Updated: 2025/Nov/16

Please read Privacy Policy. It's for your privacy.

PCAP_SETNONBLOCK(3)        Library Functions Manual        PCAP_SETNONBLOCK(3)

NAME
       pcap_setnonblock, pcap_getnonblock - set or get the state of non-
       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 ``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''.  errbuf is a buffer large enough to hold at least
       PCAP_ERRBUF_SIZE chars.

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

       pcap_loop(3) will loop forever, consuming CPU time when no packets are
       currently available; pcap_dispatch() should be used instead.
       pcap_next(3) 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(3) or opened with
       pcap_open_live(3), 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_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
       ``non-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.

SEE ALSO
       pcap(3), pcap_next_ex(3), pcap_geterr(3)

                               30 November 2023            PCAP_SETNONBLOCK(3)