docs: def store(report, address):
      """Stores the report on disk.
      """
      now = time.time()
      secs = int(now)
      msecs = int((now - secs) * 1000)
      submitted_date = filename = None  # avoids warnings
      while True:
          submitted_date = '%d.%03d' % (secs, msecs)
          filename = 'report_%s.txt' % submitted_date
          filename = os.path.join(DESTINATION, filename)
          if not os.path.exists(filename):
              break
          msecs += 1
  
      lines = [l for l in report.split(b'\n') if l]
      for line in lines:
          if line.startswith(b'date:'):
              date = line[5:]
              if date_format.match(date):
                  with open(filename, 'wb') as fp:
                      if not isinstance(address, bytes):
                          address = address.encode('ascii')
                      fp.write(b'submitted_from:' + address + b'\n')
                      fp.write(('submitted_date:%s\n' % submitted_date)
                               .encode('ascii'))
                      fp.write(report)
                  return None
              else:
                  return "invalid date"
      return "missing date field"