rails 3.2: 400 for malformed request

gistfile1.rb

# config/initializers/action_dispatch_params_parser.rb
# backport from 4.0
module ActionDispatch
  class ParamsParser
    class ParseError < StandardError
      attr_reader :original_exception

      def initialize(message, original_exception)
        super(message)
        @original_exception = original_exception
      end
    end

    private
      def parse_formatted_parameters_with_rescue(env)
        parse_formatted_parameters_without_rescue(env)
      rescue Exception => e
        raise ParseError.new(e.message, e)
      end

      alias_method_chain :parse_formatted_parameters, :rescue
  end
end

ActionDispatch::ExceptionWrapper.rescue_responses.merge!(
  'ActionDispatch::ParamsParser::ParseError'   => :bad_request,
)