copy.clj

fs.clj

(defn copy!
  [src dest]
  (with-open [src-input (FileInputStream. (io/file src))
              dest-output (FileOutputStream. (io/file dest))
              src-ch (.getChannel src-input)
              dest-ch (.getChannel dest-output)]
    (let [size (.size src-ch)]
      (loop [position 0]
        (when (< position size)
          (recur (unchecked-add position
                                (.transferTo src-ch
                                             position
                                             size
                                             dest-ch))))))))