libpcap-1.3.0/pcap_next_ex.3pcap

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.TH PCAP_NEXT_EX 3PCAP "5 April 2008"
.SH NAME
pcap_next_ex, pcap_next \- read the next packet from a pcap_t
.SH SYNOPSIS
.nf
.ft B
#include <pcap/pcap.h>
.ft
.LP
.ft B
int pcap_next_ex(pcap_t *p, struct pcap_pkthdr **pkt_header,
.ti +8
const u_char **pkt_data);
const u_char *pcap_next(pcap_t *p, struct pcap_pkthdr *h);
.ft
.fi
.SH DESCRIPTION
.B 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
.I pkt_header
argument is set to point to the
.I pcap_pkthdr
struct for the packet, and the
pointer pointed to by the
.I pkt_data
argument is set to point to the data in the packet.  The
.I 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
.BR pcap_next_ex() ,
.BR pcap_next() ,
.BR pcap_loop() ,
or
.BR pcap_dispatch() ;
if the code needs them to remain valid, it must make a copy of them.
.PP
.B pcap_next()
reads the next packet (by calling
.B pcap_dispatch()
with a
.I cnt
of 1) and returns a
.I 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
.BR pcap_next_ex() ,
.BR pcap_next() ,
.BR pcap_loop() ,
or
.BR pcap_dispatch() ;
if the code needs it to remain valid, it must make a copy of it.
The
.I pcap_pkthdr
structure pointed to by
.I h
is filled in with the appropriate values for the packet.
.SH RETURN VALUE
.B 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,
.B pcap_geterr()
or
.B pcap_perror()
may be called with
.I p
as an argument to fetch or display the error text.
.PP
.B pcap_next()
returns a pointer to the packet data on success, and returns
.B 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.
.SH SEE ALSO
pcap(3PCAP), pcap_geterr(3PCAP), pcap_dispatch(3PCAP)