Add --no-shutdown option.

[adsr]

This option solves issue #142. It prevents Ncat from putting the connection in
half-duplex mode after seeing EOF on stdin. This emulates the behavior of
OpenBSD-netcat's -d option. The -d option itself prevents a bug affecting
some versions of that program in which the sender closes the connection
prematurely upon receiving a FIN packet from a receiver.

If you'll merge this, please advise on how to regenerate docs and manpages.

[adsr]

@dmiller-nmap @bonsaiviking Gentle bump on this. Any feedback?

[dmiller-nmap]

@d33tah would you and @andrewfarabee be willing to analyze this PR in light of #142?

[jraber]

I experienced the behavior described in issue #142 in Fedora 22, using ncat 6.47, while making a systemd service that uses ncat in listen mode.

My .service file calls ncat like the below:

ExecStart = /usr/bin/bash -c "/usr/bin/ncat --recv-only -v -i 4h --allow x.x.x.x -o /var/log/somelogfile.log --append-output y.y.y.y 1234

The above command works just fine when I execute it from the command line. I was able to connect to the listening port using telnet, send data, the data is saved in the specified file, and ncat terminated when I closed the connection.

However, when started via the systemd service, it behaves differently. ncat started ok. I was able to see the process was listening for a connection on the specified port. But, when I connected to the listening port, I was immediately disconnected (telnet said 'connection closed by foreign host'), and ncat terminated with return code 0.

Using strace, I was able to see that ncat was reading 1 byte from stdin when I connected to the listening port. (By default, stdin for systemd services is connected to /dev/null). ncat then immediately shuts down the port and, since I didn't start it with --keep-open, ncat terminates.

If I include the option '--keep-open' when starting the service, the first connection attempt is immediately disconnected but all subsequent connections are successful.

I would really like to see the --no-shutdown option included. Also, it might be a good idea to include a note about this behavior in the man page under the --listen option.

[d33tah]

@andrewfarabee - adsr asked me on IRC if we have plans to take up this ticket. For now we agreed that we'll work on socks4a, is that right?

[andrewfarabee]

Yeah, that's right, sorry I missed that.

On Tue, Jun 30, 2015 at 1:08 PM, Jacek Wielemborek <notifications@github.com

wrote:

@andrewfarabee https://github.com/andrewfarabee - adsr asked me on IRC
if we have plans to take up this ticket. For now we agreed that we'll work
on socks4a, is that right?

—
Reply to this email directly or view it on GitHub
#151 (comment).

[cskeeters]

I'm using a version of ncat that doesn't support the --no-shutdown option. Instead of closing stdin I used "--recv-only" and "< /dev/zero" to prevent EOF from shutting ncat down. The zero byte read from stdin doesn't seem to be used for anything.