# File lib/stomp/client.rb, line 214
    def ack_context_for(message, headers)
      id = case protocol
        when Stomp::SPL_12
         'ack'
        when Stomp::SPL_11
         headers.merge!(:subscription => message.headers['subscription'])
         'message-id'
        else
         'message-id'
      end
      {:message_id => message.headers[id], :headers => headers}
    end