If I load the code for serve-persistent as written, my telnet session closes immediately after it receives the response. It appears that the problem is cased by having the second with-open inside the while loop. I changed the code a bit and it appears to work as expected:

(defn serve-persistent [port handler]
  (let [running (atom true)]
    (future
      (with-open [server-sock (ServerSocket. port)
                  sock (.accept server-sock)]
         (while @running
            (let [msg-in (receive sock)
                  msg-out (handler msg-in)]
              (send sock msg-out)))))
      running))

Also note that send conflicts with clojure.core/send, so in my code, I've renamed it to send-msg. I didn't change it here to match what is above.

Thanks,
Kevin