Designing client (thick) / server + extra REST API for the thin client

Question

I am redesigning the old application--better to say designing the new application for which I want to take some parts of the old application to be more useful and extendable in future.

The old application is a desktop thick application that works on data shared on a file server. (It uses DBF database free tables, but the design is not client-server -- just a thick application.)

The new application is planned to use the client-server architecture with thick client , but the server should also provide the functionality through the REST API interface.

How a specific application server should be designed to be attachable both to a thick client, and to the web service?

The implementation should be portable (Windows, Linux), and also the web server should be or IIS (Microsoft) or a portable web server (like nginx, or so). The implementation language is C++11 plus (at least for the application server, and the thick client).

I am starting from scratch, and I also need to learn the technologies. (I do have experience with C++, and some theoretical knowledge on client-server, and RESTful; however, I need to learn the practical things.)

Answer 1

Comment as answer, as requested:

Consider google protocol buffers for the message encoding and decoding. Version 3 supports both json and binary encoding. It also has stubs for RPC, which you'll find useful.