pcap_next_ex(3pcap) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | SEE ALSO | COLOPHON

PCAP_NEXT_EX(3PCAP)                                  PCAP_NEXT_EX(3PCAP)

NAME         top

       pcap_next_ex, pcap_next - read the next packet from a pcap_t

SYNOPSIS         top

       #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);

DESCRIPTION         top

       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.

RETURN VALUE         top

       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 if an error occurred while
       reading the packet, and PCAP_ERROR_BREAK if packets are being
       read from a ``savefile'' and there are no more packets to read
       from the savefile.  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.

SEE ALSO         top

       pcap(3PCAP)

COLOPHON         top

       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 2021-08-27.
       (At that time, the date of the most recent commit that was found
       in the repository was 2021-08-17.)  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

                              25 July 2018           PCAP_NEXT_EX(3PCAP)