pcap_setnonblock.3pcap - Man Page

set or get the state of non-blocking mode on a capture device


#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);


pcap_setnonblock() puts a capture handle into “non-blocking” mode, or takes it out of “non-blocking” mode, depending on whether the nonblock argument is non-zero or zero.  It has no effect on “savefiles”. If there is an error, PCAP_ERROR is returned and errbuf is filled in with an appropriate error message; otherwise, 0 is returned.

In “non-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 “non-blocking mode”; a call to pcap_setnonblock() is required in order to put it into “non-blocking” mode.

Return Value

pcap_getnonblock() returns the current “non-blocking” state of the capture descriptor; it always returns 0 on “savefiles”. If called on a capture handle that has been created but not activated, PCAP_ERROR_NOT_ACTIVATED is returned. If there is another error, PCAP_ERROR is returned and errbuf is filled in with an appropriate error message.

errbuf is assumed to be able to hold at least PCAP_ERRBUF_SIZE chars.

See Also

pcap(3PCAP), pcap_next_ex(3PCAP), pcap_geterr(3PCAP)

Referenced By

The man page pcap_getnonblock.3pcap(3) is an alias of pcap_setnonblock.3pcap(3).

5 March 2022