Skip tracking for specific domains from the Community-contributed list of referrer spammers from Matomo.

kill-referrer-spam.php

<?php
/**
 * Plugin Name: Kill Referrer Spam for Statify
 * Description: Skip tracking for domains from the Community-contributed list of referrer spammers from Matomo.
 * Plugin URI:  http://torstenlandsiedel.de
 * Version:     1.0
 * Author:      Torsten Landsiedel
 * Author URI:  http://torstenlandsiedel.de
 * Licence:     GPL 2
 * License URI: http://opensource.org/licenses/GPL-2.0
 *
 * @package Statify\Kill Referrer Spam
 */

if ( ! defined( 'ABSPATH' ) ) {
	exit;
} // Exit if accessed directly

/**
 * Checks referrer and compares with blacklist from Github file
 *
 * @return boolean Returns if tracking is skipped or not.
 */
function apply_referrer_spammer_list() {

	// Get Referrer.
	$referrer = wp_parse_url( wp_get_raw_referer() );
	$referrer = strtolower( ( isset( $referrer['host'] ) ? $referrer['host'] : '' ) );

	// Bail early if no referrer there.
	if ( ! $referrer ) {
		return false;
	}

	// Get blacklist from Github.
	// TODO: Proof of concept. This needs some sort of caching for production.
	$blacklist = file( 'https://raw.githubusercontent.com/matomo-org/referrer-spam-blacklist/master/spammers.txt', FILE_IGNORE_NEW_LINES | FILE_SKIP_EMPTY_LINES );

	// Check blacklist.
	if ( in_array( $referrer, $blacklist, true ) ) {
		return true;
	}

	return false;

};

add_filter( 'statify__skip_tracking', 'apply_referrer_spammer_list' );