freebsd/lib/libpcap/pcap.3

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.TH PCAP 3  "14 Jun 1994"
.SH NAME
pcap \- Packet Capture library
.SH SYNOPSIS
.nf
.ft B
#include <pcap.h>
.ft
.LP
.ft B
pcap_t *pcap_open_live(char *device, int snaplen,
.ti +8
int promisc, int to_ms, char *ebuf)
pcap_t *pcap_open_offline(char *fname, char *ebuf)
pcap_dumper_t *pcap_dump_open(pcap_t *p, char *fname)
.ft
.LP
.ft B
char errbuf[PCAP_ERRBUF_SIZE];
char *pcap_lookupdev(char *errbuf)
int pcap_lookupnet(char *device, u_long *netp,
.ti +8
u_long *maskp, char *errbuf)
.ft
.LP
.ft B
int pcap_dispatch(pcap_t *p, int cnt,
.ti +8
pcap_handler callback, u_char *user)
int pcap_loop(pcap_t *p, int cnt,
.ti +8
pcap_handler callback, u_char *user)
void pcap_dump(u_char *user, struct pcap_pkthdr *h,
.ti +8
u_char *sp)
.ft
.LP
.ft B
int pcap_immediate(pcap_t *p)
.ft
.LP
.ft B
int pcap_compile(pcap_t *p, struct bpf_program *fp,
.ti +8
char *str, int optimize, u_long netmask)
int pcap_setfilter(pcap_t *p, struct bpf_program *fp)
.ft
.LP
.ft B
u_char *pcap_next(pcap_t *p, struct pcap_pkthdr *h)
.ft
.LP
.ft B
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)
.ft
.LP
.ft B
void pcap_close(pcap_t *p)
void pcap_dump_close(pcap_dumper_t *p)
.ft
.fi
.SH DESCRIPTION
The Packet Capture library
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.
.PP
.SH ROUTINES
.B pcap_open_live()
is used to obtain a packet capture descriptor to look
at packets on the network.
.I device
is a string that specifies the network device to open.
.I snaplen
specifies the maximum number of bytes to capture.
.I to_ms
specifies the read timeout in milliseconds.
.I ebuf
is used to return error text and is only set when
.B pcap_open_live()
fails and returns
.BR NULL .
.PP
.B pcap_open_offline()
is called to open a ``savefile'' for reading.
.I fname
specifies the name of the file to open. The file has
the same format as those used by
.B tcpdump(1)
and
.BR tcpslice(1) .
The name "-" in a synonym for
.BR stdin .
.I ebuf
is used to return error text and is only set when
.B pcap_open_offline()
fails and returns
.BR NULL .
.PP
.B pcap_dump_open()
is called to open a ``savefile'' for writing. The name "-" in a synonym
for
.BR stdin .
.B NULL
is returned on failure.
.I p
is a
.I pcap
struct as returned by
.B pcap_open_offline()
or
.BR pcap_open_live() .
.I fname
specifies the name of the file to open.
If
.B NULL
is returned,
.B pcap_geterr()
can be used to get the error text.
.PP
.B pcap_lookupdev()
returns a pointer to a network device suitable for use with
.B pcap_open_live()
and
.BR pcap_lookupnet() .
If there is an error,
.B NULL
is returned and
.I errbuf
is filled in with with an appropriate error message.
.PP
.B pcap_lookupnet()
is used to determine the network number and mask
associated with the network device
.BR device .
Both
.I netp
and
.I maskp
are
.I u_long
pointers.
A return of -1 indicates an error in which case
.I errbuf
is filled in with with an appropriate error message.
.PP
.B pcap_dispatch()
is used to collect and process packets.
.I cnt
specifies the maximum number of packets to process before returning. A
.I cnt
of -1 processes all the packets received in one buffer. A
.I cnt
of 0 processes all packets until an error occurs (or
.B EOF
is reached).
.I callback
specifies a routine to be called with three arguments:
a
.I u_char
pointer which is passed in from
.BR pcap_dispatch() ,
a pointer to the
.I pcap_pkthdr
struct (which precede the actual network headers and data),
and a length. The number of packets read is returned.
Zero is returned when
.B EOF
is reached in a ``savefile.'' A return of -1 indicates
an error in which case
.B pcap_perror()
or
.BR pcap_geterr()
may be used to display the error text.
.PP
.B pcap_dump()
outputs a packet to the ``savefile'' opened with
.BR pcap_dump_open() .
Note that its calling arguments are suitable for use with
.BR pcap_dispatch() .
.ft B
(??? this guy is kind of weird.)
.ft
.PP
.B pcap_immediate()
sets ``immediate'' mode.
If this isn't supported by the under lying packet capture, -1 is
returned and the error text can be obtained with
.B pcap_perror()
or
.BR pcap_geterr() .
.PP
.B pcap_compile()
is used to compile the string
.I str
into a filter program.
.I program
is a pointer to a
.I bpf_program
struct and is filled in by
.BR pcap_compile() .
.I optimize
controls whether optimization on the resulting code is performed.
.I netmask
specifies the netmask of the local net.
.PP
.B pcap_setfilter()
is used to specify the a filter program.
.I fp
is a pointer to an array of
.I bpf_program
struct, usually the result of a call to
.BR pcap_compile() .
.PP
.B pcap_loop()
is similar to
.B pcap_dispatch()
except it keeps reading packets until
.I cnt
packets are processed or an error occurs.
A negative
.I cnt
causes
.B pcap_loop()
to loop forever (or at least until an error occurs).
.PP
.B pcap_next()
returns a
.I u_char
pointer to the next packet.
.PP
.B pcap_datalink()
returns the link layer type, e.g.
.BR DLT_EN10MB .
.PP
.B pcap_snapshot()
returns the snapshot length specified when
.B pcap_open_live
was called.
.PP
.B pcap_is_swapped()
returns true if the current ``savefile'' uses a different byte order
than the current system.
.PP
.B pcap_major_version()
returns the major number of the version of the pcap used to write the
savefile.
.PP
.B pcap_minor_version()
returns the major number of the version of the pcap used to write the
savefile.
.PP
.B pcap_file()
returns the name of the ``savefile.''
.PP
.B int pcap_stats()
returns 0 and fills in a
.B pcap_stat
struct with packet statistics. 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
.B pcap_perror()
or
.BR pcap_geterr() .
.PP
.B pcap_fileno()
returns the file descriptor number of the ``savefile.''
.PP
.B pcap_perror()
prints the text of the last pcap library error on
.BR stderr ,
prefixed by
.IR prefix .
.PP
.B pcap_geterr()
returns the error text pertaining to the last pcap library error.
.PP
.B pcap_strerror()
is provided in case
.BR strerror (1)
isn't available.
.PP
.B pcap_close()
closes the files associated with
.I p
and deallocates resources.
.PP
.B pcap_dump_close()
closes the ``savefile.''
.PP
.SH SEE ALSO
tcpdump(1), tcpslice(1)
.SH BUGS
.SH HISTORY