This is part of a larger program; I'll explain only the relevant parts. Basically, my code wants to create a new connection to a remote host. This should return a Deferred, which fires once the connection is established, so I can send something on it.
I'm creating the connection with twisted.internet.interfaces.IReactorSSL.connectSSL. That calls buildProtocol on my ClientFactory instance to get a new connection (twisted.internet.protocol.Protocol) object, and returns a twisted.internet.interfaces.IConnector. When the connection is started, Twisted calls startedConnecting on the factory, giving it the IConnector. When the connection is actually made, the protocol's connectionMade callback is called, with no arguments.
Now, if I only needed one connection per host/port, the rest would be easy. Before calling connectSSL, I would create a Deferred and put it in a dictionary keyed on (host, port). Then, in the protocol's connectionMade, I could use self.transport.getPeer() to retrieve the host/port, use it to look up the Deferred, and fire its callbacks. But this obviously breaks down if I want to create more than one connection.
The problem is that I can't see any other way to associate a Deferred I created before calling connectSSL with the connectionMade later on.
Looking at this some more, I think I've come up with a solution, although hopefully there is a better way; this seems kind of weird.
Twisted has a class, ClientCreator that is used for producing simple single-use connections. It in theory does what I want; connects and returns a Deferred that fires when the connection is established. I didn't think I could use this, though, since I'd lose the ability to pass arguments to the protocol constructor, and therefore have no way to share state between connections.
However, I just realized that the ClientFactory constructor does accept *args to pass to the protocol constructor. Or at least it looks like it; there is virtually no documentation for this. In that case, I can give it a reference to my factory (or whatever else, if the factory is no longer necessary). And I get back the Deferred that fires when the connection is established.