CODEWITHSUNDEEP
node.jsfirebasefirebase-realtime-database
Matt Bush
Matt Bush

Reputation: 23

Firebase onDisconnect() firing multiple times

Building an app with presence following the firebase docs, is there a scenario where the on-disconnect fires when the app is still connected? We see instances where the presence node shows the app as going offline and then back online within a few seconds when we aren't losing a network connection.

We are seeing on multiple embedded devices installed in the field where presence is set to false and then almost immediately right back to true and it's occurring on all the devices within a few seconds of each other. From the testing we have done and the docs online we know that if we lose internet connection on the device it takes roughly 60 seconds before the timeout on the server fires the onDisconnect() method.

We have since added code in the presence method that allows the device if it sees the presence node be set to false while the app is actually running it will reset the presence back to true. At times when this happens we get a single write back to true and that is the end of it, other times it is like the server and client are fighting each other and the node is reset to true numerous times over the course of 50-200 milliseconds. We monitor this by pushing to another node within the device GUID each time we are forcing presence back to true. This only occurs while the module is running and after it initially establishes presence.

Here is the method that we call from our various modules that are running on the device so that we can monitor the status of each of the modules at any given time.

exports.online = function (program, currentProgram) {
 var programPath = process.env.FIREBASE_DEVICES + process.env.GUID + '/status/' + program
  var onlinePath = process.env.FIREBASE_DEVICES + process.env.GUID + '/statusOnlineTimes/' + program
  var programRef = new firebase(programPath);
  var statusRef = new firebase(process.env.FIREBASE_DEVICES + process.env.GUID + '/status/bootup');
  var onlineRef = new firebase(onlinePath)
  amOnline.on('value', function(snapshot) {
    if (snapshot.val()) {
      programRef.onDisconnect().set(false);
      programRef.set(true);
      programRef.on('value', function(snapshot){
        if (snapshot.val() == false){
          programRef.set(true);
          console.log('[NOTICE] Resetting', program, 'module status back to True after Fireabase set to False')
          var objectToPush = {
            program: program,
            time: new Date().toJSON()
          }
          onlineRef.push(objectToPush)
        }
      })
      if (currentProgram != undefined) {
        statusRef.onDisconnect().set('Offline')
        statusRef.set(currentProgram)
      }
    }
  });

The question we have is there ever an instance where Firebase is calling the onDisconnect() method even though it really isn't losing its status? We had instances where we would see the device go offline and then back online within 60 seconds before we added the reset code. The reset code was to combat another issue we had in the field where if the power were interrupted to the device and it did not make a clean exit, the device could reboot and and reset the presence with a new UID before the timeout for the prior instance had fired. Then once the timeout fired the device would show as offline even though it was actually online.

Upvotes: 1

Views: 549

Answers (1)

Matt Bush
Matt Bush

Reputation: 23

So we were able to stop the multiple pushes that were happening when the device reconnected by adding a programRef.off() call directly before the programRef.on(...) call. What we determined to be happening is that anytime the device went online from an offline state and the amOnline.on(...) callback fired it created a new listener.

Now we are able to handle the case where a onDisconnect() fires from a earlier program PID and overwrites the currently active program with a status of offline. This seems to solve the issue we are having with the race condition of the devices in the field able to reboot and regain connection prior to the onDisconnect() firing for the instance that was not cleanly exited.

We are still having an issue where all of the devices are going off and then back online at approximately the same time (within 1-3 seconds of each other). Are there any times where Firebase resets the ./info/connected node? Because we are monitoring presence and actually logging on and off events maybe we are just catching an event that most people don't see? Or is there something that we are doing wrong?

Upvotes: 1

Related Questions