Short /go/ Links for Affiliate and Partner URLs

// Prefix of your short links: /go/amazon/ and so on.
$wpide_go_prefix = 'go';
// Short name => destination. Empty = off. Examples:
// 'amazon'  => 'https://www.amazon.com/dp/B000000000?tag=yourtag-20',
// 'hosting' => 'https://partner.example.com/?ref=you',
$wpide_go_links = array();

add_action( 'template_redirect', function () use ( $wpide_go_prefix, $wpide_go_links ) {
    // Only when no real page uses the address.
    if ( ! $wpide_go_links || ! is_404() ) {
        return;
    }

    $path = isset( $_SERVER['REQUEST_URI'] ) ? (string) wp_parse_url( wp_unslash( $_SERVER['REQUEST_URI'] ), PHP_URL_PATH ) : '';
    $base = (string) wp_parse_url( home_url( '/' . trim( $wpide_go_prefix, '/' ) . '/' ), PHP_URL_PATH );

    if ( 0 !== stripos( $path, $base ) ) {
        return;
    }

    $slug = strtolower( trim( substr( $path, strlen( $base ) ), '/' ) );

    if ( '' === $slug || empty( $wpide_go_links[ $slug ] ) ) {
        return;
    }

    nocache_headers();
    header( 'X-Robots-Tag: noindex, nofollow' );
    // 307 is temporary: browsers and search engines do not remember it, so you can change destinations any time.
    wp_redirect( esc_url_raw( $wpide_go_links[ $slug ] ), 307 ); // phpcs:ignore WordPress.Security.SafeRedirect -- destinations set by the site owner.
    exit;
}, 1 );

// Ask search engines not to crawl the short links.
add_filter( 'robots_txt', function ( $output, $public ) use ( $wpide_go_prefix, $wpide_go_links ) {
    if ( ! $public || ! $wpide_go_links ) {
        return $output;
    }

    $path = (string) wp_parse_url( home_url( '/' . trim( $wpide_go_prefix, '/' ) . '/' ), PHP_URL_PATH );

    return $output . "\nUser-agent: *\nDisallow: " . $path . "\n";
}, 10, 2 );