How to get final URL after following HTTP redirections in pure PHP?

Question

What I\'d like to do is find out what is the last/final URL after following the redirections.

I would prefer not to use cURL. I would like t

Answer 1

While the OP wanted to avoid cURL, it's best to use it when it's available. Here's a solution which has the following advantages

• uses curl for all the heavy lifting, so works with https
• copes with servers which return lower cased location header name (both xaav and webjay's answers do not handle this)
• allows you to control how deep you want you go before giving up

Here's the function:

function findUltimateDestination($url, $maxRequests = 10)
{
    $ch = curl_init();

    curl_setopt($ch, CURLOPT_HEADER, true);
    curl_setopt($ch, CURLOPT_NOBODY, true);
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
    curl_setopt($ch, CURLOPT_FOLLOWLOCATION, true);
    curl_setopt($ch, CURLOPT_MAXREDIRS, $maxRequests);
    curl_setopt($ch, CURLOPT_TIMEOUT, 15);

    //customize user agent if you desire...
    curl_setopt($ch, CURLOPT_USERAGENT, 'Mozilla/5.0 (Link Checker)');

    curl_setopt($ch, CURLOPT_URL, $url);
    curl_exec($ch);

    $url=curl_getinfo($ch, CURLINFO_EFFECTIVE_URL);

    curl_close ($ch);
    return $url;
}

Here's a more verbose version which allows you to inspect the redirection chain rather than let curl follow it.

function findUltimateDestination($url, $maxRequests = 10)
{
    $ch = curl_init();

    curl_setopt($ch, CURLOPT_HEADER, true);
    curl_setopt($ch, CURLOPT_NOBODY, true);
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
    curl_setopt($ch, CURLOPT_TIMEOUT, 15);

    //customize user agent if you desire...
    curl_setopt($ch, CURLOPT_USERAGENT, 'Mozilla/5.0 (Link Checker)');

    while ($maxRequests--) {

        //fetch
        curl_setopt($ch, CURLOPT_URL, $url);
        $response = curl_exec($ch);

        //try to determine redirection url
        $location = '';
        if (in_array(curl_getinfo($ch, CURLINFO_HTTP_CODE), [301, 302, 303, 307, 308])) {
            if (preg_match('/Location:(.*)/i', $response, $match)) {
                $location = trim($match[1]);
            }
        }

        if (empty($location)) {
            //we've reached the end of the chain...
            return $url;
        }

        //build next url
        if ($location[0] == '/') {
            $u = parse_url($url);
            $url = $u['scheme'] . '://' . $u['host'];
            if (isset($u['port'])) {
                $url .= ':' . $u['port'];
            }
            $url .= $location;
        } else {
            $url = $location;
        }
    }

    return null;
}

As an example of redirection chain which this function handles, but the others do not, try this:

echo findUltimateDestination('http://dx.doi.org/10.1016/j.infsof.2016.05.005')

At the time of writing, this involves 4 requests, with a mixture of Location and location headers involved.