check for URL Canonicalization inconsistent

I am trying to check for URL Canonicalization. It is working fine for some page while it is not working on some pages.

My code:

function getRedirect($webpage)
{
    $curlInit = curl_init($webpage);
    curl_setopt($curlInit, CURLOPT_CONNECTTIMEOUT, 20);
    curl_setopt($curlInit, CURLOPT_HEADER, true);
    curl_setopt($curlInit, CURLOPT_NOBODY, true);
    curl_setopt($curlInit, CURLOPT_RETURNTRANSFER, true);
    $response      = curl_exec($curlInit);
    $response_time = curl_getinfo($curlInit);
    curl_close($curlInit);
    return $response_time['redirect_url'];
}

function get_root_domain($url)
{
    $pattern = '/\w+\..{2,3}(?:\..{2,3})?(?:$|(?=\/))/i';

    if (preg_match($pattern, $url, $matches) === 1) {
        return $matches[0];
    }
}

function getDomain($url)
{
    $url = Trim($url);
    $url = preg_replace("/^(http:\/\/)*/is", "", $url);
    $url = preg_replace("/^(https:\/\/)*/is", "", $url);
    $url = preg_replace("/\/.*$/is", "", $url);
    return $url;
}

Main function:

$parsedUrl = get_root_domain($url);
$url_WWW = 'www.' . $parsedUrl;
$getRedirect = getRedirect($parsedUrl);
if ($getRedirect == null)
{
    // echo with or without www resolve to the same url
}
else
{
    $parsedRedirect = getDomain($getRedirect);
    if ($parsedRedirect == $parsedUrl)
    {
        // echo with or without www resolve to the same url
    }
    elseif ($parsedRedirect == $url_WWW)
    {
        // echo with or without www resolve to the same url
    }
    else
    {
        // echo with or without www DOES NOT resolve to the same url.
    }
}

I have tried modifying the first if statement to this:

if ($get_redirect == null)
{
    $get_redirect_url = get_redirect($url_WWW);
    $get_redirect_url = getDomain($get_redirect_url);
    if ($get_redirect_url == $url_WWW)
    {
        // echo with or without www DOES NOT resolve to the same url.
    }
    else
    {
        // echo with or without www resolve to the same url
    }
}

but I get the same inconsistent result.