Summary: Option to set SO_KEEPALIVE.
Contributor: Wes Chow <wes@senortoad.com>

Index: netcat-1.10/netcat.c
===================================================================
--- netcat-1.10.orig/netcat.c	2007-03-29 13:36:07.000000000 -0400
+++ netcat-1.10/netcat.c	2007-03-29 13:36:15.000000000 -0400
@@ -178,6 +178,7 @@
 unsigned int o_wait = 0;
 USHORT o_zero = 0;
 int o_quit = -1; /* 0 == quit-now; >0 == quit after o_quit seconds */
+int o_keepalive = 0;
 #ifdef IP_TOS
 unsigned char o_tos = 0;
 #endif
@@ -682,6 +683,13 @@
     holler ("nnetfd tos failed");		/* ??? */
   }
 #endif
+  if (o_keepalive) {
+    x = 1;
+    rr = setsockopt(nnetfd, SOL_SOCKET, SO_KEEPALIVE, &x, sizeof(x));
+    if (rr == -1) {
+      holler("nnetfd set keepalive failed");
+    }
+  }
 #if 0
 /* If you want to screw with RCVBUF/SNDBUF, do it here.  Liudvikas Bukys at
    Rochester sent this example, which would involve YET MORE options and is
@@ -1501,7 +1509,7 @@
 
 /* If your shitbox doesn't have getopt, step into the nineties already. */
 /* optarg, optind = next-argv-component [i.e. flag arg]; optopt = last-char */
-  while ((x = getopt (argc, argv, "abc:e:g:G:hi:lno:p:q:rs:T:tuvw:z")) != EOF) {
+  while ((x = getopt (argc, argv, "abc:e:g:G:hi:klno:p:q:rs:T:tuvw:z")) != EOF) {
 /* Debug (("in go: x now %c, optarg %x optind %d", x, optarg, optind)) */
     switch (x) {
       case 'a':
@@ -1548,6 +1556,8 @@
 	if (! o_interval)
 	  bail ("invalid interval time %s", optarg);
 	break;
+    case 'k':
+        o_keepalive = 1; break;
       case 'l':				/* listen mode */
 	o_listen++; break;
       case 'n':				/* numeric-only, no DNS lookups */
@@ -1800,6 +1810,7 @@
 	-G num			source-routing pointer: 4, 8, 12, ...\n\
 	-h			this cruft\n\
 	-i secs			delay interval for lines sent, ports scanned\n\
+        -k                      set keepalive option on socket\n\
 	-l			listen mode, for inbound connects\n\
 	-n			numeric-only IP addresses, no DNS\n\
 	-o file			hex dump of traffic\n\