I'm working on an implementation of the JSON-RPC protocol
http://www.jsonrpc.org/.
It's an extension for the network module of SFML, using TCP and UDP primarily (HTML later).
And is using an external library for handling JSON,
https://nlohmann.github.io/json/.
My intention here is create a small and clean implementation, easy to extend;
Because the real intention is create an "object oriented RPC-module", just like Java RMI or Godot's RPC networking
https://godotengine.org/.
With all this in mind, will be easy(not so hard) to embed too (Lua, Python, etc).
For now, is just a work in progress, there's not much made out yet,
but I'll open it as soon as possible.
