[cups-devel] [UNKN] STR #4373: When restarting avahi-daemon while CUPS is running, CUPS looses connection

[till.kamppeter at gmail.com]

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[STR New]

This is a follow-up to STR #4300 and STR #4370

Original issue:

I use CUPS with shared printers and the shared printers are broadcasted by
Avahi. This works well when avahi-daemon is started before cups and both
keep running. But if I restart avahi-daemon while CUPS is running, CUPS
looses connection to avahi-daemon and so stops broadcasting. What I expect
is that CUPS reconnects after the restart of avahi-daemon. This can easily
happen if for example the avahi-daemon package gets updated or the admin
changes the configuration of avahi-daemon.

Solution (patch for CUPS 1.7.1 attached):

Unfortunately, your one-line fix of STR #4370 does not work. First, the
printer registration has to be done only when avahi-daemon actually appears
and if avahi-daemon disappears, the Avahi client has to be freed and
renewed to be ready for the next time of avahi-daemon appearing. This is
done withing the client callback function of the avahi client, which is
called whenever avahi-daemon changes state. See the section

How to Write a Client That Can Deal with Daemon Restarts

on

http://avahi.sourcearchive.com/documentation/0.6.17/main.html

The patch does exactly this when built with HAVE_AVAHI and it does exactly
tghe same as before with HAVE_DNSSD or without DNS-SD support. Also the
cupsd-internal API (for the other files of cupsd) is unchanged to make the
patch as minimum-invasive as possible.

I have tested the patch with starting and stopping the local avahi-daemon
and starting and stopping cupsd on remote CUPS servers in different orders,
also both with and without presence of cups-browsed and everything works as
expected now.

Link: https://www.cups.org/str.php?L4373
Version: 1.7.1
Attachment: https://www.cups.org/strfiles/4373/cupsd-support-avahi-daemon-restarting.patch
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