scalra/core/DHT.js

node.js framework to prototype and scale rapidly

/*
	DHT.js		basic distributed hash table (DHT) functions

	functions:
		init(host_list, onDone)			// init the DHT ring with a list of initial hosts (equally valid entries)
		onDone(err, dht_obj)			// callback returns the DHT object & potential error code (if any)
		
	dht_obj:	
		set(key, value, onDone)			// set a key-value pair to the DHT ring
		get(key, onDone)				// get the value associated with a given key
		delete(key, onDone)				// delete a given key
*/

var kademlia = require('kad');
var levelup = require('levelup');
UTIL.validatePath('./store');

// DHT object (local)
function DHT (seeds, onConnect, onUpdate) {
	var l_map = {};

	// build DHT connection
	var l_dht = undefined;
		
	// init DHT
	if (seeds instanceof Array) {
		l_dht = kademlia({
  			address: '127.0.0.1',
  			port: 65535,
  			seeds: seeds,
  			storage: levelup('./store/dht_db')
		});
		
		l_dht.on('connect', function () {
			LOG.warn('DHT connected...', 'SR.DHT');
			UTIL.safeCall(onConnect);
		});		
	}
	else
		UTIL.safeCall(onConnect);
	
	this.set = function (key, value, onDone) {
		if (!l_dht) {
			l_map[key] = value;
			return UTIL.safeCall(onDone, true);		
		}
		
		l_dht.put(key, value, function (err) {
			if (err) {
				LOG.error(err, 'SR.DHT');
				UTIL.safeCall(onDone, false);
			}
			else
				UTIL.safeCall(onDone, true);
		});
	};

	this.get = function (key, onDone) {
		if (!l_dht) {
			if (l_map.hasOwnProperty(key))
				UTIL.safeCall(onDone, l_map[key]);
			else
				UTIL.safeCall(onDone);
			return;
		}

 		l_dht.get(key, function (err, value) {
			if (err) {
				LOG.error(err, 'SR.DHT');
				UTIL.safeCall(onDone);				
			}
			else {
				// remove from local & return undefined
				if (value === 'DELETED') {
					delete l_map[key];
					return UTIL.safeCall(onDone);
				}
				
				// update to local
				l_map[key] = value;
				UTIL.safeCall(onDone, value);
			}
		});
	};
	
	this.delete = function (key, onDone) {
		if (!l_dht) {
			
			if (l_map.hasOwnProperty(key)) {
				delete l_map[key];
				UTIL.safeCall(onDone, true);
			}
			else {
				UTIL.safeCall(onDone, false);
			}
			return;
		}
		
		// TODO: need a way to delete?
		l_dht.put(key, 'DELETED', function (err) {
			if (err) {
				LOG.error(err, 'SR.DHT');
				UTIL.safeCall(onDone, false);
			}
			else
				UTIL.safeCall(onDone, true);
		});
	}
}

var l_dht = undefined;

// init the DHT ring with a list of initial hosts (equally valid entries)
// onDone: when init is done, DHT ring is joined
// onUpdate: when some data in the DHT has changed, passed in key changed (optional)
exports.init = function (hosts, onDone, onUpdate) {
	LOG.warn('hosts are: ', 'SR.DHT');
	LOG.warn(hosts, 'SR.DHT');

	LOG.error('DHT function disabled for now', 'SR.DHT');
	return UTIL.safeCall(onDone);
	
	var seeds = [];
	for (var i=0; i < hosts.length; i++)
		seeds.push({address: hosts[i], port: 65535});
		
	// contact & join the inital nodes?
	l_dht = new DHT(seeds, function () {
		UTIL.safeCall(onDone, undefined, l_dht);	
	}, onUpdate);
}

// leave the DHT ring
exports.dispose = function () {
	if (l_dht) {
		delete l_dht;
		l_dht = undefined;	
	}
}