[Twisted-Python] help with listening to UDP broadcast?

[Pantelis Theodosiou]

Hi Russell,

In an old script I've written, I see the following differences with your
code:

I hadn't used at all  allsetBroadcastAllowed()
but joinGroup()   (in startPrtotocol).

And I don't think the 255.255.255.255 will work. You'll need something like
192.168.1.1 or 127.0.0.1

The code (stripped from irrelevant parts) was:

from twisted.internet.protocol import DatagramProtocol
from twisted.internet import reactor
from twisted.application.internet import MulticastServer

# Set ports and hosts
ip = '224.0.5.228'
port = 8228

# our interface
interface = '192.168.1.1'

class MulticastClientUDP(DatagramProtocol):

    def startProtocol(self):
        # Join the multicast group
        self.transport.joinGroup(ip, interface)
        self.transport.setTTL(255)

    def datagramReceived(self, datagram, address):
        print "got a UDP broadcast packet"


# set reactor to listen on multicast channels
alertsClient = MulticastClientUDP()
reactor.listenMulticast(port, alertsClient)

reactor.run()


Pantelis Theodosiou


On Fri, Aug 8, 2014 at 11:58 PM, Russell E. Owen <rowen at uw.edu> wrote:

> I've found an example for UDP broadcasting:
> <https://twistedmatrix.com/trac/browser/trunk/docs/projects/core/examples
> /udpbroadcast.py?rev=41516
> <https://twistedmatrix.com/trac/browser/trunk/docs/projects/core/examples/udpbroadcast.py?rev=41516>
> >
>
> However, it combines the sender and receiver in a way that I find
> confusing. I figured out how output UDP broadcast packets, but not how
> to make a client that receives to the packets.
>
> Here is what we have, which doesn't work. Based on a comment on the
> broadcast UDP ticket. I suspect the problem is specifying the broadcast
> address using the interface argument to listenUDP, but I'm not sure. In
> any case, no value for interface that I've tried works:
> -"<broadcast>" (which is what my senders uses) results in
> twisted.internet.error.InvalidAddressError
> -"255.255.255.255" results in twisted.internet.error.CannotListenError:
> Couldn't listen on 255.255.255.255:1235: [Errno 49] Can't assign
> requested address.
> - omitting it results in no packets received.
> I also tried listenMulticast, but it didn't work (and I didn't expect it
> to, based on comments I saw on the ticket for implementing UDP broadcast
> support).
>
> Any hints would be appreciated.
>
> #!/usr/bin/env python2
> """Attempt to listen to UDP broadcasts
> """
> from twisted.internet.protocol import DatagramProtocol
> from twisted.internet import reactor
>
> Port = 1235
>
> class BroadcastUDPClient(DatagramProtocol):
>     def startProtocol(self):
>         self.transport.setBroadcastAllowed(True)
>
>     def datagramReceived(self, datagram, address):
>         print "got a UDP broadcast packet"
>
> class UDPListener(object):
>     def __init__(self, port):
>         self.port = port
>         self.broadcastClient = BroadcastUDPClient()
>         self.listener = None
>         self.startListening()
>
>     def startListening(self):
>         if self.listener is None:
>             interface = "255.255.255.255"
>             self.listener = reactor.listenUDP(self.port,
>                 self.broadcastClient, interface)
>
>     def stopListening(self):
>         if self.listener is not None:
>             self.listener.stopListening()
>             self.listener = None
>
> if __name__ == "__main__":
>     listener = UDPListener(Port)
>     reactor.run()
>
>
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