NAME
pcap_open_live,
pcap_open_offline,
pcap_dump_open,
pcap_dump_fopen,
pcap_lookupdev,
pcap_lookupnet,
pcap_dispatch, pcap_loop,
pcap_dump, pcap_inject,
pcap_sendpacket,
pcap_compile,
pcap_setfilter,
pcap_freecode, pcap_next,
pcap_next_ex,
pcap_setdirection,
pcap_datalink,
pcap_snapshot,
pcap_is_swapped,
pcap_major_version,
pcap_minor_version,
pcap_stats, pcap_file,
pcap_fileno,
pcap_get_selectable_fd,
pcap_perror, pcap_geterr,
pcap_strerror, pcap_close,
pcap_dump_file,
pcap_dump_ftell,
pcap_dump_flush,
pcap_dump_close,
pcap_breakloop,
pcap_findalldevs,
pcap_freealldevs,
pcap_getnonblock,
pcap_setnonblock,
pcap_set_datalink,
pcap_list_datalinks,
pcap_free_datalinks,
pcap_open_dead,
pcap_fopen_offline,
pcap_lib_version,
pcap_datalink_val_to_name,
pcap_datalink_val_to_description,
pcap_datalink_name_to_val,
pcap_create,
pcap_set_snaplen,
pcap_set_promisc,
pcap_can_set_rfmon,
pcap_set_rfmon,
pcap_set_timeout,
pcap_set_buffer_size,
pcap_set_immediate_mode,
pcap_activate,
pcap_statustostr,
pcap_offline_filter —
Packet Capture library
SYNOPSIS
#include
<pcap.h>
pcap_t *
pcap_open_live(const
char *source, 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);
int
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, const struct
pcap_pkthdr *h, const
u_char *sp);
int
pcap_inject(pcap_t
*p, const void
*buf, size_t
len);
int
pcap_sendpacket(pcap_t
*p, const u_char
*buf, int
size);
int
pcap_compile(pcap_t
*p, struct bpf_program
*program, const char
*buf, int optimize,
bpf_u_int32 netmask);
int
pcap_setfilter(pcap_t
*p, struct bpf_program
*fp);
void
pcap_freecode(struct
bpf_program *program);
u_char *
pcap_next(pcap_t
*p, struct pcap_pkthdr
*h);
int
pcap_next_ex(pcap_t
*p, struct pcap_pkthdr
**pkt_header, const
u_char **pkt_data);
int
pcap_setdirection(pcap_t
*p, pcap_direction_t
d);
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
*p);
void
pcap_perror(pcap_t
*p, const char
*prefix);
char *
pcap_geterr(pcap_t
*p);
const char *
pcap_strerror(int
errnum);
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
*p, int dlt);
int
pcap_list_datalinks(pcap_t
*p, int
**dlt_buffer);
void
pcap_free_datalinks(int
*dlt_list);
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
dlt);
const char *
pcap_datalink_val_to_description(int
dlt);
int
pcap_datalink_name_to_val(const
char *name);
pcap_t *
pcap_create(const
char *device, 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_ms);
int
pcap_set_buffer_size(pcap_t
*p, int
buffer_size);
int
pcap_set_immediate_mode(pcap_t
*p, int
immediate);
int
pcap_activate(pcap_t
*p);
const char *
pcap_statustostr(int
errnum);
int
pcap_offline_filter(const
struct bpf_program *fp,
const struct pcap_pkthdr
*h, const u_char
*pkt);
DESCRIPTION
pcap_open_live 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(),
pcap_lookupnet(),
pcap_getnonblock(),
pcap_setnonblock(),
pcap_fopen_offline(), and
pcap_create() 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. source is a string that specifies the network
device to open. snaplen specifies the maximum number
of bytes to capture from one packet. 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
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_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 precedes 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 a save file previously opened using
pcap_dump_open() or
pcap_dump_fopen(). Note that the
user argument contains the handle to the save file and
should be of type pcap_dumper_t *. This makes
pcap_dump() a suitable callback function for use as
an argument to 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 buf 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_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_loop() 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. The direction is either PCAP_D_INOUT,
PCAP_D_IN or PCAP_D_OUT.
Direction is only relevant to live captures. When reading from a dump file,
pcap_setdirection() has no effect.
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 with
pcap_free_datalinks(),
which frees the list of link-layer header types pointed to by
dlt_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_set_immediate_mode()
sets whether immediate mode should be set on a capture handle when the
handle is activated. If immediate is non-zero,
immediate mode will be set, otherwise it will not be set.
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.
pcap_offline_filter()
checks whether a filter matches a packet.
SEE ALSO
AUTHORS
Van Jacobson, Craig Leres, and Steven McCanne, all of the Lawrence Berkeley National Laboratory, University of California, Berkeley, CA.