The client-server protocol is left unspecified in the roadmap. This has to be fixed asap.

In the first version, the protocol should start by a simple handshake to test the version (each side sends 1 byte with its current version number), and if they agree on this, they should use output_value/input_value to send structured messages, specified as :

type client_to_server_message =
   | C2S_... of ...

In the next version, the protocol should be specified as a binary protocol (not json or something like that), by just flattening structured messages.