Merge pull request #877 from pegasd/seeded_rand_string

seeded_rand_string() function

Author: david22swan

README.md

@@ -2176,6 +2176,10 @@ Takes an integer max value and a string seed value and returns a repeatable rand
 
 *Type*: rvalue.
 
+#### `seeded_rand_string`
+
+Generates a consistent (based on seed value) random string. Useful for generating matching passwords for different hosts.
+
 #### `shell_escape`
 
 Escapes a string so that it can be safely used in a Bourne shell command line. Note that the resulting string should be used unquoted and is not intended for use in either double or single quotes. This function behaves the same as Ruby's `Shellwords.shellescape()` function; see the [Ruby documentation](http://ruby-doc.org/stdlib-2.3.0/libdoc/shellwords/rdoc/Shellwords.html#method-c-shellescape).

lib/puppet/functions/seeded_rand_string.rb

@@ -0,0 +1,29 @@
+# Generates a consistent random string of specific length based on provided seed.
+#
+# @example Generate a consistently random string of length 8 with a seed:
+#   seeded_rand_string(8, "${module_name}::redis_password")
+#
+# @example Generate a random string from a specific set of characters:
+#   seeded_rand_string(5, '', 'abcdef')
+Puppet::Functions.create_function(:seeded_rand_string) do
+  # @param length Length of string to be generated.
+  # @param seed Seed string.
+  # @param charset String that contains characters to use for the random string.
+  #
+  # @return [String] Random string.
+  dispatch :rand_string do
+    param 'Integer[1]', :length
+    param 'String', :seed
+    optional_param 'String[2]', :charset
+  end
+
+  def rand_string(length, seed, charset = nil)
+    require 'digest/sha2'
+
+    charset ||= '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ'
+
+    random_generator = Random.new(Digest::SHA256.hexdigest(seed).to_i(16))
+
+    Array.new(length) { charset[random_generator.rand(charset.size)] }.join
+  end
+end

spec/functions/seeded_rand_string_spec.rb

@@ -0,0 +1,34 @@
+require 'spec_helper'
+
+describe 'seeded_rand_string' do
+  it { is_expected.not_to be(nil) }
+
+  # Test for erroneous params
+  it { is_expected.to run.with_params.and_raise_error(ArgumentError, %r{expects between.+got none}i) }
+  it { is_expected.to run.with_params(1).and_raise_error(ArgumentError, %r{expects between.+got 1}i) }
+  it { is_expected.to run.with_params('1', 'hello').and_raise_error(ArgumentError, %r{parameter 'length' expects an Integer value}i) }
+  it { is_expected.to run.with_params(1, 1).and_raise_error(ArgumentError, %r{parameter 'seed' expects a String value}i) }
+  it { is_expected.to run.with_params(1, 'hello', 1).and_raise_error(ArgumentError, %r{parameter 'charset' expects a.+String}i) }
+
+  # Test regular run
+  it { is_expected.to run.with_params(100, 'hello') }
+
+  # Test custom charsets
+  it { is_expected.to run.with_params(100, 'hello', 'abcd').and_return(%r{[a-d]{100}}) }
+  it { is_expected.to run.with_params(100, 'hello', 'abcdefgh').and_return(%r{[a-h]{100}}) }
+  it { is_expected.to run.with_params(100, 'hello', 'ab,|').and_return(%r{[ab,|]{100}}) }
+
+  # Test behavior
+  it 'generates the same string with the same seed' do
+    rand_str_one = call_function(:seeded_rand_string, 300, 'my_seed')
+    rand_str_two = call_function(:seeded_rand_string, 300, 'my_seed')
+
+    expect(rand_str_one).to eq(rand_str_two)
+  end
+  it 'generates different strings if seeded differently' do
+    rand_str_one = call_function(:seeded_rand_string, 300, 'my_seed_one')
+    rand_str_two = call_function(:seeded_rand_string, 300, 'my_seed_two')
+
+    expect(rand_str_one).not_to eq(rand_str_two)
+  end
+end