Added session_keepalive setting

When session_keepalive is true (default) the heartbeat will be send as
often as the half of the session timeout value.

config/config.sample.php

 /* Life time of a session after inactivity */
 "session_lifetime" => 60 * 60 * 24,
 
+/*
+ * Enable/disable session keep alive when a user is logged in in the Web UI.
+ * This is achieved by sending a "heartbeat" to the server to prevent
+ * the session timing out.
+ */
+"session_keepalive" => true,
+
 /* Custom CSP policy, changing this will overwrite the standard policy */
 "custom_csp_policy" => "default-src 'self'; script-src 'self' 'unsafe-eval'; style-src 'self' 'unsafe-inline'; frame-src *; img-src *; font-src 'self' data:; media-src *",
 

core/js/config.php

 		)
 	),
 	"firstDay" => json_encode($l->l('firstday', 'firstday')) ,
+	"oc_config" => json_encode(
+		array(
+			'session_lifetime' => \OCP\Config::getSystemValue('session_lifetime', 60 * 60 * 24),
+			'session_keepalive' => \OCP\Config::getSystemValue('session_keepalive', true)
+		)
+	)
 	);
 
 // Echo it

core/js/js.js

 var oc_current_user = document.getElementsByTagName('head')[0].getAttribute('data-user');
 var oc_requesttoken = document.getElementsByTagName('head')[0].getAttribute('data-requesttoken');
 
+window.oc_config = window.oc_config || {};
+
 if (typeof oc_webroot === "undefined") {
 	oc_webroot = location.pathname;
 	var pos = oc_webroot.indexOf('/index.php/');
 	console.warn("This function is deprecated! Use CSS instead");
 }
 
-$(document).ready(function(){
-	sessionHeartBeat();
+/**
+ * Initializes core
+ */
+function initCore() {
+
+	/**
+	 * Calls the server periodically to ensure that session doesnt
+	 * time out
+	 */
+	function initSessionHeartBeat(){
+		// interval in seconds
+		var interval = 900;
+		if (oc_config.session_lifetime) {
+			interval = Math.floor(oc_config.session_lifetime / 2);
+		}
+		// minimum one minute
+		if (interval < 60) {
+			interval = 60;
+		}
+		OC.Router.registerLoadedCallback(function(){
+			var url = OC.Router.generate('heartbeat');
+			setInterval(function(){
+				$.post(url);
+			}, interval * 1000);
+		});
+	}
+
+	// session heartbeat (defalts to enabled)
+	if (typeof(oc_config.session_keepalive) === 'undefined' ||
+		!!oc_config.session_keepalive) {
+
+		initSessionHeartBeat();
+	}
 
 	if(!SVGSupport()){ //replace all svg images with png images for browser that dont support svg
 		replaceSVG();
 	$('input[type=text]').focus(function(){
 		this.select();
 	});
-});
+}
+
+$(document).ready(initCore);
 
 /**
  * Filter Jquery selector by attribute value
 	return this.length > 0;
 };
 
-/**
- * Calls the server periodically every 15 mins to ensure that session doesnt
- * time out
- */
-function sessionHeartBeat(){
-	OC.Router.registerLoadedCallback(function(){
-		var url = OC.Router.generate('heartbeat');
-		setInterval(function(){
-			$.post(url);
-		}, 900000);
-	});
-}