I released the merb_full_url plugin that provides URL which has origin (scheme, host and port)

• http://merbi.st/plugins/13

You can install this gem like this;

   1  % sudo gem install merb_full_url --source http://merbi.st

And you get full URLs by calling full_url/full_resource methods instead of url/resource.

But I think, it is better for merb to become providing such methods in advance :-)