FILTER_SANITIZE_STRING is deprecated in php 8.1

[edwinbradford]

Describe the bug

I can't find a report of this issue so I'm submitting it.

The below error occurs when running Multisite Language Switcher in PHP version 8.1. This StackOverflow answer states FILTER_SANITIZE_STRING is deprecated in php 8.1 and there are multiple suggestions on how to update it.

I have changed...

$action = filter_input( INPUT_POST, 'action', FILTER_SANITIZE_STRING ); to
$action = filter_input( INPUT_POST, 'action', FILTER_SANITIZE_FULL_SPECIAL_CHARS );

...in MslsPlugin.php which appears to work fine but I don't understand exactly what it does.

To Reproduce
Steps to reproduce the behavior:

1. Go to Settings > General > Multisite Language Switcher.
2. Click on 'Save Changes' (you do not need to make a change).
3. See the following error:

Deprecated: Constant FILTER_SANITIZE_STRING is deprecated in /var/www/html/wp-content/plugins/multisite-language-switcher/includes/MslsPlugin.php on line 77 Warning: Cannot modify header information - headers already sent by (output started at /var/www/html/wp-content/plugins/multisite-language-switcher/includes/MslsPlugin.php:77) in /var/www/html/wp-admin/includes/misc.php on line 1431 Warning: Cannot modify header information - headers already sent by (output started at /var/www/html/wp-content/plugins/multisite-language-switcher/includes/MslsPlugin.php:77) in /var/www/html/wp-includes/functions.php on line 6896 Warning: Cannot modify header information - headers already sent by (output started at /var/www/html/wp-content/plugins/multisite-language-switcher/includes/MslsPlugin.php:77) in /var/www/html/wp-includes/pluggable.php on line 1427 Warning: Cannot modify header information - headers already sent by (output started at /var/www/html/wp-content/plugins/multisite-language-switcher/includes/MslsPlugin.php:77) in /var/www/html/wp-includes/pluggable.php on line 1430

Expected behaviour
There should be no error in PHP versions 8.1 or above.

Environment:

• OS: WSL2 Ubuntu running Docker
• Browser: Chrome in Windows
• PHP Version 8.1
• Plugin Version 2.5.8

[lloc]

This commit closes the issue. Thanks!

[edwinbradford]

Not sure if its relevant but I found three instances of FILTER_SANITIZE_STRING in the repo. There is one in MslsMetaBox.php and one in WithRequestPostAttributes.php. I've changed them all to FILTER_SANITIZE_FULL_SPECIAL_CHARS and there don't appear to be any issues but I was never able to figure out how to build the repo locally and submit a pull request so I just made the changes directly in the built plugin.