pcap



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);

     pcap_dumper_t *
     pcap_dump_fopen(pcap_t *p, FILE *f);

     char *
     pcap_lookupdev(char *errbuf);

     uint
     pcap_lookupnet(const 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_sendpacket(pcap_t *p, void *, int);

     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);

     void
     pcap_freecode(struct bpf_program *fp);

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

     int
     pcap_next_ex(pcap_t *p, struct pcap_pkthdr **hp, const u_char **pktp);

     int
     pcap_setdirection(pcap_t *p, pcap_direction_t dir);

     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);

     int
     pcap_get_selectable_fd(pcap_t *);

     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);

     FILE *
     pcap_dump_file(pcap_dumper_t *p);

     long
     pcap_dump_ftell(pcap_dumper_t *p);

     int
     pcap_dump_flush(pcap_dumper_t *p);

     void
     pcap_dump_close(pcap_dumper_t *p);

     void
     pcap_breakloop(pcap_t *p);

     int
     pcap_findalldevs(pcap_if_t **alldevsp, char *errbuf);

     void
     pcap_freealldevs(pcap_if_t *alldevs);

     int
     pcap_getnonblock(pcap_t *p, char *errbuf);

     int
     pcap_setnonblock(pcap_t *p, int nonblock, char *errbuf);

     int
     pcap_set_datalink(pcap_t *, int dlt);

     int
     pcap_list_datalinks(pcap_t *p, int **dlts);

     pcap_t
     pcap_open_dead(int linktype, int snaplen);

     pcap_t
     pcap_fopen_offline(FILE *fp, char *errbuf);

     const char *
     pcap_lib_version(void);

     const char *
     pcap_datalink_val_to_name(int);

     const char *
     pcap_datalink_val_to_description(int);

     int
     pcap_datalink_name_to_val(const char *);

     pcap_t *
     pcap_create(const char *source, char *errbuf);

     int
     pcap_set_snaplen(pcap_t *p, int snaplen);

     int
     pcap_set_promisc(pcap_t *p, int promisc);

     int
     pcap_can_set_rfmon(pcap_t *p);

     int
     pcap_set_rfmon(pcap_t *p, int rfmon);

     int
     pcap_set_timeout(pcap_t *p, int timeout);

     int
     pcap_set_buffer_size(pcap_t *p, int buffer_size);

     int
     pcap_activate(pcap_t *p);

     const char *
     pcap_statustostr(int);


DESCRIPTION

     pcap 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.

     Note that errbuf in pcap_open_live(), pcap_open_offline(),
     pcap_findalldevs(), pcap_lookupdev(), and pcap_lookupnet() is assumed to
     be able to hold at least PCAP_ERRBUF_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
     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.  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_dump_fopen() allows the use of savefile functions on the already-
     opened stream ``f''.

     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, 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.  It returns the number of bytes written or -1 on failure.

     pcap_sendpacket() is an alternate interface for packet injection
     (provided for compatibility).  It returns 0 on success or -1 on failure.

     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_freecode() is used to free up allocated memory pointed to by a
     bpf_program struct generated by pcap_compile() when that BPF program is
     no longer needed, for example after it has been made the filter program
     for a pcap structure by a call to pcap_setfilter().

     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
     timeout to pcap_open_live() and then calling pcap_dispatch() allows the
     reception and processing of any packets that arrive when the timeout
     occurs.  A negative cnt causes pcap_loop() to loop forever (or at least
     until an error occurs).  pcap_loop() may be terminated early through an
     explicit call to pcap_breakloop().  In this case, the return value of
     pcap_loop() will be -2.

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

     pcap_next_ex() reads the next packet and returns a success/failure
     indication: a return value of 1 indicates success, 0 means that the
     timeout was exceeded on a live capture, -1 indicates that an error
     occurred whilst reading the packet and -2 is returned when there are no
     more packets to read in a savefile.

     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 stream associated with the savefile.

     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 underlying 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() and pcap_get_selectable_fd() return 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(3) isn't available.

     pcap_close() closes the files associated with p and deallocates
     resources.

     pcap_dump_file() returns the stream associated with a savefile.

     pcap_dump_ftell() returns the current file offset within a savefile.

     pcap_dump_flush() ensures that any buffered data has been written to a
     savefile.

     pcap_dump_close() closes the savefile.

     pcap_findalldevs() constructs a linked list of network devices that are
     suitable for opening with pcap_open_live().

     pcap_freealldevs() frees a list of interfaces built by
     pcap_findalldevs().

     pcap_getnonblock() returns 1 if the capture file descriptor is in non-
     blocking mode, 0 if it is in blocking mode, or -1 on error.

     pcap_setnonblock() sets or resets non-blocking mode on a capture file
     descriptor.

     pcap_set_datalink() sets the datalink type on a live capture device that
     supports multiple datalink types.

     pcap_setdirection() is used to limit the direction that packets must be
     flowing in order to be captured.

     pcap_list_datalinks() returns an array of the supported datalink types
     for an opened live capture device as a -1 terminated array.  It is the
     caller's responsibility to free this list.

     pcap_breakloop() safely breaks out of a pcap_loop().  This function sets
     an internal flag and is safe to be called from inside a signal handler.

     pcap_open_dead() is used for creating a pcap_t structure to use when
     calling the other functions in libpcap.  It is typically used when just
     using libpcap for compiling BPF code.

     pcap_fopen_offline() may be used to read dumped data from an existing
     open stream ``fp''.

     pcap_lib_version() returns a string describing the version of libpcap.
     pcap_datalink_val_to_name() and pcap_datalink_val_to_description() look
     up the name or description of a datalink type by number.  These functions
     return NULL if the specified datalink type is not known.
     pcap_datalink_name_to_val() finds the datalink number for a given
     datalink name.  Returns -1 if the name is not known.

     pcap_create() is used to create a packet capture handle to look at
     packets on the network.  The returned handle must be activated with
     pcap_activate() before packets can be captured with it; options for the
     capture, such as promiscuous mode, can be set on the handle before
     activating it.

     pcap_set_snaplen() sets the snapshot length to be used on a capture
     handle when the handle is activated to snaplen.

     pcap_set_promisc() sets whether promiscuous mode should be set on a
     capture handle when the handle is activated.  If promisc is non-zero,
     promiscuous mode will be set, otherwise it will not be set.

     pcap_can_set_rfmon() checks whether monitor mode could be set on a
     capture handle when the handle is activated.

     pcap_set_rfmon() sets whether monitor mode should be set on a capture
     handle when the handle is activated.  If rfmon is non-zero, monitor mode
     will be set, otherwise it will not be set.

     pcap_set_timeout() sets the read timeout that will be used on a capture
     handle when the handle is activated to to_ms, which is in units of
     milliseconds.

     pcap_set_buffer_size() sets the buffer size that will be used on a
     capture handle when the handle is activated to buffer_size, which is in
     units of bytes.

     pcap_activate() is used to activate a packet capture handle to look at
     packets on the network, with the options that were set on the handle
     being in effect.

     pcap_statustostr() converts a PCAP_ERROR_ or PCAP_WARNING_ value returned
     by a libpcap routine to an error string.


SEE ALSO

     pcap-filter(3), tcpdump(8)


AUTHORS

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

OpenBSD 5.4                      June 25, 2013                     OpenBSD 5.4

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