NAME¶

VERSION¶

SYNOPSIS¶

    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 ...
    }

DESCRIPTION¶

  "a system-independent interface for user-level packet capture.
  libpcap provides a portable framework for low-level network
  monitoring.  Applications include network statistics collection,
  security monitoring, network debugging, etc."

EXPORTS¶

•

":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" exports the function names with the same names as the C library, so you can write "pcap_lookupdev()" instead of "Net::Pcap::lookupdev()" for example. This should also ease porting C programs to Perl.

 

It also exports 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.

FUNCTIONS¶

Lookup functions¶

pcap_lookupdev(\$err)

Returns the name of a network device that can be used with "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_findalldevs(\%devinfo, \$err)

Returns a list of all network device names that can be used with "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"
    }
    

pcap_lookupnet($dev, \$net, \$mask, \$err)

Determine the network number and netmask for the device specified in $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.

Packet capture functions¶

pcap_open_live($dev, $snaplen, $promisc , $to_ms, \$err)

Returns a packet capture descriptor for looking at packets on the network. The $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";
    

pcap_open_dead($linktype, $snaplen)

Creates and returns a new packet descriptor to use when calling the other functions in "libpcap". It is typically used when just using "libpcap" for compiling BPF code.

 

Example

 

    $pcap = pcap_open_dead(0, 1024);
    

pcap_open_offline($filename, \$err)

Return a packet capture descriptor to read from a previously created "savefile". The returned descriptor is undefined if there was an error and in this case the $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";
    

pcap_loop($pcap, $count, \&callback, $user_data)

Read $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.

    pcap_loop($pcap, 10, \&process_packet, "user data");
    sub process_packet {
        my($user_data, $header, $packet) = @_;
        # ...
    }

pcap_breakloop($pcap)

Sets a flag that will force "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_close($pcap)

Close the packet capture device associated with the descriptor $pcap.

pcap_dispatch($pcap, $count, \&callback, $user_data)

Collect $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_next($pcap, \%header)

Return the next available packet on the interface associated with packet descriptor $pcap. Into the %header hash is stored the received packet header. If not packet is available, the return value and header is undefined.

pcap_next_ex($pcap, \%header, \$packet)

Reads the next available packet on the interface associated with packet descriptor $pcap, stores its header in "\%header" and its data in "\$packet" and returns a success/failure indication:

pcap_compile($pcap, \$filter, $filter_str, $optimize, $netmask)

Compile the filter string contained in $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.

pcap_compile_nopcap($snaplen, $linktype, \$filter, $filter_str, $optimize, $netmask)

Similar to "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.

pcap_setfilter($pcap, $filter)

Associate the compiled filter stored in $filter with the packet capture descriptor $pcap.

pcap_freecode($filter)

Used to free the allocated memory used by a compiled filter, as created by "pcap_compile()".

pcap_setnonblock($pcap, $mode, \$err)

Set the non-blocking mode of a live capture descriptor, depending on the value of $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_getnonblock($pcap, \$err)

Returns the non-blocking state of the capture descriptor $pcap. Always returns 0 on savefiles. If there is an error, it returns -1 and sets $err.

Savefile commands¶

pcap_dump_open($pcap, $filename)

Open a savefile for writing and return a descriptor for doing so. If $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.

pcap_dump($dumper, \%header, $packet)

Dump the packet described by header %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_file($dumper)

Returns the filehandle associated with a savefile opened with "pcap_dump_open()".

pcap_dump_flush($dumper)

Flushes the output buffer to the corresponding save file, so that any packets written with "pcap_dump()" but not yet written to the save file will be written. Returns -1 on error, 0 on success.

pcap_dump_close($dumper)

Close the savefile associated with the descriptor $dumper.

Status functions¶

pcap_datalink($pcap)

Returns the link layer type associated with the given pcap descriptor.

 

Example

 

    $linktype = pcap_datalink($pcap);
    

pcap_set_datalink($pcap, $linktype)

Sets the data link type of the given pcap descriptor to the type specified by $linktype. Returns -1 on failure.

pcap_datalink_name_to_val($name)

Translates a data link type name, which is a "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
    

pcap_datalink_val_to_name($linktype)

Translates a data link type value to the corresponding data link type name.

 

Example

 

    $name = pcap_datalink_val_to_name(DLT_LTALK);  # returns 'LTALK'
    

pcap_datalink_val_to_description($linktype)

Translates a data link type value to a short description of that data link type.

 

Example

 

    $descr = pcap_datalink_val_to_description(DLT_LTALK);  # returns 'Localtalk'
    

pcap_snapshot($pcap)

Returns the snapshot length (snaplen) specified in the call to "pcap_open_live()".

pcap_is_swapped($pcap)

This function returns true if the endianness of the currently open savefile is different from the endianness of the machine.

pcap_major_version($pcap)

Return the major version number of the pcap library used to write the currently open savefile.

pcap_minor_version($pcap)

Return the minor version of the pcap library used to write the currently open savefile.

pcap_stats($pcap, \%stats)

Returns a hash containing information about the status of packet capture device $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.

pcap_file($pcap)

Returns the filehandle associated with a savefile opened with "pcap_open_offline()" or "undef" if the device was opened with "pcap_open_live()".

pcap_fileno($pcap)

Returns the file number of the network device opened with "pcap_open_live()".

pcap_get_selectable_fd($pcap)

Returns, on Unix, a file descriptor number for a file descriptor on which one can do a "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.

Error handling¶

pcap_geterr($pcap)

Returns an error message for the last error associated with the packet capture device $pcap.

pcap_strerror($errno)

Returns a string describing error number $errno.

pcap_perror($pcap, $prefix)

Prints the text of the last error associated with descriptor $pcap on standard error, prefixed by $prefix.

Information¶

pcap_lib_version()

Returns the name and version of the "pcap" library the module was linked against.

WinPcap specific functions¶

pcap_createsrcstr(\$source, $type, $host, $port, $name, \$err)

Accepts a set of strings (host name, port, ...), and stores the complete source string according to the new format (e.g. "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.

pcap_parsesrcstr($source, \$type, \$host, \$port, \$name, \$err)

Parse the source string and stores the pieces in which the source can be split in the corresponding variables.

 

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_open($source, $snaplen, $flags , $read_timeout, \$auth, \$err)

Open a generic source in order to capture / send (WinPcap only) traffic.

 

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.

pcap_setbuff($pcap, $dim)

Sets the size of the kernel buffer associated with an adapter. $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_setmode($pcap, $mode)

Sets the working mode of the interface $pcap to $mode. Valid values for $mode are "MODE_CAPT" (default capture mode) and "MODE_STAT" (statistical mode).

pcap_setmintocopy($pcap_t, $size)

Changes the minimum amount of data in the kernel buffer that causes a read from the application to return (unless the timeout expires).

pcap_getevent($pcap)

Returns the "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 Win32::Event.

pcap_sendpacket($pcap, $packet)

Send a raw packet to the network. $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.

pcap_sendqueue_alloc($memsize)

This function allocates and returns a send queue, i.e. a buffer containing a set of raw packets that will be transmitted on the network with "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.

pcap_sendqueue_queue($queue, \%header, $packet )

Adds a packet at the end of the send queue pointed by $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.

pcap_sendqueue_transmit($pcap, $queue, $sync)

This function transmits the content of a queue to the wire. $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.

CONSTANTS¶

•

"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)

DIAGNOSTICS¶

"arg%d not a scalar ref"

"arg%d not a hash ref"

"arg%d not a reference"

(F) These errors occur if you forgot to give a reference to a function which expect one or more of its arguments to be references.

LIMITATIONS¶

•

At present, only one callback function and user data scalar can be current at any time as they are both stored in global variables.

BUGS¶

•

the "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

EXAMPLES¶

SEE ALSO¶

Perl Modules¶

Base Libraries¶

Articles¶

AUTHORS¶

•

Marco Carnut (KCARNUT) <kiko@tempest.com.br>

•

Tim Potter (TIMPOTTER) <tpot@frungy.org>

•

Bo Adler (BOADLER) <thumper@alumni.caltech.edu>

•

Peter Lister (PLISTER) <p.lister@cranfield.ac.uk>

ACKNOWLEDGEMENTS¶

COPYRIGHT & LICENSE¶