translate_offset

# File activesupport/lib/active_support/multibyte/handlers/utf8_handler.rb, line 321
      def translate_offset(str, byte_offset)
        return nil if byte_offset.nil?
        return 0 if str == ''
        chunk = str[0..byte_offset]
        begin
          begin
            chunk.unpack('U*').length - 1
          rescue ArgumentError => e
            chunk = str[0..(byte_offset+=1)]
            # Stop retrying at the end of the string
            raise e unless byte_offset < chunk.length 
            # We damaged a character, retry
            retry
          end
        # Catch the ArgumentError so we can throw our own
        rescue ArgumentError 
          raise EncodingError.new('malformed UTF-8 character')
        end
      end