In reply to adrian,

Thank you very much for your function. There is a small issue with your relative protocol function. You need to remove the // when making the url the path. Here is the new function.

function resolve_url($base, $url) {
        if (!strlen($base)) return $url;
        // Step 2
        if (!strlen($url)) return $base;
        // Step 3
        if (preg_match('!^[a-z]+:!i', $url)) return $url;
        $base = parse_url($base);
        if ($url{0} == "#") {
                // Step 2 (fragment)
                $base['fragment'] = substr($url, 1);
                return unparse_url($base);
        }
        unset($base['fragment']);
        unset($base['query']);
        if (substr($url, 0, 2) == "//") {
                // Step 4
                return unparse_url(array(
                        'scheme'=>$base['scheme'],
                        'path'=>substr($url,2),
                ));
        } else if ($url{0} == "/") {
                // Step 5
                $base['path'] = $url;
        } else {
                // Step 6
                $path = explode('/', $base['path']);
                $url_path = explode('/', $url);
                // Step 6a: drop file from base
                array_pop($path);
                // Step 6b, 6c, 6e: append url while removing "." and ".." from
                // the directory portion
                $end = array_pop($url_path);
                foreach ($url_path as $segment) {
                        if ($segment == '.') {
                                // skip
                        } else if ($segment == '..' && $path && $path[sizeof($path)-1] != '..') {
                                array_pop($path);
                        } else {
                                $path[] = $segment;
                        }
                }
                // Step 6d, 6f: remove "." and ".." from file portion
                if ($end == '.') {
                        $path[] = '';
                } else if ($end == '..' && $path && $path[sizeof($path)-1] != '..') {
                        $path[sizeof($path)-1] = '';
                } else {
                        $path[] = $end;
                }
                // Step 6h
                $base['path'] = join('/', $path);

        }
        // Step 7
        return unparse_url($base);
}