c - pcap_pkthdr 有什么用？

Question

来自 here 的代码片段:

void packet_handler(u_char *param, const struct pcap_pkthdr *header, const u_char *pkt_data) 
{ 
    .... 
    /* retireve the position of the ip header */ 
    ih = (ip_header *) (pkt_data + 
        14); //length of ethernet header 
    .... 

什么是 const struct pcap_pkthdr *header for( definition )，我们什么时候需要它，它是如何填充的(因为数据包本身没有这样的信息，如下所示)？


(来源: lewis at www.dcs.gla.ac.uk)

Answer 1

如果您保留评论，那会容易一些。它说:

/* Callback function invoked by libpcap for every incoming packet */

Here它说的是 typedef void(*) pcap_handler(u_char *user, const struct pcap_pkthdr *pkt_header, const u_char *pkt_data) :

pkt_header is the header associated by the capture driver to the packet. It is NOT a protocol header.