File uploads via web service

I need to write a web service that accepts file uploads (even large
ones). My WS is REST based, so I have a create method that accepts
only POST.
My problem is passing the file to the method, so if someone already
solved this problem please let me know.
For example, do I need to use Base64 encoding, and decode inside ?
My method is like this:

def create
radio = Radio.create!( params[ :radio ] )
ad = params[ :ad ].merge( :user => current_user, :resource
=> radio ) )!
respond_to do |format|
format.xml { render :xml => ad.to_xml, :status => :created }
rescue ActiveRecord::RecordInvalid
respond_to do |format|
format.html { render :action => :new }
format.xml { render :xml => " #{e.message} </
error> ", :status => :unprocessable_entity }

My concern is about what gets saved inside the Radio object, I don’t
think I can pass a raw binary object (AFAIK).
Also, about rspeccing the whole thing, I think I need to write
controller tests that check that the file I begin with is exactly the
same I have after using the WS, but isn’t it something I shouldn’t do
in RSpec ? I mean, using real data. In this case I can have the
controller behaving exactly as I think it should by calling the right
methods in the right way, but having a corrupted file in the fs … I
can’t test data in the model either, because corruption will happen
exactly inside the controller.
I’m new to this stuff, so I’m pretty clueless. Every help is very