Chat on iOS. Where to dig?

Question

iOS

I want to make a chat... I just can't figure out which way to dig? In general, how should a real-time application work on iOS ?! I say right away that ready-made services are not needed. I want to stir up on the server. I made a backend on node js, but something seems to be wrong))

Answer 1

https://telegram.org/apps
All sources are open