Set a timeout for an UDP socket with Twisted (python)

Question

I'm using Twisted in a python program. I send data every minute and receive data on a UDP socket and I need to set a timeout.

I found a way to do this, but I would like to know if it's a good way to do that.

This is the idea of my code :

class UDPSocket(DatagramProtocol):
   def startProtocol(self):
       self.transport.connect(self.HOST, self.PORT)
       reactor.callLater(1, self.send_data)

   def send_data(self):
       reactor.callLater(60, self.send_data)
       self.transport.write("Some data")
       self.timeoutCallId = reactor.callLater(5, raise_timeout)

   def datagramReceived(self, data, (host, port)):
       if self.timeoutCallId.active():
           self.timeoutCallId.cancel()
       #Do something with data

   def raise_timeout(self):
       #Do something to manage timeout

reactor.listenUDP(port, UDPSocket())
reactor.run()

Thanks for your advices

EDIT :

It works but I have a problem.

If a timeout occured, I'm going into the raise_timeout function correctly, but when the next "send_data()" is called, the self.transport.write("data") function raise an exception : 'NoneType' object has no attribute 'write'.

I guess self.transport is disconnected.

How can I fix that ?

Answer 1

I found a solution.

When we use UDP, when we send a datagram, if no answer is received after less than 1 second, "self.transport" is set to None and "stopProtocol" method is called. Once we leave "stopProtocol" method, reactor stops to listen the specified UDP port.

So this is my solution code :

class UDPSocket(DatagramProtocol):
    def __init__(self, mainreactor):
        self._reactor = mainreactor

    def startListenUDP(self):
        try :
            self._reactor.listenUDP(KeepAlive.PORT, self)
        except Exception, e :
            pass

    def startProtocol(self) :
        self.transport.connect(self.host, self.port)

    def stopProtocol(self):
        print "Transport disconnected !"
        self._reactor.callLater(0.1, self.startListenUDP)

    def raise_timeout(self) :
        print "Timeout !"

    def datagramReceived(self, datagram, host):
        try :
            if self.timeout_id.active():
                self.timeout_id.cancel()
        except Exception, e :
            pass
        print datagram

    def sendDatagram(self):
        datagram = "Some Data"
        try :
            self.transport.write(datagram)
            self.timeout_id = self._reactor.callLater(TIMEOUT, 
                self.raise_timeout)
        except Exception, e :
            self._reactor.callLater(0.1, self.startListenUDP)

def main():
    protocol = UDPSocket(reactor)
    t = reactor.listenUDP(PORT, protocol)
    l = task.LoopingCall(protocol.sendDatagram)
    l.start(60)
    reactor.run()

#MAIN
if __name__ == '__main__':
    main()