I really tried to find a solution to this problem but didn't. There are some threads related to this concept, but I didn't find a comprehensive solution.
I have a server with Openfire which sends messages. When both users are online, there is no problem. However, when a user is offline I would like to send a push notification, as in Whatsapp. I heard that Whatsapp and other IM apps use a modified version of ejabber to send push notifications, but couldn't find out how.
One possibility is to use GCM, but I am not sure if this is the right way to go. Also I would like to avoid polling, for the sake of not draining battery life.
Does anyone know some solution to this or has an example?
I am studying the openfire and found some good options that I would like to share with you. I found a plugin in github and i will test it this week. It seems that will be a good solution to your goal and to my: https://github.com/meisterfuu/Openfire-GCM/
Another option is to use CallbackOnOffline Plugin that calls a specified URL with To and From parameters. This url could be a endpoint in your web service, and with that data (To and From) you could get the associated Id for push in your base, and did a push.
https://www.igniterealtime.org/projects/openfire/plugins.jsp