1333 lines
36 KiB
Groff
1333 lines
36 KiB
Groff
.\" @(#) $Header: /tcpdump/master/libpcap/pcap.3,v 1.64.2.11 2007/06/11 09:52:05 guy Exp $
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.\"
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.\" Copyright (c) 1994, 1996, 1997
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that: (1) source code distributions
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.\" retain the above copyright notice and this paragraph in its entirety, (2)
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.\" distributions including binary code include the above copyright notice and
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.\" this paragraph in its entirety in the documentation or other materials
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.\" provided with the distribution, and (3) all advertising materials mentioning
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.\" features or use of this software display the following acknowledgement:
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.\" ``This product includes software developed by the University of California,
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.\" Lawrence Berkeley Laboratory and its contributors.'' Neither the name of
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.\" the University nor the names of its contributors may be used to endorse
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.\" or promote products derived from this software without specific prior
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.\" written permission.
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.\" THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED
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.\" WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
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.\" MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
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.\"
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.\" $FreeBSD$
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.\"
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.TH PCAP 3 "27 February 2004"
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.SH NAME
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pcap \- Packet Capture library
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.SH SYNOPSIS
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.nf
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.ft B
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#include <pcap.h>
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.ft
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.LP
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.nf
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.ft B
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char errbuf[PCAP_ERRBUF_SIZE];
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.ft
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.LP
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.ft B
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pcap_t *pcap_open_live(const char *device, int snaplen,
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.ti +8
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int promisc, int to_ms, char *errbuf)
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pcap_t *pcap_open_dead(int linktype, int snaplen)
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pcap_t *pcap_open_offline(const char *fname, char *errbuf)
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pcap_t *pcap_fopen_offline(FILE *fp, char *errbuf)
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pcap_dumper_t *pcap_dump_open(pcap_t *p, const char *fname)
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pcap_dumper_t *pcap_dump_fopen(pcap_t *p, FILE *fp)
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.ft
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.LP
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.ft B
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int pcap_setnonblock(pcap_t *p, int nonblock, char *errbuf);
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int pcap_getnonblock(pcap_t *p, char *errbuf);
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.ft
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.LP
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.ft B
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int pcap_findalldevs(pcap_if_t **alldevsp, char *errbuf)
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void pcap_freealldevs(pcap_if_t *alldevs)
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char *pcap_lookupdev(char *errbuf)
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int pcap_lookupnet(const char *device, bpf_u_int32 *netp,
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.ti +8
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bpf_u_int32 *maskp, char *errbuf)
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.ft
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.LP
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.ft B
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typedef void (*pcap_handler)(u_char *user, const struct pcap_pkthdr *h,
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.ti +8
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const u_char *bytes);
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.ft B
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int pcap_dispatch(pcap_t *p, int cnt,
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.ti +8
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pcap_handler callback, u_char *user)
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int pcap_loop(pcap_t *p, int cnt,
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.ti +8
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pcap_handler callback, u_char *user)
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void pcap_dump(u_char *user, struct pcap_pkthdr *h,
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.ti +8
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u_char *sp)
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.ft
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.LP
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.ft B
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int pcap_compile(pcap_t *p, struct bpf_program *fp,
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.ti +8
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const char *str, int optimize, bpf_u_int32 netmask)
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int pcap_setfilter(pcap_t *p, struct bpf_program *fp)
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void pcap_freecode(struct bpf_program *)
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int pcap_setdirection(pcap_t *p, pcap_direction_t d)
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.ft
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.LP
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.ft B
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const u_char *pcap_next(pcap_t *p, struct pcap_pkthdr *h)
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int pcap_next_ex(pcap_t *p, struct pcap_pkthdr **pkt_header,
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.ti +8
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const u_char **pkt_data)
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.ft
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.LP
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.ft B
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void pcap_breakloop(pcap_t *)
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.ft
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.LP
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.ft B
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int pcap_inject(pcap_t *p, const void *buf, size_t size)
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int pcap_sendpacket(pcap_t *p, const u_char *buf, int size)
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.ft
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.LP
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.ft B
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int pcap_datalink(pcap_t *p)
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int pcap_list_datalinks(pcap_t *p, int **dlt_buf);
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int pcap_set_datalink(pcap_t *p, int dlt);
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int pcap_datalink_name_to_val(const char *name);
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const char *pcap_datalink_val_to_name(int dlt);
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const char *pcap_datalink_val_to_description(int dlt);
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int pcap_snapshot(pcap_t *p)
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int pcap_is_swapped(pcap_t *p)
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int pcap_major_version(pcap_t *p)
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int pcap_minor_version(pcap_t *p)
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int pcap_stats(pcap_t *p, struct pcap_stat *ps)
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FILE *pcap_file(pcap_t *p)
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int pcap_fileno(pcap_t *p)
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int pcap_get_selectable_fd(pcap_t *p);
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void pcap_perror(pcap_t *p, char *prefix)
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char *pcap_geterr(pcap_t *p)
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const char *pcap_strerror(int error)
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const char *pcap_lib_version(void)
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.ft
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.LP
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.ft B
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void pcap_close(pcap_t *p)
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int pcap_dump_flush(pcap_dumper_t *p)
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long pcap_dump_ftell(pcap_dumper_t *p)
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FILE *pcap_dump_file(pcap_dumper_t *p)
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void pcap_dump_close(pcap_dumper_t *p)
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.ft
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.fi
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.SH DESCRIPTION
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The Packet Capture library
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provides a high level interface to packet capture systems. All packets
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on the network, even those destined for other hosts, are accessible
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through this mechanism.
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.PP
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.SH ROUTINES
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NOTE:
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.I errbuf
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in
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.BR pcap_open_live() ,
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.BR pcap_open_dead() ,
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.BR pcap_open_offline() ,
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.BR pcap_fopen_offline() ,
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.BR pcap_setnonblock() ,
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.BR pcap_getnonblock() ,
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.BR pcap_findalldevs() ,
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.BR pcap_lookupdev() ,
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and
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.B pcap_lookupnet()
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is assumed to be able to hold at least
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.B PCAP_ERRBUF_SIZE
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chars.
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.PP
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.B pcap_open_live()
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is used to obtain a packet capture descriptor to look
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at packets on the network.
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.I device
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is a string that specifies the network device to open; on Linux systems
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with 2.2 or later kernels, a
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.I device
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argument of "any" or
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.B NULL
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can be used to capture packets from all interfaces.
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.I snaplen
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specifies the maximum number of bytes to capture. If this value is less
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than the size of a packet that is captured, only the first
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.I snaplen
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bytes of that packet will be captured and provided as packet data. A
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value of 65535 should be sufficient, on most if not all networks, to
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capture all the data available from the packet.
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.I promisc
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specifies if the interface is to be put into promiscuous mode.
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(Note that even if this parameter is false, the interface
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could well be in promiscuous mode for some other reason.) For now, this
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doesn't work on the "any" device; if an argument of "any" or NULL is
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supplied, the
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.I promisc
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flag is ignored.
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.I to_ms
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specifies the read timeout in milliseconds. The read timeout is used to
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arrange that the read not necessarily return immediately when a packet
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is seen, but that it wait for some amount of time to allow more packets
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to arrive and to read multiple packets from the OS kernel in one
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operation. Not all platforms support a read timeout; on platforms that
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don't, the read timeout is ignored. A zero value for
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.IR to_ms ,
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on platforms that support a read timeout,
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will cause a read to wait forever to allow enough packets to
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arrive, with no timeout.
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.I errbuf
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is used to return error or warning text. It will be set to error text when
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.B pcap_open_live()
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fails and returns
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.BR NULL .
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.I errbuf
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may also be set to warning text when
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.B pcap_open_live()
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succeds; to detect this case the caller should store a zero-length string in
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.I errbuf
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before calling
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.B pcap_open_live()
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and display the warning to the user if
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.I errbuf
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is no longer a zero-length string.
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.PP
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.B pcap_open_dead()
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is used for creating a
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.B pcap_t
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structure to use when calling the other functions in libpcap. It is
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typically used when just using libpcap for compiling BPF code.
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.PP
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.B pcap_open_offline()
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|
is called to open a ``savefile'' for reading.
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.I fname
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specifies the name of the file to open. The file has
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the same format as those used by
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.B tcpdump(1)
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and
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.BR tcpslice(1) .
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The name "-" in a synonym for
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.BR stdin .
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Alternatively, you may call
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.B pcap_fopen_offline()
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to read dumped data from an existing open stream
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.IR fp .
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Note that on Windows, that stream should be opened in binary mode.
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.I errbuf
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is used to return error text and is only set when
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.B pcap_open_offline()
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or
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.B pcap_fopen_offline()
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fails and returns
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.BR NULL .
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.PP
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.B pcap_dump_open()
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|
is called to open a ``savefile'' for writing. The name "-" in a synonym
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for
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.BR stdout .
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.B NULL
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is returned on failure.
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.I p
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is a
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.I pcap
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struct as returned by
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.B pcap_open_offline()
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or
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.BR pcap_open_live() .
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.I fname
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specifies the name of the file to open. Alternatively, you may call
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.B pcap_dump_fopen()
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to write data to an existing open stream
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.IR fp .
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Note that on Windows, that stream should be opened in binary mode.
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If
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.B NULL
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is returned,
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.B pcap_geterr()
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can be used to get the error text.
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.PP
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.PP
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.B pcap_setnonblock()
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puts a capture descriptor, opened with
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.BR pcap_open_live() ,
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|
into ``non-blocking'' mode, or takes it out of ``non-blocking'' mode,
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depending on whether the
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.I nonblock
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argument is non-zero or zero. It has no effect on ``savefiles''.
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If there is an error, \-1 is returned and
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.I errbuf
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is filled in with an appropriate error message; otherwise, 0 is
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returned.
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In
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``non-blocking'' mode, an attempt to read from the capture descriptor
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with
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.B pcap_dispatch()
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will, if no packets are currently available to be read, return 0
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|
immediately rather than blocking waiting for packets to arrive.
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.B pcap_loop()
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and
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.B pcap_next()
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will not work in ``non-blocking'' mode.
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.PP
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.B pcap_getnonblock()
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returns the current ``non-blocking'' state of the capture descriptor; it
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always returns 0 on ``savefiles''.
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If there is an error, \-1 is returned and
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.I errbuf
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is filled in with an appropriate error message.
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.PP
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.B pcap_findalldevs()
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constructs a list of network devices that can be opened with
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.BR pcap_open_live() .
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(Note that there may be network devices that cannot be opened with
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.BR pcap_open_live()
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by the
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process calling
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.BR pcap_findalldevs() ,
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because, for example, that process might not have sufficient privileges
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to open them for capturing; if so, those devices will not appear on the
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list.)
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.I alldevsp
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is set to point to the first element of the list; each element of the
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list is of type
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.BR pcap_if_t ,
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and has the following members:
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.RS
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.TP
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.B next
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if not
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.BR NULL ,
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a pointer to the next element in the list;
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.B NULL
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for the last element of the list
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.TP
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.B name
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a pointer to a string giving a name for the device to pass to
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.B pcap_open_live()
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.TP
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.B description
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if not
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.BR NULL ,
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a pointer to a string giving a human-readable description of the device
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.TP
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.B addresses
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a pointer to the first element of a list of addresses for the interface
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.TP
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.B flags
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interface flags:
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.RS
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.TP
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.B PCAP_IF_LOOPBACK
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set if the interface is a loopback interface
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.RE
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.RE
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.PP
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Each element of the list of addresses is of type
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.BR pcap_addr_t ,
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and has the following members:
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.RS
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.TP
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.B next
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if not
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.BR NULL ,
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a pointer to the next element in the list;
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.B NULL
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for the last element of the list
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.TP
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.B addr
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|
a pointer to a
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.B "struct sockaddr"
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|
containing an address
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.TP
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.B netmask
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|
if not
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|
.BR NULL ,
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|
a pointer to a
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.B "struct sockaddr"
|
|
that contains the netmask corresponding to the address pointed to by
|
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.B addr
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.TP
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.B broadaddr
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|
if not
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.BR NULL ,
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a pointer to a
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.B "struct sockaddr"
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that contains the broadcast address corresponding to the address pointed
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to by
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.BR addr ;
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may be null if the interface doesn't support broadcasts
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.TP
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.B dstaddr
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if not
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.BR NULL ,
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|
a pointer to a
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.B "struct sockaddr"
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|
that contains the destination address corresponding to the address pointed
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|
to by
|
|
.BR addr ;
|
|
may be null if the interface isn't a point-to-point interface
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.RE
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.PP
|
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Note that not all the addresses in the list of addresses are
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|
necessarily IPv4 or IPv6 addresses - you must check the
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.B sa_family
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|
member of the
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.B "struct sockaddr"
|
|
before interpreting the contents of the address.
|
|
.PP
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.B \-1
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|
is returned on failure, in which case
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.B errbuf
|
|
is filled in with an appropriate error message;
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.B 0
|
|
is returned on success.
|
|
.PP
|
|
.B pcap_freealldevs()
|
|
is used to free a list allocated by
|
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.BR pcap_findalldevs() .
|
|
.PP
|
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.B pcap_lookupdev()
|
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returns a pointer to a network device suitable for use with
|
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.B pcap_open_live()
|
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and
|
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.BR pcap_lookupnet() .
|
|
If there is an error,
|
|
.B NULL
|
|
is returned and
|
|
.I errbuf
|
|
is filled in with an appropriate error message.
|
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.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 bpf_u_int32
|
|
pointers.
|
|
A return of \-1 indicates an error in which case
|
|
.I errbuf
|
|
is filled in 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.
|
|
This is not a minimum number; when reading a live capture, only one
|
|
bufferful of packets is read at a time, so fewer than
|
|
.I cnt
|
|
packets may be processed. A
|
|
.I cnt
|
|
of \-1 processes all the packets received in one buffer when reading a
|
|
live capture, or all the packets in the file when reading a
|
|
``savefile''.
|
|
.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
|
|
.I const struct pcap_pkthdr
|
|
pointer to a structure with the following members:
|
|
.RS
|
|
.TP
|
|
.B ts
|
|
a
|
|
.I struct timeval
|
|
containing the time when the packet was captured
|
|
.TP
|
|
.B caplen
|
|
a
|
|
.I bpf_u_int32
|
|
giving the number of bytes of the packet that are available from the
|
|
capture
|
|
.TP
|
|
.B len
|
|
a
|
|
.I bpf_u_int32
|
|
giving the length of the packet, in bytes (which might be more than the
|
|
number of bytes available from the capture, if the length of the packet
|
|
is larger than the maximum number of bytes to capture)
|
|
.RE
|
|
.PP
|
|
and a
|
|
.I const u_char
|
|
pointer to the first
|
|
.B caplen
|
|
(as given in the
|
|
.I struct pcap_pkthdr
|
|
a pointer to which is passed to the callback routine)
|
|
bytes of data from the packet (which won't necessarily be the entire
|
|
packet; to capture the entire packet, you will have to provide a value
|
|
for
|
|
.I snaplen
|
|
in your call to
|
|
.B pcap_open_live()
|
|
that is sufficiently large to get all of the packet's data - a value of
|
|
65535 should be sufficient on most if not all networks).
|
|
.PP
|
|
The number of packets read is returned.
|
|
0 is returned if no packets were read from a live capture (if, for
|
|
example, they were discarded because they didn't pass the packet filter,
|
|
or if, on platforms that support a read timeout that starts before any
|
|
packets arrive, the timeout expires before any packets arrive, or if the
|
|
file descriptor for the capture device is in non-blocking mode and no
|
|
packets were available to be read) or if no more packets are available
|
|
in a ``savefile.'' A return of \-1 indicates
|
|
an error in which case
|
|
.B pcap_perror()
|
|
or
|
|
.B pcap_geterr()
|
|
may be used to display the error text.
|
|
A return of \-2 indicates that the loop terminated due to a call to
|
|
.B pcap_breakloop()
|
|
before any packets were processed.
|
|
.ft B
|
|
If your application uses pcap_breakloop(),
|
|
make sure that you explicitly check for \-1 and \-2, rather than just
|
|
checking for a return value < 0.
|
|
.ft R
|
|
.PP
|
|
.BR NOTE :
|
|
when reading a live capture,
|
|
.B pcap_dispatch()
|
|
will not necessarily return when the read times out; on some platforms,
|
|
the read timeout isn't supported, and, on other platforms, the timer
|
|
doesn't start until at least one packet arrives. This means that the
|
|
read timeout should
|
|
.B NOT
|
|
be used in, for example, an interactive application, to allow the packet
|
|
capture loop to ``poll'' for user input periodically, as there's no
|
|
guarantee that
|
|
.B pcap_dispatch()
|
|
will return after the timeout expires.
|
|
.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.
|
|
It does
|
|
.B not
|
|
return when live read timeouts occur.
|
|
Rather, specifying a non-zero read timeout to
|
|
.B pcap_open_live()
|
|
and then calling
|
|
.B pcap_dispatch()
|
|
allows the reception and processing of any packets that arrive when the
|
|
timeout occurs.
|
|
A negative
|
|
.I cnt
|
|
causes
|
|
.B pcap_loop()
|
|
to loop forever (or at least until an error occurs). \-1 is returned on
|
|
an error; 0 is returned if
|
|
.I cnt
|
|
is exhausted; \-2 is returned if the loop terminated due to a call to
|
|
.B pcap_breakloop()
|
|
before any packets were processed.
|
|
.ft B
|
|
If your application uses pcap_breakloop(),
|
|
make sure that you explicitly check for \-1 and \-2, rather than just
|
|
checking for a return value < 0.
|
|
.ft R
|
|
.PP
|
|
.B pcap_next()
|
|
reads the next packet (by calling
|
|
.B pcap_dispatch()
|
|
with a
|
|
.I cnt
|
|
of 1) and returns a
|
|
.I u_char
|
|
pointer to the data in that packet. (The
|
|
.I pcap_pkthdr
|
|
struct for that packet is not supplied.)
|
|
.B NULL
|
|
is returned if an error occured, or if no packets were read from a live
|
|
capture (if, for example, they were discarded because they didn't pass
|
|
the packet filter, or if, on platforms that support a read timeout that
|
|
starts before any packets arrive, the timeout expires before any packets
|
|
arrive, or if the file descriptor for the capture device is in
|
|
non-blocking mode and no packets were available to be read), or if no
|
|
more packets are available in a ``savefile.'' Unfortunately, there is
|
|
no way to determine whether an error occured or not.
|
|
.PP
|
|
.B pcap_next_ex()
|
|
reads the next packet and returns a success/failure indication:
|
|
.RS
|
|
.TP
|
|
1
|
|
the packet was read without problems
|
|
.TP
|
|
0
|
|
packets are being read from a live capture, and the timeout expired
|
|
.TP
|
|
\-1
|
|
an error occurred while reading the packet
|
|
.TP
|
|
\-2
|
|
packets are being read from a ``savefile'', and there are no more
|
|
packets to read from the savefile.
|
|
.RE
|
|
.PP
|
|
If the packet was read without problems, the pointer pointed to by the
|
|
.I pkt_header
|
|
argument is set to point to the
|
|
.I pcap_pkthdr
|
|
struct for the packet, and the
|
|
pointer pointed to by the
|
|
.I pkt_data
|
|
argument is set to point to the data in the packet.
|
|
.PP
|
|
.B pcap_breakloop()
|
|
sets a flag that will force
|
|
.B pcap_dispatch()
|
|
or
|
|
.B pcap_loop()
|
|
to return rather than looping; they will return the number of packets
|
|
that have been processed so far, or \-2 if no packets have been
|
|
processed so far.
|
|
.PP
|
|
This routine is safe to use inside a signal handler on UNIX or a console
|
|
control handler on Windows, as it merely sets a flag that is checked
|
|
within the loop.
|
|
.PP
|
|
The flag is checked in loops reading packets from the OS - a signal by
|
|
itself will not necessarily terminate those loops - as well as in loops
|
|
processing a set of packets returned by the OS.
|
|
.ft B
|
|
Note that if you are catching signals on UNIX systems that support
|
|
restarting system calls after a signal, and calling pcap_breakloop()
|
|
in the signal handler, you must specify, when catching those signals,
|
|
that system calls should NOT be restarted by that signal. Otherwise,
|
|
if the signal interrupted a call reading packets in a live capture,
|
|
when your signal handler returns after calling pcap_breakloop(), the
|
|
call will be restarted, and the loop will not terminate until more
|
|
packets arrive and the call completes.
|
|
.PP
|
|
Note also that, in a multi-threaded application, if one thread is
|
|
blocked in
|
|
.BR pcap_dispatch() ,
|
|
.BR pcap_loop() ,
|
|
.BR pcap_next() ,
|
|
or
|
|
.BR pcap_next_ex() ,
|
|
a call to
|
|
.B pcap_breakloop()
|
|
in a different thread will not unblock that thread; you will need to use
|
|
whatever mechanism the OS provides for breaking a thread out of blocking
|
|
calls in order to unblock the thread, such as thread cancellation in
|
|
systems that support POSIX threads.
|
|
.ft R
|
|
.PP
|
|
Note that
|
|
.B pcap_next()
|
|
will, on some platforms, loop reading packets from the OS; that loop
|
|
will not necessarily be terminated by a signal, so
|
|
.B pcap_breakloop()
|
|
should be used to terminate packet processing even if
|
|
.B pcap_next()
|
|
is being used.
|
|
.PP
|
|
.B pcap_breakloop()
|
|
does not guarantee that no further packets will be processed by
|
|
.B pcap_dispatch()
|
|
or
|
|
.B pcap_loop()
|
|
after it is called; at most one more packet might be processed.
|
|
.PP
|
|
If \-2 is returned from
|
|
.B pcap_dispatch()
|
|
or
|
|
.BR pcap_loop() ,
|
|
the flag is cleared, so a subsequent call will resume reading packets.
|
|
If a positive number is returned, the flag is not cleared, so a
|
|
subsequent call will return \-2 and clear the flag.
|
|
.PP
|
|
.B pcap_inject()
|
|
sends a raw packet through the network interface;
|
|
.I buf
|
|
points to the data of the packet, including the link-layer header, and
|
|
.I size
|
|
is the number of bytes in the packet.
|
|
It returns the number of bytes written on success. A return of \-1
|
|
indicates an error in which case
|
|
.B pcap_perror()
|
|
or
|
|
.B pcap_geterr()
|
|
may be used to display the error text.
|
|
Note that, even if you successfully open the network interface, you
|
|
might not have permission to send packets on it, or it might not support
|
|
sending packets; as
|
|
.I pcap_open_live()
|
|
doesn't have a flag to indicate whether to open for capturing, sending,
|
|
or capturing and sending, you cannot request an open that supports
|
|
sending and be notified at open time whether sending will be possible.
|
|
Note also that some devices might not support sending packets.
|
|
.PP
|
|
Note that, on some platforms, the link-layer header of the packet that's
|
|
sent might not be the same as the link-layer header of the packet
|
|
supplied to
|
|
.BR pcap_inject() ,
|
|
as the source link-layer address, if the header contains such an
|
|
address, might be changed to be the address assigned to the interface on
|
|
which the packet it sent, if the platform doesn't support sending
|
|
completely raw and unchanged packets. Even worse, some drivers on some
|
|
platforms might change the link-layer type field to whatever value
|
|
libpcap used when attaching to the device, even on platforms that
|
|
.I do
|
|
nominally support sending completely raw and unchanged packets.
|
|
.PP
|
|
.B pcap_sendpacket()
|
|
is like
|
|
.BR pcap_inject() ,
|
|
but it returns 0 on success and \-1 on failure.
|
|
.RB ( pcap_inject()
|
|
comes from OpenBSD;
|
|
.B pcap_sendpacket()
|
|
comes from WinPcap. Both are provided for compatibility.)
|
|
.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
|
|
.B pcap_dispatch()
|
|
or
|
|
.BR pcap_loop() .
|
|
If called directly, the
|
|
.I user
|
|
parameter is of type
|
|
.I pcap_dumper_t
|
|
as returned by
|
|
.BR pcap_dump_open() .
|
|
.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 IPv4 netmask of the network on which packets are being
|
|
captured; it is used only when checking for IPv4 broadcast addresses in
|
|
the filter program. If the netmask of the network on which packets are
|
|
being captured isn't known to the program, or if packets are being
|
|
captured on the Linux "any" pseudo-interface that can capture on more
|
|
than one network, a value of 0 can be supplied; tests for IPv4 broadcast
|
|
addreses won't be done correctly, but all other tests in the filter
|
|
program will be OK. A return of \-1 indicates an error in which case
|
|
.BR pcap_geterr()
|
|
may be used to display the error text.
|
|
.PP
|
|
.B pcap_compile_nopcap()
|
|
is similar to
|
|
.B pcap_compile()
|
|
except that instead of passing a pcap structure, one passes the
|
|
snaplen and linktype explicitly. It is intended to be used for
|
|
compiling filters for direct BPF usage, without necessarily having
|
|
called
|
|
.BR pcap_open() .
|
|
A return of \-1 indicates an error; the error text is unavailable.
|
|
.RB ( pcap_compile_nopcap()
|
|
is a wrapper around
|
|
.BR pcap_open_dead() ,
|
|
.BR pcap_compile() ,
|
|
and
|
|
.BR pcap_close() ;
|
|
the latter three routines can be used directly in order to get the error
|
|
text for a compilation error.)
|
|
.B
|
|
.PP
|
|
.B pcap_setfilter()
|
|
is used to specify a filter program.
|
|
.I fp
|
|
is a pointer to a
|
|
.I bpf_program
|
|
struct, usually the result of a call to
|
|
.BR pcap_compile() .
|
|
.B \-1
|
|
is returned on failure, in which case
|
|
.BR pcap_geterr()
|
|
may be used to display the error text;
|
|
.B 0
|
|
is returned on success.
|
|
.PP
|
|
.B pcap_freecode()
|
|
is used to free up allocated memory pointed to by a
|
|
.I bpf_program
|
|
struct generated by
|
|
.B 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
|
|
.BR pcap_setfilter() .
|
|
.PP
|
|
.B pcap_setdirection()
|
|
is used to specify a direction that packets will be captured.
|
|
.I pcap_direction_t
|
|
is one of the constants
|
|
.BR PCAP_D_IN ,
|
|
.B PCAP_D_OUT
|
|
or
|
|
.BR PCAP_D_INOUT .
|
|
.B PCAP_D_IN
|
|
will only capture packets received by the device,
|
|
.B PCAP_D_OUT
|
|
will only capture packets sent by the device and
|
|
.B PCAP_D_INOUT
|
|
will capture packets received by or sent by the device.
|
|
.B PCAP_D_INOUT
|
|
is the default setting if this function is not called. This isn't
|
|
necessarily supported on all platforms; some platforms might return an
|
|
error, and some other platforms might not support
|
|
.BR PCAP_D_OUT .
|
|
This operation is not supported if a ``savefile'' is being read.
|
|
.B \-1
|
|
is returned on failure,
|
|
.B 0
|
|
is returned on success.
|
|
.PP
|
|
.B pcap_datalink()
|
|
returns the link layer type; link layer types it can return include:
|
|
.PP
|
|
.RS 5
|
|
.TP 5
|
|
.B DLT_NULL
|
|
BSD loopback encapsulation; the link layer header is a 4-byte field, in
|
|
.I host
|
|
byte order, containing a PF_ value from
|
|
.B socket.h
|
|
for the network-layer protocol of the packet.
|
|
.IP
|
|
Note that ``host byte order'' is the byte order of the machine on which
|
|
the packets are captured, and the PF_ values are for the OS of the
|
|
machine on which the packets are captured; if a live capture is being
|
|
done, ``host byte order'' is the byte order of the machine capturing the
|
|
packets, and the PF_ values are those of the OS of the machine capturing
|
|
the packets, but if a ``savefile'' is being read, the byte order and PF_
|
|
values are
|
|
.I not
|
|
necessarily those of the machine reading the capture file.
|
|
.TP 5
|
|
.B DLT_EN10MB
|
|
Ethernet (10Mb, 100Mb, 1000Mb, and up)
|
|
.TP 5
|
|
.B DLT_IEEE802
|
|
IEEE 802.5 Token Ring
|
|
.TP 5
|
|
.B DLT_ARCNET
|
|
ARCNET
|
|
.TP 5
|
|
.B DLT_SLIP
|
|
SLIP; the link layer header contains, in order:
|
|
.RS 10
|
|
.LP
|
|
a 1-byte flag, which is 0 for packets received by the machine and 1 for
|
|
packets sent by the machine;
|
|
.LP
|
|
a 1-byte field, the upper 4 bits of which indicate the type of packet,
|
|
as per RFC 1144:
|
|
.RS 5
|
|
.TP 5
|
|
0x40
|
|
an unmodified IP datagram (TYPE_IP);
|
|
.TP 5
|
|
0x70
|
|
an uncompressed-TCP IP datagram (UNCOMPRESSED_TCP), with that byte being
|
|
the first byte of the raw IP header on the wire, containing the
|
|
connection number in the protocol field;
|
|
.TP 5
|
|
0x80
|
|
a compressed-TCP IP datagram (COMPRESSED_TCP), with that byte being the
|
|
first byte of the compressed TCP/IP datagram header;
|
|
.RE
|
|
.LP
|
|
for UNCOMPRESSED_TCP, the rest of the modified IP header, and for
|
|
COMPRESSED_TCP, the compressed TCP/IP datagram header;
|
|
.RE
|
|
.RS 5
|
|
.LP
|
|
for a total of 16 bytes; the uncompressed IP datagram follows the header.
|
|
.RE
|
|
.TP 5
|
|
.B DLT_PPP
|
|
PPP; if the first 2 bytes are 0xff and 0x03, it's PPP in HDLC-like
|
|
framing, with the PPP header following those two bytes, otherwise it's
|
|
PPP without framing, and the packet begins with the PPP header.
|
|
.TP 5
|
|
.B DLT_FDDI
|
|
FDDI
|
|
.TP 5
|
|
.B DLT_ATM_RFC1483
|
|
RFC 1483 LLC/SNAP-encapsulated ATM; the packet begins with an IEEE 802.2
|
|
LLC header.
|
|
.TP 5
|
|
.B DLT_RAW
|
|
raw IP; the packet begins with an IP header.
|
|
.TP 5
|
|
.B DLT_PPP_SERIAL
|
|
PPP in HDLC-like framing, as per RFC 1662, or Cisco PPP with HDLC
|
|
framing, as per section 4.3.1 of RFC 1547; the first byte will be 0xFF
|
|
for PPP in HDLC-like framing, and will be 0x0F or 0x8F for Cisco PPP
|
|
with HDLC framing.
|
|
.TP 5
|
|
.B DLT_PPP_ETHER
|
|
PPPoE; the packet begins with a PPPoE header, as per RFC 2516.
|
|
.TP 5
|
|
.B DLT_C_HDLC
|
|
Cisco PPP with HDLC framing, as per section 4.3.1 of RFC 1547.
|
|
.TP 5
|
|
.B DLT_IEEE802_11
|
|
IEEE 802.11 wireless LAN
|
|
.TP 5
|
|
.B DLT_FRELAY
|
|
Frame Relay
|
|
.TP 5
|
|
.B DLT_LOOP
|
|
OpenBSD loopback encapsulation; the link layer header is a 4-byte field, in
|
|
.I network
|
|
byte order, containing a PF_ value from OpenBSD's
|
|
.B socket.h
|
|
for the network-layer protocol of the packet.
|
|
.IP
|
|
Note that, if a ``savefile'' is being read, those PF_ values are
|
|
.I not
|
|
necessarily those of the machine reading the capture file.
|
|
.TP 5
|
|
.B DLT_LINUX_SLL
|
|
Linux "cooked" capture encapsulation; the link layer header contains, in
|
|
order:
|
|
.RS 10
|
|
.LP
|
|
a 2-byte "packet type", in network byte order, which is one of:
|
|
.RS 5
|
|
.TP 5
|
|
0
|
|
packet was sent to us by somebody else
|
|
.TP 5
|
|
1
|
|
packet was broadcast by somebody else
|
|
.TP 5
|
|
2
|
|
packet was multicast, but not broadcast, by somebody else
|
|
.TP 5
|
|
3
|
|
packet was sent by somebody else to somebody else
|
|
.TP 5
|
|
4
|
|
packet was sent by us
|
|
.RE
|
|
.LP
|
|
a 2-byte field, in network byte order, containing a Linux ARPHRD_ value
|
|
for the link layer device type;
|
|
.LP
|
|
a 2-byte field, in network byte order, containing the length of the
|
|
link layer address of the sender of the packet (which could be 0);
|
|
.LP
|
|
an 8-byte field containing that number of bytes of the link layer header
|
|
(if there are more than 8 bytes, only the first 8 are present);
|
|
.LP
|
|
a 2-byte field containing an Ethernet protocol type, in network byte
|
|
order, or containing 1 for Novell 802.3 frames without an 802.2 LLC
|
|
header or 4 for frames beginning with an 802.2 LLC header.
|
|
.RE
|
|
.TP 5
|
|
.B DLT_LTALK
|
|
Apple LocalTalk; the packet begins with an AppleTalk LLAP header.
|
|
.TP 5
|
|
.B DLT_PFLOG
|
|
OpenBSD pflog; the link layer header contains, in order:
|
|
.RS 10
|
|
.LP
|
|
a 1-byte header length, in host byte order;
|
|
.LP
|
|
a 4-byte PF_ value, in host byte order;
|
|
.LP
|
|
a 2-byte action code, in network byte order, which is one of:
|
|
.RS 5
|
|
.TP 5
|
|
0
|
|
passed
|
|
.TP 5
|
|
1
|
|
dropped
|
|
.TP 5
|
|
2
|
|
scrubbed
|
|
.RE
|
|
.LP
|
|
a 2-byte reason code, in network byte order, which is one of:
|
|
.RS 5
|
|
.TP 5
|
|
0
|
|
match
|
|
.TP 5
|
|
1
|
|
bad offset
|
|
.TP 5
|
|
2
|
|
fragment
|
|
.TP 5
|
|
3
|
|
short
|
|
.TP 5
|
|
4
|
|
normalize
|
|
.TP 5
|
|
5
|
|
memory
|
|
.RE
|
|
.LP
|
|
a 16-character interface name;
|
|
.LP
|
|
a 16-character ruleset name (only meaningful if subrule is set);
|
|
.LP
|
|
a 4-byte rule number, in network byte order;
|
|
.LP
|
|
a 4-byte subrule number, in network byte order;
|
|
.LP
|
|
a 1-byte direction, in network byte order, which is one of:
|
|
.RS 5
|
|
.TP 5
|
|
0
|
|
incoming or outgoing
|
|
.TP 5
|
|
1
|
|
incoming
|
|
.TP 5
|
|
2
|
|
outgoing
|
|
.RE
|
|
.RE
|
|
.TP 5
|
|
.B DLT_PRISM_HEADER
|
|
Prism monitor mode information followed by an 802.11 header.
|
|
.TP 5
|
|
.B DLT_IP_OVER_FC
|
|
RFC 2625 IP-over-Fibre Channel, with the link-layer header being the
|
|
Network_Header as described in that RFC.
|
|
.TP 5
|
|
.B DLT_SUNATM
|
|
SunATM devices; the link layer header contains, in order:
|
|
.RS 10
|
|
.LP
|
|
a 1-byte flag field, containing a direction flag in the uppermost bit,
|
|
which is set for packets transmitted by the machine and clear for
|
|
packets received by the machine, and a 4-byte traffic type in the
|
|
low-order 4 bits, which is one of:
|
|
.RS 5
|
|
.TP 5
|
|
0
|
|
raw traffic
|
|
.TP 5
|
|
1
|
|
LANE traffic
|
|
.TP 5
|
|
2
|
|
LLC-encapsulated traffic
|
|
.TP 5
|
|
3
|
|
MARS traffic
|
|
.TP 5
|
|
4
|
|
IFMP traffic
|
|
.TP 5
|
|
5
|
|
ILMI traffic
|
|
.TP 5
|
|
6
|
|
Q.2931 traffic
|
|
.RE
|
|
.LP
|
|
a 1-byte VPI value;
|
|
.LP
|
|
a 2-byte VCI field, in network byte order.
|
|
.RE
|
|
.TP 5
|
|
.B DLT_IEEE802_11_RADIO
|
|
link-layer information followed by an 802.11 header - see
|
|
http://www.shaftnet.org/~pizza/software/capturefrm.txt for a description
|
|
of the link-layer information.
|
|
.TP 5
|
|
.B DLT_ARCNET_LINUX
|
|
ARCNET, with no exception frames, reassembled packets rather than raw
|
|
frames, and an extra 16-bit offset field between the destination host
|
|
and type bytes.
|
|
.TP 5
|
|
.B DLT_LINUX_IRDA
|
|
Linux-IrDA packets, with a
|
|
.B DLT_LINUX_SLL
|
|
header followed by the IrLAP header.
|
|
.TP 5
|
|
.B DLT_LINUX_LAPD
|
|
LAPD (Q.921) frames, with a
|
|
.B DLT_LINUX_SLL
|
|
header captured via vISDN.
|
|
.RE
|
|
.PP
|
|
.B pcap_list_datalinks()
|
|
is used to get a list of the supported data link types of the interface
|
|
associated with the pcap descriptor.
|
|
.B pcap_list_datalinks()
|
|
allocates an array to hold the list and sets
|
|
.IR *dlt_buf .
|
|
The caller is responsible for freeing the array.
|
|
.B \-1
|
|
is returned on failure;
|
|
otherwise, the number of data link types in the array is returned.
|
|
.PP
|
|
.B pcap_set_datalink()
|
|
is used to set the current data link type of the pcap descriptor
|
|
to the type specified by
|
|
.IR dlt .
|
|
.B \-1
|
|
is returned on failure.
|
|
.PP
|
|
.B pcap_datalink_name_to_val()
|
|
translates a data link type name, which is a
|
|
.B DLT_
|
|
name with the
|
|
.B DLT_
|
|
removed, to the corresponding data link type value. The translation
|
|
is case-insensitive.
|
|
.B \-1
|
|
is returned on failure.
|
|
.PP
|
|
.B pcap_datalink_val_to_name()
|
|
translates a data link type value to the corresponding data link type
|
|
name. NULL is returned on failure.
|
|
.PP
|
|
.B pcap_datalink_val_to_description()
|
|
translates a data link type value to a short description of that data
|
|
link type. NULL is returned on failure.
|
|
.PP
|
|
.B pcap_list_datalinks()
|
|
is used to get a list of the supported data link types of the interface
|
|
associated with the pcap descriptor.
|
|
.B pcap_list_datalinks()
|
|
allocates an array to hold the list and sets
|
|
.IR *dlt_buf .
|
|
The caller is responsible for freeing the array.
|
|
.B \-1
|
|
is returned on failure;
|
|
otherwise, the number of data link types in the array is returned.
|
|
.PP
|
|
.B pcap_set_datalink()
|
|
is used to set the current data link type of the pcap descriptor
|
|
to the type specified by
|
|
.IR dlt .
|
|
.B \-1
|
|
is returned on failure.
|
|
.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 file format of the savefile;
|
|
.B pcap_minor_version()
|
|
returns the minor number of the file format of the savefile. The
|
|
version number is stored in the header of the savefile.
|
|
.PP
|
|
.B pcap_file()
|
|
returns the standard I/O stream of the ``savefile,'' if a ``savefile''
|
|
was opened with
|
|
.BR pcap_open_offline() ,
|
|
or NULL, if a network device was opened with
|
|
.BR pcap_open_live() .
|
|
.PP
|
|
.B pcap_stats()
|
|
returns 0 and fills in the
|
|
.B pcap_stat
|
|
structure pointed to by its second argument. 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
|
|
.B pcap_perror()
|
|
or
|
|
.BR pcap_geterr() .
|
|
.B pcap_stats()
|
|
is supported only on live captures, not on ``savefiles''; no statistics
|
|
are stored in ``savefiles'', so no statistics are available when reading
|
|
from a ``savefile''.
|
|
.PP
|
|
.B pcap_fileno()
|
|
returns the file descriptor number from which captured packets are read,
|
|
if a network device was opened with
|
|
.BR pcap_open_live() ,
|
|
or \-1, if a ``savefile'' was opened with
|
|
.BR pcap_open_offline() .
|
|
.PP
|
|
.B pcap_get_selectable_fd()
|
|
returns, on UNIX, a file descriptor number for a file descriptor on
|
|
which one can
|
|
do a
|
|
.B select()
|
|
or
|
|
.B poll()
|
|
to wait for it to be possible to read packets without blocking, if such
|
|
a descriptor exists, or \-1, if no such descriptor exists. Some network
|
|
devices opened with
|
|
.B pcap_open_live()
|
|
do not support
|
|
.B select()
|
|
or
|
|
.B poll()
|
|
(for example, regular network devices on FreeBSD 4.3 and 4.4, and Endace
|
|
DAG devices), so \-1 is returned for those devices.
|
|
.PP
|
|
Note that on most versions of most BSDs (including Mac OS X)
|
|
.B select()
|
|
and
|
|
.B poll()
|
|
do not work correctly on BPF devices;
|
|
.B pcap_get_selectable_fd()
|
|
will return a file descriptor on most of those versions (the exceptions
|
|
being FreeBSD 4.3 and 4.4), a simple
|
|
.B select()
|
|
or
|
|
.B poll()
|
|
will not return even after a timeout specified in
|
|
.B pcap_open_live()
|
|
expires. To work around this, an application that uses
|
|
.B select()
|
|
or
|
|
.B poll()
|
|
to wait for packets to arrive must put the
|
|
.B pcap_t
|
|
in non-blocking mode, and must arrange that the
|
|
.B select()
|
|
or
|
|
.B poll()
|
|
have a timeout less than or equal to the timeout specified in
|
|
.BR pcap_open_live() ,
|
|
and must try to read packets after that timeout expires, regardless of
|
|
whether
|
|
.B select()
|
|
or
|
|
.B poll()
|
|
indicated that the file descriptor for the
|
|
.B pcap_t
|
|
is ready to be read or not. (That workaround will not work in FreeBSD
|
|
4.3 and later; however, in FreeBSD 4.6 and later,
|
|
.B select()
|
|
and
|
|
.B poll()
|
|
work correctly on BPF devices, so the workaround isn't necessary,
|
|
although it does no harm.)
|
|
.PP
|
|
.B pcap_get_selectable_fd()
|
|
is not available on Windows.
|
|
.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.
|
|
.BR NOTE :
|
|
the pointer it returns will no longer point to a valid error message
|
|
string after the
|
|
.B pcap_t
|
|
passed to it is closed; you must use or copy the string before closing
|
|
the
|
|
.BR pcap_t .
|
|
.PP
|
|
.B pcap_strerror()
|
|
is provided in case
|
|
.BR strerror (1)
|
|
isn't available.
|
|
.PP
|
|
.B pcap_lib_version()
|
|
returns a pointer to a string giving information about the version of
|
|
the libpcap library being used; note that it contains more information
|
|
than just a version number.
|
|
.PP
|
|
.B pcap_close()
|
|
closes the files associated with
|
|
.I p
|
|
and deallocates resources.
|
|
.PP
|
|
.B pcap_dump_file()
|
|
returns the standard I/O stream of the ``savefile'' opened by
|
|
.BR pcap_dump_open().
|
|
.PP
|
|
.B pcap_dump_flush()
|
|
flushes the output buffer to the ``savefile,'' so that any packets
|
|
written with
|
|
.B pcap_dump()
|
|
but not yet written to the ``savefile'' will be written.
|
|
.B \-1
|
|
is returned on error, 0 on success.
|
|
.PP
|
|
.B pcap_dump_ftell()
|
|
returns the current file position for the ``savefile'', representing the
|
|
number of bytes written by
|
|
.B pcap_dump_open()
|
|
and
|
|
.BR pcap_dump() .
|
|
.B \-1
|
|
is returned on error.
|
|
.PP
|
|
.B pcap_dump_close()
|
|
closes the ``savefile.''
|
|
.PP
|
|
.SH SEE ALSO
|
|
tcpdump(1), tcpslice(1)
|
|
.SH AUTHORS
|
|
The original authors are:
|
|
.LP
|
|
Van Jacobson,
|
|
Craig Leres and
|
|
Steven McCanne, all of the
|
|
Lawrence Berkeley National Laboratory, University of California, Berkeley, CA.
|
|
.LP
|
|
The current version is available from "The Tcpdump Group"'s Web site at
|
|
.LP
|
|
.RS
|
|
.I http://www.tcpdump.org/
|
|
.RE
|
|
.SH BUGS
|
|
Please send problems, bugs, questions, desirable enhancements, etc. to:
|
|
.LP
|
|
.RS
|
|
tcpdump-workers@tcpdump.org
|
|
.RE
|
|
.LP
|
|
Please send source code contributions, etc. to:
|
|
.LP
|
|
.RS
|
|
patches@tcpdump.org
|
|
.RE
|