Rework heartbeat logic to be more robust

lib/controllers/heartbeat.js

@@ -8,7 +8,7 @@ var TIMEOUT_FACTOR = 3; // timeouts after 3 intervals
 function HeartbeatController(client, sourceId, destinationId) {
   JsonController.call(this, client, sourceId, destinationId, 'urn:x-cast:com.google.cast.tp.heartbeat');
 
-  this.interval = null;
+  this.pingTimer = null;
   this.timeout = null;
   this.intervalValue = DEFAULT_INTERVAL;
 
@@ -35,16 +35,24 @@ util.inherits(HeartbeatController, JsonController);
 HeartbeatController.prototype.ping = function() {
   var self = this;
 
-  this.once('pong', onpong);
-
-  function onpong() {
-    clearTimeout(self.timeout);    
-    self.timeout = setTimeout(ontimeout, self.intervalValue * 1000 * TIMEOUT_FACTOR);
+  if (this.timeout) {
+    // We already have a ping in progress.
+    return;
   }
 
-  function ontimeout() {
+  this.timeout = setTimeout(function ontimeout() {
     self.emit('timeout');
-  }
+  }, self.intervalValue * 1000 * TIMEOUT_FACTOR);
+
+  this.once('pong', function onpong() {
+    clearTimeout(self.timeout);
+    self.timeout = null;
+
+    self.pingTimer = setTimeout(function() {
+      self.pingTimer = null;
+      self.ping();
+    }, self.intervalValue * 1000);
+  });
 
   this.send({ type: 'PING' });
 };
@@ -56,17 +64,17 @@ HeartbeatController.prototype.start = function(intervalValue) {
     this.intervalValue = intervalValue;
   }
 
-  function oninterval() {
-    self.ping();
-  }
-
-  this.interval = setInterval(oninterval, this.intervalValue * 1000);
   this.ping();
 };
 
 HeartbeatController.prototype.stop = function() {
-  clearInterval(this.interval);
-  clearTimeout(this.timeout);
+  if (this.pingTimer) {
+    clearTimeout(this.pingTimer);
+  }
+  if (this.timeout) {
+    clearTimeout(this.timeout);
+  }
+  this.removeAllListeners('pong');
 };
 
 module.exports = HeartbeatController;