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Re: Weak ETags and on-the-fly gzipping

Maxim Dounin
June 18, 2013 10:24AM
Hello!

On Sat, Jun 15, 2013 at 02:58:33PM +0200, Matthijs Langenberg wrote:

> I am serving dynamic requests behind the Nginx HTTP server. HTTP requests
> are mostly from mobile HTTP clients. That's is why I care about two things.
>
> 1. Do not send the same representation twice: Use ETag caching mechanism.
> 2. Make better us of available bandwidth: Use Accept-Encoding HTTP
> compression.
>
> Today I noticed that these two don't match. My application sets the ETag
> header in the response, but when I set the 'Accept-Encoding: gzip' in the
> request header, nginx clears the ETag header when gzipping on-the-fly.
>
> I understand why this is: If two responses have the same ETag, their bodies
> should be byte-for-byte comparable. When the content is gzipped, and
> actually modified, this is of course not the case. The gzipped response is
> not equal to the non-gzipped response.
>
> That's why there are two ETag validation mechanisms. A strong validation,
> used in case of byte-for-byte comparable responses, and a weak validation,
> to indicate semantic equivalency.
>
> In the case of weak validation an ETag would look like:
> ETag: W/"123456789"
>
> Why is Nginx stripping weak ETag validators in its gzip filter?

Just stripping ETags are easier than converting them to weak
etags (and implementing weak etags support various places).

On the other hand, relevant caching functionality is still here
with Last-Modified cache validator.

--
Maxim Dounin
http://nginx.org/en/donation.html

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Subject Author Posted

Weak ETags and on-the-fly gzipping

Matthijs Langenberg June 18, 2013 10:24AM

Re: Weak ETags and on-the-fly gzipping

Matthijs Langenberg June 18, 2013 10:24AM

Re: Weak ETags and on-the-fly gzipping

neoelit May 17, 2016 10:05AM

Re: Weak ETags and on-the-fly gzipping

Maxim Dounin May 17, 2016 11:02AM

Re: Weak ETags and on-the-fly gzipping

neoelit May 18, 2016 12:41AM

Re: Weak ETags and on-the-fly gzipping

neoelit May 18, 2016 12:43AM

Re: Weak ETags and on-the-fly gzipping

Maxim Dounin June 18, 2013 10:24AM

Re: Weak ETags and on-the-fly gzipping

grosser October 18, 2013 05:12PM

Re: Weak ETags and on-the-fly gzipping

grosser October 18, 2013 05:19PM



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