pcap.3

Windows XP下的抓包程序实现

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.TH PCAP 3 "27 February 2004"
.SH NAME
pcap \- Packet Capture library
.SH SYNOPSIS
.nf
.ft B
#include <pcap.h>
.ft
.LP
.nf
.ft B
char errbuf[PCAP_ERRBUF_SIZE];
.ft
.LP
.ft B
pcap_t *pcap_open_live(const char *device, int snaplen,
.ti +8
int promisc, int to_ms, char *errbuf)
pcap_t *pcap_open_dead(int linktype, int snaplen)
pcap_t *pcap_open_offline(const char *fname, char *errbuf)
pcap_t *pcap_fopen_offline(FILE *fp, char *errbuf)
pcap_dumper_t *pcap_dump_open(pcap_t *p, const char *fname)
pcap_dumper_t *pcap_dump_fopen(pcap_t *p, FILE *fp)
.ft
.LP
.ft B
int pcap_setnonblock(pcap_t *p, int nonblock, char *errbuf);
int pcap_getnonblock(pcap_t *p, char *errbuf);
.ft
.LP
.ft B
int pcap_findalldevs(pcap_if_t **alldevsp, char *errbuf)
void pcap_freealldevs(pcap_if_t *alldevs)
char *pcap_lookupdev(char *errbuf)
int pcap_lookupnet(const char *device, bpf_u_int32 *netp,
.ti +8
bpf_u_int32 *maskp, char *errbuf)
.ft
.LP
.ft B
typedef void (*pcap_handler)(u_char *user, const struct pcap_pkthdr *h,
.ti +8
			     const u_char *bytes);
.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_compile(pcap_t *p, struct bpf_program *fp,
.ti +8
char *str, int optimize, bpf_u_int32 netmask)
int pcap_setfilter(pcap_t *p, struct bpf_program *fp)
void pcap_freecode(struct bpf_program *)
int pcap_setdirection(pcap_t *p, pcap_direction_t d)
.ft
.LP
.ft B
const u_char *pcap_next(pcap_t *p, struct pcap_pkthdr *h)
int pcap_next_ex(pcap_t *p, struct pcap_pkthdr **pkt_header,
.ti +8
const u_char **pkt_data)
.ft
.LP
.ft B
void pcap_breakloop(pcap_t *)
.ft
.LP
.ft B
int pcap_inject(pcap_t *p, const void *buf, size_t size)
int pcap_sendpacket(pcap_t *p, const u_char *buf, int size)
.ft
.LP
.ft B
int pcap_datalink(pcap_t *p)
int pcap_list_datalinks(pcap_t *p, int **dlt_buf);
int pcap_set_datalink(pcap_t *p, int dlt);
int pcap_datalink_name_to_val(const char *name);
const char *pcap_datalink_val_to_name(int dlt);
const char *pcap_datalink_val_to_description(int dlt);
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, char *prefix)
char *pcap_geterr(pcap_t *p)
char *pcap_strerror(int error)
const char *pcap_lib_version(void)
.ft
.LP
.ft B
void pcap_close(pcap_t *p)
int pcap_dump_flush(pcap_dumper_t *p)
long pcap_dump_ftell(pcap_dumper_t *p)
FILE *pcap_dump_file(pcap_dumper_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
NOTE:
.I errbuf
in
.BR pcap_open_live() ,
.BR pcap_open_dead() ,
.BR pcap_open_offline() ,
.BR pcap_fopen_offline() ,
.BR pcap_setnonblock() ,
.BR pcap_getnonblock() ,
.BR pcap_findalldevs() ,
.BR pcap_lookupdev() ,
and
.B pcap_lookupnet()
is assumed to be able to hold at least
.B PCAP_ERRBUF_SIZE
chars.
.PP
.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; on Linux systems
with 2.2 or later kernels, a
.I device
argument of "any" or
.B NULL
can be used to capture packets from all interfaces.
.I snaplen
specifies the maximum number of bytes to capture.  If this value is less
than the size of a packet that is captured, only the first
.I snaplen
bytes of that packet will be captured and provided as packet data.  A
value of 65535 should be sufficient, on most if not all networks, to
capture all the data available from the packet.
.I 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.)  For now, this
doesn't work on the "any" device; if an argument of "any" or NULL is
supplied, the
.I promisc
flag is ignored.
.I to_ms
specifies the read timeout in milliseconds.  The read timeout is used to
arrange that the read not necessarily return immediately when a packet
is seen, but that it wait for some amount of time to allow more packets
to arrive and to read multiple packets from the OS kernel in one
operation.  Not all platforms support a read timeout; on platforms that
don't, the read timeout is ignored.  A zero value for
.IR to_ms ,
on platforms that support a read timeout,
will cause a read to wait forever to allow enough packets to
arrive, with no timeout.
.I errbuf
is used to return error or warning text.  It will be set to error text when
.B pcap_open_live()
fails and returns
.BR NULL .
.I errbuf
may also be set to warning text when
.B pcap_open_live()
succeds; to detect this case the caller should store a zero-length string in
.I errbuf
before calling
.B pcap_open_live()
and display the warning to the user if
.I errbuf
is no longer a zero-length string.
.PP
.B pcap_open_dead()
is used for creating a
.B pcap_t
structure to use when calling the other functions in libpcap.  It is
typically used when just using libpcap for compiling BPF code.
.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 .
Alternatively, you may call
.B pcap_fopen_offline()
to read dumped data from an existing open stream
.IR fp .
Note that on Windows, that stream should be opened in binary mode.
.I errbuf
is used to return error text and is only set when
.B pcap_open_offline()
or
.B pcap_fopen_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 stdout .
.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. Alternatively, you may call
.B pcap_dump_fopen()
to write data to an existing open stream
.IR fp .
Note that on Windows, that stream should be opened in binary mode.
If
.B NULL
is returned,
.B pcap_geterr()
can be used to get the error text.
.PP
.PP
.B pcap_setnonblock()
puts a capture descriptor, opened with
.BR pcap_open_live() ,
into ``non-blocking'' mode, or takes it out of ``non-blocking'' mode,
depending on whether the
.I nonblock
argument is non-zero or zero.  It has no effect on ``savefiles''.
If there is an error, \-1 is returned and
.I errbuf
is filled in with an appropriate error message; otherwise, 0 is
returned.
In
``non-blocking'' mode, an attempt to read from the capture descriptor
with
.B pcap_dispatch()
will, if no packets are currently available to be read, return 0
immediately rather than blocking waiting for packets to arrive.
.B pcap_loop()
and
.B pcap_next()
will not work in ``non-blocking'' mode.
.PP
.B pcap_getnonblock()
returns the current ``non-blocking'' state of the capture descriptor; it
always returns 0 on ``savefiles''.
If there is an error, \-1 is returned and
.I errbuf
is filled in with an appropriate error message.
.PP
.B pcap_findalldevs()
constructs a list of network devices that can be opened with
.BR pcap_open_live() .
(Note that there may be network devices that cannot be opened with
.BR pcap_open_live()
by the
process calling
.BR pcap_findalldevs() ,
because, for example, that process might not have sufficient privileges
to open them for capturing; if so, those devices will not appear on the
list.)
.I alldevsp
is set to point to the first element of the list; each element of the
list is of type
.BR pcap_if_t ,
and has the following members:
.RS
.TP
.B next
if not
.BR NULL ,
a pointer to the next element in the list;
.B NULL
for the last element of the list
.TP
.B name
a pointer to a string giving a name for the device to pass to
.B pcap_open_live()
.TP
.B description
if not
.BR NULL ,
a pointer to a string giving a human-readable description of the device
.TP
.B addresses
a pointer to the first element of a list of addresses for the interface
.TP
.B flags
interface flags:
.RS
.TP
.B PCAP_IF_LOOPBACK
set if the interface is a loopback interface
.RE
.RE
.PP
Each element of the list of addresses is of type
.BR pcap_addr_t ,
and has the following members:
.RS
.TP
.B next
if not
.BR NULL ,
a pointer to the next element in the list;
.B NULL
for the last element of the list
.TP
.B addr
a pointer to a
.B "struct sockaddr"
containing an address
.TP
.B netmask
if not
.BR NULL ,
a pointer to a
.B "struct sockaddr"
that contains the netmask corresponding to the address pointed to by
.B addr
.TP
.B broadaddr
if not
.BR NULL ,
a pointer to a
.B "struct sockaddr"
that contains the broadcast address corresponding to the address pointed
to by
.BR addr ;
may be null if the interface doesn't support broadcasts
.TP
.B dstaddr
if not
.BR NULL ,
a pointer to a
.B "struct sockaddr"
that contains the destination address corresponding to the address pointed
to by
.BR addr ;
may be null if the interface isn't a point-to-point interface
.RE
.PP
Note that not all the addresses in the list of addresses are
necessarily IPv4 or IPv6 addresses - you must check the
.B sa_family
member of the
.B "struct sockaddr"
before interpreting the contents of the address.
.PP
.B \-1
is returned on failure, in which case
.B errbuf
is filled in with an appropriate error message;
.B 0
is returned on success.
.PP
.B pcap_freealldevs()
is used to free a list allocated by
.BR pcap_findalldevs() .
.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 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 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''.