How to get root domain in Wordpress

You don't need to exclude the www. With the correct basenames the plugin will follow the default scheme.

This code will retrive the home url for the current site.
Other functions to retrieve specific files from other directories.

If you want the plugin to be compatible with versions below 2.6 then you need something like this:
BTW, Path and scheme are optionals. Path, if you want to hard code the URL, and scheme if you want to hard code https.

I can see the advantages of setting a cookie on the top level domain itself, as it will be valid up and throughout all sub domains. However, if you're building a distributable plugin I'm afraid no universal solution for this exists, unless of course you're willing to incorporate a complete list of top and second level domains? The example given by phpbbxpert would only suffice providing that wordpress is installed under the sub domain of 'www'. It would not account for an installation on blog.domain.tld. The example given by strangerstudios above does not account for second level domains. I.e. domain.sld.tld. This would obviously impact the ten million second level domains in the UK, such as .co.uk and that's just one example; there are thousands of popular second level domains used around the world.

Now if I was to set myself up with the challenge of building a php function (and I am) that is independent of any list, then I would use statistics and regular expression to ensure that the function is as universal as possible. It would look something like this:

function resolve_root_domain($url, $max=6)
{
$domain = parse_url($url, PHP_URL_HOST);

if (!strstr(substr($domain, 0, $max), '.'))
return ($domain);
else
return (preg_replace("/^(.*?)\.(.*)$/", "$2", $domain));
}

This function considers that most top level domains are longer than six characters and that most sub domains precede the top level within six characters. It also considers the thousands of second level domains that are out there. The optional second parameter is for playing with the 6 character rule. It's obviously not completely universal, but it's certainly more universal than the other examples given in this post and like I said; without incorporating any lists, universal compatibility would be an impossibility. Third and fourth level domains are also fairly common, but setting a cookie on these levels will not impact on a browser a great deal in terms of wordpress.

To set a cookie in wordpress you could do something like this:


$domain = resolve_root_domain(get_option('siteurl'));
setcookie('NAME', 'DATA', time()+3600, '/', '.'.$domain);

For the benefits of global browser compatibility the 4th paremeter should always be a / if you want the cookie to be traversal, throughout the directory structure of your website and you should precede the domain name itself with a . if you want to factor in older browsers that implement the deprecated RFC 2109 standards. Without it the cookie will not be read as a wildcard that is valid throughout all sub domains.

Coffee break over! Back to do some work. :rolleyes: