PHP：获取页面的基本URL

Scenario:

User adds a URL (Like URLs below). I want to return all links on the page that appears in href attribute. I can get all links using DOMDocument class. But some links are relative. I want to convert them to absolute links.

My Problem:

Suppose I have these strings (URLs) (User may sends any link. like one of these):

http://example.com/test/index.html
http://example.com/test/test.php
http://example.com/test/
http://example.com/test

Now I get all contents of the href of user's input URL. Some of these URLs are relative so I have to merge those relative links to the base URL. My problem is that I cannot get the base URL. In this example my base URL would be http://example.com/test. So if user enters any of those URLs above I have to get the same base URL.

How can I extract the URL base correctly?

You can use parse_url method like this code:

<?php 
    $url = 'http://example.com/test';
    //get base url from link
    $base_url=parse_url($url, PHP_URL_HOST);
    //get path from link
    $path=parse_url($url, PHP_URL_PATH);
    //print base_url
    echo 'Base URL = '.$base_url;
    //print path
    echo ' PATH = '.$path;
 ?>