What technologies to choose for the implementation of the instant messenger server?

Question

Java

The task is something like this. There is a client (ios&&android) and a server. The application should work as an instant messenger, i.e. there will be authorization, a list of friends, the ability to send private messages. Messages must be sent json/xml. The task of the server is to receive messages from the client and transfer them to another client, also in the json / xml format.
To implement the server what technologies to choose? How are programs like this written? Is openfire suitable for this task as a server?

Answer 1

You just need to implement the WhatsApp XMPP protocol
for example in Erlang on the backend, but no one forbids using any other server languages

Answer 2

Put what thread ejabberd and do not torment the grandmother. :)

Answer 3

You can implement your protocol in general) using netty)

Answer 4

Java has a ready-made Openfire jabber server.