Convert UUIDs to/from base58

uu58.rb

module Uu58
  ALPHABET58 = "123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz".chars.freeze
  ALPHAMAP58 = ALPHABET58.each_with_index.to_h.freeze

  # Convert a string UUID to a base58 string representation.
  #
  # Output will be padded up to 22 digits if necessary.
  #
  # Behaviour is undefined if passing something other than a 128-bit
  # hex string in network order with optional interstitial hyphens.
  def self.uuid_to_base58(uuid, alphabet = ALPHABET58)
    ary = uuid.delete("-").hex.digits(58).reverse
    ary.unshift(0) while ary.length < 22
    alphabet.values_at(*ary).join
  end

  # Convert a base58 number to a UUID.
  #
  # Input should be a big-endian base58 string representation of
  # a whole number less than 2^128.
  def self.base58_to_uuid(base58_val, alphamap = ALPHAMAP58)
    num = 0
    base58_val.each_char do |ch|
      val = alphamap[ch] or raise ArgumentError, 'invalid base58 string'
      num = num * 58 + val
    end

    raise RangeError, 'base58 value too large for 128‑bit UUID' unless num >> 128 == 0

    "%08x-%04x-%04x-%04x-%04x%08x" % [
      (num >> 96) & 0xFFFFFFFF,
      (num >> 80) & 0xFFFF,
      (num >> 64) & 0xFFFF,
      (num >> 48) & 0xFFFF,
      (num >> 32) & 0xFFFF,
      num & 0xFFFFFFFF
    ]
  end
end

uu58_test.rb

require 'minitest/autorun'
require 'securerandom'
require_relative 'uu58'

class TestUu58 < Minitest::Test
  def test_zero_uuid
    uuid = '00000000-0000-0000-0000-000000000000'
    bs   = '1111111111111111111111'
    assert_equal bs,   Uu58.uuid_to_base58(uuid)
    assert_equal uuid, Uu58.base58_to_uuid(bs)
  end

  def test_max_uuid
    uuid = 'ffffffff-ffff-ffff-ffff-ffffffffffff'
    bs   = 'YcVfxkQb6JRzqk5kF2tNLv'
    assert_equal bs,   Uu58.uuid_to_base58(uuid)
    assert_equal uuid, Uu58.base58_to_uuid(bs)
  end

  def test_known_uuid_1
    uuid = '00112233-4455-6677-8899-aabbccddeeff'
    bs   = '11UoWww8DGaVGLtea7zU7p'
    assert_equal bs,   Uu58.uuid_to_base58(uuid)
    assert_equal uuid, Uu58.base58_to_uuid(bs)
  end

  def test_known_uuid_2
    uuid = '01234567-89ab-cdef-0123-456789abcdef'
    bs   = '199dn6s7bZoVpjzYciVNgN'
    assert_equal bs,   Uu58.uuid_to_base58(uuid)
    assert_equal uuid, Uu58.base58_to_uuid(bs)
  end

  def test_round_trip_random
    5.times do
      uuid = SecureRandom.uuid
      bs   = Uu58.uuid_to_base58(uuid)
      assert_equal uuid.downcase, Uu58.base58_to_uuid(bs)
    end
  end

  def test_overflow
    bs   = 'YcVfxkQb6JRzqk5kF2tNLw'
    assert_raises(RangeError) { Uu58.base58_to_uuid(bs) }
  end

  def test_invalid_character
    assert_raises(ArgumentError) { Uu58.base58_to_uuid('!@@@not58!!!') }
  end
end

Revised today (25-04-18)

• faster conversion to uuid with current Ruby 3.4 (up to 3x faster!)
• adding an overflow guard in conversion to uuid
• removed implied dependency on Active Support
• added test values

note that the optional second parameter of Uu58.base58_to_uuid is no longer an alphabet array but an inverse hash of character to digit value