I was thinking only about the client version of my game, for the moment.
Now I wanted to try again your example "WebSocket Client Library" using an emulator.
Surprisingly, it now also works with the emulator.
But the biggest surprise is that the server can communicate simultaneously with more than one device (that server, only one ws).
I thought I had to create a WebSocket object for each player (I also hope that it is right to create a Player object with a member of type websocket).
I am writing this question while I "study" the code "WebSocket Client Library"