How to count the number of currently connected Protocols in Python twisted framework

Question

I was trying to count the number of active protocols in twisted but i got an error:

exceptions.AttributeError: Factory instance has no attribute 'numProtocols'

Below is the code:

class EchoPro(Protocol):
    def connectionMade(self):
        self.factory.numProtocols = self.factory.numProtocols+1
        if self.factory.numProtocols > 100:
            self.transport.write("Too many connections, try later")
            self.transport.loseConnection()
    def connectionLost(self, reason):
        self.factory.numProtocols = self.factory.numProtocols-1

    def dataReceived(self, data):
        self.transport.write(data)

Answer 1

That's because self.factory does not contain the numProtocols attribute.

To customise the protocol's factory you create a Factory for your protocol by subclassing twisted.internet.protocol.Factory.

Example:

from twisted.internet.protocol import Protocol, Factory
from twisted.internet import reactor

class Echo(Protocol):
    # ... your implementation as it is now ...

class EchoFactory(Factory):  # Factory for your protocol
    protocol = Echo
    numProtocols = 0

factory = EchoFactory()
factory.protocol = Echo

reactor.listenTCP(8007, factory)
reactor.run()

Alternatively, you could just modify the factory instance once it is created, as done in the docs.

Example:

from twisted.internet.protocol import Protocol, Factory
from twisted.internet import reactor

class Echo(Protocol):
    # ... your implementation as it is now ...

def getEchoFactory():
    factory = Factory()
    factory.protocol = Echo
    factory.numProtocols = 0
    return factory

reactor.listenTCP(8007, getEchoFactory())
reactor.run()