pcap.c

linux网络编程中的经典源码

/* include open_pcap */
#include	"udpcksum.h"

#define	CMD		"udp and src host %s and src port %d"

void
open_pcap(void)
{
	uint32_t			localnet, netmask;
	char				cmd[MAXLINE], errbuf[PCAP_ERRBUF_SIZE],
						str1[INET_ADDRSTRLEN], str2[INET_ADDRSTRLEN];
	struct bpf_program	fcode;

	if (device == NULL) {
		if ( (device = pcap_lookupdev(errbuf)) == NULL)
			err_quit("pcap_lookup: %s", errbuf);
	}
	printf("device = %s\n", device);

		/* 4hardcode: promisc=0, to_ms=500 */
	if ( (pd = pcap_open_live(device, snaplen, 0, 500, errbuf)) == NULL)
		err_quit("pcap_open_live: %s", errbuf);

	if (pcap_lookupnet(device, &localnet, &netmask, errbuf) < 0)
		err_quit("pcap_lookupnet: %s", errbuf);
	if (verbose)
		printf("localnet = %s, netmask = %s\n",
			   Inet_ntop(AF_INET, &localnet, str1, sizeof(str1)),
			   Inet_ntop(AF_INET, &netmask, str2, sizeof(str2)));

	snprintf(cmd, sizeof(cmd), CMD,
			 Sock_ntop_host(dest, destlen),
			 ntohs(sock_get_port(dest, destlen)));
	if (verbose)
		printf("cmd = %s\n", cmd);
	if (pcap_compile(pd, &fcode, cmd, 0, netmask) < 0)
		err_quit("pcap_compile: %s", pcap_geterr(pd));

	if (pcap_setfilter(pd, &fcode) < 0)
		err_quit("pcap_setfilter: %s", pcap_geterr(pd));

	if ( (datalink = pcap_datalink(pd)) < 0)
		err_quit("pcap_datalink: %s", pcap_geterr(pd));
	if (verbose)
		printf("datalink = %d\n", datalink);
}
/* end open_pcap */

/* include next_pcap */
char *
next_pcap(int *len)
{
	char				*ptr;
	struct pcap_pkthdr	hdr;

		/* 4keep looping until packet ready */
	while ( (ptr = (char *) pcap_next(pd, &hdr)) == NULL)
		;

	*len = hdr.caplen;	/* captured length */
	return(ptr);
}
/* end next_pcap */