In the days of link shorteners and Ajax, there can be many links that ultimately point to the same content. I was wondering what the best way is to get the final, best link for a web site in PHP, hopefully with a library. I was unable to find anything on Google or GitHub.
I have seen this example code, but it doesn't handle things like a rel="canonical" meta tags or default ssl ports: http://w-shadow.com/blog/2008/07/05/how-to-get-redirect-url-in-php/
Facebook seems to handle this pretty well, you can see how they follow 301's and rel="canonical", etc. To see examples of the way Facebook handles it, use their Open Graph tool:
https://developers.facebook.com/tools/debug
and enter these links:
http://dlvr.it/xxb0W
https://twitter.com/#!/twitter/statuses/136946408275193856
Is there a PHP library out there that already has this pre-built, where it will check for these headers, resolve 301 redirects, parse rel="canonical", detect redirect loops and properly just grab the best resulting URL to use?
As an alternative, I am open to APIs that can be used, but would prefer something that runs on my own server.
Since I wasn't able to find any libraries that really did what I was looking for, and I was hoping to do more than just follow HTTP redirects, I have gone ahead and created a library that accomplishes the goals and released it under the MIT license. You can get it here:
https://github.com/mattwright/URLResolver.php
URLResolver.php is a PHP class that attempts to resolve URLs to a final, canonical link:
- Follows 301 and 302 redirects found in HTTP headers
- Follows Open Graph URL <meta> tags found in web page <head>
- Follows Canonical URL <link> tags found in web page <head>
- Aborts download quickly if content type is not an HTML page
I am certainly not an expert on the rules of HTTP redirection, so if anyone has suggestions on how to improve this library, it would be greatly appreciated. I have tested in on thousands of URLs and it seems to do pretty well. I followed Mario's advice and used PHP Simple HTML Parser library where needed.
Using Guzzle (a well known and robust HTTP client) you can do it like that:
<?php
use Guzzle\Http\Client as GuzzleClient;
use Guzzle\Plugin\History\HistoryPlugin;
public function resolveUrl($url)
{
$client = new GuzzleClient($url);
$history = new HistoryPlugin();
$client->addSubscriber($history);
$response = $client->head($url)->send();
if (!$response->isSuccessful()) {
throw new \Exception(sprintf("Url %s is not a valid URL or website is down.", $url));
}
return $response->getEffectiveUrl();
}
I wrote you a little function to do it. It's simple, but it may be a starting point for you. Note: the http://dlvr.it/xxb0W url returns an invalid URL for it's Location response header.
You'll need the Altumo PHP library for it to work. It's a library that I wrote, but it's MIT license, as is this function.
See: https://github.com/homer6/altumo
Also, you'll have to wrap the function in a try/catch.
/**
* Gets the final URL of a URL that will be redirected.
*
* @param string $url_string
* @throws \Exception //on error
* @return string
*/
function get_final_url( $url_string ){
while( 1 ){
//validate URL
$url = new \Altumo\String\Url( $url_string );
//get the Location response header of the URL
$client = new \Altumo\Http\OutgoingHttpRequest( $url_string );
$response = $client->sendAndGetResponseMessage();
$location = $response->getHeader( 'Location' );
//return the URL if no Location header was found, else continue
if( is_null($location) ){
return $url_string;
}else{
$url_string = $location;
}
}
}
echo get_final_url( 'your url here' );
Please let me know if you'd like further modifications or help getting it going.
