Publish/Subscribe extension system for Kad, based on Quasar.

Install kad-quasar with NPM:

npm install kad kad-quasar --save

Give kad-quasar your kad.Router:

var quasar = require('kad-quasar');
var topics = new quasar.Protocol(router);

topics.subscribe('beep', function(content) {
  console.log(content); // { "message": "boop" }
});

topics.publish('beep', {
  message: 'boop'
});

Please note that this software is alpha stage and may not be suitable for production systems.

Kad Quasar extends Kad with a publish/subscribe system, enabling different applications to run on the same overlay network.

To do this, Kad Quasar uses the kad.Router object's contact list to build an attenuated bloom filter where each filter in the series contains topics that your node and your neighbors are subscribed to represented in "hops" from your node.

This allows each node to maintain a view of what their neighbors are interested in 3 hops away. Published messages are relayed to neighbors probabilistically based on this knowledge and are appended with negative information to prevent duplication. This forms "gravity wells" in the network around groups who are interested in a given topic and serves to prevent flooding the network while still maintaining a high probability that the message will be delivered to all nodes interested.

The Quasar class implements Quasar: A Probabilistic Publish-Subscribe System, given an instance of kad.Router. It creates and manages an attenuated bloom filter representing the different topics to which your neighboring nodes are subscribed.

Publishes a message to your nearest neighbors on the given topic (and optional) content object. Those neighbors, in turn, relay the message to their neighbors in accordance with their view of the the network.

• topic - (String) identifier for the topic
• content - (Mixed) additional data describing the publication

Updates our local attenuated bloom filter to reflect our interest in the topic and notifies our neighbors to relay publications matching the topic to us. In turn, our neighbors will provide us with their local bloom filter, so we can do the same.

• topic - (String) identifier for the topic
• handler - (Function) receives arguments content with published data