added latency update

lib/node.js

@@ -82,6 +82,7 @@ function Node()
 	this._tries = 0;
 	this._down = 0;
 	this._lastSent = 0;
+	this._latency = 0;
 
 	this.blocks = [];
 
@@ -106,6 +107,10 @@ function Node()
 	.on('reconnecting', function reconnecting(opts) {
 		console.warn('We are scheduling a reconnect operation', opts);
 	})
+	.on('node-pong', function(data) {
+		var latency = (new Date()).getTime() - self._latency;
+		socket.emit('latency', { id: self.id, latency: latency });
+	})
 	.on('data', function incoming(data) {
 		console.info('Received some data', data);
 	});
@@ -364,6 +369,7 @@ Node.prototype.update = function()
 
 Node.prototype.ping = function()
 {
+	this._latency = (new Date()).getTime();
 	this.emit('node-ping', { id: this.id });
 };