silverstripe-framework/core/control/RootURLController.php

<?php
/**
 * This controller handles what happens when you visit the root URL.
 *
 * @package sapphire
 * @subpackage control
 */
class RootURLController extends Controller {
	protected static $is_at_root = false;
	
	public function handleRequest($request) {
		self::$is_at_root = true;

		$controller = new ModelAsController();
		
		$request = new HTTPRequest("GET", self::get_homepage_urlsegment().'/', $request->getVars(), $request->postVars());
		$request->match('$URLSegment//$Action');
			
		return $controller->handleRequest($request);
	}

	/**
	 * Return the URL segment for the current HTTP_HOST value
	 */
	static function get_homepage_urlsegment() {
		$host = $_SERVER['HTTP_HOST'];
		$host = str_replace('www.','',$host);
		$SQL_host = str_replace('.','\\.',Convert::raw2sql($host));
        $homePageOBJ = DataObject::get_one("SiteTree", "HomepageForDomain REGEXP '(,|^) *$SQL_host *(,|\$)'");

		if($homePageOBJ) {
			return $homePageOBJ->URLSegment;
		} else {
			return 'home';
		}
	}
	
	/**
	 * Returns true if we're currently on the root page and should be redirecting to the root
	 * Doesn't take into account actions, post vars, or get vars
	 */
	static function should_be_on_root(SiteTree $currentPage) {
		if(!self::$is_at_root) return self::get_homepage_urlsegment() == $currentPage->URLSegment;
		else return false;
	}
}

?>