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NetBSD 6.1.5 - man page for pcap_loop (netbsd section 3)

PCAP_LOOP(3)									     PCAP_LOOP(3)

NAME
       pcap_loop, pcap_dispatch - process packets from a live capture or savefile

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 time-
       outs occur.  A value of -1 or 0 for cnt is equivalent to infinity,  so  that  packets  are
       processed 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  ``savefile''  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 buffer 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 undefined; different plat-
       forms and devices behaved differently, so code that must work with older versions of libp-
       cap should use -1, nor 0, as the value of cnt.)

       callback  specifies  a  pcap_handler  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 termi-
       nated 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 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.''	It returns -1 if an error
       occurs  or  -2 if the loop terminated due to a call to pcap_breakloop() before any packets
       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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