Clojure md5 digest

digest.clj

(defn md5-sum
  "Compute the hex MD5 sum of a string."
  [#^String input]
  (let [alg (doto (MessageDigest/getInstance "MD5")
              (.update (.getBytes input)))
        hash (.toString (new BigInteger 1 (.digest alg)) 16)
        length (.length hash)]
    (if (> 32 length)
      ;; 0x065 => 65, leading zero is dropped by BigInteger
      (apply str (concat (repeat (- 32 length) \0) hash))
      hash)))

我抄过原版代码，有leading-zero 的 bug。。
早知道抄你这份了。。