<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def read (self, stream):
 """Reads PCapPacketHeader data from the given stream."""

      self._data = stream.read(self._size)

      if len(self._data) >= self._size:
          values = struct.unpack(self._swap + self._format, self._data)
      else:
          values = None, None, None, None

      self.ts_sec   = values[0]
      self.ts_usec  = values[1]
      self.incl_len = values[2]
      self.orig_len = values[3]