node_mdns adds support for multicast DNS service discovery, also known as zeroconf or bonjour to node.js. It provides an object-oriented interface to announce and browse services on the local network.

Internally, it uses the mDNSResponder API which is available on all major platforms.

On Linux and other systems using the avahi daemon the avahi dns_sd compat library and its header files are required.

node_mdns is available as a npm package. To fetch, compile and install the add-on do:

npm install mdns

If you want to play with the latest source code, here is a more manual approach:

git clone http://github.com/agnat/node_mdns
cd node_mdns
node-waf configure build && ./run_tests

Multicast DNS service discovery provides a way to announce and discover services on the local network. Here is how to announce a HTTP server running on port 4321:

var mdns = require('mdns');
var ad = mdns.createAdvertisement('http', 4321);
ad.start();

And here is how to browse all HTTP servers on the local network:

var browser = mdns.createBrowser('http');
browser.on('serviceUp', function(info, flags) {
  sys.puts("Up: " + sys.inspect(info));
});
browser.on('serviceDown', function(info, flags) {
  sys.puts("Down: " + sys.inspect(info));
});
browser.start();

As you can see the browser object is an EventEmitter. For each HTTP server a ‘serviceUp’ event is emitted. Likewise, if a server disappears ‘serviceDown’ is send. A ‘serviceUp’ info object might look like this:

{ interfaceIndex: 4
, serviceName: 'somehost'
, regtype: '_http._tcp.'
, replyDomain: 'local.'
, fullname: 'somehost._http._tcp.local.'
, host: 'somehost.local.'
, port: 4321
, addresses: [ '10.1.1.50', 'fe80::21f:5bff:fecd:ce64' ]
}

Yes, please.

Copyright © 2010 David Siegel

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