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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | SEE ALSO | COLOPHON |
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PCAP_NEXT_EX(3PCAP) PCAP_NEXT_EX(3PCAP)
pcap_next_ex, pcap_next - read the next packet from a pcap_t
#include <pcap/pcap.h>
int pcap_next_ex(pcap_t *p, struct pcap_pkthdr **pkt_header,
const u_char **pkt_data);
const u_char *pcap_next(pcap_t *p, struct pcap_pkthdr *h);
pcap_next_ex() reads the next packet and returns a
success/failure indication. If the packet was read without
problems, the pointer pointed to by the pkt_header argument is
set to point to the pcap_pkthdr struct for the packet, and the
pointer pointed to by the pkt_data argument is set to point to
the data in the packet. The struct pcap_pkthdr and the packet
data are not to be freed by the caller, and are not guaranteed to
be valid after the next call to pcap_next_ex(), pcap_next(),
pcap_loop(3PCAP), or pcap_dispatch(3PCAP); if the code needs them
to remain valid, it must make a copy of them.
pcap_next() reads the next packet (by calling pcap_dispatch()
with a cnt of 1) and returns a u_char pointer to the data in that
packet. The packet data is not to be freed by the caller, and is
not guaranteed to be valid after the next call to pcap_next_ex(),
pcap_next(), pcap_loop(), or pcap_dispatch(); if the code needs
it to remain valid, it must make a copy of it. The pcap_pkthdr
structure pointed to by h is filled in with the appropriate
values for the packet.
The bytes of data from the packet begin with a link-layer header.
The format of the link-layer header is indicated by the return
value of the pcap_datalink(3PCAP) routine when handed the pcap_t
value also passed to pcap_loop() or pcap_dispatch().
https://www.tcpdump.org/linktypes.html lists the values
pcap_datalink() can return and describes the packet formats that
correspond to those values. The value it returns will be valid
for all packets received unless and until
pcap_set_datalink(3PCAP) is called; after a successful call to
pcap_set_datalink(), all subsequent packets will have a link-
layer header of the type specified by the link-layer header type
value passed to pcap_set_datalink().
Do NOT assume that the packets for a given capture or
``savefile`` will have any given link-layer header type, such as
DLT_EN10MB for Ethernet. For example, the "any" device on Linux
will have a link-layer header type of DLT_LINUX_SLL or
DLT_LINUX_SLL2 even if all devices on the system at the time the
"any" device is opened have some other data link type, such as
DLT_EN10MB for Ethernet.
pcap_next_ex() returns 1 if the packet was read without problems,
0 if packets are being read from a live capture and the packet
buffer timeout expired, PCAP_ERROR_BREAK if packets are being
read from a ``savefile'' and there are no more packets to read
from the savefile, PCAP_ERROR_NOT_ACTIVATED if called on a
capture handle that has been created but not activated, or
PCAP_ERROR if an error occurred while reading the packet. If
PCAP_ERROR is returned, pcap_geterr(3PCAP) or pcap_perror(3PCAP)
may be called with p as an argument to fetch or display the error
text.
pcap_next() returns a pointer to the packet data on success, and
returns NULL if an error occurred, 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 packet buffer 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 occurred or not.
pcap(3PCAP)
This page is part of the libpcap (packet capture library)
project. Information about the project can be found at
⟨http://www.tcpdump.org/⟩. If you have a bug report for this
manual page, see ⟨http://www.tcpdump.org/#patches⟩. This page
was obtained from the project's upstream Git repository
⟨https://github.com/the-tcpdump-group/libpcap.git⟩ on 2024-06-14.
(At that time, the date of the most recent commit that was found
in the repository was 2024-06-04.) If you discover any rendering
problems in this HTML version of the page, or you believe there
is a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
[email protected]
5 March 2022 PCAP_NEXT_EX(3PCAP)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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