code: def ack(messageid, transactionid=None):
      
      header = 'message-id: %s' % messageid
  
      if transactionid:
          header = 'message-id: %s\ntransaction: %s' % (messageid, transactionid)
  
      return "ACK\n%s\n\n\x00\n" % header
docs: STOMP acknowledge command.
  
      Acknowledge receipt of a specific message from the server.
  
      messageid:
          This is the id of the message we are acknowledging,
          what else could it be? ;)
  
      transactionid:
          This is the id that all actions in this transaction
          will have. If this is not given then a random UUID
          will be generated for this.