[Twisted-Python] Create client in Server factory

[Kevin Horn]

On Wed, Oct 31, 2012 at 4:49 AM, Phil Mayers <p.mayers at imperial.ac.uk> wrote:
> On 10/31/2012 07:14 AM, Grégoire Leroy wrote:
>> Hi,
>>
>> I have a server who receive data from clients A/B/C (remote machines). I want
>> to use a client D (on the same machine than the server) to send this data to
>> another server (remote).
>>
>> The difficulty is, I want to use the same client D connection for any client. I
>> don't want open an new connection each time.
>>
>> First thing I would think is to create the connection in my server factory,
>> and use client's methods in my server protocol, for example with
>> [...]
>> class LocalProxyFactory(Factory):
>>          def __init__(self):
>>                  f = LocalProxyClientFactory()
>>                  reactor.connectTCP("retenodus.net", 4242, f)
>>                  reactor.run()
>
> The "reactor.run" is just wrong - remove it.
>
> You need to connect to a server, and share this connection amongst some
> protocols. But you can't control the order in which these connections
> complete, so A/B/C might connect before D is ready.
>
> You've really got two choices - accept the connections from A/B/C but
> have your server protocol "wait" until D is ready - something like this:
>
> from twisted.internet.protocol import ClientCreator
>
> class Server(...):
>    def connectionMade(self):
>      if self.factory.connD is None:
>        self.factory.waitFor(self._ready)
>        self.transport.pauseProducing()
>
>    def _ready(self):
>      self.transport.resumeProducing()
>
> d_connect = ClientCreator(reactor, DProtocol)
>
> class ServerFactory(...):
>    def __init__(self):
>      self.connD = None
>      self._wait = []
>      d_connect.connectTCP(Dhost, port).addCallback(self.dReady)
>
>    def waitFor(self, _cb):
>      if self.connD:
>        _cb(self.connD)
>      else:
>        d = defer.Deferred()
>        d.addCallback(_cb)
>        self._wait.append(d)
>
>    def dReady(self, proto):
>      self.connD = proto
>      cb = self._wait
>      self._wait = []
>      for c in cb:
>        c.callback(proto)
>
> def main():
>    reactor.listenTCP(..., ServerFactory())
>    reactor.run()
>
> ...or don't start listening until D has connected, like this:
>
> class ServerFactory(...):
>    def __init__(self, dProto):
>      self.connD = dProto
>
> def startListen(dProto):
>    reactor.listenTCP(..., ServerFactory(dProto))
>
> def main():
>    d_connect.connectTCP(Dhost, port).addCallback(startListen)
>    reactor.run()
>
> The latter is simpler, but which is appropriate depends on your needs.
>
> Note that I've used ClientCreator to get a callback when the connection
> to D is ready - remember that doesn't happen immediately.
>

See also:
http://twistedmatrix.com/trac/wiki/FrequentlyAskedQuestions#HowdoImakeinputononeconnectionresultinoutputonanother

That example only uses a single connection in place of your clients
A/B/C, but should be adaptable to your situation.

--
Kevin Horn