Re: [PATCH] [Ncat] Fix EOF handling

[Daniel Roethlisberger <daniel () roe ch>]

bensonk () acm wwu edu <bensonk () acm wwu edu> 2009-04-18:
> The standard netcat behavior as defined by the canonical
> implementation by hobbit explicitly does not halt on EOF.
> I would recommend reversing the option, and instead providing
> an option like "-q N" in gentoo's netcat.  The "-q N" option
> means "after EOF, exit after N seconds". 

I think that, in general, usefulness should supercede history.

I fail to see a use case for keeping running after EOF on the
client side.  If I want Ncat to keep receiving data, I just make
sure not to close Ncat's stdin.  By closing Ncat's stdin (^D on a
tty or close() on the fd in a shell pipe) I signal Ncat that I'm
done.  This is the Unix way of handling standard input/output,
and is what I expect from command line utilities to adhere to, in
order to be useful in constructing larger command pipes.

Do you have a use case that is better served by a -q timer than
proper EOF handling?

On the server side, there is a usefulness to keep running (i.e.
accept more connections); what should be the default is probably
a matter of taste (or typical type of workload).  Personally, I
find it more natural to exit after one connection by default.

> On Sat, Apr 18, 2009 at 08:10:23PM +0200, Daniel Roethlisberger wrote:
> > Ncat currently doesn't handle EOF events in a very intuitive way.
> > Usability for scripting mainly depends on the ability to pipe
> > into and out of Ncat:
> >
> > me@server $ ncat -l 1234 | tar xvf -
> > me@client $ tar cvf - somedir | ncat server 1234
> >
> > Currently, this does not work as expected, neither in the client
> > nor in the server.
> >
> > In connect mode, EOF on standard input does not cause Ncat to
> > exit.  `cat file | ncat somewhere 1234' will keep running forever
> > until Ncat receives a SIGINT.  To be suitable for scripting, Ncat
> > must exit after EOF on stdin.
> >
> > In listen mode, closing the TCP connection on the client side
> > does not cause Ncat to flush stdout and exit, because Ncat is
> > waiting for other connections.  SIGINT does not help here,
> > because Ncat will not write the remaining buffered bytes to
> > stdout in that case, so a received file will have some missing
> > bytes at the end.
> >
> > Cince this behaviour can be considered a feature, the attached
> > patch adds a `-k' option, modelled after the *BSD nc(1) option of
> > the same name.  `-l -k' gives current behaviour, while just `-l'
> > gives the expected, scriptable single-shot behaviour which is
> > default for all netcat variants I am aware of (which is why I'd
> > propose to make it the default).
> >
> > The attached patches fix EOF handling in both connect and listen
> > mode as I'd expect Ncat to handle EOF.  Comments?

-- 
Daniel Roethlisberger
http://daniel.roe.ch/

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