Proper way to publish and find services on a LAN using Python

Question

My app opens a TCP socket and waits for data from other users on the network using the same application. At the same time, it can broadcast data to a specified host on the network.

Currently, I need to manually enter the IP of the destination host to be able to send data. I want to be able to find a list of all hosts running the application and have the user pick which host to broadcast data to.

Is Bonjour/ZeroConf the right route to go to accomplish this? (I'd like it to cross-platform OSX/Win/*Nix)

Answer 1

it can broadcast data to a specified host on the network

This is a non-sequitur.

I'm presuming that you don't actually mean broadcast, you mean Unicast or just "send"?

Is Bonjour/ZeroConf the right route to go to accomplish this?

This really depends on your target environment and what your application is intended to do.

As Ignacio points out, you need to install the Apple software on Windows for Zeroconf/mDNS to work at the moment.

This might be suitable for small office / home use.

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However larger networks may have Layer 2 Multicast disabled for a variety of reasons, at which point your app might be in trouble.

If you want it to work in the enterprise environment, then some configuration is required, but that doesn't have to be done at the edge (in the app client instances).

Could be via a DHCP option, or by DNS service records.. in these cases you'd possibly be writing a queryable server to track active clients.. much like a BitTorrent Tracker.

Two things to consider while designing your networked app:

• Would there ever be reason to run more than one "installation" of your application on a network?
• Always consider the implications of versioning: One client is more up to date than another, can they still talk to each other or at least fail gracefully?

Answer 2

Zeroconf/DNS-SD is an excellent idea in this case. It's provided by Bonjour on OS X and Windows (but must be installed separately or as part of an Apple product on Windows), and by Avahi on FOSS *nix.

Answer 3

I think that ZeroConf is a very good start. You may find this document useful.

Answer 4

I have a list on a webpage, nice if you need internet communications.

<dl_service updated="2010-12-03 11:55:40+01:00">
 <client name="internal" ip="10.0.23.234" external_ip="1.1.1.1"/> 
 <client name="bigone" ip="2.2.2.2" external_ip="2.2.2.2">
  <messsage type="connect" from="Bigone" to="internal" />
 </client> 
</dl_service>

My initial idea was to add firewall punching and all that, but I just couldn't be bothered too many of the hosts where using external IPs for it to be a problem..

But I really recommend Zeroconf, at least if you use Linux+MacOSX, don't know about Windows at all.