def public_url(expires = (Time.now + 5 * 365 * 24 * 60 * 60))
requires :objectid
storage = Fog::Storage.new(:provider => 'Atmos')
uri = URI::HTTP.build(:scheme => @prefix, :host => @storage_host, :port => @storage_port.to_i, :path => "/rest/objects/#{objectid}" )
Fog::Storage.new(:provider => 'Atmos').uid
sb = "GET\n"
sb += uri.path.downcase + "\n"
sb += storage.uid + "\n"
sb += String(expires.to_i())
signature = storage.sign( sb )
uri.query = "uid=#{CGI::escape(storage.uid)}&expires=#{expires.to_i()}&signature=#{CGI::escape(signature)}"
uri.to_s
end