PHP 8.4 | wpdb::check_connection(): handle deprecation of mysqli_ping() (Trac 62061)

[jrfnl]

The mysqli_ping() function is deprecated as of PHP 8.4, though, in reality, the function wasn't working according to spec anymore since PHP 8.2 when the libmysql driver was dropped in favour of libmysqlnd, which was already the default (and recommended) driver since PHP 5.4.

The mysqli_ping() method was also not really correctly named as its functionality was to reconnect to the database, not just ping.

The alternative is to "manually" ping the database by sending a DO 1 query (the cheapest possible SQL query).

Now, I considered adding a PHP version based toggle, but as mentioned above, the default driver has been libmysqlnd since PHP 5.4 and in that case, the function never worked anyway, so in reality mysqli_ping() was only really functional for the odd custom PHP compilation where mysqli was build against libmysql AND reconnect was not disabled.

With this in mind, I'm proposing to replace the call to mysqli_ping() with the DO 1 query completely. If that query succeeds, we can conclude the database connection is still alive. This solution should be the most stable as it will work for both PHP 7.2 <= 8.1, independently of which driver mysqli was compiled with, as well as for PHP 8.2+.

Note: It could also be considered to remove the function call to mysqli_ping() completely and rely on standard error handling in case the connection would have dropped, as after all, the fact that the connection existed at the moment the "ping" happened, is no guarantee that the connection will still exist when the next query is send.... I choose not to do so as WP has custom error handling and does not use the PHP native mysqli exceptions for this, which would make implementing this more awkward.

Includes a test to verify that the connection check works when there is a valid connection (this was previously not covered by tests).

Refs:

• https://wiki.php.net/rfc/deprecations_php_8_4#mysqli_ping_and_mysqliping
• Fix GH-11897: fixed not to throw connection error when COM_PING php/php-src#11912 (comment)
• https://stackoverflow.com/questions/2546868/cheapest-way-to-determine-if-a-mysql-connection-is-still-alive/2546922#2546922
• Deprecate mysqli_ping php/php-src#11945
• https://wiki.php.net/rfc/mysqli_support_for_libmysql
• https://www.php.net/mysqli_ping

Trac ticket: https://core.trac.wordpress.org/ticket/62061

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[hellofromtonya]

Reasoning and approach make sense. LGTM for commit 👍

[github-actions]

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[hellofromtonya]

Committed via https://core.trac.wordpress.org/changeset/59069.