Hacker rank - infinite links - Capture the Flag contest - April 2017

infinite_links.php

<?php
set_time_limit(0);
function download($Url)
{
    if (!function_exists('curl_init')){
        die('Sorry cURL is not installed!');
    }
	$ch = curl_init();
  curl_setopt($ch, CURLOPT_URL, $Url);
	curl_setopt($ch, CURLOPT_USERAGENT, "MozillaXYZ/1.0");
	curl_setopt($ch, CURLOPT_HEADER, 0);
	curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
	curl_setopt($ch, CURLOPT_TIMEOUT, 30);
	curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, 0);
	curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, 0);
    $output = curl_exec($ch);
    curl_close($ch);
    return $output;
}
	
function goInside($page,&$urls,&$secrets)
{
	if(in_array($page,$urls)) {
		return;
	}
	array_push($urls,$page);
	echo 'Going into '.$page.'<br>';
	$html = download("https://cdn.hackerrank.com/hackerrank/static/contests/capture-the-flag/infinite/".$page);
	$a = array();
	if(preg_match("/<font color=blue><b>(.*)<\/font>/", $html, $a))
	{
		$n = count($a);
		if($n>0)
		{
			for($i=1;$i<$n;$i++){
				$a[$i] = str_replace("Secret Phrase: ","",$a[$i]);
				array_push($secrets,$a[$i]);
				echo "Found secret: ".$a[$i].'<br>';
			}
		}
	}
	$regexp = "<a\s[^>]*href=(\"??)([^\" >]*?)\\1[^>]*>(.*)<\/a>";
	if(preg_match_all("/$regexp/siU", $html, $matches, PREG_SET_ORDER)) {
		foreach($matches as $match) {
		  goInside($match[2],$urls,$secrets);
		  // $match[3] = link text
		}
	}
}
$urls    = array();
$secrets = array();
goInside('qds.html',$urls,$secrets);
sort($secrets);
echo '<h1>Results:</h2><hr>';
foreach($secrets as $secret){
	echo $secret.'<br>';
}
?>