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24 .TH PCAP 3 "27 February 2004"
26 pcap \- Packet Capture library
35 char errbuf[PCAP_ERRBUF_SIZE];
39 pcap_t *pcap_open_live(const char *device, int snaplen,
41 int promisc, int to_ms, char *errbuf)
42 pcap_t *pcap_open_dead(int linktype, int snaplen)
43 pcap_t *pcap_open_offline(const char *fname, char *errbuf)
44 pcap_t *pcap_fopen_offline(FILE *fp, char *errbuf)
45 pcap_dumper_t *pcap_dump_open(pcap_t *p, const char *fname)
46 pcap_dumper_t *pcap_dump_fopen(pcap_t *p, FILE *fp)
50 int pcap_setnonblock(pcap_t *p, int nonblock, char *errbuf);
51 int pcap_getnonblock(pcap_t *p, char *errbuf);
55 int pcap_findalldevs(pcap_if_t **alldevsp, char *errbuf)
56 void pcap_freealldevs(pcap_if_t *alldevs)
57 char *pcap_lookupdev(char *errbuf)
58 int pcap_lookupnet(const char *device, bpf_u_int32 *netp,
60 bpf_u_int32 *maskp, char *errbuf)
64 typedef void (*pcap_handler)(u_char *user, const struct pcap_pkthdr *h,
68 int pcap_dispatch(pcap_t *p, int cnt,
70 pcap_handler callback, u_char *user)
71 int pcap_loop(pcap_t *p, int cnt,
73 pcap_handler callback, u_char *user)
74 void pcap_dump(u_char *user, struct pcap_pkthdr *h,
80 int pcap_compile(pcap_t *p, struct bpf_program *fp,
82 const char *str, int optimize, bpf_u_int32 netmask)
83 int pcap_setfilter(pcap_t *p, struct bpf_program *fp)
84 void pcap_freecode(struct bpf_program *)
85 int pcap_setdirection(pcap_t *p, pcap_direction_t d)
89 const u_char *pcap_next(pcap_t *p, struct pcap_pkthdr *h)
90 int pcap_next_ex(pcap_t *p, struct pcap_pkthdr **pkt_header,
92 const u_char **pkt_data)
96 void pcap_breakloop(pcap_t *)
100 int pcap_inject(pcap_t *p, const void *buf, size_t size)
101 int pcap_sendpacket(pcap_t *p, const u_char *buf, int size)
105 int pcap_datalink(pcap_t *p)
106 int pcap_list_datalinks(pcap_t *p, int **dlt_buf);
107 int pcap_set_datalink(pcap_t *p, int dlt);
108 int pcap_datalink_name_to_val(const char *name);
109 const char *pcap_datalink_val_to_name(int dlt);
110 const char *pcap_datalink_val_to_description(int dlt);
111 int pcap_snapshot(pcap_t *p)
112 int pcap_is_swapped(pcap_t *p)
113 int pcap_major_version(pcap_t *p)
114 int pcap_minor_version(pcap_t *p)
115 int pcap_stats(pcap_t *p, struct pcap_stat *ps)
116 FILE *pcap_file(pcap_t *p)
117 int pcap_fileno(pcap_t *p)
118 int pcap_get_selectable_fd(pcap_t *p);
119 void pcap_perror(pcap_t *p, char *prefix)
120 char *pcap_geterr(pcap_t *p)
121 const char *pcap_strerror(int error)
122 const char *pcap_lib_version(void)
126 void pcap_close(pcap_t *p)
127 int pcap_dump_flush(pcap_dumper_t *p)
128 long pcap_dump_ftell(pcap_dumper_t *p)
129 FILE *pcap_dump_file(pcap_dumper_t *p)
130 void pcap_dump_close(pcap_dumper_t *p)
134 The Packet Capture library
135 provides a high level interface to packet capture systems. All packets
136 on the network, even those destined for other hosts, are accessible
137 through this mechanism.
143 .BR pcap_open_live() ,
144 .BR pcap_open_dead() ,
145 .BR pcap_open_offline() ,
146 .BR pcap_fopen_offline() ,
147 .BR pcap_setnonblock() ,
148 .BR pcap_getnonblock() ,
149 .BR pcap_findalldevs() ,
150 .BR pcap_lookupdev() ,
153 is assumed to be able to hold at least
158 is used to obtain a packet capture descriptor to look
159 at packets on the network.
161 is a string that specifies the network device to open; on Linux systems
162 with 2.2 or later kernels, a
166 can be used to capture packets from all interfaces.
168 specifies the maximum number of bytes to capture. If this value is less
169 than the size of a packet that is captured, only the first
171 bytes of that packet will be captured and provided as packet data. A
172 value of 65535 should be sufficient, on most if not all networks, to
173 capture all the data available from the packet.
175 specifies if the interface is to be put into promiscuous mode.
176 (Note that even if this parameter is false, the interface
177 could well be in promiscuous mode for some other reason.) For now, this
178 doesn't work on the "any" device; if an argument of "any" or NULL is
183 specifies the read timeout in milliseconds. The read timeout is used to
184 arrange that the read not necessarily return immediately when a packet
185 is seen, but that it wait for some amount of time to allow more packets
186 to arrive and to read multiple packets from the OS kernel in one
187 operation. Not all platforms support a read timeout; on platforms that
188 don't, the read timeout is ignored. A zero value for
190 on platforms that support a read timeout,
191 will cause a read to wait forever to allow enough packets to
192 arrive, with no timeout.
194 is used to return error or warning text. It will be set to error text when
199 may also be set to warning text when
201 succeds; to detect this case the caller should store a zero-length string in
205 and display the warning to the user if
207 is no longer a zero-length string.
210 is used for creating a
212 structure to use when calling the other functions in libpcap. It is
213 typically used when just using libpcap for compiling BPF code.
215 .B pcap_open_offline()
216 is called to open a ``savefile'' for reading.
218 specifies the name of the file to open. The file has
219 the same format as those used by
223 The name "-" in a synonym for
225 Alternatively, you may call
226 .B pcap_fopen_offline()
227 to read dumped data from an existing open stream
229 Note that on Windows, that stream should be opened in binary mode.
231 is used to return error text and is only set when
232 .B pcap_open_offline()
234 .B pcap_fopen_offline()
239 is called to open a ``savefile'' for writing. The name "-" in a synonym
243 is returned on failure.
247 struct as returned by
248 .B pcap_open_offline()
250 .BR pcap_open_live() .
252 specifies the name of the file to open. Alternatively, you may call
254 to write data to an existing open stream
256 Note that on Windows, that stream should be opened in binary mode.
261 can be used to get the error text.
264 .B pcap_setnonblock()
265 puts a capture descriptor, opened with
266 .BR pcap_open_live() ,
267 into ``non-blocking'' mode, or takes it out of ``non-blocking'' mode,
268 depending on whether the
270 argument is non-zero or zero. It has no effect on ``savefiles''.
271 If there is an error, \-1 is returned and
273 is filled in with an appropriate error message; otherwise, 0 is
276 ``non-blocking'' mode, an attempt to read from the capture descriptor
279 will, if no packets are currently available to be read, return 0
280 immediately rather than blocking waiting for packets to arrive.
284 will not work in ``non-blocking'' mode.
286 .B pcap_getnonblock()
287 returns the current ``non-blocking'' state of the capture descriptor; it
288 always returns 0 on ``savefiles''.
289 If there is an error, \-1 is returned and
291 is filled in with an appropriate error message.
293 .B pcap_findalldevs()
294 constructs a list of network devices that can be opened with
295 .BR pcap_open_live() .
296 (Note that there may be network devices that cannot be opened with
300 .BR pcap_findalldevs() ,
301 because, for example, that process might not have sufficient privileges
302 to open them for capturing; if so, those devices will not appear on the
305 is set to point to the first element of the list; each element of the
308 and has the following members:
314 a pointer to the next element in the list;
316 for the last element of the list
319 a pointer to a string giving a name for the device to pass to
325 a pointer to a string giving a human-readable description of the device
328 a pointer to the first element of a list of addresses for the interface
335 set if the interface is a loopback interface
339 Each element of the list of addresses is of type
341 and has the following members:
347 a pointer to the next element in the list;
349 for the last element of the list
354 containing an address
361 that contains the netmask corresponding to the address pointed to by
369 that contains the broadcast address corresponding to the address pointed
372 may be null if the interface doesn't support broadcasts
379 that contains the destination address corresponding to the address pointed
382 may be null if the interface isn't a point-to-point interface
385 Note that not all the addresses in the list of addresses are
386 necessarily IPv4 or IPv6 addresses - you must check the
390 before interpreting the contents of the address.
393 is returned on failure, in which case
395 is filled in with an appropriate error message;
397 is returned on success.
399 .B pcap_freealldevs()
400 is used to free a list allocated by
401 .BR pcap_findalldevs() .
404 returns a pointer to a network device suitable for use with
407 .BR pcap_lookupnet() .
408 If there is an error,
412 is filled in with an appropriate error message.
415 is used to determine the network number and mask
416 associated with the network device
425 A return of \-1 indicates an error in which case
427 is filled in with an appropriate error message.
430 is used to collect and process packets.
432 specifies the maximum number of packets to process before returning.
433 This is not a minimum number; when reading a live capture, only one
434 bufferful of packets is read at a time, so fewer than
436 packets may be processed. A
438 of \-1 processes all the packets received in one buffer when reading a
439 live capture, or all the packets in the file when reading a
442 specifies a routine to be called with three arguments:
445 pointer which is passed in from
446 .BR pcap_dispatch() ,
448 .I const struct pcap_pkthdr
449 pointer to a structure with the following members:
455 containing the time when the packet was captured
460 giving the number of bytes of the packet that are available from the
466 giving the length of the packet, in bytes (which might be more than the
467 number of bytes available from the capture, if the length of the packet
468 is larger than the maximum number of bytes to capture)
476 .I struct pcap_pkthdr
477 a pointer to which is passed to the callback routine)
478 bytes of data from the packet (which won't necessarily be the entire
479 packet; to capture the entire packet, you will have to provide a value
484 that is sufficiently large to get all of the packet's data - a value of
485 65535 should be sufficient on most if not all networks).
487 The number of packets read is returned.
488 0 is returned if no packets were read from a live capture (if, for
489 example, they were discarded because they didn't pass the packet filter,
490 or if, on platforms that support a read timeout that starts before any
491 packets arrive, the timeout expires before any packets arrive, or if the
492 file descriptor for the capture device is in non-blocking mode and no
493 packets were available to be read) or if no more packets are available
494 in a ``savefile.'' A return of \-1 indicates
495 an error in which case
499 may be used to display the error text.
500 A return of \-2 indicates that the loop terminated due to a call to
502 before any packets were processed.
504 If your application uses pcap_breakloop(),
505 make sure that you explicitly check for \-1 and \-2, rather than just
506 checking for a return value < 0.
510 when reading a live capture,
512 will not necessarily return when the read times out; on some platforms,
513 the read timeout isn't supported, and, on other platforms, the timer
514 doesn't start until at least one packet arrives. This means that the
517 be used in, for example, an interactive application, to allow the packet
518 capture loop to ``poll'' for user input periodically, as there's no
521 will return after the timeout expires.
526 except it keeps reading packets until
528 packets are processed or an error occurs.
531 return when live read timeouts occur.
532 Rather, specifying a non-zero read timeout to
536 allows the reception and processing of any packets that arrive when the
542 to loop forever (or at least until an error occurs). \-1 is returned on
543 an error; 0 is returned if
545 is exhausted; \-2 is returned if the loop terminated due to a call to
547 before any packets were processed.
549 If your application uses pcap_breakloop(),
550 make sure that you explicitly check for \-1 and \-2, rather than just
551 checking for a return value < 0.
555 reads the next packet (by calling
561 pointer to the data in that packet. (The
563 struct for that packet is not supplied.)
565 is returned if an error occured, or if no packets were read from a live
566 capture (if, for example, they were discarded because they didn't pass
567 the packet filter, or if, on platforms that support a read timeout that
568 starts before any packets arrive, the timeout expires before any packets
569 arrive, or if the file descriptor for the capture device is in
570 non-blocking mode and no packets were available to be read), or if no
571 more packets are available in a ``savefile.'' Unfortunately, there is
572 no way to determine whether an error occured or not.
575 reads the next packet and returns a success/failure indication:
579 the packet was read without problems
582 packets are being read from a live capture, and the timeout expired
585 an error occurred while reading the packet
588 packets are being read from a ``savefile'', and there are no more
589 packets to read from the savefile.
592 If the packet was read without problems, the pointer pointed to by the
594 argument is set to point to the
596 struct for the packet, and the
597 pointer pointed to by the
599 argument is set to point to the data in the packet.
602 sets a flag that will force
606 to return rather than looping; they will return the number of packets
607 that have been processed so far, or \-2 if no packets have been
610 This routine is safe to use inside a signal handler on UNIX or a console
611 control handler on Windows, as it merely sets a flag that is checked
614 The flag is checked in loops reading packets from the OS - a signal by
615 itself will not necessarily terminate those loops - as well as in loops
616 processing a set of packets returned by the OS.
618 Note that if you are catching signals on UNIX systems that support
619 restarting system calls after a signal, and calling pcap_breakloop()
620 in the signal handler, you must specify, when catching those signals,
621 that system calls should NOT be restarted by that signal. Otherwise,
622 if the signal interrupted a call reading packets in a live capture,
623 when your signal handler returns after calling pcap_breakloop(), the
624 call will be restarted, and the loop will not terminate until more
625 packets arrive and the call completes.
627 Note also that, in a multi-threaded application, if one thread is
629 .BR pcap_dispatch() ,
636 in a different thread will not unblock that thread; you will need to use
637 whatever mechanism the OS provides for breaking a thread out of blocking
638 calls in order to unblock the thread, such as thread cancellation in
639 systems that support POSIX threads.
644 will, on some platforms, loop reading packets from the OS; that loop
645 will not necessarily be terminated by a signal, so
647 should be used to terminate packet processing even if
652 does not guarantee that no further packets will be processed by
656 after it is called; at most one more packet might be processed.
658 If \-2 is returned from
662 the flag is cleared, so a subsequent call will resume reading packets.
663 If a positive number is returned, the flag is not cleared, so a
664 subsequent call will return \-2 and clear the flag.
667 sends a raw packet through the network interface;
669 points to the data of the packet, including the link-layer header, and
671 is the number of bytes in the packet.
672 It returns the number of bytes written on success. A return of \-1
673 indicates an error in which case
677 may be used to display the error text.
678 Note that, even if you successfully open the network interface, you
679 might not have permission to send packets on it, or it might not support
682 doesn't have a flag to indicate whether to open for capturing, sending,
683 or capturing and sending, you cannot request an open that supports
684 sending and be notified at open time whether sending will be possible.
685 Note also that some devices might not support sending packets.
687 Note that, on some platforms, the link-layer header of the packet that's
688 sent might not be the same as the link-layer header of the packet
691 as the source link-layer address, if the header contains such an
692 address, might be changed to be the address assigned to the interface on
693 which the packet it sent, if the platform doesn't support sending
694 completely raw and unchanged packets. Even worse, some drivers on some
695 platforms might change the link-layer type field to whatever value
696 libpcap used when attaching to the device, even on platforms that
698 nominally support sending completely raw and unchanged packets.
703 but it returns 0 on success and \-1 on failure.
707 comes from WinPcap. Both are provided for compatibility.)
710 outputs a packet to the ``savefile'' opened with
711 .BR pcap_dump_open() .
712 Note that its calling arguments are suitable for use with
716 If called directly, the
721 .BR pcap_dump_open() .
724 is used to compile the string
726 into a filter program.
730 struct and is filled in by
733 controls whether optimization on the resulting code is performed.
735 specifies the IPv4 netmask of the network on which packets are being
736 captured; it is used only when checking for IPv4 broadcast addresses in
737 the filter program. If the netmask of the network on which packets are
738 being captured isn't known to the program, or if packets are being
739 captured on the Linux "any" pseudo-interface that can capture on more
740 than one network, a value of 0 can be supplied; tests for IPv4 broadcast
741 addreses won't be done correctly, but all other tests in the filter
742 program will be OK. A return of \-1 indicates an error in which case
744 may be used to display the error text.
746 .B pcap_compile_nopcap()
749 except that instead of passing a pcap structure, one passes the
750 snaplen and linktype explicitly. It is intended to be used for
751 compiling filters for direct BPF usage, without necessarily having
754 A return of \-1 indicates an error; the error text is unavailable.
755 .RB ( pcap_compile_nopcap()
757 .BR pcap_open_dead() ,
761 the latter three routines can be used directly in order to get the error
762 text for a compilation error.)
766 is used to specify a filter program.
770 struct, usually the result of a call to
773 is returned on failure, in which case
775 may be used to display the error text;
777 is returned on success.
780 is used to free up allocated memory pointed to by a
784 when that BPF program is no longer needed, for example after it
785 has been made the filter program for a pcap structure by a call to
786 .BR pcap_setfilter() .
788 .B pcap_setdirection()
789 is used to specify a direction that packets will be captured.
791 is one of the constants
797 will only capture packets received by the device,
799 will only capture packets sent by the device and
801 will capture packets received by or sent by the device.
803 is the default setting if this function is not called. This isn't
804 necessarily supported on all platforms; some platforms might return an
805 error, and some other platforms might not support
807 This operation is not supported if a ``savefile'' is being read.
809 is returned on failure,
811 is returned on success.
814 returns the link layer type; link layer types it can return include:
819 BSD loopback encapsulation; the link layer header is a 4-byte field, in
821 byte order, containing a PF_ value from
823 for the network-layer protocol of the packet.
825 Note that ``host byte order'' is the byte order of the machine on which
826 the packets are captured, and the PF_ values are for the OS of the
827 machine on which the packets are captured; if a live capture is being
828 done, ``host byte order'' is the byte order of the machine capturing the
829 packets, and the PF_ values are those of the OS of the machine capturing
830 the packets, but if a ``savefile'' is being read, the byte order and PF_
833 necessarily those of the machine reading the capture file.
836 Ethernet (10Mb, 100Mb, 1000Mb, and up)
839 IEEE 802.5 Token Ring
845 SLIP; the link layer header contains, in order:
848 a 1-byte flag, which is 0 for packets received by the machine and 1 for
849 packets sent by the machine;
851 a 1-byte field, the upper 4 bits of which indicate the type of packet,
856 an unmodified IP datagram (TYPE_IP);
859 an uncompressed-TCP IP datagram (UNCOMPRESSED_TCP), with that byte being
860 the first byte of the raw IP header on the wire, containing the
861 connection number in the protocol field;
864 a compressed-TCP IP datagram (COMPRESSED_TCP), with that byte being the
865 first byte of the compressed TCP/IP datagram header;
868 for UNCOMPRESSED_TCP, the rest of the modified IP header, and for
869 COMPRESSED_TCP, the compressed TCP/IP datagram header;
873 for a total of 16 bytes; the uncompressed IP datagram follows the header.
877 PPP; if the first 2 bytes are 0xff and 0x03, it's PPP in HDLC-like
878 framing, with the PPP header following those two bytes, otherwise it's
879 PPP without framing, and the packet begins with the PPP header.
885 RFC 1483 LLC/SNAP-encapsulated ATM; the packet begins with an IEEE 802.2
889 raw IP; the packet begins with an IP header.
892 PPP in HDLC-like framing, as per RFC 1662, or Cisco PPP with HDLC
893 framing, as per section 4.3.1 of RFC 1547; the first byte will be 0xFF
894 for PPP in HDLC-like framing, and will be 0x0F or 0x8F for Cisco PPP
898 PPPoE; the packet begins with a PPPoE header, as per RFC 2516.
901 Cisco PPP with HDLC framing, as per section 4.3.1 of RFC 1547.
904 IEEE 802.11 wireless LAN
910 OpenBSD loopback encapsulation; the link layer header is a 4-byte field, in
912 byte order, containing a PF_ value from OpenBSD's
914 for the network-layer protocol of the packet.
916 Note that, if a ``savefile'' is being read, those PF_ values are
918 necessarily those of the machine reading the capture file.
921 Linux "cooked" capture encapsulation; the link layer header contains, in
925 a 2-byte "packet type", in network byte order, which is one of:
929 packet was sent to us by somebody else
932 packet was broadcast by somebody else
935 packet was multicast, but not broadcast, by somebody else
938 packet was sent by somebody else to somebody else
941 packet was sent by us
944 a 2-byte field, in network byte order, containing a Linux ARPHRD_ value
945 for the link layer device type;
947 a 2-byte field, in network byte order, containing the length of the
948 link layer address of the sender of the packet (which could be 0);
950 an 8-byte field containing that number of bytes of the link layer header
951 (if there are more than 8 bytes, only the first 8 are present);
953 a 2-byte field containing an Ethernet protocol type, in network byte
954 order, or containing 1 for Novell 802.3 frames without an 802.2 LLC
955 header or 4 for frames beginning with an 802.2 LLC header.
959 Apple LocalTalk; the packet begins with an AppleTalk LLAP header.
962 OpenBSD pflog; the link layer header contains, in order:
965 a 1-byte header length, in host byte order;
967 a 4-byte PF_ value, in host byte order;
969 a 2-byte action code, in network byte order, which is one of:
982 a 2-byte reason code, in network byte order, which is one of:
1004 a 16-character interface name;
1006 a 16-character ruleset name (only meaningful if subrule is set);
1008 a 4-byte rule number, in network byte order;
1010 a 4-byte subrule number, in network byte order;
1012 a 1-byte direction, in network byte order, which is one of:
1016 incoming or outgoing
1027 Prism monitor mode information followed by an 802.11 header.
1030 RFC 2625 IP-over-Fibre Channel, with the link-layer header being the
1031 Network_Header as described in that RFC.
1034 SunATM devices; the link layer header contains, in order:
1037 a 1-byte flag field, containing a direction flag in the uppermost bit,
1038 which is set for packets transmitted by the machine and clear for
1039 packets received by the machine, and a 4-byte traffic type in the
1040 low-order 4 bits, which is one of:
1050 LLC-encapsulated traffic
1067 a 2-byte VCI field, in network byte order.
1070 .B DLT_IEEE802_11_RADIO
1071 link-layer information followed by an 802.11 header - see
1072 http://www.shaftnet.org/~pizza/software/capturefrm.txt for a description
1073 of the link-layer information.
1076 ARCNET, with no exception frames, reassembled packets rather than raw
1077 frames, and an extra 16-bit offset field between the destination host
1081 Linux-IrDA packets, with a
1083 header followed by the IrLAP header.
1086 LAPD (Q.921) frames, with a
1088 header captured via vISDN.
1091 .B pcap_list_datalinks()
1092 is used to get a list of the supported data link types of the interface
1093 associated with the pcap descriptor.
1094 .B pcap_list_datalinks()
1095 allocates an array to hold the list and sets
1097 The caller is responsible for freeing the array.
1099 is returned on failure;
1100 otherwise, the number of data link types in the array is returned.
1102 .B pcap_set_datalink()
1103 is used to set the current data link type of the pcap descriptor
1104 to the type specified by
1107 is returned on failure.
1109 .B pcap_datalink_name_to_val()
1110 translates a data link type name, which is a
1114 removed, to the corresponding data link type value. The translation
1115 is case-insensitive.
1117 is returned on failure.
1119 .B pcap_datalink_val_to_name()
1120 translates a data link type value to the corresponding data link type
1121 name. NULL is returned on failure.
1123 .B pcap_datalink_val_to_description()
1124 translates a data link type value to a short description of that data
1125 link type. NULL is returned on failure.
1127 .B pcap_list_datalinks()
1128 is used to get a list of the supported data link types of the interface
1129 associated with the pcap descriptor.
1130 .B pcap_list_datalinks()
1131 allocates an array to hold the list and sets
1133 The caller is responsible for freeing the array.
1135 is returned on failure;
1136 otherwise, the number of data link types in the array is returned.
1138 .B pcap_set_datalink()
1139 is used to set the current data link type of the pcap descriptor
1140 to the type specified by
1143 is returned on failure.
1146 returns the snapshot length specified when
1150 .B pcap_is_swapped()
1151 returns true if the current ``savefile'' uses a different byte order
1152 than the current system.
1154 .B pcap_major_version()
1155 returns the major number of the file format of the savefile;
1156 .B pcap_minor_version()
1157 returns the minor number of the file format of the savefile. The
1158 version number is stored in the header of the savefile.
1161 returns the standard I/O stream of the ``savefile,'' if a ``savefile''
1163 .BR pcap_open_offline() ,
1164 or NULL, if a network device was opened with
1165 .BR pcap_open_live() .
1168 returns 0 and fills in the
1170 structure pointed to by its second argument. The values represent
1171 packet statistics from the start of the run to the time of the call. If
1172 there is an error or the underlying packet capture doesn't support
1173 packet statistics, \-1 is returned and the error text can be obtained
1179 is supported only on live captures, not on ``savefiles''; no statistics
1180 are stored in ``savefiles'', so no statistics are available when reading
1181 from a ``savefile''.
1184 returns the file descriptor number from which captured packets are read,
1185 if a network device was opened with
1186 .BR pcap_open_live() ,
1187 or \-1, if a ``savefile'' was opened with
1188 .BR pcap_open_offline() .
1190 .B pcap_get_selectable_fd()
1191 returns, on UNIX, a file descriptor number for a file descriptor on
1197 to wait for it to be possible to read packets without blocking, if such
1198 a descriptor exists, or \-1, if no such descriptor exists. Some network
1205 (for example, regular network devices on FreeBSD 4.3 and 4.4, and Endace
1206 DAG devices), so \-1 is returned for those devices.
1208 Note that on most versions of most BSDs (including Mac OS X)
1212 do not work correctly on BPF devices;
1213 .B pcap_get_selectable_fd()
1214 will return a file descriptor on most of those versions (the exceptions
1215 being FreeBSD 4.3 and 4.4), a simple
1219 will not return even after a timeout specified in
1221 expires. To work around this, an application that uses
1225 to wait for packets to arrive must put the
1227 in non-blocking mode, and must arrange that the
1231 have a timeout less than or equal to the timeout specified in
1232 .BR pcap_open_live() ,
1233 and must try to read packets after that timeout expires, regardless of
1238 indicated that the file descriptor for the
1240 is ready to be read or not. (That workaround will not work in FreeBSD
1241 4.3 and later; however, in FreeBSD 4.6 and later,
1245 work correctly on BPF devices, so the workaround isn't necessary,
1246 although it does no harm.)
1248 .B pcap_get_selectable_fd()
1249 is not available on Windows.
1252 prints the text of the last pcap library error on
1258 returns the error text pertaining to the last pcap library error.
1260 the pointer it returns will no longer point to a valid error message
1263 passed to it is closed; you must use or copy the string before closing
1272 .B pcap_lib_version()
1273 returns a pointer to a string giving information about the version of
1274 the libpcap library being used; note that it contains more information
1275 than just a version number.
1278 closes the files associated with
1280 and deallocates resources.
1283 returns the standard I/O stream of the ``savefile'' opened by
1284 .BR pcap_dump_open().
1286 .B pcap_dump_flush()
1287 flushes the output buffer to the ``savefile,'' so that any packets
1290 but not yet written to the ``savefile'' will be written.
1292 is returned on error, 0 on success.
1294 .B pcap_dump_ftell()
1295 returns the current file position for the ``savefile'', representing the
1296 number of bytes written by
1301 is returned on error.
1303 .B pcap_dump_close()
1304 closes the ``savefile.''
1307 tcpdump(1), tcpslice(1)
1309 The original authors are:
1313 Steven McCanne, all of the
1314 Lawrence Berkeley National Laboratory, University of California, Berkeley, CA.
1316 The current version is available from "The Tcpdump Group"'s Web site at
1319 .I http://www.tcpdump.org/
1322 Please send problems, bugs, questions, desirable enhancements, etc. to:
1325 tcpdump-workers@tcpdump.org
1328 Please send source code contributions, etc. to:
projects / FreeBSD / releng / 7.2.git / blob