How can I detect if the user (JID) is already logged in on login when using XMPP?

After login when you send your initial presence you get the presences of all your other resources (devices). So check all your incoming presences and you will know all your available connections.

Alex answer is correct, but let me elaborate it a little bit.

I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.