Mailman 3 June 2009 - Twisted

Re: [Twisted-Python] Twisted book(s)?
by Robert Gravina June 3, 2009

June 3, 2009

> I'm fairly new to Python and very new to Twisted. I find I learn new > material best from a book, so although I know there's lots of great > documentation and examples on twistedmatrix.com, I was considering > getting O'Reilly's Twisted book ('Twisted Network Programming > Essentials' by Abe Fettig). But that book dates back to Oct 2005 so I > was wondering if it's still a worthwhile purchase - I'd guess Twisted > has moved a good bit since the book was written. Any opinions? I got that book and to be honest, didn't find it very useful due to it being a nutshell book - it can't (due to size) go into much detail in each section and so I found the online documentation/tutorials were a better resource. A more detailed Twisted book would be awesome though! I think pragprog.com share 50% of the profits with authors (and do ebooks and betas too), so maybe someone might be interested in writing it :) Of course noone would complain about a community edited book like what the Django project has, either. :) Robert

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Re: [Twisted-Python] Guidance on Proxy-type Application
by glyph＠divmod.com June 2, 2009

June 2, 2009

On 01:23 am, asb.bush(a)gmail.com wrote: >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.) Thanks for asking! I apologize for the delay in my answer. I started writing up a simple example (attached) but was discouraged to find that it was 100 lines long and required too much explaining. Then I started documenting it and explaining every line but that was a very long, tedious message. So, it doesn't have much in the way of explanation; I hope you will find it useful regardless. >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). This is *almost* a FAQ. At least, you may find this to be a useful answer: <http://twistedmatrix.com/trac/wiki/FrequentlyAskedQuestions#HowdoImakeinput…> >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. The example that I've attached does basically this. Run it and then run 'telnet localhost 4322', and type some lines; you will see that they are transformed and echoed back to you, both by the proxy and by the protocol being proxied. At a high level, the answer to your question is so simple that it's hard to express. Basically, you just need to have all the relevant objects having references to each other, and calling methods to achieve the desired effect. The less magic, the better. More precisely, you need an object responsible for managing your outgoing connections to your legacy server, so that it can handle disconnection and reconnection, queueing messages and so on. Then you need your proxy server factory to hold a reference to that object, so that it can create references from each proxy server protocol connection object to the connection manager. This is related to another recent thread - you can see my message in that thread here: http://thread.gmane.org/gmane.comp.python.twisted/18377/focus=18385 >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'm not sure why hex-dump port-forwarding is particularly relevant to this example. Is it just because this is an application that connects from one host to another? >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? This part of your question is almost exactly the FAQ I mentioned above :). To reiterate that answer, you just need to have references between objects, and call methods on the objects you want to do stuff. If you have a client connection object, just get a reference to that from the relevant server connection object and call methods on the client object to emit messages on the client protocol, handling any responses appropriately. Deferreds can help with that latter part. It is always better if you can establish that reference as simply as possible; for example, by passing parameters to the __init__ of various classes. Again, for reasons that have nothing to do with Twisted specifically, it's a bad idea to try to establish these references by having global variables floating around. Here's a very very simple example of the "good way" to propagate some data to protocol instances that need it: class MyProtocol(Protocol): def __init__(self, data): self.data = data class MyFactory(Factory): def __init__(self, data): self.data = data def buildProtocol(self, addr): return MyProtocol(self.data) reactor.listenTCP(8765, MyFactory("some data")) and here's a simple example of a really bad way (don't do this!): class MyProtocol(Protocol): def connectionMade(self): self.bleh = bleh bleh = "some data" f = Factory() f.protocol = MyProtocol reactor.listenTCP(9876, f) Even in C, I'm pretty sure it's better style to pass structures to functions than to abuse piles of local variables :). I only illustrate this bad style here because it seems to be a common antipattern. The Protocol class itself doesn't take any parameters to __init__, and Twisted's users don't always realize that protocols and factories and so on are just regular objects, with no special rules; they just get methods called on them by the reactor. >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. Based on what you've said so far, I think you're basically on the right track. Good luck!

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[Twisted-Python] wxreactor and win32eventreactor
by Ryan Nowakowski June 2, 2009

June 2, 2009

I'm trying to use twisted's SerialPort stuff in my Win32 wxPython app. I'm using the wxreactor, however I'm getting this error: AttributeError: 'WxReactor' object has no attribute 'addEvent' When I switch to the win32eventreactor my serial port code works fine but then of course, the GUI won't work. Any idea how to get SerialPort working with wxreactor on Windows? - Ryan

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[Twisted-Python] Question about a custom byte oriented TCP protocol
by Michael Thompson June 2, 2009

June 2, 2009

Hi, I'm trying to use twisted to talk to an existing system that uses a byte oriented protocol stuffed inside a TCP packet. I have implemented this using the IntNStringReceiver modified to look at some bytes to calculate the size of the string to receive. For simple test cases where I send a single packet this works but if I send multiple requests they all end up in the same tcp packet which the existing server doesn't like. How can I ensure that only a single command\string is sent per tcp packet? I tried TCP No Delay but that didn't seem to help Regards, Michael

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[Twisted-Python] Reactor callback from the wrong thread
by Lars Ivar Igesund June 2, 2009

June 2, 2009

Hi! I have an issue where the reactor calls the callback from a different thread than the one the reactor is running in. The usecase is as follows; We are running tests using PyFit (Fitnesse), and where some of the tests depends on receiving SNMP traps in the background. So at the start we start a trap deamon defined as class TrapDeamon(Thread, netsnmp.Session) We use the pynetsnmp.twistedsnmp package and has a run() method that looks like this def run(self): self.awaitTraps(self.hostPort) twistedsnmp.updateReactor() reactor.run(installSignalHandlers=0) In the callback from the reactor, we get the pdu of the trap which is then sent into a trap buffer. On the PyFit side of things, we execute some commands, and at some points we need a confirmation from a trap before we can continue. This is done by waiting on a queue (Queue.Queue). The trap buffer has a register over queues and awaited trap OID's, and when the correct one is added to the buffer from the reactor callback, it is put onto the queue, the test rejoice, and continues. However, I noticed that fairly often (say every 3rd wait), the wait timed out even though I had seen the trap on wireshark. So I improved the logging, and noticed that in the cases where the wait timed out, the reactor callback for the trap I waited for happened in the main thread (at least main thread id is reported by python logging), and thus did not appear until immediately after the wait had failed and unblocked. Most of the trap callbacks (both before and after these misses) happens in the correct (reactor) thread though. What can cause this and how may I debug it? AFAIK, PyFit does not use twisted or threading at all, and we only have two simple background threads our selves in addition to the one running the trap deamon. Best regards, Lars Ivar Igesund

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[Twisted-Python] Twisted Question
by Brandon McGinty June 1, 2009

June 1, 2009

Hi All, I just subscribed to this list, after viewing tons of documents about twisted, factories, and all the like. Here is the situation. I am trying to design a bridge between twisted.web and twisted.words.protocols.irc. I have read a lot about using factories, and communicating with a central "program class" like in the finger tutorial. However, I can not figure out how to communicate between two running protocols. Here's an example: User connects to web server. Irc client connects to irc server User clicks on search link, and enters query. A command, along with that query, is sent to irc server via irc client. Response is returned, processed, and sent to the page that is the result of submiting that form. Process continues until user clicks log out, where in the irc client disconnects. Any help anyone can give me is greatly appreciated. Thanks, Brandon McGinty -- -- Brandon McGinty Email:brandon.mcginty@gmail.com Tel:(602)-904-6548 SMS:(602)-904-6548 Skype:brandon.mcginty MSN:brandon_mcginty@hotmail.com

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[Twisted-Python] offer of adding IRCD support to words.protocol.irc
by Patrick Thomson June 1, 2009

June 1, 2009

I'm currently about to embark on building something from twisted which has an IRCD, and I have found the capacity to run IRC servers is lacking, in contrast to the excellent client/bot backend code. I've found several other twisted projects already implement an IRCD, and whilst I'm reinventing the wheel, I may as well go the extra mile to get my code suitable for inclusion. I wouldn't be asking for a lot, just some general guidelines (e.g. I know my patch probably won't be accepted without test code as well). -- Patrick

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