Hook for page Request?

Question

I want to run a function that looks at the current url params of the page that is requested and sets a cookie based on those params.

So, I guess I'm looking for:

1. The Wordpress Hook that allows me to do this before the page is even loaded
2. A way to get the requested URL

Answer 1

// Kick in right before theme takes over, when WP is all loaded
add_action('wp', function(){
    list($uri, $qs) = explode('?', $_SERVER['REQUEST_URI']);
    // Do stuff here:
    // ... STUFF ...
});

Cheers!