pcap_loop 和 pcap_dispatch 的区别

Question

pcap_loop 和 pcap_dispatch 到底有什么区别？

Answer 1

手册对这一点的描述非常好（我是板着脸说，保证）。来自man pcap_loop：

   pcap_loop() processes packets from a  live  capture  or  ``savefile''
   until  cnt  packets  are  processed,  the  end of the ``savefile'' is
   reached when reading from a ``savefile'', pcap_breakloop() is called,
   or  an  error  occurs.   It  does  not return when live read timeouts
   occur.  A value of -1 or 0 for cnt is equivalent to infinity, so that
   packets are processed until another ending condition occurs.

   pcap_dispatch() processes packets from a live capture or ``savefile''
   until cnt packets are processed, the end of the current bufferful  of
   packets  is reached when doing a live capture, the end of the ``save‐
   file'' is reached when reading from a ``savefile'',  pcap_breakloop()
   is  called, or an error occurs.  Thus, when doing a live capture, cnt
   is the maximum number of packets to process before returning, but  is
   not a minimum number; when reading a live capture, only one bufferful
   of packets is read at a time, so fewer than cnt packets may  be  pro‐
   cessed. A value of -1 or 0 for cnt causes all the packets received in
   one buffer to be processed when reading a live  capture,  and  causes
   all  the  packets  in the file to be processed when reading a ``save‐
   file''.

这有点像文字墙，所以让我们分解一下。

两个功能：

• 处理来自实时捕获或“保存文件”的数据包，直到出现以下任一情况：
  • 达到指定的计数
  • 已到达“保存文件”的末尾
  • pcap_breakloop() 被调用
  • 发生错误
• 认为 -1 或 0 实质上意味着“处理无限数量的数据包” - 即，直到出现另一个结束条件。 （建议使用 -1 以实现与旧版本的互操作性，稍后在手册中介绍）

pcap_dispatch() 单独

• 在达到当前缓冲的数据包结束后，在进行实时捕获时也会返回（换句话说，可以更频繁地返回，因为指定的计数不是最小值）