Re: ncat behaviour - questions

[David Fifield <david () bamsoftware com>]

On Mon, Jan 14, 2013 at 02:53:11PM +0100, Michal Hlavinka wrote:
> I just found that ncat does not behave the way I'd expect.
>
> Make it listen for udp connection:
> ncat -l -u 1234 </dev/null
>
> and send "Hello":
> echo "Hello" | ncat -u localhost 1234
>
> The result is that listening ncat waits for the "Hello" message and
> when it comes, it terminates and prints nothing.
>
> In ncat_listen_dgram it select()s change on socket descriptor and
> after a few checks it goes to
> """/* stdin -> socket and socket -> stdout */""""
> while loop. Where it checks stdin first and finding it closed, it
> terminates. I'm not sure what is intended behaviour, but I guess it
> should print the message since it's waiting for it.

I think this behavior is right. Arguably the program should quit
immediately upon startup since its input is closed. I would accept a
patch to do that.

> And another question. Our QA engineers use netcat in their tests and
> one use case is to wait for connection for some time and then
> terminate.
>
> In old netcat there's -w option which has the same behaviour like
> the -i in ncat. Unfortunately, -i can't be used together with -l (it
> prints error message). Why is it that way? Is it just that nobody
> wrote the code or is there any other reason why it can't be used
> together?

My guess is that it is just not implemented.

David Fifield
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