SecureRandom.alphanumeric implemented.

[ruby-core:68098] [Feature #10849] proposed by Andrew Butterfield.

SecureRandom.choose and SecureRandom.graph is not included.
(The implementation has SecureRandom.choose but it is private.)

I feel the method name, SecureRandom.choose, doesn't represent
the behavior well.

The actual use cases of SecureRandom.graph is not obvious.



git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@60297 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

NEWS

@@ -191,6 +191,10 @@ with all sufficient information, see the ChangeLog file or Redmine
     * http://blog.rubygems.org/2017/08/27/2.6.13-released.html
     * http://blog.rubygems.org/2017/10/09/unsafe-object-deserialization-vulnerability.html
 
+* SecureRandom
+  * New methods:
+    * SecureRandom.alphanumeric
+
 * Set
   * Add Set#to_s as alias to #inspect [Feature #13676]
   * Add Set#=== as alias to #include? [Feature #13801]

lib/securerandom.rb

@@ -222,10 +222,50 @@ module Random::Formatter
     "%08x-%04x-%04x-%04x-%04x%08x" % ary
   end
 
-  private
-  def gen_random(n)
+  private def gen_random(n)
     self.bytes(n)
   end
+
+  # SecureRandom.choose generates a string that randomly draws from a
+  # source array of characters.
+  #
+  # The argument _source_ specifies the array of characters from which
+  # to generate the string.
+  # The argument _n_ specifies the length, in characters, of the string to be
+  # generated.
+  #
+  # The result may contain whatever characters are in the source array.
+  #
+  #   p SecureRandom.choose([*'l'..'r']) #=> "lmrqpoonmmlqlron"
+  #   p SecureRandom.choose([*'0'..'9'], 5) #=> "27309"
+  #
+  # If a secure random number generator is not available,
+  # +NotImplementedError+ is raised.
+  private def choose(source, n)
+    size = source.size
+    n.times.map {source[random_number(size)]}.join('')
+  end
+
+  ALPHANUMERIC = [*'A'..'Z', *'a'..'z', *'0'..'9']
+  # SecureRandom.alphanumeric generates a random alphanumeric string.
+  #
+  # The argument _n_ specifies the length, in characters, of the alphanumeric
+  # string to be generated.
+  #
+  # If _n_ is not specified or is nil, 16 is assumed.
+  # It may be larger in the future.
+  #
+  # The result may contain A-Z, a-z and 0-9.
+  #
+  #   p SecureRandom.alphanumeric #=> "2BuBuLf3WfSKyQbR"
+  #   p SecureRandom.alphanumeric(10) #=> "i6K93NdqiH"
+  #
+  # If a secure random number generator is not available,
+  # +NotImplementedError+ is raised.
+  def alphanumeric(n=nil)
+    n = 16 if n.nil?
+    choose(ALPHANUMERIC, n)
+  end
 end
 
 SecureRandom.extend(Random::Formatter)

test/test_securerandom.rb

@@ -143,6 +143,13 @@ end
     assert_match(/\A\h{8}-\h{4}-\h{4}-\h{4}-\h{12}\z/, uuid)
   end
 
+  def test_alphanumeric
+    65.times do |idx|
+      an = @it.alphanumeric
+      assert_match(/^[0-9a-zA-Z]+$/, an)
+    end
+  end
+
   def protect
     begin
       yield