Several days before I'm asked to write a project on TCP server-client communication, and I wondered why not build a simple chat service beyond that which would be much more fun?

Therefore here it is, a simple tcp server with several functions which makes it acts like a small chat app.

Functions

User register / login / logout
Remember login state for device (simple token approach though)
Send messages via users
Search users and add contacts (and accept them of course)
Message sync via different devices
Send message to offline server (a SMTP-like approach)
File handling (transfer to and fetch from server)

Notice

To support multilanguage, use base64Encode(utf8.encode(yourMessageHere)) before wrapping client messages in json object and sending that to the server (the serve will crash!)
Always open a new TCP connection to fetch or send file