUTHOR: Ajay Garg <ajay@…>

Thanks to ::

Will Thompson <will.thompson@…>
Simon McVittie <simon.mcvittie@…>
Xavier Claessens <xclaesse@…>

[ajay_garg]

Patch at ::
 http://people.sugarlabs.org/ajay/root/freedesktop_bug_51501/common-patch-for-f14-and-f17/customize-avahi-default-ttl-values.patch

RPMS at ::
 http://people.sugarlabs.org/ajay/root/freedesktop_bug_51501/platforms/f14/RPMS/
 http://people.sugarlabs.org/ajay/root/freedesktop_bug_51501/platforms/f17/RPMS/

olpc, sugar-devel discussions at ::
 http://lists.sugarlabs.org/archive/sugar-devel/2012-July/038442.html