UPnP relay daemon

A small daemon to relay UPnP announcements between different networks and/or
NICs.



DESCRIPTION
-----------

The main intention for writing this program was that our Philips TV sends
out a single NOTIFY after booting and then does not reply to any M-SEARCH
requests.  This program steps in by caching all NOTIFYs it receives and
replying to any M-SEARCH on the network with all the previously captured
NOTIFYs, transformed into proper replies. A second use-case is to have this
program running on a router between two different nets, as an alternative to
having to setup multicast routing for UPnP to work.

Good to know:
 * This program only caches the UPnP announcements. It does not serve as a
   proxy for the actual media, i.e. a route between the devices must still
   exist.
 * The program queries the net (using M-SEARCH) every half an hour on its own,
   but no more often. So if you happen to have a device which does not send
   any NOTIFYs and is on a different subnet than your controller device you'll
   have to wait that long until you'll be able to see it.
 * The TV from above actually has even more problems: After some time, it
   announces that it is going offline, even though it does not. Compile with
   IGNORE_DOWN_MESSAGES to ignore such down messages.
 * This program does not strictly obey the standard. It ignores filters in
   requests and just replies with everything it knows to all requests (except
   for services from the host the M-SEARCH originates from). Also, it will
   only forward the LOCATION, ST and USN headers. The location header is
   mandatory for services to work through this cache, because this service
   does not forge the sender IP (and services will thus try to contact the
   computer where upnprp runs instead of the service's if it is missing)



INSTALLATION
------------

Just run `make'. The program should compile fine in any GNU environment and was
especially tested in OpenWRT. The compiled program accepts no command line
arguments and forks into background right after startup. You can test if it is
working by running Wireshark and checking if your PC sends/receives UPnP
requests/responses.

LICENSE
-------

Copyright (c) 2013, Phillip Berndt

This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.