Breaking: #107943 - Frontend and backend HTTP response compression removed 

See forge#107943

Description 

The TYPO3 frontend and backend applications previously allowed compressing their HTTP responses using the configuration options $GLOBALS['TYPO3_CONF_VARS']['FE']['compressionLevel'] and $GLOBALS['TYPO3_CONF_VARS']['BE']['compressionLevel'] .

This feature, which was always disabled by default, has now been removed.

TYPO3 will no longer compress its HTTP responses itself.

Response compression should be handled by the web server rather than the application layer.

Removing this feature avoids potential conflicts when both TYPO3 and the web server attempt to compress responses and allows modern web servers to use advanced compression algorithms such as brotli or zStandard when supported by the client.

Impact 

TYPO3 can no longer compress its HTTP responses.

This responsibility is now fully delegated to the web server.

HTTP response compression had to be explicitly enabled before, so most installations will not notice a change unless they relied on this setting.

Affected installations 

Instances that configured $GLOBALS['TYPO3_CONF_VARS']['FE']['compressionLevel'] or $GLOBALS['TYPO3_CONF_VARS']['BE']['compressionLevel'] to non-zero values are affected.

Administrators should verify that the web server applies HTTP compression by checking for a response header such as:

Content-Encoding: gzip

when requesting frontend or backend documents with a header like:

Accept-Encoding: gzip, deflate

All commonly used web servers enable this feature by default.

Migration 

The configuration toggles for the backend $GLOBALS['TYPO3_CONF_VARS']['BE']['compressionLevel'] and the frontend $GLOBALS['TYPO3_CONF_VARS']['FE']['compressionLevel'] are obsolete, existing settings in settings.php configuration files are actively removed when first using the install tool after upgrade to TYPO3 v14.