uuid_generator.rb

# encoding: utf-8
# Simple UUID Generator for UUID v0 (zero padded), v1, v2, v3, v4, v5
# Author: Felix Buenemann https://github.com/felixbuenemann/
# License: Public Domain
# Note: v1 code partially based on these ruby uuid implementations:
# https://github.com/assaf/uuid/
# https://github.com/cassandra-rb/simple_uuid
require 'digest/md5'
require 'digest/sha1'
require 'securerandom'

module UUIDGenerator
  GREGORIAN_EPOCH_OFFSET = 0x01B2_1DD2_1381_4000.freeze # Oct 15, 1582

  UUID_NIL = '00000000-0000-0000-0000-000000000000'.freeze
  UUID_DNS = '6ba7b810-9dad-11d1-80b4-00c04fd430c8'.freeze
  UUID_URL = '6ba7b811-9dad-11d1-80b4-00c04fd430c8'.freeze
  UUID_OID = '6ba7b812-9dad-11d1-80b4-00c04fd430c8'.freeze
  UUID_X500= '6ba7b814-9dad-11d1-80b4-00c04fd430c8'.freeze

  @@mutex = Mutex.new

  class << self
    # if value is given, generates zero padded pseudo-uuid
    def generate_v0(value = nil)
      format_uuid 0, value.to_s
    end

    # naive implementation of uuid v1
    # doesn't synchronize sequence between processes
    # and doesn't correct for clock skew
    def generate_v1(mac = nil, time = Time.new, sequence = next_sequence)
      clock = (time.to_i * 1_000_000 + time.usec) * 10 + GREGORIAN_EPOCH_OFFSET
      mac = (mac ? mac.gsub(/:|-/, '').hex : 0) & 0x7FFF_FFFF_FFFF
      format_uuid 1, '%08x%04x%04x%04x%012x' % [
         clock        & 0xFFFF_FFFF,
        (clock >> 32) & 0xFFFF,
        (clock >> 48) & 0xFFFF,
        sequence      & 0xFFFF,
        mac           & 0xFFFF_FFFF_FFFF
      ]
    end

    def generate_v3(value, namespace = UUID_NIL)
      namespace_bytes = uuid_str_to_bytes(namespace)
      format_uuid 3, Digest::MD5.hexdigest("#{namespace_bytes}#{value}")
    end

    def generate_v4
      SecureRandom.uuid
    end

    def generate_v5(value, namespace = UUID_NIL)
      namespace_bytes = uuid_str_to_bytes(namespace)
      format_uuid 5, Digest::SHA1.hexdigest("#{namespace_bytes}#{value}")
    end

    private

    def next_sequence
      @@mutex.synchronize { @sequence = @sequence.to_i.next }
    end

    def format_uuid(version, value)
      s = value.rjust(32, '0')
      if version > 0
        s[12] = version.to_s
        s[16] = byte_to_variant(s[16])
      end
      "#{s[0..7]}-#{s[8..11]}-#{s[12..15]}-#{s[16..19]}-#{s[20..31]}"
    end

    def byte_to_variant(byte)
      [0x8,0x9,0xa,0xb][byte.hex/4].to_s(16)
    end

    def uuid_str_to_bytes(string)
      [string.gsub(/-/,'')].pack('H*')
    end
  end
end