def size
      case self.body
      when String then self.body.length
      when StringIO then self.body.length
      when File then self.body.size
      else 0
      end
    end
def size
      case self.body
      when String then self.body.length
      when StringIO then self.body.length
      when File then self.body.size
      else 0
      end
    end
get the size, in bytes, of the response. used for logging
 @return [Integer] size