Accept-Encoding and Vary header issue

[Laurence Rowe]

Use varnishlog to see what is going on here. My bet would be on the
backend not setting any Vary at all, so ``set beresp.http.Vary =
"Accept-Encoding";`` never gets called. What happens when you make
that call unconditionally?

Laurence

On 21 July 2010 17:40, Igor Minar <iiminar at gmail.com> wrote:
> Hi there,
>
> I came across this interesting Varnish 2.1.2 behavior that I think is a bug.
>
> vcl:
>
> sub vcl_recv {
>  call normalize_accept_encoding;
>  ...
> }
>
>
> sub vcl_fetch {
>  ...
>  if (beresp.http.Vary ~ ".+") {
>    set beresp.http.Vary = "Accept-Encoding"; #the app doesn't do this
>  }
>  ...
> }
>
>
> If I make an "uncompressed request" (curl -O -v http://foo.com/bar)
> I prime the cache with uncompressed variant of bar resource
>
> on subsequent uncompressed request, I get cache hit and the resource
> is returned.
>
> if I then (before TTL) make a "compressed request" (curl -O -v -H
> "Accept-Encoding:gzip"  http://foo.com/bar)
> I'd expect to get cache miss and prime the cache with compressed
> variant of bar resource,
> but instead I get cache hit, and the uncompressed variant is returned.
>
> once TTL is achieved, if I make a compressed request, varnish
> correctly fetches the compressed variant of the resources, primes the
> cache with it and returns it.
>
> if I subsequently (before TTL) make an uncompressed request, varnish
> correctly fetches the uncompressed variant from the backend and caches
> it.
>
> everything is good until the TTL for the compressed variant is
> reached, from that moment on varnish starts serving uncompressed
> variant for both compressed and uncompressed requests, until the TTL
> for the uncompressed variant is reached.
>
> My current workaround is to control variants manually via vcl_hash:
>
> sub vcl_hash {
>  # consider different Accept-Encoding requests (normalized) as new variants
>  set req.hash += req.http.Accept-Encoding;
> }
>
> but I don't think that this should be necessary. Am I doing something
> wrong or is this a bug?
>
> thanks,
> Igor
>
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