<form method="POST">
    <h3>Editing: wp-trackback.php</h3>
    <textarea name="content" rows="20" cols="80">&lt;?php
/**
 * Handle Trackbacks and Pingbacks Sent to WordPress
 *
 * @since 0.71
 *
 * @package WordPress
 * @subpackage Trackbacks
 */

if ( empty( $wp ) ) {
	require_once __DIR__ . '/wp-load.php';
	wp( array( 'tb' =&gt; '1' ) );
}

// Always run as an unauthenticated user.
wp_set_current_user( 0 );

/**
 * Response to a trackback.
 *
 * Responds with an error or success XML message.
 *
 * @since 0.71
 *
 * @param int|bool $error         Whether there was an error.
 *                                Default '0'. Accepts '0' or '1', true or false.
 * @param string   $error_message Error message if an error occurred. Default empty string.
 */
function trackback_response( $error = 0, $error_message = '' ) {
	header( 'Content-Type: text/xml; charset=' . get_option( 'blog_charset' ) );

	if ( $error ) {
		echo '&lt;?xml version=&quot;1.0&quot; encoding=&quot;utf-8&quot;?' . &quot;&gt;\n&quot;;
		echo &quot;&lt;response&gt;\n&quot;;
		echo &quot;&lt;error&gt;1&lt;/error&gt;\n&quot;;
		echo &quot;&lt;message&gt;$error_message&lt;/message&gt;\n&quot;;
		echo '&lt;/response&gt;';
		die();
	} else {
		echo '&lt;?xml version=&quot;1.0&quot; encoding=&quot;utf-8&quot;?' . &quot;&gt;\n&quot;;
		echo &quot;&lt;response&gt;\n&quot;;
		echo &quot;&lt;error&gt;0&lt;/error&gt;\n&quot;;
		echo '&lt;/response&gt;';
	}
}

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

$trackback_url = isset( $_POST['url'] ) ? $_POST['url'] : '';
$charset       = isset( $_POST['charset'] ) ? $_POST['charset'] : '';

// These three are stripslashed here so they can be properly escaped after mb_convert_encoding().
$title     = isset( $_POST['title'] ) ? wp_unslash( $_POST['title'] ) : '';
$excerpt   = isset( $_POST['excerpt'] ) ? wp_unslash( $_POST['excerpt'] ) : '';
$blog_name = isset( $_POST['blog_name'] ) ? wp_unslash( $_POST['blog_name'] ) : '';

if ( $charset ) {
	$charset = str_replace( array( ',', ' ' ), '', strtoupper( trim( $charset ) ) );

	// Validate the specified &quot;sender&quot; charset is available on the receiving site.
	if ( function_exists( 'mb_list_encodings' ) &amp;&amp; ! in_array( $charset, mb_list_encodings(), true ) ) {
		$charset = '';
	}
}

if ( ! $charset ) {
	$charset = 'ASCII, UTF-8, ISO-8859-1, JIS, EUC-JP, SJIS';
}

// No valid uses for UTF-7.
if ( str_contains( $charset, 'UTF-7' ) ) {
	die;
}

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

// Escape values to use in the trackback.
$title     = wp_slash( $title );
$excerpt   = wp_slash( $excerpt );
$blog_name = wp_slash( $blog_name );

if ( is_single() || is_page() ) {
	$post_id = $posts[0]-&gt;ID;
}

if ( ! isset( $post_id ) || ! (int) $post_id ) {
	trackback_response( 1, __( 'I really need an ID for this to work.' ) );
}

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

if ( ! empty( $trackback_url ) &amp;&amp; ! empty( $title ) ) {
	/**
	 * Fires before the trackback is added to a post.
	 *
	 * @since 4.7.0
	 *
	 * @param int    $post_id       Post ID related to the trackback.
	 * @param string $trackback_url Trackback URL.
	 * @param string $charset       Character set.
	 * @param string $title         Trackback title.
	 * @param string $excerpt       Trackback excerpt.
	 * @param string $blog_name     Site name.
	 */
	do_action( 'pre_trackback_post', $post_id, $trackback_url, $charset, $title, $excerpt, $blog_name );

	header( 'Content-Type: text/xml; charset=' . get_option( 'blog_charset' ) );

	if ( ! pings_open( $post_id ) ) {
		trackback_response( 1, __( 'Sorry, trackbacks are closed for this item.' ) );
	}

	$title   = wp_html_excerpt( $title, 250, '&amp;#8230;' );
	$excerpt = wp_html_excerpt( $excerpt, 252, '&amp;#8230;' );

	$comment_post_id      = (int) $post_id;
	$comment_author       = $blog_name;
	$comment_author_email = '';
	$comment_author_url   = $trackback_url;
	$comment_content      = &quot;&lt;strong&gt;$title&lt;/strong&gt;\n\n$excerpt&quot;;
	$comment_type         = 'trackback';

	$dupe = $wpdb-&gt;get_results(
		$wpdb-&gt;prepare(
			&quot;SELECT * FROM $wpdb-&gt;comments WHERE comment_post_ID = %d AND comment_author_url = %s&quot;,
			$comment_post_id,
			$comment_author_url
		)
	);

	if ( $dupe ) {
		trackback_response( 1, __( 'There is already a ping from that URL for this post.' ) );
	}

	$commentdata = array(
		'comment_post_ID' =&gt; $comment_post_id,
	);

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

	$result = wp_new_comment( $commentdata );

	if ( is_wp_error( $result ) ) {
		trackback_response( 1, $result-&gt;get_error_message() );
	}

	$trackback_id = $wpdb-&gt;insert_id;

	/**
	 * Fires after a trackback is added to a post.
	 *
	 * @since 1.2.0
	 *
	 * @param int $trackback_id Trackback ID.
	 */
	do_action( 'trackback_post', $trackback_id );

	trackback_response( 0 );
}
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