wikimedia/mediawiki-core

<?php
/**
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, write to the Free Software Foundation, Inc.,
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 * http://www.gnu.org/copyleft/gpl.html
 *
 * @file
 */

namespace Wikimedia\Reflection;

/**
 * Trait for accessing "ghost fields".
 *
 * Ghost fields are fields that have been created in an object instance
 * by PHP's unserialize() mechanism, though they no longer exist
 * in the current version of the corresponding class.
 *
 * Accessing non-public ghost fields offers some challenges due to
 * how they are handled by PHP internally.
 *
 * @see https://www.php.net/manual/en/language.types.array.php#language.types.array.casting
 * @since 1.36
 */
trait GhostFieldAccessTrait {

    /**
     * Get the value of the ghost field named $name,
     * or null if the field does not exist.
     *
     * @param string $name
     * @param class-string ...$aliases
     * @return mixed|null
     */
    private function getGhostFieldValue( string $name, string ...$aliases ) {
        if ( isset( $this->$name ) ) {
            return $this->$name;
        }

        $data = (array)$this;

        // Protected variables have a '*' prepended to the variable name.
        // These prepended values have null bytes on either side.
        $protectedName = "\x00*\x00{$name}";
        if ( isset( $data[$protectedName] ) ) {
            return $data[$protectedName];
        }

        // Private variables have the class name prepended to the variable name.
        // These prepended values have null bytes on either side.
        $thisClass = get_class( $this );
        $privateName = "\x00{$thisClass}\x00{$name}";
        if ( isset( $data[$privateName] ) ) {
            return $data[$privateName];
        }

        // Check old aliased class names as well.
        foreach ( $aliases as $thisClass ) {
            $privateName = "\x00{$thisClass}\x00{$name}";
            if ( isset( $data[$privateName] ) ) {
                return $data[$privateName];
            }
        }

        return null;
    }

    /**
     * In PHP <= 8.1, private fields of a class are not properly restored
     * when the class is aliased to a new name, since the private fields are
     * prefixed with the *old* name of the class.  This method can be used
     * to restore them if present after deserialization.
     *
     * @param string $name
     * @param class-string ...$aliases
     */
    private function restoreAliasedGhostField( string $name, string ...$aliases ): void {
        $data = (array)$this;
        foreach ( $aliases as $thisClass ) {
            $privateName = "\x00{$thisClass}\x00{$name}";
            if ( isset( $data[$privateName] ) ) {
                $this->$name = $data[$privateName];
                unset( $data[$privateName] );
                return;
            }
        }
    }
}