Re: #179: Relax Via MUST

I think mandating that the proxy always sends the version it supports 
breaks things that Via is the fix for. I don't propose changing that 
requirement though.

For interest though, there's also the rule about combining contiguous 
via tags if the protocol version is the same, and the entities are under 
the same administrative control. 

Therefore in terms of the arguments about breaking protocol features by 
omitting Via, that only actually happens in the request-side if the 
request received by the proxy isn't the same protocol version as the 
proxy sends.

Since for example if both are HTTP/1.1, then the proxy adding a Via: 1.1 
Gateway header doesn't give any more information in terms of protocol 
capability of the request path.

the same logic would follow for the response path if the version sent by 
the proxy were the same as received from upstream.


Jamie Lokier wrote:
> 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

Adrien de Croy - WinGate Proxy Server -

Received on Friday, 17 July 2009 12:30:55 UTC