<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def write_header(self):
 """Write the DNS message header. Writing the DNS message header is done asfter all sections have been rendered, but before the optional TSIG signature is added. """


        self.output.seek(0)
        self.output.write(struct.pack('!HHHHHH', self.id, self.flags,
                                      self.counts[0], self.counts[1],
                                      self.counts[2], self.counts[3]))
        self.output.seek(0, 2)