Zeroconf JmDNS

This repository packages android friendly sources from the jmdns project and provides some tutorial demos.

See rosjava_core readme for more information and pointers on the overall rosjava and android ecosystem.

The JmDNS Library

About

JmDNS works a little differently from avahi, although it does the same job. You can separate its functionality into two parts:

1) Zeroconf services (publishing, discovery and resolution) on a fixed, specified interface. 2) Network topology aware zeroconf services (in the author’s language - multi-homed).

What the latter means, is that it will be automatically detect what network interfaces you have and also be aware of those interfaces going up and down whilst providing a dynamic awareness of the zeroconf services that appear and disappear with those interfaces.

The network topology part of jmdns is still fairly experimental.

The Experimental Part

The network topology aware part of zeroconf is quite important. On android in particular it saves you having to worry about detecting the ip of your interface, which is rather handy. This part is quite reliable after having helped with some patches upstream.

It does have problems however handling multiple network interfaces and can also be confusing with the way it handles ipv6. I have some patches here in this code set which get it working, but either aren’t upstream yet, or probably not the proper solution yet.

Hence we have a snapshot of the sources here.

Publishing

Publishing is relatively straightforward. For ros environments, we typically only ever want or need to publish the ros master, in which case you’d publish it under something like:

_ros-master._tcp 11311

Discovery

There are two methods in the jmdns library for discovery. The first is via polling, which will always be the far more reliable method (especially if your interface is up and down alot and likely to get jmdns confused). The second is via event based listeners which give you callbacks to instantly react on a zeroconf service coming up or down.

The ROS Wrapper

I’ve got a couple of classes set up to more easily handle the jmdns library for our purposes (jmdns can be quite messy to program with). It’s not a full node, but it wouldn’t be a stretch to convert this into a full node’s functionality using zeroconf_msgs as the basis for handles that work in a similar way to the ros zeroconf_avahi package.

Tutorials

Tutorials are implemented in the jmdns_tutorials project. Instructions can be found in the zerconf_jmdns_suite package ROS wiki.