@(#) $Header: /tcpdump/master/libpcap/pcap_next_ex.3pcap,v 1.3 2008-04-06 02:53:22 guy Exp $

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pcap_next_ex, pcap_next - read the next packet from a pcap_t

#include <pcap/pcap.h>

int pcap_next_ex(pcap_t *p, struct pcap_pkthdr **pkt_header,
const u_char **pkt_data);
const u_char *pcap_next(pcap_t *p, struct pcap_pkthdr *h);

pcap_next_ex() reads the next packet and returns a success/failure indication. If the packet was read without problems, the pointer pointed to by the pkt_header argument is set to point to the pcap_pkthdr struct for the packet, and the pointer pointed to by the pkt_data argument is set to point to the data in the packet. The struct pcap_pkthdr and the packet data are not to be freed by the caller, and are not guaranteed to be valid after the next call to pcap_next_ex() , pcap_next() , pcap_loop() , or pcap_dispatch() ; if the code needs them to remain valid, it must make a copy of them.

pcap_next() reads the next packet (by calling pcap_dispatch() with a cnt of 1) and returns a u_char pointer to the data in that packet. The packet data is not to be freed by the caller, and is not guaranteed to be valid after the next call to pcap_next_ex() , pcap_next() , pcap_loop() , or pcap_dispatch() ; if the code needs it to remain valid, it must make a copy of it. The pcap_pkthdr structure pointed to by h is filled in with the appropriate values for the packet.

pcap_next_ex() returns 1 if the packet was read without problems, 0 if packets are being read from a live capture, and the timeout expired, -1 if an error occurred while reading the packet, and -2 if packets are being read from a ``savefile'', and there are no more packets to read from the savefile. If -1 is returned, pcap_geterr() or pcap_perror() may be called with p as an argument to fetch or display the error text.

pcap_next() returns a pointer to the packet data on success, and returns NULL if an error occurred, or if no packets were read from a live capture (if, for example, they were discarded because they didn't pass the packet filter, or if, on platforms that support a read timeout that starts before any packets arrive, the timeout expires before any packets arrive, or if the file descriptor for the capture device is in non-blocking mode and no packets were available to be read), or if no more packets are available in a ``savefile.'' Unfortunately, there is no way to determine whether an error occurred or not.

pcap(3PCAP), pcap_geterr(3PCAP), pcap_dispatch(3PCAP)