[Twisted-Python] AFactory

[Zooko]

Folks:

In writing my Gnutella for Twisted implementation, which I have named "Zoot", 
I encountered what seems to be a bit of a weakness in the current "Factory"
API.  This occurred when I wanted each protocol instance to have a reference to
my Zoot object (the Zoot object contains the Gnutella logic for such operations
as routing a message from one connection to another).

The way to do this is to make a subclass of Factory, which I called
ZootFactory.  ZootFactory gets a reference to the Zoot object when it
(ZootFactory) is constructed.  Then ZootFactory's `buildProtocol()' method
looks like this:

class ZootFactory(Factory):
    def __init__(self, zoot):
        Factory.__init__(self)
        self.zoot = zoot

    def buildProtocol(self, addr):
        p = Factory.buildProtocol(self, addr)
        p.zoot = self.zoot
        return p

It occurred to me that this idiom is probably useful to other developers of
applications on top of Twisted, and it is trivial to generalize it.  I defined
class AFactory, like this:

class AFactory(Factory):
    def __init__(self, protocol, application=None):
        self.protocol = protocol
        self.application = application

    def buildProtocol(self, addr):
        p = Factory.buildProtocol(self, addr)
        p.application = self.application
        return p

You can see it through viewcvs at:
http://twistedmatrix.com/users/jh.twistd/viewcvs/cgi/viewcvs.cgi/twisted/zoot/AFactory.py?rev=HEAD&content-type=text/vnd.viewcvs-markup&cvsroot=Twisted

My `updateApplication()' function in zoottap.py is now reduced to a nice
simple:

def updateApplication(app, config):
    f = AFactory(GnutellaTalker, Zoot())
    app.listenTCP(int(config["port"]), f)


I suggest that twisted.internet.protocol.Factory should be changed to do what
AFactory does, making it so that my `updateApplication()' could use the
standard Factory instead of AFactory.  I think it would be a
backward-compatible change to Factory which doesn't require other users of
Factory to change.

Regards,

Zooko

http://zooko.com/