Rails Metal POST parameters


I'm having trouble when using Rack::Request in Rails Metal. For some
reason #params isn't getting filled.

I'm calling the Metal action using:

curl -d "foo=bar" http://domain.local/metaltest

And the Metal action contains the following code in (some code omitted
for brevity):

def self.call(env)
  request = Rack::Request.new(env)
  request.params # This is empty for some reason

If I output request.body.read for debugging I see "foo=bar" but for
some reason request.params isn't getting filled with these parameters
and is just an empty hash.

Anyone have any ideas?