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  20 .TH PCAP_SETNONBLOCK 3PCAP "30 November 2023"
  21 .SH NAME
  22 pcap_setnonblock, pcap_getnonblock \- set or get the state of
  23 non-blocking mode on a capture device
  24 .SH SYNOPSIS
  25 .nf
  26 .ft B
  27 #include <pcap/pcap.h>
  28 .ft
  29 .LP
  30 .nf
  31 .ft B
  32 char errbuf[PCAP_ERRBUF_SIZE];
  33 .ft
  34 .LP
  35 .ft B
  36 int pcap_setnonblock(pcap_t *p, int nonblock, char *errbuf);
  37 int pcap_getnonblock(pcap_t *p, char *errbuf);
  38 .ft
  39 .fi
  40 .SH DESCRIPTION
  41 .BR pcap_setnonblock ()
  42 puts a capture handle into ``non-blocking'' mode, or takes it out
  43 of ``non-blocking'' mode, depending on whether the
  44 .I nonblock
  45 argument is non-zero or zero.  It has no effect on ``savefiles''.
  46 .I errbuf
  47 is a buffer large enough to hold at least
  48 .B PCAP_ERRBUF_SIZE
  49 chars.
  50 .PP
  51 In
  52 ``non-blocking'' mode, an attempt to read from the capture descriptor
  53 with
  54 .BR pcap_dispatch (3PCAP)
  55 and
  56 .BR pcap_next_ex (3PCAP)
  57 will, if no packets are currently available to be read, return
  58 .B 0
  59 immediately rather than blocking waiting for packets to arrive.
  60 .PP
  61 .BR pcap_loop (3PCAP)
  62 will loop forever, consuming CPU time when no packets are currently
  63 available;
  64 .BR pcap_dispatch ()
  65 should be used instead.
  66 .BR pcap_next (3PCAP)
  67 will return
  68 .B NULL
  69 if there are no packets currently available to read;
  70 this is indistinguishable from an error, so
  71 .BR pcap_next_ex ()
  72 should be used instead.
  73 .PP
  74 When first activated with
  75 .BR pcap_activate (3PCAP)
  76 or opened with
  77 .BR pcap_open_live (3PCAP),
  78 a capture handle is not in ``non-blocking mode''; a call to
  79 .BR pcap_setnonblock ()
  80 is required in order to put it into ``non-blocking'' mode.
  81 .SH RETURN VALUE
  82 .BR pcap_setnonblock()
  83 return 0 on success,
  84 .B PCAP_ERROR_NOT_ACTIVATED
  85 if called on a capture handle that has been created but not activated,
  86 and
  87 .B PCAP_ERROR
  88 for other errors.
  89 .BR pcap_getnonblock ()
  90 returns the current ``non-blocking'' state of the capture descriptor on
  91 success; it always returns
  92 .B 0
  93 on ``savefiles''.
  94 It returns
  95 .B PCAP_ERROR_NOT_ACTIVATED
  96 if called on a capture handle that has been created but not activated,
  97 and
  98 .B PCAP_ERROR
  99 for other errors.
 100 If
 101 .B PCAP_ERROR
 102 is returned,
 103 .I errbuf
 104 is filled in with an appropriate error message.
 105 .SH SEE ALSO
 106 .BR pcap (3PCAP),
 107 .BR pcap_next_ex (3PCAP),
 108 .BR pcap_geterr (3PCAP)