root/tags/1_0-rc1/wp-trackback.php

<?php

if (empty($wp)) {
    require_once('wp-config.php');
    wp('tb=1');
}

function trackback_response($error = 0, $error_message = '') {
    header('Content-Type: text/xml; charset=' . get_option('blog_charset') );
    if ($error) {
        echo '<?xml version="1.0" encoding="utf-8"?'.">\n";
        echo "<response>\n";
        echo "<error>1</error>\n";
        echo "<message>$error_message</message>\n";
        echo "</response>";
        die();
    } else {
        echo '<?xml version="1.0" encoding="utf-8"?'.">\n";
        echo "<response>\n";
        echo "<error>0</error>\n";
        echo "</response>";
    }
}

// trackback is done by a POST
$request_array = 'HTTP_POST_VARS';

if ( !$_GET['tb_id'] ) {
    $tb_id = explode('/', $_SERVER['REQUEST_URI']);
    $tb_id = intval( $tb_id[ count($tb_id) - 1 ] );
}

$tb_url    = $_POST['url'];
$title     = $_POST['title'];
$excerpt   = $_POST['excerpt'];
$blog_name = $_POST['blog_name'];
$charset   = $_POST['charset'];

if ($charset)
    $charset = strtoupper( trim($charset) );
else
    $charset = 'ASCII, UTF-8, ISO-8859-1, JIS, EUC-JP, SJIS';

if ( function_exists('mb_convert_encoding') ) { // For international trackbacks
    $title     = mb_convert_encoding($title, get_settings('blog_charset'), $charset);
    $excerpt   = mb_convert_encoding($excerpt, get_settings('blog_charset'), $charset);
    $blog_name = mb_convert_encoding($blog_name, get_settings('blog_charset'), $charset);
}

if ( is_single() || is_page() ) 
    $tb_id = $posts[0]->ID;

if ( !intval( $tb_id ) )
    trackback_response(1, 'I really need an ID for this to work.');

if (empty($title) && empty($tb_url) && empty($blog_name)) {
    // If it doesn't look like a trackback at all...
    wp_redirect(get_permalink($tb_id));
    exit;
}

if ( !empty($tb_url) && !empty($title) && !empty($tb_url) ) {
    header('Content-Type: text/xml; charset=' . get_option('blog_charset') );

    $pingstatus = $wpdb->get_var("SELECT ping_status FROM $wpdb->posts WHERE ID = $tb_id");

    if ( 'open' != $pingstatus )
        trackback_response(1, 'Sorry, trackbacks are closed for this item.');

    $title =  wp_specialchars( strip_tags( $title ) );
    $excerpt = strip_tags($excerpt);
    if ( function_exists('mb_strcut') ) { // For international trackbacks
        $excerpt = mb_strcut($excerpt, 0, 252, get_settings('blog_charset')) . '...';
        $title = mb_strcut($title, 0, 250, get_settings('blog_charset')) . '...';
    } else {
        $excerpt = (strlen($excerpt) > 255) ? substr($excerpt, 0, 252) . '...' : $excerpt;
        $title = (strlen($title) > 250) ? substr($title, 0, 250) . '...' : $title;
    }

    $comment_post_ID = $tb_id;
    $comment_author = $blog_name;
    $comment_author_email = '';
    $comment_author_url = $tb_url;
    $comment_content = "<strong>$title</strong>\n\n$excerpt";
    $comment_type = 'trackback';

    $dupe = $wpdb->get_results("SELECT * FROM $wpdb->comments WHERE comment_post_ID = '$comment_post_ID' AND comment_author_url = '$comment_author_url'");
    if ( $dupe )
        trackback_response(1, 'We already have a ping from that URI for this post.');

    $commentdata = compact('comment_post_ID', 'comment_author', 'comment_author_email', 'comment_author_url', 'comment_content', 'comment_type');

    wp_new_comment($commentdata);

    do_action('trackback_post', $wpdb->insert_id);
    trackback_response(0);
}
?>