utils.py 文件源码

def _write_header(self, pkt):
        self.header_present=1

        if self.append:
            # Even if prone to race conditions, this seems to be
            # safest way to tell whether the header is already present
            # because we have to handle compressed streams that
            # are not as flexible as basic files
            g = [open,gzip.open][self.gz](self.filename,"rb")
            if g.read(16):
                return

        self.f.write(struct.pack(self.endian+"IHHIIII", 0xa1b2c3d4L,
                                 2, 4, 0, 0, MTU, self.linktype))
        self.f.flush()