def read_signature
      str_sz = read(1).unpack("C")[0]
      ret = @buffy.slice(@idx, str_sz)
      raise IncompleteBufferException if @idx + str_sz + 1 >= @buffy.bytesize
      @idx += str_sz
      if @buffy[@idx].ord != 0
        raise InvalidPacketException, "Type is not nul-terminated"
      end
      @idx += 1
      # no exception, see check above
      ret
    end
def read_signature
      str_sz = read(1).unpack("C")[0]
      ret = @buffy.slice(@idx, str_sz)
      raise IncompleteBufferException if @idx + str_sz + 1 >= @buffy.bytesize
      @idx += str_sz
      if @buffy[@idx].ord != 0
        raise InvalidPacketException, "Type is not nul-terminated"
      end
      @idx += 1
      # no exception, see check above
      ret
    end
Read the signature length and signature itself from the buffer.
 Return the signature.