How to apply a function to the value $email of get_user_by to override email_exists?

Question

More precisely questions : How to override email_exists via get_user_by ?

I have chosen to render unusable/unreadable email adresses from database.

I added a few elements(chars) to email address just after sending email to admin and user (user registration), and then I must remove these added elements to verify if email exists or display on user account or use for mailing list.

To decrypt the email I must use substr whith the value associated to $email field of get_user_by to remove elements added before. I read that email_exists use get_user_by which is a pluggable function. But I don't know how to use the result of get_user_by inside email_exists.

Is it possible ? How should I do ?

        function get_user_by( $field, $db_email ) {
            $field = 'email';
            //function to decrypt my email from database
            $ex = preg_split('\'@\'', $nr , -1);
            $dem = substr(substr($ex[0],2),0,-2);
            $rdem = substr($dem,0,2).substr($dem,2+1,strlen($dem)-2);
            $db_email = $rdem. '@' .$ex[1];
            
            $userdata = WP_User::get_data_by( 'email', $db_email );

            if ( ! $userdata ) {
                return false;
            }

            $user = new WP_User;
            $user->init( $userdata );

        return $user;
        }
        
        function email_exists( $email ) {
            $user = get_user_by( $field, $db_email );
            if ( $user ) {
                $user_id = $user->ID;
            } else {
                $user_id = false;
            }
            return apply_filters( 'email_exists', $user_id, $email );
        }
        
        if (email_exists($email)){
            lq_errors()->add("emailexists","This email address already exist");
        }

Answer 1

Based on your code, I think the problem may have been that you were checking a variable that was undefined. You were checking $db_email, which in your function was an undefined value, so you'd be looking for an empty result. You need to check the value passed to email_exists() (which would be the email being validated in the form).

If the patterns applied in your pluggable get_user_by() function result in the equivalent of how you are obfuscating the emails, then you should get a correct match if the email exists.

function email_exists( $email ) {
    // You had this as checking $db_email, which would have been
    // undefined. It should be checking for the value passed to
    // this function - $email.
    $user = get_user_by( 'email', $email );
    if ( $user ) {
        $user_id = $user->ID;
    } else {
        $user_id = false;
    }
    return apply_filters( 'email_exists', $user_id, $email );
}