How To Check Whether A URL Is External URL or Internal URL With PHP?

Question

I'm getting all ahrefs of a page with this loop:

foreach($html->find('a[href!="#"]') as $ahref) {
    $ahrefs++;
}

I want to do something like this:

foreach($html->find('a[href!="#"]') as $ahref) {
    if(isexternal($ahref)) {
        $external++;
    }
    $ahrefs++;
}

Where isexternal is a function

function isexternal($url) {
    // FOO...

    // Test if link is internal/external
    if(/*condition is true*/) {
        return true;
    }
    else {
        return false;
    }
}

Help!

Answer 1

Use parse_url and compare host to your local host (often but not always it's the same as $_SERVER['HTTP_HOST'])

function isexternal($url) {
  $components = parse_url($url);    
  return !empty($components['host']) && strcasecmp($components['host'], 'example.com'); // empty host will indicate url like '/relative.php'
}

Hovewer this will treat www.example.com and example.com as different hosts. If you want all your subdomains to be treated as local links then the function will be somewhat larger:

function isexternal($url) {
  $components = parse_url($url);
  if ( empty($components['host']) ) return false;  // we will treat url like '/relative.php' as relative
  if ( strcasecmp($components['host'], 'example.com') === 0 ) return false; // url host looks exactly like the local host
  return strrpos(strtolower($components['host']), '.example.com') !== strlen($components['host']) - strlen('.example.com'); // check if the url host is a subdomain
}