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From Rainer Jung <rainer.j...@kippdata.de>
Subject Re: svn commit: r1673470 - /httpd/httpd/trunk/docs/manual/mod/mod_deflate.xml
Date Wed, 15 Apr 2015 06:56:06 GMT
Am 15.04.2015 um 00:14 schrieb Rainer Jung:
> Am 14.04.2015 um 19:06 schrieb rbowen@apache.org:
>> Author: rbowen
>> Date: Tue Apr 14 17:06:10 2015
>> New Revision: 1673470
>>
>> URL: http://svn.apache.org/r1673470
>> Log:
>> Add "pre-compressed content" recipe, as per
>> https://bz.apache.org/bugzilla/show_bug.cgi?id=51336
>>
>> Modified:
>>      httpd/httpd/trunk/docs/manual/mod/mod_deflate.xml
>>
>> Modified: httpd/httpd/trunk/docs/manual/mod/mod_deflate.xml
>> URL:
>> http://svn.apache.org/viewvc/httpd/httpd/trunk/docs/manual/mod/mod_deflate.xml?rev=1673470&r1=1673469&r2=1673470&view=diff
>>
>> ==============================================================================
>>
>> --- httpd/httpd/trunk/docs/manual/mod/mod_deflate.xml (original)
>> +++ httpd/httpd/trunk/docs/manual/mod/mod_deflate.xml Tue Apr 14
>> 17:06:10 2015
>> @@ -178,6 +178,51 @@ SetEnvIfNoCase Request_URI \.(?:gif|jpe?
>>       </example>
>>   </section>
>>
>> +<section id="precompressed"><title>Serving pre-compressed
>> +content</title>
>> +
>> +    <p>Since <module>mod_deflate</module> re-compresses content
each
>> +    time a request is made, some performance benefit can be derived by
>> +    pre-compressing the content and telling mod_deflate to serve them
>> +    without re-compressing them. This may be accomplished using a
>> +    configuration like the following:</p>
>> +
>> +    <highlight language="config">
>> +  &lt;IfModule mod_headers.c&gt;
>> +    # Serve gzip compressed CSS files if they exist
>> +    # and the client accepts gzip.
>> +    RewriteCond %{HTTP:Accept-encoding} gzip
>> +    RewriteCond %{REQUEST_FILENAME}\.gz -s
>> +    RewriteRule ^(.*)\.css $1\.css\.gz [QSA]
>> +
>> +    # Serve gzip compressed JS files if they exist
>> +    # and the client accepts gzip.
>> +    RewriteCond %{HTTP:Accept-encoding} gzip
>> +    RewriteCond %{REQUEST_FILENAME}\.gz -s
>> +    RewriteRule ^(.*)\.js $1\.js\.gz [QSA]
>> +
>> +
>> +    # Serve correct content types, and prevent mod_deflate double gzip.
>> +    RewriteRule \.css\.gz$ - [T=text/css,E=no-gzip:1]
>> +    RewriteRule \.js\.gz$ - [T=text/javascript,E=no-gzip:1]
>> +
>> +
>> +    &lt;FilesMatch "(\.js\.gz|\.css\.gz)$"&gt;
>> +      # Serve correct encoding type.
>> +      Header append Content-Encoding gzip
>> +
>> +      # Force proxies to cache gzipped &amp;
>> +      # non-gzipped css/js files separately.
>> +      Header append Vary Accept-Encoding
>> +    &lt;/FilesMatch&gt;
>> +  &lt;/IfModule&gt;
>> +</IfModule>
>> +
>> +
>> +    </highlight>
>> +
>> +</section>
>> +
>>   <directivesynopsis>
>>   <name>DeflateFilterNote</name>
>>   <description>Places the compression ratio in a note for
>> logging</description>
>
> AFAIK mod_rewrite automatically adds headers from RewriteCond to the
> Vary header as long as no "NV" flag is used. So the "Header append Vary
> Accept-Encoding" part should not be necessary.

I should probably also mention, that the recipe gets easier, once one 
accepts a non-standard convention for the names of the compressed 
content. If you add the ".gz" before the final suffix ".js", ".css" 
etc., then the web server will automatically get the content type 
correct. So you can drop the "T=" flags. My variant of the recipe was:

RewriteCond %{HTTP:Accept-Encoding} gzip
RewriteCond %{REQUEST_FILENAME} ^(.+)\.(css|js)$
RewriteCond %1.gz%2 -s
RewriteRule ^(.+)\.(css|js)$ $1.gz.$2 [QSA,E=gz:1,E=no-gzip:1]

Header append Content-Encoding gzip env=gz

The additional replacement of FilesMatch with a custom env var (here 
named "gz") one can check in the "Header append" part is independent of 
the other change.

One could drop the second and third RewriteCond, if one assumes that all 
such files have been compressed. To create the compressed files with 
non-standard name convention, one can use on Unix/Linux a script like e.g.

CONTENT_DIR=/opt/myapp/static/
PERMS=644
for suffix in css js
do
     for file in \
       `find $CONTENT_DIR -type f -name "*.$suffix" -a ! -name "*.gz.*"`
     do
         gzfile=`echo $file | sed -e 's#\.'$suffix'#.gz.'$suffix'#'`
         gzip --best -c $file > $gzfile
         chmod $PERMS $gzfile
         echo === $file $gzfile ===
         ls -ld $file $gzfile
     done
done

I like the idea of adding this as a feature to mod_deflate. I actually 
started doing this a few weeks ago but got side-tracked.

Regards,

Rainer

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