231 lines
7.0 KiB
Plaintext
231 lines
7.0 KiB
Plaintext
.\" $NetBSD: pcap_loop.3pcap,v 1.7 2023/08/17 15:18:12 christos Exp $
|
|
.\"
|
|
.\" 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_LOOP 3PCAP "5 March 2022"
|
|
.SH NAME
|
|
pcap_loop, pcap_dispatch \- process packets from a live capture or savefile
|
|
.SH SYNOPSIS
|
|
.nf
|
|
.ft B
|
|
#include <pcap/pcap.h>
|
|
.ft
|
|
.LP
|
|
.ft B
|
|
typedef void (*pcap_handler)(u_char *user, const struct pcap_pkthdr *h,
|
|
.ti +8
|
|
const u_char *bytes);
|
|
.ft
|
|
.LP
|
|
.ft B
|
|
int pcap_loop(pcap_t *p, int cnt,
|
|
.ti +8
|
|
pcap_handler callback, u_char *user);
|
|
int pcap_dispatch(pcap_t *p, int cnt,
|
|
.ti +8
|
|
pcap_handler callback, u_char *user);
|
|
.ft
|
|
.fi
|
|
.SH DESCRIPTION
|
|
.BR pcap_loop ()
|
|
processes packets from a live capture or ``savefile'' until
|
|
.I cnt
|
|
packets are processed, the end of the ``savefile'' is
|
|
reached when reading from a ``savefile'',
|
|
.BR pcap_breakloop (3PCAP)
|
|
is called, or an error occurs.
|
|
It does
|
|
.B not
|
|
return when live packet buffer timeouts occur.
|
|
A value of
|
|
.B \-1
|
|
or
|
|
.B 0
|
|
for
|
|
.I cnt
|
|
is equivalent to infinity, so that packets are processed until another
|
|
ending condition occurs.
|
|
.PP
|
|
.BR pcap_dispatch ()
|
|
processes packets from a live capture or ``savefile'' until
|
|
.I cnt
|
|
packets are processed, the end of the current bufferful of packets is
|
|
reached when doing a live capture, the end of the ``savefile'' is
|
|
reached when reading from a ``savefile'',
|
|
.BR pcap_breakloop ()
|
|
is called, or an error occurs.
|
|
Thus, when doing a live capture,
|
|
.I cnt
|
|
is the maximum number of packets to process before returning, but is not
|
|
a minimum number; when reading a live capture, only one
|
|
bufferful of packets is read at a time, so fewer than
|
|
.I cnt
|
|
packets may be processed. A value of
|
|
.B \-1
|
|
or
|
|
.B 0
|
|
for
|
|
.I cnt
|
|
causes all the packets received in one buffer to be processed when
|
|
reading a live capture, and causes all the packets in the file to be
|
|
processed when reading a ``savefile''.
|
|
.PP
|
|
Note that, when doing a live capture on some platforms, if the read
|
|
timeout expires when there are no packets available,
|
|
.BR pcap_dispatch ()
|
|
will return 0, even when not in non-blocking mode, as there are no
|
|
packets to process. Applications should be prepared for this to happen,
|
|
but must not rely on it happening.
|
|
.PP
|
|
.I callback
|
|
specifies a
|
|
.I pcap_handler
|
|
routine to be called with three arguments:
|
|
a
|
|
.I u_char
|
|
pointer which is passed in the
|
|
.I user
|
|
argument to
|
|
.BR pcap_loop ()
|
|
or
|
|
.BR pcap_dispatch (),
|
|
a
|
|
.I const struct pcap_pkthdr
|
|
pointer pointing to the packet time stamp and lengths, and a
|
|
.I const u_char
|
|
pointer to the first
|
|
.B caplen
|
|
(as given in the
|
|
.I struct pcap_pkthdr
|
|
a pointer to which is passed to the callback routine)
|
|
bytes of data from the packet. The
|
|
.I struct pcap_pkthdr
|
|
and the packet data are not to be freed by the callback routine, and are
|
|
not guaranteed to be valid after the callback routine returns; if the
|
|
code needs them to be valid after the callback, it must make a copy of
|
|
them.
|
|
.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
|
|
.BR pcap_datalink (3PCAP)
|
|
routine when handed the
|
|
.B pcap_t
|
|
value also passed to
|
|
.BR pcap_loop ()
|
|
or
|
|
.BR pcap_dispatch ().
|
|
.I https://www.tcpdump.org/linktypes.html
|
|
lists the values
|
|
.BR 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
|
|
.BR pcap_set_datalink (3PCAP)
|
|
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
|
|
or
|
|
.B DLT_LINUX_SLL2
|
|
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
|
|
.BR pcap_loop ()
|
|
returns
|
|
.B 0
|
|
if
|
|
.I cnt
|
|
is exhausted or if, when reading from a ``savefile'', no more packets
|
|
are available. It returns
|
|
.B PCAP_ERROR_BREAK
|
|
if the loop terminated due to a call to
|
|
.BR pcap_breakloop ()
|
|
before any packets were processed,
|
|
.B PCAP_ERROR_NOT_ACTIVATED
|
|
if called on a capture handle that has been created but not activated,
|
|
or
|
|
.B PCAP_ERROR
|
|
if another error occurs.
|
|
It does
|
|
.B not
|
|
return when live packet buffer timeouts occur; instead, it attempts to
|
|
read more packets.
|
|
.PP
|
|
.BR pcap_dispatch ()
|
|
returns the number of packets processed on success; this can be 0 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 packet buffer 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.'' It returns
|
|
.B PCAP_ERROR_BREAK
|
|
if the loop terminated due to a call to
|
|
.BR pcap_breakloop ()
|
|
before any packets were processed,
|
|
.B PCAP_ERROR_NOT_ACTIVATED
|
|
if called on a capture handle that has been created but not activated,
|
|
or
|
|
.B PCAP_ERROR
|
|
if another error occurs.
|
|
.ft B
|
|
If your application uses pcap_breakloop(),
|
|
make sure that you explicitly check for PCAP_ERROR and PCAP_ERROR_BREAK,
|
|
rather than just checking for a return value < 0.
|
|
.ft R
|
|
.PP
|
|
If
|
|
.B PCAP_ERROR
|
|
is returned,
|
|
.BR pcap_geterr (3PCAP)
|
|
or
|
|
.BR pcap_perror (3PCAP)
|
|
may be called with
|
|
.I p
|
|
as an argument to fetch or display the error text.
|
|
.SH BACKWARD COMPATIBILITY
|
|
.PP
|
|
In libpcap versions before 1.5.0, the behavior when
|
|
.I cnt
|
|
was
|
|
.B 0
|
|
was undefined; different platforms and devices behaved differently,
|
|
so code that must work with these versions of libpcap should use
|
|
.BR \-1 ,
|
|
not
|
|
.BR 0 ,
|
|
as the value of
|
|
.IR cnt .
|
|
.SH SEE ALSO
|
|
.BR pcap (3PCAP)
|