Add --no-shutdown option.
#151
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This option solves issue nmap#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.
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@dmiller-nmap @bonsaiviking Gentle bump on this. Any feedback? |
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@d33tah would you and @andrewfarabee be willing to analyze this PR in light of #142? |
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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. |
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@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? |
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Yeah, that's right, sorry I missed that. On Tue, Jun 30, 2015 at 1:08 PM, Jacek Wielemborek <notifications@github.com
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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. |
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
-doption. The-doption itself prevents a bug affectingsome 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.