I am pretty new to Twisted, so I am sure this is a rookie mistake. I have built a simple server which receives a message from the client and upon receipt of message the server fires a callback which prints the message to the console.
At first instance, the server works as expected. Unfortunately, when I start up a second client I get the follow error "twisted.internet.defer.AlreadyCalledError." It was my understanding that the factory would make a new instance of the deferred i.e. the new deferred wouldn't have been called before?
Please see the code below. Any help would be very appreciated.
import sys
from twisted.internet.protocol import ServerFactory, Protocol
from twisted.internet import defer
class LockProtocol(Protocol):
lockData = ''
def dataReceived(self, data):
self.lockData += data
if self.lockData.endswith('??'):
self.lockDataReceived(self.lockData)
def lockDataReceived(self, lockData):
self.factory.lockDataFinished(lockData)
class LockServerFactory(ServerFactory):
protocol = LockProtocol
def __init__(self):
self.deferred = defer.Deferred() # Initialise deferred
def lockDataFinished(self, lockData):
self.deferred.callback(lockData)
def clientConnectionFailed(self, connector, reason):
self.deferred.errback(reason)
def main():
HOST = '127.0.0.1' # localhost
PORT = 10001
def got_lockData(lockData):
print "We have received lockData. It is as follows:", lockData
def lockData_failed(err):
print >> sys.stderr, 'The lockData download failed.'
errors.append(err)
factory = LockServerFactory()
from twisted.internet import reactor
# Listen for TCP connections on a port, and use our factory to make a protocol instance for each new connection
port = reactor.listenTCP(PORT,factory)
print 'Serving on %s' % port.getHost()
# Set up callbacks
factory.deferred.addCallbacks(got_lockData,lockData_failed)
reactor.run() # Start the reactor
if __name__ == '__main__':
main()
Notice that there is only one
LockServerFactory
ever created in your program:However, as many
LockProtocol
instances are created as connections are accepted. If you have per-connection state, the place to put it is onLockProtocol
.It looks like your "lock data completed" event is not a one-off so a
Deferred
is probably not the right abstraction for this job.Instead of a
LockServerFactory
with aDeferred
that fires when that event happens, perhaps you want a multi-use event handler, perhaps custom built:(Incidentally, notice that I've dropped
clientConnectionFailed
from this implementation: that's a method ofClientFactory
. It will never be called on a server factory.)