netcat -q option doesn't work

-kc- · 06-24-2007, 01:18 PM

netcat -q option either doesn't work for me or I got it wrong:
from man 1:
-q seconds after EOF is detected, wait the specified number of seconds and then quit.

Code:

$ nc -lp 9999 <bigfile &
$ nc localhost 9999 -q seconds </dev/null

Both exit in a fraction of second, and I get always the same (small) amount of bigfile on the client side, no matter what number of seconds I use.
What does that number mean? Shouldn't it have the same effect as this one?

Code:

$ nc -lp 9999 <bigfile &
$ sleep seconds | nc localhost 9999 -q 0

This is for version 1.10-21 and 1.10-33 on Slackware 10.2.
GNU and OpenBSD netcat as well as the original nc 1.10, don't have a -q option.

thanks
kc

namit · 06-24-2007, 08:00 PM

is this not a -Q ?

-kc- · 06-25-2007, 04:32 PM

I'm afraid not:
nc: invalid option -- Q
nc -h for help

Anyone know who's the maintainer of the patch for the -q option? Slackware and Debian distribute the patched version. Here's some code from the patch:

Code:

int o_quit = -1; /* 0 == quit-now; >0 == quit after o_quit seconds */
[...]
/* quit :
   handler for a "-q" timeout (exit 0 instead of 1) */
void quit()
{
  close(netfd);
  exit(0);
}
[...]
/* if the user asked to exit on EOF, do it */
if (o_quit == 0) {
  shutdown(netfd, 1);
  close (fd);
  exit (0);
}
/* if user asked to die after a while, arrange for it */
if (o_quit > 0) {
  shutdown(netfd, 1);
  signal (SIGALRM, quit);
  alarm(o_quit);
}
[...]
case 'q':				/* quit after stdin does EOF */
 o_quit = atoi(optarg); break;

thanks
kc

nx5000 · 06-25-2007, 04:50 PM

http://packages.debian.org/changelog...0-33/changelog

From the code it looks like when EOF is reached,
if -q is given, close quickly the socket (shutdown method)
then wait for the time given and close cleanly the socket (close method)

Never saw this option!

nx5000 · 06-26-2007, 10:33 AM

I tried it and as you said, it doesn't change anything.
Quite obscure option.

-kc- · 06-30-2007, 08:44 AM

Thanks nx5000,
any idea on what can be the purpose of close quickly the socket, then wait for the time given and close cleanly?

Many pages I found about netcat have examples with the -q option followed by a small delay, but none of them explain the purpose of the delay. Maybe if you don't know what it is, then you don't need it, but then why not just use q 0 combined with a sleep?

nx5000 · 07-03-2007, 04:43 PM

The question is why use shutdown() rather than close().
Unfortunatly the last time I used this shutdown function was a long time ago.
Maybe to reconnect from the same source X port on host A to the same destination port Y on host B, to avoid TIME_WAIT state.
But this is pure speculation...