pcap - Packet Capture library
pcap_open_live(char *device, int snaplen, int promisc, int
pcap_open_offline(char *fname, char *errbuf);
pcap_dump_open(pcap_t *p, char *fname);
pcap_lookupnet(char *device, bpf_u_int32 *netp, bpf_u_int32
pcap_dispatch(pcap_t *p, int cnt, pcap_handler callback,
pcap_loop(pcap_t *p, int cnt, pcap_handler callback, u_char
pcap_dump(u_char *user, struct pcap_pkthdr *h, u_char *sp);
pcap_inject(pcap_t *p, void *, size_t);
pcap_compile(pcap_t *p, struct bpf_program *fp, char *str,
pcap_setfilter(pcap_t *p, struct bpf_program *fp);
pcap_freecode(struct bpf_program *fp);
pcap_next(pcap_t *p, struct pcap_pkthdr *h);
pcap_stats(pcap_t *p, struct pcap_stat *ps);
pcap_perror(pcap_t *p, char *prefix);
pcap provides a high level interface to packet capture systems. All
packets on the network, even those destined for other hosts,
through this mechanism.
Note: errbuf in pcap_open_live(), pcap_open_offline(),
and pcap_lookupnet() is assumed to be able to hold at least
pcap_open_live() is used to obtain a packet capture descriptor to look at
packets on the network. device is a string that specifies
device to open. snaplen specifies the maximum number of
bytes to capture.
promisc specifies if the interface is to be put into
mode. (Note that even if this parameter is false, the interface could
well be in promiscuous mode for some other reason.) to_ms
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
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
is used to return error text and is only set when
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
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
is returned and errbuf is filled in with an appropriate error message.
pcap_lookupnet() is used to determine the network number and
with the network device device. Both netp and maskp
pointers. A return of -1 indicates an error in which case
filled in with an appropriate error message.
pcap_dispatch() is used to collect and process packets. cnt
the maximum number of packets to process before returning.
A cnt of -1
processes all the packets received in one buffer. A cnt of
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
pcap_pkthdr struct (which precede the actual network headers
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
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
pcap_inject() uses write(2) to inject a raw packet through
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
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
pcap_compile(). -1 is returned on failure; 0 is returned on
pcap_freecode() is used to free up allocated memory pointed
to by a
bpf_program struct generated by pcap_compile() when that BPF
no longer needed, for example after it has been made the
for a pcap structure by a call to pcap_setfilter().
pcap_loop() is similar to pcap_dispatch() except it keeps
until cnt packets are processed or an error occurs. It does
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
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.,
pcap_snapshot() returns the snapshot length specified when
pcap_open_live() was called.
pcap_is_swapped() returns true if the current savefile uses
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
packet statistics from the start of the run to the
time of the
call. If there is an error or the underlying packet capture
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
pcap_perror() prints the text of the last pcap library error
prefixed by prefix.
pcap_geterr() returns the error text pertaining to the last
pcap_strerror() is provided in case strerror(3) isn't available.
pcap_close() closes the files associated with p and deallocates resources.
pcap_dump_close() closes the savefile.
Van Jacobson, Craig Leres and Steven McCanne, all of the
National Laboratory, University of California, Berkeley,
Please send bug reports to email@example.com.
OpenBSD 3.6 July 5, 1999
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