multihash.digest

Digest functions for creating new multihash constructors.

(ns multihash.digest
  (:refer-clojure :exclude [test])
  (:require
    [multihash.core :as multihash])
  (:import
    (java.io
      InputStream
      IOException)
    java.nio.ByteBuffer
    java.security.MessageDigest))

Map of supported multihash algorithm keys to hashing functions. Each function should take a source of binary data as the argument and return a multihash.

(def functions
  {})

Constructs a cryptographic digest for a given algorithm and content. Content may be in the form of a raw byte array, a ByteBuffer, or a string. Returns a byte array with the digest.

(defn- digest-content
  ^bytes
  [digest-name content]
  (let [algo (MessageDigest/getInstance digest-name)]
    (condp instance? content
      String
        (.update algo (.getBytes ^String content))
      (Class/forName "[B")
        (.update algo ^bytes content)
      ByteBuffer
        (.update algo ^ByteBuffer content)
      InputStream
        (let [buffer (byte-array 1024)]
          (loop []
            (let [n (.read ^InputStream content buffer 0 (count buffer))]
              (when (pos? n)
                (.update algo buffer 0 n)
                (recur)))))
      (throw (IllegalArgumentException.
               (str "Don't know how to compute digest from "
                    (class content)))))
    (.digest algo)))

Defines a new convenience hashing function for the given algorithm and system digest name.

(defmacro defhash
  [algorithm digest-name]
  (let [fn-sym (symbol (name algorithm))]
    `(do
       (defn ~fn-sym
         ~(str "Calculates the " digest-name " digest of the given byte array or "
               "buffer and returns a multihash.")
         [~'content]
         (multihash/create ~algorithm (digest-content ~digest-name ~'content)))
       (alter-var-root #'functions assoc ~algorithm ~fn-sym))))

(defhash :sha1     "SHA-1")
(defhash :sha2-256 "SHA-256")
(defhash :sha2-512 "SHA-512")

Determines whether a multihash is a correct identifier for some content by recomputing the digest for the algorithm specified in the multihash. Returns nil if either argument is nil, true if the digest matches, or false if not. Throws an exception if the multihash specifies an unsupported algorithm.

(defn test
  [mhash content]
  (when (and mhash content)
    (if-let [hash-fn (get functions (:algorithm mhash))]
      (= mhash (hash-fn content))
      (throw (ex-info
               (format "No supported hashing function for algorithm %s to validate %s"
                       (:algorithm mhash) mhash)
               {:algorithm (:algorithm mhash)})))))

mvxcvi/multihash

2.0.3

dependencies

namespaces

multihash.digest