Danw33's Redirect Log for WordPress (mu-plugin)

mu-plugin-log-wp-redirects.php

<?php
/**
 * Logs calls to wp_safe_redirect and wp_redirect to allow for server-side optimisation of common redirects
 *
 *
 * @wordpress-plugin
 * Plugin Name:       WP Redirect Log
 * Plugin URI:        https://gist.github.com/Danw33/6ad3b423ca2d57ed46a1b21461c13498
 * Description:       Logs calls to wp_redirect and wp_safe_redirect to allow for server-side optimisation of common redirects
 * Version:           1.0.0
 * Author:            Daniel Wilson
 * Author URI:        https://danw.io/
 * License:           GPL-3.0+
 * License URI:       http://www.gnu.org/licenses/gpl-3.0.txt
 */

/*
  Redirect Log for WordPress (mu-plugin)
  Copyright (C) 2018 - 2019 Daniel Wilson - @Danw33

  This program is free software: you can redistribute it and/or modify
  it under the terms of the GNU General Public License as published by
  the Free Software Foundation, either version 3 of the License, or
  (at your option) any later version.

  This program is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  GNU General Public License for more details.

  You should have received a copy of the GNU General Public License
  along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/

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

if ( ! function_exists( 'wp_safe_redirect' ) ) :
	/**
	 * Performs a safe (local) redirect, using wp_redirect().
	 *
	 * Checks whether the $location is using an allowed host, if it has an absolute
	 * path. A plugin can therefore set or remove allowed host(s) to or from the
	 * list.
	 *
	 * If the host is not allowed, then the redirect defaults to wp-admin on the siteurl
	 * instead. This prevents malicious redirects which redirect to another host,
	 * but only used in a few places.
	 *
	 * Note: wp_safe_redirect() does not exit automatically, and should almost always be
	 * followed by a call to `exit;`:
	 *
	 *     wp_safe_redirect( $url );
	 *     exit;
	 *
	 * Exiting can also be selectively manipulated by using wp_safe_redirect() as a conditional
	 * in conjunction with the {@see 'wp_redirect'} and {@see 'wp_redirect_location'} filters:
	 *
	 *     if ( wp_safe_redirect( $url ) ) {
	 *         exit;
	 *     }
	 *
	 * @since 2.3.0
	 * @since 5.1.0 The return value from wp_redirect() is now passed on, and the `$x_redirect_by` parameter was added.
	 *
	 * @param string $location      The path or URL to redirect to.
	 * @param int    $status        Optional. HTTP response status code to use. Default '302' (Moved Temporarily).
	 * @param string $x_redirect_by Optional. The application doing the redirect. Default 'WordPress'.
	 * @return bool  $redirect False if the redirect was cancelled, true otherwise.
	 */
	function wp_safe_redirect( $location, $status = 302, $x_redirect_by = 'WordPress' ) {

		// Need to look at the URL the way it will end up in wp_redirect()
		$location = wp_sanitize_redirect( $location );

		/**
		 * Filters the redirect fallback URL for when the provided redirect is not safe (local).
		 *
		 * @since 4.3.0
		 *
		 * @param string $fallback_url The fallback URL to use by default.
		 * @param int    $status       The HTTP response status code to use.
		 */
		$location = wp_validate_redirect( $location, apply_filters( 'wp_safe_redirect_fallback', admin_url(), $status ) );

		error_log( 'wp_safe_redirect : ' . $status . ' by ' . $x_redirect_by . ' to location: "' . $location . '".' );

		return wp_redirect( $location, $status, $x_redirect_by );
	}
endif;

if ( ! function_exists( 'wp_redirect' ) ) :
	/**
	 * Redirects to another page.
	 *
	 * Note: wp_redirect() does not exit automatically, and should almost always be
	 * followed by a call to `exit;`:
	 *
	 *     wp_redirect( $url );
	 *     exit;
	 *
	 * Exiting can also be selectively manipulated by using wp_redirect() as a conditional
	 * in conjunction with the {@see 'wp_redirect'} and {@see 'wp_redirect_location'} filters:
	 *
	 *     if ( wp_redirect( $url ) ) {
	 *         exit;
	 *     }
	 *
	 * @since 1.5.1
	 * @since 5.1.0 The `$x_redirect_by` parameter was added.
	 *
	 * @global bool $is_IIS
	 *
	 * @param string $location      The path or URL to redirect to.
	 * @param int    $status        Optional. HTTP response status code to use. Default '302' (Moved Temporarily).
	 * @param string $x_redirect_by Optional. The application doing the redirect. Default 'WordPress'.
	 * @return bool False if the redirect was cancelled, true otherwise.
	 */
	function wp_redirect( $location, $status = 302, $x_redirect_by = 'WordPress' ) {
		global $is_IIS;

		/**
		 * Filters the redirect location.
		 *
		 * @since 2.1.0
		 *
		 * @param string $location The path or URL to redirect to.
		 * @param int    $status   The HTTP response status code to use.
		 */
		$location = apply_filters( 'wp_redirect', $location, $status );

		/**
		 * Filters the redirect HTTP response status code to use.
		 *
		 * @since 2.3.0
		 *
		 * @param int    $status   The HTTP response status code to use.
		 * @param string $location The path or URL to redirect to.
		 */
		$status = apply_filters( 'wp_redirect_status', $status, $location );

		if ( ! $location ) {
			return false;
		}

		$location = wp_sanitize_redirect( $location );

		if ( ! $is_IIS && PHP_SAPI != 'cgi-fcgi' ) {
			status_header( $status ); // This causes problems on IIS and some FastCGI setups
		}

		/**
		 * Filters the X-Redirect-By header.
		 *
		 * Allows applications to identify themselves when they're doing a redirect.
		 *
		 * @since 5.1.0
		 *
		 * @param string $x_redirect_by The application doing the redirect.
		 * @param int    $status        Status code to use.
		 * @param string $location      The path to redirect to.
		 */
		$x_redirect_by = apply_filters( 'x_redirect_by', $x_redirect_by, $status, $location );
		if ( is_string( $x_redirect_by ) ) {
			header( "X-Redirect-By: $x_redirect_by" );
		}

		error_log( 'wp_redirect : ' . $status . ' by ' . $x_redirect_by . ' to location: "' . $location . '", current location: "' . $_SERVER['HTTP_HOST'] . $_SERVER['REQUEST_URI'] . '", referer: "' . ( $_SERVER['HTTP_REFERER'] ?? '' ) . '".');

		header( "Location: $location", true, $status );

		return true;
	}
endif;