PCAP(3)                   OpenBSD Programmer's Manual                  PCAP(3)

NAME
     pcap - Packet Capture library



SYNOPSIS
     #include <pcap.h>

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

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

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

     char *
     pcap_lookupdev(char *errbuf);

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

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

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

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

     int
     pcap_inject(pcap_t *p, void *, size_t);

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

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

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

     int
     pcap_datalink(pcap_t *p);

     int
     pcap_snapshot(pcap_t *p);

     int
     pcap_is_swapped(pcap_t *p);

     int
     pcap_major_version(pcap_t *p);

     int
     pcap_minor_version(pcap_t *p);

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

     FILE *
     pcap_file(pcap_t *p);

     int
     pcap_fileno(pcap_t *p);

     void
     pcap_perror(pcap_t *p, char *prefix);

     char *
     pcap_geterr(pcap_t *p);

     char *
     pcap_strerror(int error);

     void
     pcap_close(pcap_t *p);

     void
     pcap_dump_close(pcap_dumper_t *p);

DESCRIPTION
     pcap provides a high level interface to packet capture systems. All pack-
     ets on the network, even those destined for other hosts, are accessible
     through this mechanism.

ROUTINES
     Note: errbuf in pcap_open_live(), pcap_open_offline(), pcap_lookupdev(),
     and pcap_lookupnet() is assumed to be able to hold at least
     PCAP_ERRBUFF_SIZE chars.

     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 cap-
     ture.  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.  errbuf 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. errbuf 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 stdin. 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 associ-
     ated 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 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, EOF is reached, or the read times out
     (when doing live reads and a non-zero read timeout is specified).
     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_inject() uses write(2) to inject a raw packet through the network
     interface.

     pcap_compile() is used to compile the string str into a filter program.
     fp 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_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.  It does not return
     when live read timeouts occur.  Rather, specifying a non-zero read time-
     out to pcap_open_live() and then calling pcap_dispatch() allows the re-
     ception and processing of any packets that arrive when the timeout oc-
     curs.  A negative cnt causes pcap_loop() to loop forever (or at least un-
     til 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 name of the savefile.

     pcap_stats() returns 0 and fills in a pcap_stat struct. The values repre-
     sent 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 of the savefile.

     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
     error.

     pcap_strerror() is provided in case strerror(1) isn't available.

     pcap_close() closes the files associated with p and deallocates re-
     sources.

     pcap_dump_close() closes the savefile.

SEE ALSO
     tcpdump(8)

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

BUGS
     Please send bug reports to libpcap@ee.lbl.gov.

OpenBSD 2.6                      July 5, 1999                                4