gistfile1.clj

; Some imports we need
(import '(java.net ServerSocket Socket SocketException)
        '(java.io InputStreamReader BufferedReader OutputStreamWriter)
)

; Helper to run a callable in a new thread
(defn threaded [fun]
  ; Create a new thread
  (let [thread (new Thread fun)]
   ; And start it
   (. thread (start))
  )
)

; Accept function: whenever a new connection is made to the listening socket,
; this function spawns of a new thread running the connection handler function,
; providing the input- and output-stream
(defn accept-fun [service-fun sock]
  (threaded
    #(service-fun (. sock (getInputStream)) (. sock (getOutputStream)))
  )
)
 
; Run a service on a given port
; The given service-fun should accept 2 arguments: the input and output channel
; of the connection it should handle 
(defn run-service [service-fun port]
  ; Create the listening socket
  (let [server (new ServerSocket port)]
    ; And run the following in a thread...
    (threaded 
      ; If our socket is not closed
      #(when-not (. server (isClosed))
        ; Accept incoming connection(s)
        (try
          ; And run our accept helper given the new connection socket
          (accept-fun service-fun (. server (accept)))
          ; Unless accept fails: we don't really care for now
          (catch SocketException e)
        )
        ; And keep on going
        (recur)
      )
    )
  )
)

; Our service function, takes 2 arguments
(defn echo [sin sout]
  ; Create a BufferedReader from the input socket
  (let [rin (new BufferedReader (new InputStreamReader sin))]
    ; Set up a loop, reading one line from the input socket
    (loop [line (. rin (readLine))]
      ; Dump it to the console
      (println line)
      ; And send it back on the socket (adding a newline)
      (. sout (write (. (str line "\n") getBytes)))
      ; Now read out the next line and go back to the start of this loop
      (recur (. rin (readLine)))
    )
  )
)

; Set up our server
(def server (run-service echo 8000))