A socket question

Steve Holden sholden at holdenweb.com
Thu Jan 17 13:43:14 CET 2002


"Donn Cave" <donn at u.washington.edu> wrote in message
news:a24v3h$2r2a$1 at nntp6.u.washington.edu...
> Quoth "Steve Holden" <sholden at holdenweb.com>:
> | "Robin Munn" <rmunn at pobox.com> wrote ...
> |> On 15 Jan 2002 15:13:20 GMT, Ng Pheng Siong
<ngps at madcap.netmemetic.com>
> |wrote:
> |> >According to Robin Munn <rmunn at pobox.com>:
> |> >> "exceptional conditions" (I don't know what constitutes an
"exceptional
> |> >> condition" on a TCP/IP socket; one of the RFC's should be able to
tell
> |> >> you).
> |> >
> |> >OOB data. On the wire these will be TCP segments with the URG flag on.
> |>
> |> Thanks! I've never written an application where out-of-band data was
> |> necessary, so I didn't know that. Has anyone used this in practice?
What
> |> is it good for?
> |
> | In practice, not a lot. But consider a Telnet client, for example.
Suppose
> | the user types commands ahead, one of which places her shell interpreter
> | into an infinite loop. The client can't simply queue a "^C" character to
the
> | server, because it would sit there in the buffer stream forever. So it
sends
> | out-of-band data, which the server can respond to without processing
> | everything that preceded it.
>
> Really?  I know telnet actually does deal with OOB, and I can't say
> I understand why or when, but I'm pretty sure it doesn't do it for ^C.
> The urgency you're looking at there is a terminal driver function on
> the remote end - where it belongs, what would happen if you used ^C
> in emacs where it's just another control character?  I have seen telnets
> with odd special configurable options for ^C, and maybe they have the
> option to send it MSG_OOB, but the telnet source I have on hand (MIT
> Kerberos 5 1.2.3, derived from BSD 4.4) does not send any MSG_OOB when
> you press Ctrl-C.
>
Oh, well, if you're going to start quoting accurate facts at me ...

Thanks for correcting that mis-impression. Now take another look at that
source and tell when Telnet DOES use OOB data, and what for! :-)

regards
 Steve
--
Consulting, training, speaking: http://www.holdenweb.com/
Python Web Programming: http://pydish.holdenweb.com/pwp/








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