MYSQL_NEW_LINK constant is not honored with MySQLi

[doublesharp]

Using WordPress 3.9 and PHP5.5, the MySQLi extension is used in lieu of the deprecated mysql_* extensions, however the MYSQL_NEW_LINK constant is not honored. When this constant is set to false it would cause the $new_link passed to [mysql_connect()](​http://us2.php.net/function.mysql-connect) to indicate that an already opened link should be returned.

For MySQLi this is accomplishing by prepending a p: to the hostname - see details on [The mysqli Extension and Persistent Connections](​http://www.php.net/manual/en/mysqli.persistconns.php) page. Dynamically prepending p: to the $host based on the value of MYSQL_NEW_LINK to maintain compatibility would be ideal.

[doublesharp]

Prepend $host with "p:" for persistent mysqli connections

[pento]

Nice find. :-)

I like where you're going with this patch, but it also needs to do a PHP version check. The p: syntax was introduced in PHP 5.3, but WordPress still supports PHP 5.2.

Also, a minor coding standard thing - there's no need to use the curly brackets in "p:{$host}".

I'm okay with PHP 5.2 users who've deliberately forced mysqli to be used to not have persistent connections.

[doublesharp]

Good call on the PHP version, didn't occur to me that someone would still be running PHP 5.2. I'm going to attach two updated patches for your consideration with slightly different functionality.

The first is based on your exact recommendations to include a check for PHP 5.3+ and to nix the curly braces.

if ( ! $new_link && version_compare(PHP_VERSION, '5.3.0') >= 0 ){
        $host = "p:$host";
}

The second does basically the same thing, but prints a message indicating that persistent connections are not supported when WP_DEBUG==true and MYSQL_NEW_LINK==false.

if ( ! $new_link ){
        if ( version_compare(PHP_VERSION, '5.3.0') >= 0 ){
                $host = "p:$host";
        } elseif ( WP_DEBUG ){
                _e( 'MySQLi persistent connections are not supported with your version of PHP.' );
        }
}

[doublesharp]

check for PHP 5.3+

[doublesharp]

check for PHP 5.3+, print debug message if false

[pento]

For the version_compare() call, putting the operator in the function call would make it more readable:

version_compare( PHP_VERSION, '5.3.0', '>=' )

For consistency with the other PHP version check in wpdb, I'd use phpversion() instead of PHP_VERSION.

I like the warning, though instead of the WP_DEBUG check, you can just do a _doing_it_wrong() call instead:

} else {
    _doing_it_wrong( 'wpdb::db_connect', __( 'Disabling MYSQL_NEW_LINK with MySQLi requires PHP 5.3 or later' ), '3.9.1' );
}

(I'm not wild about that particular error message, @DrewAPicture, do you have some thoughts on this?)

And for a minor coding standard reminder, don't forget your ​whitespace.

[doublesharp]

Attaching a new patch with the latest suggestions:

if ( ! $new_link ){
        if ( version_compare( phpversion(), '5.3.0', '>=' ) ){
                $host = "p:$host";
        } else {
                _doing_it_wrong( 'wpdb::db_connect', __( 'Disabling MYSQL_NEW_LINK with MySQLi requires PHP 5.3 or later.' ), '3.9.1' );
        }
}

Thanks for the coding standards link @pento, probably should have looked at it first.

[doublesharp]

use prefered functions and code styling

[pento]

Looking good! Just a couple of small changes for spacing - there should be a space before the { in each of the if() statements.

[doublesharp]

Fourth time's the charm?

if ( ! $new_link ) {
        if ( version_compare( phpversion(), '5.3.0', '>=' ) ) {
                $host = "p:$host";
        } else {
                _doing_it_wrong( 'wpdb::db_connect', __( 'Disabling MYSQL_NEW_LINK with MySQLi requires PHP 5.3 or later.' ), '3.9.1' );
        }
}

[doublesharp]

corret styling standards

[pento]

Looking good!

I'm still not wild about the message, so we'll wait for a docs review, but this patch is ready to go!

[nacin]

Looking through the ext/mysql source, there seems to be some differences between mysql_pconnect() and mysql_connect( new_link = false ). mysqli's p: seems to be the former. Is it expected to apply MYSQL_NEW_LINK in this case?

[pento]

Well, today has been a day for digging through PHP source.

Nacin is correct, new_link = false is different to mysql_pconnect(), and mysqli's p: notation is the equivalent of mysql_pconnect().

new_link = false is for forcing subsequent calls of mysql_connect(), in the same process, to use an established link that matches the connect parameters of that call. mysqli doesn't have an equivalent to this.

With that in mind, attachment:wp-db.php.4.patch​ is unfortunately the incorrect solution for this problem - instead, MYSQL_NEW_LINK is deprecated for use with mysqli, as of 3.9.

[DrewAPicture]

I don't think we necessarily need to do anything beyond adding an inline comment describing that the value is deprecated in 3.9+.

This is done in 27933.diff​

[DrewAPicture]

Will 27933.diff​ suffice here?

[DrewAPicture]

In 28657:

Mark the MYSQL_NEW_LINK constant as deprecated in 3.9+ as no equivalent to the $new_link parameter exists in mysqli_* functions.

Fixes #27933.