WWW to non-WWW Redirect with PHP

I want to redirect all www.domain.com requests to domain.com with PHP, basically:

if (substr($_SERVER['SERVER_NAME'], 0, 4) === 'www.')
{
    header('Location: http://' . substr($_SERVER['SERVER_NAME'], 4)); exit();
}

However I do want to maintain the requested URL like in SO, for e.g.:

http://www.stackoverflow.com/questions/tagged/php?开发者_开发技巧foo=bar

Should redirect to:

http://stackoverflow.com/questions/tagged/php?foo=bar

I don't want to rely on .htaccess solutions, and I'm unsure which $_SERVER vars I'd have to use to make this happen. Also, preserving the HTTPS protocol would be a plus.

How should I do this?

Try this:

if (substr($_SERVER['HTTP_HOST'], 0, 4) === 'www.') {
    header('Location: http'.(isset($_SERVER['HTTPS']) && $_SERVER['HTTPS']=='on' ? 's':'').'://' . substr($_SERVER['HTTP_HOST'], 4).$_SERVER['REQUEST_URI']);
    exit;
}

$pageURL = (@$_SERVER["HTTPS"] == "on") ? "https://" : "http://";
if ($_SERVER["SERVER_PORT"] != "80")
{
    $pageURL .= $_SERVER["SERVER_NAME"].":".$_SERVER["SERVER_PORT"].$_SERVER["REQUEST_URI"];
} 
else 
{
    $pageURL .= $_SERVER["SERVER_NAME"].$_SERVER["REQUEST_URI"];
}
header('Location: '. $pageURL);

Would redirect the user to the exact same page, www. intact.

So, to get rid of the www. , we just replace one line:

$pageURL = (@$_SERVER["HTTPS"] == "on") ? "https://" : "http://";
if ($_SERVER["SERVER_PORT"] != "80")
{
    $pageURL .= substr($_SERVER['SERVER_NAME'], 4).":".$_SERVER["SERVER_PORT"].$_SERVER["REQUEST_URI"];
} 
else 
{
    $pageURL .= substr($_SERVER['SERVER_NAME'], 4).$_SERVER["REQUEST_URI"];
}
return $pageURL;

And that should work.

By the way, this is the method that is recommended by Google, as it keeps https:// intact, along with ports and such if you do use them.

As Gumbo pointed out, he uses $_SERVER['HTTP_HOST'] as it comes from the headers instead of the server, thus $_SERVER['SERVER_*'] is not as reliable. You could replace some$_SERVER['SERVER_NAME'] with $_SERVER['HTTP_HOST'], and it should work the same way.

if (((isset($_SERVER['HTTP_X_FORWARDED_PROTO']) && strtolower($_SERVER['HTTP_X_FORWARDED_PROTO']) == 'https') || (isset($_SERVER["HTTPS"]) && strtolower($_SERVER["HTTPS"])=="on"))) {
           $https = 1;
} else {
            $https = 0;
}
if (substr($_SERVER['HTTP_HOST'], 0, 4) !== 'www.') {
            header('location:', ($https?'https://':'http://') .'www.' .                                                                   $_SERVER['HTTP_HOST'].$_SERVER['REQUEST_URI']);
}