142 lines
4.8 KiB
Plaintext
142 lines
4.8 KiB
Plaintext
.\" Copyright (c) 1994, 1996, 1997
|
|
.\" The Regents of the University of California. All rights reserved.
|
|
.\"
|
|
.\" Redistribution and use in source and binary forms, with or without
|
|
.\" modification, are permitted provided that: (1) source code distributions
|
|
.\" retain the above copyright notice and this paragraph in its entirety, (2)
|
|
.\" distributions including binary code include the above copyright notice and
|
|
.\" this paragraph in its entirety in the documentation or other materials
|
|
.\" provided with the distribution, and (3) all advertising materials mentioning
|
|
.\" features or use of this software display the following acknowledgement:
|
|
.\" ``This product includes software developed by the University of California,
|
|
.\" Lawrence Berkeley Laboratory and its contributors.'' Neither the name of
|
|
.\" the University nor the names of its contributors may be used to endorse
|
|
.\" or promote products derived from this software without specific prior
|
|
.\" written permission.
|
|
.\" THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED
|
|
.\" WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
|
|
.\" MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
|
|
.\"
|
|
.TH PCAP_NEXT_EX 3PCAP "13 October 2013"
|
|
.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.
|
|
.PP
|
|
The bytes of data from the packet begin with a link-layer header. The
|
|
format of the link-layer header is indicated by the return value of the
|
|
.B pcap_datalink()
|
|
routine when handed the
|
|
.B pcap_t
|
|
value also passed to
|
|
.B pcap_loop()
|
|
or
|
|
.BR pcap_dispatch() .
|
|
.I http://www.tcpdump.org/linktypes.html
|
|
lists the values
|
|
.B pcap_datalink()
|
|
can return and describes the packet formats that
|
|
correspond to those values. The value it returns will be valid for all
|
|
packets received unless and until
|
|
.B pcap_set_datalink()
|
|
is called; after a successful call to
|
|
.BR pcap_set_datalink() ,
|
|
all subsequent packets will have a link-layer header of the type
|
|
specified by the link-layer header type value passed to
|
|
.BR pcap_set_datalink() .
|
|
.PP
|
|
Do
|
|
.B NOT
|
|
assume that the packets for a given capture or ``savefile`` will have
|
|
any given link-layer header type, such as
|
|
.B DLT_EN10MB
|
|
for Ethernet. For example, the "any" device on Linux will have a
|
|
link-layer header type of
|
|
.B DLT_LINUX_SLL
|
|
even if all devices on the system at the time the "any" device is opened
|
|
have some other data link type, such as
|
|
.B DLT_EN10MB
|
|
for Ethernet.
|
|
.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),
|
|
pcap_datalink(3PCAP)
|