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(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

       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.

SEE ALSO

       pcap(3PCAP)

                                                  5 March 2022                               PCAP_NEXT_EX(3PCAP)