.\" @(#) $Header: /tcpdump/master/libpcap/pcap_loop.3pcap,v 1.1.2.3 2008-04-06 03:21:56 guy Exp $ .\" .\" Copyright (c) 1994, 1996, 1997 .\" The Regents of the University of California. All rights reserved. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that: (1) source code distributions .\" retain the above copyright notice and this paragraph in its entirety, (2) .\" distributions including binary code include the above copyright notice and .\" this paragraph in its entirety in the documentation or other materials .\" provided with the distribution, and (3) all advertising materials mentioning .\" features or use of this software display the following acknowledgement: .\" ``This product includes software developed by the University of California, .\" Lawrence Berkeley Laboratory and its contributors.'' Neither the name of .\" the University nor the names of its contributors may be used to endorse .\" or promote products derived from this software without specific prior .\" written permission. .\" THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED .\" WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF .\" MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. .\" .TH PCAP_LOOP 3PCAP "5 April 2008" .SH NAME pcap_loop, pcap_dispatch \- process packets from a live capture or savefile .SH SYNOPSIS .nf .ft B #include .ft .LP .ft B typedef void (*pcap_handler)(u_char *user, const struct pcap_pkthdr *h, .ti +8 const u_char *bytes); .ft .LP .ft B int pcap_loop(pcap_t *p, int cnt, .ti +8 pcap_handler callback, u_char *user); int pcap_dispatch(pcap_t *p, int cnt, .ti +8 pcap_handler callback, u_char *user); .ft .fi .SH DESCRIPTION .B pcap_loop() processes packets from a live capture or ``savefile'' until .I cnt packets are processed, the end of the ``savefile'' is reached when reading from a ``savefile'', .B pcap_breakloop() is called, or an error occurs. It does .B not return when live read timeouts occur. A value of \-1 or 0 for .I cnt is equivalent to infinity, so that packets are processed until another ending condition occurs. .PP .B pcap_dispatch() processes packets from a live capture or ``savefile'' until .I 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'', .B pcap_breakloop() is called, or an error occurs. Thus, when doing a live capture, .I 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 .I cnt packets may be processed. A value of \-1 or 0 for .I 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''. .PP .ft B (In older versions of libpcap, the behavior when \fIcnt\fP was 0 was undefined; 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 \fIcnt\fP.) .ft R .PP .I callback specifies a routine to be called with three arguments: a .I u_char pointer which is passed in the .I user argument to .B pcap_loop() or .BR pcap_dispatch() , a .I const struct pcap_pkthdr pointer pointing to the packet time stamp and lengths, and a .I const u_char pointer to the first .B caplen (as given in the .I struct pcap_pkthdr a pointer to which is passed to the callback routine) bytes of data from the packet. .SH RETURN VALUE .B pcap_loop() returns 0 if .I cnt is exhausted, \-1 if an error occurs, or \-2 if the loop terminated due to a call to .B pcap_breakloop() before any packets were processed. It does .B not return when live read timeouts occur; instead, it attempts to read more packets. .PP .B 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 .B pcap_breakloop() before any packets were processed. .ft B 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. .ft R .PP If \-1 is returned, .B pcap_geterr() or .B pcap_perror() may be called with .I p as an argument to fetch or display the error text. .SH SEE ALSO pcap(3PCAP), pcap_geterr(3PCAP), pcap_breakloop(3PCAP)