Clojurians Log v2

Hi, I have a question specific to this example: https://github.com/pedestal/pedestal/blob/master/samples/jetty-web-sockets/src/jetty_web_sockets/service.clj Each established connection is maintained in an atom ws-clients. When server initiates a disconnect, it is clear which connection is getting closed but when the :on-close handler is triggered with only the code and reason, how does the server identify which session got closed?