NAME

       pcap_next_ex, pcap_next - read the next packet from a pcap_t

SYNOPSIS

       #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

       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.

RETURN VALUE

       pcap_next_ex() returns 1 if the packet was read without problems, 0 if packets are being read from a live
       capture and the 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 read 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

       pcap(3PCAP), pcap_geterr(3PCAP), pcap_dispatch(3PCAP), pcap_datalink(3PCAP)

                                                  7 April 2014                               PCAP_NEXT_EX(3PCAP)