Pull Request for Issue #39176 .

Summary of Changes

The Header append Content-Encoding gzip is changed to Header set Content-Encoding gzip in the section for the gzipped resource files of the htaccess.txt file.

This makes sure not to get an invalid value "gzip gzip" value but a correct "gzip" for the "Content-Encoding" header of the gzipped resource files when following conditions are met:

• Apache web server with mod_rewrite in use
• mod_gzip or mod_deflate are not enabled (otherwise you get double compression anyway).
• Joomla is installed in a subdirectory of your domain or your local webserver's document root.
• An .htaccess file is used in that subdirectory which is based on the Joomla 4 htaccess.txt file and so has the last section for the gzipped resource files in use.
• The gzipped resource files are present, i.e. you are not on a Git clone but on a real Joomla installation made with an installation package (on a Git clone you can run npm run gzip to create the gzipped resources for testing).
• In the parent directory, i.e. the domain directory or your local webserver's document root is also an .htaccess file like that in use. That can be the case e.g. if you have the above mentioned Joomla installation in a subdirectory of a Joomla installation.

See also the Drupal issue https://www.drupal.org/project/drupal/issues/1116416 linked in #39176 for a detailed description and discussion of the issue.

As concluded there in the discussion, the initial approach to do the same change also for the later Header append Vary Accept-Encoding line was abandoned because that header value can be a list of multiple http headers, see https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Vary . Therefore I also don't change that in our htaccess.txt.

In addition, a postinstall message is added, but only for updated sites, not for new installations, as the latter come already with the correct htaccess.txt file.

Testing Instructions

1. Testing the .htaccess change

1. Have an Apache webserver with mod_rewrite enabled and mod_gzip and mod_deflate disabled.

2. Have an .htaccess file in your webserver's document root which contains at least the last section of our Joomla 4 htaccess.txt file:

<IfModule mod_headers.c>
	# 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]

	<FilesMatch "(\.js\.gz|\.css\.gz)$">
		# Serve correct encoding type.
		Header append Content-Encoding gzip

		# Force proxies to cache gzipped &
		# non-gzipped css/js files separately.
		Header append Vary Accept-Encoding
	</FilesMatch>
</IfModule>

This can be because you already have a Joomla 4 installation there and you use URL rewriting.

3. Create a new subdirectory below that and install a Joomla 4.2.5 or latest 4.2.6-dev nightly build into that directory.

4. Enable URL rewriting for that installation and copy htaccess.txt to .htaccess.

5. Request some page of that installation with a forced reload and watch the network tab of your browser's developer tools.

6. Check the "Content-Encoding" in the http response of one of the gzipped css or js resources.
   Result: Value "gzip gzip", see section "Actual result BEFORE applying this Pull Request" below.

7. Change the .htaccess file of the installation in the subdirectory in the same way as this PR changes the htaccess.txt file.

8. Repeat steps 4 and 5.
   Result: Value "gzip", see section "Expected result AFTER applying this Pull Request" below.

2. Testing the postinstall message

1. Make a new installation with the installation package created by drone for this branch and verify that the new postinstall message is not shown.

2. Update a 4.2.8 or older or a current 4.2-dev branch to the update package created by drone for this PR and verify that after the update the new postinstall message is shown.

Actual result BEFORE applying this Pull Request

Header "Content-Encoding" has value "gzip gzip" in the http response for a gzipped resource file.

Expected result AFTER applying this Pull Request

Header "Content-Encoding" has value "gzip" in the http response for a gzipped resource file.

Link to documentations

Please select:

• Documentation link for docs.joomla.org: https://docs.joomla.org/Preconfigured_htaccess

• No documentation changes for docs.joomla.org needed

• Pull Request link for manual.joomla.org:

• No documentation changes for manual.joomla.org needed

When the PR gets merged, I will care for the update of the documentation mentioned above.