Re: [ftpext] Discouraging use of TCP "urgent data"

Fernando Gont <fernando@gont.com.ar> Wed, 22 September 2010 19:02 UTC

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Date: Wed, 22 Sep 2010 15:27:16 -0300
From: Fernando Gont <fernando@gont.com.ar>
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To: Daniel Stenberg <daniel@haxx.se>
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Cc: Alexey Melnikov <alexey.melnikov@isode.com>, ftpext@ietf.org
Subject: Re: [ftpext] Discouraging use of TCP "urgent data"
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Hi, Daniel,

>> So just to think out loud, I'm wondering now if the FTP client should
>> no longer depend on ABOR actually working....
> 
> Why? Surely most commands already work fine without URG so why does ABOR
> depend so hard on it?

To avoid head-of-line blocking. If the user has e.g. already sent a
number of commands to the FTP server, and then issues an ABOR, you don't
really want the server to process all the commands that are already in
the pipeline, but want it to "jump" to your ABOR. -- and that's what the
TCP urgent mechanism is leveraged for.

Thanks,
-- 
Fernando Gont
e-mail: fernando@gont.com.ar || fgont@acm.org
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