Host Wakeup Service
-------------------
This service will collect the MACs and hostnames of all stations
at the LAN on which this service is running. If a program needs
to wakeup such a station it can delegate this to this service so
it doesn't have to remember its MAC.

Homepage: https://github.com/flensrocker/hostwakeup
Author  : Lars Hanisch <dvb@flensrocker.de>

How it works
------------
hostwakeup retrieves the MAC from the network interface (eth0, can
be controlled with the parameter "-i"), starts a tcp-server on some
random port and publish this port and the hostname/mac combination
via avahi as "_host-wakeup._tcp" with a TXT record
"host=name,mac=xx:xx:xx:xx:xx:xx".

Then it starts an avahi-browser for its type and republish every
found host/mac as an additional TXT record. This makes sure every
hostwakeup service will know every host/mac. Even if on a host
shutdown its record will survive on the other hosts.

Also on shutdown the known hosts are stored on disk and reloaded
on startup (default ist /var/cache/hostwakeup/hosts.conf, can be
controlled with the parameter "-f").

This list will only grow, never reduced automatically. If it contains
old hosts they have to be removed manually from every service.

If you need to wakeup some host, you can instruct hostwakeup to do it.
It will lookup the MAC and send the WOL magic packet to the broadcast
address of its interface. If it doesn't know the host it will delegate
the wakeup via TCP to the other running hostwakeup services. But this
is only a fallback since every host should always know all hosts. But
who knows... :)

Waking up hosts
---------------
There are two ways to call hostwakeup: DBus and TCP
Since the TCP port is dynamically assigned it may be a bit complicated
to detect it. You can look for it with avahi but if you use avahi you
can also use DBus...

TCP from a shell (not recommended):
look for port:
$ avahi-browse -r -t _host-wakeup._tcp
call hostwakeup:
$ echo "wakeup hostname" | nc localhost port

DBus from shell:
$ dbus-send --system --type=method_call --dest=de.yavdr.hostwakeup \
  --print-reply /Hosts de.yavdr.hostwakeup.Wakeup string:'hostname'

Python:
import dbus
def WakeupHost(hostname):
    bus = dbus.SystemBus()
    Hosts = bus.get_object('de.yavdr.hostwakeup', '/Hosts')
    return Hosts.Wakeup(hostname, dbus_interface = 'de.yavdr.hostwakeup')

Configuration
-------------
If you want to run this service as non-root you have to allow the user
to connect to the DBus-System-Bus. Have a look at de.yavdr.hostwakeup.conf
and copy this file to /etc/dbus-1/system.d. In this example it is allowed
for the user "root".
You can also find an Upstart-Job configuration at the file hostwakeup.conf.
Since it needs DBus, Avahi and network you need the right startup
dependencies on your system.

TODO
----
- don't depend on running dbus-daemon or avahi-daemon
  just reconnect if they run again
- do error handling on avahi-service and -browser
- maybe multi-interface support?