It does seem that :chsk/ws-ping implementation is never referenced in the book. We must have overlooked it, sorry about that. It is in the code for the book here: guestbook.routes.websockets if you’re curious.

The :chsk/ws-ping message can be safely ignored, since it is just a keep-alive ping. Our default handler should do a suitable job of ignoring it.

However, the :chsk/handshake and :chsk/state messages are handled by sente itself, and notify our client of any changes to its state. The server will never receive messages of this type, and therefore doesn’t need handlers for them.