Ticket #10970: siteurl.php

<?php
/*
 * drop this in mu-plugins. by dd32
 */

add_filter('pre_update_option_siteurl', '_siteurl_pre_change', 5, 2);
function _siteurl_pre_change( $new, $old ) {
        $valid = _siteurl_is_valid( $new, $old );
        if ( ! is_wp_error( $valid ) )
                return $new;
                
        $message = sprintf(__( 'WordPress has detected that changing the WordPress Address of your Site to <code>%s</code> will result in WordPress not being accessable for the following reason(s)') , esc_html( $new ) );
        $message .= '<ul><li>' . $valid->get_error_message();
        $data = $valid->get_error_data();
        if ( is_wp_error( $data ) )
                $message .= ' <ul><li>' . $data->get_error_message() . '</li></ul>';
        $message .= '</li></ul>';
        $message .= '</p><p>' . '<input type="submit" value="' . esc_attr(__('Continue?')) . '" />';
        wp_die( $message );
        exit;
}

function _siteurl_is_valid($new, $old) {
        $_url = add_query_arg( 'testing-redirects', '1', $new );
        $res = wp_remote_head($_url);
        if ( is_wp_error($res) )
                return new WP_Error('unknown', __('WordPress cannot verify the suggested site URL'), $res );

        if ( isset($res['headers']['wordpress-redirection']) && 'ok' == $res['headers']['wordpress-redirection'] )
                wp_die( 'True: <pre>' . print_r(array($_url,$res), true) );
        
        if ( isset($res['headers']['wordpress-redirection']) && 'not-front-page' == $res['headers']['wordpress-redirection'] )
                return new WP_Error('not_wordpress_front', __('The Provided URL does not resolve to the front page of WordPress.') );
        
        if ( '200' == $res['response']['code'] ) // Something exists, but is not the WordPress we expected.
                return new WP_Error('not_wordpress', __('This WordPress Installation was not accessable at that URL.') );

        if ( in_array( $res['response']['code'], array(300, 301, 302) ) ) // Redirection elsewhere.
                return new WP_Error('unknown', sprintf(__('Redirection to %s'), $res['headers']['location']) );

        wp_die( 'Fallthrough:<pre>' . print_r(array($_url,$res), true) );
//      return true;
}

add_action('template_redirect', '_tr', 100);
function _tr() {
        if ( isset($_GET['testing-redirects']) ) {
                if ( is_front_page() )
                        header('WordPress-Redirection: ok');
                else
                        header('WordPress-Redirection: not-front-page');
                die();
        }
}