Custom URL redirect in WP

Question

I am trying to make my own redirect page for external link.

My target

My target is that, when a user open the link www.mysite.com/wp/GoTo/?URL=www.google.com, the browser open the page www.google.com

What I have done

I have saved the following GoTo.php file inside the folder wp-content/themes/theme-name/:

<?php


/*
Template Name: GoTo
*/

/**
 * The template for displaying all pages.
 *
 * This is the template that displays all pages by default.
 * Please note that this is the WordPress construct of pages
 * and that other 'pages' on your WordPress site will use a
 * different template.
 *
 * @package theme-name
 */

$url = $_GET["URL"];

// Remove all illegal characters from a url
$url = filter_var($url, FILTER_SANITIZE_URL);

if (filter_var($url, FILTER_VALIDATE_URL) !== true) {
    header("location: " . $url);
    exit;
} else {
echo("$url is not a valid URL");
}
?>

then I have created a page with the URL www.mysite.com/wp/GoTo/ with template GoTo.

At the moment:

• if I open www.mysite.com/wp/GoTo/?URL=xyz I get a 404 error (instead of the message "URL is not valid";
• if I open www.mysite.com/wp/GoTo/?URL=www.google.com I get a 404 error (instead of open google.com).

How can I fix this? Unfortunately I can't refer directly to the php page. In other words I can't write in the browser www.mysite.com/wp/wp-content/themes/theme-name/Z_GoTo.php?URL=www.google.com, as the mod rewrite contains rules against it.

Disclamer

I know that there are several questions about redirect in WP, but none of them is about a situation like mine.

Answer 1

The problem is with this expression:

filter_var($url, FILTER_VALIDATE_URL) !== true

which should or could be written as just:

filter_var($url, FILTER_VALIDATE_URL)

Because the PHP manual for filter_var() says:

Returns the filtered data, or FALSE if the filter fails.

which means, with a valid URL, filter_var() does not return a boolean; hence filter_var($url, FILTER_VALIDATE_URL) !== true never evaluates to false. I.e. all URLs would be seen as valid.

So the full code, without the comments:

$url = $_GET["URL"];

// Remove all illegal characters from a url
$url = filter_var($url, FILTER_SANITIZE_URL);

if (filter_var($url, FILTER_VALIDATE_URL)) {
    header("location: " . $url);
    exit;
} else {
    echo("$url is not a valid URL");
}

Additional Note

To redirect to an external URL/domain, you need to specify the protocol — e.g. http://. Try below header() code and you'd understand it:

Code #1:

// Has the protocol; this would always redirect to http://www.google.com
header( 'Location: http://www.google.com' );
exit;

Code #2:

// Protocol not specified; redirects to a URL on your site. For example,
// if you're on http://your-site.com/path, then you'd be redirected to
// http://your-site.com/path/www.google.com
header( 'Location: www.google.com' );
exit;