HTTP redirects usually have the response status 301 or 302 and provide the redirection URL in the “Location” header. I’ve written three complementary PHP functions that you can use to find out where an URL redirects to (based on a helpful thread at WebmasterWorld). You don’t even need CURL for this – fsockopen() will do just fine.

The PHP script

/**
* get_redirect_url()
* Gets the address that the provided URL redirects to,
* or FALSE if there's no redirect.
*
* @param string $url
* @return string
*/

function get_redirect_url($url){
$redirect_url = null;
 
$url_parts = @parse_url($url);
if (!$url_parts) return false;
if (!isset($url_parts['host'])) return false; //can't process relative URLs
if (!isset($url_parts['path'])) $url_parts['path'] = '/';
 
$sock = fsockopen($url_parts['host'], (isset($url_parts['port']) ? (int)$url_parts['port'] : 80), $errno, $errstr, 30);
if (!$sock) return false;
 
$request = "HEAD " . $url_parts['path'] . (isset($url_parts['query']) ? '?'.$url_parts['query'] : '') . " HTTP/1.1\r\n";
$request .= 'Host: ' . $url_parts['host'] . "\r\n";
$request .= "Connection: Close\r\n\r\n";
fwrite($sock, $request);
$response = '';
while(!feof($sock)) $response .= fread($sock, 8192);
fclose($sock);
 
if (preg_match('/^Location: (.+?)$/m', $response, $matches)){
if ( substr($matches[1], 0, 1) == "/" )
return $url_parts['scheme'] . "://" . $url_parts['host'] . trim($matches[1]);
else
return trim($matches[1]);
 
} else {
return false;
}
 
}
 
/**
* get_all_redirects()
* Follows and collects all redirects, in order, for the given URL.
*
* @param string $url
* @return array
*/

function get_all_redirects($url){
$redirects = array();
while ($newurl = get_redirect_url($url)){
if (in_array($newurl, $redirects)){
break;
}
$redirects[] = $newurl;
$url = $newurl;
}
return $redirects;
}
 
/**
* get_final_url()
* Gets the address that the URL ultimately leads to.
* Returns $url itself if it isn't a redirect.
*
* @param string $url
* @return string
*/

function get_final_url($url){
$redirects = get_all_redirects($url);
if (count($redirects)>0){
return array_pop($redirects);
} else {
return $url;
}
}

Here’s an example that lists all URLs that a given address redirects to (in order) :

$rez = get_all_redirects('http://daerils.gtrends.hop.clickbank.net/');
print_r($rez);

Known Issues

Most likely you won’t ever run into one of these, but here they are anyway :

  • The script doesn’t recognize infinite redirects that don’t form a loop. However, it can handle normal redirection loops – get_all_redirects() exits as soon as it encounters an URL that it has already seen.
  • Relative redirects multiple (e.g. “Location: go.php?asdf”) won’t be fully followed by get_all_redirects().
  • Not an issue per-se, yet something to note : these functions won’t tell you if an URL is valid, just what it redirects to (if anything).

On a related note, check out the Firefox extension Redirect Remover.

轉自http://w-shadow.com/blog/2008/07/05/how-to-get-redirect-url-in-php/

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