Redirection in drupal 7

I am using Drupal 7 for developing a site called http://somesite.com. My requirement is to redirect the site to http://sub.somesi开发者_运维技巧te.com if a sub.somesite.com folder exists in my directory at the time of page request itself. I have a custom module which is linked to a JavaScript file which is being called from hook_init function. This js file contains the redirection script.

But now the http://somesite.com is loaded first and then it is being redirected to http://sub.somesite.com. I need to perform the checking of file and redirecting at the time of bootstrap process itself so that the user is unaware of the site redirection.

Calling drupal_add_js function from hook_boot function throws me a fatal error (drupal_add_js() undefined).

Is there any other method to meet this requirement?

Any help would be greatly appreciated.. Thanks in advance..

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This won't work, javascript is not evaluated until the page content is built by which time it's too late to redirect the page without anyone noticing. You will always have a delay if you use javascript...instead you want to use header('Location: somewhere') in hook_boot() if your conditions are matched.