Net::Pcap - Interface to pcap LBL packet capture library |
Net::Pcap - Interface to pcap(3)
LBL packet capture library
Version 0.17
use Net::Pcap;
my $err = ''; my $dev = pcap_lookupdev(\$err); # find a device
# open the device for live listening my $pcap = pcap_open_live($dev, 1024, 1, 0, \$err);
# loop over next 10 packets pcap_loop($pcap, 10, \&process_packet, "just for the demo");
# close the device pcap_close($pcap);
sub process_packet { my ($user_data, $header, $packet) = @_; # do something ... }
Net::Pcap
is a Perl binding to the LBL pcap(3)
library and its
Win32 counterpart, the WinPcap library. Pcap (packet capture) is
a portable API to capture network packet: it allows applications
to capture packets at link-layer, bypassing the normal protocol
stack. It also provides features like kernel-level packet filtering
and access to internal statistics.
Common applications include network statistics collection, security monitoring, network debugging, etc.
Since version 5.7.3, Perl uses a mechanism called ``deferred signals'' to delay signals delivery until ``safe'' points in the interpreter. See Deferred Signals (Safe Signals) in the perlipc manpage for a detailled explanation.
Since Net::Pcap
version 0.08, released in October 2005, the module
modified the internal variable PL_signals
to re-enable immediate
signals delivery in Perl 5.8 and later within some XS functions
(CPAN-RT #6320). However, it can create situations where the Perl
interpreter is less stable and can crash (CPAN-RT #43308). Therefore,
as of version 0.17, Net::Pcap
no longer modifies PL_signals
by
itself, but provides facilities so the user has full control of how
signals are delivered.
First, there pcap_perl_settings()
function allows to select how
signals are handled:
pcap_perl_settings(PERL_SIGNALS_UNSAFE); pcap_loop($pcap, 10, \&process_packet, ""); pcap_perl_settings(PERL_SIGNALS_SAFE);
Then, to easily make code interruptable, Net::Pcap
provides the
UNSAFE_SIGNALS
pseudo-bloc:
UNSAFE_SIGNALS { pcap_loop($pcap, 10, \&process_packet, ""); };
(Stolen from Rafael Garcia-Suarez's Perl::Unsafe::Signals
)
Net::Pcap
supports the following Exporter
tags:
:bpf
exports a few BPF related constants:
BPF_ALIGNMENT BPF_MAJOR_VERSION BPF_MAXBUFSIZE BPF_MAXINSNS BPF_MEMWORDS BPF_MINBUFSIZE BPF_MINOR_VERSION BPF_RELEASE
:datalink
exports the data link types macros:
DLT_AIRONET_HEADER DLT_APPLE_IP_OVER_IEEE1394 DLT_ARCNET DLT_ARCNET_LINUX DLT_ATM_CLIP DLT_ATM_RFC1483 DLT_AURORA DLT_AX25 DLT_CHAOS DLT_CHDLC DLT_CISCO_IOS DLT_C_HDLC DLT_DOCSIS DLT_ECONET DLT_EN10MB DLT_EN3MB DLT_ENC DLT_FDDI DLT_FRELAY DLT_HHDLC DLT_IBM_SN DLT_IBM_SP DLT_IEEE802 DLT_IEEE802_11 DLT_IEEE802_11_RADIO DLT_IEEE802_11_RADIO_AVS DLT_IPFILTER DLT_IP_OVER_FC DLT_JUNIPER_ATM1 DLT_JUNIPER_ATM2 DLT_JUNIPER_ES DLT_JUNIPER_GGSN DLT_JUNIPER_MFR DLT_JUNIPER_MLFR DLT_JUNIPER_MLPPP DLT_JUNIPER_MONITOR DLT_JUNIPER_SERVICES DLT_LINUX_IRDA DLT_LINUX_SLL DLT_LOOP DLT_LTALK DLT_NULL DLT_OLD_PFLOG DLT_PCI_EXP DLT_PFLOG DLT_PFSYNC DLT_PPP DLT_PPP_BSDOS DLT_PPP_ETHER DLT_PPP_SERIAL DLT_PRISM_HEADER DLT_PRONET DLT_RAW DLT_RIO DLT_SLIP DLT_SLIP_BSDOS DLT_SUNATM DLT_SYMANTEC_FIREWALL DLT_TZSP DLT_USER0 DLT_USER1 DLT_USER2 DLT_USER3 DLT_USER4 DLT_USER5 DLT_USER6 DLT_USER7 DLT_USER8 DLT_USER9 DLT_USER10 DLT_USER11 DLT_USER12 DLT_USER13 DLT_USER14 DLT_USER15
:pcap
exports the following pcap
constants:
PCAP_ERRBUF_SIZE PCAP_IF_LOOPBACK PCAP_VERSION_MAJOR PCAP_VERSION_MINOR
:mode
exports the following constants:
MODE_CAPT MODE_MON MODE_STAT
:openflag
exports the following constants:
OPENFLAG_PROMISCUOUS OPENFLAG_DATATX_UDP OPENFLAG_NOCAPTURE_RPCAP
:source
exports the following constants:
PCAP_SRC_FILE PCAP_SRC_IFLOCAL PCAP_SRC_IFREMOTE
:sample
exports the following constants:
PCAP_SAMP_NOSAMP PCAP_SAMP_1_EVERY_N PCAP_SAMP_FIRST_AFTER_N_MS
:rpcap
exports the following constants:
RMTAUTH_NULL RMTAUTH_PWD
:functions
short names of the functions (without the "pcap_"
prefix)
for those which would not cause a clash with an already defined name.
Namely, the following functions are not available in short form:
open()
, close()
, next()
, dump()
, file()
, fileno()
.
Using these short names is now discouraged, and may be removed in the future.
By default, this module exports the symbols from the :datalink
and
:pcap
tags, and all the functions, with the same names as the C library.
All functions defined by Net::Pcap
are direct mappings to the
libpcap functions. Consult the pcap(3)
documentation and source code
for more information.
Arguments that change a parameter, for example pcap_lookupdev()
,
are passed that parameter as a reference. This is to retain
compatibility with previous versions of Net::Pcap
.
pcap_open_live()
function. On error, the $err
parameter
is filled with an appropriate error message else it is undefined.
Example
$dev = pcap_lookupdev();
pcap_open_live()
function. On error, the $err
parameter
is filled with an appropriate error message else it is undefined.
Example
@devs = pcap_findalldevs(\%devinfo, \$err); for my $dev (@devs) { print "$dev : $devinfo{$dev}\n" }
@devs = pcap_findalldevs(\$err);
@devs = pcap_findalldevs(\$err, \%devinfo);
The first form was introduced by Marco Carnut in Net::Pcap
version 0.05
and kept intact in versions 0.06 and 0.07.
The second form was introduced by Jean-Louis Morel for the Windows only,
ActivePerl port of Net::Pcap
, in versions 0.04.01 and 0.04.02.
The new syntax has been introduced for consistency with the rest of the Perl
API and the C API of libpcap(3)
, where $err
is always the last argument.
$dev
. The function returns 0 on success and sets the $net
and
$mask
parameters with values. On failure it returns -1 and the
$err
parameter is filled with an appropriate error message.
$dev
parameter specifies which network interface to
capture packets from. The $snaplen
and $promisc
parameters specify
the maximum number of bytes to capture from each packet, and whether
to put the interface into promiscuous mode, respectively. The $to_ms
parameter specifies a read timeout in milliseconds. The packet descriptor
will be undefined if an error occurs, and the $err
parameter will be
set with an appropriate error message.
Example
$dev = pcap_lookupdev(); $pcap = pcap_open_live($dev, 1024, 1, 0, \$err) or die "Can't open device $dev: $err\n";
libpcap
. It is typically used when just using libpcap
for compiling BPF code.
Example
$pcap = pcap_open_dead(0, 1024);
$err
parameter will be filled. Savefiles
are created using the pcap_dump_*
commands.
Example
$pcap = pcap_open_offline($dump, \$err) or die "Can't read '$dump': $err\n";
$count
packets from the packet capture descriptor $pcap
and call
the perl function &callback
with an argument of $user_data
.
If $count
is negative, then the function loops forever or until an error
occurs. Returns 0 if $count
is exhausted, -1 on error, and -2 if the
loop terminated due to a call to pcap_breakloop()
before any packets were
processed.
The callback function is also passed packet header information and packet data like so:
sub process_packet { my ($user_data, $header, $packet) = @_;
... }
The header information is a reference to a hash containing the following fields.
len
- the total length of the packet.
caplen
- the actual captured length of the packet data. This corresponds
to the snapshot length parameter passed to open_live()
.
tv_sec
- seconds value of the packet timestamp.
tv_usec
- microseconds value of the packet timestamp.
Example
pcap_loop($pcap, 10, \&process_packet, "user data");
sub process_packet { my ($user_data, $header, $packet) = @_; # ... }
pcap_dispatch()
or pcap_loop()
to return rather than looping; they will return the number of packets that
have been processed so far, or -2 if no packets have been processed so far.
This routine is safe to use inside a signal handler on UNIX or a console control handler on Windows, as it merely sets a flag that is checked within the loop.
Please see the section on pcap_breakloop()
in pcap(3) for more
information.
$pcap
.
$count
packets and process them with callback function
&callback
. if $count
is -1, all packets currently buffered are
processed. If $count
is 0, process all packets until an error occurs.
$pcap
. Into the %header
hash is stored the received
packet header. If not packet is available, the return value and
header is undefined.
$pcap
, stores its header in \%header
and its data in
\$packet
and returns a success/failure indication:
1
means that the packet was read without problems;
0
means that packets are being read from a live capture, and the
timeout expired;
-1
means that an error occurred while reading the packet;
-2
packets are being read from a dump file, and there are no more
packets to read from the savefile.
$filter_str
and store it in
$filter
. A description of the filter language can be found in the
libpcap source code, or the manual page for tcpdump(8)
. The filter
is optimized if the $optimize
variable is true. The netmask of the
network device must be specified in the $netmask
parameter. The
function returns 0 if the compilation was successful, or -1 if there
was a problem.
compile()
except that instead of passing a $pcap
descriptor,
one passes $snaplen
and $linktype
directly. Returns -1 if there was an
error, but the error message is not available.
$filter
with the packet
capture descriptor $pcap
.
pcap_compile()
.
$mode
(zero to activate and non-zero to deactivate). It has no
effect on offline descriptors. If there is an error, it returns -1 and sets
$err
.
In non-blocking mode, an attempt to read from the capture descriptor with
pcap_dispatch()
will, if no packets are currently available to be read,
return 0 immediately rather than blocking waiting for packets to arrive.
pcap_loop()
and pcap_next()
will not work in non-blocking mode.
$pcap
.
Always returns 0 on savefiles. If there is an error, it returns -1 and
sets $err
.
$filename
is "-"
data is written to standard output. On error, the
return value is undefined and pcap_geterr()
can be used to
retrieve the error text.
%header
and packet data $packet
to the savefile associated with $dumper
. The packet header has the
same format as that passed to the pcap_loop()
callback.
Example
my $dump_file = 'network.dmp'; my $dev = pcap_lookupdev(); my $pcap = pcap_open_live($dev, 1024, 1, 0, \$err);
my $dumper = pcap_dump_open($pcap, $dump_file); pcap_loop($pcap, 10, \&process_packet, ''); pcap_dump_close($dumper);
sub process_packet { my ($user_data, $header, $packet) = @_; pcap_dump($dumper, $header, $packet); }
pcap_dump_open()
.
pcap_dump()
but not yet written to the save
file will be written. Returns -1 on error, 0 on success.
$dumper
.
Example
$linktype = pcap_datalink($pcap);
$linktype
. Returns -1 on failure.
DLT_
name with the DLT_
part removed, to the corresponding data link type value. The translation is
case-insensitive. Returns -1 on failure.
Example
$linktype = pcap_datalink_name_to_val('LTalk'); # returns DLT_LTALK
Example
$name = pcap_datalink_val_to_name(DLT_LTALK); # returns 'LTALK'
Example
$descr = pcap_datalink_val_to_description(DLT_LTALK); # returns 'Localtalk'
pcap_open_live()
.
$pcap
. The hash contains the following fields.
This function is supported only on live captures, not on savefiles; no statistics are stored in savefiles, so no statistics are available when reading from a savefile.
ps_recv
- the number of packets received by the packet capture software.
ps_drop
- the number of packets dropped by the packet capture software.
ps_ifdrop
- the number of packets dropped by the network interface.
pcap_open_offline()
or undef
if the device was opened
with pcap_open_live()
.
pcap_open_live()
.
select()
or poll()
to wait for it to be possible to read
packets without blocking, if such a descriptor exists, or -1, if no such
descriptor exists. Some network devices opened with pcap_open_live()
do not support select()
or poll()
, so -1 is returned for those devices.
See pcap(3) for more details.
$pcap
.
$errno
.
$pcap
on
standard error, prefixed by $prefix
.
pcap
library the module was linked
against.
The following functions are specific to the Perl binding of libpcap.
PERL_SIGNALS_SAFE
, PERL_SIGNALS_UNSAFE
respectively enable safe
or unsafe signals delivery. Returns the previous value of PL_signals
.
See Signals handling.
Example:
local $SIG{ALRM} = sub { pcap_breakloop() }; alarm 60;
pcap_perl_settings(PERL_SIGNALS_UNSAFE); pcap_loop($pcap, 10, \&process_packet, ""); pcap_perl_settings(PERL_SIGNALS_SAFE);
The following functions are only available with WinPcap, the Win32 port
of the Pcap library. If a called function is not available, it will cleanly
croak()
.
"rpcap://1.2.3.4/eth0"
)
in $source
.
This function is provided in order to help the user creating the source
string according to the new format. An unique source string is used in
order to make easy for old applications to use the remote facilities.
Think about tcpdump(1), for example, which has only one way to specify
the interface on which the capture has to be started. However, GUI-based
programs can find more useful to specify hostname, port and interface name
separately. In that case, they can use this function to create the source
string before passing it to the pcap_open()
function.
Returns 0 if everything is fine, -1 if some errors occurred. The string
containing the complete source is returned in the $source
variable.
This call is the other way round of pcap_createsrcstr()
. It accepts a
null-terminated string and it returns the parameters related to the source.
This includes:
PCAP_SRC_IF_STRING
and so on);
the host on which the capture has to be started (only for remote captures);
the raw name of the source (file name, name of the remote adapter, name of
the local adapter), without the source prefix. The string returned does not
include the type of the source itself (i.e. the string returned does not
include "file://"
or "rpcap://"
or such).
The user can omit some parameters in case it is not interested in them.
Returns 0 if everything is fine, -1 if some errors occurred. The requested values (host name, network port, type of the source) are returned into the proper variables passed by reference.
The pcap_open()
replaces all the pcap_open_xxx()
functions with a single
call.
This function hides the differences between the different pcap_open_xxx()
functions so that the programmer does not have to manage different opening
function. In this way, the true open()
function is decided according
to the source type, which is included into the source string (in the form of
source prefix).
Returns a pointer to a pcap descriptor which can be used as a parameter to
the following calls (compile()
and so on) and that specifies an opened
WinPcap session. In case of problems, it returns undef
and the $err
variable keeps the error message.
$dim
specifies the size of the buffer in bytes.
The return value is 0 when the call succeeds, -1 otherwise.
If an old buffer was already created with a previous call to
setbuff()
, it is deleted and its content is discarded.
open_live()
creates a 1 MB buffer by default.
$pcap
to $mode
.
Valid values for $mode
are MODE_CAPT
(default capture mode) and
MODE_STAT
(statistical mode).
Win32::Event
object associated with the interface
$pcap
. Can be used to wait until the driver's buffer contains some
data without performing a read. See the Win32::Event manpage.
$pcap
is the interface that will be
used to send the packet, $packet
contains the data of the packet to send
(including the various protocol headers). The MAC CRC doesn't need to be
included, because it is transparently calculated and added by the network
interface driver. The return value is 0 if the packet is successfully sent,
-1 otherwise.
sendqueue_transmit()
.
$memsize
is the size, in bytes, of the queue, therefore it determines
the maximum amount of data that the queue will contain. This memory is
automatically deallocated when the queue ceases to exist.
$queue
. The packet
header %header
has the same format as that passed to the loop()
callback. $ackekt
is a buffer with the data of the packet.
The %headerr
header structure is the same used by WinPcap and libpcap to
store the packets in a file, therefore sending a capture file is
straightforward. ``Raw packet'' means that the sending application will have
to include the protocol headers, since every packet is sent to the network
as is. The CRC of the packets needs not to be calculated, because it will
be transparently added by the network interface.
$pcapt
is
the interface on which the packets will be sent, $queue
is to a
send_queue
containing the packets to send, $sync
determines if the
send operation must be synchronized: if it is non-zero, the packets are
sent respecting the timestamps, otherwise they are sent as fast as
possible.
The return value is the amount of bytes actually sent. If it is smaller than the size parameter, an error occurred during the send. The error can be caused by a driver/adapter problem or by an inconsistent/bogus send queue.
Net::Pcap
exports by default the names of several constants in order to
ease the development of programs. See EXPORTS for details about which
constants are exported.
Here are the descriptions of a few data link types. See pcap(3) for a more complete description and semantics associated with each data link.
DLT_NULL
- BSD loopback encapsulation
DLT_EN10MB
- Ethernet (10Mb, 100Mb, 1000Mb, and up)
DLT_RAW
- raw IP
DLT_IEEE802
- IEEE 802.5 Token Ring
DLT_IEEE802_11
- IEEE 802.11 wireless LAN
DLT_FRELAY
- Frame Relay
DLT_FDDI
- FDDI
DLT_SLIP
- Serial Line IP
DLT_PPP
- PPP (Point-to-point Protocol)
DLT_PPP_SERIAL
- PPP over serial with HDLC encapsulation
DLT_PPP_ETHER
- PPP over Ethernet
DLT_IP_OVER_FC
- RFC 2625 IP-over-Fibre Channel
DLT_AX25
- Amateur Radio AX.25
DLT_LINUX_IRDA
- Linux-IrDA
DLT_LTALK
- Apple LocalTalk
DLT_APPLE_IP_OVER_IEEE1394
- Apple IP-over-IEEE 1394 (a.k.a. Firewire)
arg%d not a scalar ref
arg%d not a hash ref
arg%d not a reference
The following limitations apply to this version of Net::Pcap
.
Please report any bugs or feature requests to
bug-Net-Pcap@rt.cpan.org
, or through the web interface at
http://rt.cpan.org/Dist/Display.html.
I will be notified, and then you'll automatically be notified
of progress on your bug as I make changes.
Currently known bugs:
ps_recv
field is not correctly set; see t/07-stats.t
pcap_file()
seems to always returns undef
for live
connection and causes segmentation fault for dump files;
see t/10-fileno.t
pcap_fileno()
is documented to return -1 when called
on save file, but seems to always return an actual file number.
See t/10-fileno.t
pcap_dump_file()
seems to corrupt something somewhere,
and makes scripts dump core. See t/05-dump.t
See the eg/ and t/ directories of the Net::Pcap
distribution
for examples on using this module.
the Net::Pcap::Reassemble manpage for reassembly of TCP/IP fragments.
the POE::Component::Pcap manpage for using Net::Pcap
within POE-based programs.
the Net::Packet manpage or NetPacket for decoding and creating network packets.
the Net::Pcap::Easy manpage is a module which provides an easier, more Perl-ish
API than Net::Pcap
and integrates some facilities from the Net::Netmask manpage
and NetPacket
.
pcap(3), tcpdump(8)
The source code for the pcap(3)
library is available from
http://www.tcpdump.org/
The source code and binary for the Win32 version of the pcap library, WinPcap, is available from http://www.winpcap.org/
Hacking Linux Exposed: Sniffing with Net::Pcap to stealthily managing iptables rules remotely, http://www.hackinglinuxexposed.com/articles/20030730.html
PerlMonks node about Net::Pcap, http://perlmonks.org/
Current maintainer is Sébastien Aperghis-Tramoni (SAPER) <sebastien@aperghis.net> with the help of Jean-Louis Morel (JLMOREL) <jl_morel@bribes.org> for WinPcap support.
Previous authors & maintainers:
To Paul Johnson for his module Devel::Cover
and his patience for
helping me using it with XS code, which revealed very useful for
writing more tests.
To the beta-testers: Jean-Louis Morel, Max Maischen, Philippe Bruhat, David Morel, Scott Lanning, Rafael Garcia-Suarez, Karl Y. Pradene.
Copyright (C) 2005, 2006, 2007, 2008, 2009 Sébastien Aperghis-Tramoni. All rights reserved.
Copyright (C) 2003 Marco Carnut. All rights reserved.
Copyright (C) 1999, 2000 Tim Potter. All rights reserved.
Copyright (C) 1998 Bo Adler. All rights reserved.
Copyright (C) 1997 Peter Lister. All rights reserved.
This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.
Net::Pcap - Interface to pcap LBL packet capture library |