Hi Adam - I'm in pretty much the same situation as you and am working on a similar problem. Very much a Python and Twisted newbie.
The program I'm working on needs to talk to a variety of clients and to a single server, with more-or-less permanent connections to all of them. My problem is somewhat different from yours (and probably a little simpler), since all input from all clients goes to the server, and all output from the server goes to all clients (so I don't have to tag and remember which response goes to which client.) However, there are other messages from the clients that don't go to the server, but instead do other things, some requiring responses. So the message handling in my program (what happens when dataRecieved gets called) may be more complicated than in yours. But that is (at least from my perspective) the easy part. Getting the twisted app to talk to the server and all the clients, and not to fall over dead when a client goes away, etc. is (to me) the hard part, and I feel like I've just gotten over a huge hump now that that is (mostly) working (as of two days ago.) I am using two factories, one to generate the object that talks to the server (using conch.telnet), and one to generate objects to talk to the clients. The clients can come and go but would typically be permanent. (Actually 3 factories right now, since I'm using the StdioProxyFactory from the example for debugging, but that will go away as I get the client protocol working.) I started from the dataforward.py example in Twisted book, but by now it has been massively changed. Before starting the reactor, I do a reactor.connectTCP to the server using the factory for the server connections and a reactor.listenTCP using the client connection factory, to listen for client connections. One change I had to make to the example was to promote the InputForwarder object from an attribute of the client connection object to a global object since it is common to all the client connections. (I hope I have the terminology correct here; as I've said, I'm a Python newbie.) It turns out to be fairly small amount of code, and I think it can still be simplified some more. So I think you are on the right track. HTH! -- John Santos Evans Griffiths & Hart, Inc. 781-861-0670 ext 539
I have just started to look at the Twisted framework and would like to put it to use for a new project I am working on. Not being very familiar with the framework and fairly new to Python in general I would like to ask a design/architecture question. (I have written similar applications in C but would prefer to start this in the right direction and not write Python like C.) The application has the following model: Many clients connect to the Application and prefer to leave the connection open. They will send messages across this connection. They will expect to get a message back at some point later, they do not wait for a response (async). The clients are already coded (legacy) and just need to send their proprietary protocol to the new Application (written using Twisted). The Twisted application will take the data from the clients and do some transformation on it then send the message on to another server (3rd party). This connection to "another" server must be a single connection, not one connection per client. This connection should also be persistent and not opened/closed for each client message sent. Ideally if the 3rd party server is down then I would also not accept client connections as the messages are time sensitive and should not be stored and forwarded. At some point the 3rd part will send a message back and the Application will route it back to the original source. Basically request/reply pattern. I have been reading through the archives and the twisted docs and have also looked over the Hex-dump port-forwarding recipe but not found anything that explains how to use twisted for this model. Hex-dump is close but opens/closes the connection to the server on each client connection. I am thinking that there will be two Factories [and two protocols: 1) for clients and 2) for 3rd party]. I am not sure how to best establish both the listening factory and the client to 3rd party factory. Once they are established what is the preferred way in Twisted to pass a message from one protocol to another? Any pointers or sample code that you can offer is greatly appreciated. I would really like to cook this in Twisted and not go back to the C way. Thanks, -ab
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