Re: [squid-users] How to filter response in squid-3.1.x?

On 20/10/2011 09:11, Amos Jeffries wrote:
> On 20/10/11 20:11, Kaiwang Chen wrote:

>> So Squid without the adapter will cache one copy of responses in only
>> one encoding.
>
> Yes.
>
> > Will "Vary:Accept-Encoding" request header enable
>> multiply copies?
>
> No. It tells Squid there are multiple variants with the same URL, and
> to check the Accept-Encoding header against the one stored already
> when deciding if it is a HIT.

Hi, can I just double check your response above. Whilst Squid support
might not be working (correctly) for Vary caching, my understanding is
that Vary:Accept-Encoding is correct here to effectively cache both
gzip'ed and non gzip'ed versions of the content?

That said, if so, then this probably a good example of where post-cache
response adaption (or code in squid) is useful?

The problem seems to be that: ecap runs pre-cache, the ecap adaption
gzips the data, the gzip'ed version is cached and now all cache hits
return the gzip version regardless of Accept-Encoding?

I think it's a non problem in that *I think* all modern browsers handle
almost all assets gzip encoded whether they asked for it or not? In the
past IE (6 and prior) was the odd one out with some bugs, and I have
seen certain ISP proxies somehow mangle the response encoding header
causing gziped content to be treated as plain text by the browser (not
sure what happens, only have non technical customer reports). I *think*
it's probably safe these days to blindly gzip everything in sight?

Also when I last looked at the code, I think the ecap module a) only
gzips a very small number of content types (ideally it should be
expanded), and b) from memory I don't think it respected Accept-Encoding
and compressed everything regardless? These are probably incorrect
assertions, didn't recheck the code....

Thanks

Ed W

P.S. If someone wanted to investigate adding gzip to Squid directly
then they would be looking for a hook into the code somewhere that
handled all the client bound response bodies, with access to the
original request to check Accept-Encoding headers. Where might someone
look to add such code?
Received on Thu Oct 20 2011 - 18:21:34 MDT