puppetlabs-stdlib/lib/puppet/parser/functions/fqdn_rotate.rb

#
# fqdn_rotate.rb
#

module Puppet::Parser::Functions
  newfunction(:fqdn_rotate, :type => :rvalue, :doc => <<-EOS
Rotates an array a random number of times based on a nodes fqdn.
    EOS
  ) do |arguments|

    raise(Puppet::ParseError, "fqdn_rotate(): Wrong number of arguments " +
      "given (#{arguments.size} for 1)") if arguments.size < 1

    value = arguments[0]
    require 'digest/md5'

    unless value.is_a?(Array) || value.is_a?(String)
      raise(Puppet::ParseError, 'fqdn_rotate(): Requires either ' +
        'array or string to work with')
    end

    result = value.clone

    string = value.is_a?(String) ? true : false

    # Check whether it makes sense to rotate ...
    return result if result.size <= 1

    # We turn any string value into an array to be able to rotate ...
    result = string ? result.split('') : result

    elements = result.size

    seed = Digest::MD5.hexdigest([lookupvar('::fqdn'),arguments].join(':')).hex
    # deterministic_rand() was added in Puppet 3.2.0; reimplement if necessary
    if Puppet::Util.respond_to?(:deterministic_rand)
      offset = Puppet::Util.deterministic_rand(seed, elements).to_i
    else
      if defined?(Random) == 'constant' && Random.class == Class
        offset = Random.new(seed).rand(elements)
      else
        srand(seed)
        offset = rand(elements)
        srand()
      end
    end
    offset.times {
       result.push result.shift
    }

    result = string ? result.join : result

    return result
  end
end

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