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PCAP_SETNONBLOCK

Section: Misc. Reference Manual Pages (3PCAP)
Updated: 30 November 2023
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NAME

pcap_setnonblock, pcap_getnonblock - set or get the state of no-blocking mode on a capture device

SYNOPSIS

#include <pcap/pcap.h>

char errbuf[PCAP_ERRBUF_SIZE];

int pcap_setnonblock(pcap_t *p, int nonblock, char *errbuf);
int pcap_getnonblock(pcap_t *p, char *errbuf);

DESCRIPTION

pcap_setnonblock() puts a capture handle into ``no-blocking'' mode, or takes it out of ``no-blocking'' mode, depending on whether the nonblock argument is no-zero or zero. It has no effect on ``savefiles''. errbuf is a buffer large enough to hold at least PCAP_ERRBUF_SIZE chars.

In ``no-blocking'' mode, an attempt to read from the capture descriptor with pcap_dispatch(3PCAP) and pcap_next_ex(3PCAP) will, if no packets are currently available to be read, return 0 immediately rather than blocking waiting for packets to arrive.

pcap_loop(3PCAP) will loop forever, consuming CPU time when no packets are currently available; pcap_dispatch() should be used instead. pcap_next(3PCAP) will return NULL if there are no packets currently available to read; this is indistinguishable from an error, so pcap_next_ex() should be used instead.

When first activated with pcap_activate(3PCAP) or opened with pcap_open_live(3PCAP), a capture handle is not in ``no-blocking mode''; a call to pcap_setnonblock() is required in order to put it into ``no-blocking'' mode.

RETURN VALUE

pcap_setnonblock() return 0 on success, PCAP_ERROR_NOT_ACTIVATED if called on a capture handle that has been created but not activated, and PCAP_ERROR for other errors. pcap_getnonblock() returns the current ``no-blocking'' state of the capture descriptor on success; it always returns 0 on ``savefiles''. It returns PCAP_ERROR_NOT_ACTIVATED if called on a capture handle that has been created but not activated, and PCAP_ERROR for other errors. If PCAP_ERROR is returned, errbuf is filled in with an appropriate error message.