PHP: How to resolve a relative url

Question

I need a function that given a relative URL and a base returns an absolute URL. I've searched and found many functions that do it different ways.

resolve("../abc.png", "http://example.com/path/thing?foo=bar")
# returns http://example.com/abc.png

Is there a canonical way?

On this site I see great examples for python and c#, lets get a PHP solution.

Answer 1

Perhaps this article could help?

http:// nashruddin.com/PHP_Script_for_Converting_Relative_to_Absolute_URL

Edit: reproduced code below for convenience

<?php
    function rel2abs($rel, $base)
    {
        /* return if already absolute URL */
        if (parse_url($rel, PHP_URL_SCHEME) != '' || substr($rel, 0, 2) == '//') return $rel;

        /* queries and anchors */
        if ($rel[0]=='#' || $rel[0]=='?') return $base.$rel;

        /* parse base URL and convert to local variables:
         $scheme, $host, $path */
        extract(parse_url($base));

        /* remove non-directory element from path */
        $path = preg_replace('#/[^/]*$#', '', $path);

        /* destroy path if relative url points to root */
        if ($rel[0] == '/') $path = '';

        /* dirty absolute URL */
        $abs = "$host$path/$rel";

        /* replace '//' or '/./' or '/foo/../' with '/' */
        $re = array('#(/\.?/)#', '#/(?!\.\.)[^/]+/\.\./#');
        for($n=1; $n>0; $abs=preg_replace($re, '/', $abs, -1, $n)) {}

        /* absolute URL is ready! */
        return $scheme.'://'.$abs;
    }
?>