Okay, very precisely, I've been tasked with a Magento admin module that doesn't involve layouts, blocks or views. Nothing is ever to be displayed. However, when I call an action in my module's adminhtml controller, Magento keeps trying to render a layout and failing that, redirects to the Dashboard with a "Failed to load source for: http://www.example.com/index.php/admin/modulename/adminhtml_index/actioname" blah, blah, blah.
Now, I've looked at FireBug's Net output for a familiar system action like clearing the cache like so: http://www.example.com/index.php/admin/cache/flushSystem/key/88848f202df8f254b3db13762ad7e949/ and this too responds with "Failed to load source for: http://www.example.com/index.php/admin/cache/flushSystem/key/88848f202df8f254b3db13762ad7e949/"
First of all, this has to be a controller that extends Mage_Adminhtml_Controller_Action because otherwise I can't tell if the admin is logged in and has permission to action my controller. Second of all, I don't have a debugging system (and my company's to cheap to spend any money on software engineering) so I have to cave man debug. So my question is, how on earth do debug my code and get output from Magento without loading a layout and rendering blocks? I've tried to output in the predispatch method and exiting before the predispatch ends and this WORKS, but I would prefer not to do any coding in predispatch. Any help would be greatly appreciated.
When Firebug says "Failed to load source" it means there is no data to display, typically during a 302 redirect. In a redirection only headers are sent and no body. This matches what you are experiencing.
Secondly your URL contains admin/modulename/adminhtml_index/actionname which has four parts. In Magento there should only be three parts like "router/controller/action", which part is extra in yours?
When you have the right action firing don't call $this->loadLayout()->renderLayout() because that would, um, load the layout. To output any other content use:
$this->getResponse()->setBody($content);