generate_mac function

generates mac addresses for virtual machines

lib/puppet/functions/generate_mac.rb

@@ -0,0 +1,38 @@
+# frozen_string_literal: true
+
+require 'digest'
+
+# generates a deterministic pseudorandom mac address, using hostname as seed
+#
+# prefix validated to follow the following parameters:
+#   - must contain exactly 6 hex digits
+#   - second digit must be one of [2,6,a,e] (per RFC7042 §2.1, see "Local bit")
+#   - case is ignored
+#   - may contain unlimited number of non-alphanumerics as delimeters
+#
+# generated address contains
+#   - 3 byte fixed OUI (prefix)
+#   - 21 "random" bits (seeded from hostname)
+#   - 3 bit sequential number (index)
+Puppet::Functions.create_function(:generate_mac) do
+  dispatch :generate_mac do
+    param "String", :prefix
+    param "String", :hostname
+    param "Integer", :index
+  end
+
+  def generate_mac(prefix, hostname, index)
+    unless(index.between?(0,7))
+      raise(ArgumentError, "#{index} must be between 0 and 7, I can only generate 8 mac addresses per host!")
+    end
+
+    oui = prefix.downcase.gsub(/[^0-9a-z]/,'')
+    unless(oui =~ /^[a-f0-9][26ae][a-f0-9]{4}$/)
+      raise(ArgumentError, "invalid mac prefix!")
+    end
+
+    integer_id = (Digest::SHA256.hexdigest(hostname)[0,6].to_i(16) & 0xFF_FF_F8) + index
+    hex_id = sprintf('%06x',integer_id)
+    "#{oui}#{hex_id}".each_char.each_slice(2).map{|x| x.join}.join(':')
+  end
+end

spec/functions/generate_mac_spec.rb

@@ -0,0 +1,29 @@
+# frozen_string_literal: true
+
+# Copyright (c) 2020 The Regents of the University of Michigan.
+# All Rights Reserved. Licensed according to the terms of the Revised
+# BSD License. See LICENSE.txt for details.
+require "spec_helper"
+
+describe "generate_mac" do
+  it "generates simple addresses" do
+    is_expected.to run.with_params('02:00:00', 'example.com', 0).and_return('02:00:00:a3:79:a0')
+    is_expected.to run.with_params('12-0f-00', 'example.com', 2).and_return('12:0f:00:a3:79:a2')
+  end
+  it "fails on invalid chars" do
+    is_expected.to run.with_params('g2:00:00', 'example.com', 0).and_raise_error(ArgumentError)
+  end
+  it "correctly masks final 3 bits" do
+    is_expected.to run.with_params('06 12 34', 'my.host.name', 0).and_return('06:12:34:3b:d9:98')
+    is_expected.to run.with_params('5a.67.89', 'my.host.name', 3).and_return('5a:67:89:3b:d9:9b')
+    is_expected.to run.with_params('AE:BC:DE', 'my.host.name', 7).and_return('ae:bc:de:3b:d9:9f')
+  end
+  it "fails on non-private oui" do
+    is_expected.to run.with_params('03:00:00', 'example.com', 0).and_raise_error(ArgumentError)
+  end
+  it "fails on out of range index" do
+    is_expected.to run.with_params('02:00:00', 'example.com', 11).and_raise_error(ArgumentError)
+    is_expected.to run.with_params('02:00:00', 'example.com', -1).and_raise_error(ArgumentError)
+  end
+end
+