Occasional problem of corrupted html

[demis-palma]

When the compression of the response is delegated to Apache with mod_deflate, two headers are set during the compression:

Content-Encoding: gzip
Vary: Accept-Encoding

Vary: Accept-Encoding is important to prevent proxies, intermediate caches, or CDNs from serving compressed resource to clients that does not support compression and vice versa.
"Vary: Accept-Encoding" header specifies that caches should only be used if the incoming request matches the "Accept-Encoding" information in the cache.

When the mod_deflate is disabled in the web server, and the compression is delegated to Joomla through Global Configuration → Server → Gzip Page Compression, in this case the header "Content-Encoding: gzip" is set, but "Vary: Accept-Encoding" no, which causes the problem mentioned above on modern networks.

Testing Instructions

Disable mod_deflate in your web server and enable Joomla compression Global Configuration → Server → Gzip Page Compression.
Browse any page.
Check that the response headers include Vary: Accept-Encoding in addition to Content-Encoding: gzip

Note

See joomla-framework/application#79

[ggppdk]

It is not only about older browser seeing corrupted HTML

There is 1 more reason to add this
and thus have proxies, etc store both compressed and uncompressed version

If an old browser (or some browser) is the first to request a content as uncompressed

then the proxy will cache only the uncompressed content
and it will serve it to browsers that can accept compressed content
thus having worst responce time

[viocassel]

I have tested this item ✅ successfully on a07e67d

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_{This comment was created with the J!Tracker Application at issues.joomla.org/tracker/joomla-cms/19525.}

[SharkyKZ]

I have tested this item ✅ successfully on a07e67d

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_{This comment was created with the J!Tracker Application at issues.joomla.org/tracker/joomla-cms/19525.}

[ghost]

Status "Ready To Commit".

[HLeithner]

It took some time but thanks for adding this header to Joomla.