# File lib/rmail/parser/pushbackreader.rb, line 53
      def read(size = @chunk_size)
        case size
        when nil
          chunk = nil
          while temp = read(@chunk_size)
            if chunk
              chunk << temp
            else
              chunk = temp
            end
          end
          chunk
        when Fixnum
          read_chunk(size)
        else
          raise ArgumentError,
            "Read size (#{size.inspect}) must be a Fixnum or nil."
        end
      end