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.TH PCAP_SETNONBLOCK 3PCAP "5 March 2022"
.SH NAME
pcap_setnonblock, pcap_getnonblock \- set or get the state of
non-blocking mode on a capture device
.SH SYNOPSIS
.nf
.ft B
#include <pcap/pcap.h>
.ft
.LP
.nf
.ft B
char errbuf[PCAP_ERRBUF_SIZE];
.ft
.LP
.ft B
int pcap_setnonblock(pcap_t *p, int nonblock, char *errbuf);
int pcap_getnonblock(pcap_t *p, char *errbuf);
.ft
.fi
.SH DESCRIPTION
.BR pcap_setnonblock ()
puts a capture handle into ``non-blocking'' mode, or takes it out
of ``non-blocking'' mode, depending on whether the
.I nonblock
argument is non-zero or zero.  It has no effect on ``savefiles''.
If there is an error,
.B PCAP_ERROR
is returned and
.I errbuf
is filled in with an appropriate error message; otherwise,
.B 0
is returned.
.PP
In
``non-blocking'' mode, an attempt to read from the capture descriptor
with
.BR pcap_dispatch (3PCAP)
and
.BR pcap_next_ex (3PCAP)
will, if no packets are currently available to be read, return
.B 0
immediately rather than blocking waiting for packets to arrive.
.PP
.BR pcap_loop (3PCAP)
will loop forever, consuming CPU time when no packets are currently
available;
.BR pcap_dispatch ()
should be used instead.
.BR pcap_next (3PCAP)
will return
.B NULL
if there are no packets currently available to read;
this is indistinguishable from an error, so
.BR pcap_next_ex ()
should be used instead.
.PP
When first activated with
.BR pcap_activate (3PCAP)
or opened with
.BR pcap_open_live (3PCAP) ,
a capture handle is not in ``non-blocking mode''; a call to
.BR pcap_setnonblock ()
is required in order to put it into ``non-blocking'' mode.
.SH RETURN VALUE
.BR pcap_getnonblock ()
returns the current ``non-blocking'' state of the capture descriptor; it
always returns
.B 0
on ``savefiles''.
If called on a capture handle that has been created but not activated,
.B PCAP_ERROR_NOT_ACTIVATED
is returned.
If there is another error,
.B PCAP_ERROR
is returned and
.I errbuf
is filled in with an appropriate error message.
.PP
.I errbuf
is assumed to be able to hold at least
.B PCAP_ERRBUF_SIZE
chars.
.SH SEE ALSO
.BR pcap (3PCAP),
.BR pcap_next_ex (3PCAP),
.BR pcap_geterr (3PCAP)