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.