pcap_dispatch man page on NetBSD

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PCAP_LOOP(3)							  PCAP_LOOP(3)

NAME
       pcap_loop, pcap_dispatch - process packets from a live capture or save‐
       file

SYNOPSIS
       #include <pcap/pcap.h>

       typedef void (*pcap_handler)(u_char *user, const struct pcap_pkthdr *h,
				   const u_char *bytes);

       int pcap_loop(pcap_t *p, int cnt,
	       pcap_handler callback, u_char *user);
       int pcap_dispatch(pcap_t *p, int cnt,
	       pcap_handler callback, u_char *user);

DESCRIPTION
       pcap_loop() processes packets from a live capture or ``savefile'' until
       cnt  packets are processed, the end of the ``savefile'' is reached when
       reading from a ``savefile'', pcap_breakloop() is called,	 or  an	 error
       occurs.	 It does not return when live read timeouts occur.  A value of
       -1 or 0 for cnt is equivalent to infinity, so  that  packets  are  pro‐
       cessed until another ending condition occurs.

       pcap_dispatch()	processes  packets from a live capture or ``savefile''
       until cnt packets are processed, the end of the	current	 bufferful  of
       packets	is  reached  when doing a live capture, the end of the ``save‐
       file'' is reached when reading from a ``savefile'', pcap_breakloop() is
       called,	or  an	error occurs.  Thus, when doing a live capture, cnt is
       the maximum number of packets to process before returning, but is not a
       minimum	number;	 when  reading	a  live capture, only one bufferful of
       packets is read at a time, so fewer than cnt packets may be  processed.
       A  value of -1 or 0 for cnt causes all the packets received in one buf‐
       fer to be processed when reading a live capture,	 and  causes  all  the
       packets in the file to be processed when reading a ``savefile''.

       (In  older  versions  of libpcap, the behavior when cnt was 0 was unde‐
       fined; different platforms and devices  behaved	differently,  so  code
       that  must work with older versions of libpcap should use -1, nor 0, as
       the value of cnt.)

       callback specifies a pcap_handler routine to be called with three argu‐
       ments:  a  u_char  pointer  which  is  passed  in  the user argument to
       pcap_loop() or pcap_dispatch(),	a  const  struct  pcap_pkthdr  pointer
       pointing	 to  the  packet  time	stamp  and lengths, and a const u_char
       pointer to the first caplen (as	given  in  the	struct	pcap_pkthdr  a
       pointer	to which is passed to the callback routine) bytes of data from
       the packet.

RETURN VALUE
       pcap_loop() returns 0 if cnt is exhausted, -1 if an error occurs, or -2
       if  the	loop  terminated  due to a call to pcap_breakloop() before any
       packets were processed.	It does not return  when  live	read  timeouts
       occur; instead, it attempts to read more packets.

       pcap_dispatch()	returns	 the  number  of packets processed on success;
       this can be 0 if no packets were read from  a  live  capture  (if,  for
       example,	 they  were discarded because they didn't pass the packet fil‐
       ter, 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.''  It returns -1 if an error occurs or -2 if
       the  loop terminated due to a call to pcap_breakloop() before any pack‐
       ets were processed.  If your application	 uses  pcap_breakloop(),  make
       sure that you explicitly check for -1 and -2, rather than just checking
       for a return value < 0.

       If -1 is returned, pcap_geterr() or pcap_perror() may be called with  p
       as an argument to fetch or display the error text.

SEE ALSO
       pcap(3), pcap_geterr(3), pcap_breakloop(3)

			       24 December 2008			  PCAP_LOOP(3)
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