HexIdMethods: secure, prefix-based IDs for ActiveRecord models for WEB2

HexIdMethods.rb

# WEB2 Secure Random ID generator 
# app/models/concerns/hex_id_methods.rb
# include HexIdMethods in any model that uses :hex_id
module HexIdMethods
  extend ActiveSupport::Concern

  # Create a safe character set: a-k, m-z, 0, 2-9 (no l, 1) - 34 characters
  SAFE_CHARS   = (('a'..'k').to_a + ('m'..'z').to_a + ['0'] + ('2'..'9').to_a).freeze
  MAX_RETRIES  = 3

  included do
    before_validation :generate_hex_id, on: :create
    validates :hex_id, presence: true, uniqueness: true
    around_create :retry_on_hex_id_collision
  end

private

  def generate_hex_id
    return if hex_id.present?
    self.hex_id = build_hex_id
  end

  def build_hex_id
    "#{hex_id_prefix}_#{secure_random_safe_string}"
  end

  def hex_id_prefix
    self.class.const_get(:HEX_ID_PREFIX)
  rescue NameError
    raise "Missing HEX_ID_PREFIX in #{self.class.name}"
  end

  def retry_on_hex_id_collision
    retries = 0

    begin
      yield
    rescue ActiveRecord::RecordNotUnique
      raise if (retries += 1) > MAX_RETRIES
      self.hex_id = nil
      generate_hex_id
      retry
    end
  end

  def secure_random_safe_string(length=10)
    chars = []
    n = SAFE_CHARS.length
    max = 256 - (256 % n)

    while chars.length < length
      SecureRandom.random_bytes(1).each_byte do |b|
        next if b >= max
        chars << SAFE_CHARS[b % n]
        break if chars.length == length
      end
    end

    chars.join
  end
end