Finally, we can remove our handle-message method for :chsk/ws-ping, since we’re
handling it directly from receive-message! now.
This hints that :chsk/ws-ping was defined earlier in websockets.clj. As far as I can tell only websockets.cljs has :chsk/handshake and :chsk/state defined on page 150 but nothing for websockets.clj on page 146 and page 147. Perhaps :chsk/ws-ping was missed for both clj/cljs and the clj was also missing handshake/state methods.
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.
