PCAP(3)			   BSD 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);

     int
     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 *);

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_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 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 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 (provid-
     ed 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 er-
     ror 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 indi-
     cation: 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 pack-
     ets 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 sup-
     port 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 cal-
     ling 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 da-
     talink name. Returns -1 if the name is not known.

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.

MirOS BSD #10-current		 July 5, 1999				     5

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