path: root/lib/libpcap/pcap.3

.\"	$NetBSD: pcap.3,v 1.2.6.1 1996/06/05 18:04:43 cgd Exp $
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.Dd June 4, 1999
.Os
.Dt PCAP 3
.Sh NAME
.Nm pcap
.Nd Packet Capture library
.Sh SYNOPSIS
.Fd #include <pcap.h>
.Ft "pcap_t *"
.Fn pcap_open_live "char *device" "int snaplen" "int promisc" "int to_ms" "char *errbuf"
.Ft "pcap_t *"
.Fn pcap_open_offline "char *fname" "char *errbuf"
.Ft "pcap_dumper_t *"
.Fn pcap_dump_open "pcap_t *p" "char *fname"
.Ft "char *"
.Fn pcap_lookupdev "char *errbuf"
.Ft uint
.Fn pcap_lookupnet "char *device" "u_int32_t *netp" "u_int32_t *maskp" "char *errbuf"
.Ft int
.Fn pcap_dispatch "pcap_t *p" "int cnt" "pcap_handler callback" "u_char *user"
.Ft int
.Fn pcap_loop "pcap_t *p" "int cnt" "pcap_handler callback" "u_char *user"
.Ft void
.Fn pcap_dump "u_char *user" "struct pcap_pkthdr *h" "u_char *sp"
.Ft int
.Fn pcap_inject "pcap_t *p" "void *, size_t"
.Ft int
.Fn pcap_immediate "pcap_t *p"
.Ft int
.Fn pcap_compile "pcap_t *p" "struct bpf_program *fp" "char *str" "int optimize" "u_int32_t netmask"
.Ft int
.Fn pcap_setfilter "pcap_t *p" "struct bpf_program *fp"
.Ft "u_char *"
.Fn pcap_next "pcap_t *p" "struct pcap_pkthdr *h"
.Ft int
.Fn pcap_datalink "pcap_t *p"
.Ft int
.Fn pcap_snapshot "pcap_t *p"
.Ft int
.Fn pcap_is_swapped "pcap_t *p"
.Ft int
.Fn pcap_major_version "pcap_t *p"
.Ft int
.Fn pcap_minor_version "pcap_t *p"
.Ft int
.Fn pcap_stats "pcap_t *p" "struct pcap_stat *ps"
.Ft "FILE *"
.Fn pcap_file "pcap_t *p"
.Ft int
.Fn pcap_fileno "pcap_t *p"
.Ft void
.Fn pcap_perror "pcap_t *p" "char *prefix"
.Ft "char *"
.Fn pcap_geterr "pcap_t *p"
.Ft "char *"
.Fn pcap_strerror "int error"
.Ft void
.Fn pcap_close "pcap_t *p"
.Ft void
.Fn pcap_dump_close "pcap_dumper_t *p"
.Sh DESCRIPTION
.Nm
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.
.Sh ROUTINES
.Sy Note:
.Fa errbuf
in
.Fn pcap_open_live ,
.Fn pcap_open_offline ,
.Fn pcap_lookupdev ,
and
.Fn pcap_lookupnet
is assumed to be able to hold at least 
.Dv PCAP_ERRBUFF_SIZE
chars.
.Pp
.Fn pcap_open_live
is used to obtain a packet capture descriptor to look
at packets on the network.
.Fa device
is a string that specifies the network device to open.
.Fa snaplen
specifies the maximum number of bytes to capture.
.Fa to_ms
specifies the read timeout in milliseconds.
.Fa errbuf
is used to return error text and is only set when
.Fn pcap_open_live
fails and returns
.Dv NULL .
.Pp
.Fn pcap_open_offline
is called to open a
.Dq savefile
for reading.
.Fa fname
specifies the name of the file to open. The file has
the same format as those used by
.Xr tcpdump 8 .
.\" and
.\" .BR tcpslice(1) .
The name
.Ql -
is a synonym for
.Dv stdin .
.Fa errbuf
is used to return error text and is only set when
.Fn pcap_open_offline
fails and returns
.Dv NULL .
.Pp
.Fn pcap_dump_open
is called to open a
.Dq savefile
for writing. The name
.Ql -
is a synonym for
.Dv stdin .
.Dv NULL
is returned on failure.
.Fa p
is a
.Fa pcap
struct as returned by
.Fn pcap_open_offline
or
.Fn pcap_open_live .
.Fa fname
specifies the name of the file to open. If
.Dv NULL
is returned,
.Fn pcap_geterr
can be used to get the error text.
.Pp
.Fn pcap_lookupdev
returns a pointer to a network device suitable for use with
.Fn pcap_open_live
and
.Fn pcap_lookupnet .
If there is an error,
.Dv NULL
is returned and
.Fa errbuf
is filled in with an appropriate error message.
.Pp
.Fn pcap_lookupnet
is used to determine the network number and mask
associated with the network device
.Fa device .
Both
.Fa netp
and
.Fa maskp
are
.Fa u_int32_t
pointers.
A return of \-1 indicates an error in which case
.Fa errbuf
is filled in with with an appropriate error message.
.Pp
.Fn pcap_dispatch
is used to collect and process packets.
.Fa cnt
specifies the maximum number of packets to process before returning. A
.Fa cnt
of \-1 processes all the packets received in one buffer. A
.Fa cnt
of 0 processes all packets until an error occurs (or
.Tn EOF
is reached).
.Fa callback
specifies a routine to be called with three arguments: a
.Fa u_char
pointer which is passed in from
.Fn pcap_dispatch ,
a pointer to the
.Fa 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
.Tn EOF
is reached in a savefile.
A return of \-1 indicates an error in which case
.Fn pcap_perror
or
.Fn pcap_geterr
may be used to display the error text.
.Pp
.Fn pcap_dump
outputs a packet to the savefile opened with
.Fn pcap_dump_open .
Note that its calling arguments are suitable for use with
.Fn pcap_dispatch .
.Pp
.Fn pcap_inject
uses
.Xr write 2
to inject a raw packet through the network interface.
.Pp
.Fn pcap_immediate
sets
.Dq immediate
mode.  If this isn't supported by the underlying packet capture, \-1 is
returned and the error text can be obtained with
.Fn pcap_perror
or
.Fn pcap_geterr .
.Pp
.Fn pcap_compile
is used to compile the string
.Fa str
into a filter program.
.Fa fp
is a pointer to a
.Fa bpf_program
struct and is filled in by
.Fn pcap_compile .
.Fa optimize
controls whether optimization on the resulting code is performed.
.Fa netmask
specifies the netmask of the local net.
.Pp
.Fn pcap_setfilter
is used to specify the filter program.
.Fa fp
is a pointer to an array of
.Fa bpf_program
struct, usually the result of a call to
.Fn pcap_compile .
.Pp
.Fn pcap_loop
is similar to
.Fn pcap_dispatch
except it keeps reading packets until
.Fa cnt
packets are processed or an error occurs. A negative
.Fa cnt
causes
.Fn pcap_loop
to loop forever (or at least until an error occurs).
.Pp
.Fn pcap_next
returns a
.Fa u_char
pointer to the next packet.
.Pp
.Fn pcap_datalink
returns the link layer type, e.g.
.Tn DLT_EN10MB .
.Pp
.Fn pcap_snapshot
returns the snapshot length specified when
.Fn pcap_open_live
was called.
.Pp
.Fn pcap_is_swapped
returns true if the current savefile
uses a different byte order than the current system.
.Pp
.Fn pcap_major_version()
returns the major number of the version of the pcap used to write the savefile.
.Pp
.Fn pcap_minor_version
returns the minor number of the version of the pcap used to write the savefile.
.Pp
.Fn pcap_file
returns the name of the savefile.
.Pp
.Fn pcap_stats
returns 0 and fills in a
.Fa pcap_stat
struct with packet statistics. 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
.Fn pcap_perror
or
.Fn pcap_geterr .
.Pp
.Fn pcap_fileno
returns the file descriptor number of the savefile.
.Pp
.Fn pcap_perror
prints the text of the last pcap library error on
.Dv stderr ,
prefixed by
.Fa prefix .
.Pp
.Fn pcap_geterr
returns the error text pertaining to the last pcap library error.
.Pp
.Fn pcap_strerror
is provided in case
.Xr strerror 1
isn't available.
.Pp
.Fn pcap_close
closes the files associated with
.Fa p
and deallocates resources.
.Pp
.Fn pcap_dump_close
closes the savefile.
.Sh SEE ALSO
.Xr tcpdump 8
.\" , tcpslice(1)