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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | SEE ALSO | COLOPHON |
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(), or pcap_dispatch(); 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() routine when handed the pcap_t value also
passed to pcap_loop() or pcap_dispatch().
http://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() 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 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, -1 if an error occurred while reading the packet,
and -2 if packets are being read from a ``savefile'' and there are no
more packets to read from the savefile. If -1 is returned,
pcap_geterr() or pcap_perror() 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), pcap_geterr(3PCAP), pcap_dispatch(3PCAP),
pcap_datalink(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 2017-07-05. 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 man-pages@man7.org
20 January 2017 PCAP_NEXT_EX(3PCAP)