I recently switched from Apache/Linux to IIS/Windows in order to develop ASP.NET applications on my shared web host (ixwebhosting.com). Unfortunately, IIS6 doesn’t support WordPress permalinks because it doesn’t have the ability to use mod_rewrite unless you install a third-party ISAPI filter. Because I’m on a shared hosting plan, I don’t have access to install ISAPI filters and my web host won’t install them for me.

There are a few different 404 page-based hacks that allow you to retain your permalinks, even with IIS. The most popular fix, which worked fine for me, was Keyboard Face’s IIS Permalink Fix. I used his fix, and a GET variable fix from Ikailo to make a PHP-based 404 page that redirects all 404 pages back into WordPress, thereby bypassing the need for mod_redirect.

The two fixes above are great, except for the fact that they don’t allow for a real 404 page. In other words, if a visitor types in an invalid URL, they won’t be redirected to a friendly 404 page — they’ll get a blank, white page. This is a common complaint, and to date I haven’t seen a fix for it.

Although I’m not proud of it, I have found a temporary fix until my web host upgrades to IIS7 and/or adopts an ISAPI filter solution for permalink redirections:

<?php

function customError($errno, $errstr, $errfile, $errline)
  {
	echo chr(0);
  }
set_error_handler("customError");

//http://www.keyboardface.com/archives/category/installing-wordpress/
$qs = $_SERVER['QUERY_STRING'];
$_SERVER['REQUEST_URI'] = substr($qs, strpos($qs, ':80')+3);
$_SERVER['PATH_INFO'] = $_SERVER['REQUEST_URI'];

//http://www.ikailo.com/94/url-modrewrite-workaround-iis-60/
foreach ( $_GET as $var => $val ) {
	if ( substr($var, 0, 3) == '404') {
		if ( strstr($var, "?") ) {
			$newvar = substr($var, strpos($var, '?') + 1);
			$_GET[$newvar] = $val;
		}
		unset($_GET[$var]);
	}
	break;
}
include('index.php');
?>

As you can see, I added a custom error handler into the script. When the error handler is called, it’ll send a chr(0) code (which for all intents and purposes is a blank, length-less character). Once this code is sent, no header()’s or location-redirects can be sent, meaning that the code won’t die and present a blank page. Instead, it will redirect to your wordpress 404 template page you have installed.

Again, this is not a pretty fix, but it gets the job done.

Update 9/22/2009 – Be advised that this hack will force all your 404 pages to be sent as 200 OK headers, which can hurt your SEO standing with websites. It’s a buggy fix, so hopefully someone more experienced with PHP/WordPress will come up with a better solution soon.