module ActionDispatch::Http::URL

def host

req.host # => "example.com"
req = Request.new 'HTTP_HOST' => 'example.com:8080'

end
include ActionDispatch::Http::URL
class Request < Rack::Request

Returns the host for this request, such as example.com. 
def host
  raw_host_with_port.sub(/:\d+$/, ''.freeze)
end