2009-03-21 20:43:56 +00:00
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.\" Copyright (c) 1994, 1996, 1997
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.\" The Regents of the University of California. All rights reserved.
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.\" Redistribution and use in source and binary forms, with or without
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.\" retain the above copyright notice and this paragraph in its entirety, (2)
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.\" distributions including binary code include the above copyright notice and
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.\" this paragraph in its entirety in the documentation or other materials
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.\" ``This product includes software developed by the University of California,
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.\" Lawrence Berkeley Laboratory and its contributors.'' Neither the name of
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.\" or promote products derived from this software without specific prior
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.\" written permission.
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.\" THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED
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.\" WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
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.\" MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
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.\"
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2019-10-06 04:26:37 +00:00
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.TH PCAP_LOOP 3PCAP "25 July 2018"
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2009-03-21 20:43:56 +00:00
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.SH NAME
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pcap_loop, pcap_dispatch \- process packets from a live capture or savefile
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.SH SYNOPSIS
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.nf
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.ft B
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#include <pcap/pcap.h>
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.ft
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.LP
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.ft B
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typedef void (*pcap_handler)(u_char *user, const struct pcap_pkthdr *h,
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.ti +8
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const u_char *bytes);
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.ft
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.LP
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.ft B
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int pcap_loop(pcap_t *p, int cnt,
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.ti +8
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pcap_handler callback, u_char *user);
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int pcap_dispatch(pcap_t *p, int cnt,
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.ti +8
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pcap_handler callback, u_char *user);
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.ft
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.fi
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.SH DESCRIPTION
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.B pcap_loop()
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processes packets from a live capture or ``savefile'' until
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.I cnt
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packets are processed, the end of the ``savefile'' is
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reached when reading from a ``savefile'',
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2019-10-06 04:26:37 +00:00
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.B pcap_breakloop(3PCAP)
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2009-03-21 20:43:56 +00:00
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is called, or an error occurs.
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It does
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.B not
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2018-05-18 12:21:19 +00:00
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return when live packet buffer timeouts occur.
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2009-03-21 20:43:56 +00:00
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A value of \-1 or 0 for
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.I cnt
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is equivalent to infinity, so that packets are processed until another
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ending condition occurs.
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.PP
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.B pcap_dispatch()
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processes packets from a live capture or ``savefile'' until
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.I cnt
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packets are processed, the end of the current bufferful of packets is
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reached when doing a live capture, the end of the ``savefile'' is
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reached when reading from a ``savefile'',
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.B pcap_breakloop()
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is called, or an error occurs.
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Thus, when doing a live capture,
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.I cnt
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is the maximum number of packets to process before returning, but is not
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a minimum number; when reading a live capture, only one
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bufferful of packets is read at a time, so fewer than
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.I cnt
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packets may be processed. A value of \-1 or 0 for
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.I cnt
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causes all the packets received in one buffer to be processed when
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reading a live capture, and causes all the packets in the file to be
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processed when reading a ``savefile''.
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.PP
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2017-02-12 07:04:44 +00:00
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Note that, when doing a live capture on some platforms, if the read
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timeout expires when there are no packets available,
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.B pcap_dispatch()
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will return 0, even when not in non-blocking mode, as there are no
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packets to process. Applications should be prepared for this to happen,
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but must not rely on it happening.
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.PP
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2009-03-21 20:43:56 +00:00
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.ft B
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(In older versions of libpcap, the behavior when
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\fIcnt\fP
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was 0 was undefined; different platforms and devices behaved
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differently, so code that must work with older versions of libpcap
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2013-05-30 06:41:26 +00:00
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should use \-1, not 0, as the value of
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2009-03-21 20:43:56 +00:00
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\fIcnt\fP.)
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.ft R
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.PP
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.I callback
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Update libpcap to 1.1.1.
Changes:
Thu. April 1, 2010. guy@alum.mit.edu.
Summary for 1.1.1 libpcap release
Update CHANGES to reflect more of the changes in 1.1.0.
Fix build on RHEL5.
Fix shared library build on AIX.
Thu. March 11, 2010. ken@netfunctional.ca/guy@alum.mit.edu.
Summary for 1.1.0 libpcap release
Add SocketCAN capture support
Add Myricom SNF API support
Update Endace DAG and ERF support
Add support for shared libraries on Solaris, HP-UX, and AIX
Build, install, and un-install shared libraries by default;
don't build/install shared libraries on platforms we don't support
Fix building from a directory other than the source directory
Fix compiler warnings and builds on some platforms
Update config.guess and config.sub
Support monitor mode on mac80211 devices on Linux
Fix USB memory-mapped capturing on Linux; it requires a new DLT_
value
On Linux, scan /sys/class/net for devices if we have it; scan
it, or /proc/net/dev if we don't have /sys/class/net, even if
we have getifaddrs(), as it'll find interfaces with no
addresses
Add limited support for reading pcap-ng files
Fix BPF driver-loading error handling on AIX
Support getting the full-length interface description on FreeBSD
In the lexical analyzer, free up any addrinfo structure we got back
from getaddrinfo().
Add support for BPF and libdlpi in OpenSolaris (and SXCE)
Hyphenate "link-layer" everywhere
Add /sys/kernel/debug/usb/usbmon to the list of usbmon locations
In pcap_read_linux_mmap(), if there are no frames available, call
poll() even if we're in non-blocking mode, so we pick up
errors, and check for the errors in question.
Note that poll() works on BPF devices is Snow Leopard
If an ENXIO or ENETDOWN is received, it may mean the device has
gone away. Deal with it.
For BPF, raise the default capture buffer size to from 32k to 512k
Support ps_ifdrop on Linux
Added a bunch of #ifdef directives to make wpcap.dll (WinPcap) compile
under cygwin.
Changes to Linux mmapped captures.
Fix bug where create_ring would fail for particular snaplen and
buffer size combinations
Update pcap-config so that it handles libpcap requiring
additional libraries
Add workaround for threadsafeness on Windows
Add missing mapping for DLT_ENC <-> LINKTYPE_ENC
DLT: Add DLT_CAN_SOCKETCAN
DLT: Add Solaris ipnet
Don't check for DLT_IPNET if it's not defined
Add link-layer types for Fibre Channel FC-2
Add link-layer types for Wireless HART
Add link-layer types for AOS
Add link-layer types for DECT
Autoconf fixes (AIX, HP-UX, OSF/1, Tru64 cleanups)
Install headers unconditionally, and include vlan.h/bluetooth.h if
enabled
Autoconf fixes+cleanup
Support enabling/disabling bluetooth (--{en,dis}able-bluetooth)
Support disabling SITA support (--without-sita)
Return -1 on failure to create packet ring (if supported but
creation failed)
Fix handling of 'any' device, so that it can be opened, and no longer
attempt to open it in Monitor mode
Add support for snapshot length for USB Memory-Mapped Interface
Fix configure and build on recent Linux kernels
Fix memory-mapped Linux capture to support pcap_next() and
pcap_next_ex()
Fixes for Linux USB capture
DLT: Add DLT_LINUX_EVDEV
DLT: Add DLT_GSMTAP_UM
DLT: Add DLT_GSMTAP_ABIS
2010-10-28 16:22:13 +00:00
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specifies a
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.I pcap_handler
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routine to be called with three arguments:
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2009-03-21 20:43:56 +00:00
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a
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.I u_char
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pointer which is passed in the
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.I user
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argument to
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.B pcap_loop()
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or
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.BR pcap_dispatch() ,
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a
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.I const struct pcap_pkthdr
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pointer pointing to the packet time stamp and lengths, and a
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.I const u_char
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pointer to the first
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.B caplen
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(as given in the
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.I struct pcap_pkthdr
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a pointer to which is passed to the callback routine)
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2012-01-31 17:22:07 +00:00
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bytes of data from the packet. The
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.I struct pcap_pkthdr
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and the packet data are not to be freed by the callback routine, and are
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not guaranteed to be valid after the callback routine returns; if the
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code needs them to be valid after the callback, it must make a copy of
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them.
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2015-01-06 18:58:31 +00:00
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.PP
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The bytes of data from the packet begin with a link-layer header. The
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format of the link-layer header is indicated by the return value of the
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2019-10-06 04:26:37 +00:00
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.B pcap_datalink(3PCAP)
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2015-01-06 18:58:31 +00:00
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routine when handed the
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.B pcap_t
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value also passed to
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.B pcap_loop()
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or
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.BR pcap_dispatch() .
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2019-10-06 04:26:37 +00:00
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.I https://www.tcpdump.org/linktypes.html
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2015-01-06 18:58:31 +00:00
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lists the values
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.B pcap_datalink()
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can return and describes the packet formats that
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correspond to those values. The value it returns will be valid for all
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packets received unless and until
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2019-10-06 04:26:37 +00:00
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.B pcap_set_datalink(3PCAP)
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2015-01-06 18:58:31 +00:00
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is called; after a successful call to
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.BR pcap_set_datalink() ,
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all subsequent packets will have a link-layer header of the type
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specified by the link-layer header type value passed to
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.BR pcap_set_datalink() .
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.PP
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Do
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.B NOT
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assume that the packets for a given capture or ``savefile`` will have
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any given link-layer header type, such as
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.B DLT_EN10MB
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for Ethernet. For example, the "any" device on Linux will have a
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link-layer header type of
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.B DLT_LINUX_SLL
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even if all devices on the system at the time the "any" device is opened
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have some other data link type, such as
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.B DLT_EN10MB
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for Ethernet.
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2009-03-21 20:43:56 +00:00
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.SH RETURN VALUE
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.B pcap_loop()
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returns 0 if
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.I cnt
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2013-05-30 06:41:26 +00:00
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is exhausted or if, when reading from a ``savefile'', no more packets
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2019-10-06 04:26:37 +00:00
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are available. It returns
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.B PCAP_ERROR
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if an error occurs or
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.B PCAP_ERROR_BREAK
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if the loop terminated due to a call to
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2009-03-21 20:43:56 +00:00
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.B pcap_breakloop()
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before any packets were processed.
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It does
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.B not
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2018-05-18 12:21:19 +00:00
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return when live packet buffer timeouts occur; instead, it attempts to
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read more packets.
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2009-03-21 20:43:56 +00:00
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.PP
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.B pcap_dispatch()
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returns the number of packets processed on success; this can be 0 if no
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packets were read from a live capture (if, for example, they were
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discarded because they didn't pass the packet filter, or if, on
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2018-05-18 12:21:19 +00:00
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platforms that support a packet buffer timeout that starts before any
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packets arrive, the timeout expires before any packets arrive, or if the
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file descriptor for the capture device is in non-blocking mode and no
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packets were available to be read) or if no more packets are available
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2019-10-06 04:26:37 +00:00
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in a ``savefile.'' It returns
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.B PCAP_ERROR
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if an error occurs or
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.B PCAP_ERROR_BREAK
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if the loop terminated due to a call to
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2009-03-21 20:43:56 +00:00
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.B pcap_breakloop()
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before any packets were processed.
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.ft B
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If your application uses pcap_breakloop(),
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2019-10-06 04:26:37 +00:00
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make sure that you explicitly check for PCAP_ERROR and PCAP_ERROR_BREAK,
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rather than just checking for a return value < 0.
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2009-03-21 20:43:56 +00:00
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.ft R
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.PP
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2019-10-06 04:26:37 +00:00
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If
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.B PCAP_ERROR
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is returned,
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.B pcap_geterr(3PCAP)
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2009-03-21 20:43:56 +00:00
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or
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2019-10-06 04:26:37 +00:00
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.B pcap_perror(3PCAP)
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2009-03-21 20:43:56 +00:00
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may be called with
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.I p
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as an argument to fetch or display the error text.
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.SH SEE ALSO
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2019-10-06 04:26:37 +00:00
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pcap(3PCAP)
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