Check if user is online for a chat app made using Firebase

Question

Using Real Time Database of Firebase to create a Chat App.

The users class looks like this (default is JSON in Firebase)

"users" : {
     "-K2ib62mjHh34CAUfig" : {
      "lastvisibleat" : "2016-09-30 07:10:40",
      "name" : "Peter Parker",
      "online" : "1"
    },
    "--K2ib62mjHh34CAUh18" : {
      "lastvisibleat" : "2016-09-30 07:26:17",
      "name" : "Riddhi Dixit",
      "online" : "1"
    }
}

I want to change the status from online: "1" to online : "0" when the user's internet suddenly gets unavailable or browser crashes of its own or something as such that cannot be handled with sess_destroy() method of CodeIgniter.

Server is build in PHP using CodeIgniter.

Answer 1

I recommend using Firebase's built-in onDisconnect() hook. It enables you to predefine an operation that will happen as soon as the client becomes disconnected.

See Firebase documentation: Managing presence for Web clients.

The linked document targets web clients, but equivalent functionality is available for Android and iOS clients too.