make_yaml_safe.rb

# Attempt at porting https://gist.github.com/nelhage/4507129 to ruby 2.0
#
# I just removed all traces of Syck

def self.make_yaml_safe!
  if defined?(Psych)
    Psych.const_set("UnsafeYAML", Class.new(StandardError))
    Psych.module_eval do
      def self.load(yaml, *args)
        result = parse(yaml, *args)
        check_safety(result)
        result ? result.to_ruby : result
      end
 
      private
      def self.check_safety(o)
        check_node(o)
        case o
        when Psych::Nodes::Scalar
        when Psych::Nodes::Sequence
          o.children.each {|child| check_safety(child)}
        when Psych::Nodes::Mapping
          o.children.each {|child| check_safety(child)}
        when Psych::Nodes::Document
          check_safety(o.root)
        when Psych::Nodes::Stream
          o.children.each {|child| check_safety(child)}
        when Psych::Nodes::Alias
        else
          raise Psych::UnsafeYAML.new("Found unknown node type: #{o.class}")
        end
      end

      def self.check_node(n)
        # Note thbar: we're allowing HashWithIndifferentAccess here
        # to cope with https://www.pivotaltracker.com/s/projects/971396
        unless n.tag.nil? || ['!ruby/sym', '!ruby/symbol', '!map:HashWithIndifferentAccess', '!map:ActiveSupport::HashWithIndifferentAccess', '!ruby/hash:ActiveSupport::HashWithIndifferentAccess', '!binary', '!'].include?(n.tag)
          raise Psych::UnsafeYAML.new("Found node with tag: #{n.tag}")
        end
      end
    end
  end
end


make_yaml_safe!