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NAME    [Toc]    [Back]

     pcap - packet capture library

LIBRARY    [Toc]    [Back]

     library ``libpcap''

SYNOPSIS    [Toc]    [Back]

     #include <pcap.h>

     pcap_t *
     pcap_open_live(char *device, int snaplen, int promisc, int to_ms,
             char *ebuf);

     pcap_t *
     pcap_open_offline(char *fname, char *ebuf);

     pcap_dumper_t *
     pcap_dump_open(pcap_t *p, char *fname);

     char errbuf[PCAP_ERRBUF_SIZE];

     char *
     pcap_lookupdev(char *errbuf);

     pcap_lookupnet(char *device, bpf_u_int32 *netp, bpf_u_int32 *maskp,
             char *errbuf);

     pcap_dispatch(pcap_t *p, int cnt, pcap_handler callback, u_char *user);

     pcap_loop(pcap_t *p, int cnt, pcap_handler callback, u_char *user);

     pcap_dump(u_char *user, struct pcap_pkthdr *h, u_char *sp);

     pcap_compile(pcap_t *p, struct bpf_program *fp, char *str, int optimize,
             bpf_u_int32 netmask);

     pcap_compile_nopcap(int snaplen, int linktype, struct bpf_program *fp,
             char *str, int optimize, bpf_uint32 netmask, char *errbuf);

     pcap_setfilter(pcap_t *p, struct bpf_program *fp);

     const u_char *
     pcap_next(pcap_t *p, struct pcap_pkthdr *h);

     pcap_datalink(pcap_t *p);

     pcap_snapshot(pcap_t *p);

     pcap_is_swapped(pcap_t *p);

     pcap_major_version(pcap_t *p);

     pcap_minor_version(pcap_t *p);

     pcap_stats(pcap_t *p, struct pcap_stat *ps);

     FILE *
     pcap_file(pcap_t *p);

     pcap_fileno(pcap_t *p);

     pcap_perror(pcap_t *p, char *prefix);

     char *
     pcap_geterr(pcap_t *p);

     char *
     pcap_strerror(int error);

     pcap_close(pcap_t *p);

     pcap_dump_close(pcap_dumper_t *p);

DESCRIPTION    [Toc]    [Back]

     The pcap library provides a high level interface to packet capture systems.
  All packets on the network, even those destined for other hosts,
     are accessible through this mechanism.

ROUTINES    [Toc]    [Back]

     pcap_open_live() is used to obtain a packet capture descriptor to look at
     packets on the network.  device is a string that specifies the network
     device to open.  snaplen specifies the maximum number of bytes to capture.
  promisc specifies if the interface is to be put into promiscuous
     mode.  (Note that even if this parameter is false, the interface could
     well be in promiscuous mode for some other reason.)  to_ms specifies the
     read timeout in milliseconds.  ebuf is used to return error text and is
     only set when pcap_open_live() fails and returns NULL.

     pcap_open_offline() is called to open a ``savefile'' for reading.  fname
     specifies the name of the file to open.  The file has the same format as
     those used by tcpdump(8).  The name ``-'' is a synonym for stdin.  ebuf
     is used to return error text and is only set when pcap_open_offline()
     fails and returns NULL.

     pcap_dump_open() is called to open a ``savefile'' for writing.  The name
     ``-'' is a synonym for stdout.  NULL is returned on failure.  p is a pcap
     struct as returned by pcap_open_offline() or pcap_open_live().  fname
     specifies the name of the file to open.  If NULL is returned,
     pcap_geterr() can be used to get the error text.

     pcap_lookupdev() returns a pointer to a network device suitable for use
     with pcap_open_live() and pcap_lookupnet().  If there is an error, NULL
     is returned and errbuf is filled in with an appropriate error message.

     pcap_lookupnet() is used to determine the network number and mask associated
 with the network device device.  Both netp and maskp are bpf_u_int32
     pointers.  A return of -1 indicates an error in which case errbuf is
     filled in with an appropriate error message.

     pcap_dispatch() is used to collect and process packets.  cnt specifies
     the maximum number of packets to process before returning.  A cnt of -1
     processes all the packets received in one buffer.  A cnt of 0 processes
     all packets until an error occurs (or EOF is reached).  callback specifies
 a routine to be called with three arguments: a u_char pointer which
     is passed in from pcap_dispatch(), a pointer to the pcap_pkthdr struct
     (which precede the actual network headers and data), and a u_char pointer
     to the packet data.  The number of packets read is returned.  Zero is
     returned when EOF is reached in a ``savefile''.  A return of -1 indicates
     an error in which case pcap_perror() or pcap_geterr() may be used to display
 the error text.

     pcap_dump() outputs a packet to the ``savefile'' opened with
     pcap_dump_open().  Note that its calling arguments are suitable for use
     with pcap_dispatch().

     pcap_compile() is used to compile the string str into a filter program.
     program is a pointer to a bpf_program struct and is filled in by
     pcap_compile().  optimize controls whether optimization on the resulting
     code is performed.  netmask specifies the netmask of the local net.

     pcap_compile_nopcap() is similar to pcap_compile() except that instead of
     passing a pcap descriptor, one passes the snaplen, linktype, and error
     buffer (which must be PCAP_ERRBUF_SIZE in length) explicitly.  It is
     intended to be used for compiling filters for direct bpf usage, without
     necessarily having called pcap_open().

     pcap_setfilter() is used to specify a filter program.  fp is a pointer to
     an array of bpf_program struct, usually the result of a call to
     pcap_compile().  -1 is returned on failure; 0 is returned on success.

     pcap_loop() is similar to pcap_dispatch() except it keeps reading packets
     until cnt packets are processed or an error occurs.  A negative cnt
     causes pcap_loop() to loop forever (or at least until an error occurs).

     pcap_next() returns a u_char pointer to the next packet.

     pcap_datalink() returns the link layer type, e.g.  DLT_EN10MB.

     pcap_snapshot() returns the snapshot length specified when
     pcap_open_live() was called.

     pcap_is_swapped() returns true if the current ``savefile'' uses a different
 byte order than the current system.

     pcap_major_version() returns the major number of the version of the pcap
     used to write the savefile.

     pcap_minor_version() returns the minor number of the version of the pcap
     used to write the savefile.

     pcap_file() returns the standard I/O stream of the ``savefile'', if a
     ``savefile'' was opened with pcap_open_offline(), or NULL, if a network
     device was opened with pcap_open_live().

     pcap_stats() returns 0 and fills in a pcap_stat struct.  The values represent
 packet statistics from the start of the run to the time of the
     call.  If there is an error or the under lying packet capture doesn't
     support packet statistics, -1 is returned and the error text can be
     obtained with pcap_perror() or pcap_geterr().

     pcap_fileno() returns the file descriptor number from which captured
     packets are read if a network device was opened with pcap_open_live(), or
     -1, if a ``savefile'' was opened with pcap_open_offline().

     pcap_perror() prints the text of the last pcap library error on stderr,
     prefixed by prefix.

     pcap_geterr() returns the error text pertaining to the last pcap library

     pcap_strerror() is provided in case strerror(3) isn't available.

     pcap_close() closes the files associated with p and deallocates

     pcap_dump_close() closes the ``savefile''.

SEE ALSO    [Toc]    [Back]


AUTHORS    [Toc]    [Back]

     The original authors are:

     Van Jacobson, Craig Leres and Steven McCanne, all of the Lawrence Berkeley
 National Laboratory, University of California, Berkeley, CA.

BSD                              June 24, 1998                             BSD
[ Back ]
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