It’s just data

Etag vs Encoding

Learn something new every day.

Despite being the way Apache httpd currently behaves, and how I would read the HTTP spec apparently it is the behavior of IIS 7 and the apparent consensus of the Apache httpd developers (including one of the authors of the spec) that a different ETag value should be used if the response is compressed over when it is not.

Section 3.2 of Clarifying the Fundamentals of HTTP has a good explanation of this issue.

Posted by Robert Sayre at

Etags can also be unique based on the server too, so if you’ve got multiple servers for a given site each could send a different etag for an identical file.  Yahoo!'s 13 simple rules for speeding up your web site recomends turning off etags all together.  Check out [link] (and the whole article).  Also, if you install the Firebug YSlow add on for Firefox you can check each of these rules against any page on your site.  It’s a pretty cool tool...

Posted by Joe O'Brien at

I disagree with your reading of the specification based on this sentence from RFC 2616:

The content-coding is a characteristic of the entity identified by the Request-URI.

Change the Content-Encoding and you change a characteristic of the entity, not a mere transmission artefact.

Posted by Jim at

Is the reason mod_deflate doesn’t use Transfer-Encoding: gzip lack of browser support?

The Transfer-Encoding general-header field... differs from the content-coding in that the transfer-coding is a property of the message, not of the entity.

Seems a more accurate description of what’s actually done with an output filter, as opposed to say, what happens with AddEncoding gzip .gz .tgz or suchlike.

The Internet Assigned Numbers Authority (IANA) acts as a registry for transfer-coding value tokens. ...the registry contains... “gzip”...

Posted by anonymous at

Is the reason mod_deflate doesn’t use Transfer-Encoding: gzip lack of browser support?

Another likely reason could be the fact that Transfer-Encoding is hop-by-hop.

Posted by James Snell at

Content-Encoding versus Transfer-Encoding

Today I discovered a “problem” where Apache’s mod_deflate changes a resource’s ETag value from “foo” to "foo"-gzip when compressing the representation. This problem has been a while in coming , and after some research I’m convinced that Apache’s...

Excerpt from News You Can Bruise at

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