pcap_dispatch man page on FreeBSD

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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 routine to	be  called  with  three	 arguments:  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)

				 5 April 2008			  PCAP_LOOP(3)
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