<?php

$urlsString = "http://f...content-available-to-author-only...o.com/barhttps://b...content-available-to-author-only...r.com//foo.com/foo/bar";
preg_match_all('~(?:https?:)?//.*?(?=$|(?:https?:)?//)~', $urlsString, $urls);
print_r($urls[0]);