31 October, 2011

Pingback Killer

Pingbacks are a way for blog/web authors to learn when someone links to them. Essentially, they are an API call from one site to another. If I link to a site in a post on my WordPress blog, it will send an XML-RPC request to the linked site and a pingback is created.

The thing about pingbacks is they suck.

Most often ping backs are used for spam: they’re a way for a spammer to get links in your comment section by linking to your site. They don’t even have to build a bot to go submit comments, just put a link in their posts.

I dislike pingbacks so much that I decided to kill them with a brand new WordPress plugin, Pingback Killer.

Pingback Killer was originally built for a client, but we decided to release it so other folks could benefit from it.

What Pingback Killer Does

Remove the X-Pingback header WordPress sends
Causes called to bloginfo( 'pingback_url' ) or get_bloginfo( 'pingback_url' ) to return an empty string
Hijacks the default_ping_status and default_pingback_flag to return false/zero – evaluation of those boolean options will never return true
Completely disables the pingback.ping XML-RPC call
Removes all the rewrite rules that end with /trackback/

Read on to find out how Pingback Killer does all this, or you can simply download and install the plugin from the WordPress repository.

1. Removing the X-Pingback Header

You can filter the headers WordPress sends with the wp_headers filter hook. Pingback Killer does this.

&lt;?php<br /><br />
add_filter( ‘wp_headers’, ‘pmg_pk_filter_headers’, 10, 1 );<br /><br />
function pmg_pk_filter_headers( $headers )<br /><br />
{<br /><br />
	if( isset( $headers[‘X-Pingback’] ) )<br /><br />
	{<br /><br />
		unset( $headers[‘X-Pingback’] );<br /><br />
	}<br /><br />
	return $headers;<br /><br />
}

<?php

add_filter( ‘wp_headers’, ‘pmg_pk_filter_headers’, 10, 1 );

function pmg_pk_filter_headers( $headers )

{

if( isset( $headers[‘X-Pingback’] ) )

{

unset( $headers[‘X-Pingback’] );

}

return $headers;

}

2. Taking bloginfo( ‘pingback_url’ ) off the table

Like almost every WordPress core fuction, get_bloginfo comes with a filter hook. In this case, it’s bloginfo_url.

&lt;?php<br /><br />
add_filter( ‘bloginfo_url’, ‘pmg_pk_kill_pingback_url’, 10, 2 );<br /><br />
function pmg_pk_kill_pingback_url( $output, $show )<br /><br />
{<br /><br />
	if( $show == ‘pingback_url’ )<br /><br />
	{<br /><br />
		$output = ”;<br /><br />
	}<br /><br />
	return $output;<br /><br />
}

<?php

add_filter( ‘bloginfo_url’, ‘pmg_pk_kill_pingback_url’, 10, 2 );

function pmg_pk_kill_pingback_url( $output, $show )

{

if( $show == ‘pingback_url’ )

{

$output = ”;

}

return $output;

}

3. Hijacking Options
get_option and update_option both come with hooks to control what gets saved for an option or gets sent back. You can use those hooks to filter the content. __return_false and __return_zero are both WordPress core functions that do exactly what their names say: return false and 0 respectively. They’re useful for disabling things, just like we’re doing here.

&lt;?php<br /><br />
add_filter( ‘pre_update_default_ping_status’, ‘__return_false’ );<br /><br />
add_filter( ‘pre_option_default_ping_status’, ‘__return_zero’ );<br /><br />
add_filter( ‘pre_update_default_pingback_flag’, ‘__return_false’ );<br /><br />
add_filter( ‘pre_option_default_pingback_flag’, ‘__return_zero’ );

<?php

add_filter( ‘pre_update_default_ping_status’, ‘__return_false’ );

add_filter( ‘pre_option_default_ping_status’, ‘__return_zero’ );

add_filter( ‘pre_update_default_pingback_flag’, ‘__return_false’ );

add_filter( ‘pre_option_default_pingback_flag’, ‘__return_zero’ );

4. No More XML-RPC

Every XML-RPC callback function has an action hook called xmlrpc_call. You can hook into it and stop WordPress from continuing by calling wp_die if the XML-RPC server is processing a pingback.

&lt;?php<br /><br />
add_action( ‘xmlrpc_call’, ‘pmg_pk_kill_xmlrpc’ );<br /><br />
function pmg_pk_kill_xmlrpc( $action )<br /><br />
{<br /><br />
	if( ‘pingback.ping’ === $action )<br /><br />
	{<br /><br />
		wp_die(<br /><br />
			__( ‘Pingbacks are not supported’ ),<br /><br />
			__( ‘Not Allowed!’ ),<br /><br />
			array( ‘response’ => 403 )<br /><br />
		);<br /><br />
	}<br /><br />
}

<?php

add_action( ‘xmlrpc_call’, ‘pmg_pk_kill_xmlrpc’ );

function pmg_pk_kill_xmlrpc( $action )

{

if( ‘pingback.ping’ === $action )

{

wp_die(

__( ‘Pingbacks are not supported’ ),

__( ‘Not Allowed!’ ),

array( ‘response’ => 403 )

);

}

5. Cleaning Up Rewrite Rules

Rewrite rules are filtered only when they get rebuilt (doesn’t happen often). But when it does happen, you can hook into rewrite_rules_array and filter out anything that ends with trackback.

&lt;?php<br /><br />
add_filter( ‘rewrite_rules_array’, ‘pmg_pk_filter_rewrites’ );<br /><br />
function pmg_pk_filter_rewrites( $rules )<br /><br />
{<br /><br />
	foreach( $rules as $rule => $rewrite )<br /><br />
	{<br /><br />
		if( preg_match( ‘/trackback/?$$/i’, $rule ) )<br /><br />
		{<br /><br />
			unset( $rules[$rule] );<br /><br />
		}<br /><br />
	}<br /><br />
	return $rules;<br /><br />
}

<?php

add_filter( ‘rewrite_rules_array’, ‘pmg_pk_filter_rewrites’ );

function pmg_pk_filter_rewrites( $rules )

{

foreach( $rules as $rule => $rewrite )

{

if( preg_match( ‘/trackback/?$$/i’, $rule ) )

{

unset( $rules[$rule] );

}

return $rules;

}

Keeping it Simple

Pingback Killer is a very simple plugin. There are no options pages. Just install it, turn it on, and enjoy the lack of spam pingbacks. We already have this in use on several client blogs and this one.

Categories: Development

Tags: api, dev, Development, pingback, wordpress

About the author

Christopher Davis

A classical guitarist by training, Chris began creating software during grad school to learn more about managing WordPress sites. Since then he's moved on to building full fledged applications using PHP (using Silex, Symfony, and Doctrine), Python (Django, Flask, SQLAlchemy), or any tool more suited for the job. Chris is passionate about testing and software quality and helps PMG's internal tools hum along smoothly.

Pingback Killer

What Pingback Killer Does

Keeping it Simple

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Christopher Davis

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Pingback Killer

What Pingback Killer Does

Keeping it Simple

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Christopher Davis

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