A WordPress plug-in to fill comment form from cookies client-side, eliminating a whole class of uncacheable variants

client-side-comment-fill.php

<?php
/*
Plugin Name: Client-Side Comment Fill
Author: Andy Skelton
Description: Fills comment form from cookies client-side, eliminating a whole class of uncacheable variants
*/

function cscf_get_current_commenter( $commenter ) {
        foreach ( $commenter as &$string )
                $string = '';
        return $commenter;
}
add_filter( 'wp_get_current_commenter', 'cscf_get_current_commenter', 10, 1 );

function cscf_comment_form_after() {
	if ( is_user_logged_in() )
                return;
        $format = 'document.cookie.match(/comment_author%s_'.COOKIEHASH.'=([^;]+)/)';
        ?>
        <script>
        var v;
        if ( v = <?php printf($format, '')      ?> ) document.getElementById('author').value=unescape(v[1]);
        if ( v = <?php printf($format, '_email') ?> ) document.getElementById('email').value=unescape(v[1]);
        if ( v = <?php printf($format, '_url')     ?> ) document.getElementById('url').value=unescape(v[1]);
        </script>
        <?php
}
add_action( 'comment_form_after', 'cscf_comment_form_after', 10 );