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Re: #179: Relax Via MUST

From: Jamie Lokier <jamie@shareable.org>
Date: Fri, 17 Jul 2009 13:12:16 +0100
To: Henrik Nordstrom <henrik@henriknordstrom.net>
Cc: Adrien de Croy <adrien@qbik.com>, Mark Nottingham <mnot@mnot.net>, "Roy T. Fielding" <fielding@gbiv.com>, HTTP Working Group <ietf-http-wg@w3.org>
Message-ID: <20090717121216.GD948@shareable.org>
Henrik Nordstrom wrote:
> fre 2009-07-17 klockan 19:05 +1200 skrev Adrien de Croy:
> 
> > Transparent proxies are still required to insert Via?
> 
> Intercepting proxies does not exists in the HTTP specifications, and
> there is things which need to be done differently in such setups.
> 
> But Via is not one of them. A intercepting proxy which do not insert Via
> will break things just the same ways as a normal proxy or intermediary
> so yes it MUST insert Via.
> 
> A semantically transparent proxy is just a proxy, and MUST insert Via.

What does omitting Via break, if the intercepting proxy does not
change the messages, only filters them (and replaces responses with
errors in the case where something is blocked)?

Or even if they rewrite URLs and/or edit the content of responses, if
they don't do any caching?

Which reminds me.

I've seen intercepting proxies used by a few ISPs on port 80,
presumably to reduce their upstream bandwidth costs.  They are very
annoying because they tend to be down from time to time and there's no
easy way to bypass them.  (When it happens, I run a real proxy on a
server in a data centre, and configure my browser to use that.
Something other people generally can't do).

I think the ISPs' intercepting proxies I've seen as a mixture of
adding Via and not adding Via.

Intercepting proxies may also be used for censorship.  Such proxies try
to be hidden, so they're unlikely to insert Via.

-- Jamie
Received on Friday, 17 July 2009 12:13:00 GMT

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