Fix fatal error on IIS after r16797. props peaceablewhale. Limit variable string searching when possible. See #10187

git-svn-id: http://svn.automattic.com/wordpress/trunk@16904 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/functions.php

@@ -3421,6 +3421,34 @@ function apache_mod_loaded($mod, $default = false) {
 	return $default;
 }
 
+/**
+ * Check if IIS 7 supports pretty permalinks
+ *
+ * @since 2.8.0
+ *
+ * @return bool
+ */
+function iis7_supports_permalinks() {
+	global $is_iis7;
+
+	$supports_permalinks = false;
+	if ( $is_iis7 ) {
+		/* First we check if the DOMDocument class exists. If it does not exist,
+		 * which is the case for PHP 4.X, then we cannot easily update the xml configuration file,
+		 * hence we just bail out and tell user that pretty permalinks cannot be used.
+		 * This is not a big issue because PHP 4.X is going to be depricated and for IIS it
+		 * is recommended to use PHP 5.X NTS.
+		 * Next we check if the URL Rewrite Module 1.1 is loaded and enabled for the web site. When
+		 * URL Rewrite 1.1 is loaded it always sets a server variable called 'IIS_UrlRewriteModule'.
+		 * Lastly we make sure that PHP is running via FastCGI. This is important because if it runs
+		 * via ISAPI then pretty permalinks will not work.
+		 */
+		$supports_permalinks = class_exists('DOMDocument') && isset($_SERVER['IIS_UrlRewriteModule']) && ( php_sapi_name() == 'cgi-fcgi' );
+	}
+
+	return apply_filters('iis7_supports_permalinks', $supports_permalinks);
+}
+
 /**
  * File validates against allowed set of defined rules.
  *